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PROFESSOR LADD'S WORKS
OUTLINES OF DESCRIPTIVE PSYCHOLOGY. A Text-Book
of Mental Science for Colleges and Normal Schools. 8vo.
$1.50 net
PSYCHOLOGY: DESCRIPTIVE AND EXPLANATORY. A
Treatise of the Phenomena, Laws, and Development of
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OUTLINES OF PHYSIOLOGICAL PSYCHOLOGY. A Text-
Book of Mental Science for Academies and Colleges. Il-
lustrated. 8vo. I2.00.
ELEMENTS OF PHYSIOLOGICAL PSYCHOLOGY. A Treat-
ise of the Activities and Nature of the Mind, from the
Physical and Experimental Point of View. With nu-
merous illustrations. 8vo. $4.50.
PRIMER OF PSYCHOLOGY. i2mo. $1.00 net.
PHILOSOPHY OF MIND. An Essay in the Metaphysics of
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PHILOSOPHY OF KNOVi^LEDGE. An Inquiry into the
Nature, Limits, and Validity of Human Cognitive Fac-
ulty. 8vo $4.00.
INTRODUCTION TO PHILOSOPHY. An Inquiry after a
Rational System of Scientific Principles in their Relation
to Ultimate Reality. 8vo. I3.00.
THE DOCTRINE OF SACRED SCRIPTURE. A Critical, His-
torical, and Dogmatic Inquiry into the Origin and Nature
of the Old and New Testaments. 2 vols. 8vo. I7.00.
WHAT IS THE BIBLE? An Inquiry into the Origin and
Nature of the Old and New Testaments in the Light of
Modern Biblical Study. i2mo. $2.00.
THE PRINCIPLES OF CHURCH POLITY. Crown 8vo. $2.50.
ELEMENTS
Physiological Psychology
A TREATISE OF THE ACTIVITIES AND NATURE
OF THE MIND
FROM THE PHYSICAL AND EXPERIMENTAL POINT OF VIEW
BY
GEORGE T. LADD
PKOFESSOE OF PHILOSOPHY IN YALE CNIVERSITy
NEW YORK
CHARLES SCRIBNER'S SONS
1900
COPTBIGHT, 1887, BT
CHARLES SCRIBNEE'S SONS
TROW DIRECTORY
PRINTING AND BOOKBINDING COMPANY
NEW YORK
PREFACE.
-«3
There can be no doubt that an important movement in psychol-
ogy has arisen in recent times through the effort to approach the
phenomena of mind from the experimental and physiological point
of view. Different students of psychological science will estimate
differently both the net result already reached by this effort and
the promise of further additions to the sum of our knowledge from
continued investigation of the same kind. Some writers have cer-
tainly indulged in extravagant claims as to the past triumphs of so-
called Physiological Psychology, and in equally extravagant expec-
tations as to its future discoveries. On the other hand, a larger
number, perhaps, have been inclined either to fear or to depreciate
every attempt to mingle the methods, laws, and speculations of the
physical sciences with the study of the human soul. These latter
apparently anticipate that some discovery in the localization of
cerebral function, or in psychometry, may jeopard the birthright
of man as a spiritual and rational being. Or possibly they wish
to regard the soul as separated, by nature and with respect to its
modes of action, from the material body in such a way as to render
it impossible to understand more of the one by learning more
about the other.
As a result of some years of study of the general subject, I express
with considerable confidence the opinion that there is no grormd for
extravagant claims or expectations, and still less ground for any fear
«f of consequences. In all cases of new and somewhat rankly growing
^ scientific enterprises, it is much the better way to waive the discus-
g sion of actual or possible achievements, as well as of welcomed or
;* dreaded revelations of new truth, and proceed at once to the busi-
^ ness on hand. It is proposed in this book to follow this better way.
It will be the task of the book itself to set forth the assured or al-
leged results of Physiological Psychology ; and this will be done at
Ul
Q
352441
iv PEEFACE.
every step with such degree of assurance as belongs to the evidence
hitherto attainable upon the particular subject discussed. With
declamation, either in attack or defence of the " old psychology,"
of the " introspective method," etc., one may dispense without seri-
ous loss.
The study of the phenomena of consciousness by the method here
proposed necessarilj' requires some acquaintance with a consider-
able circuit of sciences which are not usually all alike closely allied.
The number of scholars who can form opinions with equal freedom
and confidence in all of these sciences is very small. Moreover,
since all psycho-physical laws ai'e supposed — as the very term indi-
cates— to govern the correlations of phenomena of consciousness
with phenomena of the nervous sj'stem, a peculiar mystery belongs
to much of the domain within which psycho-physical science is com-
pelled to move. These facts may fitly, on the one hand, excite
caution in the writer ; and, on the other hand, excuse him for many
inevitable failures to set forth with perfect definiteness and confi-
dence the conclusions he has to propose. Much will be said that
must be accepted as provisional, as only probably true. Much
room must also be made for conjecture and speculation. What is
most important, however, is that conjecture should not be put forth
as ascertained fact, or speculation as unquestioned law.
It would have been a great assistance to me if I had had more
predecessors in the path which I am to take. But with the ex-
ception of Wundt's masterly work (Grundziige der physiologischen
Psychologic, second edition in 1880), no one book has attempted to
cover, even in a summary way, the entire ground. The number of
monographs, however, which have dealt with individual questions
subordinate to, or part of, the main inquiry is very great. These
two facts also render the attempt at a general survey of Physiolog-
ical Psychology for readers of English both peculiarly attractive
and peculiai-ly difiicult. I can only indulge the hope that I have
done something toward breaking this path and rendering it easier
and more secure, both for mj'self and for others, in the future.
The investigatox'S and authors to whom I am under obligations
for material upon the various questions discussed, or statements
made, in this book are by no means all mentioned by name. Of
course, much of what is said on the structure of the nervous system,
and on the phenomena of sensation and perception, has already
become part of that general fund of facts and laws which belongs
alike to all students of the subject. But by quoting certain author-
PEEFACE. V
ities in the text, and by a few (in comparison with the number
which might have been cited) references in foot-notes, I have con-
nected some of the discoveries and views of modern psycho-physical
science with their authors. These may serve somewhat as guide to
those persons who wish to pursue such studies still further.
I am under particular obligations to Dr. James K. Thacher, Pro-
fessor of Physiology in the Yale Medical School, for valuable as-
sistance in that description of the Nervous Mechanism, its structure
and functions, which- the First Part of the book contains. If I
have escaped the mistake of assuming to teach more than is really
known upon this subject, it has been in large measure due to his
friendly and skilful guidance. Valuable assistance has also been
received from Kussell H. Chittenden, Professor of Physiological
Chemistry, and Charles S. Hastings, Professor of Physics — both of
the Sheffield Scientific School.
The method and arrangement of the book have been chosen so
as to fit it for use, both as a text-book by special students of the
subjects of which it treats, and also by the general reader who is
interested in knowing what results have been reached by the more
modern — and even the latest — psycho-physical researches.
George T. Ladd.
Yale Univeksity, New Haven, February, 1887.
TABLE OF CONTENTS.
PAGE
Introduction 1-14
PART EIRST.
THE NERVOUS MECHANISM.
CHAPTER I.
The Elements of the Nervous System 17-55
§§ 1-4, General Function of the Nervous System. — §§ 5-16, Chem-
ical Constitution of the Nervous Elements. — §§ 17-30, Structural
Form of the Nervous Elements. — §§ 31-36, Common Properties of
the Nervous Elements.
CHAPTER n.
Combination of the Nervous Elements into a System 56-101
§§ 1-3, Threefold Plan of the Nervous System.— § 4, The Sympa-
thetic and Cerebro-spinal Systems. — § 5, Membranes of Brain and
Spinal Cord.— §§ 6-13, Structure of the Spinal Cord.— §§ 13-14,
General Arrangement of the Encephalon. — § 15, Structure of the
Medulla Oblongata.— §16, Structure of the Cerebellum.— § 17, Struct-
ure of the Pons Varolii.— §§ 18-24, Structure of the Cerebrum. —
§§ 25-27, Cortex of the Cerebral Hemispheres.— §§ 28-29, Arrange-
ment of the Nerve-Tracts. — § 30, The Cranial and Spinal Nerves.
CHAPTER IIL
The Nerves as Conductors 102-129
§§ 1-3, General Oflce of the Nerves.— § 4, The Nerve-Muscle Ma-
chine.—§§ 5-8, The Conditions of Neural Action.— §§ 9-19, Phenom-
ena induced in the Nerves by different Stimuli.— §§ 20-23, Electrical
and other Processes in the excited Nerve-Stretch.— §§ 24-26, Laws
Viii TABLE OF CONTENTS.
of the Nerve-Commotion. — § 27, Speed of the Nerve-Commotion. —
§ 28, Effect of Section.— § 29, Nervous Conduction in the Central Or-
gans.—i;§ 30-32, Paths of Conduction in the Spinal Cord.— §§ 33-35,
Paths of Conduction in the Brain.
CHAPTER IV.
PAGB
Automatic AND Reflex Functions of the Central Organs.. 130-162
§§ 1-2, Nature and Kinds of Reflex Action.— §§ 3-5, TheSpinal
Cord as a Central Organ. — ^§ 6-9, Laws of Spinal Reflexes.— § 10,
Irregular Automatism of the Cord. — § 11, Centres of the Cord. — t^ 12,
Excitability of the Cord.— § 13, Inhibition of the Cord. — § 14, The
Brain as a Central Organ. — §§ 15-16, Functions of the Medulla Ob-
longata—-§§ 17-19, Centres of the Medulla Oblongata.— § 20, Influ-
ence of the Cerebral Lobes, — § 21, Functions of the Cerebellum. —
g§ 22-27, Functions of the Basal Ganglia.— § 28, Gray Matter of the
Third Ventricle.
CHAPTER V.
End-Organs of the Nervous System 163-197
§y 1-2, Characteristics of the End-Organs. — § 3, The Kinds of End-
Organs.— §^ 4-5, The End-Organs of Smell.— §§ 6-7, The End-Or-
gans of Taste.— §§ 8-10, The End-Organs of Touch.— § 11, The End-
Organ of Sight. — §§ 12-16, Tunics, Media, and Appendages of the
Eye. — g 17, The Mechanism of Accommodation. — §§ 18-21, Structure
and Functions of the Retina — § 22, Photo-Chemistry of Vision. —
§§ 23-26, External and Middle Ear.— § 27, Structure of the Labyrinth.
■ — § 28, End-Apparatus of the Vestibule. — § 29, The Organ of Corti. —
§§"30-31, Problem solved by the Labyrinth.— § 32, End-Organs of
Motion.
CHAPTER VI.
The Development of the Nervous Mechanism 198-21 S
§ 1, Nature of Embryonic Life. — §§ 2-5, Earliest Development of
the Ovum. — §§ 6-8, Blastodermic Layers and their Differentia. — §§ 9-
11, Head-Fold and Brain-Vesicles. — § 12, Development of Cranial
and Spinal Nerves. — §§ 13-15, Subsequent Development of the
Brain. — §§ 16-17, Development of Eye and Ear. — § 18, Histogenetic
Changes in the Embryo. — § 19, Conclusions.
CHAPTER VII.
Mechanical Theory of the Nervous System 214-23(1
§ 1, Machine-like Nature of the Body.— §§ 2-6, The Nervous Sys-
tem as a Mechanism. — § 7, Summation and Interference in Nerves. —
i^ 8, Evidence from the Electrical Phenomena. — i^ 9, Theory of du
Bois-Roymond. — §^5 10-11, Theory of Hermann. — S^i5 12-13, Theory
of Wundt. — §§ 14-15, General Conclusions as to a Mechanical Theory.
TABLE OF CONTENTS. IX
PART SECOND.
CORRELATIONS OF THE NERVOUS MECH-
ANISM AND THE MIND.
CHAPTER I.
PAGE
The Localization of Cerebral Function 239-263
§§ 1-3, Proofs of the Brain's Special Significance. — §§ 4-7, The
Brain as a Measure of Intelligence. — § 8, Special Significance of the
Cerebral Hemispheres. — ^§ 9-10, The Question of Localization. —
§§ 11-13, The History of Discovery.— §g 14-16, The Evidence from
Experiment.— § 17, The Evidence from Pathology.— § 18, The Evi-
dence from Anatomy. — § 19, True Method of Investigation.
CHAPTER IL
The Localization of Cerebral Function [Continued] 263-802
§§ 1-4, Difliculties from Negative Cases. — §§ 5-6, Experiments in
Stimulation. — ^ 7, Experiments in Extirpation. — ^§ 8-9, Nature of
so-called Motor Centres. — §§ 10-15, Method and Results of Bxner. —
§ 16, Confirmatory Conclusions from other Sources. — § 17, The Evi-
dence of Histology. — § 18, Relation of Motion and Sensibility. — §§ 19-
21, Visual and Auditory Centres of Ferrier and Munk. — ^ 22, Ex-
ner's Cerebral Field of Vision. — g 23, Relations between the Retinas
and the Cerebrum. — § 24, Localization of Smell and Taste. — §§ 25-
27, The Phenomena of Aphasia. — § 28, Cerebral Lesions in Aphasia.
— § 29, Conjectures as to the Frontal Lobes. — § 30, Negative Conclu-
sions of Goltz. — § 31, Conclusion as to three leading Principles.
CHAPTER III.
The Quality op Sensations 303-324
§§ 1-5, Sensations and Things. — § 6, The Subjects investigated. —
§ 7, Specific Energy of the Nerves. — §§ 8-11, Sensations of Smell.
— §§ 12-15, Sensations of Taste.— §§ 16-17, The Varieties of Sound.
— §§ 18-20, The Pitch of Tones. -^§§ 21-22, The Composition of
Clangs. — § 23, Analysis of Sounds by the Ear.
CHAPTER IV.
The Quality of Sensations [Continued] 325-355
§ 1, Analysis of Sensations of Sight. — §§ 2-3, The Stimulus of Sight.
— § 4, Relation of Quality and Quantity. — §§ 5-8, The Different Color-
TABLE OF CONTENTS.
Tones. — § 9, The Complementary Colors. — §§ 10-13, Conditions of
Changes in Coloi-. — § 14, Phenomena of Contrast. — §§15-17, Theories
of Visual Sensations. — § 18, Symbolism of Visual Sensations. — § 19,
Sensations of the Skin. — § 30, The Muscular Sensations. — § 21, Sen-
sations of Pressure. — §§ 22-24, Sensations of Temperature. — § 25,
Specific Energy of the Nerves.
CHAPTEK V.
FAOg
The QuAwriTY of Sensations 356-381
§§ 1-3, Distinction of Variations in Quantity. — §§ 4^5, The Meas-
urement of Sensations. — § 6, Nature of the Least Observable Differ-
ence.— § 7, The Determining of the Limits. — § 8, Methods of Experi-
ment.— § 9, Statement of Weber's Law. — § 10, Measurement of
Sensations of Pressure. — § 11, Measurement of Sensations of Tem-
perature.—§§ 12-15, The Intensity of Sounds.— §§ 16-18, The In-
tensity of Visual Sensations. — ^§ 19-21, Measurement of Taste and
Smell.— §§ 32-23, Value of Weber's Law.
CHAPTBE VI.
The Presentations of Sense 382-419
§§ 1-2, Sensations and Things. — § 3, General Nature of the Pres-
entations of Sense. — §§ 4-5, Laws of the Synthesis of Sensations. —
§§ 6-7, Nativistic and Empiristic Theories. — §§ 8-11, Nature of the
Spatial Series.— §§ 12-15, The Theory of Local Signs.— § 16, The
Stages of Perception. — § 17, Perceptions of Smell. — § 18, Perceptions
of Taste.— §§ 19-20, Perceptions of Hearing.— §§ 21-22, Sense of Lo-
cality by the Skin.— §§ 23-25, Weber's Sensation-Circles.— § 26, The
Discernment of Motion. — § 27, Localizing of Temperature-Sensa-
tions.— § 28, Localizing of Muscular Sensations. — §§ 29-30, Construc-
tion of the Field of Touch. — § 31, Feelings of Double Contact.
CHAPTEK Vn.
The Presentations of Sense [Continued] 420-46']
§ 1, General Principles ai)plied to the Eye. — § 3, Data or Motifs of
Vision. — §§ 3-6, Nature of the Primary Retinal Field. — § 7, Value of
the Retinal Elements. —ij^ 8-9, Motions of the Eye.— § 10, The Law
of Listing. — § 11, Meridians of the Field of Vision. — § 12, Effect of
Accommodation. — i:§ 13-16, Single and Double Images.— § 17, The
Fixation of Attention.— §§ 18-20, Stereoscopic Vision and Vision of
Perspective.- §§ 21-23, The Use of Secondary Helps.— §§ 24-25,
General Office of Experience. — §§ 26-28, Judgment of Spatial Exten-
sion and Relations.— i^ 29, Visual Perception of Motion.— §§ 30-34,
Errors of Sense.— § 35, Development of Visual Percei:)tiou.
TABLE OF CONTENTS. XI
CHAPTER Vm.
PAGE
TrME-REIiATIONS OF MENTAL PHENOMENA 468-497
§§ 1-3, Time-Form as belonging to Mental Phenomena. — i^§ 3-4,
Elements of Physiological and Psycho-physical Time. — §§ 5-7, Effect
of the Inertia of the Nervous System. — §§ 8-12, Nature and Length
of Simple Reaction-Time. — §§ 13-15, Methods for discovering Ap-
perception-Time.— §§ 16-18, Length of Apperception-Time. — §§ 19-
30, Nature of Will-Time.— §§ 21-23, Subjective Estimate of Time.—
§§ 24-85, Reaction-Time of complex Mental Processes. — § 86, The
Circuit of Consciousness. — § 37, Various Influences upon Psycho-phys-
ical Time. — § 88, Conclusions.
CHAPTER IX.
Feelings and Motions 498-581
§ 1, Nature of the Inquiry. — §§ 3-4, Physiological Theory of the
Nature of Feeling. — §§ 5-7, Psychological Theory of the Nature of
Feeling. — §^ 8-9, Classification of the Feelings. — §§ 10-11, Charac-
teristics of all Feeling. — § 13, Physical Apparatus of Feeling. — §§ 13-
14, Nature of Common Feeling. — §§ 15-18, Feelings of Sensation. —
§§ 19-31, The Emotions.— § 33, Mental Moods.— §§ 33-34, The Es-
thetic Feelings. — § 35, The Intellectual Feelings.— § 36, The Feeling
of Effort. — §§ 27-31, Voluntary and Involuntary Movements.
CHAPTER X.
Physical Basis of the Higher Faculties 533-559
§§ 1-3, The Method of Investigation. —§§ 4-6, Physiological Basis
of Acts of Will.— §§ 7-9, The Will in Attention.— §§ 10-11, Cerebral
Processes in Attention. — § 13, Freedom of Will. — § 13, Physical Basis
of Consciousness. — §§ 13-14, Physiological Basis of Memory. — §§ 15-
17, Memory as Retentive. — §§ 18-19, Memory as Reproductive. —
§§ 30-31, Organic Memory. — § 33, Memory as a Psychical Process.
— § 33, Physical Basis of Conception.
CHAPTER XI.
Certain Statical Relations of the Body and Mental Phe-
nomena 560-583
§§ 1-3, Popular Estimate of the Relations of Body and Mind. —
§§ 3-9, Relations Dependent on Age and Development. — §§ 10-18,
Relations Dependent on Sex. — § 13, Characteristics of different Races.
— § 14, The Theory of Temperament. — §§ 15-17, Kinds of Tempera-
ment.— § 18, Physical Basis of Temperament. — § 19, General Corre-
lations of Body and Miud.
XU. TABLE OF CONTENTS.
PART THIRD.
THE NATURE OF THE MIND.
CHAPTEE I.
PAGE
The Faculties of the Mind, and its Unity 585 -613
§§ 1-4, The Method of Investigation. — §§ 5-6, Mental Phenomena
and Cerebral Changes. — §§ 7-9, Physical Theory of the Cause of
Psychical States.— § 10, The Subject of Psychical States.— g§ 11-13,
Variety of the Phenomena of Consciousness — ^§ 14-16, Classification
of Psychical States.— § 17, Nature of the Mental Faculties.— §§ 18-23,
The Unity of Consciousness.
CHAPTER 11.
The Development of the Mind 614-632
§§ 1-2, Genetic Study of the Mind.— §§ 3-5, Reality of Mental
Development. — §§ 6-8, Stages of Mental Development.— §§ 9-10,
Dependence of Mental on Physical Growth.— § 11, Psychical Factors
in Development.— §§ 12-16, The Theory of Mental Evolution.
CHAPTER III.
Real Connection of Brain and Mind 633-667
§ 1, General Question of a Connection of Brain and Mind. — §§ 2-6,
The Brain as the " Seat" of the Mind.— §§ 7-9, The Brain as the
"Organ" of the Mind. — § 10, Special "Bond" between Brain and
Mind. — § 11, Figurative Connection of Brain with Mind. — § 12, Causal
Relation of Brain and Mind. — §§ 13-14, Occasionalism and Pre-estab-
lished Harmony. — § 15, Positivism and Monism. — § 16, The Position
of Dualism. — § 17, Conservation and Correlation of Energy. — §§ 18-
24, The Causal Nexus declared Valid.
CHAPTER IV.
The Mind as Real Being 668-688
§ 1, The Metaphysical Treatment of Mind.— §§ 2-8, The Mind as
a Real Being.— §§ 9-10, The Spirituality of Mind.— §§ 11-15, The
Unity of Mind.— § 16, First and Last Things of the Mind.
PHYSIOLOGICAL PSYCHOLOGY.
nSTTEODUOTIOH.
§ 1. A CLEAR conception oi Physiological Psychology requires some
special knowledge of the nature and methods of those two sci-
ences, the results of whose investigation it endeavors to combine.
These sciences are, of course, Psychology and Physiology — the latter
being understood in a broad way as including also various apphca-
tions of the general theory of physics to the functions of the animal
organism. But as the form taken by this compound term would
itself seem to indicate, the two do not stand upon precisely the
same level in effecting this combination, whether we consider the
end that the one science into which both enter desires to reach,
or the means that it employs to reach the end. For the noun
("psychology") in the compound term may be said more particu-
larly to define the end desired; the adjective ("physiological")
the character of the means which it is proposed especially to em-
ploy. Hence "Physiological Psychology" can scarcely claim to be
an independent science, or even a definite branch of the science of
psychology in general. It is rather to be regarded simply as psychol-
ogy approached and studied from a certain — the so-called " physi-
ological " — side or point of view. It is necessary, then, in the first
place, to define what we understand by the science of psychology,
and how it is proposed to treat this science as subject to the physi-
ological method, and as approached by means of physiological ex-
perimentation and researches.
§ 2. Perhaps the most common definition of psychology, up to the
present time, has regarded it as " the science of the human soul."
If this definition had always been given, on beginning the pursuit
of the science, only in a provisional way, and with the implied or
open confession that it is the business of psychology itself to de-
monstrate the existence of a particular entity called " the soul," and
2 INTRODUCTION".
to show how this entity is needed to explain the phenomena of con-
sciousness, then httle valid objection could have been made to
it. But such has by no means been the case. For example,
one writer on the subject (Drbal), at the very commencement of
his treatise, asserts that "psychology is the science of the human
soul as the real foundation of the spiritual life ; " and another (Erd-
mann) declares that " the subject-matter of psychology is the sub-
jective spirit," meaning by this term the human soul. Objections
have, therefore, been more or less fitly and forcefully urged agninst
this definition as ordinarily employed. It has been said that clearly
■we have no right to assume any such entity as the soul ; and
even that a careful study of all the phenomena — especially by the
experimental and physiological method — does not compel or induce
us to conclude that such entity exists. It has been claimed, espe-
cially of late, that there may be a " psychology without a soul," and,
indeed, that this kind of psychology is alone worthy of being con-
sidered truly scientific. Further objection to the same definition
has been made in other quarters, because it seems to regard the
question as settled, whether man has not moi-e than one subject (or
"ground") of the manifold phenomena called psychical ; whether,
in fact, he may not be the fortunate possessor of both an " animal "
and a "rational" soul, etc. It would be aside from the course of
our inquiries to consider these objections in detail at this time ; or
to state at any length how far we are inclined to agree with them and
how far to express dissent. They may all be, for the present, set
aside by stating the course of procedure which the study of psy-
chology from the physiological point of view seems to us plainly to
recommend.
The satisfactory definition of any science is often one of the latest
and most difficult achievements of that science. When such defini-
tion is placed at the beginning of an investigation, it must often
really include results reached only by going carefully and repeatedly
over the entire ground of the science. In all such cases the learner
of the science is quite unable fully to comprehend the definition, or
to understand the positions upon various disputed questions which
it may really involve. In general, then, it is better that the earliest
so-called definition should be simply a description of that class of
phenomena which it is proposed, as far as possible, to isolate for
purposes of inquiry. This remark applies with peculiar force to
psychology, both on account of such objections as those mentioned
above, and also on account of certain difficulties inherent in the
subject itself. Accordingly, it will serve our purpose best to "de-
fine " this science simply by ascribing to it a certain more or less
INTRODUCTION. 3
definite sphere of plienomena. Thus we shall consider psychology
as that science which has for its primary subject of investigation all
the phenomena of human consciousness, or of the sentient life of
man. If the term " sentience " be employed as preferable to con-
sciousness, it must be understood as equivalent to consciousness in
the broader sense of the latter word. This definition, or rather de-
scription, plainly implies an acquaintance experimentally with cer-
tain phenomena that cannot, strictly speaking, be defined. These
are the phenomena of consciousness ; and one result of all our sub-
sequent investigations will be to show us that consciousness and
its primary phenomena can never be defined. The definition of
psychology need not, however, be understood to imply the real
existence of any one entity such as a soul.
Nevertheless it would be very inconvenient, not to say impos-
sible, to begin and continue the investigation of psychical phenom-
ena, using only roundabout phrases through fear of implying the
real existence of some spiritual entity called the Soul or the Mind.
In some sort there cannot be any description, much less any scien-
tific study, of the phenomena of consciousness without implying
somewhat which requires us to use a word like these. In all lan-
guages, and in the constant everyday use of them all, men in stating
and describing the phenomena of their own sentient life employ
such terms as "I" and "me," and place in a kind of contrast with
them such other terms as " thou " and " he " or "it." Inasmuch
as recollection, and the assumption of some kind of continuous
personal identity, enter into all their experience, and underlie all
their relations with each other and with the physical world which
surrounds them, they are compelled to use language implying a
permanent subject of the phenomena of consciousness. No one
doubts as to his right to ascribe to himself the phenomena of his
own consciousness ; and as well to ascribe certain other phenom-
ena, which are not attributed to himself as their subject, to other
subjects (so-called " persons "), which he supposes to have, each one,
a consciousness of his own. No one doubts that this subject is in
every case somehow the same with itself from hour to hour and day
to day, and even from year to year. In all the earlier part of this
treatise the word "mind" will be employed simply as the equiva-
lent of the subject (which all language as expressive of universal
experience necessarily recognizes) of the phenomena of conscious-
ness. In other words, whatever all men inevitably mean by the
word "I" (the empirical ego of philosophy), whenever they say /
think, or feel, or intend this or that ; and whatever they under-
stand others to mean by using similar language — thus much, and
4 INTRODUCTION.
no more, we propose at first to include under the term "mind."
This term is preferred to the word "soul," in part out of concession
to the prejudices to which allusion has already been made, and in
part because it seems to admit of the handling which it is proposed
to give to it subsequently, with more freedom from entangling alli-
ances with ethical, social, aad religious ideas. In other words, we
wish to begin and continue as far as possible upon purely scientific
grounds. And when, subsequently, these grounds are in part aban-
doned for certain fields of rational speculation, we wish to have the
connection between the two kept open and unimpeded.
§ 3. In accordance with what has already been said concerning
the nature of psychology, Ave may define Physiological Psychology
as the science which investigates the phenomena of human con-
sciousness from the " physiological " point of view or method of
approach. Remembering the cautions which have akeady been
expressed, we may also say that it is the science of the human mind
as investigated by means of its relations to the human physical or-
ganism. A more accurate definition, however, requires that some-
thing further should be said concerning the nature and method of
that science which furnishes the adjective to our compound term.
Human Physiology is the science of the functions (or modes of the
behavior in its correlated action) of the human physical organism.
As studied at present it implies an acquaintance with the fields of
gross and special microscopic anatomy (histology), of embryology
and the general doctrine of development, of biology, — including the
allied phenomena of plant life, — of molecular physics and chemistry
as related to the structure and action of the bodily tissues, and of
other forms of kindred knowledge. It is only a relatively small part
of this vast domain, however, with which Physiological Psychology
has directly to deal ; for it is only a part of the human organism
which has any direct relation to the phenomena of consciousness.
As will appear subsequently, it is with the nervous system alone,
that our science has its chief immediate concern. Indeed it might
be described — though in a stiU somewhat indefinite, but more full
and complete, way — as the science which investigates the correla-
tions that exist between the structure and functions of the human
nervous mechanism and the phenomena of consciousness, and which
derives therefi'om conclusions as to the laws and nature of the
mind.
§ 4. Physiology is compelled, from its very nature as a physical
science, to regard the nervous system as a mechanism. Physiological
Psychology, inasmuch as it relies so largely upon physiology for its
data and method and points of view, is also required to consider
IlSrTRODTJCTION". 5
this system in the same way. Those unique relations in which the
structure and functions of the nervous substance of the body stand
to the phenomena of the mind cannot deter the investigator from as-
s)iming toward it the so-called mechanical point of view. Physiology
presents psychology with a description of this nervous substance as
a vast and complex system of material molecules, which are acted
upon by different forms of the energy of nature outside (external
stimuli), and by intimate changes in the contiguous molecules of
the other substances of the body (internal stimuli) ; and which be-
have as they do on account of the influences thus received, as well
as on account of their own molecular constitution and arrangement.
But all this is the description of a material mechanism. The word
"mechanism "is preferable to the word "machine" for describing
such a system of interacting molecules as constitute the living ner-
vous substance, because we attach to the latter word the mental pict-
ure of something which has a certain magnitude and rigidity of
parts that act and react upon each other in a palpable way under
the ordinary laws of mechanics. A steam-engine is a machine
whose parts may be seen to push and pull and turn each other after
the ordinary fashion of all levers and wheels. But the molecules
of the steam, from the activity of which all the motion of the rigid
and ponderous parts of this machine is derived, are no less mate-
rial and governed by physical law in their changing relations to
each other than are the masses of the machine itself. The inter-
action of the minute particles of the steam falls more fitly, how-
ever, under the conception of mechanism. Indeed, it is only as
falling under this general conception that these molecules admit of
any scientific treatment at all. Now it is not our purpose to begin
the consideration of the human nervous system by debating the
question, how completely it falls under the conception of mechan-
ism, and whether some other conception be not needed to supple-
ment this when the unique relations of this system to the phenomena
of the mind are taken into account. Whatever is to be said upon
such a question must appear in its proper place in the order adopted
for the discussion of the general subject. Physiological Psychology,
however, can scarcely establish itself at all unless it be willing to
receive from the proper one of the two sciences which enter into it
that conception of the nervous system at which this science has
arrived as the result of the most successful modern researches. As
far as the nervous system admits of being subjected at all to scientific
treatment, for the purpose of attaining a more complete knowledge
of the nature of its functions, it is necessarily considered as a com-
plex molecular mechanism. We shall, then, receive, in a grateful
6 IlSiTRODUCTION.
and docile manner, all tliat the noble science of human physiology
has to teach us, under the guidance of the conception of a mech-
anism, both directly concerning the manner in which the nervous
matter of the human body performs its wonderful functions, and
more indirectly concerning the relations in which these functions
stand to the phenomena of consciousness.
§ 5. Physiological Psychology — it is by this time apparent — par-
takes of the nature and methods of two sciences that differ widely
from each other. One is a science which involves introspection ;
for it is only by the method of introspection that the real and pres-^
ent facts of human consciousness can be reached. The other is a
physical science, and involves external observation to determine the
external facts of the structure, development, and functions of a
physical mechanism. Two sets of phenomena must then be exam-
ined in their relations to each other, and, so far as possible, the
laws (or permanent modes) of these relations pointed out. It is
due to this fact, in part, that both the peculiar difficulties and the
peculiar interest and value of psycho-physical researches are so
great.
In every science a beginning is first made by ascertaining and
comparing together all the important phenomena ; the laws, or
regular modes of the occurrence of the phenomena in relation to
each other, are then investigated ; and, finally, certain conclusions
are drawn concerning the nature and significance of those real be-
ings which reason compels us to assume as permanent subjects of
the different classes of phenomena. In its effort to establish itself
upon a scientific basis. Physiological Psychology has no choice but
to follow essentially the sarce method of procedure. In its case,
however, as has already been remarked, the phenomena which are
to be ascertained and compan d belong to two orders that obviously
differ greatly from each other ; and the laws which it is sought to
discover ai'e laws which maintain themselves between these two or-
ders of phenomena. The phenomena of the nervous system, like
all physical phenomena, consist in changes in the constitution and
mutual relation of material masses and molecules. They are, then,
of a kind to be related to each other, under the conception of mech-
anism, inside of the nervous system and of the entire human body ;
and also, outside of the body, to the various forms of physical energy
in nature which act upon these masses and molecules. But the
psychical jDhenomena are states of consciousness, constantly shifting
modes of the behavior of that subject which Ave have agreed — as
much as possible without involving any j^remature assumptions — to
call the Mind. Still the above-mentioned two orders of phenomena
IlsrTKODUCTION". 7
are obviously to a large extent related to each other ; they may, in
fact, be said to be correlated in a unique manner. The constant
forms of this correlation constitute the laws for the discovery of
which Physiological Psychology undertakes its special researches.
It endeavors to bring the two orders of phenomena face to face, to
look at them as they stand thus related to each other, and, as far as
possible, to unite them in terms of a uniform character, under law.
It might seem that simjDly to attempt the accomplishment of the
task just described should satisfy all legitimate demands. And,
indeed, no little protest has of late been made against any attempt
on the part of scientific psychology (and how much more when
studied from the physiological and experimental point of view) to
proceed further than this. All inquirers have been warned, not only
against introducing metaphysical assumptions into the beginnings
of psychology, but also against allowing any admixtui'e of the two
during the investigations pursued by the latter. We have, indeed,
just agreed that metaphysical assumptions as to the natui-e of mind
should prejudice as Httle as possible our statement of psychological
facts and laws. But if the warning against so-called " metaphysics "
be understood to mean that inquiry must be stopped when the
phenomena and their uniform modes of relation have been enume-
rated, and that no venture must be made upon any discussions or
conclusions regarding the real nature of the subject of them all
(the mind), such warning may very weU be quietly disregarded.
What we are chiefly interested in, on undertaking aU josychological
investigation, is the real nature — the permanent characteristics, the
claims to be a substantial existence, a spiritual unity — and the ori-
gin and destiny of the mind. To assume as little as possible con-
cerning all this, at the first, is simply a matter of wise reserve and
self-control in the interests of scientific investigation. We feel no
hesitancy, however, in announcing our intention, ultimately, to
draw whatever conclusions seem to us legitimate and desirable con-
cerning many of these so-caUed "metaphysical" inquiries. Psy-
chology— no less truly when studied from the physiological and ex-
perimental point of view — has the undoubted right, and is under
the obhgation, to contribute as much as possible toward the solu-
tion of these inquiries. Nor do observation and wide reading
show that the advocates of " psychology without a soul," and freed
from all metaphysics, are at all certain to avoid drawing con-
clusions, not to say introducing illegitimate assumptions, upon
these very same inquiries. In brief, Physiological Psychology has
the right, which belongs to it as a science, to introduce whatever
conclusions as to the natiire of mind follow legitimately from its
8 INTRODUCTION.
discussions of plienomena and laws. It has even a right to in.
dulge in well-founded and reasonable speculation. Such things are
not necessarily objectionable when indulged in by any of the more
purely physical sciences. Indeed, there is not one of these sciences
which would not look comparatively bare and unattractive if wholly
stripped of its more or less questionable inferences, its metaphysi-
cal assumptions, its guessings, and speculations.
§ 6. The remai'ks immediately foregoing serve to indicate what
are the principal Divisions of this work. The Fii'st Part will
consist of a description of the structure and functions of the Ner-
vous System. This system will there be considered tmder the
conception of a mechanism, and as far as possible without any
direct or indirect reference to the phenomena of consciousness as
determined by introspection. The Second Part will describe the
various classes of correlations which exist between the phenomena
of the nei'vous mechanism and mental phenomena. It will also
attempt to state what is known of the laws which maintain
themselves over these various classes. No attempt will be made,
however, to describe and discuss any of the phenomena which may
be classed as abnormal, or as consisting (so far as they are psychical)
in so-called " disturbances of consciousness," except when reference
to such abnormal phenomena is necessary in order to explain those
which are called ordinary or normal. The phenomena of insanity,
delirium, hypnotism, somnambulism, ecstasy, mind-reading, spir-
itualism, and even of sleep and dreaming, will therefore be defi-
nitely excluded. The chief reason for such exclusion is to be found
in a lack of space, it being difl&cult even to bring within the limits
of a single volume a sufficiently thorough discussion of the more
ordinary phenomena with which Physiological Psychology is caUed
upon to deal.
The various correlations of the mind and the nervous mechanism
(of which the Second Part treats) may be conveniently consid-
ered under several principal groups or classes. The first of these
includes more particularly such relations as can be established be-
tween the condition and activity of the supreme nei-vous centres
and the phenomena of conscious sensation and voUtion. Most of
what can be said at present upon this point may be summed up in
the discussion of the localization of cerebral function, as taken in
connection with the description of the automatic and reflex action of
these centres considered as parts of the nervous mechanism. The
second class of these correlations covers all the phenomena with
whifh psycho-physics (in the more precise use of the term) attempts
to deal. It- discusses the relations which exist between the quality,
INTKODUGTIOI^". 9
quantity, combination, and order of succession in time, of the vari-
ous stimuli which act upon the nervous system, and the kind, mag-
nitude, composite result, and time-relations of the mental phe-
nomena. Hence the significance of the term psycho-physics. As
Physiological Psychology is ordinarily and legitimately treated,
it includes these more specially psycho-physical researches. An-
other class of these correlations covers certain related phenomena
of mind and body as dependent upon age, sex, race, etc.
Besides the foregoing groups, or classes, certain observations
which have more or less of scientific confirmation and value,
may be made regarding the physical basis of the feelings and voli-
tions controlling the bodily members, and of the higher faculties of
memory, association of ideas, etc. The Third Part will fitly intro-
duce, at the close of the psycho-physical researches, the presenta-
tion of such conclusions as may be legitimately gathered, or more
speculatively inferred, concerning the nature (considered as a real
being) of the human mind. The justification of the order and ex-
tent of the entire discussion, and especially of the Third Part as a
whole, has already been given to some extent ; the rest must be
left to the progress and result of the discussion itself.
§ 7. It has already been said that the peculiarity of Physiological
Psychology, considered as a branch of the general science of mind,
consists largely in the method of its approach to its subject. At-
tention must now be more specifically called to this method as
necessarily partaking of the methods of the two sciences whose
researches it undertakes to combine. The method of physiology,
which is in general that of external observation as employed in all
the physical sciences, should be applied only when supplemented by
the many delicate and accurate instruments of observation now at
command, and guarded and checked by that accumulation of expe-
rience concerning the best ways of studying nature and concern-
ing her ways of working which the whole body of such sciences
has made. On the other hand, the method of psychology has or-
dinarily been defined as solely the method of introspection or self-
consciousness. These two methods are obviously very different.
It would not be strange, then, if the science which finds it neces-
sary to combine the two should experience some special difficulty.
This difficulty has, however, more often been exaggerated than ex-
plained and (what is quite possible) for the most part removed.
Our present purpose does not require that we should examine at
length the question whether the introspective method is the only
one possible in psychology. Scarcely moi-e is necessary than the
statement of the bearing of this question upon the inquiries it
10 INTKODUCTION.
is proposed to make. There should in general be no mystery or
arrogant assumption' about the use of such words as "science" and
"scientific method." Science is nothing but knowledge — real, veri-
fiable, and systematic. Scientific method is nothing but the way
of arriving at such knowledge. Now, although Physiological Psy-
chology brings the investigator face to face with some of the most
interesting and distinctive mysteries, it is not, as a science, to be
regarded as especially mysterious. Inasmuch as its specific busi-
ness is to ascertain and combine, under definite laws, two widely
differing classes of facts (facts of the human nervous mechanism and
facts of human consciousness) it is, of course, compelled, first of all,
to ascertain both kinds of facts. The phenomena of consciousness,
as primary facts, can be ascerlained in no other way than in and by
consciousness itself. Whatever fault may be found with the so-
called introspective method in psychology, on account of its alleged
inaccuracy, lack of scientific and progressive quality, etc, from the
very natui'e of the case no other way of ascertaining what the phe-
nomena of consciousness in themselves are can ever take the place
of the dii'ect examination of consciousness. And there is no way of
directly examining consciousness but the way of being conscious
one's self. On the other hand, it is perfectly obvious to students
of psychology and of its history (on grounds which need not be
stated here) that the scientific treatment of the facts of conscious-
ness can never be, to any satisfactory extent, accomplished by in-
trospection alone. For psychology, in order to make valid its claim
to be a science, must not merely display the alleged facts of individ-
ual mental expex'ience ; it must treat these facts analytically, must
resolve them into their ultimate factors, and trace the stages of
their development from what is simpler to what is more complex ;
it must also show on all sides their connections and causes, thus
placing the phenomena of the mind as much as possible in interac-
tion with the rest of the world. It is because human physiology can
contribute largely to such scientific treatment (as distinguished from
the mere observation, grouping, and cataloguing) of the phenomena
of the mind that it is entitled to be considered as furnishing one
distinctive and fruitful branch of psychological researches.
§ 8. The following statements will, accordingly, be found to hold
good concerning the method of Physiological Psychology. It must
employ faithfully the methods distinctive of both the two sciences
which it endeavors to combine. Facts as to the structure and
functions of the nervous mechanism, and as to the effect upon it of
various kinds of physical energy acting as stimuli, must be ascer-
tained by external observation. In general they must be accepted
INTEODUCTION. 11
by us as contributed from the modern science of human physiology.
The primary facts of consciousness must be ascertained from con-
sciousness itself ; or, since they have already been for a long time
subjected to this form of observation, and tabulated, compared, and
classified, they may be accepted from the science of introsjjective
psychology. Care must be taken, however, to make sure that all
alleged psychical facts are really facts ; but iipon this point, again,
there is no other way of making sure than in and through conscious-
ness. The principal laws and inferences also of introspective psy-
chology may be accepted (at least in a provisional way) on begin-
ning the study of Physiological Psychology. The final result of
such study will doubtless be, not only to sujDplement and explain,
but also to modify and correct, the statement of these laws and in-
ferences. But here, as in other scientific research, we are obliged
to work our way through many mistakes, obscurities, and other ob-
stacles, progressively nearer the complete and verifiable knowledge
of the truth.
Furthermore, from the nature of the case. Physiological Psychol-
ogy takes its point of starting from the facts and laws of physiology
as reached by the method of external observation. This follows
necessarily from the relation in which the two sciences of physiol-
ogy and psychology stand as entering into the proposed combina-
tion. The enlargement of our knowledge of the latter is the
end to be reached ; but the former is to give us the way by which,
and the guidance under which, the approach to this end must be
made.
It will also become evident, in the course of the following inves-
tigation, that we are seldom or never able to proceed directly with
the work of comparing the immediate physical antecedents or con-
sequents of the mental phenomena with these phenomena them-
selves, and so of drawing conclusions at once as to the laws by
which the two classes of facts are connected. Such immediate an-
tecedents and consequents are hid in the inexplorable recesses of
the living and molecularly active brain. It is seldom, indeed, that
our direct observation can approach within the tenth, or it may be
within the hundredth, remove of what goes on in these recesses. We
are obliged to examine the physical phenomena from a greater dis-
tance and in a more indirect way. For example, physics can inform
us what combinations of what wave-lengths of the vibration of ether
fall on the eye when a certain form of conscious sensation, which
we call " yellow " or " red " or " blue " arises ; physiology can lo-
cate the nervous elements of the retina upon which the waves fall,
can conjecture something as to the chemical changes there produced,
12 INTEODUCTIOlSr.
and trace doubtfully the paths along which the resulting nervous
impulses rise to the brain and diffuse themselves over certain of
its areas ; psycho-physics can tell approximately the relatious in
which the varying quantities of the stimulus stand to the resulting
degrees of the sensations. But in all this we are still at a great dis-
tance from the enjoyment of those opportunities which would seem
necessaiy to make the science of Physiological Psychology as com-
prehensive and exact as could readily be wished. As a rule, certain
kinds and amounts of physical energy, more or less definitely meas-
urable, are known to be acting on the peripheral parts of the body,
and the next series of observed facts is the emergence in conscious-
ness of a psychical experience quite unlike all kinds of physical en-
ei'gy. To be sure, Fechner's ' conception of psycho-physics is that
it treats those "physical activities which are the bearers {Trdger) or
conditions of the psychical, and accordingly stand in direct func-
tional relation with them ;" or again, "psycho-physics is an exact
doctrine of the relations of function or dependence between body
and soul — of the universals that lie between the bodily and spirit-
ual, the physical and psychical world." But it will be seen that of
such physical activities we have little or no assured knowledge ; al-
though we have the best of grounds for believing that such activities
exist, and that they stand in important relations under law with the
facts of the conscious psychical life.
It follows, then, that Physiological Psychology is, pre-eminently,
first experimental and then speculative ; it can never become
strictly demonstrative, or even deductive to any considerable ex-
tent. That a strictly demonstrative science of the relations be-
tween the structure and functions of the nervous mechanism and
the phenomena of consciousness is impossible, we might argue from
the most ordinary experience. To infer from certain movements
of material molecules that certain facts of consciousness munt take
place, under the most universal laws of all Being, involves a kind
and amount of knowledge of which we cannot even clearly conceive.
In brief, our proper course will be, first, to explain, as completely
as possible, the structure and functions of the nervous mechanism ;
and then to set forth, as fully as the present means at disposal will
permit, the various relations in which its action under stimuli
stand to the phenomena of the mind. In attempting the latter
problem we shall come upon a few, but only a few, general state-
ments of fact which deserve to be s^ooken of as laws in any strict
meaning of the word.
1 Elemente d. Psychophysik, pp. 8 and 10. Leipzig, 1860.
INTRODUCTIOlSr. 13
§ 9. If the correctness of the remarks last made be admitted, the
inquiry may be raised : What justification has this so-called sci-
ence of Physiological Psychology for the large claims which it has
made of late ; and, indeed, what right has it to exist as a special
discipline at all? The full answer to the call for self-justification
must be made by the actual achievements of the science itself. It
will be better, then, to leave it to the convictions of the reader when
the presentation of these achievements shall have been made. But
even at this point an appeal may be taken to certain facts. We
have already repeatedly conceded the fact that we are to investigate
the phenomena of consciousness (that is, study psychology) by a
special method rather than try to establish an independent science
or even separate branch of the general science of mind. The de-
mand for a justification is then reduced to this — Is there valid
reason for studying psychology in this particular way ; for approach-
ing its domain through the researches and conclusions of physi-
ology ? To such a question there can be but one intelligent answer.
There is an abundance of valid reason.
The history of modern investigation, and the conclusions of the
modern science of man, both physical and psychological, emphasize
the necessity of studying his nature and development as that of a
living unity. Such science shows man to be at the head of a series
of physical and psychical existences ; he cannot be understood as
he is, in his whole nature and in his place within nature at large,
without taking both sides of this living unity into account. For
man is known to himself as body and mind — and not as bodiless
spirit or a mindless congeries of moving molecules. That the struct-
ure and functions of the body, especially of the nervous mechan-
ism, and the activities of the mind, are extensively and intimately
correlated, is a fact beyond all doubt. It is the particular task of
Physiological Psychology to show in what manner, and to what ex-
tent, such correlation exists. Moreover, there are few questions
more interesting, from a philosophical and an ethical point of view,
than such as the following : What is the nature of mind, considered
in the light of its correlations with the body ? and. Do the so-called
physiological and the so-called psychical phenomena belong to one
subject, or to more than one? But these and similar questions
can be scientifically answered only by giving a speculative treat-
ment to the conclusions of psycho-physical investigation.
In brief, it may be said that introspective psychology, important
as its results have been, and indispensable as its method is, has
shown its incompetency to deal with many of the most interesting
inquiries which it has itself raised. On the other hand, psychology
14 INTKODUCTIOW.
as pursued by tlie experimental and physiological method has al-
ready thi'own a flood of fresh light upon many of these inquiries.
We may affirm with Wundt,' without fear of successful contradic-
tion : "Psychology is compelled to make use of objective changes
in order, by means of the influences which they exert on our con-
sciousness, to establish the subjective properties and laws of that
consciousness." On this fact and on th§ real achievements of the
method we confidently rest its claims to serious and permanent con-
sideration.
' Art. "Ueber psychophysiken Methoden," Philosophisclie Studien, 1881,
heft 1, p. 4.
PART FIRST.
THE NERYOUS MECHANISM.
CHAPTER I.
THE ELEMENTS OF THE NEEVOUS SYSTEM.
§ 1. In all forms of animal life, except the very lowest, the pres-
ence and activity of a nervous system constitutes the chief charac-
teristic of their difference from all the more nearly corresponding
forms of plant life. Both animals and plants are organisms, and
their structure — regarded as a whole composed of an indefinite
number of material masses or particles, which move with reference
to each other for the accomplishment of a common piece of work
— may be considered as a "natural mechanism." Both have mate-
rial parts of superior firmness, adapted to divide off and to support
their softer parts. Plants, as well as animals, are possessed of liv-
ing, and, more especially, of contractile tissue ; they are therefore
capable of the functions of nutrition, of propagation, and of that
so-called automatic motion which is thought to be a fundamental
property of protoplasm. As is well known, science is not yet able
always to distinguish between the lowest forms of animal and the
lowest forms of plant life. But nervous tissue and its functions
do not belong to the vegetable kingdom ; on the contrary, the pos-
session and use of at least a rudimentary mechanism of nerve-fibres
and nerve-cells are found in most members of the animal kingdom.
It is true that, even in the case of animals which do possess
a nervous system, the structure and functions of the nervous tissue
are very closely related to those of the merely contractile tissue.
Thus the muscular tissue of the animal might seem to be a connect-
ing-link between its own nervous tissue and the contractile tissue
of the plant. For the motor nerves, at least, are anatomically con-
nected by means of their end-plates with the contractile substance
of the muscular fibre, and the result of modern experimentation,
with both muscles and nerves, has been to make clear many feat-
ures of resemblance between them. On the other hand, even the
isolated nervous elements, when subjected to the same exjDeri-
mental tests as those which are used to determine the funda-
mental properties of contractile tissue, exhibit certain marked
differences of behavior ; while the functions of such elements,
3
IS FUlSrCTION OF A IS^ERVOUS MECHANISM.
when combined into a very simple nervous system, are alto-
gether unique. Moreover, as the nervous system of the animal
becomes more elaborate and complex, and especially as its central
organs — spinal cord and brain — are relatively developed, other new
and wonderful functions are seen to be connected with it. In the
case of the superior vertebrate animals, and especially of man, the
significance of this particular form of a physical mechanism be-
comes, therefore, vastly increased. Thus the minute structure of
the nervous mechanism invites the student of chemistry, molecular
physics, and histology, to investigations of the greatest interest and
yet of extreme difficulty ; while the functions of this mechanism
are so curiously and intimately connected with the phenomena, not
merely of all higher animal life, but also of human consciousness,
that inquiry into them is, among all physical inquiries, the one of
unparalleled intellectual interest and importance.
§ 2. It will be the work of this entire treatise to set forth in some
detail the unique functions of the human nervous mechanism, to
which allusion has just been made. For the present a very gen-
eral and somewhat indefinite statement of these functions must suf-
fice. In general, and somewhat indefinitely, it may be said, then,
that the one great function of the nervous system is to concatenate (or
link together into a whole) the manifold elements, both physical and
psycho-physical, which enter into the twofold life of man. Differ-
ent and distant parts of the body, whether they belong to the same
or to different so-called systems (as, for example, the circulatory,
the secretory, the digestive, the muscular), are bound together, and
made to exercise their functions in reciprocal dependence and for
common ends, by the nervous mechanism. The whole body is also
linked to the external world, and kept in either unconscious or con-
scious adjustment to the changeful play of its forces, by the same
mechanism. And further, the development of the mental life, at
least in all its more primitive and fundamental factors, is mediated
by the nervous system. For it is certainly in connection with the
exercise of nervous functions that sensation takes place ; and, by
development and combination of the sensations, all our perceptions
of the so-called " Things " of the external world. It is the nervous
mechanism which uiiites the entire body with the physical stimuli
of tlie external world, on the one hand, and, on the other, with the
primitive activities of mind. What relation the nervous functions
have, and whether they have any direct relation at all, to memory,
judgment, and the higher activities of mind in general, we do not
now even inquire.
The significance of the above-mentioned function of " concatena-
. EXAMPLES OF EEFLEX ACTION". 19
tion," so far as it concerns the different and distant parts of the
body, might be illustrated in many ways. Inasmuch as the plant
is an organism, there is a reciprocal dependence of the structure
and action of all its parts. But each part of the plant acts directly
and slowly on only contiguous parts in effecting the distribution
of the fluids, upon the spread of which the life and growth of the
plant depend. In the case of the animal, however, an effect pro-
duced in one part of the body may quickly spread to other distant
parts by the mediation of the nervous system. The circulation of
the blood is made to affect, and to be affected by, the state of the
skin and the muscles, the state of the respiratory organs, or the
state of the mind's feeling as determined by the ideas before the
mind. A draught of cold air, for example, strikes some peripheral
portion of the body ; the heart and lungs modify their activities,
the muscles contract, and a shudder runs through the physical
framework ; the secretions are disturbed, and the mind is, perhaps,
seized with a vague feeling of fear. Such a complex effect of the
stimulus of cold on some region of the skin has been brought about
by the action of the nervous system, with its peripheral end-organs,
conducting nerve-fibres, and nervous centres. Or, again, the seeing
of some sight or the hearing of some sound is followed by ideas and
emotions of shame, or of fear, or of joy. A complex co-ordination
of the muscles then takes place, so as to move the limbs in running,
to give or ward off a blow, to extend the hand in greeting, to lift
up or bow down the head. In this case, also, the action of heart
and lungs and secretory organs is greatly modified ; the capillary
circulation is altered, and the cheeks are blanched or reddened ;
the pupils and lachrymal ducts of the eyes are moved ; the very
hair of the head seems to sympathize with the state of the mind.
Thus, changes which involve the functions of almost all the tissues
and organs of the body are accomplished by the mediation of the
nervous mechanism. Unlike the modifications in expression of
function which take place in the plant, they are accomplished with
what seems a practical instantaneousness. The complexity of the
reciprocal changes which characterize the life of the higher animals
is due to the general functions of the nervous system ; the speed
with which the changes are accomplished is dependent upon the
laws of the propagation of nervous impulses within that system.
Further illustration of this general office of the mechanism of
nerve-fibres and nerve-cells in " concatenating " the manifold ele-
ments of physical and psycho-physical life may well be left to the
progress of our examination.
§ 3. The application of the term " mechanism " to the nervous sys-
2;) FUNCTION OF A NERVOUS MECHANISM.
tern of man has already (see p. 4 £f.) been partially explained and
justified. We now describe the elementary parts of such a system
as considered from the same general point of view which induces
us to aj^ply this term to the structure and functions of the entire
system. In order to do this, it is necessary to speak, first, of the
structure, and, second, of the function of these parts, regarded as the
fundamental and distinguishing factors of a complex mechanism.
That is to say, two inquiries must be made : What is the composi-
tion and form of those ultimate structures called nervous elements,
into which microscopic anatomy analyzes the nervous system ? and,
W^hat can such stnictures do which fits them to act as parts of a
" mechanism " like that of the nervous system ? It is obvious that
the answers to these inquiries lie at the very entrance upon the
way toward a complete science of the nervous mechanism. But
even if the fullest imaginable answers were already attained, much
would remain to be done in order to perfect the science. Histology
would still have to inform us precisely how the elements are com-
bined into the manifold organs of a system. Physiology would
have to discover the laws according to which the functions of the
elements are modified, when they act as thus combined. Of course,
to know completely the nature, number, and properties of all the
individual factors of a mechanical system, and to know also pre-
cisely how those factors are combined into the system, as well as
how their modes of behavior are affected by such a combination,
would be to have a complete science. of such system.
A strictly deductive science of the molecular motion, and con-
sequent function of the elements of the nervous mechanism, is, in-
deed, a conceivable attainment. But it need scarcely be said that
we are indefinitely far from, not only the attainment, but even the
reasonable px'ospect of such a complete physical science of the ner-
vous system. None of the questions raised respecting the struct-
ure and functions of its elements, whether considered apart or in
combination, can be answered with complete satisfaction. More-
over, the scientific study and description of the neiwous mechanism
is compelled from the first to pui'sue a somewhat different path
from that open to many forms of physical science. The direct
path to the complete science of the subject is impassable ; it is ren-
dered impassable by the most fundamental and universal of our
experiences respecting the nature of the phenomena of the nervous
system. The immediate effects of the molecular changes which
take place in the nervous elements, even when isolated as much as
possiV^le, can only with difficulty be made the subject of direct obser-
vation. Histology has enormous difficulties to overcome in its effort
STUDY OF NEEVOUS ELEMENTS. 21
to describe how these elements are combined in the living human
body, and physiology has like difficulties in the way of its effort to
determine the functions of those organs which are constructed by
means of such combination. Only the beginning of a theory which
shall correlate that mode of molecular motion which is peculiar to
nervous matter with other modes of the motion of matter has yet
been made.
In spite of the foregoing concessions, a careful study of the ele-
ments of the nervous system is the indispensable mode of approach
to the subject of physiological psychology. It is these elements
which, when variously combined, constitute all the organs of the
system ; it is they which, when acting in combination, do all the
woi'k of the system.
§ 4. The Elements of the Nervous System of Man, as elements, do
not differ in any essential known respect from those of other verte-
brate animals. Upon this subject, then, histology with its micro-
scope, and physiology with its experimentation, can describe the
nerve-fibres and nerve-cells of other animals, and then safely draw
certain inferences from them which will apply to the case of man.
It is, however, the development of enlarged or of new organs by
the combination of these elements, and the development and elab-
oration of function as dependent upon such organs, which consti-
tute the difference between the nervous system of man and that of
the lower animals. It is here that histology meets with its supreme
difficulties and its most interesting problems ; it is here that physi-
ology is most insecure when trying to carry over to the structure and
functions of the human nervous mechanism the conclusions which
have been reached by experiments upon the lower animals. On
the contrary, the nerve-fibres and nerve-cells of these animals are,
in most respects, perfectly competent to tell us all we need to know
regarding the nerve-fibres and nerve-cells of man. In describing
the constitution, structure, and function of the nervous elements,
therefore, it will not generally be necessary to pay attention to the
specific animal form from which the description is taken. In other
wordSj the discussion of the nervous elements belongs to the most
general histology and physiology of the nervous system.
§ 5. The elements of the nervous mechanism require to be con-
sidered in three ways : (1) as respects their chemical constitution ;
(2) as respects their formal structure ; (3) as resjDects their general
physiological function.
§ 6. The Chemistry of the Nervous System is of necessity in an
exceedingly unsatisfactory condition. The facts concerning which
perfect certainty is attainable are very few in number ; the bearing
22 CHEMISTEY OP NERVOUS ELEMENTS.
of those facts on our theory of nerve-function is both slight and
disputable. Physiological chemistry is in general encompassed
with many difficulties. These difficulties are not due simply to the
complex constitution of most of the substances with which it has
to deal. They are also very largely due to the fact that these sub-
stances are products of life ; and living tissue cannot be at the
same time kept in normal condition and subjected to the handling-
necessary for chemical analysis. As soon as it is no longer alive,
or at any rate long before any chemical analysis can be completed,
the constitution of such tissue is changed. However carefully the
chemical elements, the constituents, which enter into the ner-
vous substance may be preserved, their constitution, their chemical
arrangement and behavior, cannot be preserved. It is impossible
— for example — for the chemist even to determine the specific
gravity of uncoagulated blood, " except by operating with extreme
expedition and at temperatures below 0° C."
Moreovei', the difficulties which belong to the chemistry of all
living tissue are especially great in the case of the nervous tissues.
In their natui'al state the proximate principles which compose these
tissues are very complex and unstable compounds. To obtain spe-
cific portions or kinds of nervous substance free from foreign ingre-
dients— as, for example, the axis-cylinder of the nerves, or the rods
and cones of the retina — is by no means always easy. The analysis
of such substance, when once the substance is obtained, is often ex-
tremely tedious in respect to process, and doubtful in respect to
result. Nevertheless, the principal conclusions, which may be ac-
cepted with considerable confidence in their correctness, are as
follows :
§ 7. Nervous Matter is of two kinds,. called white or fibrous, and
gray or vesicular, which differ not only in color and microscopic
structure, but also in specific gravity and chemical constitution.
The specific gravity of the white nervous matter is greater than that
of the gray. Danilewski ' found the specific gravity of the gray
matter in man to vary from 1.02927 to 1.03854 ; that of the white
matter from 1.03902 to 1.04334. Others (as Bastian, W. Krause,
and L. Fischer) calculate the mean specific gravity of the gray mat-
ter at about 1.031, of the white at 1.036-1.040. This difference in
the weight of the two is chiefly due to the difference in the relative
amount of water and of solids which they contain. Of 100 parts of
each, from the brain of the ox, the gray matter was found to be
' See Med. Centralbl , xviii., p. 241, as cited by Dreclisel, with apparent
confidence, in Hermann's Handbuch der Physioiogie, V., i. , p. 577. Leipzig,
1«83.
NON-PHOSPHORIZED BODIES IN BRAIN.
23
composed of 81.60 parts of water and 18.40 of solids ; the white,
of 68.35 of water and 81.65 of solids. The amount of water is also
larger in the brain of the young animal than in that of the adult.
The brain of the foetus was found by Weisbach to consist of from
87.9 to 92.6 parts of water. The amount of water entering into the
composition of the different parts of the central nervous system is
unequal. The following is a tabulated statement * of the facts to
which allusion has just been made :
Pkopoktion of Water in One Hundred Parts.
Age, 20 to 30.
Age, 30 to 50.
Age, 70 to 94.
White substance of the brain
69.56
83.36
78.83
73.46
74.43
68.31
83.60
77.87
73.55
73.25
73.61
Gray substance of the brain
Cerebellum
84.78
80.34
Pons Varolii
72.74
Medulla oblongata
73.63
The amount of water varies in the different regions of the spinal
cord. Bernhardt found a smaller proportion of water in the cervi-
cal (73.05 per cent.) than in the lumbar (76.04) region of the cord.
The gray matter also contains more of albumen, lecithin, and lactic
acid than the white, and less of cholesterin, fat, and protagon.
§ 8. Of the solids contained in the matter of the nerve-centres,
more than one-half in the gray, and about one-quarter in the white,
consist of certain proteid or albuminous substances. Bodies of
this general class are the only ones never absent from the active
living cells ; they therefore exist in the primordial structures of
all vegetable and animal organisms, and occupy a peculiar place
among organic proximate principles. Of these proteid substances
found in the nerve-centres very little is as yet known. Gamgee '
mentions three such substances — one soluble in water and probably
derived from the gray matter, another a globulin-like body which
is dissolved by a ten per cent, solution of common salt, still another
a myosin-like body which remains in solution when a ten per cent,
salt solution of brain is boiled.
§ 9. Three other non-phosphorized bodies of different classes
from that above mentioned are found in nervous tissues : these are
Cholesterin, Neurokeratin, and, more doubtfully, Cerebrin. Cho-
' Derived from Weisbach's observations, and found in Gamgee, Physiologi-
cal Chemistry of the Animal Body, i. , p. 445. London, 1880.
"^ Physiological Chemistry, i., p. 433 ; see, also, the article of D. Petrowsky,
*' Ziisammensetzung der grauen und der weissen Substanz des Gehirns," Pflii-
ger" s Archiv, vii., p. 367.
24 CHEMISTEY OF NERVOUS ELEMENTS.
lesterin is among the most abundant of the constituents of the ner-
vous tissues — especially of tbe white matter of the cerebro-spinal
axis and of the nerves. It is a " monad alcohol," the only alcohol
which occurs in the human body in a free state. On account of its
solubility in ether, cold or hot, and in warm alcohol, cholesterin
finds its way into both ethereal and alcoholic extracts of the ner-
vous tissues. It is a non-nitrogenous body, crystallizing in beau-
tiful white crystals, which, when separated pure from its solutions
in ether or chloroform, takes the shape of fine needles, and when
sejDarated from alcohol takes the shape of rhombic tables. It is sup-
posed to exist preformed in the brain. Its formula is C^gH^^O + H^O-
Neurokeratin is most easily derived by treating the meduUated
nerve-fibres with boiling alcohol and ether, so as to extract the fatty
matters of the medullary sheath ; in the place of this sheath there
is left, as a kind of irregular framework, a highly refractile sub-
stance which resembles the horny matter of epidermis in its power
of resistance to chemical agents. This substance is also found in
the gray matter of the nerve-centres, and in the retinal epithelial
cells and pigment cells of the choroid ; but not in the non-medul-
lated nerve-fibres. It contains nitrogen, 2.93 per cent, of sulphur,
and leaves 1.6 per cent, of ash.
Cerebrin was announced by Milller, in 1858, as a non-phosphorized
nitrogenous body, obtained from a precipitate from the brain when
pounded up with baryta water to the consistence of thin milk and
then boiled. He described it as a loose, Avhite, very light powder,
destitute of smell and taste, soluble in boiling alcohol and ether, but
insoluble in water. He gave to it the formula Cj^H.^^NO^. Thudi-
chum believes that brain matter contains a class of nitrogenous bod-
ies free from phosphorus, to which he gives the name of "cerebrins."
Gamgee, however, thinks it very unlikely that a body produced,
like Mailer's cerebrin, "by the prolonged action of a solution of
boiling barium hydrate on so complex an organic mixture as brain
should be a definite proximate principle of the unaltered organ ; " '
but the same authority admits " that the precipitate which sepa-
rates itself from an alcoholic solution of brain contains, besides
cholesterin, pi-otagon, and the so-called lecithins, " a body for
which we may retain the name of cerebrin."
Nuclein was discovered by Miescher in the nuclei of pus-corpus-
cles and in the yellow corpuscles of yolk of egg. Other observers
subsequently obtained it from various other substances, especially
from the nuclei of the red blood-corpuscles of birds and amphibia.
' Physiological Chemistry, i. , p. 439.
'Ibid., i.,p. 433.
, PHOSPHORIZED BODIES IIST BRAIlSr. 25
Von Jaksch ' thinks lie has discovered nucleiu in the human brain.
His claim seems to be credited by Drechsel.^ Its formula is given
as C2gH^;,N^P30j2- But the veiy existence of nuclein, as a definite
body, has been denied by chemists Hke Worm-Miiller and Gam-
gee ; and the analyses of Von Jaksch do not agree with those ob-
tained from other sources than the substance of the human brain.
The whole question of nuclein must then be left in doubt.
§ 10. No other substances found in the nervous system are, how-
ever, both so interesting and so difficult to consider, from the mixed
chemical and psycho-physical point of view, as certain complex phos-
phorized fats. The entire progress of our inquiry will make it obvi-
ous how inadequate and misleading is the use often made of such
off-hand remarks as the celebrated dictum : " No thought without
phosphorus." Yet it is doubtless true that the highly elaborate and
unstable compounds containing phosphorus, which enter into the
composition of nervous matter, have a significance for physiological
and psychological researches such as belongs to no other material
bodies. These comj)lex bodies are especially characteristic of the
centres of the nervous system. The strife of discovery and of con-
firmatory experiment has been chiefly carried on over the following
three : Protagon, Lecithin, and Cerebrin. Of these three, however,
probably only the two former are phosphorized bodies. The main
question involved in controversy concerns the relation in which leci-
thin and cerebrin stand to protagon. Is protagon a definite prox-
imate principle of the brain, and are lecithin and cerebrin bodies of
ill-defined properties and doubtful claim to existence as proximate
principles of the brain ? or, are lecithin and cerebrin definite prox-
imate principles, and is protagon a mechanical admixture of the
two ? The latter view of protagon has been held by Diaconow,
Hoppe-Seyler, and Thudichum ; on the contrary, its claims to the
position of the " only well-chax'acterized phosphorized proximate
principle " of the brain as yet discovered have been defended (and,
it may be said, apparently established) by the researches of Gam-
gee and others.
Protagon was discovered, as a new proximate principle that -can
be separated from the brain, in 1864, by Dr. Oscar Liebreich ; his
discovery was announced in a paper ^ published in 1865. This in-
vestigator gave to this substance the name which it still bears, as
' See article " Ueber das Vorkommen von Nuclein im Menscliengeliirn,"
Pfliiger's Archiv, xiii., p. 469.
''^ In Hermann's Handb. d. Physiol., V., 1., p. 578.
' 'Ueber die cbemisclie Bescbaflfenheit der Geliirnsubstanz." Annalen der
Chemie und Pbarmacie, cxxxiv. , pp. 29-44.
26 CHEMISTRY OF NERVOUS ELEMENTS.
in his opinion the first to be definitely ascertained among the spe-
cific constituents of the brain (Trpwrayo?, leading the van). He as-
signed to it the formula Cj^^H^^jN^O^^P. In spite of subsequent
denials and disproofs of its existence, the extremely careful and
often-repeated researches of Gamgee ' and Blankenhorn have cor-
roborated the discovery of Liebreich. The process by which pro-
tagon is obtained from the brain may be thus briefly described (the
description will serve to illustrate in general the processes of physi-
ological chemistry) : Perfectly fresh ox's brains are freed from the
blood and membranes, and are then digested for about a day in
eighty-five per cent, alcohol ; from this fluid, when filtered, a quan-
tity of white flocculent precipitate is obtained, and the cholesterin
and other bodies soluble in ether are dissolved out ; from the sub-
stance left undissolved, when dried and reduced to powder and
digested for many hours with alcohol, and then filtered and cooled,
microscopic crj- stals separate themselves, arranged for the most part
in rosettes. The substance thus crystallized is protagon. It is con-
sidered by some chemists the easiest to obtain, and indeed the only
very well-established phosphorized proximate principle of the brain.
Such a material substance is indeed a long way removed from the
living nervous mass, with its capacity for exercising such marvel-
lous physiological and psycho-j)hysical functions. But it is the best
representative that chemistry can as yet present of a scientific result
upon which to base any attempt to point out definite relations be-
tween psychical activities and the chemical constitution of those
complex phosphorized fats which exist in the central nervous
mechanism. The empirical formula of protagon, as given by Gam-
gee, is C|j„H3„„Nj.P03j. It has been made highly probable that pro-
tagon cannot be a compound or mixture of cerebrin and lecithin ; it
may, then, be announced as a proximate principle of the brain.
Lecithin is an organic phosphorized compound which exists in
large quantities in ova, spermatozoa, etc., as well as in the nervous
tissues. It is described as a yellowish-white, waxy, very hygro-
scopic solid, which in thin layers shines with a silky lustre. It is
soluble in ether and alcohol ; on being stirred with water it forms a
starch-like solution difficult to filter. Diaconow assigns to it the for-
mula C.^H^^NPOj, -f H^O. Gamgee supposes that the lecithin of Dia-
conow is only one of a group of similar bodies which possess a higher
percentage of phosphorus than protagon, and the "general smeary
characters " of lecithin. We may, then, speak of " the lecithins " as
highly phosphorized compounds existing in the matter of the brain.
' See his Physiological Chemistry, i. , pp. 425-429 ; and article in the Jour
nal of Physiology, ii., pp. 113-131.
nsro:EGA]sric bodies iisr beaiis'.
27
The various products of the decomposition of protagon and leci-
thin it is not necessary to describe. Neurin is the only one of
these products which deserves for our purpose even to be named.
It may be obtained from either protagon or lecithin. Dr. Thudi-
chum's elaborate " Eesearches on the Chemical Constitution of the
Brain " ^ conclude that at least three well-defined groups of phos-
phorized bodies may be separated from the brain ; these are dis-
tinguished as (1) kephalins, (2) myelins, (3) lecithins. The exist-
ence of a group of bodies which may be termed "lecithins " has just
above been declared probable. Thudichum thinks that all these
bodies contain phosphoric acid combined proximately with glyce-
rin, but " differ in the manner in which they contain the nitrogen
and the acid radicles which constitute the great bulk of their sub-'
stance." The researches of Dr. Thudichum still await confirmation.
§ 11. In addition to the substances already mentioned, the brain
contains certain extractive matters which are found also in other
tissues, especially in muscle. Among these bodies are creatin,
inosite, xanthin, and lactic acids.
§ 12. The brain also contains an extremely small amount of inor-
ganic matters— so small, indeed, that few facts can be relied on
concerning it. The estimates of this amount vary from 0.1 to 1
per cent, of the fresh brain. Among such inorganic matters are
alkaline phosphates and sulphates, chalk, magnesia, oxide of iron,
etc. It is said that the ash of the gray matter has an alkaline reac-
tion, that of the white matter an acid reaction,^ and that the reac-
tion of the former during life is acid, while that of the latter is
neutral or weak alkaline.
§ 13. All quantitative analyses of the brain are exceedingly doubt-
ful ; the older results are wholly worthless. The following table of
Petrowsky,' which gives the chief organic constituents of the brain
of the ox, is an object of interest rather than of complete confidence :
Substance.
Gray Matter.
White Matter,
Albumen and gelatin
55.87+
0,53+
17.24+
18.68 +
6.71 +
1.45 +
per cent.
24.72 +
9.55-
9.90+
51.91-
3.34+
0.57+
per cent.
Cerebrin
Lecithin
Cholesterin and fats
Substances insoluble in
Salts
ether
' Reports of Medical Officer of the Privy Council and Local Government
Board, 1874, pp. 113 ff.
2 See Gamgee, Physiological Chemistry,!., p. 445; Hermann, Handb. d.
Physiol., v., i., p. 577.
^ " Zusammensetzung der grauen und der weissen Substanz des Gehirns,"
Pfliiger's Archiv, vii., p. 367.
28 CHEMISTEY OF NERVOUS ELEMENTS.
§ 14. The specific chemistry of the elements of the nervous sys.
tem, or of the various parts of such elements which histological
science reveals, is yet more meagre and doubtful than its general
chemistry. The micro-chemistry of the nerve-cells tells us simply
that they are in the main protoplasmic, and therefore rich in pro-
teid substances ; and since an analysis of the two kinds of nervous
matter shows that the gray is much the poorer in complex phos-
phorized constituents and in cholesterin, we conclude that the cells
which enter so largely into the gray matter are also poor in the
same substances. The different structural parts of the nerve-fibres
have doubtless a different chemical constitution. This is proved
by the difference in their appearance under the microscope, by the
different action of reagents upon them, and, to some extent, by
chemical analysis. The neurilemma, or membranous envelope of
the nerve-fibres, like the sarcolemma, on prolonged boiling, yields
gelatin. The axis-cylinder appears to be a mixture of proteid with
complex fat-like bodies. The white substance of Schwann is rich
in complex phosphorized fats, in cholesterin, and in the so-called
cerebrins.
The researches of Kiihne ' and others — for the most part his
pupils — have developed certain interesting results with respect to
the chemical constitution and chemicals change of the nervous tis-
sue of the eye. Many of the various non-nervous parts of the ear
and the eye have been carefully analyzed. The extremely small
amount of such material which is obtainable for chemical analysis
is one reason why so little can be known concerning the chemical
constitution of the substance of the retina. It is said to have an
acid reaction. It is a fair surmise, on general grounds, that it con-
tains the same bodies as the central nervous system. The two seg-
ments into which the rods and cones break up exhibit marked dif-
ferences in their chemical as well as optical characters. The inner
segments are composed of protoplasm of "a marvellous transpar-
ency." The outer limbs of the rods have an external envelope
which agrees in its physical characters with neurokeratin. This
envelope encloses a mixture of proteid bodies and of other sub-
stances similar to those found in the other nervous tissues.
§ 15. If knowledge of the chemical constitution of the nervous
system is so far behind what Ave could wish, knowledge of the
chemical proce ses and chemical changes which are connected with
the physiological functions of this system must be declared to be
' For a list of papers by Kuhne and liis pupils on this subject, see Gamgee,
Physiological Chemistry, i., p. 462 f. ; and for an account by him of his re-
searches and their results, see Hermann, Handb. d. Physiol., I., i., pp. 235 ff.
USTTRA-MOLECULAK OXYGEN. 29
almost wholly wanting. Even the beginnings of scientific general
statements, ox' laws, respecting the relations between the chemical
constitution of the nervous system and its various physiological
activities have yet to be made. Different investigators will doubt-
less differ as to the prospect for such discovery in the future.
When chemistry can deduce the molecular behavior of the most
highly complex chemical compound from the nature and number
of its component chemical elements, and physiology can definitely
connect all the physiological functions of nervous matter with the
molecular motions of its chemical constituents, we shall have the
means for a strictly scientific solution of such problems.
§ 16. It need scarcely be said that we have little knowledge re-
specting the relation which exists between the chemical constitu-
tion and chemical processes of the nervous system, on the one hand,
and, on the other, the jDhenomena of so-called mind.
Nevertheless, certain important general relations may be point-
ed out between the chemical nature of the nervous mechanism
and its psycho-physical functions. The extremely high organiza-
tion and chemically sensitive constitution of this mechanism are
bej'ond doubt related to all its distinctive functions. Like every
other natural material structure, the nervous system is obviously
adapted to its peculiar kind of work. Chemically considered, it
appears as composed of a number of extremely complex and highly
unstable compounds. It therefore holds in its chemical consti-
tution a large amount of disposable energy ; this energy it yields
readily when the equilibrium of its molecules is in any way dis-
turbed. Within certain limits, it explodes with increasing surren-
der of its disposable energy as the number and intensity of the
demands upon it are increased — very much as would a gun which
should be arranged so as to go off with greater energy as the press-
ure of the finger on its trigger is repeated or increased.
It is probable that the substance of the nerves is the seat of a
chemical synthesis, as the result of which still more complex bodies
are constructed from the already complex alimentary material fur-
nished by the blood ; such bodies have a high value as combus-
tibles, and thus, as has been said, possess a significant amount of
disposable energy. The relation of a supply of oxygen to the
nerve-centres is also important to notice. The nexwe-fibres require
comparatively a small amount of oxygen. It may be conjectux*ed
that in their case, as in the case of muscle-fibre, intra-molecular
oxygen is of some use in preparing explosive materials. But at
present we must be satisfied Avith conjecture on this point. On the
contrary, the vascular xiature of the central organs creates a pre-
80 FORM OF THE NERVOUS ELEMENTS.
sumption that the chemical processes which have their seat in them
require an abundance of oxygen. Experience confirms this pre-
sumption. The respiratory centre in the medulla oblongata is
chiefly controlled in its action by the amount of oxygen which
reaches it in the blood. The phenomena of consciousness vanish
when the supply of oxygenated blood is cut off from the brain.
Although we are still in the dark as to the precise significance of
the visual purple, the phenomena which the study of it has brought
to light are suggestive of unseen chemical processes that are set up
in the retina, and so serve as stimulus for the fibrils of the optic
nerve. In general we know that certain sensations are dependent
upon the chemical constitution and activity of the various end-
organs of sense.
Further researches will undoubtedly greatly enlarge our knowl-
edge of those facts of relation which exist between the chemical
constitution and changes of the nervous mechanism and the phe-
nomena of psychical life. Perhaps such particular .statements of
fact may be gathered into such more general statements of fact,
verifiable by experiment, as we consider sufficient to constitute
scientifically established laws. But lohy certain chemical constitu-
ents, when combined and changed in definite fashion, should be
specifically connected with certain conscious experiences will always
remain an unanswerable inquiry.
§ 17. From the chemical constitution of the elements of the ner-
vous system we now pass to their Structural Form. The science
which must be our guide is no longer chemistry, but microscopic
anatomy, or histology; this science furnishes us with a large amount
of trustworthy information mingled with a still larger amount of
conjecture and doubt. Even the number of those elements upon
which histology is entitled to focus its microscope and declare that
such, and no others, are capable of performing distinctively ner-
vous functions can scarcely be said, as yet, to be placed beyond all
doubt ; neither can it be claimed that the microscope has yet dem-
onstrated the ultimate structure of those two species of such ele-
ments the reality of whose nervous functions is beyond doubt.
It is customary to speak of nerve-fibres and ganglion-cells as the
only structural elements of the nervous system. If, however, by the
term " ganglion-ceU " we intend only such bodies as histology usu-
ally describes under this type (for example, the so-called motor
ganglion-ceiis of the spinal cord) the limitation is without sufficient
warrant. For there are many cells, which almost certainly have
some significance as parts of the nervous system, that differ in
form very widely from the typical ganglion-cell. Moreover, by such
COEPUSCLES OF DOUBTFUL CHARACTER. 31
an off-hand twofold division the important question is often silently
passed by : What is the significance for the nervous functions of that
diffuse, finely granular substance, found in considerable quantity in
the great nerve-centres, and called neuroglia, or nerve-cement {Ner-
ven-kitt ; Kittsubstanz) ? This substance is most frequently classed
with the connective tissue; but, according to Henle,* "it is at all
events to be distinguished from connective tissue on account of its
chemical properties." That certain microscopic forms of so-called
"neuroglia" are largely unlike other forms recognized as being
nerve-cells beyond doubt cannot be argued in proof of its ina-
bility to perform any of the strictly nervous functions, except upon
the basis of the assumption that we already know beyond reasonable
question what are all the elementary structural forms of true ner-
vous matter. But, assays Eckhard,^ "if we start the inquiry, what
formal elements of the brain and spinal cord take part in the activi-
ties of these (the nervous) organs, and in what way do they take
part, we are able to give to it only a very unsatisfactory answer."
We are not in a position, then, either to affirm or to deny abso-
lutely the claim sometimes set up for the neuroglia, that it con-
tains true nervous elements.
It is best to recur to the facts which microscopic anatomy dis-
closes as a basis for classifying the different structural elements of
the nervous system. These may be briefly described as follows : '
As to the true nervous character of fibres of various kinds, not only
as conducting bands between the nervous centres and the peripheral
parts of the body, but also within the substance of these centres,
there is no dispute. Nerve-fibres undoubtedly constitute one of
the structural elements of the nervous mechanism. Besides the
nerve-fibres, histology distinguishes in the gray substance of the
nervous centres — where all the structural elements of the nervous
system are to be found in greatest abundance and variety — three
other species of structural form. Such are (a) certain cells, known
more particularly as the " ganglionic nerve-cells." These cells (to
be described more minutely hereafter) are irregular magses of finely
granular protoplasm, possessed of a clear nucleus and one or more
nucleoli, and sending off one or more processes.
(6) Corpuscles, consisting either of naked nuclei or of nuclei
with only a small amount of surrounding protoplasm, and having
various shapes sometimes difficult to make out, are also found
abundantly in the gray matter of certain nervous centres. Such
* Anatomie des Mensclien. Text, p. 306. Braunschweig, 1880.
^ Hermann, Handb. d. Physiol , II., ii.,p. 15.
^ Comp. Henle, Anatomie des Menschen. Text, p. 306.
32 FOEM OF THE ISTERVOUS ELEMENTS.
bodies are usually much smaller than the cells of undoubted ner-
vous character described above, many of them being scarcely more
than ■j-g'iro - -gVo 0"' ^^' ^ven -g-uVoj ^^ ^^ inch in diameter. Some of
them, like the typical ganglionic cell, give off processes which are
thought to be continuous with nerve-fibres. It is altogether prob-
able that these cells of the second class differ only in their dimen-
sions from the cells of the first class. In some places (for example,
in the cortex of the cerebrum, or large brain) they appear to have
the characteristics of transitional forms between the undeveloped
gi'anules of the same class and the more highly developed ganglion-
cells. In other places (as in the cerebellum) they form indeiDend-
ent layers. They may be described as nuclei "invested by only
a small quantity of cell-substance." ' Some are multipolar, some
bipolar, some unipolar. Admitting, as we seem compelled to do on
account of their resemblance to the typical form of the ganglionic
nerve-cell, that some of these cells are true nervous elements, it is
impossible for histology to draw the line through the entire class,
and so to affirm beyond doubt that any of them are without claim
to be counted among such elements.
(c) The diffuse, finely granular substance, already referred to as
so-called "neuroglia," which fills in the gaps between the nerve-
fibres and the cells of the two preceding classes, constitutes the other
form of matter observed in the nervous centres. It exists in quan-
tity large enough to form an essential constituent of some locali-
ties of the brain and spinal cord. It is not always clear, however,
to what this appearance of granular or molecular matter, in which
the nerve-cells seem embedded, is due. According to some author-
ities, it may result from a confused interlacement of fine nerve-
fibrils and fine ramifications of nerve-cells ; or from the crushing
of such nervous matter in the process of examination." The neu-
roglia itself is described as a delicate reticulum, or network, in
which certain small cells (neuroglia-cells) supposed to belong to
the sustentacular tissue, and other more conspicuous cells, usually)
stellate in section (" cells of Deiters "), are found.
§ 18. Of the three foregoing kinds of structural forms found in
the gray nervous matter, it is perhaps safest to class the first two
together under the term "nerve-cells." We should then have to
remember how greatly these vary in size and formation — all the
way from the naked, or almost naked, nucleus to the large ganglion-
cell with its many processes and complex microscopic structure.
' See Max Schultze in Strieker, Human and Comparative Histology, i., p
183. London, 1870.
'■'See Quain's Elements of Anatomy, ii., p 149. London, 1882.
STRUCTUEE OF A NERVE.
33
The last of the three (neuroglia) may then be regarded as a susten-
tacular tissue ; though with the confession that in the brain and
spinal cord it is by no means always easy to distinguish susten-
tacular from true nervous tissue.'
Of the structures known as nerve-fibres and nerve-cells, his-
tology enables us to give a further more minute, if not a com-
plete, description ; it also excites our interest by making it possi-
ble to conjecture what is the regular anatomical relation between
the two. When combined wdth physiological researches, histology
also enables us to make considerable progress toward distinguish-
ing the separate as well as the combined functions of these ele-
ments. We consider, then, with particular detail, the structure and
functions of nerve-fibres and ganglionic nerve-cells.
§ 19. What is ordinarily called a nerve appears to the naked eye,
when dissected from an animal, as a cord of a whitish or grayish
Fig. 1. — Cross-section of the Sciatic Nerve of Man. ^/,. (After Key and Retzius.) The left lower
half is schematic, n, n. Bundles of nerve-fibres, surrounded by pn, pn, the perineurium : be-
tween them appears the connective tissue, epineuruim (ep, ep), and adipose substance (ad).
color, and of uniform stnicture. The nerve is really, however, one
or more bundles, or fascicles, of a larger or smaller size, bound to-
gether by connective tissue. Accordingly, on following it toward
its peripheral termination we find that it divides and subdivides
until its subdivisions consist of a sinaie nervous element called a
' Comp. Ranvier, Traite Tecliuique d'Histologie, i. , p. 717. Paris, 1875.
3
34 FOEM OF THE NERVOUS ELEMENTS.
Nerve-fibre. The bundles have a special sheath formed of con-
nective tissue {neurilemma, or perineurium), which in the finest
branches becomes reduced to a single layer of cells cemented to-
gether edge to edge, and is called the "sheath of Henle." On fol-
lowing the fibres backward again toward the central organs, it is
found that several of them are bound together to form a nerve-
fascicle ; a small amount of fibrillar connective tissue appears be-
tween the several fibres within the same sheath ; the character of
the sheath itself is changed, and it becomes attached to surround-
ing structures by a layer of connective tissue. It is the fibres into
which the nerves break up on being followed toward their periph-
eral terminations, or by junction of which, successively, they are
composed on being followed toward their central termination, that
are to be considered as the true elements of the nervous system.
§ 20. Such nerve-fibres as compose the nerves which stretch from
the central organs to the peripheral parts of vertebrate animals
may readily be divided into two classes : one called meduUated
fibres or nerve-tubes, and the other non-medullated fibres or fibres
of-Remak. Nerves in which there is a large proportion of medul-
lated fibres have a characteristic white or watery appearance ; those
in which only non-medullated fibres, or only a few medullated fibres,
exist are grayish and slightly translucent. Vertebrates alone have
the former. The medullated nerve-tubes belong particularly to
the cerebro-spinal system, and are, therefore, of prime interest in
psycho-physical researches ; the fibres of Remak are very abundant
in all the nerves belonging to the sympathetic system. This two-
fold division of nerve-fibres, while admitting of easy application to
the constituent elements of the nerve-trunks, becomes more diffi-
cult when we attempt to carry it out within the complex nervous
matter of the central organs. Here Max Schultze ' points out sev-
eral varieties of nerve-fibres. There are, first, those "very fine
threads which lie on the extreme verge of microscopic mensura-
tion," and which require an enlargement of from 500 to 800 diame-
ters in order to be made visible. In such fibres no internal struct-
ure can be detected by the microscope. To these Schultze gives
the name of " primitive nerve-fibrils." Second : certain very deli-
cate transparent fibres of albuminous composition, and distinguished
from the foregoing by their greater size and their manifest fibrillar
structure, are found in the central organs. These are the so-called
naked axis-cylinders. Both the foregoing, when invested with a
medullary sheath, become converted into the third, or medullated,
form of nerve-fibre. These fibres in the nerves, while running be-
' See Strieker's Human and Comparative Histology, i. , pp. , 147 £E.
VARIETIES OF NERVE-FIBEES. 35
tween the central orgaus and the end-organs, become invested with
a delicate membrane, and are thus converted into nerve-tubes of
the well-known threefold structure. A fourth form of nerve-fibre
occurs in the peripheral nerves, and is distinguished from the fore-
going by the absence of the medullary sheath. This is the pe-
ripheral non-medullated fibre, or fibre of Eemak, already alluded to.
As they appear to the mici'oscopist, then, on an examination of all
the kinds of nerve-fibres which are found in all the different parts
of the nervous system, the following table of varieties is proposed
by Schultze :
I. Non-medullated (J" P^iiiiitive fibrils.
oi -< 2. Fascicuh of primitive fibrils.
I 3. These last, with a sheath of Schwann.
r 1. Primitive fibrils with medullary sheath.
II. MeduUated fibres. J ^- ^^f^^'^^^ «f primitive fibrils with such
j sheath.
I 3. These last, with a sheath of Schwann.
The exposition of Schultze, although of value in setting forth
the variety of forms in which the nerve-fibre is actually found by
the histologist, does not constitute an objection to the twofold di-
vision first proj)osed. On the contrary, it leads directly to such a
division. For it will be noticed that both of the chief classes of
fibres are regarded as composed of a number of primitive fibrils ;
both are also regarded as becoming invested in their peripheral
course with an outside membrane. The two classes, however, are
really derived upon the basis of the fact that some of the primitive
fibrils, whether they have already become invested with this mem-
brane or not, possess a medullary sheath, and others do not. It is
the presence or absence of this medullary sheath which constitutes
the one important difference between the different classes of nerve-
fibres.
§ 21. MeduUated nerve-fibres, or nerve-tubes, have a threefold
structure. Such fibres, when separated by teasing with needles
from the fascicle of nerve-fibres and examined under the microscope
while still fresh, appear pellucid, with a central part and a border
on each side, like a translucent liquid in a tube of translucent
walls. The lines of this double contour are at first comparatively
sharp and regular ; lengthening the focus of the instrument ob-
scures slightly the central part, and causes the parts on the border
to appear brighter. Little by little the appearance of the fibres
changes. The contours become irregular, and the substance (myelin)
66
rOEM OF THE NERVOUS ELEMENTS,
composing the borders becomes folded, striated, and granulated in
appearance. The myelin wells over the sides of the ends of the
fibres in irregular globular or contorted masses. Occasionally a
pale filament may be seen projecting beyond the torn end of a
fibre. Owing to the fact that various solutions have different effects
upon the different parts of the nerve-fibres, it is
possible to prepare specimens which shall exhibit
clearly their threefold structure. Thus, for ex-
ample, a solution of picrocarminate of ammonia
colors the central part of the fibre, or axis-cylin-
der, but not the myelin ; whereas osmic acid
stains the axis-cylinder slightly, the myelin thor-
oughly, but not the substance of the annular
rings. By use, then, of various reagents, to color
the nerve-fibres, and by numerous observations
of them under various circumstances, their three-
fold nature in a living state is thought to be dem-
onstrated. We distinguish, then, in the medul-
lated fibres : (1) An outer membrane, extremely
thin, pellucid, with nuclei in it, and called the
primitive sheath or sheath of Schioann ; (2) an in-
terior layer of dimly granular, white, and highly
Fig. 2.— Medulla ted refracting substaucc, semi-liquid during life, and
i^Tmrtaeguiar contour after death undergoing a jorocess resembling co-
sbowing. (schwaibe.) agulatiou— Called the medullanj sheath or loMte
substance of Schwann; and (3) a cylindrical band of albuminous
material, transparent, but with marks of fibrillation — called the
axis-cylinder. Only the last is supposed to constitute the essen-
tial nervous structure ; for, as we have already seen, many nerve-
fibres are simj^le naked axis-cylinders, and all fibres for a certain
distance from the cells in which they originate are devoid of the
medullary sheath. There is considerable evidence that the presence
of this sheath depends upon the need of insulation only.
§ 22. Besides the threefold longitudinal structure of the medul-
lated nerve-fibre, we have to notice certain structural modifications
that occur at intervals in its length. The peripheral nerve-tube
does not run along as a regular cylinder, but places of constriction
appear at certain points situated beneath the outer sheath ; these
constrictions are made at the expense of the medullary sheath or
myelin. They are called annular constrictions or nodes of Eaiivier ,
the portion of nerve-fibre included between two of these constric-
tions is called an interannular segment. At the constrictions the
ends of the segments of the outer sheath are joined together by a
MEDULLATED NEEVE-FIBRES.
A B
37
ar-fi
i"T-
Fig. 3.— a, Medullated Nerve-fibres from the
Sciatic of a Rabbit, stained with osmic acid,
and dissociated in water. (Ranvier.)
B, Single Fibre Enlarged ^""/j, a, a. An-
nular constrictions, or nodes of Ranvier,
nearly midway between which is n, the nu-
cleus, with protoplasm, p, surrounding it ;
ca, axis-cylinder.
Fig. 4. — Medullated Nerve-fibres. (Schwalbe.)
rt, Ajds-cylinder ; s, sheath of Schwann ; n,
nucleus ; p, p. granular substance at the poles
of the nucleus ; r, r, Ranvier's nodes, where
the medullary sheath is interrupted and
the axis-cylinder appears ; i, »", incisures of
Schmidt.
38
FORM OF THE NERVOUS ELEMENTS.
tbin layer of cementing substance which extends inward toward
the axis-cyUnder. These interannular segments of the nerve-fibre
vary greatly in length. When several nerve-fibres lie parallel with
each other, the segments of four or five of them often seem to have
about the same length, and then the series appears interrupted by
some segment considerably longer or shorter than the rest.
Each interannular segment of a nerve-fibre has a flattened ellip-
tical nucleus, situated nearly equidistant between the two annular
constrictions which limit the segment. This nucleus
often has a nucleolus ; between the nucleus and the
myelin there exists a minute mass of protoplasm which
is spread beneath the membrane of Schwann and fixed
to it.
Scattered irregularly along each interannular seg-
ment are delicate lines or fissures which seem to run
obliquely through the medullary sheath from the mem-
brane on the surface of the nerve-fibre to the axis-cyl-
inder. Their significance is not yet determined ; they
are called the " incisures of Schmidt." (See Fig. 4.)
§ 23. The complex microscopic structure of the med-
ullated nerve-fibre, as described above — outer sheath,
meduUai'y sheath, axis-cylinder, interannular segments
limited at each end by annular constrictions, nucleus
and nucleolus, and incisures of Schmidt — cannot be
considered as "ultimate," even in the restricted sense
in which we use the word as applied to what the eye
can see by the aid of optical instruments. Other still
more minute characteristics of its structure must be
briefly mentioned, although with the understanding
that their interpretation, and even their existence, is
more doubtful than are the characteristics already de-
scribed.
The fact that isolated axis-cylinders, when submitted
to the action of picrocarminate of ammonia, are stained red along
their median line, while an extremely thin homogeneous border is
left comparatively uncolored, and the additional fact that minute
flakes or scales sometimes seem to appear upon their surface, have
led to the conjecture that the axis-cylinder has a double structure.
The clear homogeneous border probably corresponds to the so-called
"sheath of Mauthner." '
The "fibrillated" appearance of the axis-cylinder under the mi-
croscope has already been referred to as undoubted ; but the exact
' See Ranvier, Traite Technique d'Histologie, i., pp. 738, 742.
f-cy
Fig. 5.— Medul-
]ated Nerve-
tihre from the
Sciatic of an
Adult Kahbit.
«»»/!• (E-an-
vier.) ff, An-
n u 1 a r c o n-
Btriction ; and
c7/, axis - cyl-
i n d e r with
double con-
tour showing.
DOUBLE COIs^TOUR OF AXIS-CYLINDEE.
39
nature and the interpretation of this appearance are still matters
of dispute. On account of the fact that the light must be passed
through two or perhaps three cylinders in order to reach the inte-
rior structure of the nerve-fibre, its examination under the high
powers of the microscope which are necessary to see this fibrillated
structure is extremely difficult. In spite of this difficulty, however,
Hans Schultze ' claims that the fibrils of the axis-cylinder can be
Fig. 6.— Fibrillated Appearance of the Ajus-cylinders of Medullatecl Nerve-fibres. (Hans Schultze.)
distinctly traced in hving fibres, when these are in process of form-
ing and are still naked, or where they issue from the cells without
a medullary sheath, or where they lose this sheath at the annular
constrictions or in the peripheral end-plexuses. Various prepara-
tions of dead nerve-fibre, treated with different reagents, seem to
demonstrate the same fibrillated structure. Moreover, from the
fact that the nervous substance of the fibrils takes a carmine tinge,
while the interfibrillary nucleated substance remains stained steel-
blue with the nitrate of silver, Schultze argues that the axis-cylinder
consists of two chemical substances. The fibrillated appearance
can, therefore, scarcely be considered as due to the arrangement of
' In the Archiv f. Anat. und Physiol., 1878, Anat. Abtli., pp. 259-285.
40
FOKM OF THE NERVOUS ELEMENTS.
rows of granules in straight lines.' According to T. W. Engel-
mann,'^ in good preparations these fibrils appear distinct, and are
never seen to anastomose or form a plexus of fibrils. By actual count
the number of fibrils remains the same — at any rate, between any
two annular constrictions ; nor are they apparently interrupted in
their course by these constrictions. The fibrils, as found in different
nerve-fibres, seem not to differ in respect to size or closeness of
contact, but their number
differs in nei've-fibres of
different sizes. Engel-
mann counted about four
rHlinW hundred in the thickest
fibres taken from the mo-
tor roots of the spinal
cord of the frog. The
closeness of their contact,
and the smallness of their
number, as compared
with that of the fibrils into
which the fibre breaks up
at its peripheral termina-
tions, make it difiicult to
see how these subdivi-
sions of the axis-cylinder
can have any separate
function as the conduc-
tors of nervous impulses.
Further information I'e-
garding them must be left
to subsequent researches.
(See Fig. 6.)
The strict continuity of
the axis-cylinder through
the annular constrictions
maybe called in question.
Engelmann found that, on being treated with nitrate of silver, the
axis-cylinders, as a rule, were broken off at the annular constric-
tions or nodes.' Out of a hundred cases of broken cylinders only
four appeared where they had not parted in the middle of these
constrictions. It is not to be inferred from this, however, that nor-
mal and living nerve-fibres are interrupted by a space of even mi-
' So article of H. D. Schmidt, in tlie Monthly Micr. Jour., 1874, vol. xii.
' Pfluger'B Archiv, xxii. , p. 36. ^ PflUger's Arcliiv, xxii., pp. 1-24.
Via. 7.— Fibrillated Axis-cylinders broken at the Nodes
of Ranvier. (Kngeimann.)
THE FIBRES OF REMAK.
41
croseopic proportions at these nodes ; no such interruption appears.
But it is by no means impossible that these fibres are to be regarded
as composed of a number of annular segments cemented together —
each separate fibril placed exactly end to end with its fellow in the
adjoining segments. Such an arrangement
would accord with the theory which regards
the segments as elongated and developed
nerve-cells.
§ 24. Non-meduUated nerve-fibres, or fibres
of Be male, differ from those already described
in that they do not possess a medullary
sheath. They are grayish and translucent,
longitudinally striated, with flattened elon-
gated nuclei lying at frequent intervals upon
their surface. When gathered together within
a sheath of neurilemma, they are not placed
side by side as are the medullated nerve-
tubes ; they are rather formed in the interior
of the nerve, where they unite and divide and
make an intricate plexus or network of fibres.
They are grouped in larger bundles, some-
times alone, but more frequently in connec-
tion with medullated fibres. Their striated
appearance is probably due to the fact that
they, like the axis-cylinder of the medullated
nerve-fibres, are composed of numerous fibrils.
As has already been said, they belong to the
sympathetic system.
§ 25. The size of different nerve-fibres in
the human body varies greatly, according to
their kind, position, and, perhaps, function.
As a rule the non - medullated fibres are
smaller than the medullated, the former be-
ing from -g-oVo- to -g-oVo' ^^ ^^ inch in diam-
eter, and the latter (in the trunk and branches fig. 8.— Fibres of Remak from
„,, Nj, ^ , , „ .. the Pneumogastric of the
oi the nerve) trom y^oo- to g-gVo ^i an inch. nog. "o/^. (Ranvier.) n,
-o J. i.1 • T • J. 1 i? 11 -I T ii Nucleus with surrounding
JtJut this rule is not always lollowed. In the protoplasm, p ,• 6, strise cor°
white matter of the cord the medullated responding to fibrils.
fibres range in size from y^Vo- ^^ ^ oVt ^^ ^^ inch, in parts of the
anterior columns, and about , oVt of an inch in those regions of
the lateral and posterior columns which are nearest the gray matter
of the cord. In the gray matter of the cord and brain the fibres are
much finer — being from ^qVo ^o tt^o ¥ o^ ^^ i^^h in diameter, or
42 FOEM OF THE NERVOUS ELEMENTS-
even of an almost immeasurable fineness ; they are finest of all in
the superficial layers of the brain and in the nerves of special sense.
In some instances the axis-cylinder may be not more than jo-oWo"
of an inch in diameter.
§ 26. The number of fibres which enter into the composition of
individual nerves also varies greatly. In the common motor nerve
of the tongue it has been estimated at about five thousand, in that
of the eyes at fifteen thousand, in the optic nerve at one hundred
thousand at least.
§ 27. So-called ganglion-cells, or nerve-cells, are the second of
the two structural elements which can be more minutely described
as undoubtedly belonging to the nervous system. These bodies
vary greatly in size and shape, but they all show, when subjected
to microscopic examination, certain well-recognized common charac-
teristics. Nerve-cells are irregular masses of protoplasm, finely
granular and delicately striated, with a large nucleus which is well-
defined and vesicular in appearance, and which usually contains a
shining nucleolus ; they send off one or more processes. In the gray
matter of the cord and brain they are embedded in the neuroglia
or so-called " nerve-cement ; " in the smaller nervous centres, such
as the ganglia of the sympathetic and the ganglia on the posterior
roots of the spinal cord, they are surrounded by a capsule of con-
nective tissue.
§ 28. Careful microscopic investigation of the nerve-cell with high
magnifying powers of the instrument reveals the great complexity
of its structure. In describing this complex structure the bipolar
ganglion-cell of the fish may be considered as a common type. Such
a cell is caUed by Max Schultze ' a " nucleated swelling of the axis-
cylinder." When found in the course of a nerve-fibre it appears
at first sight as a complete interruption to the continuity of the
fibre. Further examination is thought to show, however, that,
when the fibre reaches the cell, the axis-cylinder loses its medul-
lary sheath, and the fibrils which constitute the substance of the
cylinder become dissociated, and continue their course over the
surface of the "ganglionic globe" to its opposite pole ; here they
reunite and form a fibre identical with the one that approached
the nearer jDole of the cell. The "ganglionic globe " itself appears
to be composed of granular substance. We may distinguish, then,
in such a ganglion-cell these two parts : (1) a fibrillary covering,
the fibrils of which are continuous with the fibrils of the axis-
cylinder on either side of the cell ; and (2) a granular globe con-
taining near its surface a nucleus, within which one or more nucleoli
1 In Strieker, Human and Comparative Histology, i., p. 174.
NERVE-CELL FROM SPINAL GANGLION.
43
appear. ' A repetition of these parts of the structure of the bipolar
cell, it is claimed, may be expected and found in ganglionic nerve-
cells in general.
A microscopic structure substantially like that of the bipolar
ganglion-cell of the fish, as already described,
is found to belong to the multipolar cells of
the anterior horns of the spinal cord of man,
and of the ox, or of other mammals. Among
the many processes given out by such a cell,
the researches of Deiters and of others have
demonstrated that ordinarily only one be-
comes continuous with the axis-cylinder of the
peripherally running nerve-fibre. This one,
called the -'prolongation (or process) of Dei-
ters," has sometimes been distinctly seen to
be fibrillated ; and it is supposed that its
fibrils are, as a rule, continuous with those
of the axis-cylinder of the nerve-fibi'e. Hence
it is called the " axis-cylinder process." The
other processes from the cell also seem to be
fibrillar ; but the quantity of interfibrillar
granular substance which they contain is
greater than that in the axis-cylinder process.
These fibrils ramify, anastomose with each
other, and become lost in an intricate net-
work of extremely minute nervous filaments.
Over the surface and within the interior of the
" ganglionic globe " of the multipolar cell the
fibrils of all these processes run in every di-
rection with bewildering complexity. Their
relation to one another, and to the various
parts of the substance of the cell, cannot be
said to be determined with any degree of cer-
tainty. Most of the fibrils appear only to tra-
verse the ganglion-cells, but some of them,
perhaps, originate within the cells. In the case
of auy thus originating, it is not as yet possible to say whether
or not they arise out of the nuclei and nucleoli, and so, whether we
may consider these parts of the cells as the special sources or cen-
tres of the nerve-fibrils, asHarless, Meynert, and others have done.^
' See Ranvier, Traite Technique d'Histologie, i. , p. 712.
" See, on this whole subject. Max Schultze in Strieker, Human and Compara-
tive Histology, i., jip. 172-187 ; Ranvier, Traite Technique d'Histologie, i., pp.
710 if. ; and Hans Schultze, Archiv f. Auat, u. Physiol., 1878, pp. 259-285.
Fig. 9.— Nerve-cell from the
Spinal Ganglion of the
Ray. 350/j, (Ranvier.)
my. Medullary sheath of
nerve-fibre, enclosing ca,
the axis-cylinder, the fi-
brils of vrhich (/) separate
and run over the gangli-
onic globe, m; n, nii-
cleus.
44
FORM OF THE NERVOUS ELEMENTS.
§ 29. The variety of shapes taken by the nerve-cells has already
been mentioned, as well as the fact that they may be classified as
unipolar, bipolar, and multipolar. Some are nearly round ; others
ovoidal, caudate, stellate, or shaped like a flask or the blade of a
paddle. Still others appear somewhat like the foot of an animal
with claws ; while the branching processes of others give them the
appearance of sprawling out irregularly in a half-score of different
directions. To a certain extent the shape of the cells is character-
istic of that region of the central nervous system where they are
Pig. 10.— Multipolar Ganglion-cell from the Anterior Horn of the Gray Substance of the Spinal
Cord of the Ox. (After Deiters.) 1, Nucleus ; 2, axis-cylinder process ; 3, 3, branching
processes.
found, in most abundant numbers, embedded in the neuroglia.
For example, large ganglion-cells of irregular shape, with branch-
ing processes, which have been called " motor," are found in the ante-
rior horns of the gray matter of tlie spinal cord ; pyramidal cells of
various sizes, with i^rocesses from both base and apex, are character-
istic of the cortex of the cerebrum ; and just at the inner edge of
the gray cortical matter in the cerebellum appear irregular globu-
lar or ovoidal cells, which send off one or two branching processes
toward the surface of the cerebrum. The ganglion-cells of the sym-
pathetic also are usually globular or ovoidal, and have one or more
processes which pierce their capsule and become non-medullated
THE GANGLION-CELL AS A TYPE. 45
nerve-fibres. Uuipolar cells are found in the spinal ganglia of tlie
higher animals, bipolar in the spinal ganglia of fishes.
Nerve-cells vary in size as much as in shape ; the limits may per-
haps be given as from about ^|-q- to 3-V0 °^ ^^ inch.' No special
physiological significance can in any case be assigned to the shape
of the nerve-cell ; we are wholly ignorant of the meaning of such
a variety of forms, and of the value of any particlar form in a
given position. It is possible, however, that the large size of the
so-called " motor-cells " of the anterior horns of the spinal cord is
indicative of theii- special physiological function. We may also
fairly incline to interpret the multiplication of ganglion-cells in the
central parts of the nervous system as significant of the large
amount and high quality of work which must be done by them
within these centres. It is possible that the shape of the cells is
largely due to the mechanical conditions which control their de-
velopment within the embryo ; but upon this subject we have
scarcely any trustworthy information.
§ 30. The structure of the nerve-fibres and nerve-cells, and the
nature of the histological relations which apparently exist between
the two, have led to a captivating theory intended to reduce all the
elements of the nervous mechanism to modifications of a single
form. Extremely different in structure as the various parts of the
nervous system obviously are, we are told that modern histological
science refers them all, for their elements, to "one perfectly defi-
nite type ; " " this ty^De is the ganglionic nerve-cell. The important
common characteristic, that they send out prolongations which
become nerve-fibres, is assumed to belong to all such cells. The
fibres are, accordingly, considered to be prolongations of the cells,
and to be formed of substance like that of the source from which
they appear to arise. Nerve-fibres may then be described as nerve-
cells drawn out into an extremely long peduncle, which serves to
connect them with other similar cells and fibres, or with certain
muscular fibres which the nervous matter commands. This mor-
phological theory of the nervous elements rests, however, upon a
doubtful basis, and certain strong objections may be brought against
it. We are probably warranted simply in asserting that both classes
of these elements, Hke the other primary structural forms of the
body, may be regarded as differentiations of one type (the cell)
under conditions of which we are almost wholly ignorant.
There is accumulating evidence in favor of the view that nerve-
^ See an article of J. Hoffmann in the American Journal of Neurology and
Psychiatry, August, 1883 pp. 432 ff.
- Eanvier, Traite Technique d'Histologie, i. , p. 710.
46 rOKM OF THE NEEYOUS ELEMENTS.
fibres are, in general, connected, both histologically and physiologi-
cally, with the nerve-cells. One of the processes of each cell may,
therefore, as a rule, be regarded as continuous with the axis-cylin-
der of a nerve-fibre. It is true that this connection can by no
means always be traced by the microscope. A score of years ago
one investigator ' declared that, after having examined the gray
matter of the spinal cord a great number of times, he had demon-
strated this alleged connection only very rarely. Kepeated obser-
vations since, of the improved modern kind, have not done away
with the comparative infrequency of the desired demonstration.
But from the very nature of the case a great number of the nerve-
fibres must have their connection with the cells broken off by the
treatment they receive in preparation for examination. And the
positive cases where such connection has been traced may fairly be
said to have indicated the rule. Moreover, the facts of physiology
(to which reference will be made subsequently) seem to favor such
a view of the anatomical relation of these two elements of the ner-
vous system.
Additional evidence upon this subject may perhaps be derived
from the recent researches of E. A. Birge.^ This investigator under-
took the gigantic task of counting the nervous elements in the gan-
glia and roots of the spinal cord of a large number of frogs. He
apparently discovered a general relation indicating some agreement
in the number of the so-called motor-cells and the fibres alleged to
originate from these cells. In one case (No. 42) an actual count of
ten motor-roots gave 5,734 fibres and 5,777 cells on the right, and
5,740 cells on the left side of the cord. Other results of counting,
however, were by no means so favorable to the statement that the
number of the fibres in the roots agrees exactly with the number of
cells in the corresponding x-egion of the cord. Nor could more
complete results of this kind form any sufficient warrant for the
conclusion that everywhere in the nervous system the number of
fibres corresponds with the cells, or that the nerve-fibres all spring
from the nerve-cells ; much less, that they may be reduced to one
form of such cells as to a perfectly definite type.
§ 31. The discussion of the chemical constitution and structural
form of the elements of the nervous system introduces the ques-
tion as to the Functions of these Elements. This question must
be answered, if at all, by the science of physiology. And in view
' Vulpian, see Lemons sur la Pliysiologie du Systeme Nerveux, p. 318, Lect-
ure of July 9, 1864. '
'Archiv f. Anat. u. Physiol., 1882, Physiolog. Abtli., pp. 435-479, espe-
cially p. 471.
EXCITABILITY AND COISTDUCTIVITY. 47
of our ignorance of the genuine nervous character of all other
claimants to a place among the elem'ents of the nervous system, our
inquiry is narrowed to the following terms : What can nerve-fibres
and ganglionic nerve-cells do ? With the activities of these ele-
ments, as combined into the complex organs of the human nervous
mechanism, the whole of our subsequent examination is designed
to deal We speak here very briefly of certain fundamental prop-
erties of the two nerve-elements already described — that is, of .the
nerve-fibres as gathered into bundles called nerves, and of the cells
as collected into ganglia and connected with these nerves.
Nerves and nerve-cells have certain properties in common ; that
is to say, within certain limits both can do the same things. Both
are capable of becoming the subjects of a specific kind of molecu.
lar motion which we are entitled to consider as distinctively " neu-
ral" but about whose nature and mathematical or physical relations
to other modes of the molecular motion of matter we are still al-
most totally ignorant. Both are also capable of projDagating this
distinctively " neural commotion " from one portion of their struct-
ure to another. In a word, both nerve-fibres and nerve-cells have
the properties of Excitability and Conductivity ; and the excitation
and conduction of excitation which these nervous elements display
are of a kind peculiar to themselves. It is the production, propa-
gation, modification, and distribution of this distinctive nerve-com-
motion which constitutes the one constant function, or projDerty,
of the nervous elements, whether considered as isolated or as com-
bined into organs. It is customary with some writers to speak of
the production of psychical phenomena as the crowning function
of the nervous system. But whatever may be the view we shall
find ourselves compelled to take of the relations between the loca-
tion, quantity, quality, and combinations of this neural molecular
motion and the phenomena of self-conscious life, from our present
point of view the utterances of such writers — if designed as anything
other than figures of speech which need to be explained in detail
to be even suggestive of those real facts and relations which they, in
truth, only symbolize — are of little interest or value. We are speak-
ing of a material structure, which, although alive and standing in
altogether unique relations to psychical phenomena, is, nevertheless,
in itself considered, nothing but a very complex collection of moving
molecules. The peculiar form of molecular motion which charac-
terizes this structure — namely, so-called " nerve-commotion " — is
its unique function. Inasmuch as such nerve-commotion may be
considered as originally set up in a single nervous element or group
of elements, and then propagated from this initial point along cer-
48 FuisrcTioisr of the itervous elements.
tain more or less definitely marked tracts to other elements oi
groups of elements, we may divide the one function into two — the
function of excitation and the function of conduction.
§ 32. Nerve-commotion, or neural molecular action, is, of course,
never an uncaused event. It begins at certain points in the ner-
vous elements, where it is set agoing by the application of appropri-
ate causes of excitation. The causes of the excitation of the ner-
vous elements are called "stimuli." Stimuli are of two general
kinds — external and internal. External stimuli comprise all such
modes of the motion of matter as act upon the peripheral parts of the
nervous system, and so produce wdthin it a state of excitation or
nerve-commotion ; among these are light, heat, chemical changes,
etc. Internal stimuli are such as act upon the nerve-cells of the
central organs ; they consist, in general, of changes in the blood
produced by an increase or decrease of oxygen, the presence of
drugs, etc. The susceptibility of a nerve to any form of external
stimulus is called its " irritability ; " and when a nerve will no
longer respond to such stimulus by being thrown into a condition
of excitation, it is said to have lost its irritability. As the word is,
generally used, then, the irritability of a nerve is its property' of
excitability under the action of some form of external stimulus.
When excited by such stimulus it is said to be irritated. We shall
use both sets of words, reserving the words " pynitn.tinn " and " ex-
citabilitv" for the gene^gLalaie and fuj^^^tJQ^ 'sf all nervous tissue
considerecl as capable of a specific molecular commotion ' — a nerve-
commotion.
§ 33. But although all the nervous elements may be said to have
the properties of neural excitability and conductivity, important
difiierences arise as to the conditions under which, and as to the
modes in which, they exercise their functions when combined into
a complex nervous system. In the normal condition of such a sys-
tem it is by no means all of its parts which are directly excitable,
whether by external or by internal stimuli ; nor is the efi'ect of the
excitation of both the elementary structural forms of such a system
exactly the same. A single nerve may, indeed, be separated from
the other parts of the nervous system, with a muscle attached, and
may then be made to exercise its neural function in moving the
muscle by being itself stimulated with dififerent kinds of stimuli at
different points along its course. But in their normal place and
condition nerves are never excited by the direct application of
' It is a pity that we have in English no one word which can be nsed under
all conditions, and compounded ad libitum^ in order to designate a property, a
process, a state, etc., as can the German word Erregen, Erregung, etc.
GAFGLION-CELLS AS DISTRIBUTOEY. 49
stimuli ; they are always excited indirectly by the propagation to
them of nerve-commotion which originates in the central organs- or
in the end-organs. The distinctive office of the nerves is, then, to
act as conductors of molecular motion set up in themselves by the
du-ect excitation of the nervous elements in which they either cen-
trally or peripherally terminate. Moreover, large portions of the
central organs do not respond to the direct application of various
kinds of stimuli to their surface. We are obliged, then, to suppose
that many of the nerve-cells which compose these organs are excita-
ble only by stimulation through the nerve-fibres that run into them.
The case of the normal nervous system, with respect to its excita-
bility, may, then, be briefly described in the following terms : The
end-organs of sense are directly excitable by external stimuli, and
each specific kind of end-organ which is characteristic of a particu-
lar sense is excitable only by the specific kind of stimuH appropri-
ate to that sense. The afferent or centripetal nerves are excited
only by the end-organs of sense ; their specific function is to con-
duct the nerve-commotion, started by the external stimuli in these
end-organs, toward the central organs. The efferent or centrifugal
nerves are not directly excited by either internal or external stimuli,
but only by the central organs ; their specific function is to conduct
the nerve-commotion started in them by the central organs to the
muscles, glands, etc.— to the peripheral parts of the body which
are to be moved through their excitation. The central nerve-cells
themselves are excited either through the nerve-commotion brought
to them by the afferent nerves or by internal stimuli. Nerve-
commotions are also said , to arise in them automatically ; but
the facts covered by the term " automatic " require further distinc-
tions to be made as to the functional activity of the different nerve-
elements.
§ 34. If the distinctive normal function of the nerves is the con-
ducting of neural molecular motion between the central organs
and the end-organs, the function of the ganglion-cells can by no
means be pronounced so simple. These cells are, indeed, also con-
ductors of nerve-commotion ; within the central organs they form
important parts of the tracts along which such commotion passes.
They serve also as points for the division and redistribution of this
commotion ; they may be spoken of as switching-places in the sys-
tem or network of tracts. In these " shunting-places" of the cell
many lines of conduction meet ; and the one of them taken by any
impulse entering the ceil may depend upon the relative amount of
resistance offered by these Hues. The work of the cell may then
be considered as "re-directive." The office of the cell in distri-
4
50 ruNCTioisr of the nervous eleme]S"ts.
bution of the nerve-commotion may also be either to condense or
to disperse it ; in the former case the distribution might be spoken
spoken of as "associative," in the latter as "dissociative."' They
may also intensify or diminish the nerve-commotion entering them.
But the nerve-cells have also other functions, or forms of the one
neural function, which have been classed as either (a) automatic,
(6) reflex, or (c) inhibitory.
(a.) Automatism, or the power of initiating the peculiar form of
molecular motion known as "vital impulses," independently of
the action of any discoverable stimulus from without, is one of the
fundamental propei'ties of protoplasm. An amoeba, for example, is a
minute mass of such protoplasm ; it executes movements which can-
not be wholly explained by reference to any changes in its environ-
ment. The difficulty of distinguishing automatic from reflex action
in the spinal cord, and muscular from nervous automatism in the
sporadic ganglia, need not concern us at present. According to
Eckhard "^ two kinds of this automatic function of the ganglion-cells
may be distinguished — viz., the automatic-tonic and the automatic-
rhythmic. In the foi'mer case the control of the cells over the
muscular structvires by means of the efferent nerves is irregular ;
in the latter this control results in the nearly simultaneous contrac-
tion of the same set of such structures, repeated at regular intervals ;
as is the case in the movements of the heart and lungs. In neither
case, however, can we form any clear conception of the origin within
the cells of this neural commotion, of the nature of the forces at
work to produce it, or of the changes in material that are involved
in it. We can only say that as yet we know no reasons lying out-
side of the structui-e and activities of the living nerve-cells them-
selves which will account for the starting of the excitation. In this
sense, at least, such neural action is "automatic."
(6.) The reflex function of the ganglion-cells admits of a some-
what more detailed and satisfactory statement ; but the phenomena
and laws of reflex nervous action are properly discussed as belong-
ing to the central organs of the nervous system. It is enough, at
present, to note that the great changes which take place in the
character of nervous impulses, when, after entering the central
organs by the afferent tracts, they are, as it is said, " reflected "
from those organs along the efferent tracts, are indubitable evi-
dence of the specific molecular activity of the ganglion-cells. For
the afferent impulses are, in fact, not simply reflected in these cells ;
' See A. Hill, Tlie Plan of the Central Nervous System, p. 2. Cambridge
1885.
'•^ Hermann's Haudb. d. Physiol., II., ii., p. 19 f.
GATS^GLIOIST-CELLS AS INHIBITORY. 51
they are greatly modified as to their number, intensity, character,
and distribution. This modification is proof of profound molecu-
lar changes that are instituted in the substance of the cells them-
selves. It is one proof, among others, that a large expenditure of
energy in the cells accompanies the transmutation of afferent into
efferent impulses.
(c.) The function of inhibition, as ascribed to ganglion-cells, must
be pronounced more doubtful in character than either of the two
foregoing. It was found by Wundt ' that nervous impulses are
delayed on passing through the sj^inal ganglion. Such impulses
seem also to consume an amount of time in travelling along or
through the cord that cannot readily be accounted for as wholly
due to the length of the nervous tracts which they thus traverse.
But until our information is more precise as to the microscopic
structure of the cord, and as to the tracts within it which the ner-
vous impulses follow, we cannot say with confidence how much of
this delay is due to molecular changes peculiar to the cells them-
selves. That the automatic and reflex functions of the medulla
oblongata may be compounded, as it were, in such way as either to
inhibit or to accelerate the action of the heart and lungs and mus-
cular walls of the arteries, is a well-known fact. It has already
been said that nerve-cells may diminish as well as intensify the
nerve-commotion entering them. When afferent impulses reach the
ganglion-cells of the centres, and find them already at work, such
impulses result, according to circumstances, in either inhibiting or
augmenting this activity.^ Moreover, the tone given forth by a
muscle, when tetanized by stimulating the nerve to which the mus-
cle is attached with repeated induction-shocks, has the same num-
ber of vibrations per second as there are of such shocks ; but the
tone given forth by muscle tetanized through tlie spinal cord, or
by action of the will, has a constant number of vibrations, namely,
about nineteen per second. It would appear from this, also, that
the central apparatus of nerve-cells controls the impulses which
tetanize the muscle, according to the molecular structiu-e and
changes of those cells. In this sense, then, the cells may be said
to exercise inhibitory functions under certain conditions.
§ 35. A consideration of the different effects produced by the
conduction of nervous impulses along the different nerves of the
system would seem at first to justify the classification of the nerves
according to the varieties of their functional activity. In this way
' Untersuchungen zur Mechanik der Nerven, 1876, Abth. ii., pp. 45 ff.
- Comp. Foster, A Text-book of Physiology, fourth, edition, p. 134. New
York, 1«80.
52 ruNCTiojsr or the neevous elements.
we should distingiiisli the following classes : (a) nerves of motion
controlling- the muscular apparatus, whether of smooth or of striated
muscular fibres ; (6) nerves of inhibition ; (c) nerves of secretion ;
(d) trophic nerves, or nerves which have a direct influence upon nu-
trition ; (e) centripetal nei-ves that have no sensory function ; and,
finally, (/"") sensory nerves, or those the excitation of which may
result in conscious sensation.'
That the irritation of different nerves may have results so differ-
ent as are indicated by the foregoing classes must indeed be ad-
mitted ; but it is quite another question whether this difference is
not wholly due to the sources of origin for the nerve-commotions
sent along them, and to the structures in which it terminates, rather
than to any difference in the essential physiological function of the
nerves themselves. Just as the same electrical current may pass
along the same kind of wire, and write a message, or ring a bell, or
move the legs of a frog ; just so the irritation of certain fibres of the
pneumogastric nerve results in controlling the motion of the heart ;
the ii'ritation of other nerves seems to have an immediate metabohc
effect in directing the secretory processes ; that of still others pro-
foundly modifies the nutrition of the portions of the body to which
they are distributed. All these effects are in ajDpearance greatly
riulike the movement of a muscle under stimulation fi-om a nerve.
With regard to the influence of the nerves on nutrition (then- ^?-o-
phic function) it is not necessary, in order to account for it, that
some specific action of a particular kind of nerves should be as-
sumed. We should sup230se, of course, that the chemical j)rocesses
in which nutrition consists would be changed in character by the
molecular changes in the tissue which irritating any of the nerve-
fibres running into it would inevitably bring about.
Further consideration of the six possible classes of nerves given
above reveals the fact that they may all be reduced to two, accord-
ing to the direction in which their function of conducting nerve-
commotion is exercised. The first four conduct it outward from
the nervous centres, and are therefore called "efferent;" the last
two conduct it inward toward the nervous centres, and are there-
fore called " afferent." Into these two kinds all nerves are custom-
arily divided, so far as their physiological function is concerned.
§ 36. The further question now arises, W^hether the general phy-
siological function of these two jDrincipal classes of nerves differs in
kind as well as in direction ; or are afferent and efferent nerves to
be identified so far as their specific neural function is concerned ?
Inasmuch as every nerve-fibre, in the normal condition of the ner-
' Comp. Sigmund Mayer, in Hermauu, Handb. d. Pliysiol., II., i., pp. 200 ft
AFFERET^T AT^D EFFEEENT NERVES. 63
vous system, is a stretch of nervous matter between two termina-
tions— a point of origin and a point of issue for the state of excita-
tion— it might, at first, seem simpler to consider it as intrinsically
capable of propagating nerve-commotion in one direction only. It
would be concluded, then, that the behavior of afferent and effer-
ent nerves, when stimulated, is essentially different with respect
to their molecular processes. Certain phenomena are sometimes
urged in favor of such a conclusion.
The application of heat to an efferent (or motor) nerve causes no
contraction in the muscle which the nerve supplies ; heat does not
appear to be a stimulus of such nerves. On the contrary, Griitzner ^
concluded that heating the different kinds of afferent nerves to
from about 115° to 125° Fahr. does excite them. The passage of
a constant current along an efferent nerve, so long as this cur-
rent does not suddenly change in strength, does not stimulate this
nerve so that the muscle contracts ; but such a current does excite
nervous impulses in a sensory nerve. Moreover, certain chemical
substances are said to act as stimuli on efferent nerves which have
no such effect upon sensory nerves.
On the other hand, the rate of conduction in both afferent and
efferent fibres, under similar conditions, is about the same. The
laws which evince the behavior of nerves under stimulation by elec-
tricity, and which are most relied upon as a basis for a mechanical
theory of the nervous system, are largely the same for both kinds
of fibres. There is a large amount of scientific information, called
" general physiology of the nerves," which looks in the direction of
identifying the molecular processes in the two classes of nerve-
fibres. This is true in particular of the remarkable phenomenon
known as the "negative variation "of the nerve-current. More-
over, the marked difference (referred to above) in the results ob-
tained by stimulating motor nerves on the one hand, and sensory
nerves on the othei', is plainly, to a great extent, due to the differ-
ence in the sources of the stimulation ; the former are excited by
the central organs, the latter by the end-organs of sense. The mo-
lecular structure of these two sets of organs, and their consequent
molecular motion when acted upon by the appropriate stimuli, dif-
fer widely ; we do not, then, need to assume a specific difference
in the function of the connecting nerve-strands in order to account
for a marked difference in the results. Thus it may be assumed
that molecular disturbances, which would be quite powerless to stir
the sluggish muscle-fibres when transmitted to them by a motor
nerve, would occasion profound changes in the more sensitive
' Pflijger's Arcliiv, xvii., p. 215.
54 FUNCTIOlSr OF THE NERVOUS ELEMENTS.
structui^e of the ganglion-cells when transmitted to the latter by a
sensory nerve.
Various attempts have been made to demonstrate, experimen-
tally, that motor and sensory nerves can perform each other's func-
tions. Such experiments have not yet been altogether successful.
They consist, in general, of attempts to unite by healing the cen-
tral part of a divided sensory nerve and the peripheral part of a
divided motor nerve, and then to show that the nerve thus united
discharges certain sensory or motor functions, as the case may
be. Philipeaux and Vulpian,' after various rather unsuccessful
attempts of Flourens, Bidder, Schiff, and others, succeeded in
uniting the central portion of the liugual (or sensory gustatory)
nerve of young dogs with the peripheral end of the hypoglossal
(motor nerve of the tongue) on the same side. Stimulation of the
lingual nerve above the point of union then produced contractions
in the hypoglossal of the same side, and that even when the lin-
gual was divided high up so as to preclude any reflex action. But
the action obtained was found to be apparently due to the dtorda
(motor) fibres present in the lingual. In 1863 Bert succeeded in
reversing the course of the nerve-fibres in the tail of a rat, by bend-
ing this appendage over and implanting its end in the animal's
back. After healing had taken place, the transplanted tail was cut
off near its origiu, and found to be sensitive — of course, in the re-
verse direction of the nerve-fibres from the natural one. This
experiment would seem, then, to show that sensory nerve-fibres,
when reversed, can transmit sensory impulses in the direction
which was formerly centrifugal. The experiments of Kiihne '^ and
others upon the intramuscular ramifications of the nerve-fibres in
the sartorius muscle of the frog point in the same direction. If
the broad end of this muscle be divided by a longitudinal slit into
a forked shape, then stimulation of one of the two tines of the fork
beyond their division will stimulate the fibrils of the other tine ;
that is, the minute twigs of the motor nerve in the tine which is
directly stimulated have acted centripetally, and the excitation has
then descended the twigs of the other tine.
For all the foregoing, and for other reasons, we seem warranted
in assuming that there is no such specific difference in the func-
tion of the two kinds of nerves as is dependent upon the peculiar
structure or molecular processes of each kind. Both afferent and
' See Vulpian, Legons sur la Thysiologie du Systi^me Nerveux, etc , pp.
274 ff. ; and comp the remarks of Hermann, Handb. d. Physiol., II., 1., pp.
lOflf., and of Foster, Text-book of Physiology, pp. 503-508.
^ Archiv f. Auat., Physiol., etc., 1859, pp. 595 fE.
PROPERTIES OE ALL NERVES. 56
efferent nerves are probably capable of the same kind of molecular
commotion called nervo as excitation, and of conducting this commo-
tion in either direction. The marked difference in the results of the
exercise of this function in the two cases is probably due chiefly to
the difference in the organs from which the excitation of the nerve
starts, and into which it is discharged. With respect to neural mo-
lecular disturbances, all nerves are excitable, conductors of excita-
tion, and exciters of nerve-cells and muscle-fibres. And if to this
description we add the statement that nerve-cells can, acting auto-
matically, originate this nerve-commotion, can modify its character
profoundly as it passes through them, and distribute it in various
directions, we state, in the most general form, w^hat is at present
known as to the functions of the nervous elements.
CHAPTER II.
COMBINATION OF THE NEEVOUS ELEMENTS INTO A
SYSTEM.
§ 1. In the last chapter the nervous elements were considered, as
far as possible, without reference to their combination for the ac-
complishment of a common work. Regarded as isolated, and as
possessed only of those properties which belong to all living mat-
ter of the peculiar chemical constitution and structural form which
are described by the word "nervous," these elements are of great
interest to physiological and psycho-physical researches. But in
their normal position and activity the nerve-fibres and nerve-cells
are always combined into certain organs, which are then arranged
in a symmetrical whole. Thus combined they are dependent upon
each other for the parts which they play in the entire s^'stem. The
condition and function of each element are thus determined by the
condition and function of the rest. One part of this system excites
another, or modifies the excitation received from another. We are
unable to isolate perfectly any one of these elements, and so study
its normal functions apart. It is, indeed, possible to dissect out a
nerve with a muscle attached, to keejj it alive for a time, and thus
to inquire what an isolated nerve will do. In this way many of the
most important discoveries in the general physiology of the nerves
have been made. But every nerve is itself a compound of nervous
elements which have been placed for purposes of experiment under
abnormal conditions. The action of the nerve-cells, even when
gathered into small masses called ganglia, is not open to direct in-
spection. Moreover, when different tracts of nerves, or different
regions in the central organs where ganglion-cells abound, are par-
tially isolated by being laid bare for the direct application of stimu-
lus, just so far as they are separated from the system they are in
abnormal condition and show abnormal results ; and just so far as
they are normal in condition and function they are still connected
with the system. It is the mutual condition and reciprocal action
of the elements, when combined into this totality, which constitute
MECHANISM OF THE AMCEBA. 57
the nervous mechanism. A brief description of the manner of this
combination is, then, indispensable at this point.
§ 2. It will be of great service toward understanding such a de-
sci'iption if it is begun under the guidance of some appropriate idea.
Nerve-fibres and nerve-cells exist in enormous numbers within the
human nervous system, and are combined in different proportions
to make the different organs of this system. The significance of
the combination appears only in the light of reflection upon the
amount and kind of work which is to be done. The office of the
nervous mechanism has been said (p. 18 f.) to be that of " concate-
nating " all the functions of the living body in accordance with the
complex internal and external conditions to which it is subject.
But in the case of any of the higher animals, and especially in the
case of man, this one office requires the doing of a quantity and
variety of work that are proportionate to the complexity of these
conditions. How shall such a quantity and variety of work be done ?
To answer this question may be said — speaking figuratively — to be
the problem before the nervous system. The actual arrangement
of the elements of this system, in the exercise of their reciprocally
conditioned activities, is the solution of the problem. As in all
very complex questions of this sort, so this particular problem is
solved by a wise division of labor.
The manner in which the human nervous mechanism is developed
as a response to the before-mentioned problem is made clear by con-
sidering, in the first place, a much simpler form of the same prob-
lem. The simple protoplasmic speck called an amoeba may be con-
sidered as a living molecular mechanism. It appears, even under
the higher powers of the microscope, as almost wholly, if not quite,
composed of undifferentiated protoplasm, in the midst of which, as
a rule, lies a single nucleus. If differentiated at all, it may be ob-
served to have a somewhat solid external layer, called an ectosarc,
and a more fluid granular interior, called endosarc. But minute
and almost structureless as it appears, the amoeba is really com-
posed of a great number of molecules that are undergoing constant
change ; and it is capable of exercising several wonderful functions
that do not belong to any non-living collection of molecules. Its sub-
stance is metabolic, respiratory, reproductive. The protoplasm of
the amoeba is the subject of constant chemical alterations, by which
the old protoplasm is broken up and its products cast off, while
new protoplasm is formed. Oxygen is assumed by this substance
and carbonic acid excreted. The unit which is constituted by the
amoeba may, by fission (or by other means), divide into two parts,
Bach of which becomes a fresh unit. But more important for our
58 PLAN OF A NERVOUS SYSTEM.
purpose is the fact that the amoeba is irritable aacl automatic. It
is almost unceasingly in motion. It is living matter ; and when
acted on by stimuli, it suffers an explosion of energy which gener-
ally results in a change of place and form. Inasmuch as these pe-
culiar " amoeboid " movements seem substantially identical with
those which occur in a muscle and result in its contraction, the
animalcule may be said to be contractile. But inasmuch as some
of these movements cannot be ascribed to irritation of the external
molecules of the amoeba by the surrounding medium, but seem
rather to be due to energy set fi'ee in consequence of unknown in-
ternal changes, we call it automatic. We say, " it has a will of its
own." Thus does the molecular mechanism of this small bit of
protoplasm, under the stimulus of changes in the pressure and
temperature of its medium, and in accordance with the unknown
laws of its internal self -originating changes, solve the problem pre-
sented to it.
Let it be supposed that the problem becomes more complicated,
and the animal structure which is to solve it correspondingly com-
plex. The metabolic function of the animal may then be assigned
to a separate system of structui'es ; and the closely related secretory
and excretory functions as well. The reproductive function may
then also acquire its own peculiar organs. The muscles perform
movements in masses because they retain in an eminent degree the
" amoeboid " contractility. But the property of being irritable and
automatic becomes the special endowment of the nervous system.
All these different systems, in order that they may be moved in
united masses, are then adjusted to a mechanical framework (of in-
different value so far as really vital changes are concerned) of carti-
lage, bone, etc.
But the eminently irritable and automatic system of molecules
called nervous must undergo a further differentiation of function.
In the structureless protoplasm of the amoeba, the external mole-
cules are, of course, the ones primarily to be affected by the exter-
nal stimuli. It is with the intei'nal molecules, on the other hand,
that the changes called " automatic " begin. But the continual
flux of its protoplasmic substance indicates that, in its simplest
form, any of the molecules of the animalcule may in turn act either
as irritable or as automatic. The primary differentiation of this
substance into ectosarc and endosarc points, however, to a division
of labor.
By this primary differentiation of the substance of the animal,
one cell, or group of cells, becomes more eminently irritable,
another automatic. The former has thus been fitted for the spe-
, TRIPLE FORM OF THE SYSTEM. 59
cial work of responding to external stimuli by vital impulses ;
the latter for that of initiating so-called automatic impulses. The
position of the former in the animal mechanism will then natu-
rally be at the surface, where it can be acted upon by the appro-
priate external stimuli ; the position of the latter will naturally be
withdrawn from the surface, where it can be protected from such
stimuli and left undisturbed for action that is either automatic
or excited by only internal stimuli. But if the two kinds of sub-
stance are to perform one work, although by division of labor,
they must be connected ; that is, the eminently irritable protojDlasm
of the surface must be joined by irritable protoplasmic material
with the eminently automatic protoplasm of the interior. Three
sets of organs are then called for in this rudimentary differentiation
of the nervous substance : (1) superficial cells susceptible to exter-
nal stimuli ; (2) central and eminently automatic cells, also suscep-
tible to internal stimuli ; (3) a strand of irritable protoplasm con-
necting the two.
Yet one more step in the distribution of functions between the
irritable and the automatic protoplasm of the complex animal or-
ganism must be taken, in order to reach the fundamental triple ar-
rangement of a nervous system. The system of eminently contrac-
tile tissue called muscular must be brought into connection with the
parts already described. In order that the more highly organized
animal may, like the amoeba, both have and exercise " a will of its
own," certain of its muscle-fibres must be placed under the control
of the central and automatic cells. In order, also, that the entire
muscular system may feel the reflex influence of external stimuli,
and so, by co-ordinated contractions adapt the organs of the body
to the changes of its environment, the muscle-fibres must be indi-
rectly connected, through the automatic cells, with such superficial
cells as are sensitive to these stimuli. The nervous system, there-
fore, in its most fundamental form consists of these three sets of
contrivances with their respective functions : (A) sensitive cells
upon the surface of the body ; (B) central cells that are both auto-
matic and modifiers and distributers of sensory impulses; (C) con-
necting cords, or strands, that can convey the nervous impulses
either centripetally from A to B, or centrifugally from B to the con-
tractile muscular tissues of the body.
Higher developments of this triple-formed fundamental type of
a nervous system are reached by further differentiations of A, B,
and G. If various kinds of stimuli are to act upon this system,
then the sensitive cells upon the surface {A) must be modified into
various external organs of sense : and with these organs the ter-
60 PLAN OF A NERVOUS SYSTEM.
minations of the centripetal or sensory nei'vous strands must be
variously connected. The terminations of the centrifugal or motor
nervous strands may also be variously modified so as to connect
■with and control the contractile tissue of many sets of muscles.
The central cells may be variously grouped and arranged, with
functions more or less localized, so as to receive, modify, and dis-
tribute, in manifold ways, the diiferent sensory impulses ; and so
as to co-ordinate these impulses for definite results in the periph-
eral parts of the body. Other such central cells may become more
particularly related to the phenomena of conscious sensation and
volition. Such a highly developed nervous system will then con-
sist of the following parts : (^4) End-organs of Sense, like the skin,
the eye, and the ear ; {A') End-organs of Motion, like the so-called
motor end-plates and terminal nerve-bulbs ; (B) Central Organs,
like the various peripheral and sjDoradic ganglia, the spinal cord,
and brain, in which may come to exist (6) certain portions more
distinctively automatic, (&') certain others more concerned in re-
ceiving and distributing reflexly the sensory impulses, and (6") still
others more particularly connected with the phenomena of con-
sciousness ; and (G) Conducting Nerves, which will be either (c)
centripetal, afferent, and sensory, or (c') centrifugal, efferent, and
motor, designed to connect the central organs and the end-organs.
We are now to consider the details with which such a highly de-
veloped nervous system is actually constructed in the case of man.
Our guides will, of course, be anatomy and histology.
§ 3. In the manner already described (Chapter I., § 19) the indi-
vidual nerve-fibres are collected and bound together in fascicles or
groups of fascicles, called nerves, and in larger bundles or nerve-
trunks. The nerve-cells are grouped into minute masses of nervous
matter, such as the sporadic ganglia found in the sinus, auricular
walls, and auriculo-ventricular groove of the heart ; or they are
gathered into larger bodies, intersected with most intricate ramifi-
cations of the nerves and intersi^ersed with the finely granular sub-
stance called neuroglia, such as constitute the various parts of the
brain and spinal cord.
§ 4. The nerves and ganglionic masses of nervous matter in the
human body are arranged in two great systems, the Sympathetic
and the Cerebro-spinal. The Sympathetic Nervous System consists
of a pair of nervous cords, situated one on each side of the spinal
column ; of three main plexuses, situated in the cavities of the
thorax and abdomen ; of a great number of smaller ganglia, lying
in relation with the viscera of the same cavities, and widely distrib-
uted over the body, especially in connection with the vascular sys<
GANGLIA OF THE SYMPATHETIC. 61
tem ; and of a great multitude of fine distributory nerves. Each
of the two cords consists of a number of gangHa united by interme-
diate nerves. In the other regions of the spinal column the num-
ber of these ganglia equals that of the vertebra) (sacral 5, lumbar
5, thoracic or dorsal 12), but in the neck (cervical) there are only
3. From this ganglia ted cord a communicating and a distribu-
tory series of nerve-branches are derived. By the communicating
branches — each of which contains not only non-meduUated nerve-
fibres from the sympathetic system to the cerebro-spinal nerves,
but also meduUated fibres from the cerebro-spinal to the sympa-
thetic— the two systems are brought into close anatomical and
physiological relation, and a kind of double interchange takes place
between them. The distributory branches of nerves in the sympa-
thetic system bring the gangiiated cord into connection with the
blood-vessels and viscera of the body. The involuntary muscles
in the coats of these vessels and in the walls of the viscera are
thus bound together, and through the sympathetic fibres brought
under the control of the cerebro-siDinal axis. The three main plex-
uses referred to are collections of nerve-cells and a dense plexiform
arrangement of nerve-fibres. One of them is situated at the base
of the heart, to which it gives off branches that wind around that
organ and penetrate its muscular substance ; another is placed at
the upper part of the abdominal cavity, and gives origin to numei--
ous plexiform branches that supply the viscera of the abdomen ;
the third is in front of the last lumbar vertebra, and supplies the
vaso-motor nerves and nerves of the muscular coats and mucous
membranes of the various organs in that region of the body. Fur-
ther details in the anatomy of the sympathetic nervous system are
of little interest to psycho-physical studies. To such studies it is
of great interest, however, to know that this system forms a bond
between the sensations, emotions, and ideas which have their
physical basis in the molecular condition of the cerebro-spinal
centres, and those various organs in the thoracic and abdominal
regions whose condition is so closely related to such psychical
states. The effect of certain emotions, for example, upon the con-
dition of the circulation, digestion, etc., is too well known to re-
quire a lengthy statement.
§ 5. The Brain and Spinal Cord are the great centres of the cere-
bro-spinal system. These bodies are situated in the bony cavity of
the skull and spinal column. They have three Coverings or Mem-
branes, the innermost one of which is directly united with the sur-
face of the nervous substance, and sends numerous processes into
its interior. (1) The Dura Mater, which is the membrane lying
Fig. 11.— View of the Cerebro-spinal Axis.
(After Bourgery.) '/j. The right half of the
cranium and trunk has been removed, and
the roots of the spinal nerves dissected out
and laid on their several vertebrte. P, T, O,
cerebrum ; C, cerebellum ; P, pons Varolii ;
in o, medulla oblongata ; m «, m s, upper and
lower extremities of the spinal marrow. CI.
to CVIII. are cervical nerves ; DI. to DXII.,
dor!=al ; LI. to LV., lumbar : SI. to SV., sa-
cral : Col., coccygeal.
PROCESSES OF THE DUEA MATER.
63
next to the wall of the bony cavity, is tough, white, fibrous, and of
structure somewhat different in the cranial from the spinal cavity.
In the former position it is identical with the inner periosteum of
the bones of the skull ; on passing into the spinal column, how-
ever, the periosteum divides into two or more lamellse, the inner-
most of which is prolonged into the cylindrical tube that includes
the spinal cord. Three processes of the dura mater divide — only
incompletely — the cavity of the skull into two symmetrical halves
and into an upper and lower space : (a) the /ate cerebri, a sickle-
shaped process between the two hemispheres of the large brain ;
Fro. 12. — The Cranium opened to show the Falx Cerebri and Tentorium Cerebelli, and the Places
of Exit for the Cranial Blood-vessels. }4. (Schwalbe.) a, a, Falx ; 6, b, the tentorium : 3, 3,
Sinus transversu.'!, and 2 to 3, Sinus rectus, receiving from in front the Vena magna Galena.
4, internal jugular vein ; 5, superficial temporal vein ; and 6, middle temporal vein.
(b) the falx cerebelli, a similar process between the two lateral lobes
of the cerebellum, or small brain ; and (c) the tentorium cerebelli,
an arched process over the cerebellum separating it fi'om the back
portions of the large brain. The fluid necessary to fill up the gaps
and smooth over the surfaces of the closed area made by the dura
mater is contained in the intercommunicating spaces of the mem-
brane lying next inward and called (2) Arachnoid ; this membrane
is transparent and of delicate connective tissue. Toward the dura
mater it presents a smooth, firm surface, like that of a serous mem-
brane, and is covered by a layer of scaly endothelium ; this layer
is reflected on to the roots of the spinal and cranial nerves, and
becomes continuous with the lining of the dura mater when the
64 THE SPINAL COED.
nerves pierce the latter membrane. The space below this surface
is called subarachnoid ; the subarachnoid or cerebro-spinal fluid (al-
ready referred to as filling the intercommunicating compartments
into which this space is divided by bundles of delicate areolar tis-
sue) is alkaline and poor in albumen. (3) The Pia Mater is a vas-
cular membrane, a minute network of fine branches of arteries
and veins held together by delicate connective tissue. These rami-
fications of the blood-vessels in the pia mater are on their way to
or from the nervous substance of the spinal cord and brain. The
membrane, therefore, closely invests this substance, being, how-
ever, more intimately attached to the cord than to the brain. Un-
like the arachnoid membrane, the pia mater dips into the fissures
between the convolutions of the cerebrum. It also sends its pro-
longations, not only into the fissures of the cord, but also, as slen-
der bands (trabeculce) from its inner surface, into the columns of the
cord. These trabeculse branch and anastomose within the white
substance of the cord hke the midrib of a leaf. The pia mater
is well supplied with nerves.
By these three membranes the nervous masses of the cerebro-
spinal system are protected, held together and in place with a soft
and yielding but sufficiently firm pressure, and nourished by the
blood. This great nervous system, as a whole, consists of the cen-
tral organs — spinal cord and brain — and of various roots, divisions,
and branches of spinal and cranial, or encephalic nerves.
§ 6. The Spinal Cord, or Medulla Spinalis, extends in the spinal
canal from the aj)erture in the cranial cavity [foramen magnum),
above which it is continuous with the medulla oblongata, down-
ward to opposite the body of the first lumbar vertebra, where, after
tapering ofij it is s]3un out into a slender thread of gray nervous
substance [filuni ierminale) that lies in the axis of the sacral canal.
Its length is from fifteen to eighteen inches ; its weight, when di-
vested of membranes and nerves, about an ounce and a half, or not
far from one thirty-third of that of the brain. It is nearly cylin-
drical in shape, its front and back surfaces being somewhat flat-
tened ; it has two considerable enlargements of its girth — an up-
per (cervical), from which arise the nerves that supply the upper
limbs ; and a lower (lumbar), which supplies the lower limbs with
nerves.
§ 7. The external structure of the spinal cord requires us to no-
tice (1) the Fissures which almost completely divide it for its whole
length into right and left (lateral) halves, and are, therefore, fitly
called " median ; " of these fissures (a) the one in front {anterior
median) is somewhat broader than (6) the one behind (posterior
1-8
40-
Fig 13 —A. Anterior, anri B, Posterior. View of the
Spinal Cord and Medulla Oblon.sata. B', the Filum
terminals, whirl) has been cut off from A and B. I,
Pyramids of the medulla, and 1'. their decussation.
2 olives ; :i lateral strands of the medulla ; 4% cala-
mus scriptorins ; 5, the funiculus gracilis; and 6,
the funiculus cuneatus ; 7. the anterior, and 9, the
posterior, fissures ; 8, the antero-latej-al impression ;
10, postero-lateral groove. C, the cervical, and L,
the lumbar, enlargements of the cord.
«0-
9-
66
THE SPINAL COED.
median). Both fire filled to their bottom with processes of the pia
mater ; and the sides of the posterior fissure are bound closely to-
gether by the same membrane.
Each of these symmetrical and nearly half-cylindrical halves of
the cord is subdivided by the lines of the entrance of the posterior
and anterior nerve-roots into (2) three Columns : (a) the anterior,
which lies between the anterior median fissui'e and the anterior
roots ; (6) the j^osterior, which lies between the posterior median
fissure and the posterior roots ; and (c) the lateral column, which
lies at the side of the cord between the other two columns.
(3) The Commissures of the spinal cord are two bands of ner-
vous matter which unite
its halves, thus prevent-
ing it from being com-
pletely separated into
two portions by the
fissures. The one in
front, at the bottom of
the anterior median
fissure, is composed of
transverse nerve-fibres
and is called (a) the
anterior white commis-
sure ; the one behind,
at the bottom of the
posterior fissure, is (6)
the posterior gray com-
missure. The gray
commissure is nearly
Fig. 14.— a, Anterior, and B, Lateral,View of a Portion of the twiCC aS large aS the
Cord from the Cervical Region. Vi- (Schwalbe.) 1, Anterior ■rY|jjJ;;e CXCCpt at the
median, and 2, posterior median, fissures. At 3 is the an- ' ^
terolateral impression, over which spread the anterior roots cCrvical and lumbar CU-
(5). The posteri(jr roots (6), with tlieir ganglion ((>'), arise
from the postero-lateral groove, and uniting with the ante- largCmentS of the COrd,
rior roots form the compound nerve (7). , , .
where the white is
larger.' Along its whole length the gray commissure incloses a
circular or elliptical canal [central canal), whose diameter is about
one-twenty-fifth of an inch and which is lined by ciliated cells. Near
the central canal lies ai,hin layer of gelatinous substance. The rest
of the gray commissure consists for the most part of extremely fine
nerve-fibres devoid of medullary sheath; while the white com-
missure is composed of meduUated fibres. The thickness of the
See Henle, Anatomie des Menschen. Text, p. 309.
CEESCEISTT SHAPE OF THE HORlSrS.
67
commissures is, as a rule, proportional to the size of the corre-
sjDonding nerve-roots ; their form, as they pass into the lateral
parts of the cord, varies in different sections of its length.
§ 8. Transverse sections of the spinal cord show us that, as its
external appearance v^'ould indicate, the substance of which it is
composed is arranged in two symmetrical halves, almost, but not
quite separated by the median fissures. This substance, like that
of all the nervous centres, consists of both white and gray nervous
matter. The former is external and composes the columns of the
cord ; while the latter is internal and is surrounded by the white.
The relative amount of the two kinds of nervous matter varies in the
different parts of the cord. At its beginning from the filum termi-
nale scarcely any white matter appears ; the amount of such matter,
however, increases from below upward, and is largest in the cervi-
cal part of the cord. The amount of gray matter is greatest in the
ujDper and lower enlargements of the cord.
The gray columns on either side of the cord, together with the
commissures which unite them, form a figure somewhat like a large
Eoman X, with diverging
sides; but the lateral masses — --'''^
of these crescent-shaped bodies
are narrower in the thoracic
(or dorsal) region, and broader
in the cervical and lumbar en-
largements. Sometimes the
figure is rather like that of a
large X, or a pair of butterflies'
wings. The two limbs of each
side of the figure into which
the gray columns are thus
formed are called (4) Horns ;
(a) the anterior horn is round-
ed, (6) the 2^osterior long and
narrow. The division into an-
terior, posterior, and lateral
columns, which is well marked
on the external surface of the spinal cord, is gradually lost as we
pass inward toward the central gray substance. Of the two horns
of each side, the anterior has the appearance of " spongy sub-
stance," the posterior of a kernel of such substance surrounded by
gelatinous substance.
§ 9. Careful study of the spinal cord with the higher powers
of the microscope has enabled histologists to describe with further
Fig. 1.5. — Transverse Section through the Spinal
Cord. AF, antero-median, and PP, postero-median
fissures; PC, posterior, LC, lateral, ami AC, anteri-
or columns ; AR, anterior, and PR, posterior nerve-
roots : C, central canal of cord, with its column,. r
endothelial lining-. The pia mater is shown invest-
ing the cord, sending processes into the anterior
and posterior fissures, as well as delicate prolonga-
tions into the columns. The crescentic arrange-
ment of the gray matter is shown by the darker
shaded portion.
68
THE SPINAL COED.
details the manner in which the nervous elements, both fibrillar and
granular, are arranged within the connective substance.
The White Substance of the spinal cord, besides connective tis-
sue and lymph- and blood-
vessels, is composed of
nerve-fibres of compara-
tively large or of medium
size. The essential constit-
uent of these fibres is the
axis-cylinder, the diameter
of which is generally one-
third or one-fourth of their
breadth. When fully de-
veloped, they are rarely or
never without a medullary
sheath, but probably have
no neurilemma. Their di-
ameter is not constant ;
the thickest fibres ( j-^'oir ^^
"SirV^ °^ ^^^ inch) are found
in the outer portions of the
anterior columns, where
their size is tolerably uni-
form. In the lateral col-
umns the nerve-fibres vary
greatly in size, the finer
ones lying inward near ths gi'ay matter. In the posterior columns
they increase in thickness as they approach the posterior gray com-
missure. In the upper thoracic, and through the whole of the cer-
vical, region, there is found a wedge-shaped bundle of fine fibres
that is separated off from the posterior columns toward the middle
line of the cord by a strong seiDtum ; this is called fasciculus gracilis,
or "column of Goll."
The direction of some of the nerve-fibres in the white substance
of the cord is vertical, of others, horizontal, of still others, oblique.
The vertical fibres are most abundant, are united with a parallel
arrangement into fascicles of various sizes, and ascend toward the
brain. Horizontal fibres in the white substance of the spinal cord
are of two kinds — commissural fibres and fibres of the roots. The
fibres of the white commissure run horizontally along the median
border of the gray matter of the horns, and become interwoven with
the vertical bundles of the anterior columns. Most of them pass
from the substance of the anterior horn of one side across to the
Fig. 16.— Section of Dorsal Part of the Spinal Cord phow-
ing the Gray Matter of the Horns. ^%. (Henle.)
Ca, anterior while, and Cr. graj' commissure ; Co, cen-
tral canal ; v, vesicular column ; s. spongj' substance of
the posterior horn, surrounded by g. gelatinous sub-
stance ; Pr, reticular process ; Ti, intermedian lateral
tract.
COURSE OF FIBRES IN THE CORD.
69
finterior column of the other side. The fibres of the posterior spi-
nal roots run in a nearly horizontal direction inward ; they divide
into anastomosing' bundles so minute and so intricately interwoven
with the vertical fibres of the posterior column that their course
is difficult to trace. Part of them (the lateral ones) run directly
into the substantia gelatinosa of the posterior horns, and are, per-
haps, continuous with the axis-cylinder processes of the nerve-cells
of its spongy kernel ; part of them appear to enter the gray sub-
stance of these horns only after curving and running a variable dis-
.'f^ocu
co.l.
Fig. 17 — Section of the Spinal Cord at the Level of the Eighth Pair of Dorsal Nerves, ^jy
(Schematic, from Schwalbe.) s.a., anterior fissure; s.p., posterior septum (or Assure); c.a.,
anterior, and c.p., posterior, commi>sures ; c.c, central canal : co.a, anterior horn ; co.l., lateral
horn ; vo.p., posterior horn ; n, anterior lateral, and 6, anterior median cells ; r, cells of the
lateral horn ; d, columns of Clai-ke ; e, solitary cells of the posterior horn ; r.a.. the anterior^
and r.p,, the posterior, roots : f, bundle of fibres of the posterior horn ; and /', bundle of the
posterior column ; /", iongirudinal fibres of the posterior horn ; s.g.R., gelatinous substance of
Rolando; /.a., anterior, /.i., lateral, and/.p., posterior, columns.
tance upward, or perhaps downward, in the posterior columns;
The fibres of the anterior roots of the spinal cord traverse its white
substance obliquely ; some of them enter the gray matter of the
anterior horns on the same side, where they probably become con-
tinuous with the axis-cylinder processes of its large ganglion-cells ;
others of them pass through the anterior commissure to the other
side of the cord ; still others pass into the lateral columns and the
posterior horns.
The Gray Substance of the spinal cord, in addition to the same
constituents as those of the white substance, has numerous nerve-
70 THE SPIJSTAL CORD.
cella Its nerve-fibres, wliicli foiin the chief part of its mass, and
are generally non-medullatecl, differ from those of the white sub-
stance in that they frequently subdivide and thus become attenu-
ated into extremely minute plexuses. The ganglion-cells of the
spinal cord are multipolar, and give off two kinds of processes ; one
an unbranched axis-cylinder process and the others branching pro-
cesses, both being of a fibrillated character (comp. Chap. I., §§ 28
and 29). The iinbranched processes of the ganglion-cells of the
anterior horns are probably continuous with the axis-cylinders of
the nerve-fibres of the anterior spinal roots. Of most of the simi-
lar processes from cells in the posterior horns we cannot yet make
the same afiirmation. The branching processes of the nerve-cells
were traced by Gerlach ' until he thought himself able to affirm
that their finest ramifications participate in those plexuses of nerve-
fibres which he regards as an essential constituent of the gray sub-
stance of the cord. Henle ^ and others consider the fate of these
processes to be still unknown.
Characteristic groups of ganglion-cells occur at various places in
the sections of the gray matter of the spinal cord. In the anterior
horns of the cervical and lumbar regions are three groups of large
cells ; one of these is on the side of the horn (lateral), one farther
to the front, one on its median border. They all coalesce in the
anterior horns of the thoracic region. In the anterior horns also
occur isolated nerve-cells of different sizes. The middle part of
the gray lateral halves of the spinal cord contains, in parts of the
cervical and thoracic regions, isolated groups of cells ; one impor-
tant group is situated at the inner angle of the base of the posterior
horn, and is called the "columns of Clarke." The other nerve-cells
of the posterior horns are small, and are not collected into groups,
but are distributed through that part of the substance of the horns
which is also traversed by the above-mentioned fine plexuses of
nerve-fibres (see Fig. 17).
§ 10. By careful counting, E, A. Birge ' ascertained the number
of the elements in the spinal cords of several frogs. From his con-
clusions something may perhaps be gained toward forming a better
conception of this organ. In seven cases Bu-ge found that the num-
ber of fibres in the anterior roots varied from 5,984 in the smallest
animal to 11,468 in the largest ; the number increasing at the i-ate of
about one thousand four hundred and fifty motor fibres to each added
ounce of weight (51.5 to the gram). The diameter of the fibres was
' See in Strieker's Human and Comparative Histology, ii., pp. 352 fE.
- Anat. des Menschen. Text, pp. 810 ff.
3 Archiv f. Anat, u. Physiol, 1882, Pliysiolog. Abtli., pp. 435-479.
NERVE-TKACTS IN THE COED. 71
also found to be much enlarged, according to tlie size and weight of
the animal ; and the average diameter widely different in the different
nerve-roots. For example, it varied from 3,550 fibres, in the sev-
enth pair of nerves, to 14,133 in the tenth pair, for a cross-sec-
tion one twenty-fifth of an inch square. So, too, were the so-
called motor-cells of the anterior gray columns found to vary from
4,871 to 11,517, according to the weight of the animal. It was
found that the large masses of cells lie in two principal gToups,
corresponding to the cervical and lumbar enlargements of the
cord,
§ 11. It would be of great interest to our inquiries if it were
possible to give a complete descrii^tion of the tracts of the nerve-
fibres in their passage along the spinal cord ; but it is impossible
for the microscope to unravel them, and the evidence of physiology
is (as we shall see subsequently), somewhat doubtful and even con-
flicting. Of late, however, certain of these paths have been traced
with considerable certainty by combining the methods of embry-
ological and pathological observation. In the development of the
spinal cord, the medullary substance of the nerve-fibres along cer-
tain tracts of the white columns is formed later, so as to render
them distinguishable in cross-sections. Moreover, when the nerve-
fibres are separated from their place of origin, degeneration of their
elements takes place. The place of the degenerated nervous sub-
stance is taken by connective tissue, which behaves differently un-
der the influence of staining fluids. By following the course of
this degeneration toward their periphery, the paths of conduction
in the nerves may be traced. Some time ago, Tiirck ' attempted to
mark out certain motor tracts in the brain by using this process of
degeneration as his guide. Our great authority at present on the
paths of the nerve-fibres in the sjDinal cord and brain, as ascer-
tained chiefly by the former of these methods, is the work of
Flechsig.'
Two tracts in the antero-lateral columns, which extend along the
greater part of the spinal cord and into certain parts of the brain,
are thus quite certainly made out. From their upper connections
they have been named the i^yramidal tract (or tracts) and the direct
lateral cerebellar tract. The former is directly traceable down from
the anterior pyramid of the medulla oblongata. Most of the fibres
of this tract cross over in the extreme upper part of the cord, and
pass down it in the back part of the lateral column as a compact
' Sitzgsb. d. Kaiserl. Acad., vi., pp. 303 ff.
■^ Die Leitungsbaliuen im Gehirn u. Riickenmark d, Menschen. Leipzig,
1876.
72
THE SPIISTAL CORD.
bvmdle. This crossed (or lateral) /^ari of the pyramidal tract can
be traced as far as the third or fourth pair of the sacral nerves.
But some of the fibres from the pyramids of the medulla do not
cross in the upper part of the cord. These
form the uyicrossed (or anterior) part of the
pyramidal tract ; this part gradually dimin-
ishes as it passes downward, and ceases in
the dorsal region of the cord. The direct
lateral cerebellar tract lies between the late-
ral pyramidal tract and the outer surface of
the cord. It disappears in the lumbar re-
gion. It is thought that the rest of the ante-
rior column of the cord, besides the anterior
pyramidal tract, may be, for the most part,
commissural in nature — that is, it serves to
bind together the two halves of the cord on
the same level, or somewhat obliquely those
lying slightly below or slightly above.
In the posterior white column a tract can
be traced as far downward as the middle of
the dorsal region of the cord ; this is the
one already referred to as the "tract (or
column) of Goll."
§ 12. The spinal cord is, therefore, shown
to be a mechanism composed by combining
the nervous elements so as to serve the
great purpose of conducting nerve-commo-
tion and acting as a series of reflex and auto-
matic centres. In it we find tracts of con-
nected nervous elements for the movement
of ascending and descending nervous im-
pulses. It is also a column or pile of ner-
vous centres, each one of which may have a
particular value for particular functions ;
but which are also all bound together, up
and down, right and left, and obliquely, so
as to act unitedly under a certain control
from each other and from the central organs
lying above. It is especially strong in nerve-
cells, just where it needs to be so— namely, at the enlargements,
where it sends off nerves to the upper and lower limbs. Its paths
for the passage and diffusion of molecular disturbance are indefi-
nitely numerous, and their intricacy extremely great. It has groups
Fig. 18.— Sections through the
Spinal Cord at diflferent ele-
vations, to show the tracts of
White Substance. /., eleva-
tion of the sixth cervical
nerves. //., of the third ;
///., of the sixth ; and IV.,
of the twelfth, dorsal nerves;
and v., of the fourth lumbar
nerves ; pr, uncrossed (or
anterior) pyramidal tract ;
pn, crossed (or lateral) p.\ra-
midal tract ; kn, direct late-
ral cerebellar tract ; g, tract
of Goll.
ELEMENTS OF THE INTEECEAlSriAL OEGAlSrS. 73
of nerve-elements, such as belong to the central organs generally,
of gangiion-celis embedded in neuroglia ; it has special local mech-
anisms within, and yet connected with its general mechanism. It
is adapted to do a large amount and variety of work through its
pairs of nerves, without calling upon the higher nervous centres ; it
is constructed so as to act like a system of relays, not only trans-
mitting, but also modifying, inhibiting, enhancing, and distributing
the impulses which it receives, both from the more central and from
the peripheral portions of the cerebro-spinal system.
§ 13. The same elements of nerve-fibres and nerve-cells, in con-
junction with connective tissue and neuroglia, and enveloped in the
three inclosing membranes (dura mater, arachnoid, and pia raater)
already described, are combined with an increased variety and com-
plexity of arrangement to form those intercranial central organs
with which the upper end of the spinal cord is continuous. Here,
too, these elements are gathered into fascicles of nerve-fibres
which converge, or diverge, and mn their courses in various direc-
tions, and into ganglionic masses, in which, besides the nerve-fibres,
nerve-cells and diffused finely granular substance of a doubtful
physiological character are found. Uniformity of elementary parts,
together with the greatest intricacy of arrangement, prevails, above
all other regions of the body, in the structure of the brain. The
significance of the elements and elementary parts can, therefore,
only be understood when they are considered in the localities and
relations to other parts which are assigned them by this so intricate
arrangement.
§ 14. The Encephalon, or Brain, in the most extended sense of
the word, includes all that portion of the central nervous axis which
is contained within the cavity of the skull. This grand mass of
nervous matter may be divided into several parts, somewhat differ-
ently marked off according to the point of view from which the
division proceeds. The division proposed by Meynert ' — to which
reference will be made later — is based upon the supposed physio-
logical significance of the different parts, and upon their arrange-
ment so as to discharge the functions of conduction and " suscep-
tibility to impressions." For, as this authority rightly claims, " a
purely histological description " is of comparatively little service
in comprehending the meaning of the architecture of the brain.
We shall, first of all, however, describe briefly the contents of the
cranial cavity, as it appears both to the unaided eye and under the
microscope, without reference to theory.
' In Strieker, Human and Comparative Histology, ii. , pp. 367 S.
74
STEUCTUKE OF THE BEAIN.
On removing tlie entire brain from the skull, the following foul
divisions of its mass engage the attention of even the inexperienced
observer. Immediately above the section by which it has been sepa-
rated from the spinal cord, and appearing as an enlarged prolonga-
tion of the cord, is (I.) the Medulla Oblongata. Covering the ujojoer
back part of this oi'gan, and extending beyond it on both sides,
with its surface divided into small lobes by furrows, is (II.) the
Cerebellum, or little or hinder brain. Swelling out in front of and
above the medulla is (m.) the Pons Varolii, or so-called "bridge"
of the brain. While in two hemispheres separated by a deep fis-
sure, above both pons and cerebellum, and filling the larger part
of the cranial cavity, is seen (lY.) the Cerebrum, or large brain, or
Fig. 19. — View of the Brain in Profile, y,. (Henle.) C6, cerebrum; C5?, cerebellum ; Jfo, me-
dulla oblongata ; P, pons Varolii,
brain proper. These divisions are all readily distinguishable on
the external surfaces of the Encephalon.
On laying the encephalic mass open, however, certain bodies of
nervous matter are disclosed that have been concealed beneath the
cerebellum and the cerebrum, and that — although ordinarily re-
garded as parts of the latter — are scarcely to be included in any one
of the four main divisions of the brain. We shall describe in order
the organs just named.
§ 15. I. The Medulla Oblongata is somewhat pyramidal in form,
about one and one-fourth inch in length, from three-fourths to one
inch broad in its widest part, and one-half inch thick ; it extends
from the spinal aperture of the cranial cavity {foramen magnum) to
the lower border of the pons Varolii. It is continuous with the
spinal cord, and somewhat resembles it in the divisions of its ex-
ternal surface. Its anterior pyramids appear superficially continu-
extekjstal aspect of the medulla.
75
Fva.
ous with the anterior columns of the cord ; its lateral area shows
upon its upper end an oval-shaped elevation called the " olivary
body ; " its posterior tracts also appear continuous with the poste-
rior columns of the cord. Just outside the upper portion of each
posterior tract, and behind the olive, ascends to the cerebellum a
strong tract named
the "restiform body."
That portion of the
posterior column of
the upper cord (al-
ready referred to, p.
G8) which is marked
off from the rest by a
septum of pia mater,
is continued up into
the medulla oblonga-
ta, and becomes more
strongly marked. It
is known as the fu-
niculus gracilis ; and
when traced still far-
ther upward is seen to
broaden out into an
expansion called the
clava. A prolongation
of the posterior lateral
column also gradually
expands as it ascends, so that it acquires a " wedge-shape " form,
and is accordingly known as the cuneate funiculus.
The medulla oblongata, like the spinal cord, is composed of white
and gray nervous matter ; it differs from the cord, howevei", in hav-
ing its gray matter not confined to the central part, but gath-
ered more into special masses or nuclei. A redistribution of the
nerve-elements takes place in the medulla, and their arrangement
becomes more complex. An important part of this redistribution
is accomplished by the divergence of the posterior tracts and resti-
form bodies, which opens up the central gray mass, and lets it
come to the surface between the sides of the surrounding white
matter. Looking at this redistribution as it appears from below,
the elements of the cord may be said to be spread out and increased
by the addition of new elements ; looking at it as it appears from
above, the tvro great nerve-tracts of the cerebrum (tegmentum and
crusta of the crus cerebri), and the tract of the cerebellum, may be
Fig. 90. — Back View of the Medulla Oblongata, the Cerebellum
being removed. (Henle.) Cq, corpus quadrigeminum ; Lc,
locus ccei-uleus ; F, flocculus of the cerebellum; Ac, ala ci-
nerea ; and Ac' Siilling's nucleus accessorius ; 01, clava ; Fc,
funiculus cuneatus ; Fg, funiculus gracilis.
76
STKUCTURE OF THE BRAIN.
said to be gathered up in the medulla, and compi-essed so as to
form in the cord a continuous and symmetrical medullary invest-
ment for its central gray matter.
The intimate structure of this organ is exceedingly complicated ;
much of it is doubtful, and as yet impossible to make out satis-
factorily. The two important considerations are (1) to trace the
nerve-fibres as they ascend through the medulla from the various
columns of the cord, and (2) to locate the particular collections
of gray matter, whether as continuous with those of the cord or as
consisting of independent masses.
The various tracts of White Matter in the medulla oblongata,
although they supei-ficially appear to be prolongations of the col-
fr
Fig. 21. — Section showing the Decussation of the Pyramids at the point ■where the Spinal Cord
passes into the Meriulla Oblongata. "/, . (Sohwalbe. ) f.l.a., longitudinal anterior fissure,
through which the bundles of pyramidal fibres (py, lyy'), are crossing over at d ; V, anterior,
and S. lateral pyramids: C.a., anterior hnrn with srroups of ganglion-cells, a and t> : cc. cen-
tral canal; /.»■., formatio reticularis; ce, the nick, and fir, the head, of the posterior horn;
n.c, nucleus of the funiculus cuneatus ; and w.fif., of the funiculus gracilis ; B', funiculus gra-
cilis ; JJ ^, funiculus cuneatus ; x, group of ganglion cells.
umns of the spinal cord, are reall}^ so to a small extent only. This
fact is most clearly made obvious by a comparison of successive
transverse sections. A large bundle of fibres, which in the cord
lies in the posterior part of the lateral column (see p. 71 f.), pushes
its way obliquely through the gray matter of the anterior horn, and
passes in front of the central canal to the pyramid of the opposite
side. The crossing of this bundle, as seen in the anterior median
DECUSSATION" OF THE PYKAMIDS. 77
fissure at the lowei* part of the medulla, is called the " decussation
of the pyramids." The abrupt passage of so many fibres through it
breaks up the anterior horn, separates part of it from the rest, and
pushes this sej^arated part over to one side, so that it comes to lie
close to a part of the posterior horn. The latter also becomes gradu-
ally shifted sidewise by an increase in the size of the posterior
tracts, so that it comes to lie almost at right angles to the posterior
median fissure ; its head enlarges and approaches close to the sur-
face, where it forms a projection (funiculus of Rolando), and, higher
up, a distinct swelling {tubercle of Rolando). Tracing the princi-
]Dal bundles of fibres on their course from the columns of the spinal
cord upward through the medulla oblongata, we find (in accordance
with what has already been said) that the posterior column forms the
substance of the three posterior funiculi of the medulla — namely,
gracilis, cuneatus, and funiculus of Rolando : a considerable part
of the lateral column {tlie lateral pyra-niidal tract, see p. 72) passes
into the opposite pyramid of the medulla, and ascends in it toward
the cerebrum in company with a small part of the anterior column
of the same side ; while another part of the lateral column (the
direct lateral cerebellar tract) passes at about the middle of the
medulla obliquely backward to the restiform body, and the rest of
it dips under the olives, and is continued toward the corpora quad-
rigeminum and optic thalamus. Most of the anterior column dips
under the pyramid, and passes upward toward the cerebrum, but
part is continued into- the pyramid of the same side.
Curved fibres may also be seen running their course in the plane
of the different transverse sections — some superficial, some deep
(arciform or arcuate fibres).
As the medulla is a bilateral organ, its halves are bound together
by commissural fibres, which run obliquely and decussate in the
mesial plane, forming a well-marked band called raphe. In addi-
tion to the fibres of the medulla oblongata which are continuous
Avith those of the spinal cord, others originate within the organ
itself. It is a centre of origin for several pairs of encephalic
nerves.
The Gray Matter of the medulla oblongata is, in part, continu-
ous with that of the cord, and in j)art consists of independent masses.
The former part is, as we have seen, broken up and rearranged by
the decussation of the j^yramids. The fate of the posterior horns
and of the central gray substance has already been described. The
substance of the anterior horns becomes divided into many little
masses by the nerve-fibres that traverse it, so as to form a coarse
network of nervous matter (formatio reticularis) containing nerve-
rs
STEUCTUEE OF THE BEAIN".
cells, and intersected by bundles of fibres. In the upper part of
the organ its interior gray matter appears upon the floor of the
fourth ventricle, into which the central canal dilates. Four special
kernels or nuclei, of gelatinous
appearance and containing few
multipolar nerve-cells, are to be
noted in each half of the me-
dulla. These are (1) the nucle-
us arciformis, which is situated
just beneath the pia mater, at
the front of the anterior pyra-
mid ; (2) the nucleus olivaris, or
dentate body (corpus dentatum),
which is within the inferior
olive, a mass of gTay matter
folded in a zigzag or denticu-
lated manner, forming a sort of
capsule through the openings
of which closely packed masses
Fig. 22.— Section showing Gray Matter of the of fibres run into the SUrrOUnd-
Medulla Oblongata, in the region of the upper . /o\ j.i 7 ?•
crossing of the Pyramids. Vi- (Schwalbe.) lUg SpaCC ; [6) tlie nUCieUS OLl-
f.l.a., anterior, and ft.lp., posterior, fissures; . - ■,■•
n.XI. i,nd n.XII., nuclei of the vagus accessori- WTIS aCCeSSOTlUS, a Smaller gray
us and hypoglossal nerves ; d.a.. so called upper „,„„„ Ivitio- on thp nnt«?iVlp nf
crossing of the pyramids; py. anterior pyra- mdbb 1^ ing OH UUe OULblUe OI
mid in which i- .*.«»• the nucleus arciformis; ^j^g dentate bodv ; and (4) the
o, beguniing of the olivary :iucleus: oi, acces- J ^ \ I ^
sory olivary nucleus; /^.r. formatio reticularis; nUClcUS pyramid allS (sOmetimCS
{7, substantia gelatinosa; /.a., /.«.', /.a.-', arci- .
form fibres. ^-Iso Called " inner accessory nu-
cleus " of the olive), lying on the inside of the same body. Another
kind of collections of gray matter in the medulla consists of those
groups of multipolar cells to which the nerves that have here their
so-called roots of origin can be traced. These cells, resemble those
of the gray columns of the cord — the larger ones apparently being
connected with the roots of the motor nerves, the smaller with
those of the sensory. It may be assumed that some of their pro-
cesses are continuous with the axis-cylinders of the fibres of the
nerve-roots, and that others serve to place the medulla in direct
connection with the cerebrum ; positive demonstration of these as-
sumptions, however, requires further histological researches. The
nerve-nuclei in the medulla receive their name from the nerves
whose fibres originate in them,
§ 16. n. In the Cerebellum, or Little Brain, the general arrange-
ment of the two kinds of nervous matter is the reverse of that of
the spinal cord and the medulla oblongata : the gray matter is
external, the white internal. More precisely, the cerebellum is
PEDUNCLES OF THE CEREBELLUM. 79
a white or medullary mass rising out of three large bundles or
stalks of nerve-fibres on each side, and enveloped with a covering
of gray nervous matter. Like the other organs of the cerebro-
spinal system, it is a bilateral structure. These stalks of nerves
connect the cerebellum with three other organs, with parts of
which they are continuous. Considered, as connections, they are
called the " peduncles " or crura of the cerebellum. Of the three
peduncles, (1) one {inferior peduncle) on each half of the organ is
identical with the restiform fascicle which ascends from the me-
dulla to the cerebellum ; (2) another {superior j^edunde), similar to
the first in size, passes forward, over the anterior end. of the fourth
ventricle, and. connects the cerebellum with the tegmentum of the
crus ; (3) a third {middle peduncle) passes down on each side into
the pons. This middle peduncle forms the larger portion of the
white core of the organ. In addition to the fibres from these three
sets of peduncles, this core is in part constituted by others which
arise in the cerebellum itself ; some of the latter connect together
the different regions of the organ lying above or below each other,
some unite the opposite and symmetrical regions of its hemi-
spheres.
The interior relations of the fibres from the three peduncles are,
on account of the extreme intricacy of their course, not yet fully
made out. United in the white core of the cerebellum, they form
a rather uniform mass, which is interrupted, however, by certain
nuclei of a gelatinous appearance. Within either hemisphere, and
to be disclosed by cutting through it a little to the outer side of the
median lobe, is a mass of nervous matter arranged like the den-
tate body of the medvilla oblongata ; it is the corpus dentatum of
the cerebellum. Other smaller, round, or oblate masses of gray
matter are found toward the middle of the core from the dentate
body.
The arrangement of the gray matter which forms the rind or
cortex of the cerebellum is somewhat peculiar ; its characteristics
are best seen by examining a cross-section. It is thus found that
this cortical gray substance is arranged in thin plates, or lamellae,
which are penetrated by prolongations of the white matter of the
core ; these prolongations branch off into the interior of the lamel-
lae, and give to the coi'tex the arborescent appearance known by
the name of "arbor vitce." The primary branches of this tree-like
prolongation of the white matter of the core within the gray mat-
ter of the cortex stand either perpendicular or a little inclined to
the surface of the core. The smaller branches run from one side to
another transversely or forward in concave curves.
80
STRUCTURE OF THE BRAITST.
The external surface of the cerebellum presents two hemispheres,
or lateral lobes, united by a central lobe called the vermiform pro-
cess. This central lobe on its upper (or tentorial) surface is a mere
elevation, but the "vermiform" character of its lower (or occipital)
surface is well defined. The process here lies at the bottom of a
deep fossa {vallecula). From the middle peduncle of each hemi-
sphere a large horizontal fissure extends backward along its outer
border, and divides the hemisphere into its tentorial and occipital
Pig. 23 — Lower Surface of Cerebellum. %. (After Sappey. ) ], in f prior vermiform process;
2, 2, vallecula : 5, flocculus ; 6, pons Varolii ; 8, middle jieduncle of the Cerebellum : 9, medulla
oblongata. Various pairs of nerves are seen thus: 12 and 13, roots of fifth pair ; 14, sixth
pair; 15, facial nerve; 17, auditory; 18, glosso-pharyngeal ; 19, pneumo-gastric ; 20, spinal
accessory ; 21, hypoglossal.
surfaces. Each of these surfaces is divided by fissures into smaller
lobes or lobules.
In the gray matter of the cortex of the cerebellum three distinct
layers of nervous substance maj' be distinguished. Of these the
pure gray layer is the most external ; it is sometimes called the
" molecular layer." It consists of an extremely delicate framework
of connective tissue, in which, together with nuclei of the connec-
tive tissue, a few roundish cells and minute fi.bres of nervous struct-
ure appear. The middle layer is cellular and composed of a single
irregular row of large ganglion-cells, called " cells or corpuscles of
Purkinje." Comparatively large processes from these cells branch
into and ramify within the outer layer. According to most observers
(Kolliker, Deiters, and others) each of the cells sends a single me-
dullated and unbranched process inward, which becomes continu-
ous with the axis-cylinder of a fibre of the medullary portion of this
organ ; but according to Stilling there are several branches from
each, which divide to form a network in the internal layer. This
THE PO]SrS VAROLII.
81
layer is rust-colored and merges gradually into the white substance
of the core ; it appears to contain multitudes of granules, with a
well-defined nucleus surrounded by branching protoplasm. The
nature of the granules is not known ; they have been considered
by some as elements of sustentacular tissue, by others as lymph-
corpuscles, by others as multipolar nerve-corpuscles.
The cerebellum is thus constituted by a complex arrangement
of the nervous elements as a kind of side mechanism of the nervous
system, lying out of the course of its direct tracts and yet bound
by nervous cords (the peduncles) in all directions to the other
oi'gans of the brain.
§ 17. in. The Pons Varolii, or Bridge of the Brain, has its princi-
pal office in the mechanism of the central organs of the cranial
cavity as a meeting- and switching-place of nerve-tracts between
other organs ; but it is also itself a central organ, as well as a cen-
tre of origin for certain nerve-fibres. The pons is really a thicken-
ca>
Fig. 24.— Median Section through the Stem of tTie Brain. (After Reichert.) M, medulla oblon-
gata ; of whichPa are the pyramid?, decussating atprf ; c, central canal ; pp. restiform body ;
Pv, pons Varolii ; F4, fourth ventricle, au, arbor vitte of the cerebellum ; p, pyramid ; u,
nvula ; re, nodule ; as, aqueduct of Sylvius ; CV, crus cerebri ; Q, corpora quadrigemina ; P,
pineal gland ; Th, optic thalamus. Commissures : ra. the anterior; cm, the mollis ; and cp, the
posterior. F3, the third ventricle ; /I, corpus albicans; Zc, tuber cinereum ; i, infundibulum.
ing of the ventral wall of the fourth ventricle, composed of the mid-
dle peduncles of the cerebellum encircling and partly blending with
the continuation upward of the medulla oblongata. Its superficial
fibres on the ventral surface are transverse in their general direc-
tion ; but the middle fibres pass directly across, the lower ascend
sUghtly, and the superior are more curved, and descend obliquely
6
82 STRUCTURE OF THE BRAIN.
to reach the crus cerebelli. On removing these superficial fibres
the prolonged fibres of the anterior pyramids are exposed to view.
These, as they ascend through the pons, are intersected by the
transverse fibres. At the low^er part of the organ, behind the fibres
from the anterior pyramids, a special set of transverse fibres (tra-
riezium) begins at a collection of gray matter [superior olivary
nucleus) on one side, and crosses the middle line to ascend to the
cerebellum on the other side.
Nuclei of gray matter with small multipolar nerve-cells are found
everywhere between the fibres of the ventral part of the pons.
Many of its transverse fibres are probably connected with these
cells. The posterior portion of this oi'gan is chiefly constituted by
a continuation upward of the formatio reticularis, and of the gray
matter of the medulla oblongata. In the reticular formation two
or three important collections of nerve-cells lie embedded. One
of these is the " superior olivary nucleus," which lies behind the
outer part of the trapezium and gives origin to some of its nerve-
fibres. Of the other nuclei in this region, one gives origin to the
seventh or facial nerve, and others to portions of the fifth nerve.
§ 18. IV. The Cerebrum, or Large Brain, much exceeds in size all
the other contents of the cranial cavity ; but it surpasses them more
especially in the variety and complexity of the arrangement here
given to the nervous elements ; while its significance for the in-
quiries of Physiological Psychology is altogether unique.
As ordinarily described, this nervous mass includes a consider-
able number of organs, which vary in structure, relations, and
physiological functions. Besides the hemispheres of the cerebrum,
and the great ganglia (corpora striata and optic thalami) which lie
at their base, custom includes in this term certain bodies that ap-
pear connected with the lower surface of the mass, viz., the corj)ora
quadrigemina, pineal gland, crura cerebri, etc.
§ 19. The Cerebrum is of ovoid shape and is divided — above, in
front, and behind — into two hemispheres by a deej) median longi-
tudinal fissure. If these hemispheres are drawn asunder by open-
ing this fissure, they are seen to be connected at its bottom by
a broad white band of nervous matter, the corjnis callosum. The
outer surface of each hemisphere is convex and fitted to the con-
cave inner side of the bones of the skull ; the inner surface along
the median fissure is flat, and separated from the corresponding-
surface of the other hemisphere by a process of the dura mater
{falx cerebri) ; its under surface is separated from the cerebellum
and the pons by another process of the same membrane [tentorium).
From the front of the pons the large wliite nervous cords, called
BASAL ASPECT OF THE CEREBRUM. 83
cerebral peduncles, or crura cerebri, pass upward and forward to
connect the cereln-um with the organs lying below it. Around
each crus winds a flat band, the optic tract ; these tracts come to-
gether in front to form the optic commissiire from which the two
optic nerves arise. The lozenge-shaped space enclosed by the
crura cerebri, the optic tracts, and optic commissure, contains a
Fig. 25 Under Aspect of the Brain. (Henle.) B, basis of the crura cerebri ; Oca, corpora al-
bican Ha : I', olfactorv bulb; II'. optic tract; Tc, tuber cinereum ; Lpp, posterior perforated
space : Ccl, corpus ca'llosum ; Let. lamina cinerea terminalis ; Spa, anterior perforated space ;
T, tegmentum ; Tho. thalamus opticus; P, pons; Mo, medulla oblongata; I. to VIII., tirst to
eigrhth pair of cranial nerves.
gray layer {posterior perforated space), two small white bodies (cor-
pora albicaniia), and a gray nodule {tuber cinereum) which is joined
to a small reddish-gray oval mass {pituitary body) by a conical pro-
cess of gray matter {ivfundibulum). In front of the optic commis-
sure is a thin layer of gray substance (lamina cinerea) ; and on each
side of the deep longitudinal fissure stretches the olfactory tract,
84
STRUCTURE OF THE BRAllSr.
with its bulb. The intercranial j)art of this "nerve " is now known
really to be a projecting portion of the brain. All these structures,
together with the cut ends of the several pairs of cranial nerves,
may be seen upon the under surface of the cerebrum.
§ 20. The upper surface of the cerebral hemispheres presents the
appearance of gray nervous matter arranged in folds which are
called " convolutions " or gyri. These convolutions are separated by
"fissures " or sulci of varying depth, some of which are so constant
and strongly marked that their presence is employed to divide the
surface of the hemispheres into lobes, while others, less strongly
marked, separate from each other the convolutions of the same
lobe. It is the arrangement of the convolutions, with their sep-
arating fissures, which gives the hemispheres of the brain their
characteristic appearance, and which fits them for their unique
functions in the economy of the nervous mechanism.
FlQ. 26.— To show the Right Ventricle and the Left Half of the Corpus Callosum. a, transverse
fibres, and &, longitudinal fibres of corpus callosum ; c, anterior, and d, posterior cornua of lat-
eral ventricle ; e, septum lucidum ; /, corpus striatum ; (), ttenia semicircularis ; h, optic thala-
mus ; k, choroid plexus ; I, teenia hippocampi ; ni, hippocampus major ; n, hippocampus
minor ; o, eminentia coUateraLis.
§ 21, By cutting off successive slices from the upper part of the
hemispheres their general internal structure may be seen. It re-
YENTRTCLES OF THE CEREBRUM.
85
sembles the plan upon which the cerebellum is constructed. A
core of white nervous matter is surrounded by a shell or cortex of
gray ; the two lateral halves of the core are bound together by a
strong band of fibres,
usually described as
commissural {corpus
callosum), which is
itself overlapped by
one of the most
marked convolutions
of the brain {gyrus
fornicatus). By cut-
ting still deeper it is
found that the cor-
pus callosum forms
the roof of a space in
the interior of each
hemisphere [the late-
ral ventricles). These
two cavities or ven-
tricles are moistened
by a serous fluid and
separated by a thin
transparent wall {sep-
tum lucidum). The
roof of another cav-
ity, the third ventri- fo
cle, is formed by an *- -■
expanded fold of the
pia mater {velum in-
terpodtum), the mar-
gins of which are
fringed by the so-
called "choroid plex-
uses ; " the latter
contain the minute
arteries which sup-
ply the nervous structures of this region. Each lateral ventricle is
divided into a central space and three curved prolongations or coi'-
nica ; of the cornua, one (the anterior) extends forward and outward
toward the fi"ont part of the cerebrum ; one (the posterior^) curves
backward, outward, and then inward ; and the third (the descending)
curves backward, outward, downward, and then forward and inward.
Fia. 27. — Basal Ganglia of the Cerebrum seen from above. (Henle.)
Col, genu of the corpus callosum ; Cs, corpus striatum ; Vsl,
ventricle of the septum lucidum ; Of, column of the fornix ; St,
stria terminalis : Tho, optic thalamus ; and Ts. its anterior tu-
bercle ; Com, middle coiimiissure between the thalami and over
the third ventricle ; Pv, pulviiiar ; On, conarium or pineal
gland ; Cop, corpus quadrigeminum.
STRUCTUKE OF THE BEAIN.
On the floor of each lateral ventricle the exposed portions of the
great basal ganglia of the cerebrum are visible. A large pear-shaped
body of gray color is here seen with its broad extremity directed
forward into the anterior cornu of the ventricle and its narrow
end outward and backward.' This body, on account of the striped
Fig. 28. — A Deeper DisEection of the Lateral Ventricle, and of the Velum Interpositura. a, un-
der surface of corpus callosum, turned back ; 6, ft, posterior pillars of the fornix, turned back ;
c, c, anterior pillars of the fornix ; d, velum interpositum and veins of Galen ; e, fifth ventricle ;
f. f, corpus striatum ; (/, (j, taenia semicircularis ; h. h, optic thalamus ; A', choroid plexus ; /,
taenia hippocampi ; m, hippocampus major in descending cornu; n, hippocampus minor ; o,
eminentia collateralis.
appearance which it presents when cut open, is called a " striate
body" (corpus striatum). It consists of two masses, the upper one
of which (nucleus caudatus) projects into the lateral ventricle ; the
lower one is embedded in the white substance of the hemisphere and
forms the principal part of the body (nucleus lenticiilaris). The two
are separated by a layer of white matter called the " internal capsule.''
Between the diverging portions of the striate bodies are the obloug
' Dalton (Topographical Anatomy of the Brain, Philadelphia, 1885, ii. , p.
76) and others speak as though the caudate nucleus alone were to be called
corpus striatum, the nucleus leuticularis by this name ; and the twococsidered
as separate bodies.
THE CRUSTA AND THE TEGMENTUM. 87
oi' somewhat ovoid masses of the " optic thalami." Each thalamus
rests upon and partially embraces one of the crura cerebri ; its me-
dian surface forms the side wall of the third ventricle, and upon its
outer and back part are two small elevations, one on each side of
the optic tract {corpora geniculata, internum and externum). In the
depression between each striate body and the optic thalamus is a
narrow, whitish, semitransparent band of medullary substance
{f.amia semicircular is). Along the entire length of the floor of the
descending cornu of the ventricle is a white eminence {jivppocampus
major or cornu Ammonis) which is the iuuer surface of the gyrus
fornicatus doubled upon itself like a horn. An arch-shaped band
of nerve-fibres, consisting of two lateral halves, which, in front,
form two pillars that descend to the base of the cerebrum and be-
come the corpora alhicantia, and which diverge behind into two pil-
lars that descend with the descending cornu of the ventricle and
connect with a convolution of the brain (gyrus hippocampi), is situ-
ated beneath the corjDus callosum ; it is called the fornix. Behind
and between the optic thalami, and resting on the back surface of
the crura cerebri, are four rounded eminences in two pairs, called
corpora quadrlgemina ; the front pair are the nates, the back pair,
testes.
§ 22. Without mentioning other more minute subdivisions, super-
ficial or internal, in the structure of the cerebrum as seen by the
unaided eye, we now consider the arrange- 2_
ment of the nerve-fibres and nerve-cells in /'''^^~^^\
the more important organs already named. y^ ■^- \.
Of the fascicles of nerve-fibres belonging s^j t \ \
to the cerebrum, some connect it with the /^>v ; ^/^ \
lower organs of the encephalon ; some con- ( -p ^s^A^x^-"'- J
nect together its hemispheres ; some join X^ ^ /o\^ ^^
different structures in the same hemisphere ; fig- 29.— section through the
. Mid-brain. (Schwalhe. ) aq ,
some are roots of origin for certain nerves. aqueduct of syivius; .«.?*., sub-
_-. ^, PIT 1 • J.1 stantia nigra : p. crusta of the
The fibres of the crura cerebri — those cms cerebri ;«, tegmentum of
, T 1 J! ii 1 • XT i T the crus cerebri.
strong peduncles oi the brain that ascend
from the pons to the optic thalami and the striate bodies — are
arranged in two groups (criista and tegmentum) separated by the
gray matter of the substantia nigra. An important part of the
fibres of the crusta, or front part (pes) of the crus, is continuous
with the longitudinal fibres of the pons which come from the
pyramids of the medulla ; it receives some fibres from the gray mat-
ter of the substantia nigra. Many of the fibres of the crusta ter-
minate in the nuclei of the striate bodies ; but some radiate upward
through the internal capsule directly to the gray cortex of the
88 STRUCTUEE OF THE BEAH^T.
cerebrum. (Comp. Fig. 24.) Some of the more diffused fibres of
the tegmentum, or back and deeper part of the crus, are probably
continued from the anterior column of the cord, and may be traced
above to the optic thalami. Others of its fibres are collected into
more well-defined tracts ; one of the most important of which
comes from the superior peduncle of the cerebellum, and has al-
ready been traced as it passes forward over the anterior end of the
fourth ventricle (see p. 79). The formatio reticularis is continued
into the tegmentum ; the latter, therefore, has a considerable
amount of gray matter containing nerve-cells. Some of its fibres
arise in these cells. The superior peduncle of the cerebellum as-
scends, crosses over to the other side beneath the Sylvian aque-
duct, and terminates in a collection of large pigmented cells (the
nucleus of the tegmentum or red nudeua).
The intimate structure of the striate bodies is not as yet entirely
made out. On its deeper side, which is turned toward the internal
capsule, the nucleus caudatus receives from the capsule several
bundles of fibres. According to Meynert, some of these bundles
serve to connect this nucleus downward with the peduncle of the
cerebrum, some upward with its cortex ; but, according to Wer-
nicke, it is doubtful if any of them pass to the white matter of the
hemispheres, or come directly (that is, without traversing the len-
ticular nucleus) from the crusta. All parts of the nucleus lenticu-
laris are pervaded with white fibres. Some pass into its inner zone
from the adjacent part of the internal capsule ; some connect it with
the caudate nucleus ; some pass from it into the corona radiata,
and then to the cerebral cortex. These nuclei appear to have a
special connection with the frontal and parietal lobes, but also with
some convolutions of the temporal lobe and the island of Keil. The
gray matter of this organ is composed of delicate connective tissue,
with "free nuclei siDaringiy distributed through it." The nerve-
cells of the nucleus caudatus are multipolar and of two sizes ; some
are about -g-J-y inch in diameter with many processes, but most are
much smaller (y^'o-g- inch). Between the fibres of the gray matter
of the nucleus lenticularis are many cells with yellow pigment in
them.
The three collections of gray matter — the locus niger, and the cau-
date and lenticular nuclei of the striate body — with the nerve-fibres
which originate in them and bind them together, have been held to
constitute a connected chain of nervous organs, to which the name
"ganglia of the crusta" has been given by Meynert. Eecently,
however, this relation of the corpora striata as "basal gangHa," or
"middle-men "between the spinal cord and the cerebral cortex, has
COEPUS GENICULATUM AND OPTIC THALAMUS.
89
been called in question by Wernicke and A. Hill. The latter argues, '
chiefly on morphological grounds, that the nucleus caudatus should
be separated from the optic thalamus, and connected immediately
with the cortex. This connection, he thinks, is favored by the na-
ture of its development, by its minute structure, which differs from
that of the thalamus, and by its resemblance to another nucleus
(the amygdaloid) which has an undoubted origin from the cortex.
23. Another chain of nervous organs, leading between the pons
Yarohi and the hemispheres of the
brain, consists of the tegmentum of
the crus and its ganglia— the red
nucleus (already described), corpus
subthalamicon, the corpora genicu-
lata, and the optic thalami.
The arrangement of the nervous
elements in the external corpus
Corpus
taUoswii
Sept.
peUuctd
Binttrer
Iheil des
Nucleus
Cornn
posteriua
Fig
Fig. 31.
These and the following two FiRures show the arrangement of the white and gray substance in
the interior of the cerebrum. (All four are from Gegenbaur.)
Fig 30 —Horizontal Section through the Right Hemisphere. _
Fig 31.-Frontal Section through the Cerebrum in front of the Fornix. Posterior surface of the
section displayed.
geniculatum is peculiar : it consists of alternate layers of white and
gray matter, as though occasioned by laying a lamina of the gray
between two medullary lamina?, and then folding them in a zigzag
manner. The nerve-cells of this organ are from ^-J-g- to gfo- of an
inch in length, and ^ gVo »* an inch in breadth ; they are coarsely
granular and pigmented.
The ojMc thalamus is a mass of gray matter, with multipolar and
fusiform cells, traversed by nerve-fibres. This gray matter is par-
tially subdivided into two parts, an inner and an outer nucleus.
1 The Plan of tlie Central Nervous System, pp. 35 fE.
90
STRUCTURE OF THE BRAIIf,
Its free surface (inner and upper) is covered by a layer of white
fibres. On its outer surface is the white matter of the internal
capsule, formed by fibres diverging from the crusta into the hemi-
spheres. All along this surface fibres radiate from the interior of
this organ, and mingle with those of the internal capsule on their
way to the cerebral hemispheres. Those in front pass to the frontal
lobe ; those in the middle pass to the back part of the same lobe
and to the parietal lobe ; those behind to the temporo-sphenoidal
and occipital lobes.
"The external and under surfaces of the thalamus are not free,
but are united with the other parts of the brain. The under sur-
face is united with the tegmental j^art of the crus cerebri, while
the external surface is covered by white substance, that is formed
Fig. 32.
FiQ. S3.
Fig. 32.— Frontal Section through the Right Hemisphere of the Cerebrum in front of the Com-
missura Mollis. Posterior surface of section displayed.
Fig. 33.— Frontal Section through the Cerebrum back of the Commissura Mollis. Front surface
of section displayed.
of fibres of the crusta, which here diverge into the substance of the
hemisphere and pass between the thalamus and the lenticular nu-
cleus, forming the so-called 'internal cajDsule"" (comp. p. 87 f.).
The cells of its substance average about yiy- inch in length and
^jj-g in breadth ; their long axis is parallel to the course of the
nerve-fascicles. According to a recent authority," the thalamus
is the primary centre of the optic nerve, and is also connected with
the olfactory nerve — originally by way of the fornix.
The nervous substance of the corpora quadrigemina consists
mainly of gray matter covered externally with a thin layer of
nerve-fibres. In the interior of the upper or front pair the most
' Quain's Anatomy, ninth edition, ii.. p. 324.
^ A. Hill, The Plan of the Central Kervous System, pp. 20 ff.
FIBRES OF THE COIlOiS^A EADIATA. 91
characteristic portion of this organ is found; it is a layer of fine
nerve-fibres running longitudinally, between which are small, scat-
tered nei've-cells. In the external strata of these bodies multipolar
cells are abundant ; in their interior, at the sides of the Sylvian
aqueduct, is a collection of gray matter which forms a continuation
of the lining of the third ventricle. The nerve-cells in the corpora
quadrigemina vary greatly in size. Most of those in the superficial
strata are small ; but in the deeper strata some of them reach the
maximum of nearly g^^g- of an inch. The centres of origin for the
third and fourth nerves are in that nervous structure of fine fibrils
and fusiform cells which lies along the Sylvian aqueduct.
§ 24. The arrangement of the nervous elements in all the basal
ganglia, as connected with the cerebral peduncles, indicates the na-
ture of the mechanism of this region of the brain. It is constructed
so as to co-ordinate all the nerve-tracts of motion with those of
sense, and thus give to these ganglia important reflex and auto-
matic powers over the sensory-motor apparatus, while subordinating
them to the control of the nervous centres of the cerebral cortex
that lie farther above.
To the highest and dominating nervous centres in the cerebral
hemispheres the paths of nervous impulse are laid from the basal
ganglia by that blossoming out, as it were, of the nerve-fibres on
their way to the white core of the cerebrum, which is called the
" corona radiata." The corona is formed by the fibres that radiate
from the striate bodies, from the optic thalami, and the internal
capsule, into the convolutions of the lobes of the hemispheres.
§ 25. The combination of the nervous elements into the pre-
eminently complex mechanism of the convolutions of the human
cerebrum may be described from two points of view ; the first is
that from which their various external surfaces may be regarded by
the unaided eye, the second that which histology assumes when it
examines under the microscope various sections made from layers
of their substance.
The details of the external aspect of the convolutions vary so much
in each individual, and even in the two hemispheres of the same brain,
that the only chance of bringing order out of this apparent confusion
is to discover what is genei'al, and for the most part constant, in the
midst of what is particular and subject to change. In making such
discovery the study of embryology is especially important. Certain
sulci and their corresponding gyri appear with a marked regular-
ity in the earlier and more fundamental stages of the development
of the foetal brain. So, too, does the examination of the surfaces
of the hemispheres of the adult brain show certain degi'ees of
92 THE CEREBRAL CORTEX.
strength with which the sulci and gyri are distinguishable, and
thus enable the investigator to divide them into so-called pri-
mary, secondary, and even tertiary classes. Bischoff, Ecker, and
others have aptly compared the primary gyri to the large mountain
ranges whose sinuosities give to an entire region its characteristic
features ; the secondary gyri are like those subordinate ranges
which are brought into existence through the formation of longi-
tudinal valleys (secondai-y sulci) in the main ranges ; while the ter-
tiary convolutions may be compared to the small sj)urs which run
out into the valleys between the principal ranges and from their
sides. Only the primary gyri are, as a rule, pretty regularly dis-
posed.
It is by means of the primary sulci that the surfaces of the hem-
ispheres of the brain have been divided by modern anatomy into
five territories or Lobes. ' The frontier lines of these lobes, how-
ever, are clearly laid down only on some of the surfaces, while on
other surfaces the lobes encroach on each other without distinct
boundaries. The five lobes are called Frontal, Parietal, Temporo-
sphenoidal (also Temporal or Sphenoidal), Occipital, and Central,
or Insula, or Island of Reil ; the latter does not stand in immediate
relation with the walls of the skull. The Frontal Lobe is divided
from the parietal on its upper and lateral surface by the Fissure of
Bolando (sulcus centralis) ; and on its lower surface from the tem-
poral lobe by the horizontal branch of the Fissure of Sylvius. The
Parietal Lobe is divided from the temporal for the greater part
by the Fissure of Sylvius, and from the occipital — on its median
surface completely, but on its upper surface only very incompletely
— by the parieto-occipital fissure. The Temporo-sphenoidal lobe
is distinctly marked off from the frontal and parietal, as already
described ; while the boundary line between it and the occij)ital
lobe is ill defined. The Island of Reil lies concealed between the
frontal, parietal, and temporo-sphenoidal lobes; its surface, when
exposed by drawing aside the margin of the Sylvian Fissure, shows
a few short convolutions which radiate forward, upward, and back-
ward from a central sj^ot on the lower surface. The occipital, tem-
poro-sphenoidal, and frontal lobes, all have three principal convolu-
tions arranged in parallel tiers (superior, middle, and inferior) ; in
the frontal lobes these three spring from the anterior part of the
ascending convolution just in front of the Fissure of Rolando (that
is, from the gyrus centralis anterior) and run forward to the front
end of the cerebrum.
' The convolutions are here described in dependence upon the work o.t
Ecker, The Convolutions of the Human Brain. London, 1873.
ARRANGEMENT OF THE SULCI AND GYRI.
93
§ 26. A few of the most important of the sulci and gyri need
separate mention ; the accompanying diagrams will make clear
Fig. 34.
Fig. 35.
Figs. 34 and 35.— Profile and Vertex Views of Cerebrum. Fr, the frontal lobe ; Par, parietal;
Of, occipital ; Ts, temporo-sphenoidal lobe ; SS, Sylviiin fissure ; RE, fissure of Rolando ; PO,
parieto-occipital fissure ; IP, iiitra-parietal fissure ; PP, Parallel fissure : SF and IF, supero-
and infero-froutal fissures ; 1, 1, 1, inferior, 2, 2, 3. middle, and 3, 3, 3, superior frontal convo-
lutions ; 4, 4, ascending frontal convolution : 5, 5, 5, ascending parietal, 5', postero-parietal,
and 6, fi. angular convolutions ; A, supra-marginal, or convolution of the parietal eminence ; 7,
7, superior, 8, 8, 8, middle, and 9, 9, 9, inferior temporo-sphenoidal convolutions; 10, i-uperioi,
11, middle, and 12, inferior occipital convolutions ; a, |3, 7, 5, four annectent convolutions.
further details (see Figs, 34, 35, and 36). Among the sulci which
bound the main territories of the cerebral hemispheres the Fissure
94 THE CEKEBEAL CORTEX.
of Sylvius is much the most important. "It can," says Ecker,
" in nowise be considered in the same category as the rest of the
sulci on the surface of the brain." The other sulci may be re-
garded as mere folds of the cerebral cortex ; the Fissure of Sylvius,
on the contrary, is made by folding the entire hemisphere into an
arch, with its concave surface downward, about the point of en-
trance of the crus cerebii. This fissure exists in the foetal brain at
the third month. " It arises," say Foster and Balfour,' " at the time
when the hemispheres, owing to their growth in front of and be-
hind the corpora striata, have assumed somewhat the form of a
bean." The Fissure of Rolando is also always present in the human
brain. It makes its appearance in the foetus as early as the end of
the fifth month. It is rarely, if ever, bridged over by a secondary
gyrus ; it, therefore, forms a point of departure in the examination
of all the convolutions. It is botmded for its entire length by two
Pig. 36. — Convolutions of the Inner and Tentorial Snrfaoes of the Left Hemisphere, i. i, i, cal-
loso-marginal fissure, /, I, calcarine fissure; m,m, hippocampal fissure; n, n, collateral fis-
sure; PO, parieco-oocipiUI fissure ; 17, 17, marginal convolution ; 18, 18, gyms fornicatus; 18',
quadrilateral lobule ; 19, hippocampal gyrus ; 19', its recurved end ; 25, occipital lobule ; 9, 9,
inferior teraporo-sphenoidal convolution.
important convolutions (the anterior and posterior central or as-
cending frontal and ascending parietal), which at both of its ends
connect together in the form of an arch. The fissure which sepa-
rates the parietal from the occipital lobe [parieto -occipital) and the
one which runs from before backward through the parietal lobe
(intra-parietal) are also to be mentioned among the more important.
The intraparietal fissure, on the convexity of the parietal lobe, in-
cludes, between it and the median line, the upper parietal convolu-
tion, and embraces in its downward and outward bend the angular
convolution. The latter convolution, and the marginal convolution
form the inferior parietal lobule.
> Elements of Embryology, p. 384. London, 18S3,
THE FIVE LAMINA OF THE CORTEX. 95
Besides the superior, middle, and inferior convolutions of the
frontal, temporo-sphenoidal, and occipital lobes, and the two cen-
tral convolutions on each side of the Fissure of Rolando, the follow-
ing, which belong to the median aspect of the hemispheres, ai'e
to be noted in particular. The convolution which arches around
the corpus callosum, and is separated from the median aspect
of the first frontal convolution by a deep and constant fissure
(the sulcus calloso-marginalis) is called from its shape, gyrus forni-
catus. The back end of this convolution curves downward and then
forward, under the name of gyrus hippocampi, to the inner tip of
the temporal lobe. The passage of the former convolution, without
break, into the latter, Ecker considers one of the most important
differences between the hemispheres of the brain of man and those
of the ape.
§ 27. Although the general arrangement of gray nervous matter
upon the surface, and of white matter within, is adhered to in all
parts of the cerebral cortex, the form and disposition of the cells
in the gray matter differ in different regions, and also in different
layers of the same regions. But its most common form, which is
that seen in the convolutions of the parietal lobe, corresponds to
what Meynert ' has called " the general or five-laminated type of
the cortex of the cerebrum." There are, as a rule, that is to say,
five layers or laminae to be discovered in the gray matter of the
cerebral cortex. The thickness of the entire cortex, thus com-
posed, is, in the adult, from -^^ to \ of an inch. The first of
the layers consists of a matrix, in which delicate nerve- fibrils run
parallel to the surface and interlace with a few small globular or
elongated branching nerve-cells scattered here and there. The na-
ture of this matrix has been the subject of dispute ; by some it is
looked upon as connective tissue (Kolliker), by others as neuroglia
(Virchow). The second and third layers contain a large number
of pyramidal, or spindle-shaped cells ; of these layers the third is
the broadest, and contains the largest (but fewest) cells. The cells
of the second layer are about -j-g^u^o of an inch in diameter, and are
closely pressed together to form its substance ; but in the third
layer they augment gradually in size until they reach a diameter of
tt/oF' ^o perhaps gi^ of an inch, with their long axes perpendicu-
lar to the cortical surface. The fourth layer contains large num-
bers of small, globular, and irregularly-shaped and branching cells ;
the fifth, spindle-shaped bodies with long tapering processes, and
also a certain number of smaller irregular cells. This innermost
layer consists chiefly of a compact accumulation of cells which give
' In Strieker's Human and Comparative Anatomy, 11., p. 381.
96
THE CEEEBEAL COETEX.
off lateral processes. Gerlach discovers here, as in the spinal cord
(see § 9), a very minute network with which these processes are
apparently continuous. It is also an assumption, verified by direct
observation of some cases, and by the general analogy of the nervous
system, that many of the extremely attenuated nerve-fibrils which
El i !
,'W. ^ii ''■',.■'
3C
Fig. 37. — Section through the Cerebral Cortex of Man, prepared with Osmio Acid ^sy^^
(Schwalbe.) /, principal external, and //. internal, layer ; x, laj'er lying as a limit between the
two ; »M, medullary substance sending out bundles of nerve-tibres into //; i, layer poor in cells,
but with an external plexus of nerve-fibres {Id) ; ^, layer of small, and 3, of large, pyramidal
cells ; k, inner layer of small nerve-cells.
radiate from the white core of the convolutions are continuous with
the basal axis-cylinder processes of the cells in the layers of gray
substance. Small rounded corpuscles and small stellate cells, so
pellucid that they seem to be only free nuclei, are contained in the
neuroglia of the gray substance of the cerebral cortex. It is doubt-
WHITE SUBSTAjSTCE OF THE HEMISPHERES. 97
ful whether these are true nervous elements or not. The number
of nerve-cells in the cortical substance is very great. In a portion
of this substance, only one millimeter square and J^- millimeter
thick, 100 to 120 have, on an average, been counted.'
Modifications of the arrangement which prevails in most of the
gray substance of the hemisjpheres of the brain are found in certain
regions. In the cortex of the occipital lobe the number of layers
is increased by the intercalation of additional granule layers to
seven or eight. In the cortex of the Island of Eeil, and of the con-
volutions bounding the Fissure of Sylvius, a large proportion of
fusiform cells is found. In the fourth layer of the cerebral cortex
of the dog, in the region which Hitzig considei'ed to be motor,
Betz discovered certain cells lying in scattei-ed groups, with two
large and several small processes ; these cells, on acccount of their
great size, he called " giant-cells:" Similar cells, have been found
by him in certain regions of the human cerebral cortex — namely, in
the entire anterior central, and the upper end of the posterior cen-
tral convolutions, and along the lobe which is prolonged backward
from the two.
§ 28. The white substance of the hemispheres of the brain may
all be considered as originating in its cortical gray substance ; but
the nerve-fibres of which it is composed constitute three classes,
according to the destination of the fascicles into which the fibres are
gathered. These three are the down-going or peduncular, the com-
missural, and the arcuate (or fibres 2droprice). It is the business of
the peduncular system to connect the cerebrum with the lower parts
of the encephalon. This system, called the corona I'adiata, is nar-
rowed into the internal capsule and continued downward to the
crura cerebri ; its diminished size shows that a considerable por-
tion of its fibres have entered into the optic thalami and striate
bodies. But it is also probable that many fibres of the crusta pass
directly into the brain's medullary centre, and through this to its
gray cortex, without entering these ganglia. Of such tracts the
best known is the loyramidal (probably motor). According to
Flechsig and others, this is traceable through the internal capsule
and corona radiata to certain frontal and parietal convolutions.
Another tract, traceable directly to the convolutions of the cortex,
passes from the external part of the crusta into the white matter
of the occipital lobe (so-called direct sensory tract). The fibres
which come from the tegmentum, and are lost, for the most pai-t, in
the thalamus and the subthalamic region, stream outward from the
other side of this organ, join the general system of the corona radi-
' See Luys, The Brain and its Functions, p. 17. New York, 1883.
7
98 THE CEREBRAL CORTEX,
ata, and diverge to nearly every part of tlie hemispheres ; but espe-
cially to the temporo-sphenoidal and occipital lobes (probably sen-
sory).
The commissural system of fibres has hitherto universally been
supposed to connect the two hemispheres of the brain ; but Pro-
fessor Hamilton, of xiberdeen, and others, have recently called this
statement in question. The principal tract of such fibres is in the
coi-pus callosum. Since this commissure lies in a plane above that
of the corona radiata, the two systems of fibres intersect each other
on their way to the convolutions of the cerebral hemispheres. A
smaller commissure (the anterior) passes below the lenticular nuclei
of the striate bodies and connects the convolutions around the Syl-
vian fissure — binding together the right and left temporo-sphen-
oidal lobes ; it also furnishes a root of origin for the olfactory
nerve.
The arcuate fibres extend over more or less territory on the
same side, and connect the gray matter of adjacent, or more or
less distant, convolutions in the same hemisphere — " a garland-like
interweaving " of two convolutions around the sulcus between them.
In certain localities, where the fascicles into which these fibres are
gathered are strongly marked, they have received special names ;
such are the fasciculus uncinatus which crosses the bottom of the
Sylvian fissure and connects the convolutions of the frontal with
those of the temj)oro-splienoidal lobe ; the fillet of the gyrus forni-
catus, extending longitudinally in that convolution ; the longitudi-
nal inferior fasciculus, connecting the convolutions of the occipital
and temporo-sphenoidal lobes. Such fibi-es are sometimes called
longitudinal or collateral fibres. It is by the commissural and arcu-
ate fibres that the innumei-able ganglion-cells and nerve-granules of
the cortex are bound into a unity of form and of function. The pro-
cesses of the cells anastomose, and are thus united with immedi-
ately adjoining cells by means of a gray fibre-plexus. The axis-
cylinder processes become continuous with the meduUated fibres,
which, gathered into bundles (the fasciculi of the arcuate fibres),
line as a continuous layer the inner surface of the cortex. In this
manner the nervous elements of that crowning mechanism, which
is known as the chief glory of man's nervous system, are made to
exhibit a manifoldness, and at the same time a unity of structure,
suggestive of a common service joined with diversity of mode in
Avhich the service is rendered.
§ 29. The view of Meynert — to which reference has already been
made (p. 73) — regards the gray masses and converging and diverg-
ing tracts of the cerebro- spinal nervous mechanism as a " Projec-
MEYIS'EET'S PEOJECTIOJST SYSTEMS.
99
tion System " (or rather as a series of "projection systems"), wliich
is capped and dominated by the hemispheres of the cerebrum. The
sensory nerves may thus be figuratively described as the " feelers,"
and the motor nerves as the " arms " of its cortical gray matter.
This matter is both a "sensory shell," upon which the centripetal
nerve-commotions gather and dispose themselves ; aud is also the
"motor shell" in which certain centrifugal motions originate. It
is, therefore, an internal " Projection Field " for the muscular sys-
Ccl' ^'"ft
Fig. 3S. — Median Section of the Brain. A, aqueduct of Sylvius : Cba, white commissure ; Cbl,
cerebellum ; Oca, corpus albicans ; Ccl, corpus cailosum, of which the different parts are Ccl',
rostrum, CcP, the genu, Ccls, the body, and Ccl^, splenium ; On, conarium, or pineal gland;
Coa, anterior. Com, middle, and Cop. posterior, commissures ; PM, foramen of Monro ; Fta,
the anterior, and Ftii, the posterior, transverse fissures ; Let, lamina cinerea terminalis ; and
Lq, lamina of the corpora quadrigemina : Mo, medulla oblongata : P, pons Varolii ; SI, septum
lucidum ; SM, sulcus- of Monro ; Tc, tuber cinereum ; Vma. anterior velum medullare ; V,
fourth ventricle ; II, optic nerve ; II', chiasm of the optic nerve.
tern. The gray masses of the brain below its hemispheres (with
the exception of the internal tubular mass) may — according to
Meynert — be described as either (a) "Interruption Masses" of the
projection system, or as belonging to (b) the " Region of Reduc-
tion " of the mass of this system. It is in these lower gray masses
that the great bulk of the nerve-tracts (the corona radiata) coming
from the cortex of the cerebrum are not only broken and inter-
rupted in their course, but are also greatly reduced in size.' The
' For a clear and concise summary of Meynert's entire view, see Quain's
Anatomy, ninth edition, ii., pp. 370 ff.
100
NERVES OF THE CEREBRO-SPINAL SYSTEM.
functional significance of this relation in which the cerebral cortex
stands to all the rest of the nervous mechanism will appear more
clearl}' further on in the discussion.
§ 30. The cerebro-spinal axis, or central nervous mechanism of
the cavit}^ of the spinal column and skull, is connected with the
end-organs of motion and of sense by thirty-one pairs of Spinal,
and twelve pairs of Cranial or Encephalic Nerves.
The thirty-oue pairs of Spinal Nerves originate in the spinal
cord and pass out of the spinal canal through the openings called
C
Fig. 39.— Posterior View of the Spinal Cord with its Nerven. }4. (After Sappey. ) I- VIII in A
are cervical : I, II, and III in A, and IV-XII in U, dor.sal ; the last in B, and down to V in C,
lumbar: I-V in C, Bacnil ; lu, in, origin of the posterior roots; 11, 11, posterior median tis-
sure ; 12, 19, spinal pan^lia : i;j, 13, united i). rve ; 15, tapering of the lower end, becoming 16,
10, the filum terininale ; IT, caudii equina.
"intervertebral foramina." Of the entire number — enumerating
from above — eight pairs are cervical, twelve thoracic or dorsal,
five lumbar, five sacral, one coccygeal. Each nerve arises from the
side of the cord by two roots, an anterior and a posterior. The
posterior root has a swelling or ganglion upon it, the anterior has
none ; the former is composed of sensory nerve-fibres, the latter.
THE TWELVE PAIRS OF CRAlSriAL NEEVES. 101
of motor nerve-fibres. The ganglion of the posterior roots contains
unipolar nerve- cells. The roots themselves vary, in the different
regions of the cord, both as respects direction and length. Imme-
diately outside the ganglion the anterior root joins the posterior,
and the united nerve — containing a mixture of motor and sensory
fibres — soon after separates into two divisions, that are formed of
elements from each root and that are distributed, one upon the
back and the other upon the front and sides, to all parts of the
trunk and limbs.
Of the twelve pairs (adopting the Continental instead of the
English division) of Cranial Nerves, which arise fi-om the base of
the encephalon and pass thi'ough the openings (foramina) in the
floor of the cranial cavity, three groups may be distinguished : (a)
the sensor}' nerves, or nerves of special sense ; (b) the motor nerves ;
(c) the mixed nerves, which contain both sensory and motor fibres.
To the first grouj) belong the olfactory nerve (first pair), the optic
(second pair), and the auditory (eighth pair) ; to the second group
belong the nerves that supply the principal muscles of the eyeball
(oculo-motor, third pair), the superior oblique (trochlear, foui'th
pair), and external rectus (abducent, sixth pair), muscles of the eye,
the muscles of facial expression (seventh pair), the muscles of the
tongue (hypoglossal, twelfth pair), and the spinal accessory nerve
(eleventh pair) ; to the third group belong the three nerves which
are so widely distributed over the mucous membranes and muscles
of the face, tongue, pharynx, and internal organs — namely, the tri-
geminus (fifth pair), the glossoj)haryngeal (ninth pair), and the pneu-
mogastric or vagus (tenth pair).
§ 31. It is, then, by a process of differentiation of a few compara-
tively simple elements, and of infinitely varied arrangement and
combination of the elements thus differentiated, that the elaborate
mechanism of the human nervous system is constructed, and made
fit for the great variety of interconnected functions which it is
called upon to jDerform. Material atoms are chemically united into
the comjDlex and unstable molecules of which nervous matter is com-
posed. These molecules are arranged into the structural forms of
nerve-fibres and nerve-cells ; and the lattei", at least, are modified
in form according to their location, and perhaps also function.
The elements are combined into conducting cords, end-organs, and
central organs, according to the threefold plan of a nervous sys-
tem ; and the organs are arranged, in the case of man, with an in-
tricacy of relations which can be only very inadequately described.
The description of the mechanism being finished, we consider
more in detail what it can do.
CHAPTER III.
THE NERVES AS CONDUCTORS.
§ 1. In that threefold economy of organs which characterizes the
developed nervous mechanism, the office of propagating the neural
process between the central organs and the end-organs has been
assigned to the nerves. The power to originate this process under
the action of external stimuli, although experiment shows that it
belongs to the nerves, is not exercised by them while in their nor-
mal place within the mechanism. It is the office of the end-organs
to transmute the physical molecular processes, which are their stim-
uli, into the physiological and neural process, and hand it over, as it
were, to these conducting cords. But the office of the nerves as
conductors is, of course, not like that of a tube which conducts along
its channel some kind of fluid, nor is it like that of the wire or bell-
metal which is thrown into vibration throughout. It is a molecular
commotion which, when started at any point in the nerves, moves
in both directions from point to point along its course. The
intimate connection between the two functions of excitation and
conduction becomes, then, at once apparent. Indeed, excitation
may be considered as the setting uj) of the process of conduction ;
conduction as the uninterrupted continuance, or propagation from
point to i^oint, successively, of the process of excitation. Each
minute subdivision of the nerve, then, must be regarded as consti-
tuting, in some soi't, a source or centre of stimulation with respect
to its neighboring subdivisions. If the nerve-commotion is to
move along the nerve N, between two distant portions of its struct-
ure, a and z, then a must act upon its neighbor 6 as a stimulus, b
upon c, and so on successively until y is found stimulating z, and
the process of progressive excitation or conduction is complete.
§ 2. It follows from what has just been said that, in considering
the nerves as conductors, the conditions and laws of the origination
of that process of excitation which they conduct must be taken into
account. It is neither necessary nor convenient, however, to carry
throughout a distinction between the two functions — the excitabil-
ity and the conductivity — of the nerves ; it is better to regard them
QENERAL PHYSIOLOGY OF NERVES. 103
as one process from somewhat different points of view. The arising
and progressive movement of a unique molecular commotion con-
stitutes the distinctively neural action or function of the nerves.
And since this so-called nerve-commotion has eluded all the at-
tempts hitherto made to discover its more intimate nature, and to
bring it under a strict theory, we must be content with describing
the following three classes of facts : (1) The Conditions of the pro-
cess ; (2) the Phenomena evoked with it, or as part of it, by differ-
ent kinds of stimuli ; (3) the Laws of its propagation.
What is called " the genei'al physiology of nerves " attempts to
consider their action while excluding the influence upon it from
the central organs aud the end-organs. That is, the function of the
nerves, as we now consider it, is exercised under ahnormal conditions.
It has been objected to the view which regards each element of
the nerve as the stimulus of neighboring elements, that the ef-
fects of direct artificial stimulation must differ in important respects
from those obtained by stimulation in the normal way. For exam-
ple, Ziemssen and others have shown that the crushed nerve of an
animal, or the paralyzed nerve of a man, may be made to set up a
nerve-process hy reflex stimulation when it will no longer respond
to stimulation applied directly to its trunk. And Grtinhagen af-
firms that after a stretch of nerve has been reduced by the effects
of carbonic acid to a lower degree of excitability under direct stim-
ulation, it will still propagate through itself the excitation set
up elsewhere with undiminished force. Such facts, however, only
prove that the application of stimuli to the nerve for purposes of
experiment is a very rough and ineffective way compared with nat-
ure's method of preparing the stimuli by the modifying influence
of the nervous tissues themselves. They do not prove that the
neural process is not fundamentally the same in whatever way it is
brought about. On the contrary, there is abundant evidence to
show that this abnormal activity, when carefully studied, will give
us the key to the normal function of the nerves. The advantages
of simplifying the problem by experiments upon isolated nerves
are too great, and the fund of valid information thus obtained is
too important for us to neglect the method proposed. The science
called " genei'al physiology of the nerves " is, indeed, very largely
built upon experiments with the motor nerves of frogs ; and, of
course, it may be said that frogs, with respect to their nervous sys-
tems as otherwise, are very unlike men. But with respect to the
character of that specific molecular process which is set up in the
nerve when excited, frogs apjDcar to be essentially the same as men.
At any rate, we have no physical means adequate for detecting any
104 THE NERVES AS CONDUCTORS.
essential differences. In other words, nerves are nerves the world
over ; and what they do as nerves simply, is essentially one thing in
all cases. What they do in their vastly different arrangements and
connections with central organs and end-ox"gans differs vastly in
different cases.
§ 3. The view that each element of every nerve, irrespective of
its kind or specific place in the animal mechanism, can only stimu-
late its neighbor and be stimulated by its neighbor, suggests an-
other interesting inquiry. Is this stimulus of the nerve-elements,
this effect in exciting contiguous elements, aniologous to any of the
so-called external stimuli ? Or, in other words, the inquiry may be
raised : Is the process of nerve-commotion in the nerves similar to,
or identical with, any of those molecular processes which act as in-
direct stimuli upon the nerves through the end organs ? In answer-
ing this question it has long been customary to ally nerve-commo-
tion with electricity. In a posthumous work b}'' the mathematician
Hansen, in 1743, it was first proposed to consider the efficient
j)rinciple of nervous action as identical with that of the electrical
machine.' Exactly a century later (1843) du Bois-Reymond an-
nounced the discovery of an electrical current in unexcited nerves
(the so-called " current of rest "). Since then the phenomena of this
current, of the negative variation of the nerve, and of electrotonus
— all discovered almost simultaneously by the same investigator —
have been the subject of much painstaking research. This research
has resulted in showing that important differences exist between
the neural process and that of the electrical current, and in making
more and more clear the impossibility of forming a purely electri-
cal theory of the nervous functions. On the other hand, it has also
revealed many important similarities between the two. It is by
experiment with the effect of electrical currents, of different kinds
and directions, and under varying conditions, that the science of
general physiology of the nerves has been built up.
§ 4. In order to understand the general results of experiment
upon the nerves, the nature and use of the so-called Nerve-muscle
Ilachine must be understood.
A "nerve-muscle preparation" consists of muscle freshly taken
from the living animal with its attached nerve dissected out ; for
example, the gastrocnemius muscle of the frog with the attached
sciatic nerve. Such a preparation may be kept alive for some time
in a moist chamber. By the simple contrivance of connecting the
' See in du Bois-Reymond's great work the history of opinions on this
point : Untersucltuiigen iiber thieriache Electricitiit, 11. . i. ,pp. 209 ff. Berlin,
Vi49.
THE IN'EEVE-MUSCLE MACHINE. 105
end of the muscle with a lever, arming the lever with some means
of making a mark — either pen, or bristle, or needle — and bringing
its point thus armed to bear on a rapidly travelling surface (plain
paper, or smoked paper, or glass), the time and amount of the con-
tractions of the muscle may be recorded. The most refined means
for noting the exact instant when the stimulus is applied, and also
the state of the effects produced at every succeeding instant of their
duration, are of first importance. The nerve may be stimulated
with different kinds, degrees, and directions of the electrical cur-
rent (or with other forms of stimuli) at any points preferred in its
stretch, and under a great variety of conditions with respect to tem-
perature, moisture, mechanical pressure or stricture, integrity and
vitality of its structure, etc. ; and the effects of such stimulations
upon the contractions of the muscle may be noted and compared
as they have been recorded. Means for testing the most delicate
and rapid changes in the electrical or thermometric conditions of
the nerve may be applied to it at any point of its stretch. Varia-
tions and refinements of experiments essentially the same may be
almost indefinitely multiplied ; the experiments may be repeated,
and verified or corrected, by the same observer or by others. In-
asmuch as the preparation is both muscle and nerve, an acquaint-
ance with the behavior of the muscle, and with the laws of its con-
traction, is necessary in order that it may be known how much of
the complex phenomena is to be ascribed to the functional activity
of muscle, how much to that of nerve. But into a statement of the
general laws of contractile tissues, and of the nature and explana-
tion of the behavior of muscle when irritated, we cannot enter.'
Certain terms in constant use to describe the methods and results
of experiments with the nerve-muscle machine also require a brief
explanation. The line traced by the armed end of the lever, as it
rises and falls with the contractions of the muscle, is known as the
" muscle-curve." In so far as it shows changes that are due to the
condition of the attached nerve, or to the quality, intensity, and
order of the stimulations applied to that nerve, this curve is a
measure of the process of neural excitation and conduction. If
the electrical current flows with the course of the motor nerve-
stretch — that is, from the central toward the 'oeripheral parts — it
is called " descending," or direct ; if in the opposite direction
" ascending," or inverse. The current to be detected in an unex-
' For a description of the method and results of experimenting with the
nerve-muscle preparation, more accessible to the general reader than the books
to which reference will chiefly be made, see Foster's Text-book of Physiology,
pp. 43 ff.
106 THE NERVES AS CONDUCTOKS.
cited nerve (a nerve, that is, whose functional activity is not at the
time in exercise on account of the appHcation of any kind of stim-
lus) is called a " natural current," or a " current of rest." The cur-
rent produced by stimulating the nerve, and so calling into exer-
cise its physiological function, is a "current of action." When
a single induction-shock, or a number of such shocks repeated
at sufficient intervals, is sent through a nerve-stretch, the contrac-
tile spasm of the muscle in response to each shock shows that
a single "nervous impulse " is passing along the nerve. When the
single stimulations are repeated with sufficient rapidity, the single
spasms fuse into one apparently continuous effort, known as " tet-
anus," or "tetanic contraction." The term "tetanus" applies
primarily to the muscle only ; but the application of rajDidly re-
peated shocks to the nerve, such as would produce "tetanic con-
traction " of the muscle, may be called the " tetanization of a nerve."
The contraction which follows the closing of the current is called
the "making contraction," or "closing contraction;" that which
follows its opening, the "bi'eaking" or "opening" contraction.
§ 5. Of the conditions under which alone the nerve is capable of
exercising its function of neurility the most important are these
three : Vitality, Oxygen, and Recovery from previous exhaustion.
A nerve cannot act as a conductor of the neural process unless
it is vital ; but the death of the nerve is not necessarily simultane-
ous with that of the body from which it is taken, or of the muscle
to which it is attached. On the contrary, by careful treatment with
respect to moisture and temperature, and by guarding it from
mechanical or chemical injury, it may be preserved alive for some
time after excision. The indirect irritability of the muscle through
the excised nerve attached to it frequently continues in warm-
blooded animals and in high temperature not longer than about
an hour ; in the frog and in a low tempei'ature it may last for sev-
eral days. The nerves of the summer frog are much more perish-
able than those of the same animal in winter. A nerve is, of course,
alive as long as it will excite the muscle to contract. But the nerve
is not necessarily dead when the attached muscle no longer resjDouds
to its excitation ; the failure may be due to the death of the very
sensitive and perishable end-organs which connect the two. Her-
mann * considered that the existence of electrical phenomena in the
nerves of rabbits showed the nerves to be alive for several hours
after they would no longer stimulate the muscle, and also after the
muscle itself could not be irritated directly. Nerves may even be
alive after they cease to exhibit electrical phenomena that can be
1 Handb. d. Physiol., II., i., p. 120.
VITALITY AT^D DYING OF THE NERVE. 107
eletected by the most delicate tests available. It is possible that
the capacity for excitation may linger after the capacity for con-
ducting the excitation is lost. Since the nerve, unlike the muscle,
has no death-rigor, we cannot say just when it is wholly dead.
During the stages of dying, nerves exhibit two interesting changes
of excitability. Immediately after it is severed from the body
the irritability of the nerve increases temporarily, and afterward
diminishes by successive degrees until it is wholly lost. The
course of these changes in its irritability is found to be different
for different parts of the same nerve-sti*etch. It was discovered by
Valli and Ritter ' that a nerve which has once ceased to stimulate
its attached muscle to contract will again excite muscular contrac-
tion if the electrodes be applied farther down its stretch ; there-
fore the lower portion of the nerve-stretch seems to preserve a
given degree of vitality for the longest time. From this fact " Valli's
principle " has been derived : Nerves die from the centre to the
periphery. The temporary increase of the irritability of the ex-
cised nerve belongs indeed to its entire stretch ; but it appears first
in the upper part. This fact is connected with the important in-
fluence which the cross-section of a nerve has upon its electrical
and neural condition. As to the reason for this increase of nervous
excitability which accompanies the first stage in the dying of the
nerve, we are quite in the dark.
§ 6. Closely allied to the foregoing changes are those which take
place in the structure and functional activity of a nerve that re-
mains in the living animal organism after having been separated
from the central organs. Such a nerve, after a time, completely
loses its irritability. Two investigators, Giinther and Schon," found
this time to be, in the case of rabbits or dogs, about three or four
days ; in a cold-blooded animal like the frog, the time may be pro-
longed to a week, or even more. The law of increased irritability,
produced in the entire nerve-stretch, but first manifested in the
portion nearest the cross-section, immediately after separation from
the central organ, holds good for most observations on nerves cut
in situ ; its application is obvious, however, only to the case of the
motor nerves. In 1850 Waller announced ' the discovery that the
anatomical changes (a fatty or granular degeneration) which take
place in the nerve-fibres after being severed from the central organs
proceed fi.-om the place of section to the extreme peripheral portion
1 See in du Bois-Rejinond's Untersuchungen, etc., i., pp. 321 ff.
2 See the Archiv f. Anat. Physiol., etc., 1840, p. 270.
^ In Philosophical Transactions, 1850, ii., p. 423; and see, also, Archiv f.
\nat. u. Physiol., 1852, p. 392.
108 THE NERVES AS CONDUCTORS.
of the fibre ; and that the sensory nerves do not degenerate in theii
peripheral, but in their central portion, when the posterior roots
are cut above the ganglion. The central portion of the nerve, when
cut at a point lying toward the periphery from the ganglion, may
be shown (in the case of the sensory nerves, which alone admit of
being experimented upon for this purpose) to retain its irritability
for a long time, although it finally loses it through lack of exercise.
A cut nerve remaining in situ may be regenerated, and so regain its
functional jDowers. Regeneration takes place by the axis-cylinders
growing out from the central portion and running into and between
the sheaths of Schwann of the peripheral portion ; it is accom-
plished, then, by the influence of the central organs. The irrita-
bility of the nerve returns as its structure is regenerated. Accord-
ing to some investigators its conductivity is regained earlier than
its power of local irritability. Duchenne ' and others claim that
the influence of the will is the first form of stimulus to regain con-
trol of regenerated motor fibres.
§ 7. Oxygen, as furnished by the circulation of the arterial blood,
is the second condition for the performance by the nerves of their
distinctive functions. But nerves, as compared with the central
organs or end-organs of the nervous system, or even with the mus-
cles, are relatively independent of the presence of oxygen. Indeed,
since the muscle is so much more sensitive to changes in the qual-
ity of the blood, and is supplied by the same arteries that supply
the attached nerves ; and since the irritability of the nerve is tested
by the vital contraction of the muscle — it is difiicult to determine
by experiment the exact effect upon the nerves of withdrawing
from them the oxygen of the blood. The irritability of the nerves
continues about as long in a moist vacuum, or in indifferent gases,
as in the air. What little is known of the chemical processes
which take place ir. the nerves confirms the view that they are rel-
atively independent of the presence of oxygen ; and the experi-
ments of Severini, who thinks that he has discovered a restorative
effect of ozone (if not of ordinary oxygeu) upon these organs when
dying, are not yet fully confirmed. It may be argued, however,
from the marked dependence of the other forms of nervous tissue
upon a supply of arterial blood, as well as from the general theory
of the nervous system, that the presence of some oxygen is a nec-
essary condition of the functional activity of the nerves.
§ 8. Exhaustion is a condition of the nerves recovery from which
is necessary in order that they may exercise their normal functions ;
but exhaustion of the nerves is difiicult to distinguish experimen-
' Traitu de I'clectrisatiou localisee, second edition. Paris, 1861.
MECHAlSriCAL PROPERTIES OF NERVES. 109
tally from exhaustion of the central organs or of the end-organs.
The experiments of du Bois-Eeymond upon the negative varia-
tion of the nerve-current under repeated irritation give us the
first item of the desired proof. The variation under these circum-
stances becomes constantly weaker. By ingeniously separating the
proofs of exhaustion in the muscle from those of exhaustion in the
nerve, Bernstein ' has shown that the latter comes on much more
slowly than the former ; and that by far the greater amount of
the effects attributed to exhaustion in the nerve-muscle macliine
belong to the muscle-element of this machine. When tired, how-
ever, the nerve recovers more slowly than the muscle. Nerve-
cells — and therefore the central oi-gans and end-organs of the ner-
vous mechanism — tire much more easily and quickly than nerve-
fibres. Indeed, according to Hermann," it is conceivable that all
the phenomena of exhaustion which take place in the normal expe-
rience of the nervous system belong really to the organs connected
with the nerves rather than to the nerves themselves. When we
are tired nervously, it is not ordinarily the nerves that are tired.
And yet the law of the exhaustion and recovery of functional ac-
tivity doubtless belongs to normal, as it does to excised, nerve-fibres.
§ 9. The various classes of phenomena which are evoked in con-
nection with the starting and propagation of nerve-commotion
along a nerve-stretch will be considered from two points of view :
First, as regards their dependence upon the character, amount, and
method of the application of the stimuli which are used ; and, sec-
ond, as indicative of certain processes — chemical, thermic, electri-
cal, etc. — ^set up in the nerves themselves. We shall thus, as far
as possible, avoid repetition.
§ 10. The mechanical properties of the nerves are of little inter-
est to psycho-physical researches ; and comparatively little con-
cerning their physiological functions has been learned by the ap-
plication to them of mechanical stimuli. The elasticity of nerves
in the dead body was found by Wertheim to follow the same laws
as that of the muscle — their absolute ductility is less than that of
muscle ; their cohesion greater. All kinds of mechanical attacks on
the nerves excite them, and are followed by pain in the case of
sensory nerves, contraction of the muscles in the case of motor
nerves. By rapid shocks of this kind — for example, with a toothed
wheel or a hammer — tetanus may be produced. A certain sudden-
ness of influence is, in general, necessary to the effect. Yet Pon-
tana succeeded in cutting nerves very quickly with a sharp knife
without producing any muscular conti-action. Pi'essure of a neiwe
'In Pfliiger's Arcliiv, xv., p. 289 f. "Handb. d. Physiol., II., i., p. 135.
110 THE NERVES AS CONDUCTORS.
may be increased very gradually to a high degree without exciting
it ; but its jDower of conductivity is thus temi^orarily suspended.
Veiy moderate jDressure or slight traction of the nerve has been
found by several investigators to increase, at least for a moment,
the irritability of the nerve ; and perhaps, also, the speed of con-
duction in it. All neural function is, of course, destroyed by any
considerable mechanical injury of the nerve, such as often happens
by stricture or pressure from a swelling.
§ 11. IViermfc influences upon the phenomena of the neural pro-
cess are very marked and important. On the other hand, almost
nothing is known as to the specific heat of nerves or as to their
power to conduct heat. Hermann thinks it probable that the
latter is different in the two main directions of the fibres. The
results of experiment differ as to the degree of heat which is neces-
sary to act upon the nerves as a stimulus. Valentin, the first ob-
server in this line, found that clipping the motor nerves of frogs
in water heated to about 100° Fahr. (38° C.) caused contractions ;
but Eckhard obtained such results only from temperatures above
150.8° to 154.4°, or below 25° to 22°— that is, temperatures that
are either deadly or permanently injurious to the nerve. Nor,
according to the latter, is the nerve excited by changes in tempera-
ture as it is by changes in the electrical current. Slighter changes
near the dead-line may have an effect to excite the nerve ; but con-
siderable changes in the medium temperatures, as a rule, have no
such effect. It is the opinion of some, however, that such thermic
changes, when marked and sudden, may act as a stimulus to mo-
tor nerves. It Avas shown by E. H. Weber ' that heat and cold have
no effect in producing sensations when applied directly to the sen-
sory nerve-trunks of man.
While there is little evidence, then, to show the direct excitatory
effect of heat upon the nerves, there is no doubt whatever as to
the importance of thermic influences upon their excitability and
conductivity. High degrees of temperature may destroy the pow-
er of the nei've to perform its functions, but without killing it.
Warmth increases the immediate expenditure of energy in an ex-
cised nerve, and so hastens its death ; cold delays this expenditure,
and so conserves the nerve. The limit of this increased irritability
of the nerve under the influence of heat is reached at about 122°
Fahr. ; as the degree of heat applied rises from this point toward
150°, its effect is rapidly felt in causing the death of the nerve.
Sudden cooling from about 68° down to 50° may produce a tem-
' In Wagner's Handworterb. d. Physiol., III., ii., pp. 496, 578 ; and Archiv
f. Anat., Physiol., etc., 1847, p. 342, 1849, p. 273.
EFFECT OF CHEMICAL INFLUENCES. Ill
porary rise of irritability ; but, in general, cooling below 59° di-
minishes the irritability of nerves. The effect of temperature upon
the speed of conduction will be referred to elsewhei-e.
§ 12. Chemical influences have, for the most part, surprisingly
little effect upon the irritability and conductivity of the nerves,
especially in view of their great sensitiveness to other external in-
fluences. Such indifference is probably due to the protection of
the nerve by its membranes. The effect of most chemical agents,
when long continued, is to destroy the nerve without irritating it ;
but some agents in a concentrated form act upon it as stimuli.
The researches of Eckhard, KoUiker, and Ktlhne have given us
most of the information we have upon this matter. Only two
points need mention here. First : Changes of the amount of water
in the substance of the nerve affect its functional activity. Drying
the nerve produces contractions ending in tetanus ; although, ac-
cording to some authorities, these effects do not follow if the dry-
ing be very sudden. A. slight amount of drying raises temporarily
the irritability of the nerve. The amount of the decrease of water
necessary to produce contractions in the attached muscle is given
by Birkner at four to eight per cent, of the weight of the nerve ;
irritability ceases, although the dried nerve is not dead, with a
loss of forty per cent. Others, however, give the latter figure as
between eight per cent, and nineteen per cent. Swelling the nerve
in water or other indifferent fluids decreases its irritability slowly
to the point of entire cessation.
Second : The effect of certain acid and alkaline solutions upon
the nerve is much hke that of drying it. Various neutral salt so-
lutions, and free alkalies in solution, produce strong muscular con-
tractions, ending in tetanus and death. Certain organic sub-
stances in concentrated solutions — for example, urea, sugar, and
glj^cerine — irritate the nerve ; so, according to most observers, does
alcohol of from ninety per cent, to eighty per cent. The law seems
to be, that all chemical stimulation of the nerves is closely connected
with the destruction of the nervous tissue.
§ 13. The phenomena evoked by applying the stimulus of elec-
tricity to the nerve-muscle machine are very numerous and diffi-
cult of disentanglement, since they depend upon such a variety of
changing conditions. Following is a y&cj brief statement of some
of the more important of such phenomena, in as far as they relate
to the direct excitatory effect of this stimulus, and also to its effect
in modifying the excitability of the nerve.'
' Here, as throughout the subject of the general physiology of the nerves,
the chief reliance has been placed upon Hermann, Handb. d. Physiol., II., i.
112 THE ISTERVES AS CONDFCTOES.
The resistance which living nerves oifer to the electrical current
does not differ much from that of living muscle ; it is given by
most authorities as somewhat greater. According to Weber's in-
vestigationp its resistance is about 50,000,000 times as great as
that of copper wire. According to Harless, the conductivity of the
nerve is on the average about 14.86 times that of distilled water.
Hermann found the conductivity to be much greater in the longi-
tudinal than in the transverse direction of the nerve.
As to the direct excitatory effect upon the nerve of constant
currents and of their variations, the main principle is that formu-
lated by du Bois-Reymond in 1845.* This principle may be stated
as follows : The excitatory effect of the constant current, as judged
by the contraction-curve of the muscle, does not correspond to the
absolute value of the intensity of the current at each moment,
but to the change in this value from one moment to another ; and
the effect is greater the less the time in which changes of the same
magnitude in the current occur, or the greater their magnitude in
the same length of time. The essential fact is that constant cur-
rents, while they remain constant, do not irritate the nerve ; vari-
ations in such currents do irritate it. The variation may be either
frovi zero or to zero (the making or the breaking of the current),
but it must have a certain degree of suddenness to be of any effect.
Hence induction-shocks are, relatively to their actual strength,
much more effective than the constant current in exciting the
nerve. Great difficulties, however, stand in the way of stating
definitely the relations that exist between variations in the strength
of the constant current and changes in the excitation of the nerve
produced by these variations ; Hermann, indeed, pronounces the
difficulties "insuperable."
It is not absolutely certain that the constant cvxrrent itself, apart
from variations in its strength, has any excitatory effect upon the
sensory nerves. The sensory effects produced bj such a current, —
for example, pain in the skin, roaring in the ears, sensations of
light and color, electrical taste, giddiness (as when the current is
passed transversely through the head at the mastoid processes),
etc. — are due to the end-organs and the central organs. It is per-
haps probable that such a current itself may produce tetanus in
certain nerves ; but the effect is very small compared with that
produced by variations of this current, Pfluger found tetanus pro-
' In a paper communicated to the Physiological Society in Berlin, August
8th, of that year ; see, also, his Untersuchungen uber thierische Electricitat,
I., p. 25».
DIRECTIOlSr OF THE CURRENT.
113
duced by weak currents of about tlie order of the so-called muscle-
current ; but not by strong ones.
§ 14. The excitatory effect of the constant current is dependent
upon its direction. If three grades of strength are assigned to all
sacli currents — namely, weak, medium, and strong — the results of
all the experimenters will be found to agree as to the dependence
of the effect of medium and strong currents upon their direction ;
as to the case of weak currents, authorities differ. The following
table, given by Pfliiger,' states the conclusion agreed to by the
larger number of observers :
Ascending Current.
Descending Current.
Making.
Breaking.
Making.
Breaking.
Weak
Medium
Contraction.
Contraction.
Rest.
Rest.
Contraction.
Contraction.
(Contraction.
Contraction.
Contraction.
Rest.
Contraction.
Strong
Rest or weak
contraction.
The results here tabulated are obtained by experimenting with
the excised motor nerves of frogs. In experiments with the sen-
sory nerves, or with any of the nerves while remaining in the liv-
ing animal, the conditions become so complicated that satisfactory
results in confirmation of Pfliiger's conclusions have not yet been
reached.
§ 15. The excitatory effect of the constant current is also depend-
ent upon its absolute strength. Du Bois-Reymond, after discovering
his law, proceeded to raise the inquir}^ whether the height of the
current upon which the variation is piled up, as it were, has any
influence upon its effect. Various attempts to answer the inquiry
have been made ; but the discovery of Pfliiger's laAv of electvotonus
has, according to Hermann,'' changed the form of the question to
the following : What influence upon the excitatory effect of in-
creasing catalectrotonus and diminishing anelectrotonus does the
absolute amount of existing electrotonus have ? In this form it will
be referred to again.
§ 16. The excitatory effect of the electrical current is influenced
by the length of the nerve-stretch through which it flows. From
the beginning of electro-physiology the opinion has prevailed that
the excitatory effect is increased by the length of the nerve-stretch.
This view accords theoretically with deductions from Pfluger's law
of electrotonus. The experimental proof, however, is somewhat
vacillating ; in part, doubtless, on account of the admixture of
' See Untersuchungen iiber die Physiologie d. Electrotonus, p. 453. Ber-
lin, 1859. ^ Haudb. d. PliysioL, II., i., p. 76.
8
114 THE ]srERVES AS COE^DUCTORS.
different local conditions where different considerable lengths of a
nerve are passed through. Different investigators have found the
increase of irritability in the nerve, as dependent upon its length,
confined within different limits ; one has fixed the limit at from
jig to ^ inch, another at from ^ to f inch. Willy found the rule,
in general, to hold good only for descending currents.
§ 17. The excitatory effect of a constant current is influenced by
the angle between the axis of the nerve and the direction of the
current. After considerable experimentation, Avith varying results,
the more modern researches have, according to careful experiments
made by Albrecht and A. Meyer, in the laboratory of Hermann,'
confirmed the opinion of Galvani : The electrical current does not
excite the nerve when it flows precisely at right angles to the
nerve's axis.
§ 18. The duration of the current also influences its effect as a
stimulus.
Attention has already been called to the exhausting effects of
long-continued stimulation of the nerve, whether by electricity or
otherwise. But can a shock be so brief as not to stimulate the
nerve at all? The reason why vei-y brief currents, on breaking the
circuit, are not followed by a contraction of the muscle is obvi-
ously to be found in the fact that the condition of anelectrotonus,
on which the breaking conti'action depends, has not had time to
develop itself. But J. Konig, working under Helmholtz's direc-
tion, found that currents which would produce the making but not
the breaking contraction, j)rovided they had sufficient duration, pro-
duced no contractions at all if they lasted only 0.001 of a second.
On increasing the duration of the current the strength of the con-
tractions increased also, until at 0.017-0.018 of a second they
reached the same height as that of the contraction produced by the
corresponding constant ciu'rent. It may be said, then, that the
electrical current must act uj)on a nerve for at least about 0.001^
of a second in order to excite it. The nerve on being cooled
becomes more sluggish in its resj)onse to the stimulus ; at the
freezing-point it requires a duration of nearly 0.02 of a second for
the stimulus to start it into action.
§ 19. Besides the direct excitatory effect upon the nerve of elec-
trical currents, we have to consider their effect in modifying the
action of the nerve under stimuli, whether electrical or of some
other kind. If a nerve-stretch is under the influence of a constant
current which is being passed through it, the effect of stimuli,
when applied to any part of the nerve and judged by sensation or
' See his Handb. d. Physiol,, II., i., p. 81 f.
pfluger's law of electrotontjs. 116
muscular contraction, is increased. This changed condition of the
nerve with respect to its excitabihty, which the electrical current
produces, is called " Electrotonus." The term was introduced into
physiology by du Bois-Eeymond, who was preceded in his in-
vestigations by Kitter, Nobili, and Matteucci, and followed by
Valentin, Eckhard, and others. It is Pfliiger, however, who is en-
titled to have his name permanently attached to the law of elec-
trotonus; for it is he who most thoroughly analyzed the facts,
separated the variables from the constants, and gave scientific form
to the result. It is found that the modified excitability of the
electrotonized nerve (that is, of the nerve which has been thrown
by the passage of the electrical current into this modified condition
of excitability) is not uniform through its entire stretch, but is
greatest in the immediate region where the electrodes are applied.
Moreover, it differs at the two electrodes — the condition at the
anode (or positive pole) from that at the cathode (or negative pole).
It differs, also, for that part of the stretch which lies between the
electrodes as compared w^ith that which is outside of the electrodes.
Pfluger's law states the whole case as follows : The excitability of a
nerve under the action of the constant current is increased in the
catelectrotonized region (that is, on both sides of the negative elec-
trode), and diminished in the anelectrotonized region (that is, on both
sides of the positive electrode). This law is declared by Hermann '
to hold good of all kinds of stimulus, and in all cases — with the only
ajDparent exception of the suprapolar region of an ascending current.
This electrotonic eifect of the constant current, like its direct
excitatory effect, is influenced by the strength of the current, by its
making and breaking, and by the length of the stretch through
which it flows. The change in the excitability of the electrotonized
nerve increases with the strength of the current, from the low-
est observable point until it soon reaches a maximum ; after this
maximum is reached, further increase of electrotonus is to be rec-
ognized only by the expanding of this condition over the extra-
polar parts of the nerve-stretch. Electrotonus increases also with
the length of the nerve-stretch affected ; but this relation also
finally reaches a maximum. Electrotonic changes in the catelec-
trotonic region occur immediately upon making the current ; they
then speedily but slightly increase, and more slowly diminish again.
The anelectrotonic condition develops and extends itself compar-
atively slowly, reaches a maximum, and then gradually falls off
again. The immediate consequence of breaking the current is to
increase the electrotonic condition of the nerve in the anelectrotonic
' Handb. d. Physiol., II., i., p. 43.
116 THE NERVES AS CONDUCTORS.
region, and very briefly to decrease it in tlie catelectrotonic region 5
the former increase gradually vanishes ; the latter decrease is fol-
lowed, after a few seconds, hj an increase which lasts from one-
half a minute to fifteen minutes.
The so-called "laws of electrotonus " are almost wholly based
"upon esjDeriments with the motor nerves of frogs. Great and even
insuperable difficulties stand in the way of proving experimentally
its application to sensory nerves, or to the nerves of living and self-
conscious man. The conditions of influence — from the central
organs and end-organs, from sensation and will — upon the nerves
in such cases are so complicated as to bafile all attempts to analyze
them by means of direct experimentation.
Further consideration of electrotonus, and of its bearing upon
a mechanical theory of the nerves, must be for the present post-
poned.
§ 20. The phenomena evoked in connection with the starting
and propagating of nerve-commotion along a nerve-stretch may be
presented — in the second place (see § 9) — as indicative of certain
Processes set up within the nerves themselves. That the effect
of a constant current is not exhausted in direct excitation of the
nerve is proved by the changed condition of excitabiUty which it
also produces.
No mechanical process that can be made directly appreciable by
the senses or accurately measured by mechanical means, like that
which takes place in the contracting muscle, occurs in the nerve
when excited to its physiological activity by means of appropriate
stimuli. Whatever changes then take place in it are invisible and
impalpable.
§ 21. Nor are we much better able, on the ground of experi-
mental tests, to affirm the existence of any thermic process in
connection wdth the excitation of the nerves. If any rise of tem-
perature in the nerve is caused by the application of stimulus, it
is exceedingly small. Helmholz,^ in connection with his investiga-
tions into the heating of the muscle when in a state of tetanus,
could detect no development of heat in the nerve, although his
means would have revealed a change of only a few thousandths of
a degree. On the other hand, Schiff and Heidenhain both de-
tected a rise of temperature in the brain due to nervous excitation.
But it is still a question how far this fact indicates anything more
than change in the distribution of the arterial blood. Moreover,
the former of the two observers failed to obtain any evidence of
heating in the cerebellum by sensory excitation. The ease of the
' Archiv f. Anat, Physiol., etc., 1848, p. 158.
THE KATUEAL ISTERVE-CURRENT. Il7
conducting nerve-cords and that of the cellular tissue of the cen-
tral organs may very likely be different in this regard.
§ 22. Nor have any chemical processes been indubitably proved
to occur in the nerves as an accompaniment or result of the exez'-
cise of their physiological function. The only experimental evi-
dence of such a process is the change of reaction which some ob-
servers have found. Funke and others have asserted that, not only
a certain time after death, but also after exertion as caused by
cramping produced with strychnine-poisoning, the nerves show an
acid reaction. But Heidenhain and other observers contest this
alleged fact. Other assertions of chemical changes set up in the
nerves by exciting them are even more uncertain. Eanke's theory
of a "respiration of the nerves" is quite without any sufficient ex-
perimental proof ; and so is his claim that an absorption of the
water of the nervous tissue results from tetanus. If any chemical
changes are produced in the nerve by exciting it, they are like the
thermic — exceedingly small. This fact is proved by the almost
comjDlete independence of the nerve with respect to the oxygen
of the arterial blood, and by the absence of any observable changes
in its temperature when functionally active. But here again we
must distinguish between the case of the nerves as conductors and
that of the nervous tissue of the central organs.
§23. Evidence of the electrical j^rocess in nerves functionally ac-
tive is not wanting. It was not, however, until the discovery of du
Bois Eeymond, announced in 1843, that any experimental evidence
had been obtained to show the existence of electrical currents in
the nerves, although it had previously been conjectured that the
distinctively neural process is a phase of electricity. This ex-
perimenter found that in the case of the nerve, as in that of the
muscle, the cross- section artificially made is negative toward the
longitudinal surface of the nerve-stretch. Weak longitudinal cur-
rents also show themselves between the two cross-sections of a
nerve-stretch thus prepared. The current outside the nerve-stretch
may be considered as completed by a current in the nerve-stretch
from its cut end to the equator. This current (called "natural
nerve-current," or " current of rest ") is the same in the sensory,
the motor, and the mixed nerves of the same animal ; but its elec-
tro-motive force is greater the larger and thicker the nerve. Its
absolute strength in the sciatic nerve of the frog is given by du
Bois-Eeymond as 0.022 of a Daniell's cell, but by Engelmann as
0.046. It gradually becomes extinct in the nerves of the dead
body, but it continues for some time after their irritability is lost.
The same discoverer, du Bois-Eeymond, found that the current
118 THE NERVES AS CONDUCTOES.
of rest is diminished in energy by tetanizing the nerve-stretch with
an electrical current. That is, if when one of the electrodes is placed
at the equator, and the other at the cut end of a nerve-stretch, the
needle of the galvanometer indicates the passage of a so-called cur-
rent of rest, and then the muscle to which the nerve is attached be
tetanized by passing an interrupted current through the nerve, the
needle will swing back toward zero. This variation is called the
"negative variation " of the nerve-current. It may be produced by
chemical and mechanical, as well as by electrical, stimulation ; and
when the nerve is no longer irritable the negative variation sinks
to zero. It shows, therefore, that the electro-motive force of the
nerve is diminished by the nerve being excited ; and the degree
of the negative variation is a measure of this diminution, although
it does not wholly nullify the so-called current of rest. The nega-
tive variation of the electrical current in the nerve is closely con-
nected with the nerve-commotion which is started and conducted
in the nerve. Since the excitation of the nerve is known to be
progressive, or of a wave-like character, the nature of this connec-
tion, according to Hermann, may be more definitely stated as fol-
lows : The electrical condition of each excited place in a nerve-
stretch is negative toward all the places of the same nerve-fibre
that are unexcited. Hence, between any two points in a nerve-
fibre, while the nerve-commotion is passing over the distance, two
phases of the current of action occur ; the first phase is in the
same direction as the course of the wave of excitation, the second
is in the opposite direction.
§ 24. The Laws which are known to govern the starting and prop-
agation of nerve-commotion along the nerves as conductors are
few in number ; they deal chiefly with relations between the mag-
nitude of the stimulus and the amount of the resulting impulses,
and with the conditions for, and speed of, the unbroken propaga-
tion of these impulses.
The relations which exist between the magnitude of the stimulus
applied to the nerves in their normal condition and the amount of
resulting nervous impulse cannot be given with accuracy. For, in
the first i^lace, there is no absolute measure for either of the two
values which it is desired to compare. Of the various stimuli
which act upon the nerve-fibres, electricity is the only one that ad-
mits of even a fairly approximate measurement as an excitant of
these fibres ; and the excitatory effect of electricity does not vary
in direct proportion to the strength of the current, but in propor-
tion to the changes in its strength. With reference to attaining a
direct measurement of the amount of the process set up in the
EFFECT OF SEVERAL EXCITATIOISTS, 119
nerve by the stimulus, we seem to be in a yet more helpless con-
dition. The effect of this process is almost wholly manifested- in
the organs with which the nerve is connected rather than in the
nerve itself. There is evidence in the case of the nerves, however,
as in that of the muscles, that their excitation consists in the set-
ting free, by the stimulus, of potential energy due to the molecular
constitution of the nerve itself. But the exact nature of this en-
ergy, and of its mathematical relations, both to the stimulus and to
the resulting energy called forth in the organs connected with the
nerve, we shall probably never discover. Still further, as Griitzner '
and others have shown, the same kind and degree of stimulus pro-
duces different effects when applied to different nerves.
§ 25. Allowing for the uncertain factors, however, some approxi-
mate statement may be ventured as to the i*elation between the
magnitude of the stimulus and that of the resulting nerve-commo-
tion. Measuring the amount of the process in the nerve by the
resulting contraction in the muscle, Hermann ° found that this
amount increases, at first rapidly and then more slowly, with the
increase of the stimulus. According to Fick,^ the height to which
the lever is raised by the contractions of the muscle varies, within
certain limits, in direct proportion to the amount of the stimulus.
The last-mentioned observer also noted two remarkable phenom-
ena : (1) On increasing the amount of the stimulus beyond the
point necessary to produce the first maximum contraction, another
stage is reached in which the effect further increases, in proportion
to the stimulus, until a second maximum is gained. (2) In some
circumstances, after reaching the first maximum, the effect dimin-
ishes with the increase of the stimulus, then rises on further in-
crease, until it attains a second maximum.
The effect of several excitations may be supposed to pass along
the nerve as separate waves of nerve-commotion ; but in order to
keep the waves separate the interval between them must be more
than about yro °^ ^ second (the fraction differing for different
nerves, different animals, etc.), otherwise they fuse in the muscle
and tetanus results. The combined effects of stimulations havine
the requisite interval may be piled up, or summed up, in the
nerve, and be seen in superimposed contractions of the muscle.
Two simultaneous excitations of the same jplace of the nerve-stretch
are thus "summed up " as long as the maximum of excitation is
not reached ; the two are, in fact, one. If the cathodes of the two
' Pfluger's Arcliiv, xvii., pp. 215 ff. ; and xxv., pp. 255 ff.
2 See Archiv f. Anat. u. Physiol., 1861, p. 392.
3 Untersuchungen iiber electrische Nerveiireizung. Braunschweig, 1864.
120 THE NERVES AS CONDUCTORS.
exciting currents unite, the same effect takes place. A similar re-
sult may be gained by combining the effects of two different kinds
of stimuli — as, for example, electricity and the drying oft' of the
nerve.
§ 26. In a rough way the specific excitability also of different
nerves, or of different localities in the same nerve, may be dis-
covered. Harless found that the excitability of the nerves of the
frog is twenty-two times as great in winter as in summer. In the
cut nerve it is greater near the artificial cross-section. Many
observers have contended that the excitability of the normal nerve
diminishes toward its peripheral portion. Matteucci investigated
the subject of local differences of excitability in the sensory nerves ;
moi-e recently Eutherford ' discovered that the reflex effects of
stimulating a sensory nerve are greater the nearer the central
organ the stimulus is applied. Finall}', Helmholtz " and Hermann '
observed that the lower part of the nerve-stretch is more excitable
under the action of an ascending, the upper under that of a de-
scending induction-current.
§ 27. The Speed with which the process of conduction takes
place in the nerves has been determined with considerable accu-
racy, under a variety of circumstances ; this, notwithstanding the
fact that the physiologist Joh. Miiller' declared it to be forever
impossible no longer ago than 1844. In only 1850, however,
Helmholtz ^ announced that he had succeeded in measuring the
speed of nervous impulses in the motor nerves of the frog. The
rate he found to be 26.4 meters, or about 86.6 feet, per second.
Another series of investigations, in which the pendulum-myograph
was used, gave a result about 3 feet larger (27.25 m.). Subsequent
investigators have substantially confirmed the figures of Helm-
holtz. Bernstein, by a still different method of measurement, found
that the speed of conduction in the nerves varies between 25 and
33 meters. In the motor nerves of man the number was still later
fixed by Helmholtz and Baxt at 33.9 meters, or about 111 feet, per
second. Von Wittich found it to be about 98.5 feet per second.
The complexity of the elements which enter into the measurement
of the speed of nervous impulses in the sensorij nerves makes it neai'-
ly impossible to obtain satisfactory results by experiment. And so
far as the calculations take into account changes produced in the
1 See Journal of Anat. and Physiol., 1871, v., pp. 329 ff.
''Archiv f. Anat. u. Physiol., 1850, p. 337.
^ Pflager's Archiv, viii., p. 261; and xvi., p. 262.
*See his Handbuch der Physiologie, i., pp. 581 fE. Coblenz, 1844.
""See Archiv f. Anat. u. Physiol., 1850, pp. 276-364.
.SPEED OF NERVOUS IMPULSES. 121
nervous centres with accompanying phenomena of sensation and
attention, their discussion belongs elsewhere. Of the four factors
that enter into the entire time ("reaction-time") Avhich elapses
between the application of stimulus to a sensory nerve and the
resulting contraction of the muscle — namely, (1) time of conduction
in the sensory nerve ; (2) processes in the central organs ; (3) time of
conduction in the motor nerve ; and (1) latent period of the muscle
— it is difficult to disentangle the factor (No. (1) ) required by
the attempt at analysis. Hirsch, by experimenting with stimuli ap-
plied to the skin at different distances from the brain, found the
speed of conduction in the sensory nerves of man to be about 111.5
feet per second— a result in exceedingly close agreement with the
figure obtained by Helmholtz for the motor nerves. Schelske
used another method of measurement ; by applying the stimulus
to the groin and the foot, and recording the difference of time in
the two classes of cases, he obtained results varying between
25.294 and 32.608 meters per second. Others have given figures
differing more or less widely from those just stated. The general
conclusions, however, favor numbers lying between 98 and 131
feet per second as giving the speed of conduction in the sensory
nerves of man.
The speed of conduction in all nerves depends upon several va-
rying conditions, such as their temperature, the strength of the
stimulus, length of the nerve-stretch, and its electrical condition.
Experiments in winter give different results from those in summer.
In the motor nerves of man the rate can be made, by changes of
temperature, to vary from about 98 feet to 295 feet per second.
It has been disputed by different observers whether the speed of
conduction is dependent in any degree uj)on the strength of the
stimulus ; and even Hermann considers the question undecided.
But Vintschgau ' has recently shown, as the result of a large number
of carefully conducted experiments, that as soon as the stimulus
rises above a certain limit of intensity, the speed of the nervous
impulses increases with the increase of the intensity of the stimulus.
This limit depends, however, upon the direction of the current, upon
whether it is a making or a breaking current, upon the animal
chosen for experiment, etc. Whether the speed of the nervous im-
pulses is directly dependent upon the length of the nerve-stretch
is scarcely decided beyond doubt. The effort of the science, gen-
eral "nerve-physiology," is directed toward showing how these
variations in speed, as experimentally determined, may be explained
from the laws of Electrotouus.
> In Pfliiger's Archiv, 1883, xxx., pp. 17 fE.
122 THE NERVES AS CONDUCTORS.
§ 28. Finally, it sliould be remembered that the fact of any
propagation of nervous impulses whatever presupposes the con-
tinuity, integrity, and isolation of the nerve tract along which the
impulses move. The slightest separation of the substance of the
nerve by cross-section, even when the cut ends are left in the
closest mechanical contact, destroys the unity of the nerve's
phj^siological function. The ancients knew that tying the nerve
prevented its action ; they explained the fact by saying that the
flow of nervous fluid was thus hindered. So also does the fineness
of the localization which belongs to the organs of motion, but
especially to those of sense, as well as the fact that partial section
of a nerve only lames part of the field cared for by that nerve,
indicate the physiological isolation of the nerve-fibre during its
course between end-organs and central organs. Since the result of
stimulating a given nerve is in quality invariably the same, it would
seem that the law of the " specific energy " of each nervous element
(to which we shall leier elsewhere) is connected with the assump-
tions necessary to explain the phenomena attendant upon the
starting and propagating of nervous impulses in the conducting
nerves.
§ 29. Inasmuch as the central organs are to a large extent com-
posed of nerves, a complete account of the nerves as conductors
should include a description of the nature of that nerve-commotion
which is propagated from point to point along the nervous ele-
ments within these organs, and of the paths or tracts along which
it passes. But unfortunately our knowledge upon these matters is
exceedingly scanty and uncertain. This is in part due to the fact
that the influence of the ganglion-cells, with which the nerve-fibres
are mixed to form the central organs, profoundly modifies the
neural processes of excitation and conduction. The subject be-
longs, then, to a consideration of the functions of the central or-
gans rather than of the nerves alone. Certain statements, how-
ever, may most fitly be given in this connection.
"When speaking of conduction in the spinal cord or brain we
are not to think of a nerve-commotion as always moving along one
fixed path, after the analogy of the far simpler case of the nerve in
the nerve-muscle machine. It is true that the nerve-fibre in its
normal place in the body runs insulated, as it were, between the
spinal cord and the end-organ at the periphery. But the spinal
cord itself does not act as a perfectly isomorphic medium. The
very complex structure of this organ, in which nerve-fibres and
nerve-cells are intricately interwoven, has already shown us that it
is not adapted to act as such a medium. The case of the brain is
IMPULSES IN THE SPINAL COED. 123
even clearer. It accords, therefore, with the structure of all central
organs, that we should find the speed of conduction slower in them
than in the peripheral nerves. Exner ' calculated, from thie delay
which sensory impulses experience in the cord of man, that their
speed there is not more than about 26|- feet (8 meters) per sec-
ond. The speed of the motor impulses in the cord he gives doubt-
fully as varying between 36 feet and 49 feet (11 to 12 and 14 to 15
meters). These numbers are substantially confirmed by the con-
clusions of Burckhardt (8 to 14 meters). The latter also maintains
that the speed of the impulses which occasion sensations of touch is
greater than that of those which occasion pain (as 27 to 50 meters
compared with 8 to 14). It has also been observed that, in some
cases of persons with disease of the posterior strands of the spinal
cord, sensations of pain arise in consciousness notably later than
those of touch. But the interpretation of all these phenomena is
complicated with questions of the cerebral functions ; for sensations
of pain are pre-eminently of cerebral origin. Moreover, we can
have but meagre confidence in our ability to tell with any pre-
cision the length of the paths by which nervous impulses travel in
the spinal cord of man. The fact observed by du Bois-Reymond,
that the vibrations of the muscle tetanized through the cord are
less than would be expected from the number of shocks given by
the stimulus, and the fact discovered by Helmholtz, that muscle
when tetanized by an act of will has a uniform tone indicating
nineteen vibrations to the second (the rate of vibration into which
the muscle is thrown by direct stimulation of the motor nerve, on
the contrary, corresponding to the number of shocks), show the
profound effect of the central organs over the nervous impulses.
Although, then, the experimental evidence is not perfectly conclu-
sive, it, on the whole, confirms what we should expect from the
anatomical structure of the spinal cord, as to the complexity and
relative slowness of conduction in this organ.
§ 30. Various attempts have been made by experimental physi-
ology to demonstrate the paths of conduction in the spinal cord.
The evidence from histology on this difiicult subject has already
been given (p. 71 f.). It is not always easy to make the two lines
of evidence coincide. As to one point of experimental physiology^
however, no doubt has existed since the " epoch-making discov-
ery " of Sir Charles Bell and Magendie. The sensory fibres en-
ter the spinal cord by the posterior root, the motor fibres by the
anterior. The demonstration of this fact is performed by dividing
these roots, respectively, and observing the results. When a pos-
' Pfliiger's Arcliiv, vii., pp. 632 ff. ; and compare Ibid., viii., pp 532 ff.
124 PATHS OF ISTERVOUS CONDUCTIOl^T.
terior i^oot is divided all the structures supplied by the same nerve
lose their sensibility ; while the muscles supplied by its correspond-
ing anterior root continue to be thrown into action by the will
and b}^ reflex stimulation. Moreover, stimulation of the central
end of the posterior root thus divided produces sensory effects, but
stimulation of its peripheral end produces no motion. When an
anterior root is divided, on the contrary, the muscles supplied by
its nerves cannot be made to act either by volition or by reflex
stimulation ; but no sensory paralysis is produced. Moreover,
stimulation of the peripheral end of the nerve will now throw the
muscles into contraction, but stimulation of the central end will
produce no effects. An exception to the exclusively motor effects
of the peripheral end occurs in certain cases of so-called "recurrent
sensibility;" the sensibility shown in these cases is probably due
to the fact that a few sensory fibres from the posterior root, after
running a short distance in the mixed nerve, turn back and run
upward in the anterior root. The proof is then complete, so far
as the direct motor paths to the striated muscles, and the specifi-
cally sensory paths which conduct impulses to the cerebral hemi-
si^heres, are concerned. According to Sigmund Mayer ' it does
not necessarily follow, however, that onhj centripetal impulses are
conducted by the posterior, and only centrifugal by the anterior
roots.
§31. The general aiTangement of the motor paths in that part
of the spinal cord, on the same side, where they enter by the an-
terior roots of the nerves, and of the sensory paths in the posterior
part of the cord, is maintained throughout. In man, that is to
say, the impulses pass up or down the cord in that region of it
at which they leave, or by which they enter with, the anterior or
the posterior roots. But histology shows that the two halves of the
cord are anatomically connected by the commissures, and that every
part of each half is bound with other parts of the same half, both
up and down and to and fro. Physiology, too, indicates that the
paths of sensory impulse undei'go a partial crossing from right to
left, and from left to right. For, after complete section of one lat-
eral half of the cord, complete loss of sensibility of either side in
that part of the body which is supplied by those nerves of the same
side that enter the cord below the place of section does not re-
sult. The effects that do result depend upon the animal chosen
for experiment, and upon the height at which the section is made.
Experiments upon the lower animals seem also to show that in
their case a partial crossing of the motor paths takes place in the
' Hermann's Handb d. Physiol., II., i., p. 217.
PATHS IN THE SPINAL COLUMNS. 125
spinal cord ; the evidence from pathology makes it doubtful whether
in man any crossing from side to side occurs in the voluntary
motor paths, at least below a point very high up in the neck. All
the evidence shows that in the lateral columns both, sensory and
motor paths are to be found.
§ 32. In addition to the general statement just made, experi-
mental physiology has little to say confirming or correcting the con-
clusions of histology (see p. 71 f.) as to the paths of neural impulses
in the spinal cord of man.' Experiments which attempt to make
a section, either of all the fibres in the anterior columns, leaving all
the other fibres intact, or of all the other columns, leaving the fibres
in the anterior columns intact, can never, indeed, be quite sure of
their success. But, on the whole, their resvilts are confirmatory of
the statements made in the last article. Some investigators have
endeavored to solve the same problem by directly stimulating the
fibres of the different columns in such manner as to confine, as far as
possible, the influence of the excitatory current (or other stimulus)
to certain definitely selected fibres, and so to exclude all reflex ac-
tion. It is found that no reaction, indicative of any sensory im-
pulses whatever, follows the stimulation of the central ends of the
anterior white columns of the spinal cord ; but stimulation of the
peripheral ends of these same columns may be followed by muscu-
lar contraction, sometimes (so Longet and Kiirschner found) when
mechanical stimuli are used, but oftener with weak electrical cur-
rents. . Careful cutting of these columns is followed by no signs of
pain.
On the other hand, stimulation of the central cut ends of the
posterior columns produces signs of pain, and other sensory effects ;
for this pui-pose Longet has used electrical, and Eigenbrodt and
Schiff mechanical stimulation. According to Schiff and others the
entire cord can be cut through from before back to the posterior
columns, and if these are left the animal will retain the sense of
feeling. As to a further differentiation of the sensory function of
these columns, different experimenters do not agree. Some would
confine their function to impulses that give rise to sensations of
touch, on the ground that animals, the substance of whose cord has
been entirely cut through with the exception of the posterior col-
umns, retain their sensations of touch, but loose their susceptibil-
ity to pain from impressions made on the surfaces whose nerves
enter the cord below the place of section. Impulses which give
' Comp. the generalizations of Eckliard in tlie chapter on " Verlauf d. mo-
torischen u. seusiblen Innervatiouswege im Riickenmarke," Hermann, Handb.
d. Physiol., II., ii., pp. 148 ff.
126 PATHS OF l^ERVOUS CONDUCTION.
rise to sensations of pain must therefore pass elsewhere than by
the posterior strands ; that is, chiefly by the gray matter of the
cord. According to others, however, these strands conduct sen-
sory processes only in so far as they serve for the passage through
them of the nerves from the sensory roots ; it is, then, the gray sub-
stance of the cord which conducts these processes along upward.
In addition to the more marked sensory effects of stimulating the
posterior columns, some experimenters get effects which they in-
terpret as showing the presence of motor, and even of voluntary-
motor, paths in these columns. Stilling, for example, found that
voluntary motions occurred after one entire anterior half of the
cord had been cut through. But in the absence of proof that
no motor paths in the lateral columns were left intact by his ex-
periments, and in view of the fact that a crossing of such paths
may take place in some of the animals, the evidence is not conclu-
sive. Moreover, Ttirck and others have found that the posterior
white columns may be entirely cut through without causing motor
disturbances.
In the lateral columns of the cord, paths of both motor and sen-
sory impulses are probably to be found. As to the case of motor
paths there is, indeed, no reasonable doubt — at least there is no dis-
pute. Ludwig and "Woroschiloff found that, in the case of the rab-
bit, voluntary movements of the hinder extremities took place even
after section of the anterior and posterior strands, and of the gray
matter of the cord in the cervical region. As to the proofs of sen-
sory paths in the lateral columns, the evidence is somewhat con-
flicting. Longet and Stilling discovered no proof of their existence ;
Schiff pronounces the matter doubtful ; Tiirck found that unmistak-
able signs of pain followed the cutting of these portions of the cord.
Experiments upon animals and pathological observation, however,
on the whole, confirm the view that the sensory are mixed with the
motor paths in the lateral columns. As Wundt ' expresses the ap-
parent truth — in the side strands of the coi'd a part of the system of
motor fibres is shoved off toward the limits of the posterior columns
and surrounded on all sides by branches of the sensory tract.
It must be borne in mind that the function of neither the motor
nor the sensory tracts is such that a nerve-commotion, when started
in one of the columns, must necessarily run its course by the short-
est path in that one column, or else not be propagated at all to its
destination. Both histology and physiological experiment indi-
cate that the interlacing of the nerve-fibres, and the interruption of
theu' course with nerve-cells, provide various secondary paths in
'Grundziige d. pliysiolog. Psjchologie, i., p. 101, Leipzig, 1880.
PATHS IN" THE BRAIN. 127
addition to that which may be called the primaiy or chief. More-
over, the gray substance of the cord not only distributes, but also
carries forward the nervous impulses. After entire half- section of
the cord the sensory tracts of the other half still seem able, in a
partially substitutionary way, to accomplish the work normal to
both sides. And even in the case of the voluntary motor tracts in
man's spinal cord, though such a work of substitution does not take
place, we cannot affirm that the paths of voluntary innervation
for a definite set of muscles are invariably the same through their
entire length. A certain latitude of movement from the straight-
forward course of the impulse undoubtedly exists even in such a
case.
§ 33. Difficult as it is for experimental physiology to deal with
the tracing of those paths along which the sensory and motor
impulses flow in the spinal cord, it is much more so within the
nervous mass which fills the cranial cavity. Both the structure and
the functions of the cerebrum, as a group of chief central organs,
make it nearly impossible experimentally to distinguish between
paths of voluntary and paths of merely reflex motion ; or even to
conjecture where, within its substance, impulses that have been
moving along some more clearly defined tract may not divide and,
subdivide indefinitely, or — conversely — impulses that enter along-
several converging paths be concentrated, as it were, into one or two
that are more definitely fixed.
The evidence by which histology has succeeded in tracing cer-
tain tracts through the brain, from the medulla oblongata to the
convolutions of the cerebral cortex, has been presented at sufficient
length in the last chapter (see pp. 76 f., 87 f., and 97 f.). The fuller
discussion of the evidence from experimental physiology concerning
the same subject will more properly appear in subsequent chapters
upon the automatic and reflex functions of the central organs and
upon the localization of cerebral function. Certain tracts which pass
directly from the crusta through the internal capsule, without en-
tering the basal ganglia, into the frontal and parietal convolutions
have already been referred to as probably motor. Others which
come from the tegmentum, enter the thalamus and subthalamic
region, and emerge after being redistributed to find their way es-
pecially to the tempero-sphenoidal and occipital lobes, have been
declared, in all probability, to be sensory. With this statement,
so far as the motor tracts are concerned, we shall see that the con-
ckisions of experimental physiology accord very well.
§ 34. But our assured knowledge from experiment concerning the
paths by which sensory impulses travel in the brain is exceedingly
128 PATHS OF NEEVOUS CONDUCTIOlSr.
meagre. These paths are probably much more numerous and in-
tricate than those along which the motor impulses are propagated.
Moreover, we can seldom draw conclusions with safety conceriung
the sensations of the lower animals ; we therefore largely lose our
help fi'om experiment upon them to determine these sensory paths.
The phenomena connected with all sensory disturbances are exceed-
ingly complicated, and the conclusions they seem to warrant are
often conflicting. For example, the effect of destroying a sensory
nerve-tract in the head does not consist simply in the destruction
or laming of some one definite function. On the contrary', if a
sensory cranial nerve is severed, the various different functions of
feeling pain, of pressure, and temperature, and the power of localiz-
ing, in the region supplied by the nerve are all lost. But disease
of the cerebro-spinal axis may impair one or more of these func-
tions, and leave the others intact, in a given region of the periph-
ery. Anaesthetics also may obliterate the sense of pain while leav-
ing that of contact relatively unimpaired.
Still more difficult of comprehension from the point of view fur-
nished by the general physiology of the nerves are the degrees of
tenacity with which different sensory functions, even when adminis-
tered by the same sensory nerve, are combined. Loss of the sense
of temperature and of the muscular sense rarely or never occur
separately ; but muscular sense not infrequently disappears and
the sensitiveness of the skin to pressure is retained. Upon such
phenomena we have little clear light to throw. It can simply be said
that the distribution of the sensory nerves within the centi'al or-
gans must be enormously complicated, and that we have absolute-
ly no knowledge as to any differences in the kinds, or velocity, or
paths, of the nerve-commotions there, that will help us to account
for the facts. Yet such differences in the sensations doubtless rest
upon differences in the nerve-commotion that causes them, within
that inner projection system of sensory impressions which is fur-
nished by the cortex of the cerebrum.
It has already been seen that the paths of sensory imjDulses cross
over more or less completely within the spinal cord. They also,
like the paths of motor impulses, cross in the region where the
nerve-fibres in general decussate — namely, in the pons varolii and
medulla oblongata. Experiment and pathology both show that
the principal paths of sensory impulses from all the peripheral
parts of the trunk of the body and from its mucous membrane lie
close to those of the motor impulses in the white nervous substance
surrounding the basal ganglia. Effusions of blood in this region
not only cause hemiplegia, but also produce more or less impair-
PATHS IN THE BASAL GANGLIA. 129
ment of the different modifications of touch, both in the skin and
in the mucous membrane. According to some authorities, lesions
in the same region often so impair the muscular sense that the
contraction of the muscles which is produced by electrical stimula-
tion is no longer felt. Veyssiere and others suppose that injuries
to the white fibrous matter of the crura cerebri, the internal cap-
sule, and the foot of the corona radiata, invariably produce a loss
of sensibility on one side of the body ; while those which are more
definitely confined to the striate body have this effect only imper-
fectly and for a time — the amount of the effect depending upon the
amount of the adjoining white substance which is involved in the
injury. This view, like many others on the general subject, is
doubtful.
§ 35. Attempts have been made to localize the paths of sensory
impulses in the optic thalami and those of motor impulses in the
striate bodies ; and in connection with this view it has been held
that the former are chiefly concerned in the elaboration of sensory
impulses (as sensory ganglionic centres), and the latter in the
elaboration of motor impulses (as motor centres). This theory has
been wrought out (with much rhetoric and conjecture) by J.
Luys.* Luys finds in the optic thalami four centres which — lying-
in order, one behind the other in an antero-posterior line — conduct
and " condense " respectively the olfactory, the visual, the tact-
ual, and the auditory impressions ; the corpora striata perform
a similar ofiice for the motor impulses. The sensory impressions
which come from the periphery, therefore, all run through the op-
tic thalami, according to this theory, in order that they may be
"intellectualized" (whatever that may mean); the motor through
the striate bodies, in order that they may be "materialized." It
is enough in this connection to say that no such comjjlete dis-
tinction of function in the basal ganglia, whether as conductors
or as central organs, has yet been made out. It is true, however,
that the paths in the crusta and in and surrounding the striate
bodies are probably mainly motor, while those in the tegmentum
and in and around the optic thalami are mainly sensory. The
tendency of the most recent investigation is toward placing more
emphasis upon the fibrous nei-ve-matter surrounding these organs
as furnishing paths for the conduction of both kinds of impulses.
^ Recherches anatomiques, physiologiques, et pathologiques sur les Centres
Nerveux, 1865 ; and The Brain and its Functions, New York, 1883.
9
CHAPTER lY.
AUTOMATIC AND KEFLEX FUNCTIONS OF THE CENTEAL
OEGANS.
§ 1. When a physiological function is occasioned in a peripheral
nerve, independently of a so-called act of will, by the stimulation
of some other peripheral nerve, this function is said to be " reflex."
Such a reflex function of the nerve is regularly brought about, how-
ever, by the mediation of a collection of ganglion-cells and inter-
lacing nerve-fibres, known as a central orgav. In other words, the
secondary stimulation of one peripheral nerve, through a central
organ, as a result of a primary stimulation of some other periph-
eral nerve, is a reflex action of the nervous elements. The entire
cerebro-spinal axis is a pile of nervous centres, increasing, on the
whole, in complexity of structure and of function from below up-
ward, which, with the nerve-tracts running into and out of it, con-
stitutes a complicated mechanism capable of an indefinite variety
of such reflex functions. But the spinal cord and the medulla
oblongata are the special seat of many such functions. On the
other hand, all excitations of the nervous system which originate
in the nervous centres themselves — that is as distinguished from
being called out there by the nerve-commotion brought to them
through the afferent nerves — are called " automatic." The word
automatic must doubtless often be used to conceal our ignorance
of the real origin of a neural process. And doubtless, also, many
processes which, on first inspection, appear to be automatic, may
be discovered, or suspected, to be in reality reflex. But, as far as
our information goes at present, not only movements of the mus-
cles through the stimulating of the efferent nerves connected with
them, but also the inhibiting of such movements, and the rise of
sensations, must be ascribed to the automatic action of the central
organs. Changes in the vital conditions to which these organs are
subjected by their immediate surroundings, and especially changes
in the condition of the blood with which they are supplied, ordina-
rily constitute the internal stimuli to which they respond by exer-
cising their peculiar functions. Automatic activities belong dis-
tinctively to the central ganglia of the brain ; it is more difficult to
KINDS OF REFLEX ACTIOIST. 131
vindicate tlieir existence in the spinal cord. In general, it is by no
means easy confidently to distinguish between the purely reflex
and the purely automatic action of particular central organs. The
two forms of action are doubtless uniformly blended ; so that what
is accomplished by any central organ depends both upon its own
internal condition and molecular activity at the moment when the
sensory impulse reaches it, and also upon the character of that im-
pulse. Inasmuch as it is a vital molecular mechanism connected
by an indefinite number of ties with other similar mechanisms, the
central organ constantly acts both reflexly and automatically.
§ 2. It follows, therefore, that several kinds of reflex action are
theoretically supposable in the nervous system. When motor
nerves are stimulated in a secondary way through a central organ,
by ajDjDlying stimulus to the sensory nerve-endings, the effect may
be called reflex-motor. If an excitation of a motor nerve were
transferred, without action of the will, to one or more sensory paths,
such a conversion of nervous action might be called reflex-sensory.
In this way the attemjDt has been made to explain the feeling of
weariness in the muscles when they have been overexerted, or the
feeling which we describe as that of a limb being "asleep." It has
also been pi'oposed to speak of "co-motor reflexes," in cases where
two motor nerves are assumed to be reciprocally combined in their
influence, through a centi'al organ; or of "co-sensory," in cases
Avhere the same relation is sustained by two sensory nerves. As an
example of the latter, attention has been called to the sensation
which is felt in the nose when trying to look at the sun. Examples
of the three last classes of alleged reflex functions of the nervous
system are, however, for the most part very doubtful ; or they
admit of explanation by recognized causes in another way.' It is.
only concerning the laws of the first class of reflex actions — the
reflex-motor or sensory-motor — that we have assured scientific
evidence. The reflex function of a central organ may be defined,
then, as being (at least in its simplest form) the " conversion " or
"reflexion" of a sensory impulse into a motor excitation. We
must guard ourselves carefully, however, against the misconception
that lurks in these words : the eftect of the central organ is never
that of merely converting or reflecting a nerve-commotion from one
perfectly definite sensory path to an equally definite motor path.
No such simple figure of speech will serve to describe its function,
§ 3. The spinal cord — complex as its structure and functions
are — is much the simplest and most accessible for experimental
purposes of any of the organs of the cerebro- spinal system ; it is
' Comp. Eckhard in Hermann's Handb. d. Physiol., II., ii., pp. 33 tL
132 THE COED AS A CENTRAL ORGAN.
pre-eminently the seat of unconscious reflex-motor functions. It is
a column or pile of centres, bound together for the reception of
sensory impulses by its posterior roots and for redistributing them,
as modified by its own molecular structure and condition, through
the efferent fibres of the anterior roots. Such is its office as an
organ of reflex action in distinction from its ofiice as an organ for
conducting neural impulses. We consider, then, in the first place,
the Sj)inal Cord as a Central Organ.
§ 4. As the "nerve-muscle machine" is a preparation for testing
experimentally the laws of the action of the nerves as conductors,
so preparations may be made for testing the laws of the reflex and
automatic functions of the spinal cord, by separating that organ
from the brain by section below the medulla oblongata. For the
purpose of experiment, the "brainless frog " is the most convenient
of such preparations and the most fruitful of results.' If the flank
of such a frog be lightly touched, the resulting reflex motion will
be limited to a slight twitching of the muscles that lie immediately
beneath the spot on the skin thus stimulated. If its legs be
stretched out and one of them j)inched, all the segments of the
limb thus irritated will be rapidly flexed in the definite purposeful
way necessary to withdraw it from the irritation. If the skin of
the region near the anal orifice be pinched, a new combination of
muscular contractions will take place and a different form of defen-
sive movements will result : the feet will be drawn up toward the
spot irritated and the legs brusquely extended, as though to push
away the irritating agent. If the stimulus applied to the skin of
one hind leg be increased by forcibly pinching it, the resulting
reflex motions may involve the fore leg of the same side, then the
hind leg and fore leg of the opposide side, and finally almost all
the muscles of the body. Moreover, changes in the chai-acter of
these reflex motor activities take place which are plainly adapted to
provide for changes in the animal's circumstances. For if the
right flank of a brainless frog be irritated with a drop of acid, and
at the same time the right leg be held (the member which, if un-
hindered, would be, almost without exception, used in the attempt
to remove the irritation), or the right foot cut off, the left foot
may be used for the same purpose of defence.
. Phenomena, similar to those obtained in the case of the frog,
are obtained from other brainless animals. Thus the decapitated
salamander, when the skin of one of its sides is pinched, Avill bend
this side into concave shape in order to withdraw it. Not succeed-
' For detailed information see Vulpian, Le90iis sur la Physiologic du Sys-
tume Nerveux, pp. 311-465.
REFLEXES OF THE SPINAL CORD. 133
ing in this way, it will make a movement with its foot as though to
push away the cause of the irritation. In the case of the higher
animals the reflexes of the spinal cord appear, on first inspection,
to be comparatively feeble and lacking in purposeful character.
The mammal, for a relatively long time after the division of the
cord from the brain, exhibits only very imperfect reactions in parts
of the body supplied by nerves which spring from the cord below
the point of its section. But if the animal be kept alive for some
time, and even without any physiological union of the severed jDarts,
more strong, varied, and complex movements will follow upon the
stimulation of the sensory nerves of those parts. Immediately
after the spinal cord of a dog is divided low down in the dorsal
region, the hind limbs hang limp and motionless ; irritating the
skin calls forth only feeble and irregular movements, or none at all.
But after some weeks or months have elapsed, reactions resembling
those already described in the case of the frog (taking into account,
of course, the difference in the structure and normal functions of the
two animals) begin to appear. The hind limbs, instead of remain-
ing motionless, will, when the animal is held so that they are pen-
dent, be drawn up and let down again with a kind of regular rhythm,
as a result of the constant stimulation of their motor nerves by the
sensory nerves, through the spinal cord. Moreover, it is found that
the breed, age, sex, and training of the animal determine the charac-
ter of these brainless reflex movements. That is to say, the spinal
cord, as a nervous mechanism, embodies in its very structure and
functions all the peculiarities due to these causes. And when its
activities are elicited through the stimulus which, arising in many
various regions, flows in upon it along the sensory nerve-tracts, or
through some stronger but limited impulse occasioned by the a]>-
plication of stimulus to a particular spot on the skin with a definite
degree of energy, these activities bear the character both of the
stimulation and of the mediating central organ.
§ 5. Little need be added to what has already been said (Chap.
n., § 9), in description of that mechanism of the cord to which
the foregoing remarkable functions are referred. Earlier investi-
gators ' assumed the existence of a special sj'stem of sensory and
motor nerve-fibres, with connecting nerve-cells, designed and apjjro-
priated solely for executing these reflex-motor activities. That the
motor tracts for reflex movements are to a certain extent distinct
in the spinal cord from those devoted to sj)ecifically voluntaiy ac-
tivities, there seems to be good reason for affirming ; but the older
' For example, Marshall Hall, in liis New Memoir on tlie Nervous System.
London, 1848.
134 THE CORD AS A CENTEAL ORGAN.
supposition, that there are double tracts, — one connected with con-
scious and voluntary reaction upon sensation, and one connected
with unconscious and involuntary, or merely reflex-motor, reac-
tion,— between the spinal cord and the end-organs of sensation
and motion, is almost certainly incorrect. It seems antecedently
very improbable that every spot of the skin should be equij)ped
with such a twofold outfit of both kinds of nerve-fibres. No par-
ticular nerves which serve merely for reflex-motor functions, and
which have no connection either with conscious sensation or with
voluntary motion, can be pointed out.
"What happens with respect to conscious sensation — the rise of
it or its failure to rise — depends rather upon the effect of the
stimulus on the end-organ, and upon the condition in which that
stimulus finds the central organ on its arrival there. In consider-
ing that mechanism of the spinal cord which comes into use when
it acts as a central organ in all the reflex-motor activities belonging
to it, the ofl&ce of the ganglion-cells is usually made prominent.
And it can be definitely proved that these cells are an important
part of the reflex mechanism of the cord. But the extremely del-
icate network of interlacing nerve-fibres in which the processes
of these cells lose themselves also bears an important part in the
same functions. Precisely what elements of the central substance
alone act, and precisely how the elements act that do act, it is im-
possible to say.
§ 6. The following laws embody the most important general re-
sults of experiment upon the reflex-motor functions of the spinal
cord, as applied to a variety of animals under a great number of
chan":ing conditions and circumstances.
The primary stimulation of the sensory nerves must have a cer-
tain degree of strength and suddenness in order to produce a sec-
ondary excitation of the motor nerves through the centres of the
spinal cord. This is true of all the different kinds of stimuli by
application of which spinal reflexes can be obtained.. Continuous
irritation of the skin, if very slowly increased, may be carried to
the extent necessary to destroy its sensitive surface, without giving
rise to any reflex movements ; but a less degree of stimulus, if
suddenly applied, will call forth such movements. Different chem-
ical substances, when used as irritants, j)roduce effects dependent
upon the strength of the solution. Thus a weak solution {\-\ fo)
of sulphuric acid is recommended by some exj^erimenters ; and
it is asserted that in this way exactly the same reflex move-
ments, as respects kind and degree, can be repeatedly got from the
same nerve-preparation, with a machine-like regularity. Each chem-
SPEED OF REFLEX PROCESSES. 135
ical stimulus lias its lower limit of concentration which will produce
any reflex movement, and also its latent period. The time of the
latent period for weak solutions of sulphuric acid is said by Baxt '
to increase nearly in geometrical ratio, while the concentration of
the acid diminishes in ai'ithmetical ratio. The chemical stimulus,
like the mechanical, can be so slowly increased in strength as to
produce no effect. The same thing is also true of thermic stimu-
lus. A decapitated frog may be placed in water, and the water
gradually heated to the point at which heat- rigidity sets in, without
showing any reflex activity. This fact, however, may be in part
ascribed to the direct effect of the heat, diffused from the skin
upon the central organ. The same law which renders stimulus
inoperative, when very gradually increasing in strength, applies to
the use of the electrical current. Repetition of the shocks is much
more effective than a slow increase in the strength of the current.
Single induction-currents are relatively powerless, and produce no
effect unless they have a high degree of strength. Frequent inter-
ruptions greatly increase the efficiency' of the constant current in
producing reflex movements. It Avould seem, then, that a kind of
summation of afferent impulses may take place in the spinal cord ;
that is to say, the repeated excitation of the nervous centre starts
a nerve-commotion in its substance, which gathers intensity until
it breaks over, as it were, into the adjoining motor tracts. We can
scarcely affirm, however, that such summation of many impulses is
necessary to start off the nervous centre, as it were, since the sin-
gle making of the constant current, or a single strong induction-
shock, may be followed by a number of reflex movements.
§ 7. The speed of reflex processes is apparently increased by
increasing the strength of the stimulus. We have already spoken
(p. 123) of the delay which the process of conduction suffers in the
spinal cord when passing longitudinally. The time of cross-con-
duction also in the cord seems to be a function of the strength of
the stimulus, Exner ° calculated by an experiment, which con-
sisted in causing one eyelid to move by stimulating the other, that
the time consumed in the specifically central operations of the re-
flex act can be made to vary between 0.055 and 0.047 of a second
by increasing the strength of the stimulus. Rosenthal ^ and others
have found that the time for any reflex act diminishes cousiderabl}'^
with the increase of the strength of the stimulus ; is greater in trans-
verse than in longitudinal conduction ; and is much increased by ex-
' Quoted in Hermann, Handb. d. Physiol., II., ii., p. 29.
^ See Pflliger's Archiv, viii., p. 530 ff.
3 Mooatsbericlit d. Berlin. Acad., 1873, p. 104.
138 THE COED AS A CENTEAL OEGAI<r.
haustion of the cord. With veiy strong stimuli it becomes almost
too brief for observation. Wundt, ' however, denies that the time of
the reflex act is dependent upon the strength of the stimulus ; on the
contrary, he affirms that the time is either very little or none at all
affected by changes in strength of the stimulus, or else is even
changed in the contrary direction to that required by the alleged
law of Exner and Rosenthal.
§ 8. The condUion of the sjyinal cord, at the time when it re-
ceives the impulses of the sensory nerves, undoubtedly determines
to a large extent the character of the resulting reflex motions.
Lesion increases the excitability of the part below the lesion, and
this — for example, in the case of reflex movements of the posterior
limbs — according to the amount of the cord removed from the por-
tion of it lying anterior to its nervous connections with these limbs.^
Marked effects are also produced by certain drugs, as strychnine,
chloroform, aconite, quinine, etc. Of these drugs, some heighten
and some depress its excitability. In an animal slightly poisoned
with strychnine, the excitability of the cord is more or less height-
ened ; and in cases of strong poisoning with the same drug, the
least stimulation may call forth a condition of tetanus or convul-
sive cramping extending to the whole body. Two ways of exjDlain-
ing' this effect upon the mechanism of the central organ are pos-
sible : one, that the excitability of those portions of this organ
which mediate between the sensory and motor impulses is so much
increased by the poison that, on being stimulated, they explode
their molecular energy, as it were, and cause it to be diffused with
great strength into unaccustomed paths ; the other, that the effect
of the poison is to diminish the resistance along all the network
of paths, both habitual and unaccustomed, in the spinal cord.
Between these two explanations Eckhard ^ Avill not decide ; Rosen-
thal seems to prefer the former, Foster' and others the latter.
Chloroform and various other anaesthetics diminish the reflex ac-
tion of the cord. As to the effect of changes in temperature, and
in electrical condition, upon the spinal reflexes, the conclusions of
different experimenters are somewhat divergent. This power of
the nervous mechanism is, as we have already seen, retained longer
in low than in high temperatures. According to Cayrade, Avhen
the temperature of the whole cord is raised, the reflex movements,
however produced, become more energetic and the single con-
1 Mechanik d. Nerven, abth. ii., pp. 14 ff. Stuttgart, 1876.
" Vulpian, Leyoiis, etc., p. 438.
•'In Hermann, Haudb. d. Physiol., II.. ii., p. 42.
* Text-book of Plijsiologj, p. 602.
THE EFFECT OF LOCALITY. 187
tractions last longer. Another observer found a temporary rise of
excitability, followed by a depression, on beating sections of the
cord between 75° and 158° Fabr. On the other hand, some observ-
ers are of the opinion that cold increases the excitability of the
cord. In experimenting with the electrical current it is very diffi-
cult to distinguish between its effect upon the central organ as the
mediating mechanism and the effect of the same stimulus upon
the nerve-roots and nerve-paths between which the mediation
occurs.
§ 9. The locality to which the stimulus is applied has a marked
influence in determining the extent and character of the resulting
reflex movements. The most important difference of aU is that
found by stimulating some spot of the skin, and then comparing
the resulting reflex action with what follows upon the application
of the same stimulus to the trunk of the nerve which is distributed
to that region of the skin. The simple nervous impulses, which
result from stimidating the afferent nerve-fibres directly, call forth
irregular spasms in a few muscles only ; the complicated nervous
impulses, which result from applying the same stimulus to the
skin, are followed by extended movement of many muscles directed
toward definite ends. Moreover, it is much more easy to produce
reflex action by a shght pressure on the skin than by even strong
induction-shocks when applied to the nerve-trunk. By separating
a small bit of skin from that surrounding it on the back of a brain-
less frog, while taking care not to injure the nerves that attach it
to the body, the foregoing difference may be made strikingly clear
in an experimental way.' What particular reflex actions will
be evoked by the stimulus is, in each case, dependent ujDon the
particular locahty of the skin to which the stimulus is applied.
Such facts suggest the truth that the entu-e mechanism of the cord
is broken up into centres of activity, which, however, are in close
molecular relation with each other, and which are of a somewhat
expansive nature.
In view of the foregoing truths Pfliiger" has formulated the fol-
lowing laws of relation between the stimulation and the resulting
reflex action : {a) In the case of a spinal cord from which the
medulla oblongata is wholly severed, all reflex motion confined to
one side of the body is due to stimulation of that side, (b) Reflex
movements of both sides never occur in a diagonal direction ; that
is to say, stimulating one hind limb can never evoke reflex move-
' See the article of Fick and Erlenmeyer m Pfliiger's Archiv, iii., p. 326.
'^ In his work, Ueber d. sensorischen Functionen d. Riickenmarks. Berlin.
1853.
138 THE COKD AS A CENTKAL ORGAN".
merit of that limb and of the fore Hmb of the opposite side. ' (c) If
reflex action is called out in the limbs of both sides, and such action
is stronger on one side than on the other, then it is stronger on the
side stimulated, (d) If the motor effects of the stimulation show
that the excitation has been "irradiated," as it were, from one
centre to another, then such movement of irradiation is always
downward toward the medvdla oblongata in the brain, and upward
in the cord toward the same organ. It is by no means certain,
however, that these formulas (especially the second — No. b) admit
of no exceptions which are involved in the peculiar structure and
functions of the cords of certain animals. But the general rule
appears to be, that the excitation of a sensory nerve witli a slight
degree of stimulus gives rise to reflex movements which originate
in the cord on the same side, at about the same altitude as that at
which the sensory imjDulses enter the cord ; with an increased amount
of stimulus, it gives rise to those also that arise in the other half of
the cord at the same altitude ; with a stiU greater amount, to those
which arise above and below on both sides of the cord, with the
preference given to the same side. That is, the molecular disturb-
ance, as it is dispersed or radiated, passes from the cells and net-
work of fibres situated near together on the same side of the cord,
first to those on the other side of the cord at the same altitude, and
then diffuses itself on both sides up and down the cord." Accord-
ingly, it is only after allowing for a difference in the obstacles to be
overcome along the different paths anatomically open to any nerve-
commotion in the spinal cord, that we can adopt the declaration
of Luchsinger : ^ When an excitation is started anywhere in the
spinal cord, it radiates from this point in all directions, but with
diminishing intensity. Hence the title Avhich Flourens and Vul-
pian,^ following him, have given to the spinal cord — "the organ for
the dispersion of irritations."
§ 10. Besides such undoubted reflex action as the foregoing,
other cases where the spinal cord controls the muscles of the body
are less certainly of a purely reflex character. Indeed, for some
such cases the title of " automatic " has been employed. The cord
is not capable of " irregular automatism " — that is, of spontaneous
excitation like that which takes place in the higher nervous centres
' See the observations of Luchsinger, which seem to show that in some ani-
mals— as, e.g., the salamander, turtle, and even dogs, when under the inttu
ence of ether — cross reflexes in violation of Pflliger's law do sometimes occur
Pflijger's Archiv, xxii., pp. 179 fE.
'^ Compare Wundt, Grundzijge d. physiol. Psychologie, i., pp. 103 and 109.
^ Pflliger's Archiv, xxii., p. 178.
^ Lec^ous sur la Physiologie, etc. , p. 404.
TONIC ACTION OF THE CORD. 139
on volition. If a brainless frog, for example, be kept in a condi-
tion of perfect equilibrium with respect to stimulus, it will remain
wholly motionless. But the cord of such an animal will continue
to influence certain muscles of the body through the motor nerves,
even in cases where sensory impulses are diflficult or impossible to
trace. What is called the '• tonic action " of the cord upon the
skeletal and sphincter muscles, or the smooth muscles of the ar-
teries, is a chief illustration of this influence. The fact that such
tonic action does not contract all the muscles connected with the
cord at the same time, or any one set of them with the same en-
ergy as any other, throws some suspicion on its alleged automatic
character. A careful sifting of the evidence rather induces us to
ascribe this influence to the constant reflex action of stimulus from
subtle changes in the external circumstances in which the animal
is placed. Moreover, the sensory nerves in the muscles and ten-
dons, as well as in the skin and organs of special sense, may occa-
sion the rise and continuance of such reflex action. Different in-
vestigators, almost without exception, have failed to notice any
lengthening of a muscle (or loss of its tone) when the nerve going
to it is severed from the cord. That this so-called "tonic" influ-
ence is largely reflex-motor is also shown by the fact that the tone of
the muscles is lost when the skin covering them is removed, or when
the posterior root which furnishes sensory impulses for the motor
nerves connected with them is cut, Brondgeest has shown that,
when a decapitated frog is hung up after having the sciatic plexus
cut on one side, the leg is more flexed (that is, the muscles have
more of tone) on the other side. But the same flaccid condition of
the muscles can be produced by cutting only the posterior (or sen-
sory) roots of this plexus. This observer is satisfied that the con-
traction of. the muscles in the uninjured limb is due to stimulation
from the nerves of the skin ; the tonic action of the cord on the
skeletal muscles is, therefore, reflex. The only objection to consid-
ering the tone of the sphincter muscles reflex lies in the fact that this
tone continues to exist after all other reflex-motor action has been
suppressed by narcotics ; but our knowledge of the nervous mechan-
ism wliich conti'ols these muscles is not sufficiently complete to make
it certain that we have excluded all possible forms of reflex influence.
Of the marked influence of the nervous system upon the cali-
bre of the arteries, and through this upon the character of the
circulation of the blood, there is abundant evidence. Besides the
main vaso-motor centres in the medulla oblongata, certain parts of
the spinal cord are caj^able of actiug as such centres. Circulation
may continue with regularity in a beheaded frog ; but the removal
140 THE CORD AS A CENTEAL OEGAIST.
also of any considerable part of tlie cord affects the circulation
tkrough the loss of tone in the blood-vessels which it occasions.
The mechanisms for expanding and contracting the arteries are
apparently interlaced with those for contracting the skeletal mus-
cles, in all portions of the cord. But their chief work undoubt-
edly consists in transforming afferent impulses into efferent vaso-
motor impulses directed toward the dilatation or constriction of the
arteries. Whether they are capable of automatic action — in the
sense in which the medulla oblongata seems to be thus capable —
is a question we need not discuss in detail here.
§ 11. The facts already alluded to, and others similar, form the
basis for the assumption of " Centres " in the spinal cord. In general,
the application of a given amount of stimulus to a definite group of
sensory nerves calls forth reflex-motor activities in definite groups
of muscles by means of a certain region of the cord. What groups
of muscles are thus moved depends upon the amount of the stimu-
lus and the locality of its application. This fact is due to disper-
sion of that nerve-commotion which is set up at different points
in the course of the cord by the excitation of those points through
the sensory nerves. That is to say, the mechanism of this central
organ is so constructed as to connect the sensory with the motor
tracts, more favorably in some regions than in others. Such re-
gions are the so-called reflex centres of the spinal cord. If, how-
ever, a more or less constant flow of motor impulses takes place
from any region, and this flow is due to molecular activity not
occasioned by the sensory nerve-fibres of the region, then such
region may also be called an automatic centre. Nothing would
seem to prevent the same region from acting as both a reflex and
an automatic centre. The general principle may then be formulated
as follows : " The spinal cord is the proximate centre, the proximate
physiological hearth of excitation, for all the nerves that originate
from it." This principle has been defended and illustrated with many
researches by Legallois, Volkmann, Pfliiger, Goltz, Luchsinger, and
others. In accordance with it, and especially since the "epoch-
making " experiments of Goltz upon the spinal cord of dogs, many
functions which were formerly ascribed to the brain have been
shown to have their proximate centre in the spinal-cord. In ac-
cordance with the same principle, it is discovered that different
animals have different spinal centres varying in relation to their
peripheral structure and their habits.'
' Compare the results of the researches of LangendorfF in the Archiv f.
Anat. u. Physiol., Physiolog. Abth., 1880, pp. 518 ff., and 1881, pp. 519 ff.;
aud of Luclisiuger iu Plluger's Archiv, xxii., pp. 158 fE., and xxiii., pp. 308 fE.
CEISTTKES IlSr THE SPIISTAL COED. 141
In illustration of the last point the following facts may be men-
tioned : By the sufficiently long-continued and strong stimulation
of any portion of the skin of a decapitated frog, reflex movements
may be induced in all of its muscles. With rabbits, however, a reflex
action of one hind leg can be caused by stimulating the sensory
nerves of a fore leg, only in case a portion of the medulla oblon-
gata (at least about one-third) be left attached to the cord. With
the cord alone, the stimulation of one hind leg fails to excite ac-
tion in either of the fore limbs. By using great care and artificial
respii'ation, Luchsinger ' succeeded in obtaining what he calls a
" trotting reflex " from the spinal cord — after being completely sev-
ered from the medulla oblongata — of several young animals with
which that form of movement is natural. Thus the diagonal op-
posite extremities of goats and cats were moved in response to
even such weak stimulation as passive motion of the fore leg, gen-
tle pressui'e, and weak electrical currents. In general, then, it
would seem that the spinal cord of every animal is a series of con-
nected mechanisms, which are arranged so as to move the muscles
of the body, either under the control of the higher nervous centres
or in response to stimulation entering it at any point through the
sensory peripheral nerves, in accordance with the specific structure
and habits of the animal.
Many of the chief special centres connected with the organic and
vital functions are located in the medulla oblongata ; those con-
nected with the co-ordination of impressions of the special senses
and muscular action belong to the still superior portions of the
cerebro-spinal system. But the spinal cord also contains mechan-
isms which serve as centres of both these kinds." Their location,
however, is so much a matter of the special physiology of particular
species of animals, and is so indirectly connected with the inquiries
of physiological psychology, that it is unnecessary to add anything
further upon the subject.
§ 12. The question whether the spinal cord is excitable as a
whole, and in its several parts, by artificial stimulation, has been
much debated. Its direct excitability as a whole is denied by
' See Pflliger's Arcliiv, xxviii. , pp. 65 ff.
^ Besides the vaso-motor centres already referred to, those for micturition,
defecation, erection, parturition, etc., may also be mentioned. Goltz, ui his
celebrated researches in 1874 (see Pfluger's Archiv, viii., pp. 474 ff. ), showed
that normal micturition may take place in a dog in which the lumbar region
has been completely severed from the dorsal region. The influence of the
cerebral centres seems, however, to be necessary to cause a steady increase or
decrease of the action of the sphincter ani. The cilio-spinal centre, located by
Budge at the seventh and eighth cervical rootSi is more doubtful.
142 EXCITABILITY OF THE CORD.
SeLiff, ' who declares that the motions obtained by stimulating any
part of the cord with electricity comprise only those muscles which
are j)hysiologically related, to the exclusion of those which are ana-
tomically contiguous through the stimulated part of the cord. A
strong local stimulus, he affirms, produces just the same reflex mo-
tions as those which are accustomed to arise on occasion of an ex-
tended irritation of the skin at the places to which the nerves is-
suing from this locality of the cord are distributed. It is inferred,
then, that the resulting motions are obtained only reflexly, by in-
volving the sensory nerve-roots. Bat that certain longitudinal parts
of the cord can be directly stimulated seems capable of demonstra-
tion. For Fick and Engelken'^ found that movements of the mus-
cles were obtained when the anterior columns were isolated from
the rest of the cord for a considerable distance and then stimulated.
Lucbsinger's' experiments, moreover, contradict the conclusions of
Schiff; and Mendelssohn" found that the reaction-time of the an-
terior half, and especially of the anterior columns of the cord, was
uniformly less than the reaction-time of its posterior columns. The
latter also found that weaker stimuli would suffice to excite motion
when applied to the anterior columns. But, according to Schiff ^
again, the cord contains no motor elements that are directly exci-
table except the central paths of the nerve-roots. He also agrees
with van Deen in denying that the gray matter of the cord can be
made, by direct stimulation, to originate either motor or sensory
impulses. It affords paths, however, for the transmission of both
these kinds of impulse when once started by the other nervous ele-
ments. Schiff accordingly speaks of the posterior gray columns,
and of those parts of the posterior white columns which are not
direct prolongations of the nerve-roots, as " cesthesodic." The corre-
sponding parts of the anterior cord he calls "kinesodic." The sen-
sitiveness of the posterior columns which others discover on experi-
ment he regards as only indirect. Vulpian," on the contrary, agrees
with Bell, Magendie, Flourens, and Longet, in holding that, while
the gray matter is absolutely inexcitable and the posterior columns
very excitable, the anterior columns possess only a moderate degree
of excitability.
' See, especially, articles in Pfliiger's Archiv, xxviii., pp. 537-555, and xxix.,
pp. 537-555.
■-' Du Bois-Reymond's Archiv, 1867, p. 198 ; and Pfliiger's Archiv, ii., p. 414.
•'Pfliiger's Archiv, xxii., pp. 169-176.
■■ Archiv f. Anat. u. Physiol., 1883, Physiolog. Abth., pp. 283 fE.
'■ Pfliiger's Archiv,, xxix. , p. 598.
•^ Legons sur la Physiologie du Systeme nerveux, p. 362.
INFLUENCE OF THE BRAIN OlST THE CORD. 143
By an ingenious arrangement for applying the mechanical stimu-
lus of pricks from an extremely fine needle-point to definitely cir-
cumscribed spots in the spinal cord of the frog, E. A. Birge ' seems
to have demonstrated the susceptibility of the ganglion-cells to di-
rect stimulus. Pricking these cells produces movements in defi-
nitely located groups of muscles ; and the te tanusis invariably
confined to the muscles of the same side as that of the cells stimu-
lated, unless (as microscopic examination shows) the effect of the
needle has reached certain cells on the other side. Birge also
found that different regions of a single cross-section of the cord are
excitable in different degrees ; the region from the posterior fissure
to the median line of the gray matter being most inactive, and that
of the large ganglion-cells in the anterior horn sinvariably being
able to produce tetanus.
In view of such conflict of testimony it can only be said that
certain longitudinal parts of the spinal cord are plainly susceptible
to direct stimulation, but at present it is difficult to decide which
parts, exclusively, ai'e sensitive.
§ 13. Thus far the spinal cord has been considered as a series of
related centres, that act automatically or reflexly when separated
from the brain. But in its normal condition the cord always acts,
of course, under the influence of the brain. The brain thus exer-
cises a profound modifying influence over the automatic and reflex
activities of the inferior organ. The cord alone can be dej)ended
upon, as it were, to respond with great regularity, in the form of
definite reflex movements, to a given amount of stimulus, when
applied at a given locality. But the action of the brain, when at-
tached to the cord, interferes with this regularity, so that the ex-
pected muscular movements may not result when the stimulus is
applied. They are then said to be inhibited by the action of the
brain. The phenomena of "inhibition," when connected with vo-
lition, are familiar enough ; for example, one may voluntarily re-
strain those movements of one's legs which the cord, if left to it-
self, would produce as the result of tickling the soles of the feet.
But the brain without conscious volition exercises the same in-
hibitory action over the spinal cord. If a frog is suspended by the
head, and its legs allowed to dip into a vessel of dilute acid, the in-
terval between the contact of the acid and the withdrawal of the
legs is considerably lengthened when the spinal cord remains un-
divided below the medulla oblongata ; that is to say, the cord alone
withdraws the legs quicker than the cord when influenced, or in-
hibited, by the brain. The interval between tlje application of the
' Arcliiv f. Anat. u. Physiol , 1882, Physiolog. Abth., pp. 481-489.
144 THE BRAIN AS A CENTRAL ORGAN.
acid and the contraction of the muscles can also be prolonged, when
the brain is still connected with the cord, by applying chemical
irritation at the same time to the optic lobes ; that is to say, the
cord is hindered from performing its reflex-motor function by the
stimulation, and consequent influence upon itself, of the higher
nervous centre. Moreover, if at the time that one leg of a brain-
less frog is dipped into the acid, the sciatic nerve of the other is
strongly stimulated with an interrupted current, the same prolon-
gation of the period of incubation will be observed ; in some cases,
indeed, the reflex act will not take place at all. In discussing the
reciprocal relations of the higher centres of the brain, we shall dis-
cover many phenomena similar to the foregoing. All these centres
may exercise this so-called " inhibitory " action upon other centres,
according to their several physiological connections. The phenom-
ena of inhibition are not, therefore, confined to the influence of the
brain on the spinal cord.
Elaborate attempts have been made to point out a special mech-
anism of inhibition. Thus Setschenow ' has advocated the view
that localized inhibitory centres exist in the brain, and that the de-
pressing effect travels by certain definite tracts in the spinal cord.
But on this subject our doubts are entitled to go even beyond the
remark of Terrier : ^ " The nature of the inhibitory mechanism is
exceedingly obscure." We cannot be said to have sufficient grounds
for assuming the existence of any such specific mechanism. In
general, nerve-commotions modify each other within the central
organs ; they either facilitate and increase, or inhibit and diminish,
each other's effect, according to the structure and functions of the
organs, the amount and kind of stimulus thrown in upon them from
without, and the exact condition in which this stimulus finds them.
The inhibition of the cord by the brain is, then, only a special case
under the general molecular theory of the nervous mechanism.
The factors entering into every such case will very likely always
prove too varied and complex to be analyzed with complete success.
§ 14. On passing from the spinal cord into thfe brain, the diffi-
culty of defining the specific functions — whether automatic or re-
flex—of the different central organs becomes greatly increased.
The phenomena are vastly more complicated, and the methods of
analyzing them experimentally much less readily applied. The
' TJeber d. Hemmungsmeohanismen f. d. Reflexthatigkeit im Gehirn d.
Frosches, Berlin, 1863 ; and other papers.
'-functions of tlie Brain, London, 1876, p. 18, where he refers to the
elaborate paper on Inhibition in the West Riding Reports, vol. iv., by Dr. L
Brunton.
THE METHODS OF RESEARCH. 145
most complex portions of the nervous substance, in respect both
to structure and to function, are most completely withdrawn from
the use of strictly scientific methods of research. "What is known,
however, of the anatomical structure and connections of the dif-
ferent organs of the brain, and of the paths along which the ner-
vous impulses are propagated between them, prepares the way for
the more specific physiology of eacli organ. The methods of such
physiological research are in general these two : Observation of the
results which follow the application of stimulus to each of the en-
ceiDhalic organs, or to any definite locality in each ; and observation
of the results which follow the total extirpation or lesion of these
organs, or of any portion of each. Of course, both of these
methods are almost wholly applicable only to the lower animals.
In using the method of stimulation, the stimulus cannot be ap-
plied to the nervous substance of the brain without a certain
amount of injury to that substance. To stimulate any of the cranial
organs with precision they must be exposed ; those that lie deepest
cannot be exposed without injury to other organs and the death of
the animal. Moreover, it is diflftcult jjrecisely to circumscribe the
application of the stimulus. Just that form of stimulus which is
most convenient, effective, and fruitful in results — namely, the
electrical current — is liable to diffuse its direct effects beyond the
region which it is desired to circumscribe. When no result follows
the application of the current to a definite locality of the nervous
substance, the failure may be due to the weakness of the stimulus,
or to the fact that this particular centre is at the moment inhib-
ited by its condition or by the activity of some connected centre.
When a result does follow, it may be that this particular result is
due to the direct or indirect stimulation of some other so-called
centre, or to the stimulus hitting, by diffusion or otherwise, some
of the contiguous sensory or motor nerve-tracts.
Objection may also be raised against the nature of the argument
by which an inference is drawn from the facts gained by the sec-
ond of the above-mentioned methods. Such argument not only as-
sumes that the activities which remain, when some of the organs
of the brain are partially or wholly destroyed, belong to those
organs that remain, but also that those activities whicii have dis-
appeared belong to the organs that have disapj)eared. Both of
these assumptions are, however, doubtful, when we come to apply
them to the organs in their normal condition and connections
under the action of natural stimuli ; the latter of the two is partic-
ularly doubtful. In a word, the different mechanisms of the human
brain, in their normal condition and relations, constitute an in-
10
146 THE BP.AIlSr AS A CENTEAL ORGAN".
ter-clejoendent and intimately related system ; what each so-called
organ or centre does, or can do, depends not only upon its own
structure and condition at the time, but also upon the condition
and behavior of the other organs and centres at the same time.
Such interde23endence extends not only to those divisions which
gross anatomy can mark off and. consider under the name "the
organs of the brain," nor simply to those minuter subdivisions
which histology can distinguish by aid of the microscope ; it doubt-
less also extends to the last details of that molecular mechanism
which the brain-substance is. These details are different for
every individual animal, and for every individual case. Specific
differences belonging to the different species of animal life, as well
as those idiosyncrasies with which pathology is familiar, must alike
be recognized. It is by no means strange, then, that the physi-
ology of the brain is able only very slowly and imperfectly to win
from nature the truth, and to remove the reproach of apparently
conflicting facts.
In spite of the above-mentioned difiiculties certain results may
be claimed as resting upon more or less of clear evidence regard-
ing the specific automatic and reflex-motor functions of those inter-
cranial organs that lie inferior to the cerebral hemispheres. The
case of these hemispheres themselves will be subsequently consid-
ered in detail. For they are those portions of the nervous mechan-
ism about the immediate correlation of which with the phenomena
of consciousness there can be no doubt. Since we are now con-
sidering the nervous system and its, central organs merely as a
physical mechanism, we definitely rule out, as far as possible, all
allusion to any special relation between it and the phenomena of
self-conscious mind.
§ 15. Besides the spinal cord, the Medulla Oblongata is the cen-
tral organ concerning whose automatic and reflex-raotor functions
the largest amount of precise information exists. The reflex-motor
functions of this organ are more intricate and of a higher order
than those belonging jjrimarily to the cord. They are especially
such as stand related to the vital functions of the heart and blood-
vessels ; to respiration and its allied movements of the organs in
coughing and sneezing, etc. ; to the movements of the muscles in
swallowing and vomiting ; to the mimetic movements of laughing,
weeping, etc. Among the different movements in the execution of
which the medulla oblongata is concerned, some are more purely
reflex and some less so. Thus one cannot swallow if the sen-
sory tracts from the throat to this central organ are broken ; but
the movements of the heart and lungs continue after the reflex-
THE MEDULLA AS AUTOMATIC. 147
motor paths to them are destroj-ed. Sensory stimulations of the
medulla oblongata, as a rule, occasion reflex movements by second-
ary stimulation of a number of motor tracts. Swallowing, sneezing,
coughing, shedding of tears, changes in respiration and in the
movements of the heart, contortions of the countenance, may all
be occasioned, through the mediation of this organ, by one and the
same sensory impulse. There is also a marked difference in the
extent of the domain over which the motor results of stimulating
the different sensory paths connected with the medulla spread
themselves. Stimulation of the optic nerve occasions only very
limited reflex movements, such as the winking of the eyes, the se-
cretion of a few teai's, and a slight tendency to sneeze. Stimula-
tion of the nerves of taste extends over a wider area of motor
tracts ; that of the palate and lar^^nx still wider.
§ 16. The most important reflex centres of the medulla oblon-
gata are also automatic ; of such centres he chief ai"e those con-
nected with breathing, the movements of the heart, and the inner-
vation of the blood-vessels. The excitation in these cases must be
considered as a neural process arising within the central organ
itself. The cause of its origin is doubtless to be found in the
changes that occur in the supply and character of the blood. Not
only all abnormal conditions of respiration, like dyspnoea and
apncea, but also the rhythm of normal respiration, are dej)endent
upon the changing condition of the blood with respect to its more
or less perfect oxidation. The stimulus to action of the respiratory
centre in the medulla, from the condition of the blood, may be in
part reflexly applied through the peripheral ends of the afferent
nerves in various parts of the body ; but the main effect is doubt-
less produced by the direct action of the blood on this centre. Its
rhythmic nervous action may then very well be dependent upon the
rhythmic action of the lungs, and upon the resulting periodic re-
oxidation of the blood. For the nervous substance of the medulla
oblongata seems to be peculiarly susceptible to the condition of
the blood.
§ 17. This small central organ into which the spinal cord ex-
pands on entering the skull may then be said to be thickly
crowded with reflex and automatic centres. To speak of the more
important will best serve to exhibit what is known of its mech-
anism.
The respiratory centre was first located by Flourens in that part
of the medulla oblongata which serves as the place of origin for
the vagus nerve, and then more definitely in the V-shaped apex
of the fourth ventricle, or beak of the calamus scriptorius. Since
148 THE BRAIlSr AS A CENTRAL ORGAN.
extirpation or injury of this small portion of the nervous sub^
stance, when all other parts of the body are left intact, causes
immediate and final cessation of respiration, Flourens called it the
" vital knot " (nceud vital). Foster ' locates this centre below the
vaso-motor centre, and between it and the calamus HcriptorUis.
Schiff concludes that it is double, and Hes on either side in the
region of the anterior part of the ala cinerea ; the function of each
side, he thinks, is separate. In case of need it may be shifted
slightly backward toward the spinal cord. The efforts of Gierke ''
to fix it in a definite gi"oup of ganglion-cells were not successful.
With this same centre all the modifications of respiration in sigh-
ing, sobbing, yawning, crying, laughing, coughing, sneezing, and
hiccoughing are connected.
A nervous centre intimately connected with the vaso-moto?' sys-
tem of the different parts of the body exists in the middle part of
the medulla oblongata. Since we cannot examine experimentally
the efi'ect upon the action of this centi-e which would be produced
by severing all the afferent nerves that lead into it, we cannot
demonstrate dii'ectly how much of its action is automatic, how
much reflex. It is probably both automatic and reflex. But the
removal of the parts in frout of the medulla, inclusive of the cor-
pora quadrigemina, exercises no perceptible influence on the blood-
pressure. The principal vaso-motor centres in the brain are then
found in this portion of the medulla oblongata. Through it reflex
motions are called forth of the most different kinds, and involving
muscles widely separated from each other and from the region of the
skin where the stimulus is applied. Witness the effect of a draught
of air upon the circulation of the blood. The arteries of a i-abbit's
ear can be made to contract by stimulating any one of more than a
half-dozen different sensory nerves, including the sciatic plexus. In
this same central organ must be located the so-called cardio-inhib-
itory centre. In cases where the heart is stopped by sudden and
great emotion, or by severe pain, the stimulus probably reaches the
medulla from the hemispheres of the brain.
The centre of deglutition lies in the medulla higher up than that
of respiration. If this part of the organ be destroyed, swallowing
is impossible. This centre has been located in the floor of the
fourth ventricle. In the floor of the same ventricle, and in the
adjoining region, are j^i'obably located centi-es for different secre-
tions— as, for example, of spittle, or sweat, of tears, and possibly
of the pancreatic and other digestive juices. The connection of
' Text-Book of Physiology, p. 370.
" See Ptliiger's Arcliiv, vii. , pp. 583 ff.
INFLUENCE OF MEDULLA ON THE LIMBS. 149
various sensations and emotions with these secretions is too famil-
iar to need description. A central mechanism for winking the
eyes Esner would place near the beak of the calamus scriptoriun.
The centi-al mechanism for the reflex movement of the muscles of
the oesophagus and stomach also lies in the medulla oblongata. Of
the centre for the production of artificial diabetes, and of other
more conjectural centres which are packed within this small bit
of nervous matter, scarcely more than an inch in length, we do not
need to speak.
§ 18. The alleged functions of the medulla oblongata in the co-
ordination of the movements of the skeletal muscles ally this organ
more closely with certain other inferior parts of the brain. The
prepai\ation of a frog which has retained this organ, in addition to
the spinal cord, although without any of the rest of the brain, will
execute movements of the muscles that are not possible for the cord
alone. It will not, indeed, move spontaneously ; it still requires
external stimulation to start the mechanism of such a preparation.
Under such stimulation, however, it will assume a j)ositiou natural
to it in an uninjured state. When laid on its back it will make
efforts— generally unsuccessful — to turn over. The movements of
the limbs with which it responds to various sensory impulses are
more complicated than those executed by the spinal cord alone ;
they even resemble crawling motions or short leaps. Placed in the
water, what is left of the animal will swim ; and if its motions are
less perfect than those of the perfect frog, they are much more so
than those of the cord alone. It is doubtful whether, when placed
beneath the water, it will ascend to the surface to breathe, or
make efforts to escape from water gradually heated to about 104°
Fahr., — as will the animal that retains its cerebellum and optic
lobes.
Reflex movements of considerable complexity can also be exe-
cuted by mammals that have been deprived of all the enceiDhalic
centres above the medulla. Vulpian claims that a yoang rat in
this condition will emit a cry, as of pain, when its toes are pinched.
Such a mechanism will swallow and execute cei-taiu co-ordinated
movements of the limbs. Infants whose nervous centres above the
medulla are undeveloped will perform the associated movements
of sucking when put to the breast. Moreover, the effects of le-
sion of the centres of the medulla are very marked in respect to the
co-ordination of motion. Eolando observed that convulsive move-
ments followed extensive injury of this central organ. More recent
researches seem to show that the seat of these epileptiform move-
ments is at the place of union between the medulla and the pons ;
150 THE BRAIN AS A CENTRAL ORGAN.
it can, therefore, scarcely be located in either alone.' One-sided
lesions are followed by certain so-called " forced " and rotai-y move-
ments of the head, and eyes, and trunk. Such effects are most
likel}' to be produced when the injury affects the region of the
taherculum acusticum. In the opinion of Bechterew " the olivary
bodies are in relation with the gray matter of the third ventricle,
and with the semicircular canals, as central organs for the co-or-
dination of the muscles used in balancing according to impressions
of touch. It would then be one chief function of the medulla to
secui'e equipoise through these sensory impressions. On the
whole, it appears certain that considerable work in co-ordinating
the muscular movements falls upon its mechanisms. Of such work
it is probable that the movements concerned in articulate speech
are a part. Any indirect relation which it may have to the produc-
tion of those sensations and images which are woven into our
dreams does not belong in this connection.
§ 19. The associations among the different centres of the me-
dulla oblongata are curious enough ; they involve an extremely
intricate physiological apparatus. Some of these centres are in-
directly connected with psychical activities. They are not all alike
excitable ; they are not all voluntarily so. Thus we can volun-
tarily control, within certain limits, the movements of the lungs,
but not those of the heart and blood-vessels ; we can cough, but
cannot sneeze, at wiU. Some of their functions are associated
together regularly ; some of them seldom ; some never. Swallow-
ing is not necessarih' connected with the activity of the other cen-
tres, unless it be with that for the secretion of saliva ; it takes
place, however, during arrest of respiration. The excitation of no
other centre necessarily affects this centre. The secretion of saliva
is constantly connected with a change in the circulation through
the submaxillary glands.
§ 20. An animal which possesses all, or a considerable part of
the other nervous mechanisms of the brain that lie below the cere-
bral hemispheres is capable of executing movements which differ
greatly from those already described as belonging to the spinal
cord and medulla oblongata. Very few of the movements of such
a preparation are, indeed, even apparently spontaneous ; for al-
most all of them a definite form and degree of stimulus acting on
the sensory surfaces can be assigned. We are inclined, then, to sus-
pect that those movements which are apparently spontaneous are
really due to some stimulation from wdthout the central organs
'See Eckliard, in Hermann, Handb. d. Physiol., II., ii., p. 98.
'Pfluger's Archiv, xxxi., pp. 479 If., aud xxix., p. 258 f.
IlSTFLUEISrCE OF THE CEREBEAL LOBES. 151
which has escaped our observation. But the range of reflex-motor
activities vrhich an animal deprived simply of its cerebral hemi-
spheres will execute, in i-esponse to appropriate stimuli, is very
great ; it may be said to include every form of movement possible
for the uninjured animal. The statement is, therefore, wan-anted
by all our knowledge of the facts, that the medulla, pons, crura
cerebri, cerebellum, corpora quadrigemina (or optic lobes), and
basal ganglia generally are the special mechanism for co-ordi-
nating the movements of the muscles with the various impulses of
sense.
A frog from which the cerebral lobes have been removed will
respond to appropriate stimuli with all the movements of which a
perfect frog is capable. It will swim, leap, and crawl. When
placed on its back, it will easily and at once regain its natural posi-
tion. When placed on a tilting board, it will constantly adjust
the position of its body so as to maintain an equilibrium. It will
croak with the regularity of a music-bos when its flanks are gently
stroked. Thrown into the water it will swim with great regularity
of motion until it is exhausted or finds something — as a small piece
of wood placed in contact with it — upon which it can crawl. When
submerged in the water, it will rise to the surface for air ; it wall
not, like a mere spinal cord, remain quietly in water the temper-
ature of which is gradually raised, but will make violent efibrts to
escape. It is guided by the light, for it avoids objects that cast a
strong shadow. On the other hand, it appears stupid ; it jDays no
attention to the flies that are placed near it ; by careful exclusion
of all stimuli it may be kept motionless for hours. We cannot
argue from this, however, that it is without sensations, for it may
not be hungry ; and Heubel ' asserts that a sound frog may, with
careful manipulation, be made to lie still upon its back for a long
time.
Similar phenomena occur in the case of the mammal whose cere-
bral hemispheres have been removed. The rabbit or rat thus
operated upon will stand and run and leap. Placed on its back,
it will regain its feet. It will follow with its head a bright light
held in front of it ; it will start and tremble, or run, at a shrill or
loud noise. It will utter a prolonged cry when pinched. Its mus-
cular motions are obviously co-ordinated in response to sensory
impulses from the organs of touch, hearing, and sight. The bird
thus operated upon will easily regain its feet when laid upon its
side or back, and will stand in a natural and easy posture. It will
tuck its head under its wings, clean its feathers, and pick up corn
' Pfluger's Archiv, xiv. , pp. 163 ff.
152 THE BRAIN AS A CENTEAL ORGAN.
or drink water presented to its beak. Thrown into the air, it will
fly with considerable precision for some distance, and in its flight
will guide itself, though imperfectly, so as to avoid obstacles in its
way. It will start at sharp sounds or flashes of light. Such ani-
mals have on the whole the appearance of being sleepy and stupid
rather than of being deprived of any of their powers for co-ordi-
nating sensation and motion. We conclude, then, that the organs
which such animals possess are functionally capable of exex'cising
all these powers of co-ordination ; we do not at present raise the
question whether this implies the existence of psychical j)henomena
or not. The phenomena which follow the partial loss of the cere-
bral hemispheres in the higher mammals confirm the same conclu-
sion.
It is much more difficult, however, to assign the special place
which belongs to each of the organs that lie between the medulla
oblongata and the cerebral hemispheres, under their general func-
tion as already stated. They are all very intimately related ; act
to a large extent dependently ; can, within certain limits, assume
each other's functions ; and have largely the same connections with
the peripheral organs of sense and of motion, and the same Avork
to do as mediating between the two.
§ 21. It is impossible to determine the special functions of the
Cerebellum, so conflicting is the testimony of different experiment-
ers. A high degree of probability, however, attaches itself to the
statement that this organ is largely concerned in the co-ordination
of motion ; although such statement cannot be held to exhaust its
functions. The more specific theory of Wundt ' — "It is the central
organ that brings such movements of the animal's body as are ex-
cited by impulses from the cerebrum, into accord with its situation
as a whole in space" — is more doubtful, precisely because it is
more specific. Comparative anatomy seems to show that the office
of the cerebellum in some animals differs from its office in man ;
reasoning from the former to the latter is, therefore, especially pre-
carious. Moreover, its functions are so closely connected anatom-
ically with those of the pons, the crura cerebri, and the medulla,
that it is difficult precisely to separate its work from that done by
these organs.
Testimony as to the result of the extirpation or lesion of the cere-
bellum is vei-y conflicting. Apparently almost the entire length
and breadth of its surface (in the direction of the posterior bones
of the skull), and not only the gray matter, but also the white, as
far as near the bifurcation of its strands, may be removed without
'Grundzuge d. physiologische Psychologie, i., p. 301.
LESIONS OF THE CEEEBELLUM. 153
any observable result.' On approacbing the middle of its thick-
ness and removing the strands connected with the middle peduncles,
disturbances of motion begin and increase rapidly in proportion to
the amount of substance removed. Most of these disturbances, if
the animal recovers w^ell, prove to be only temporary ; they are,
therefore, probably due largely to traumatic excitation. Permanent
disturbances, however, occur when the injuries reach the lower
third of the organ, or when they are confined to this third. Vulpian
accordingly concludes that the disturbance of gait which results
from injury of the cerebellum, is due to the irritation of its more
profound white parts or of the adjoining cerebral isthmus. But
Sehiff believes that the mass of the organ, apart from locality, has
a definite influence upon the co-ordination of the bodily movements ;
though what that influence is cannot yet be clearly defined. The
influence of locality seems to be considerable upon the effect which
results from lesions in a given amount of the cerebellar substance ;
but since this influence is much more marked near the connections
of the cerebellum with other contiguous organs, some observers
attribute it largel}- or wholly to the injury — by extension of the
lesion, by pressure, or by inflammation — of these organs. Thus
the place of its union with the medulla oblongata and the regions
near the crura cerebri are especially important. But Schifi" found,
in experimenting upon mammals, that complete vertical section of
the cerebellum, in the exact median line of the vermiform process,
and removal with the knife or pincers of the entire substance, with
the exception of the flocculi and the parts external to the peduncles,
produced no appreciable loss of the power of co-ordination.
The efi'ect of one-sided lesions of the cerebellum in the disturb-
ance of motion seems to be, as a rule, much more certain and
marked than that of symmetrical lesions of both sides. Sehiff, in-
deed, asserts that when a bilateral lesion is perfectly symmetrical
it pi'oduces no impairment whatever of the functions of motion.
But the entire evidence from experiment shows that sudden lesion
of one hemisphere of this organ is almost uniformly followed by
at least temporary impairment of the motor functions. Section of
the middle peduncle of the cerebellum of a bird or mammal almost
always occasions so-called " forced " movements ; the animal rolls
around its own longitudinal axis, generally, though not invariably,
toward the injured side. Nystagmus, or the peculiar rolling move-
ment of the eyes suggestive of vertigo, and strabisrnus, take place
' Compare Vulpian, Lemons sur la Physiologic, etc., pp. 603 ff.; Eckhard, in
Hermann, Handb. d. Physiol. II., ii., pp. 102 ff.; Sehiff, m Pfluger's Archiv.,
xxxii., pp. 427 ff. ; and Ferrier, Functions of the Brain, pp. 85-123.
154 THE BRAIjST as A CENTRAL ORGAK.
in such cases. One eye may be moved inward and downward, the
other outwai-d and upward. Hitzig ' and Ferrier ° found the same
results to follow injm-y of the lateral lobe. The latter observed that
strong stimulation of the cerebellar surface with the interrupted
current causes associated movements of the eyes and head and
hmbs, in cats and dogs and monkeys. But these effects may
be largely due to the connection of the cerebellum with the me-
dulla oblongata.
The evidence from pathological cases in man conflicts, to a con-
siderable extent, with the conclusions which we might hasten to
derive from experiment upon the animals. According to Vulpian '
it is by no means rare to have unilateral lesions of the cerebellum
followed by no paralysis of either side. In a gTcat number of such
cases no genuine hemijDlegia results ; the resulting enfeeblement of
motion, moreover, is as often on the same as on the opposite side.
M. Andral is said to have made a collection of ninety-three cases
of diseases of the cerebellum, in only one of which ataxy was ob-
served in any marked way. In most cases where crossed hemi-
plegia does result, Vulpian thinks it due to the destruction or
compression of the adjacent parts, especially the roots of the cere-
bellar peduncles. The same authority denies that the superficial
parts of this organ are excitable, or that lesion of them is followed
by pain or by convulsions of the body, face, or eyes. Such results
do, however, follow excitation and lesion of its deeper parts, in
proportion to the degree of approach to the peduncles. The dis-
crepancy between experiment and pathology may perhaps be re-
moved, at least in part, by remembering that the injury is sudden
in the one case and not in the other. Moreover, few of the patho-
logical cases are clearly enough defined to serve as a sure basis for
conclusions. Some of them, however, would seem to warrant cer-
tain inferences. More than fifty years since, the well-known case of
the girl Alexandrine Labrosse was reported by Combette,'' and after-
ward made known to students of physiology generally by Longet.^
This girl was found, on post mortem, to have no cerebellum ; in its
stead was a gelatinous membrane attached to the medulla by two
peduncles of like construction. A true pons was also wanting, but
no loss of substance seemed to have taken place here. Yet she
could co-ordinate all the limbs voluntarily, and had the f\ill use of
' Untersuchungen iiber d. Gehirn, pp. 198 ff.
^Functions of the Brain, p. 106 f.
^ Lef;oiis sur la Physiologie, etc. , p. 607 f.
* Revue madicale, II., p. 57 (1831).
^ Anatomie et Physiologie du Systeme nerveux, I., p. 764 (1842).
LESIONS OF THE CEREBELLUM. 155
all the senses. She was, however, subject to falling (se laissait
tomber souvent) and spoke imperfectly. Bouillaucl has reported
another case of an adult whose entire cerebellum was changed into
a brown purulent mass ; this patient could walk, tliough in a tot-
tering and insecure way. Vulpian ' also describes a case which
came under his own observation. A woman, dying at the age of
sixty-nine, after twenty years in the hospital of La Salpetriere, was
found to have suffered an entire atrophy of all the cortical gray
substance of the cerebellum. This patient preserved great muscu-
lar vigor, and could co-ordinate all the muscles ; but her "locomo-
tion " wag disordered and difficult.
On the whole, then, it must be admitted that the evidence con-
cerning the sj)ecific functions of the cerebellum of mammals, and
especially of man, is not such as to warrant us in making definite
affirmations. Scarcely a single case can be adduced in which it
is not j)0ssible to maintain that the motor disturbances which fol-
lowed lesion or excitation of this organ should be ascribed to an
indirect effect upon contiguous organs. Yet the coincidence of
evidence from several different lines gives sufficient support to the
view that the functions of the cerebellum are in some way con-
nected with the balancing, and therefore with the precise and se-
cure locomotion of the body in space. More definitely, with refer-
ence to the nature of this connection, it is not possible to speak
confidentl}'. No disturbance of the senses of hearing, of sight, or
of muscular feeling, can be shown to follow injuries of this organ
where other parts of the brain are not involved ; on the contrary',
all these senses appear to have been perfect in certain cases of the
complete absence of this organ. The only disturbance of sensi-
bility which frequently follows affections of the cerebellum is ver-
tigo ; the same symptom can be produced by passing a current of
electricity through the back part of the head, or by the effusions
of blood in this region which are sometimes occasioned by alcohol.
Vulpian and others are, however, probably right in holding that
the result is only indirectly to be ascribed to this organ. Indeed
the view of Schiff has much in its favor : this view maintains that
the aberration of motion due to lesion of the cerebellum should
not be called a loss of co-ordination at all, since all the limbs may
be moved in exactly the right relations necessary to carry the body
forward or to maintain its equipoise ; bi,it the precision of the mo-
tion is impaired, because the nervous impulses from this organ
that innervate the neighboring groups of muscles are not rightly
adjusted to each other in amount along the difiereut tracts. The
' Lemons sur la Physiologic, etc., p. 629.
156 THE BRAIN AS A CENTIIAL OKGAlSr.
balance of the innervating cells is destroyed ; and the result is a
loss of nice adjustmeut of the amount of innervation sent to the
particular muscles employed in equipoise and locomotion.
It scarcely need be added that modern physiology distinctly dis-
proves the hypothesis of Gall, who connected the sexual instinct
Avith the cerebellum. There is no good evidence that the hinder
brain directly participates in any way in those activities of the
nervous system which are immediately correlated with psychical
phenomena, whether of emotion, instinct, or intelligence.
§ 22. The functions of only three other parts of the encephalon
require consideration in this connection ; these are the corpora
quadrigemina, the optic thalami, and the corpora striata. The
crura cerebri and the pons Varolii are, as we have already seen,
significant chiefly as organs of conduction. So far as they have
also the intermediating functions of central organs, it is not possi-
ble to treat of them otherwise than as concerned in that general
reflex-motor mechanism which occupies all this region of the brain.
§ 23. Experiments upon the Corpora Quadrigemina are rendered
especially difficult by the small size and deep situation of these
organs ; they cannot easily be exposed for stimulation without
great effusion of blood, or subjected to lesion without extending the
injury to contiguous parts. These difficulties render conclusions
from the effect of stimulating or extirpating the corresponding
organs (optic lobes) of the frog more than usually precarious.
There is no doubt, however, as to some sj)ecial connection between
the corpora quadrigemina and sensory impulses of sight ; such con-
nection is, then, of course, to be extended to those motor activities
that are dependent upon the sensory impulses of sight. Flourens
and many subsequent observers have found that one-sided extirpa-
tion of the optic lobes of birds, or of the corpora quadrigemina of
mammals, with the cerebral hemispheres intact, produces blindness
in the ojDj^osite eye. The amount of this blindness is different in
different animals, as the decussation of the fibres in the optic chi-
asm is more or less complete in different animals. In the rabbit
such decussation appears to be complete ; in the cat and dog in-
complete. The fact that hemianopsia in both eyes is connected
with disease of one side of the brain is an evidence that it is incom-
plete in man also. Moreover, when the brain is removed in front
of the corpora quadrigemina, and these organs left intact, the ani-
mal can still guide and co-ordinate its motions in response to visual
impulses. (We do not in this place consider whether we are war-
ranted in calling these impulses " sensations " — not to say "percep-
tions"— of sight.) These organs are, then, in some sort, central
LESIONS OF THE CORPORA QUADRIGEMINA. 157
organs of sight. Since they are connected by nerve-tracts -with the
cortex of the cerebrum, motor innervation in response to stimulus
from the optic nerve may arise either immediately in the corpora
quadrigemina themselves or in the gray matter of the cortex. We
may therefore suppose, with Wundt,' that destruction of the cere-
bral substance abolishes only those movements of the muscles, in
response to the stimulus of light, which involve complicated co-or-
dinations with other excitations of sense, or with earlier established
experience. It is scarcely allowable, however, to locate this special
relation to visual imjDulses definitely in the substance of the corpora
C[uadrigemiua considered as isolated from the optic thalami, the
optic tracts, and the gray matter at the floor of the third ventricle.
There is sound sense in Eckhard's ^ remark that the functions
commonly attributed to these bodies should rather be ascribed to
the region in which they lie. The nates (or anterior pair) seem to
be more especially connected with the sensory, and the testes (or
posterior pairj with the motor activities of sight.
Abnormal movements of a " forced " nature, and impairment of
the power of co-ordination, follow the injury or extii-pation of the
corjDora quadrigemina. These phenomena may be due in part to
the loss of guidance by visual impressions ; but they are probably
due chiefly to the extension of the efiiects of the injury to the crui-a
cerebri and other surrounding parts. The o'^iia lobes, according
to Groltz, are the principal central mechanism for the croaking of
the frog deprived of its hemispheres. Vulpian ^ makes a distinction
between a mei^ely reflex-motor cry and the plaintive utterance of
an animal {e.g., the rabbit) which retains these organs and the pons
Varolii. Ferrier,^ however, was unable to make the distinction so
clearly. The latter observer found that very marked phenomena —
such as dilating the pupils, clenching the jaws, retraction of the
ears and angles of the mouth, extending the legs, etc. — followed
the stimulation of these organs with an electrical current, in the
case of cats and dogs. But his experiments do not enable us to
say how much of all this belongs to the specific function of the
corpora quadrigemina as central organs, and how much to the irri-
tation of the nerve-tracts in all the surrounding region. "While we
seem warranted in connecting these organs with the cerebellum,
medulla, and pons, as concerned in the co-ordination of motions
necessary for equipoise and locomotion, it is not safe at present to
attempt a more precise localization of function.
1 Physiologische Psychologie, i , p. 184.
'^ In Hermauu's Handb d. Physiol., II., ii. , p. 131.
^ Lecous sur la Physiologie, etc., p. 541 f.
* Functions of the Brain, p. 76.
158 THE BEAIN AS A CENTEAL OEGAN.
§ 24. The office of the so-called basal ganglia— Optic Thalami
and Corpora Striata — in that "projection-sj^stem" which connects
the cerebral hemispheres with the periphery of the body, has
already been spoken of; one chief function of these ganglia has
usually been held to be that of acting the part " of middleraen be-
tween the cerebral convolutions and the rest of the brain." ' But
they both have further functions as specifically central organs in co-
ordinating the movements. of the body according to impressions of
sense. It is difficult, if not impossible, however, to define precisely
what these functions are. Some special relation of the optic
thalami to impressions of sight must be admitted. The fact that
animals deprived of the cerebral hemispheres are capable of com-
plex co-ordination of their muscles as reflex effects of visual im-
pressions, seems to indicate that the mechanism of the optic
thalami is associated with that of the corpora quadrigemina in
performing this function. In mammals complete extirpation of
the posterior portion of one thalamus results in permanent ex-
pansion of the pupil of the opposite eye ; and Renzi was confident
that injury of the upper surface of the anterior portion occasioned
bhndness. Lussana and Lemoigne found blindness in the opposite
eye to be the invariable result of lesion of one thalamus. Cases of
the disturbance of vision, or even of complete blindness, have been
observed in human patients as the apparent result of disorgani-
zation of this organ. It must be admitted, however, that the sig-
nificance of the optic thalami for vision may be due simply to the
fact that certain fibres of the optic nerve have their origin in it,
and are rendered inoperative by injuring it. Experiments and
jjathological cases connecting the optic thalami with the sensations
of smell and taste are more doubtful and conflicting, Ferrier ^ con-
cludes that lesions in and around this organ destroy the cutaneous
sensation of the opposite side of the body in the monkey ; Veyssiere
found the same thing true in dogs. But Nothnagel found that no
effect upon sensation followed the destruction of these organs in
the rabbit. Not a few cases of disease of the oj^tic thalami in man
seem to point to some connection with tactile imjDressions ; other
cases, however, are decidedly unfavorable to this view. On the
basis of this rather meagre evidence "Wundt ^ is willing to rest the
theory that the optic thalami are special centres for the reflex-
motions of touch ; by the same theory he also accounts for the dis-
turbances of motion which follow injury to these organs. He
' See Foster, Text-Book of Physiology, p. 653.
''■ Functions of the Brain, pp. 288 ff.
* Physiologische Psychologic, i. , p. 188.
LESIONS OF THE STRIATE BODIES. 159
thinks it probable, nevertheless, that their function is not exhausted
by this description. "Forced " positions and movements, and various
other marks of impaired motor activities, follow the experimental
lesion of these organs. But such disturbances largely or wholly
vanish after a brief time, although they can be again called out by
stimulation. They occur, as a rule, only when the lesion affects
the posterior part of the thalamus, or the edges of the opening
leading from above into the third ventricle. Most of the phenom-
ena may be explained as due to the working of a mechanism that
has been stimulated to abnormal activity by the mechanical irrita-
tion due to the extirpation.' We can scarcely, then, be anymore ex-
plicit than to quote the remark of Vulpian, made some years since : "
"We know nothing of the special functions of the optic thalami."
§ 25. The special motor significance of the Corjjora Striata is
undoubted ; although we cannot go to the length of holding that
these bodies are concerned only in the elaboration and downward
transmission of efferent impulses. Ferrier ^ and others have ob-
served that stimulating these bodies with an interrupted current
produces strong convulsive movements of the opposite side of the
body ; with a very powerful stimulus the whole side is drawn
into an arch. No such effect could be produced by stimulating
the optic thalami. Ferrier holds ^ that "in man and the monkey
there is little, if any, difference perceptible between the complete
destruction of the cortical motor-centres and destruction of the
corpus striatum." Vivisection of this organ is sometimes followed
by hasty forward running motions. Lesions of the striate bodies, in
the case of the animals, are usually followed by laming of the limbs
of the opposite side ; sometimes, however, no pathological symp-
toms result. As a rule, in the case of man, paralysis of the arms
and legs of the opposite side follows disease of these organs. Here,
as elsewhere in this region of the nervous system, a certain sud-
denness of the disturbance appears necessary to secure any marked
result. Some experiments seem to point to a difference in the
effects of injury to the two main nuclei of the corpora striata.
Nothnagel asserted that all mechanical injury to the nucleus len-
ticularis of one side results in laming of the opposite side : destruc-
tion of this nucleus on both sides brings the animal into nearly
the same condition as the removal of the cerebral hemispheres.
But voluntary movements persisted after complete destruction of
both the nuclei caudati of the rabbit.
' Comp. Eckhard in Hermann, Handb. d. Physiol., II., ii., p. 125 f.
^ Lemons sur la Physiologie, etc., p. 659.
3 Functions of the Brain, p. 161. "Ibid., p. 349.
160 THE BRAIJST AS A CENTRAL ORGAN.
There is much evidence, then, to show that the corpora striata
are, as compared with the optic thalami, more especially connected
with motor activities. AVundt * considers them to be pre-eminently
sio-nificant as ganglia for the co-ordination of those motor impulses
which are derived from the cerebellum and the cerebrum. The '
relative importance which they seem to have in the higher-, as com-
pared with the lower, animals (the monkey and man as compared
with the rabbit, etc.) he thinks is like that of all the anterior por-
tions of the brain ; such portions are in general, more significant
in man than in the other animals. Wundt's view has considerable
in its support — among other things, the fact that, in case of lesions
of the striate bodies, voluntary motions, or those motions whose
motor innervation originates above these organs, seem to suffer
most. But we positively must not adopt without qualification the
statement '^ that the corpora striata are exclusively motor, and the
optic thalami exclusively sensory. In addition to what has already
been said (p. 129) to caution one against this view, it may now
be added that numerous cases are recorded where injury, appar-
ently confined to one corpus striatum, has resulted in loss of feeling
on the opposite side ; and other cases where disease, apparently
confined to one optic thalamus, has caused loss of motion as well
as of sensation. Moreover, the chief motor effects of injury to the
striate bodies (if not all of them) may be due to the fact that the
descending motor tracts are necessarily involved in the injury,
rather than to any special motor function belonging to these
bodies as a central organ. Another theory of the office of the
striate bodies rejects entirely the view which regards them as in
any true sense basal ganglia, with either specially motor or specially
sensory functions ; and regards them as belonging to the cerebral
hemisj)heres, rather than subordinate to the hemispheres in func-
tion.^ But inasmuch as this theory has its principal support, of a
physiological kind, from a single case of an idiot's brain, in which
these bodies were of nearly normal size, while the cortex was defi-
cient in the motor regions and the base of the brain in general
small, it can scarcely be regar-ded as sufficiently confirmed.
§ 26. The researches of the last few years have tended to show
that some S23ecial relation exists between the nervous substance of
the organs lying at the base of the cerebrum, and the temperature
' Physiologische Psychologie, i., p. 193 f.
^ As propounded by Carpenter and Todd, and apparently adopted by Fer-
rier, Functions of the Brain, 2.52 f.
'^ See A. Hill, The Plan of the Central Nervous System, p. 276 ; and Jour-
nal of Anat. and Physiol., July, 1885.
GKAT MATTER OF THE THIRD VElSTTEICLE. 161
of the body. The earlier observations ' pointed out the limits be-
tween the medulla oblongata and the pons as a region, lesion of
which was followed by a sudden and large rise of temperature.
Still later, other observers ascribed vaso-motor functions to the
optic thalami,^ or asserted the existence of vaso-motor fibres in the
crura cerebri (so Budge). In 1884, J. Ott pointed out that cutting
the corpora striata is speedily followed by a marked rise of tem-
perature. Yet more recently two experimenters,' working together,
have arrived at certain conclusions based upon a large number of
experiments, chiefly on rabbits, but also on guinea-pigs and dogs.
They discover that, while the cortical substance can be subjected
to the most severe and extended lesions without producing a fever-
ish rise of temperature, puncturiDg the brain at the juncture of the
sagittal and coronal sutures, down to the level of the striate bodies
or deeper, invariably j^roduces a marked rise of temperature. If
the lesion only hits the striate bodies (especially the medial side,
near Nothnagel's nodus cursorius) the coming-on of the fever is
slow and gradual ; but if the needle is carried further toward the
base of the brain, the fever springs up at once and reaches a max-
imum in two to four hours. In what way these organs act as
" fever-centres," or precisely what nervous elements are chiefly in-
volved in the action, has not yet been made clear.
§ 27. Eckhard * is inclined to lay down the law that in all verte-
brates the mechanisms for a change of place lie rather in the ante-
rior part of this general region — corpora quadrigemina, etc.; while
those for maintaining the upright posture and the equipoise of the
body are localized in the region of the pons, cerebellum, and me-
dulla oblongata.
§ 28. It should be added that almost all observers have hitherto
failed to attach sufficient importance to the central functions of
the gray matter which lines the floor and walls of the third ven-
tricle. Bechterew ^ has recently contributed the results of very
important exiDeriments to determine the specific function of this
central nervous substance. He finds that frogs retain the function
of balancing even when the optic lobes are crushed, if no injury is
done to the gray substance of the third ventricle or to the crura
' By Tschetscliicliin, in Archiv. f. Anat. u. Physiol., 1866, pp. 151 ff. ; and
Sclireiber, Pfliiger's Archiv., viii., pp. 576 ff.
" Lussana and Christiani (No. 16 of the Verhandlungen d. physiolog. Gesell-
schaft zu Berlin, 1883-84).
^ Ed. Aronsohn and J. Sachs: See Pfliiger's Archiv., xxxvii. (1885), ppi
232 ff.
^In Hermann's Haudb. d. Physiol., II., ii., p. 138.
5 Pfliiger's Archiv, xxxi. (1883), pp. 479 ff.
11
162 THE BRAIN AS A CENTRAL ORGAN.
cerebri ; they lose this function, however, when a section is made
into the third ventricle. Birds (hens and pigeons), also, show the
same loss of function when a lesion is produced by running a very
fine needle into the cavity of this ventricle. In the case of dogs,
Bechterew considers himself able to localize the function of equi-
poise precisely, and to point out the special effect of injury done
to different definitely fixed localities. For example, bilateral lesion
of the lateral or postero-lateral parts of the wall of the third ven-
tricle results in the impairment or loss of equipoise and co-ordi-
nated motion on both sides of the body : the lost function is re-
gained only after a long time, and then but partially. In none of
these cases were any of the phenomena of motor laming of the
extremities apparent, or any very marked disturbance of sensation.
This gray matter of the third ventricle operates, Bechterew thinks,
in connection with the olivary bodies for the co-ordination of motor
impulses in response to sensations of touch, and with the semi-
circular canals in response to sensations of sound. It is especially
important also in equipoise through visual impulse connected Avith
the changes in the axial direction of the eyes. Thus all the above-
mentioned organs operate with the cerebellum as complex and
correlated mechanisms for keeping the body balanced in response
to changing sensory impulses.
We stop at this point in our ascending review of the automatic
and reflex-motor functions of the central mechanisms. For dis-
tinctly psycho-physical and psychological questions the most im-
portant of the activities of the nervous mechanism still await our
examination ; these are the activities of the cerebral hemispheres.
But nothing is known as to the molecular structure of these hemi-
spheres, or as to their automatic and reflex-motor centres and activ-
ities, which adds anything of importance to the description of the
nervous system as a mechanism, or to the mechanical theory of its
action. It is with such description and theory that we are now
concerned. The correlations which exist between the structural
condition, or j)hysiological function of the nervous system, and the
phenomena of mind, are chiefly (if not wholly) capable of study as
illustrated in the cerebral hemispheres. But the nature of the
nervous molecular machiner}', and of its working as mere machinery,
is understood, as far as our present information will permit, by an
examination of the physiology of the spinal cord and of the inter-
ci'anial ganglia lying below the hemispheres. As to the alleged
psychical functions of these inferior organs we shall adduce further
considerations when we come to consider such functions as belong-
ing to the brain proper.
CHAPTER Y.
END-OEGANS OF THE NERVOUS SYSTEM.
§ 1. In order to understand the end-organs it is necessary to
refer again to the place which they hold in the threefold arrange-
ment of the nervous mechanism (compare Chapter II., § 2). In the
general division of labor among its organs, certain cells situated
at the surface of the body become especially sensitive to external
stimuli. The special function of these cells accordingly becomes
that of receiving the action of such stimuli, of modifying this action
in accordance with their own peculiar structure, and thus of set-
ting up in the conducting nerves the neural process which is prop-
agated to the central organs. It is obvious, then, that the struct-
ure and grouping of the superficial cells must bear some definite
relation both to the external stimulus and also to the nerve-fibres
Avhich convey inward the nervous impulse occasioned by it. The
end-organs of sense may then all be described as special adapta-
tions of the superficial cells to the different kinds of stimuli. With
such special adaptations the peripheral terminations of the nerve-
fibres must be connected. For the end-organs, as it were, look both
outward and inward. They act as mediators between those different
modes of external molecular motion which can occasion sensations
in us, and the nerves which convey the results of this motion, when
it has been changed into a nerve-commotion, onward to the central
organs.
§ 2. In the end-organs of the special senses the fibrils of the
sensory nerves, as a rule, terminate in cellular structures which have
the morphological significance of metamorphosed epithelial cells. The
end-organs of smell and taste show this characteristic development
most clearly. These end-organs are, in genei-al, made up of cells
which, posteriorly, pass into nerve-threads that are gathered to-
gether into the sensory nerve of the special sense ; and which, an-
teriorly, pass into conical or fusiform processes. The simplest type
of an end-organ may then be described as follows : A hair-like pro-
cess extending outward, and connected by a sensitive cell with a
nervous filament extending inward. Such processes are probably
164 END-OEGANS OF SENSE.
extreinelj' sensitive to external stimuli ; and perhaps peculiarly so
to tlie chemical changes which, at least in the case of three of the
special senses (smell, taste, and sight), are their immediate excit-
ants.
All the end-organs of sense may be regarded as modifications of
the type described above. Only a small part, however, of what are
ordinarily called " the organs of the special senses " {e.g., the nose,
the mouth, the ear, the eye, the skin) belongs, strictly speaking,
to the nervous system. By far the greater part consists of me-
chanical contrivances, designed to prepare the external stimuli and
conduct to the true nervous apparatus the impulses they occasion.
These non-nervous mechanical contrivances, however, modify the
nature of the stimulus in so important a manner as to merit some
brief description in our consideration of the nervous mechanism,
§ 3. Besides the end-organs of sense, histology points out another
kind of terminal apparatus. The efferent nerves, in order that they
may stimulate the muscles, must have some special form of attach-
ment to them. Special contrivances for connecting the motor
nerves and the muscles are actually discoverable. We distinguish,
then, two classes of end-organs : first, End-organs of Sense, and,
second. End-organs of Motion.
§ 4. Among the end-organs of sense, those of Smell have been
least successfully investigated. That portion of the mucous mem-
brane of the nose which clothes the upper region of the nasal cavity
and is marked by a brown-yellow color — the region of the expansion
of the olfactory nerve — is called " regio olfactoria ;" it contains the
end-organs of smell. Here Ecker and Eckhardt (in 1855) discovered
two different kinds of cells ; but we are indebted to Max Schultze for
the first detailed description of them. The epithelial portion of the
olfactory organ is supposed to be constructed upon the same type in
all the vertebrate animals. Of the two kinds of cells which the last-
mentioned investigator described, one is called " epithelial," the other
"olfactory." The epithelial cells are the larger, have an oval nucleus
of considerable size, and extend through the whole epithelial layer.
Their external half appears more or less cylindrical or columnar (at
least in the Triton and Proteus), and is described by some observers '
as striated longitudinally. The form of the inner half of these cells
is varied. The olfactory cells are spindle-shaped, with a large,
round nucleus, and very long, fine processes. The external process
is elongated into a stiff hair, at least in many cases, although
Schultze considers that in man the olfactory cells have no cilia.
' See Professor Babucliin in Strieker's Human and Comparative Histology,
iii., p. 207 f.
THE REGIO OLFACTOEIA.
165
These cells are surrounded by the epithelial cells. Most physiol-
ogists follow Schultzein holding that the two kinds of cells are dis-
tinct both in form and in function, and that only the " olfactory "
cells are connected with the end-fibrils of the nerve of smell ; Ex-
ner ' and others, however, believe that the distinction is not a fixed
one. In his opinion the structure of one is merged into that of the
other, and both are connected, though in a different manner, with
the subepithelial net-work in which the fibres of the olfactory nerve
are lost. The exact histological relation of the fibrils of the ol-
factory nerve to the epithelium of the regio
olfactoria is not yet made out. It is probable,
however, that the finest of these fibrils, after pen-
etrating the epithelial layer, closely embrace the
large epithelial cells and enter into connection
with the inner extremities of the olfactory cells.
According to Exner, the fibres of the nerve do
not pass over directly into the processes of the
end-organ cells, but are lost in a net-work whose
interstices are filled up with granules of nervous
matter. The first pair of cranial nerves, the ol-
factorius, which, as we have already seen on p. 84,
is really a lobe of the brain itself, is the specific
nerve of smell.
§ 5. The contrivance for applying the stimulus
to the end-organs of smell is very simple ; in gen-
eral it is only necessary that a current of air, in
which the stimulating particles float, shall be pjg 40
drawn through the nasal passages over the mu-
cous membrane of the regio olfactoria. Even am-
monia and camphor, when placed under the nos-
trils, have no smell so long as the breath is held or drawn through
the mouth. In quiet inspiration much the greater part of the cur-
rent of air is conducted to the pharynx du-ectly, and comparatively
little reaches the ridge situated above the nasal dam at the back of
the nose, where the end-organs of smell are placed. In full inspir-
ation, and still more when short and deep draughts are drawn
through the nasal passages, a considerable amount of the air
is forced over the sensory parts. By snuffing we increase the
amoimt of air drawn into the region by first creating a partial vac-
uum in its cavity. In expiration the breathing passage is so located
as to carry nearly all the air past the sensory parts without striking
them. For this reason smelling is almost exclusively confined to
' Sitzgsber. d. Wiener. Acad., Ixiii., p. 44 f. and Ixv., p. 7 f.
—Olfactory Cells
and Epithelial Cells
from the Mucous Mem-
brane of the Nose, ^""/l
(After Schultze.)
166 END-ORGANS OF SENSE.
inspiration ; it has been disputed whether the current of expiration
can be smelled at all. But Debrou showed that the odor of orange
blossoms, when water tinctured with them has been drunk, can be
detected in the expired air. The cui'rent which passes through
the anterior part of the nasal passages seems to be the more impor-
tant. This is probably the reason why the loss of the nose is so fre-
quently attended with loss of the sense of smell.
§ 6. The end-organs of Taste are situated in certain papiike,
found on the upper surface of the root of the tongue, on the bor-
ders and apex of the tongue, and in some cases on the anterior por-
tion of the soft palate. These papillae of the tongue, ave' the jMpil-
Ice circumvallakn and the jMjnUccfungiformes. The lateral portions
of the former are pre-eminently the regions of the mucous mem-
brane of the tongue where the end-organs of taste are found. The
same organs are also found more sparsely distributed in the fungi-
form papillae. The cii'cumvallate papillae are composed of connective
tissue, which is invested by a jDavement epithelium arranged in
laminae. The epithelial layer is thinner than elsewhere at the sides of
the papillae, in which the end-organs of taste (gustatory flasks or
bulbs) form a zone that extends upward to about the level at which
the papillae are no longer protected by their lateral wall. In the
fungiform papillae the end-organs api^ear in the epithelium which
covers their upper surface, and in the side surfaces. A. Hoffmann
also found them in the papillae of the region of the soft palate. It
is more doubtful whether they exist, as has been alleged, on the epi-
glottis. The papillce filiformes, which are sometimes classed with
the two others, probably have nothing to do with sensations of
taste.'
Methods of experimenting to discover what surfaces are sensitive
to taste arc not easily made exact, because the stimulus must be in
solution to excite the end-oi'gans, and because the nature of the ex-
citatory changes is chemical. There is scarcely a spot from the lips
to the stomach which some physiologist has not described as be-
longing to the organ of taste. But the regions where the above-
described papillae, with their gustatory flasks, are found, are doubt-
less the principal — and probably they are the only — sensitive
surfaces. Considerable differences exist, however, among different
species of animals, and even among different individual men — es-
pecially as to the sensitiveness of the tip and edges of the tongue,
and of the anterior surface of the palate. All the evidence tends to
show that the gustatory flasks are the sole end-organs of taste.
' Comp. Briicke, Vorlesungen iiber Pliysiologie, ii., p. 257; and von
Vintscligau in Heimauu s Handb. d. Plijsiol. , III., ii., p. 147.
THE GUSTATORY CELLS.
167
Fig 41. — Giistatoi-y Bulbs from the Lateral Gustatory
Organ of the Kabbit. ^=%. (Engelmann.)
§ 7. The microscopic structure of tlie end-organs of taste is de-
scribed in substantially the same way by all investigators, al-
though these structui-es vary
considerably, according to
their position, and accord-
ing to the different species
of animals. In general they
are like a glass knob with a
short neck, and with its
length somewhat greater
than its greatest width.
Hence they are called" gus-
tatorij knobs" or "bulbs"
(so Henle), or, better, " gus-
tatory flasks " (so M. Schultze). They occupy flask-shaped cavities
of the epithelium, which they completely fill. Their lower or inner
part rests on the connective
tissue of the mucous mem-
brane ; theu' upper and more
slender part is sun'ounded by
epithelial cells and has an
opening, or pore, of from ^jqVb"
to ysVo '^f ^^ inch in diameter,
at the surface of the epithe-
lium. The margin of this pore
is usually formed by placing
several cells together, but
sometimes by a single cell which appears perforated with a round
hole. Each of the gustatory flasks consists of from fifteen to thirty
long, thin cells, arranged like the leaves of a bud in closely com-
pressed rows around the axis.
All the gustatory flasks are comjjosed of two kinds of cells :
some are, essentially, epithelial cells, and have probably no direct
connection with the nerves ; the others are highly differentiated
structures, are probably directly continuous with the nerve-fibrils
and are thought to be true gustatory cells. The epithelial or iu-
vesting-cells are long, narrow, spindle-shaped, bent, with a nucleus
well marked ; the outward end is pointed, the central end branch-
ing. The gustatory cells are thin, long, and highly refractive of
light, with nearly the whole body of the structure occupied by an
elliptical nucleus. The body of the cell is elongated into two pro-
cesses, of which the upper or peripheral is tolerably broad and
bears a short and fine point like a hair or pencil-point. This point
Fig. 49. — Transverse Section through a Papilla
Circumvallata of a Calf. Showing the arrange-
ment and distribution of the gustatory buib.
2^/j. (Engelmann.)
168
END-ORGANS OF TASTE.
lies in a canal, in the epithelial layer, and rarely projects from the
pore of the flask. The lower or central process of the cell is much
attenuated, and usually divides into two branches. A direct con-
Fis. 43. — Isolatecl Gustatory-
Bulb, from the Lateral
Gustatory Organ of the
Kabbit. ^""/j. (Engelmann.)
Fig. 44.— a. Isolated Gustatory Cells, from the Lateral
Organ of the R.abbit ; 6, an Investing and Two Gusta-
tory Cells, isolated but still in connection, ^""/i. (En-
gelmann.)
nection of these processes with the fibrils of the gustatory nerve is
assumed by all investigators. The manner in which the nerve-fibres
terminate within the papillae is different in different animals.
The gloaso-pharyngeal nerve is the principal nerve of taste. It is
distributed to the back of the tongue, enters the circumvallate pa-
pillae, where it forms a minute plexus, interspersed with nerve-cells,
from which both meduUated and non-medullated fibres pass to the
base of the gustatory flasks. The lingual branch of the trigeminus
has also some claims to be, in a minor degree, a nerve .of taste.
Sehiff ' considers it as designed for sour taste, with a slight sensi-
tiveness to bitter also.
§ 8. In considering the end-organs of Touch, attention should
be directed to the great variety of sensations which are grouped
together under the word "touch," in the broadest meaning appli-
cable to it. The question is thus raised whether any histological
difference is to be detected in the nervous apparatus which may
serve as a physical basis for the difference in the sensations. We
may set aside for the present all consideration of the feelings of
pain, of exertion and fatigue, and the so-called " common feeling "
and "muscular sense." The question is thus reduced to this nar-
row form : Can histology point out two specifically distinct kinds of
end-organs in the skin, one of which serves for sensations of tem-
perature, and the other for sensations of pressure ?
§ 9. Histological examination shows that the sensory nerves dis-
tributed to the skin — the general organ of touch — terminate in two
' Molesch. Unters.. X., p. 406 f., as referred toby von Vintschgau in Her*
mann's Haudb. d. Physiol., III., ii., p. 171 f.
THE TACTILE CORPUSCLES.
169
ways, either in free end-fibrils or in special constructions called
"tactile corpuscles" or "end-bulbs." The different varieties/ all,
however, essentially alike, of these special end-organs of touch have
been named after as many different investigators. Their general
office is that of modifying and multiplying the effect of the stimu-
lus upon the nerve-fibres which terminate in them. The so-called
" corpuscles of Pacini " were the fii'st end-apparatus to be discovered
in connection with the peripheral termination of the sensory nerves ;
they were seen more than one hundred and fifty years ago by Vater.
In man they are constantly present in the subcutaneous connective
tissue of the palms of the hand and of
the soles of the feet ; but are most
numerous in the palmar surfaces of
the fingers and toes, especially the
third phalanges, although they occur
in the neck, arms, etc. In some places
they are visible to the naked eye as a
minute gTain of from -^^ to i of an
inch in diameter. They may be said
to be nothing more than the ends of
medullated nerve-fibres remarkably
thickened.^ Each corpuscle consists
of layers of connective tissue, arranged
concentrically and more closely packed
near the centre ; these surround a cav-
ity containing a soft nucleated mate-
rial, into the interior of which the
nerve penetrates. Here the nerve-
fibre, having become a naked axis-cyl-
inder, appears to terminate in a little
bulb. Examination with the highest
powers of the microscope shows that the axis-cylinder of the fibre
is fibrillated, and that the terminal bulb consists of finely granular
substance.
Closely allied to the foregoing structures are the so-called " end-
bulbs of Krause." These are small capsules of connective tissue in
which nuclei can be detected. In them the nerve-fibrils of touch
terminate either in a coiled mass or in a bulbous extremity. They
are from ^^-^ to yoVo ^^ ^^ inch in diameter, and exist in the con-
' On the different kinds of terminal corpuscles, a principal monograph is by
Fr. Merkel, Ueber die Endigungen der sensibleu Nerven in der Haut der
Wirbelthiere, Rostok, 1880.
'^ So Biesiadecki in Strieker's Human and Comparative Anatomy, ii., p. 232.
Fig. 45. — Corj^iuscle of Pacini (or Vater)
from the Mesentery of the Cat, (After
Frey. ) a, nerve with its sheaths ; 6,
system of tunics constituting the cap-
sule of the corpuscle ; f, axial canal,
in which the nerve-tibre ends.
170
END-ORGANS OF SENSE.
Fig. 46. — End-bulbs from the
Conjunctivfi of the Human
Eye. (After KoUiker.) 1,
has two nerve-fibres which
form a coil within the end-
bulb ; 2, has a fatty core.
The nerve-fibre of 3 ends
within in the form of a knot.
junctiva of the eye, in the tongue, the Hps, the floor of the buccal
cavity, etc. The " corpuscles of Wagner " (or Meissner, -who has
furnished most of the details) may be described as oval-shaped
bodies, made up of superimposed laminae and
bearing some resemblance to a miniature fir-
cone. The medullated nerve-fibres, like
" creeping roots," wind beneath the cutane-
ous papillse, and here and there penetrating
them, terminate in the corpuscles. Within
the corpuscles,
according to
Kolliker, the
fibrils form two
or three coils,
and finally join
together in
loops. These
tactile end-organs are most constant
and numerous in the terminal pha-
langes of the fingers; they occur in
smaller numbers on the palm and
back of the hand, on the sole and
back of the foot, and sometimes on
the nipple, lips, etc. They are seated
in the papillse of the skin. Meissner
counted four hundred papillse in -^V
of an inch square on the third pha-
lanx of the index-finger, and found
these corpuscles in one hundred and eight of them. Their long
diameter lies in the direction of the papillse and extends from -g^-g^
to Yj-Q ^^ ^^ ^^^^ » ^^®y ^^'® about -g-J-jj- of an inch in thickness.
§ 10. Since the surface of the skin is in general sensitive to press-
ure and to temperature, it follows that the special structures de-
scribed above as occurring in parts of this surface, cannot be the
sole end-organs of touch. Modern histology has demonstrated
the presence of an intricate plexus of non-meduUated nerve-fibres
which end in free extremities between the cells of the mucous
layer. This terminal plexus of nerve-fibres is also the end-organ
of so-called general sensibility and of touch.
None of the attempts hitherto made to establish specific relations
between the varieties in the structure of the tactile end-organs and
the varieties of the sensations which they administer can be joro-
nounced successful. Ivrause has tried to deduce from the coustruc-
tG. 47. —Corpuscles of Touch. (After
Frey.) a, from the soft skin of the
duck's bill ; b and c, from the papillse
of the tongue of the same animal.
THE TACTILE COEPUSCLES. 171
tion of the corpuscles of Pacini their fitness to act as the end-
organs of pressure ; but these corpuscles are wanting in many
parts of the body that are sensitive to pressure. Wagner con-
sidered the corpuscles which bear his name to be special organs of
touch. But it has been shown by Merkel that these corpuscles are
nothing but aggregates of more elementary forms, the so-called
" tactile cells." Some have argued that the end-bulbs of Krause and
the corpuscles of Pacini are the organs of general feeling {sensus
communis) ; but others, with more probabihty, assign this function
to the free nerve-endings ; while Merkel is of opinion that the latter
are specifically concerned in sensations of temperature. Nothing
is known on this point beyond the fact that the skin, within which
the sensory nerve-fibres terminate, either in free ends or in special
tactile corpuscles, is the organ for all the varieties of sensation
brought under the most general meaning of the word " touch."
The more precise manner in which the terminal fibres of the
nerves of touch stand related to the individual tactile cells is also
still in doubt. Some investigators consider that the fibres enter
into the very protoplasm of the cells (Merkel, Frey) ; others that
they spread themselves on end-plates superimposed on the cells
(Retzius, Ranvier).
§ 11. With the exception perhaps of the ear, the Eye is by far
the most elaborate and comphcated of the end-organs of sense.
This is true of those portions of it which are designed merely to
bring the external stimulus to bear upon the nervous structure, as
well as of this structure itself. Considering it as a whole, we
may say that the peripheral organ of sensations of light and color
is an optical instrument constructed on the plan of a water camera
obscura, with a self-adjusting lens, and a concave, sensitive, nervous
membrane as a screen on which the image is formed.
§ 12. The eyeball consists of three coats or tunics inclosing
three translucent refracting media. Since, however, the front part
of the outer one of these coats is itself translucent and refracting,
the number of refracting media in the eye is really four. (1) The
first or external coat consists of two parts : (a) the Sclerotic or
posterior five-sixths part ("white of the eye"), which is a firm,
fibrous membrane formed of connective tissue intermingled with
elastic fibres ; and (b) the Cornea, or translucent anterior one-sixth
part, which is circular and convex in form, and covered with con-
junctival epithelium. The cornea rises and bulges in the middle
like a watch-glass. (2) The second coat, or tunic of the eye, also
consists of two parts : these are (a) the Choroid coat, which com-
prises much its larger portion, is of a dark brown color, due to ita
172
THE HUMAlSr EYE.
pigment cells (except in the case of albinos), and is abundantl;f
provided with nerves and blood-vessels ; and (b) the Iris, a circular,
flattened, disk-shaped diaphragm in front of the lens (the colored
part of the visible eyeball), bathed with aqueous humor, and hav-
ing in its centre a circular aperture called the ' ' pupil "' of the eye.
The anterior border [corpus ciliare) around the iris consists of the
JPi: ci%
ScJffj:
PiQ. 48.
-Het.
■CJior.
-Horizontal Section through the Left Bye. ^/j. (Schematic, from Gegenbaur.)
ciliary muscle and the ciliary processes. (3) The Retina is the
third or inner coat of the eye. It is a delicate membrane of ex-
quisite ti'ansparency and almost perfect optical homogeneity ; it
has a highly comj)lex structure, consisting of nine or ten layers, th^
truly nervous portions of which contain nerve-fibres, nerve-cells,
and special end-organs, together with connective tissue and blood-
vessels. The inner surface of the retina is moulded on the vitreous
THE FOUR EEFRACTING MEDIA. 173
body, and it extends from the entrance of the optic nerve nearly
as far forward as the ciHary processes.
§ 13. The eyeball has four translucent refracting media. The
first of these — enumerating inward from the outside front — is (1)
the Cornea, already spoken of as the anterior one-sixth of the
outer coat of the eye. (2) The Aqueous Humor fills the space
between the cornea and the lens, and is divided by the iris into
two chambers, of which the front one is much the larger. It is
limpid and watery ; it holds in solution the salts of the blood-
serum, with traces of organic substances. (3) The Crystalline Lens
is situated between the iris and the vitreous body. It is a transpar-
ent biconvex lens, with its antero-posterior diameter about one-third
less than the transverse diameter. It consists of a capsule and in-
closed body. It is of " buttery consistency," composed, like an
onion, of a number of easily separable layers. Each layer consists
of fibres which, within the layer are, as a rule, radial. Between
the entire ciliary part of the retina and the corresponding part of
the vitreous humor is interposed a structureless membranous body,
to which the edge of the lens is attached, and which radiates out-
ward and maintains the lens in tension. It is called the suiipen-
sory ligament, (or Zonula of Zinn) and its office is very important
in the accommodating of the eye to different distances. (1) The
Vitreous Humor consists of a number of firm sheets or layers
(lamellae), between which fluid is contained, built iuto a body that
is, optically considered, transparent and homogeneous. It occupies
most of the space inclosed by the tunics of the eye. It is thought
to be a gelatinous form of connective tissue, and is composed most-
ly of water with salts in solution, of proteids and mucin, fats and
extractive matters — especially urea. Its peculiar structure is of
little significance for the physiology of the eye.
§ 14. Of the appendages or accessory parts of the eye — such as
the eyebrows, the eyelids, lachrymal apparatus, muscles of the eye-'
ball — only the mechanism by which the eye is moved in its or-
bit has any special significance for physiological psychology.
The building-up of a world of visible objects, and even the forma-
tion of a so-called " field of vision," is dependent upon the great
mobility of the eye. The eyeball is moved in its bony socket,
where it is embedded in a mass of fat as in a socket-joint, by sis
muscles, which are attached to it somewhat like the bridle to the
horse's head. Four of these muscles spring from the bony wall
near the point where the optic nerve enters, extend through the
length of the socket and pass directly to the eyeball, where they
are attached to it, one above, one below, one on the outer, and one
]74
THE HUMAlSr EYE.
on the inner side, (the recti; intemiis and externus, superior andinfe*
rior). In moving both eyes up or down, the same muscles in both
contract simultaneously ; in moving the eyes to the right, the outer
Fig. 49. — Muscles of the Left Human Eye,
seen from above, rs, rectus superior ;
re, i-ectus externns ; and rit, rectus
internus ; os, superior oblique, with
its tendon, t, which runs through the
fnembranous pulley, ?«, at the inner
wall of the cavity of the eyeball.
Fig. 50. — Muscles of the Left Human Eye, seen
from the outside. Ir, levator of the upper eye-
lid, which covers the rectus superior, rs, re, os,
as in the preceding figure ; rif, rectus inferior ;
oi, inferior oblique.
muscle of the right eye and the inner of the left, contract simul-
taneously (and mce versa) ; in turning both eyes inv^ard to converge
them upon a near object, the two inner muscles contract together.
We cannot move the eyes so that the optical axes do not either
meet or remain parallel ; we cannot look with one eye upward and
the other downward, nor with one eye to the left and the other to
the right ; nor can we voluntarily turn the eyes farther apart than
when their axes are parallel.
The other two of the six muscles of the eye are called oblique. Of
these one is superior and internal ; it does not pass directly forward
from its place of origin, at the posterior aperture through which
the optic nerve enters to the eye, but first runs through a ring, then
turns around, and is attached obliquely to the upper surface of the
eyeball. The other oblique muscle begins at the inner wall in the
socket, passes under the eye-ball, and is attached to it opposite to
the superior oblique muscle. The two oblique muscles combine
with the four recti to move the eyes in various directions which
would be impossible for the latter alone.
§ 15. The problem which is to be solved by the end-organ of
vision may be stated in a general form as follows : A mosaic of
localized sensations must be so constructed that changes in the
quantity, quality, local relation, and sequence of these sensations
THE FOEMING OF THE IMAGE. 175
shall be quickly interpreted as indicative of the size, shape, lo-
cality, and motion of external visible objects. The most important
part of the solution of this problem falls tipon the nervous struct-
ure of the retina. It is itself a mosaic of nervous elements, the
excitation of which may vary in quality, quantity, local coloring,
and sequence of the different elements excited. But in order that
the retina may exercise its function with the precision and delicacy
of detail for which its structure fits it, the rays of light reflected
from a single point of the surface of the visible object must excite a
single one, or at most a small and definite group, of the retinal
nervous elements. The sensations thus occasioned can then un-
dergo a systematic arrangement by the mind. It is the work of
the translucent refracting media of the eye to apply the stimulus to
retinal elements exactly discriminated, and in an order correspond-
ing to the object ; that is to say, the cornea, the humors of the eye,
and the lens must form an image on the retina. To show the pos-
sibility of this by calculating how the general laws of optics apply
to the special structure of the eye, as anatomy describes it, and to
make the calculations accord approximately with the facts, has been
the labor of a number of investigators, especially of Helmholtz and
his pupils. To the results of this labor only a brief allusion must
suffice.
§ 16. The four media of the eye constitute a system of refracting
surfaces, each of which is separated from the one adjoining by a
circular cut, as it were, in the whole refraction -substance. Espe-
cially is this true of the lens with its concentric layers. The " image "
formed upon the first member of this system of surfaces, by its re-
fraction of such bundles of rays, from the object, as all lie in a plane
at right angles to the axis of the system, thus becomes an " object ''
for the second refracting surface of the system ; and the image-
formed by the second an object for the third ; and so on. The re-
sult of any number of such refractions will accordingly always be
an image whose points lie in a plane at right angles to the axis of
the system of refracting surfaces, and which, as a whole, is in true
perspective to the original object. The last image and the object
are geometrically similar.
In tracing the course of the rays of light through the refracting
media of the eye, two things must be taken into the account : (1)
the indices of refraction of these media, and (2) the geometrical
form and position of all the limiting surfaces. (1) The means for
attaining a knoAvledge of the former is by taking the average result
of an examination of a number of eyes supposed to be normal
Fortunately for science, death has, for the first twenty-foiir hours,
176
THE HUMAN EYE.
little or no effect in changing the indices of refraction of the eys.
Krause ' found the mean index of refraction of the cornea to be =:
1.3507, of the aqueous humor = 1.3420, of the vitreous body =
Fig. 51. — Median Section through the Axis of the Lens of the Bye. (Schematic, after Babuchin.J
1.3485. But Helmholtz (subsequent observers have agreed better
with his result than with Krause's) found the two latter indices of
refraction to be = 1.3365 and i= 1.3382,
respectively. The lens of the eye, espec-
ially, is not homogeneous throughout as
to its index of refraction. Each layer has
its own index, and the amount of the
index of each layer increases regularly
toward the kernel of the lens. The work
of refraction done by the lens is, there-
fore, greater even than that which could
be done by a homogeneous lens with an
index of refraction equal to that of the
kernel, or most highly refracting part of
the lens.
(2) The position and form of the separating surfaces of the re-
fracting media can be only approximately determined in the living
eye. Three of these surfaces are of chief importance — the anterior
surface of the cornea, and the anterior and posterior surfaces of the
lens. The convexity of the first of these three is found to depart
perceptibly from a sphere ; it is greater toward its edge than at its
vertex, where it resembles rather a section of an ellipsoid. The
advantage of such a shape is seen in the fact that the images
' Krause's experiments refer to rays of the wave-length to which the bright-
est place in the solar spectrum corresponds ; that is, to the place at the end of
the first third, or quarter between D and E. The refraction-index of water for
these rays he assumed at =1.33424.
Fig. 52. — View of the Lens
Profile. Vi- (After Arnold.)
THE PROCESS OF ACCOMMODATIOlSr. 177
formed when the pupil is expanded are thus made sharper than
they could otherwise be. No observable refraction takes place on
the posterior surface of the cornea, because the difference between
the indices of refraction of the cornea and of the aqueous humor is
so slight that the faint images from this surface vanish by proxim-
ity to the stronger ones refracted from the front part of the cornea.
§ 17. The power of altering the refracting conditions of the eye,
so as to enable the media to form a single perfect image on the
retina, for varying distances of the object, is called its power of
" accommodation " or adjustment. Plainly such adjustment of the
eye cannot take place, like that of a camera obscura, by changiuo-
to any appreciable extent the distance of the lens from the screen
on which the image is formed. It must therefore take place, either
by increasing the indices of refraction of the media of the eye, or
by increasing the curvature of one or more of the refracting surfaces.
It is now known to be due to changes in the convexity of the lens,
principally, if not wholly, of its anterioi- surface. The posterior
apex of the lens remains unmoved. There are several methods of
experiment which demonstrate that in accommodation for near dis-
tances the front of the lens becomes more strongly arched. When
accommodation is taking j)lace, the pupil may be seen not only to
contract, but also to draw its edge forward. Helmholtz calculated
the amount of this forward movenient for two cases at about J^y and
-gJg of an inch, respectively. Moreover, by an ingenious contrivance
the image reflected from the anterior surface of the lens may be
watched as it becomes smaller and more distinct on adjustment
for near distances, thus showing that the surface from which it is
reflected has increased its curvature.
It is obvious that the mechanism for adjusting the eye must be
under the brain's control, since adjustment is voluntary ; and that
it must consist of muscles which lie within the eyeball. The ac-
cepted hj-pothesis concerning the nature and action of this mechan-
ism was first proposed by Helmholtz. This investigator assumes
that the lens, when the eye is at rest, does not have the form which
corresponds to a condition of equilibrium in its own elastic power.
If it were not held in by its surroundings, it would be more arched
than it is both before and behind. But it is kept flattened by the
radial tension of the susjjenso7-i/ ligament ; when this tension is with-
drawn the lens becomes curved by the action of its own elasticity.
The withdrawal of the tension is accomplished by the action of the
ciliary muscle, the fibres of which have their point of fixation at the
edge of the cornea, and run from here in the direction of a merid-
ian toward the equator o fthe eye. When the ciliary muscle cou-
12
178
THE HUMAN EYE.
tracts, the free ends of its fibres are drawn toward its fixed ends
on the edge of the cornea ; the radial tension of the suspensory hg-
ament is thus relaxed, and the lens is allowed to assume its natural
form under the equipoise of its own elastic forces.
Conjumfiva
cprneae
fun. Sciuemmii
Jiiy. Jiect. iridis
Coiijnnclivn
sclerac
Fig. 53.
Proc. ciliarix
railiarer circulurev
Ciliarmvslcel
-Sectional View of the Connections of the Cornea, Ciliary Muscle, Ciliary Processes, etc.
'"/j. (Gegenbaur.)
The occulo-motor nerve furnishes the fibres that serve the ciliary
muscle ; these fibres run in the posterior strands of its roots. Their
central place of origin is in the posterior part of the floor of the
third ventricle ; stimulating the front division of this part produces
accommodation of the lens ; stimulating the back division of the
same part produces contraction of the pupils. Stimulation still
further back, where the third ventricle passes into the aqueduct of
Sylvius, produces contraction of the internal rectus muscle of the
eye ; and the innervation of this muscle is, of course, regularly con-
nected with adjustment for near distances. Thus all the mechan-
ism of accommodation, both that of the central organs and that of
the end-organs, is made to work together for the production of an
image upon the retina.
§ 18. Given the formation of the image upon the retina, it is fur-
ther required in order to vision that this physical process should
be changed into a physiological process. We now examine briefly
the mechanism by which such a change is accomplished. [The
reader is referred to the larger specific treatises for the detailed
theory of the schematic, the emmetropic, the myopic, and the hy-
permetropic eye.] The retina, or inner tunic of the eye, contains
the nervous elements by whose action the system of refracted rays
THE LAYERS OF THE RETINA.
179
is changed into a mosaic of nerve-commotions. But light does not
act as a stimulus to the nei'vous substance, either fibres or cells,
unless it have an intensity which is neai'ly deadly to that sub-
stance. Since we are able to see the feeblest rays of the moon as
reflected from white paper, the nervous excitation which is the con-
dition of vision cannot be produced by the direct action of light on
the nerve-fibres or nerve-cells of the eye. A photo-chemical sub-
stance and process, as well as a special end-apparatus, seems there-
fore to be necessarily involved in the problem which is given to
the retina to solve.
§ 19. The nervous and other elements of the retina are arranged
Outer surface.
10 ^^^^m^WS^msmm!mPm«^fr?^y^'^' 10 Layer of pigment cells.
9 Layer of rods and cones.
S Membrana limitans externa.
7 Outer nuclear layer.
f .... Outer molecular layer.
y Inner nuclear layer.
[5reJ'?|tdg*|!'„'K| 4 . . . .Inner molecular layer.
. Layer of nerve-cells.
. . . Layer of nerve-fibres.
=^^-:^:|^^^: J . . . .Membrana limitans interna.
Inner surface.
Fig. 54. — Diagrammatic Section of the Human Retina. (Schultze.)
in tlie following ten layers, counting from within outward and
backward : (1) the membrana limitana interna, which is the retinal
180
f- .i„<; A/ ' ' ■ ' —
Fig. 55.— Diagrammatic represen-
tation of the Connections of the
Nerv(' - fibres in the Retina.
(Schultze.) Tlie numbers have
the same reference aa in Fig. 54.
THE HUMAN EYE.
border toward the vitreous body ; (2) the
layer of optic nerve-fibres distributed from
the papilla where this nerve breaks in
through the tunics of the eye ; (3) the
ganglion-cell layer ; (4) the imier molecular
layer ; (5) the inner nuclear layer ; (6) the
outer molecular layer ; (7) the outer nu-
clear layer ; (8) the membrana limitans
externa ; (9) the bacillary laj'er, or layer
of rods and cones ; (10) the pigmenl-epiihe-
lium layer. The membranes (Nos. (1)
and (8)) are not really uninterrupted
layers, but an extremely fine network.
By no means all the retinal substance
is nervous. Indeed, the numerous radial
fibres {fibres of Midler) which seem to
penetrate its entire thickness are now held
to be in great part elements of the suj)-
porting tissue ; moreover, the whole con-
nective substance is a kind of sponge-like
tissue, in the gaps of which the true ner-
vous elements lie embedded. The gaps
thus filled are especially large in the
second, third, fifth, and seventh layers.
A description of the undoubtedly ner-
vous elements of the retina includes the
following particulars : (a) The retinal
fibres of the optic nerve lie parallel to the
surface, are non-medullated, and extreme-
ly fine ; in general, they are arranged in
ray-like bundles, radiating on all sides
from the place of the entrance of the
nerve. The arrangement is special at the
yellow spot, so as to surround, and not
cover it. This nerve-fibre layer is thickest
at the papilla of the retina, and diminishes
continuously from this sjjot toward the
ora serrata ; at about one-third of the
distance it becomes single. (6) The gan-
glion-cells, which form the principal part
of layer No. 3, like the multipolar cells of
the rest of the cerebro-spinal sj-stem,
have one large process of more trans-
THE LATER OF RODS AISTD CONES.
181
lucent appearance. This process subdivides into fibrils of vanishing
fineness, that enter and are lost in the next layer. At the yellow
spot these cells are eight or ten deep ; from this centre they dimin-
ish toward the ora serrata, where spaces are found between the
cells, (c) The nervous elements of the inner molecular layer (No. 4)
are not clearly made out. They probably consist of extremely fine
filaments, which are connected with the external processes of the
ganglion-cells, (d) Most of the nucleus-like bodies of the inner
nuclear layer (No. 5) are probably nervous. Each such body has
two processes — one directed inward, the other outward. The
former is thought to be connected with the filaments of the
inner (No. 4), and the latter with those of the outer (No. 6) molec-
ular layer. («) In the outer molec-
ular layer (No. 6) are nervous fila-
ments, like those in No. 4, which are
probably connected with the external
processes of the inner nuclear layer.
Here are also found numerous star-
shaped cells probably not nervous.
(/) In the outer nuclear layer (No.
7) the undoubtedly nervous elements
preponderate. Each nucleus-like
body in this layer is connected by a
radial fibre with one of the nervous
elements of the rod- and- cone layer
(No. 9). These nuclear bodies are
called rod-granules and cone-granules
respectively, and are to be distin-
guished, not only by their connection
with these elements, but also by
their size and position ; the latter are
larger, and lie on the more external
side of the layer, {g) The layer of
rods and cones (No. 9) consists of a multitude of elongated bodies
arranged side by side, like rows of palisades, with their largest ex-
tension in the radial direction. These bodies are of two kinds —
one cylindrical, and called "rods of the retina," the other rather
flask-shaped, and called "cones of the retina."
The rods extend the entire thickness of the layer, and are about
3^„ inch in length, but the cones are shorter ; the rods are
about TXoTTo ^^^^^ ^^ diameter, the smallest cones of the central
depression ^ o|)qq inch. The inner ends of both are continuous
with the rod-fibres and cone-fibres of the outer nuclear layer.
Fig. 56. — Diagrammatic Section of tne
Posterior Part of the Retina of a Pig.
80»/i. (Schultze.) 7, part of outer nu-
clear laj"er ; 8, membrana limitana ex-
terna ; 9, rods n.nd cones. Each of the
cones, which are in very close apposition,
contains in its inner segment a highly re-
tractile bod3', the func ion of which is
unknown.
182
THE HUMAN EYE.
Each rod or cone is composed of an inner and outer segment
or limb ; the latter is highly retractile, the former only feebly so.
The inner limbs appear under the microscope like a mass of pro-
toplasm. The appearance of a most delicate longitudinal line in
the inner and outer segments has led to the belief that a nerve-
fibril is, as it were, drawn through their axis. The description
Fig. 57. — Rods and Cones of the Human Retina. (Schultze.)
A, showing inner segments of the rods, .s' s s, and of the
cones, zz'; the latter in connection with the cone-nuclei and
fibres as far as the outer molecular layer. """Z]. A inner
segment of a cone with a cone-nucleus. ^200^^, C, isolated
interior portion of a cone.
Fig. 58. — Rod and Cone from
the Human Retina, preserved
in perosmic acid, showing
the fine fibres of the surface
and the different lengths of
the internal segment, '"""/i.
(Schultze.) The outer seg-
ment of the cone is broken
into disks which are still ad-
herent.
of the two shows that there is no essential anatomical difference
between the rods and cones ; nor are we able to distinguish any
difference in their physiological significance. The distribution of
the two elements is different for different parts of the retina. In
the yellow spot only cones appear, but these are of more slender
form, and of increased length, so that not less than one million are
supposed to be set in a square y^ inch ; ' while not far from this
' See Le Conte, Sight, p. 58. New York, 1881.
YELLOW SPOT AND BLIISTD SPOT.
183
m^
Figs. 59 and 60.— Superficial Aspectof the Arrangement
of the Rods and Cones in the Retina. *"%. (Schultze.)
The former is from the region of the macula lutea ;
the latter from the peripheral region.
spot each cone is surrounded by a crown-shaped border of rods.
Toward the ora serrata the cones become continually rarer. In
close connection with the
rods and cones stand the
cells of the pigment-epithe-
lium. These cells form a
regular mosaic of flat, six-
sided cells, which send out
pigmented processes
tween the outer limbs of the
rods and cones.
The fibres of the optic
nerve are supjDOsed to be
connected with the rods and cones by means of the ganglion -cells,
and of the radial fibres in which the granules of the outer and inner
nuclear layers are embedded.
§ 20. Two minute portions of the inner surface of the retina re-
quire to be distinguished from the rest of its area ; the yellow spot
(macula lutea) and the " blind spot " [papilla optica). The yellow spot
S Ch is of oval shape, about -^-^ of an
inch in its long diameter, and has
in the centre a depression called
ihQ fovea centralin. It is the place
of clearest vision, and the physi-
ological centre of the eye. About
\ of an inch inside the eye from
the middle of the yellow spot is
the middle of the papilla, or place
where the optic nerve breaks into
the retina. The blind spiot, or
portion of the retina which can
be experimentally shown to be
inoperative in vision, has been
proved by Helmholtz to corre-
sj)ond in both size and shape to
that covered by this papilla. Its diameter is about J^ or J-j of an
inch, varying considerably for different eyes. It is wanting in all
the nervous elements.
§ 21. In answer to the question, What elements of the retina are
directly affected by the light ? both anatomy and physiology refer
to the layer of rods and cones. This layer alone possesses that
mosaic nervous structure which appears to correspond to the de-
mands made upon the end-apparatus of vision. It can be demon.-
PlG. 61.— Equatorial Section of the Right Eye,
showing the Papilla of the optic nerve, the
Blood-vessels radiating from it, and the
Macula lutea. 7i- (Henle.) S, sclerotic;
Ch, choroid ; and R, retina.
184 THE HUMAN EYE.
strated that the waves of light pass through the structure of the
retina, and that the nervous process must begin in the back part of
this structure. Indeed, it is possible, by an experiment (devised by
Purkinje), to perceive with one's own retina the aborescent figure
formed by the shadow of the blood-vessels expanded upon its front
part.
§ 22. We have already seen (Chapter I., §§ 14, 15) that a chemi-
cal process may reasonably be conjectured to accompany the action
of the nerves in general. Undoubtedly a photo-chemical process
is concerned in vision. But after all the careful researches of many
observers, especially of Ktihne ' and his pupils — it is difficult to
point to any results of chemical investigation which serve better to
define the exact nature of the physiological action of the end-oi'-
gaus of the eye. The relation of the light to any chemical pro-
cesses which may take place in the gray substance of the retina can
be only indirect. The opto-chemical hypothesis must, therefore,
regard the epithelial cells, with which the end-fibrils of the optic
nerve are in physiological connection, as the bearers (Trager) of cer-
tain photo-chemically decomposable materials or visual substances
(Seh^toff^e) ; these substances, however, cannot excite chemically
the irritable part of the visual cells — the protoplasm of the inner
limbs of the rods and cones — without being themselves decomposed.
Visual substance is necessarily some kind of matter easily decom-
posable by light, or chemically sensitive to light. The first process,
then, in the excitation of the optic nerve, is the decomposition by
the light of some substance found in certain epithelial elements of
the retina. The second process is the action, as visual excitants
(Sehreger), of the decomposition-products of the epithelial cells
upon the protoplasm of the end-organs. But in order that such
decomposition-products may act as excitants of the end-organs of
vision, the visual substance must be rightly placed — that is, it must
be in local connection with the protoplasm of the outer limbs of
the rods and cones. The relation of the two last layers of the
retina is such as to secure this necessary connection. We are as
yet unable, however, to say what are the visual substances which
the successful working of the opto-chemical hypothesis demands.
The location of the pigmentum nigrum, and the changes produced
m it by light, favor the conjecture that this substance is of the
most fundamental and general importance for visual sensations.
Visual purple may also be supposed to be a visual substance. The
fact that light of different wave-lengths effects changes in this pig-
' The few statements here given are taken for the most part from the article
of this investigator in Hermann's Handb. d. Physiol., III., i. , pp. 335 fE.
PIGMENTS OF THE EYE. 185
ment with different degrees of speed, suggests the view that it is
related to the susceptibility of the eye for different colors. But
since invertebrates do not have the visual purple ; since the cones
(a thing which no one doubts) see without this purple, and since
the rods of some animals, such as hens and doves, and the rods of
the ora serrata, perform their functions without it, this pigment
can scarcely be said to be the only visual substance. The opto-chem-
ical hypothesis, then, seems to require several colored visual sub-
stances. Moreover, since animals can see with bleached retinas,
and albinos have the power of vision, we are compelled to assume
also a colorless visual pigment. As to the nature of the chemical
changes necessary to be produced in the protoplasm of the outer
limbs of the rods and cones by the action of the decomposition-
products of the visual substances, we are quite ignorant.
§ 23. The end-organ of hearing is the Ear. But in this case, as
in that of the eye, a very large part of the apparatus of sense is sig-
nificant simjDly as a contrivance for applying the stimulus to the
true end-organ, to the differentiations of epithelial cells and nervous
cells connected with the terminal fibrils of the sensory nerve. The
entire human ear consists of three parts, or ears ; namel}^ the ex-
ternal ear, the middle ear, or tympanum, and the inner ear, which
is also called the " labyrinth," from its complex construction.
I. The External Ear — exclusive of the cartilaginous plate which is
extended from the side of the head — consists of (a) the concha, a
deep hollow, and {b) the external meatus, or passage leading from the
bottom of this hollow to the drum of the ear. The concha is prob-
ably of little or no use in sharpening our perceptions of sound ;
for if a tube be inserted so as to secure a canal for the air to the
drum of the ear, the entire concha may be filled with wax, and the
result is to increase rather than diminish the sharpness of the
sound. It is possible, however, that vibrations of more than one
thousand in a second are concentrated by reflection ' from the con-
cha. The external ear appears to be of some service in perceiv-
ing the direction of sound. Kinne's experiments seem to show
that — as Harless ' thought— the cartilage of the ear can be thrown
into sympathetic vibration with certain acoustic waves, and so re-
inforce the sound. At best, however such work done by the con-
cha is small.
The most patent office of the external meatus is the protection
of the ear-drum ; the passage is so curved that the drum cannot be
' See Hensen, Physiologie d. Gehors, in Hermann's Haadb. d. Physiol.,
III., ii., p. 23.
-Article Horen, in Wagner's Handworterbuch d. Physiol., FV , 1853.
186
THE HUMAN EAE.
reached from the outside in a straight hne. Helmholtz called at-
tention to the fact that certain tones of a high pitch resound
strongly in the ear when the meatus is of normal length, but cease
so to resound when its length is increased artificially. The meatus
probably, therefore, modifies certain tones by its own resonant
action — strengthening the high ones, and deadening the low, in
some degree.
Various simple experiments — such as placing a resounding body
in contact with the teeth — prove that the surrounding cranial bones
conduct sound to the ear. It is probable, howevei", that the path
of such conduction is not, for the most part, as was formerly sup-
posed, directly to the inner ear by way of the cranial and petrous
bones, but indirectly, through the ear-drum and bones of the middle
ear to the fenestra ovalis. The amount of direct conduction pos-
sible, has not as yet been determined precisely.
§ 24. n. The Middle Ear, or Tympanum, is a chamber irregu-
larly cuboidal in form, and situated in the temporal bone, between'
the bottom of the meatus and the inner ear. Its outer wall is (a)
Fio. 62.— Dnim of the Right Ear with the Ham-
mer, seen from the inside. 2/,. (Henle.) 1,
chorda tympani ; 2, Eustachian tube ; *, ten-
don of the tensor tympani muscle cut off close
to its insertion ; m a, anterior ligament of the
malleus ; M c p, its head ; and M 1, its long
process. S t p, Spina tympanica posterior.
Cliorda tijDiEani
Fig. 63.— Side Wall of the Cavity of the Tym-
panum, with the Hammer (M) and the Anvil
(.J). The former shows the connection of its
handle with the drum. T, Eustachian tube.
^/,. (Gegenbaur.)
the membrana tympani, which consists of three layers — an external
tegumentary, an internal mucous, and the intermediate membrana
propria, composed of unyielding fibres arranged both radially and
circularly. In the inner wall, which separates the tympanum from
the labyrinth, are two openings or windows — the fenestra ovalis,
which corresponds to the vestibule of the labyrinth, and the fenestra
rotunda, which corresponds to the tympanic passage in the cochlea.
Near its anterior part the tympanum opens into (6) the Eustachian
THE THREE AUDITORY BONES. 187
tube, a canal which communicates with the nasal compartment of
the pharynx.
(c) The auditory bones are three in number, called Malleus,
Incus, and Stapes, and arranged so as to form an irregular chain
stretched across the cavity from the outer to the inner wall of the
tympanum. The malleus has a head, separated by a constricted
necli from an elongated handle ; its handle is connected with the
centre of the membrana tympani ; its head articulates with the in-
cus. The incus has a body and two processes. On the front sur-
face of the body is a saddle-shaped hollow, in which the head of
the malleus fits ; the short process is bound by a ligament to the
posterior wall of the tympanum ; the
long process ends in a rounded pro-
jection {os orbicular e) through which
it articulates with the stapes. The
stapes, or stirrup-shaped bone, has " "'
a head and neck, a base and two
crura. The head articulates with
the incus ; from the constricted neck
the two crura curve inward to the
base, which is attached to the fenes-
tra ovalis. These bones are moved
on each other at their joints by {d)
two or three small muscles — the ten- „ ^, „ ^.^ „ . ^.
Fig. 64. — Bones of the Ear, as seen in their
SOr tympani, the stapedius, and, more connection from in front. Vi- (Henle.)
I, Incus (anvil _), of which lb is the short,
doubtfully, the taxator tympani. Ihe and Ilthe Icng, i>rocess; c. its body, and
n 1 e L^ • • j. i • j. xi P'> ^^^ process for articulation with the
first 01 these is inserted into the st&^'esiprocessusorbiciaaris.) M, Malleus
TT J.1 J. T L (hammer), of which Mc is the neck, Mcp
malleus, near the root, and serves to the head, mi the long process, and Mm the
tighten the tympanic membrane by erpUuhm^cp.^' '"'^'' ^''^™''^' ''"^ '*'
drawing the handle of the malleus
inward ; the stapedius is inserted into the neck of the stapes,
but its function is doubtful — apparently it draws the stapes from
the fenestra ovalis, and so diminishes the pressure of the chain
of bones in that direction. The laxator tympani is inserted into
the neck of the same bone, and its action has been supposed by
some to be antagonistic to that of the tensor tympani ; but its
muscular character is now denied by most observers.
§ 25. The general of&ce of the tympanum may be described as
that of transmitting the acoustic waves to the inner ear, while at the
same time modifying their character. Some modification is neces-
sary in order that these waves may occasion such \T.brations in the
elements of the inner ear as shall be adapted for the excitation of
its end-organs. The acoustic motion of the molecules of air, in the
188 THE HUMAN EAR.
form in wliicli it reaches the ear-drum, has a large amphtude, but
a small degree of intensity. This motion must be changed into one
of smaller amplitude and greater intensity ; and it must be trans-
mitted, with as little loss as possible, to the fluids of the labyrinth.
The transmitting vibrating media must also have the power of an-
swering to the different tones of any pitch perceptible by the ear.
The description of the manner in which this apparatus of membrane
and bones solves so complicated a mechanical problem belongs to
the physics of anatomy ; it has been worked out with great detail
by Helmholtz and others, although certain points still remain un-
solved. "VVe can here only indicate one or two particulars.
A flat membrane, evenly stretched, whose mass is small in pro-
portion to the size of its superficies, is easily thrown into vibration
by the impact of acoustic waves upon one of its sides. Such a
membrane resjjonds readily to tones which approach its own funda-
mental tone ; but if divergent tones are sounded the membrane is
unaffected. A motion which consists of a series of harmonious
partial tones cannot then be repeated by such a membrane in the
form in which the air brings it. If, then, the membrane of the
tympanum were not so arranged and connected as to have no pre-
pondei'ating tone of its own, it could not be the medium of our
hearing a great variety of tones. The projaerty of taking up with
the vibrations, as it were, of a large scale of tones is secured for the
tympanum by its funnel-shaped form and by its being loaded. It
is contracted inward into a dej)ression of the right shape by means
of the handle of the hammer ; it is therefore unequally and only
slightly stretched, and has no fundamental tone. It is also load-
ed with the auditory bones, Avhich deprive it of every trace of such
a tone and act as dampers to prevent long-continued vibrating.
Moreover, since the apex of its funnel bulges inward, the force of
the vibrations from all sides is concentrated in vibrations of greater
intensity in the centre, where it is spent in setting the chain of ear-
bones in motion.
The acoustic vibrations of the auditory bones, which are occa-
sioned by the movements of the ear-drum, are not longitudinal,
but transverse ; they do not, however, resemble the vibrations of a
stretched cord or a fixed pin. They do not vibrate by reason of
their elasticity, but like very light small levers — vibrating as a sys-
tem, with a simultaneous motion around a common axis. Direct
observation of these bones in motion shows that their sympathetic
vibrations vary greatly for tones of different pitch and similar in-
tensity, from a scarcely observable motion to a surprisingly great
elonpfation.
THE EUSTACHIAN TUBE.
189
The effect of the muscles of the tympanum upon the transmis-
sion of tones of different pitch is not as yet clearly demonstrated.
In general, the stretching of the tensor muscle, within the hmits
which have thus far been investigated, seems to weaken the higher
much less than the lower tones. But the tension of the drum un-
der the influence of this muscle does not indicate the slightest
change on passing from low to high tones. The stretching of the
tendon of the stapedius muscle has no observable influence on the
acoustic vibrations of the tympanum.
§ 26. The Eustachian Tube, when in its normal position, is neither
closely shut nor wide open. Its office is to effect a renewal of the
air in the tympanum, to maintain the equilibrium of atmospheric
pressure on both sides of the tympanic membrane, and to convey
away the fluids which collect in the tympanic cavity. If it re-
mained open, so as to permit the acoustic waves of the air fi'om the
mouth to enter, our own voices would be heard as a roaring sound,
and the passage of air inward and outward during respiration
would affect the position and tension of the tympanic membrane.
That it is opened, however, on swallowing, Valsalva proved two
centuries ago. For if we keep the nose and mouth closed and then
swallow, with the cheeks blown violently out, a feeling of press-
ure is felt in the ears and the hearing is weakened. These effects
are due to the forcing of the air through the Eustachian tube into
the tympanic cavity. The tube is thus of indirect service in re-
spect to the physiological functions of the middle ear.
§ 27. III. The Internal Ear, or Labyrinth, is the complex organ
in which the terminal fibrils of the auditory nerve are distributed
and the end-organs of hearing situated. It lies in a series of cav-
ities channelled out of the petrous bone. It consists of three parts
—the Vestibule, the Semicircular Canals, and the Cochlea. In each
osseous part a membranous part is suspended, corresponding to it
in shape, but filHng only a small portion of the bony cavity which
contains it. It is in the labyrinth that the acoustic waves trans-
mitted by the tympanum are analysed and changed from a physi-
cal molecular process to a nerve-commotion, by the special end-
apparatus of hearing.
(A) The Vestibule is the central cavity of the internal ear ; it is
the part of the labyrinth which appears first in animals and is most
constant. The membranous vestibule is composed of two sac-like
dilatations-the upper and larger of which is named utriculus, the
lower mcculas. In its outer wall is the fenestra ovalis ; its anterior
wall communicates with the scala vestibuli of the cochlea, and at its
posterior wall the fine orifices of (B) the Semicircular Canals open
190
THE HUMAN EAE.
into the utriculus. These canals are three in number, are bent so
as to form nearly two-thirds of a circle, and are about, an inch in
length and ^^ of an inch in diameter. They are called the supe-
No. 1.
No. 3.
No. 3.
Ke vaa
Ks \ \ ^^
■?pa
Fig. 65. No. 1, Osseous Labyrinth of the Left Ear, from below ; No. 2, of the Right Ear, from
the inside ; No. 3, of the Left Ear, from above. (Henle.) Av, aqueduct of vestibule ; Fc. fossa
of the cuchlea ; Fee, its fenestra {rotunda) ; Pv, fenestra of the vestibule {ovalU) ; ha, external
ampulla ; h, external semicircular canal ; Tsf, traetua spirnH-i foraminosus ; vaa, ampulla of
the superior semicircular canal ; vc, posterior semicircular canal ; and vpa, its ampuUa.
rior, the posterior or vertical, and the external or horizontal canals.
The contiguous ends of the superior and posterior canals blend to-
gether and have a common orifice into the vestibule. They all
Fee
Fio. 66.— Osseous Cochlea of the Right Ear, ex-
posed from in front. ■•/, . (Henle.) t, section
of the division-wall of the cochlea ; +t, upper
end of the same. Fee, Fenestra ; H, hamulus ;
Md, modiolus ; Ls, lamina spiralis.
Fig. 67. — Cross-section through the Acoustic
Nerve and the Cochlea, ^/j. (Henle.) Nc,
nerve of the cochlea ; Nv, nerve of the vesti-
bule ; St, .scala tympani ; Sv, scala vestibuli ;
and between them the ductus cochlearis, Dc.
Ls and Md, as in preceding figure.
have a regular relative position, their planes being at right angles
to each other. Near the vestibule they dilate to about twice their
average diameter and form the so-called ampullce. Both the osseous
STEUCTUKE OF THE COCHLEA.
191
Ligamentuiii
spirals
vestibule and the osseous canals contain a fluid (the penlymi^h), in
which the membranous vestibule and canals are suspended ; the
membranous labyrinth is also distended with a similar fluid (the
endolymph).
(C) The Cochlea is by far the most complex part of the laby-
rinth ; it is about ^ of an inch long, and is shaped like the shell of
a common snail. It, too, consists of a membranous sac embedded in
the osseous cavity. The whole passage of the cochlea is imperfectly
divided into two canals by a partition-wall of bone, which is wound
2|- times around an axis (the modiolus), from the base to the apex,
somewhat like a spiral stair-case. It is called the osseous lamina
spiralis. Of the two canals or passages thus formed, the one which
faces the base of the cochlea is called the scala tympani ; since it
has its origin in the cir-
cular aperture (fenestra
rotunda) which leads to
the tympanic cavity. The
other, which faces to-
ward the apex, opens
into the vestibule, and
is called the scala vesti-
buli. At the apex of the
cochlea these two scalae
communicate with each
other through a small
hole [helicotrema). The
division of the mem-
branous cochlea is com-
pleted by a membrane
(the basilar membrane, or membranous spiral lamina), which bridges
the interval between the free edge of the osseous spiral lamina and
the outer wall of the passage ; it is attached to this wall by the spiral
ligament. Another membrane (the membrane of Reissner) arises
from a spiral crest (limbus, or crista spiralis) attached to the free
edge of the osseous lamina, and extends to the spiral ligament, so
as to form a small aqueduct between it and the basilar membrane
(the scala intermedia, or ductus cochlearis, or canal of the cochlea).
It is in the vestibule, in the ampullae of the canals, and in the scala
intermedia that the nervous end-organs of hearing are to be found.
§ 28. The auditory nerve, on approaching the labyrinth, divides
into a vestibular and a cochlear division. The former enters the
vestibule and subdivides into five branches — one for the utriculus,
one for the sacculus, and one for each of the three ampullae. In
Fig.
^7i
3. — Section through one of the Coils of the Cochlea.
(Schematic, from Gegenbaur.)
192
THE HUMAIST EAE.
each of these dilatations the membranous wall forms a projecting
ridge, called the crista acoustica. The endothelial investment of
the crista is elongated into columnar cells, intercalated between
which are fusiform cells. Each of the latter, according to Max
Schultze, and others, has the peripheral and the central process
with which we are already familiar in the nerve-cells of other end-
organs of sense. The peripheral process projects into the eudo-
lymph as an auditory
hair ; while the central
extends into the subendo-
thehal tissue where the
nerve-plexus of the audi-
tory nerve ramifies, with
the terminal branches of
which it is probably con-
tinuous. According to
more recent observers
(Eetzius and others) the
auditory hairs are con-
nected with the columnar
cells, and do not project
into the endolymph, but
into a soft material of in-
distinctly fibrillar struct-
ure. The inner surface
of the epithelium of the
crista is thus clothed with
a thick-set " wood " of
these hairs. Max Schultze
found their length to be
about ^1^ inch — their ul-
timate ends, however, be-
ing too fine to discriminate. Calcareous particles, called " ear-
stones " (otoliths) apj)ear in both saccule and utricle, embedded in
a soft matrix and lying in contact with the nerve-epithelium. In
the vestibule the hair-like prolongations of the epithelial cells are
more scanty than in the ampullae.
§ 29. The terminal nerve-apparatus of the cochlea is even far
more complicated and remarkable. The cochlear branch of the
auditory nerve pierces the axis of the cochlea (modiolus) and gives
off lateral branches which pass into the canals of the osseous spiral
membrane. Here they radiate to the membranous spiral lamina,
and are connected with a ganglion of nerve-cells ; beyond the gan-
Fig. 69. — Scheme of the Nerve-endings in the Ampullse.
(After Kiidiiiger.) 1, membranous wall of the anipiillag,
with a structureless border. 2 ; through which the nerve-
fibre, 3, sends its axis-cylinder, 4 ; 5, plexiform connection
of the nerve-fibres ; 6, auditory cells ; 7, supporting cells ;
8, auditory hairs.
THE OEGA]^ OF CORTI.
193
glion they form a plexiform expansion, from wliicli the delicate
fibrils — losing their medullary sheath and becoming extremely
fine axis-cylinders — pass through a gap in the edge of the lamina
into the organ of Corti. The connection of their ultimate fibrils
with the cone-cells of this oi'gan may be assumed, but is difiicult to
demonstrate.
The organ of Corti is situated on that surface of the basilar
membrane which is directed toward the ductus cochlearis. Its
structure is a wonderful arrangement of cells. Some of these cells
are curved, elongated, and placed in two groups — an inner and an
outer. They are called the "rods," or "pillars," or ''fibres of
Fig. to. — Organ of Corti in the Dog. ^00/^. (Waldeyer.) h — c, homogeneous layer of the basilar
membrane ; u, its vestibular layer ; v. its tympanal layer ; d, blood-vessel ; f, nerves in spiral
lamina ; g, epithelium of spiral groove ; A, nerve-fibres passina; toward inner hair-cells, /, k ; I,
auditory hairlets on inner hair-cells ; / — l^, lamina reticularis ; m, heads of the rods of Corti
jointed together ; the inner rod seen in its whole length ; the outer one broken off : n, cell at
base of inner rod ; p, q. r, outer hair-cells ; s. a cuticnlar process probably belonging to a cell
of Deitcrs : t, lower ends of hair-cells, two being attached by cuticular processes to the basilar
membrane ; to, a nerve-fibril passing into an outer hair-cell ; «, a sustenticular cell of Deiters.
Corti." The cells of the inner grouj) rest by a broad foot on the
inner part of the basilar membrane, project obliquely forward and
outward, and expand into a dilated head ; the cells of the outer
gi'oup rest in the same way, incline forward and inward, and fit
into a depression in the head of the cells of the inner group. The
two thus make a boio, which arches over an exceedingly minute
canal (the canal of Corti) formed between them and the basilar
membrane. These rods of Corti increase in length from the base
to the apex of the cochlea. The basilar membrane is composed
of fibres arranged in a transverse direction, so that each rod rests
upon one, or upon a pair of these fibres. Internal and almost
parallel to the inner group of rods is a row of compressed conical
13
194 THE HUMAN EAE.
cells with short and stiff hair-like processes [inner hair-cells).
External and almost parallel to the outer group are four or
five rows of hair-cells {outer hair-cells) which are attached to the
basilar membrane, while their other extremity projects as a brush
of hairs through the reticular membrane (membrane of Kulliker).
This latter membrane is a very delicate framework, perforated
with holes, through which the hairs of the outer hair-cells project,
and which extends from the inner rods to the external row of hair-
cells. It acts as a support for the ends of these cells. The inter-
val between the outer hair-cells and the spiral ligament is occupied
by cells of a columnar form (the sujpporting cells of Hensen). The
organ of Corti is covered over and separated from the endolymph
of the ductus cochlearis by the so-called membrana, tectoria.
§ 30. The problem before the labyrinth of the ear is in part the
same as that solved by the tympanum, namely, the problem of con-
veying the acoustic waves to the true end-apparatus of hearing.
The repeated shocks of the stirrup at the fenestra ovalis — and per-
haps, in far less degree, the pulsations of air at the fenestra ro-
tunda— produce waves in the fluid of the labyrinth. Any mole-
cular oscillations of this fluid, thus occasioned, cannot, however,
act directly as the appropriate stimulus of the sensations of sound.
Since the dimensions of the whole mass thrown into vibration are
so small in comparison with the length of the acoustic Avaves that
the extension of the shock from the stirrup would be practically
instantaneous tln-oughout, and since the surrounding walls may be
regarded as absolutely immovable by any such impact, the laby-
rinth-water would act as an incompressible fluid. It would, there-
fore, be unsuitable for the transmission of various kinds of acoustic
waves. But different parts of the labyrinth are capable of yielding
to the waves in the fluid caused by the repeated shocks of the
stirrup. Four such places, into which, as they yield, the fluid of the
labyrinth can retreat (as it were) are designated by Hensen ; ' these
are the two openings of the aqueduct of the vestibule, the mem-
branes of the aqueduct of the cochlea, the pores of the blood-vessels
in the bone, the membrane of the fenestra rotunda by bulging out
into the tympanic cavity. Impulses started in the fluid of the
labyrinth would thus result in its movement back and forth, so as
to produce a friction of the end-apparatus. This friction would
be increased by the action of the otoliths, or minute calcareous
particles, found in the fluid. Thus the waves started at the fenes-
tra ovalis would be diffused over the vestibule and into the scala
vestibuli of the cochlea, where they would flow to its head, being
' In Hermann's Handb. d. Physiol., III., ii., p. 106.
THE ATSTALTSTS OF SOUKDS. 195
prevented by the separating membrane from entering the scala
tj'inpaui. To what extent these waves flow through the helico-
trema, or small hole at the apex of the cochlea, into the scala tjm-
pani, and wliat are the exact relations between the waves in this
latter scala and those in the scala vestibuli — cannot be stated con-
fidently. Nor can the exact part of the basilar membrane at which
the excitation of the end-organs by the oscillations of the structure
begins, be indicated with certainty. This membrane is, however,
undoubtedly thrown into vibration through the unequal pressure
of the moving fluid ; and by its vibration it excites the nervous
structures Avith which it is intimately connected.
§ 31. A still more difficult problem for the labyrinth to solve
may be described in one word as a problem of "analysis." The
inner ear is not, indeed, contrived so as to reproduce changes in
the form of the acoustic oscillations, as such, after the manner in
which these changes can be made apparent to the eye or to touch.
But all our analogies for the analysis of composite tones — the
" clangs ■' or musical notes of ordinary experience — are derived from
the process of sympathetic vibrations. We are led, then, to inquire
whether any part of the structure of the ear is capable of enough
such sympathetic vibi'ations to account for the experience which
we have in recognizing all the possible degrees of pitch in the scale
of musical sounds. The structure must also be such as to receive
the impressions produced by a number of simultaneous tones, com-
posing a harmony. Moreover, it must be such as to represent
tones that follow each other in rapid succession, as do the notes of
a melody. The sympathetic vibratory apparatus of the labyrinth
must therefore cease its vibrations immediately upon the cessation
of the sounds in sympathy with which it vibrates. In other words,
it must either have a damper, or be so constructed as to return
at once to a state of rest without such a damper. It must be capa-
ble of being thus excited, and of returning to a state of rest, no
fewer than five hundred times in a second, since the crackling
of electric sparks, between which the interval is no more than .002
of a second, can be heard as distinct noises. Still further, the end-
apparatus of hearing must suffice for all kinds of noise, as distin-
guished from musical (ones ; and it is extremely difficult to see how
the same apparatus which serves for the analysis of the clang can
also suffice for all the various sensations of noise.
The manner is not known in which the auditory hairs and stones
and cells of the vestibule and ampuUse, and the rods of Corti, the
fibres of the basilar membrane, and the conical hair-cells of Dei-
ters, in the cochlea, actually discharge the required functions. The
196 THE HUMAN EAE.
structure of the end-apparatus in the vestibule and semicireulai:
canals is plainly not adapted to the analysis of musical tones. The
otoliths found in the vestibule, and the hairs of the ampullse, are
not capable of regular sympathetic vibrations ; moreover, they form
no scale of structures corresponding to the scale of sensations of toue.
This fact has led to the assumption that these organs are designed to
act as the end-organs of noise instead of musical sound. The more
complicated structures of the ductus cochlearis do seem, on the
contraiy, to be adapted for the required analytic functions. It was
first argued by Helmholtz that the bov^s formed by the rods or
fibres of Corti are enough in number to constitute such a scale of
structures that this work of analysis can be assigned to them.
Some three thousand of these fibres, arranged in rows upon the
basilar membrane hke the keys of a piano-forte, if distributed over
seven octaves would give about thirty-three for a semitone. They
might then be supposed to be elastic ; and since they differ in
size, to be tuned for particular sounds, so that the sympathetic
vibration of each one of them cori-esponds to the sensation of a
given toue. But the rods of Corti are stiff and not easily vibratory ;
and their office is probably simply to constitute a support for the
hair-cells. Moreover, birds, which are undoubtedly capable of ap-
preciating musical notes, have no rods of Corti.
Hen sen has shown ' that the basilar membrane is itself in a good
degree gi'aded to pitch ; its continuous structure and expansion in
size from the beginning to the end of the ductus cochlearis en-
courage the assumption that its individual radii act like stretched
strings to respond to the different tones, from the lowest to the
highest. The calculations of Helmholtz have tended to confirm the
view of Hensen.. It is assumed, then, that the parts resting upon
this membrane would be moved up and down, and that the excita-
tion of the conical hair-cells — with which the terminal fibrils of the
auditory nerve are supposed to be connected — is thus brought
about. The number of the acoustic cells is claimed to be about
great enough to correspond to the demands made upon the organ
which shall be instrumental in the physical analysis required as a
basis for the sensations of musical tones. The claim is at best
doubtful. As Hensen himself remarks,^ the possibility is by no
means excluded that the working of this complicated and delicate ap-
paratus may be altogether different from that conjectured by all such
theory. In other words, the physiology of the peripheral mechanism
of hearing is as yet in a very incomplete and unsatisfactory state.
1 Zeitschrift f. wiss. Zool., XIII., p. 481 f.
2 In Hermaun's Ilaudb. d. Physiol., III., ii., p. 104 f.
EISTD-OEGANS OF MOTIOTST. 197
8 32. A brief description of the End-Organs of Motion, or motor
end-plates, will suffice for our purposes. In general, the termina-
tions of the efferent nerves are connected either with electrical
organs (as, for example, in the torpedo), or with secretory glands,
or with the muscular fibre. We consider only the last of these
three cases.
After an efferent nerve has entered the substance of the so-called
voluntary or striated muscle, it subdivides among the individual
muscular fibres, separating these fibres from each other. Such
nerve-twigs usually lose their medullary sheath, and their axis-
cylinder splits up into fibrils, whose exact mode of termination has
been much debated. It appears now to be demonstrated (by
Kiihne, Margo, Eouget, and others) that the axis-cylinder itself
pierces the sarcolemma or sheath of the muscular fibre ; that the
neurilemma becomes continuous with the sarcolemma ; ' and that
the fibrils, into which the axis-cylinder divides, form a flat, branch-
ing mass within certain peculiar, disk-shaped bodies situated inside
the sarcolemma, and called "motor end-'plates.'" In the non-striated
(or non-voluntary) muscles, the nerves divide and subdivide to form
more and more minute plexuses of nerve-fibres, which are distrib-
uted in the connective tissue that separates the muscular fibres from
each other. The exact relation between this extremely minute in-
tramuscular network of fibrils and the nuclei of the cells of mus-
cular "fibre " is not yet made out.
The shape and structure of the motor end-plates are different for
different animals, and even for different muscles of the same ani-
mal. Indeed, the mode of the termination of the motor nerves in
the muscle appears to be somewhat distinctive of the different
parts of the muscular structure. Sometimes the axis-cylinders are
somewhat enlarged, with strongly granular corpuscles attached or
adjacent. Sometimes a granular mass with its nuclei forms a kind
of base or floor for the terminal nerve-fibres ; and this eminence
may be elongated, elliptical, or circular. But the character and
variety of these forms are of no particular interest to psychology,
even as approached from the physiological point of view.
' The question of histology is debated, whether the neurilemma actually
becomes continuous with the sarcolemma. Strictly speaking, according to
Kiihne, it does not ; but then, strictly speaking, it is not continuous with it-
self. It is, as we have seen (p. 36 f), divided by the annular constrictions into
members which are separate structures. It is to be considered as fringed
out on its edge and cemented to the sarcolemma [See on this subject the
monograph. Die Verbindung d. Nervenscheiden mit dem Sarkolemm, Sepa-
ratabdruck aus der Zeitschrift fiir Biologie, by Kiihne.]
CHAPTEK YI.
THE DE^TELOPMENT OF THE NERVOUS MECHANISM.
§ 1. The life of the individual man, so far as it can be made an
object of immediate observation and scientific description begins
as an undifferentiated germ, "without apparent distinction of bodily
organs or of physical and psychical activities. This living germ
undergoes a development. Before it can be subjected to ordinary
inspection it has unfolded itself into an elaborate organism ; and,
in its normal relation to the other sj'stems of this organism (mus-
cular, respiratory, metabolic, reproductive, etc.), the nervous system
has acquired all its complex mechanism, consisting of an indefinite
number of parts. Wliat are the different stages of the development
of this nervous system, and what are the laws according to which
its different factors and organs become differentiated, it belongs to
the science of Embryology to describe. But it belongs to psychology
to make such doubtful inferences as suggest themselves concerning
the psychical activities that are to be ascribed to the unfolding
mind of the embryo. Psychology, indeed, attempts in such a case
to form a picture of those earliest and most obscure mental states,
the elements of which can no longer be rejDroduced or recombined
in the developed consciousness of the adult. To this fact is due,
in part, the doubt which clings to all such inferences. But this
doubt is also due to the fact that embryology itself is so incomplete,
even in respect to its possession of single facts, and yet more in-
complete in respect to its power to set forth any system of general
truths and laws.
Our knowledge of all the earlier states and changes of con-
sciousness is wholly a matter of the interpretation of states and
movements of the bodily organism, in terms of our own conscious
mental experience. If, then, it were found that certain physical states
and motions of the human embryo need for their interpretation
the assumption of preceding or accompanying mental states, we
should have the right to carry our psychological principles back to
the life of this embryo — even back to its beginning in the undif-
ferentiated germ from which the whole development proceeds.
THE TWO-FOLD PROCESS. 199
But as the case now stands, the proper physical science cannot
claim to have furnished us with the requisite description of these
antenatal-physical movements and states. Little use for the main
purposes of Physiological Psychology, therefore, can be made of
facts accessible as to the embryonic development of man. "We
might even seem warranted in passing by the whole subject with
two or three general observations like the following : The two-fold
life of man, both nervous mechanism and mind, begins in what is
apparent only as a physical unity, in that system of moving mole-
cules which constitutes the living germ. Out of this unity, and in
indissoluble connection with it, the two-fold human life then pro-
gressively develops. The mechanism unfolds itself, increases the
complexity of its molecular activities, runs its course of changes, and
is broken up again into its material elements. The mind manifests
itself in primitive activities, unfolds itself, increases the complexity
of its psychical life, and then ceases to make itself known through
the physical mechanism, when the mechanism itself is dissolved.
And all the while the molecular mechanism and the mind are most
closely and mysteriously correlated in their development as a to-
talit}', and in their particular activities.
But in spite of the fact that embryology furnishes psychology
with scanty material for any extended and trustworthy conclusions
with regard to the earliest activities and development of the mind,
at least a sketch of its principal outlines, so far as the nervous sys-
tem is concerned, seems desirable. Of knowledge fi*om direct ob-
servation concerning the early development of the human embr^^o
there is exceedingly little. Yet the comparatively few facts which
are indisputably known, throw considerable light upon the nature
and functions of the human nervous mechanism. Moreover, in cer-
tain most important particulars there is good reason to believe that
the earliest history of the development of the embryos of other
animals is substantially like that of the human embryo. The very
first things in the life of the chick — or better, one of the mammals
—for example, may be described as probably holding good in all
important respects for the life of man. And when those diifei'ences
wlaich are most strikingly human begin plainlj'^ to appear, they
show what parts of the nervous system are most worthy of em-
phasis as distinctively connected with man's mental life.'
§ 2. The immature ovarian ovum of the common fowl — lil^e that
' The following description is taken to a large extent, and in some places
almost verbatim, from Foster and Balfour's Elements of Embryology, London,
ly83, and F. M. Balfour, Comparative Embryology, vol. ii. , pp. 177 ff., Lon-
don, 1881.
200 EMBRYONIC LIFE OF MAN.
of every other animal — presents the characters of a simple cell. It
is seen to consist of a naked protoplasmic body which contains in
its interior a nucleus (the germinal vesicle) and within this a nucle-
olus (the germinal sjjot). It is enclosed in a capsule of epithelium,
called the "follicle," or "follicular membrane." As the ovum ma-
tures, the body of it grows in size and a number of granules make
their appearance in the interior ; while the outermost layer of the
protoplasm remains free from them. But as the granules grow
larger in the centre, other granules appear also in the periphery
of the ovum. The germinal vesicle, during the growth of the ovum,
travels toward the periphery where the protoplasm surrounding-
it i-emains comparatively free from granules. Accessory germinal
spots make their appearance. The cells of the follicular membrane,
which were at first arranged in a single row, now become two or
more rows deep ; and, whereas the immature ovum is naked, its
superficial layer is now converted into a radiately striated mem-
brane. Still later, a second membrane appears between this striated
membrane and the cells of the follicle ; and the former disappear-
ing as the ovum approaches maturity, the second membrane (called
the "vitelline") remains alone. Other changes which take place
after the ovum has ripened and has been discharged into the ovi-
duct, it is not necessary to describe. They result in the formation
of the accessoi-y parts of the egg. The only essential constituent
of the body of the ovum is an active living protoplasm.
§ 3. Impregnation takes place in the upper portion of the oviduct,
and consists in the entrance of a single spermatozoon into the
ovum, followed by the fusion of the two. The spermatozoon itself
may be considered as a cell, the nucleus of which is its head. On
entering the ovum, the substance of its tail becomes mingled with
the protoplasm of the ovum ; while the head enlarges, moves to-
ward and fuses with a part of the substance of the ovum, thus
constituting the nucleus of the impregnated e^Q. In this manner
the jDhysical and mental peculiarities of both parents are trans-
mitted or carried over to the offspring by means of the actual fu-
sion of substance derived from the bodies of both.
§ 4. A process known as segmentation or "yolk-cleavage" follows
the fecundation of the ovum. This process consists in a succes-
sive division of the ovum into a number of cells, from which all the
cells of the full-grown animal are, as it were, the lineal descendants.
This process has many variations among the different animals.
The chief peculiarity among the mammals is that the whole mass of
the yolk is subject to this change.
By segmentation the germinal disk of the ovum is broken up
THE OVARIAlSr OVUM.
201
into a large number of rounded segments of protoplasm, called the
blastoderm. Of these segments those that lie uppermost are smaller
than those beneath. The beginning of the two layers into which
the blastoderm divides is thus made. The behavior of the nucleus
formed by the union of substance from the male and the female,
during the process of segmentation, has not been so satisfactorily
traced ; it appears probable, however, that a pi'ocess of division goes
on in it also. Other nuclei, thought to be derived from the primi-
tive nucleus, make their appearance immediately below the blasto-
derm. The distinction between the upper and lower layers of the
blastoderm now becomes more obvious, for the segments of the
former arrange themselves side by side, with their long axes vertical,
as a membrane of columnar nucleated cells ; while those of the
latter continue granular and round, and form a close, irregular
net-work of cells, whose nuclei are not easily seen.
§ 5. The principal difference between the ovum of a mammal and
that of a bird depends upon the amount and distribution of the
food-yolk. The ovum of the mammal is small — the human ovarian
ovum being only from
t\s ^^ -ih of an inch
in diameter — because
it contains so little
food-yolk ; but this
small supply is dis-
tributed uniformly
throughout. In con-
sequence of the above-
mentioned difference,
the ovum is able to
break up into seg-
ments through the
whole of its protoplasmic mass. As the process of segmentation
goes on, the differences among the ova of different species of ani-
mals become more clearly marked. For example, in the rabbit,
although the details are differently described by different observers,
at the close of the process of segmentation the ovum appears to be
comj)osed of " an outer layer of cubical hyaline cells, almost en-
tirely surrounding an inner mass of highly granular, rounded, or
polygonal cells." In a small circular area, however, the inner mass
remains exposed. The outer cells soon close over the exposed spot
(called by van Beneden, hlaatopore), and thus form a superficial
layer. A narrow cavity then appears between the two layers,
which extends so as to separate them completely, except in the
Fig. Tl.
Fig. 72.
[GS. 71 and 73.— Fructified Human Egg of 12-1.3 days, seen
from the surface and the side. In the centre o£ the former is
what Keichert considers the embryonic area.
202 EMBKYONIC LIFE OF MAN.
region near to the spot originally exposed. The enlargement of
the ovum and of the cavity together, soon give the whole structure
the appearance of a vesicle with a thin wall and a large central
cavity. This vesicle is called the blastodermic vesicle. The greater
part of its walls is composed of a single row of outer flattened
cells ; while an inner lens-shaped mass of cells appears attached to
Fig. 73. — Vascular Area and Embryonic Area of the Embryo of a Babbit, seven days old. ^^j^,
(Kolliker.) o o, the vascular or opaque area ; ag, embryonic area; pr, primitive streak and
groove ; rf, medullary groove.
a portion of the inner side of the outer layer. The " blastodermic
vesicle " enlarges rapidly ; its inner mass of cells loses its lens-like
shape, becomes flattened, and spreads out on the inner side of the
outer layer. Its central part remains thicker and forms an opaque
circular spot on the blastoderm, which is the beginning of the area
where the embryo is to fol-m (the embryonic area).
§ 6. The immediately subsequent history of the development of
the mammalian ovum, until the appearance of the so-called "primi-
tive streak," is less perfectly understood : Foster and Balfour ' speak
of the following description as "tentative." In the embryonic
area the cells of the inner mass become divided into two distinct
strata, an upper one of i-ounded cells which lies close to the
flattened outer layer, and a lower one of flattened cells (the "hypo-
' Elements of Embryology, p. 316 f.
THE THREE GERMINAL LATEPwS.
203
blast"). The former becomes fused with the outer layer, and
thus gives rise to a layer of columnar cells (the " epiblast "). In
this way the embryonic area consists of two layers of cells ; the
upper one of which is the epiblast, and the under one the hypoblast.
The blastoderm at first, then, consists of only two layers, which
constitute a double-walled sac (the gastrula) ; but a third layer
soon makes its appearance between the other two. These three
l^jevB— epiblast, mesoblast, and hypoblast— are called "germinal
layers " and are found in the embryos of all forms of vertebrate,
and most forms of invertebrate animals. The middle one, or meso-
blast, arises from certain parts of the other two primitive layers, in
a manner which need not be described. From these three germi-
nal layers, all the different parts of the organism of the animal are
developed. The history of the development of every animal in its
earlier stages is, therefore, a narrative of the changes which take
place in the three layers of the blastoderm. The hypoblast^ is
the secretory layer ; and from it almost all the epithelial hning
of the alimentary tract and its glands is derived. The mesoblast
is the source of "the skeletal, muscular, and vascular systems, and
of the connective tissue of all the parts of the body. But it is the
epiblast which produces the central and peripheral nervous system,
the epidermis, and all the most important parts of the organs of
sense. It is to the development of the epiblast exclusively, then,
that we now direct our attention.
§ 7. The process of differentiating the layers of the embryo is
intimately connected with another, which results in forming a
Fig ''4 -Primitive Stroak of the Embryo of a Rabbit, eight days and nine hoiars old. 22"/,.
(Kmliker) No medullary groove has yet been formed, ax, primitive streak: pr primitive
groove f;;/, primitive fold ; ect, ectoderm (or epiUast) ; mes, mesoderm (or mesoblast) ; ent, en-
toderm {hypoblast).
structure known as the primitive groove. This process is substan-
tially alike in mammals and in birds. A short sickle-like thickening
of the blastoderm, which afterward becomes a " narrow strap-like
opacity"— due to a forward propagation (linear proliferation) of
204 EMBEYONIC LIFE OF MAN.
epiblast cells in a straight line — arises near the junction between
the pellucid and the opaque areas of the blastoderm, and stretches
inwai'd upon the embryonic area ; it is called the primitive streak.
The median line of the primitive streak then shows a shallow fur-
row, running along its axis. This furrow is called the primitive
groove. (Compare Fig. 73.)
§ 8. Now occurs the formation of the medullary groove. In that
portion of the embryonic area which is in front of the primitive
streak, the axial pai't of the epiblast thickens ; two folds arise along
the boundaries of a shallow median groove ; the folds meet in front,
diverge behind, and then enclose between them the front part of the
primitive streak. These are the medullary folds, and they constitute
the first definite features of the embryo. The part bounded between
these folds is called the " medullary plate ; " its supreme impor-
tance in the embryo ajopears in the fact that it is the portion of the
epiblast which gives rise to the central nervous system. At about
the time of the development of the medullary groove (a little earlier)
an important change is taking place in the constitution of the
hypoblast in front of the primitive streak. An opaque line ap-
pears, as seen from the surface, and is continued forward from the
front end of the streak, but stops short at a semicircular fold near
the front part of the pellucid area. This fold is the future head-
fold of the embryo. The opaque line is due to a concentration of
cells in the form of a cord ; it is the beginning of what is known as
the nolochord. It is to subsequent changes in connection with the
notochord that we are to look for the development of the distinct-
ively vertebral structure of the animal.
§ 9. From this point onward the shaping of recognizable parts
of the embryo proceeds rapidl}'. The pellucid area, which was at
first quite flat or slightly curved, has, in the process of its growth,
suffered a " tucking in " — as it were — ^of a portion of the blasto-
derm, in the form of a crescent. It is this tuck which, when viewed
from above, appears as a curved line marking the margin of the
medullary groove. Thus the blastoderm is at this spot folded in
the form of the i-eversed letter 8 ; the fold is the one already re-
ferred to as the "head-fold." Of the two limbs of this 8-fold,
the upper is continually growing forward and the lower is contin-
ually growing backward. As the head-fold enlarges rapidly, the
crescentic groove becomes deeper ; and at the same time, the over-
hanging margin of the groove rises up above the level of the blasto-
derm. The medullary folds meantime increase in height and lean
over from either side toward the middle line. They soon come in
contact in the region which will afterward become the brain, and
FIRST CEREBRAL VESICLE.
205
thus form a tubular canal (the medullary or neural canal), although
they do not for some time coalesce. As the upper limb or head of
the embryo becomes more prominent, the medullary folds close
rapidly, and, in the region of the head quite coalesce. The open
medullary groove is thus converted into a canal or tube, which is
closed in front but remains open behind. The fi-out end of this
Fig. 75. — Pore-part of an Embryo-chirk at the
end of the second day, viewed from the Dorsal
Side. 'I/,. (Kolliker.) V h. fore-brain ; A b I.
occular vesicles ; JIh. mid-brain : /?/*, hind-
brain : /T, part of the heart seen bulginsr to
the rig'ht side; Vom. vitelline veins; J/"*',
medullary canal, spinal part ; Mr', raednllary
wall of the mid-brain ; U w, proto-vertetral
somites.
Fig. 76 — Embryo of a Rabbit, eight days and
fourteen hours old. ^-'"/j (Kolliker.) a p.
pellucid area ; v. anterior edge of the circuit
of the head; A', fnre-brain ; //', region of
later mid-brain ; h'", position of the hinder
brain ; hz, po.sition of the heart ; rf, medullary
groove ; I'lr, medullary ridge ; uw. meso-
blastic somite; pz, lateral zone ; si?, vertebral
zone.
neural canal — having a more rapid grovrth than the rest — dilates
into a small bulb or vesicle, the ca\ity of which remains continuous
with that of the rest of the canal, while its walls are similarly formed
of epiblast. This bulb is the so-called first cerebral vesicle ; and the
lateral processes which soon grow out from its sides are called optic
vesicles. Behind the first vesicle, a second, and afterward behind the
second vesicle, a third is soon formed. Thus these three brain-buds,
206
EMBEYONIC LIFE OF MAN.
Hincl-hrain
Rudimentary
cerehellum
& medulla
or germinal Drains, are made. At the level of the hind end of the
head, two shallow pits appear (the auditory piti^) which are the rudi-
ments of the organ of hearing. Thus the closing-up of the medul-
lary canal has converted the original medullary groove into a
neural tube ; and three cerebral vesicles have been grown which
are to develop into the fore-brain, the mid-brain, and the hind-
brain.
§ 10. The most important changes which now take place in
the development of the nervous mechanism, are connected with
the growth of the three cerebral vesicles and with the flexure of
the medullary canal. The front portion of this canal— that is, the
fore-brain with its vesicles — in consequence of inequalities of
growth in the different
parts of the brain, be-
comes bent downward ;
this is the commence-
ment of the cranial flex-
ure. As the flexure pro-
gresses, the front portion
becomes more and more
folded down, so that the
second vesicle, or mid-
brain, comes to project in
front of it. From the
front part of the fore-
brain the vesicles of the
cerebral hemispheres
grow out and swell lat-
erally, so as to make two
buds corresponding to
the two hemispheres of
the brain. Each of these side-buds has a cavity which is continu-
ous behind with the cavity of the fore-brain ; each cavity becomes a
lateral ventricle of the brain. The original vesicle of the fore-brain,
having ceased to occupy its front position, is developed into the
parts surrounding the third ventricle. In the hind-brain, or third
cerebral vesicle, the part nearest to the mid-brain becomes marked
off by a constriction ; the hind-brain is thus separated into two
parts — the rudimentary cerebellum with the pons in front, the
rudimentary medulla oblongata behind.
§ 11. Various differentiations of the lining of the epiblast, which
is involuted along the cerebro-spinal cavity, take jDlace. Through
the length of the neural canal this lining is thickened at each
Plexus
chorioidc.
Foramer
Monroi
N. trig.
Fig. 77. — 4, Brain of an Embryo of the Rabbit. B, Brain
of an Embryo of the Ox. In both cases the side-wall of
the left hemisphere is removed. (After Mihalkovics.)
CRANIAL AISTD SPHSTAL ISTERVES. 207
side, so that tlie cavity is no longer circular, but resembles a narrow
vertical slit. In the region of the cerebral hemispheres the sides
and floor of the canal are much thickened, but in the region of
the third and fourth ventricles, its roof becomes excessively thin,
^ so as to foi-m a membrane consisting of scarcely more than a single
layer of cells.
§ 12. Another important event, at about this stage in the
development of the embryo, is the formation of the cranial and
spinal nerves. The cranial nerves sprout out of a continuous
band (the neural band), composed of two plates, which connects
the dorsal edges of the neural canal with the external epiblast.
This band separates from the epiblast and becomes a crest on the
roof of the brain, with its two plates fused together. The crest
extends forward as far as the roof of the mid-brain. As the roots
of the cranial nerves grow centrifugally and become established,
the crest connecting them is partially obliterated. The posterior
roots of the spinal nerves are outgrowths of a series of median
processes of cells that appear on the dorsal part of the cord. These
outgrowths are symmetrically arranged, and attached to the walls
of the cord ; but their original attachment is not permanent. Such
rudimentary posterior spinal nerves divide subsequently into three
portions— a rounded portion nearest to the cord, an enlarged
middle portion forming the rudiment of a ganglion, and a periphe-
ral portion forming the commencement of the nerve. The origin
of the anterior roots of the spinal nerves is less satisfactorily made
ou^.
§ 13. In the further development of the hind-brain the medulla
oblongata undergoes changes of a somewhat complicated character.
Its roof becomes extended and thinner ; where the two lateral halves
of the brain were at first united (at the raphe) a separation takes
place, so that the sole union of the two sides is by a single row of
cells. The thin roof of the fourth ventricle is thus formed. The
floor of the whole hind-brain becomes thickened, and on its outer
surface a layer of longitudioal non-medullated nerve-fibres appears.
The roof of the anterior part of the hind-brain, which has become
thickened instead of thinned out — thus forming the rudimentary
cerebellum — is developed, first, by the formation of the median lobe
(or vermiform process) and, afterward, by the swelling of its sides so
as to constitute the cerebellar hemispheres.
§ 14. The changes in the development of the mid-brain (or
mesencephalon) are comparatively simple. When the cranial flex-
ure has taken place, the mid-brain is left at the front end of the
axis of the body, as a single vesicle with a vaulted roof and a curved
208
EMBRYOlSriC LIFE OF MAK.
floor, whose cavity is known as the aqueduct of Sylvius. The cor-
uora quadrigemina of the two sides are marked off from each other
by the appearance of a vertical
furrow about the sixth month ;
and about a month later a
transverse depression sepa-
rates the anterior (nates) and
posterior [testes) pairs. The
thickening of the floor of the
mid-brain gives rise to the
crura cerebri.
§ 15. Of the two divisions
into which the fore-brain has
already become divided, the
posterior constitutes the so-
called " thalamen-eephalon."
Pig. 78.— Head of the Embryo of a Sheep, cut Tllis bodv is at first a simple
through the middle. 3/]. (Kiilliker.) u, under ■ -, \, n j. • m
jaw ; z, tongue ; s, septum ?iarmm ; occipitale vesicle, formed OI Spmule-
basilare ; th. thalamus opticus; vt, roof of the , i n •,! m e
third ventricle: cp. posterior commissure ; m//, sliapcd CellS, Wltll WailS OI
mid-brain divided by a fold into two parts ;/, falx - .„ j.i • i Ti„
cerebri ; /', terminal plate of the fore-brain. At nearly Unilorm thlCkUCSS. ItS
the prolongation of the line of fm is the foramen
of Monro, t, tentorium cerebelli ; cl, cerebellum ;
pi, plexus of the fourth ventricle.
floor gives rise to the optic chiasm
and the origin of the optic nerves,
and to the rudiment of the infundi-
bulum ; and its sides become thick-
ened to form the optic thalami, while
the interval between them enlarges
toward the base and constitutes the
cavity of the third ventricle. The
more complicated changes which its
roof undergoes give rise to the pineal
gland and other small surrounding
structures. It is the anterior and
larger portion of the fore-brain which
constitutes the rudiment of the cere-
bral hemisiDheres. In this cerebral
rudiment, also, a floor and a roof may
be distinguished. The former is de-
veloped into the principal basal gan-
glia, the striate bodies ; the latter into the structures of the cerebral
hemispheres proper. The formation of the striate bodies (corpora
striata) is in fact due to thickenings of the walls of the floor of this
Fig. 79 —Brain of Human Embryo of five
months, with Basal Ganglia laid bare.
Natural size. (Kolliker.) st, corpus
striatum ; o, optic thalamus ; la, ante-
rior lobe (lunatus) of the cerebellum,
and Ip, posterior lobe of the same ; ss,
semiltinariR superior, and si, inferior ;
p, pyramid.
DEVELOPMENT OF THE BKAHS".
209
rudiment. The laying of the commissures is the characteristic
feature of the development of the mammalian hemispheres. These
Tire the anterior commissure, the fornix,
and the corpus callosum. But into the
details of this process we do not need
to enter. One characteristic of the em-
bryonic development of mammals is the
early enlargement of the cerebral hemi-
spheres ; in the human embryo they are
even by the tenth week much larger
than all the other parts of the brain.
At this time they are hollow bodies
with comparatively thin upper walls, the
lateral ventricles being dilated and com-
municating with each other through a
wide opening, and with the thii'd ven-
by the foramen of Monro. They
from befoie backward, and thus
cover up, one after the other, the optic
thalami, corpora quadrigemina, and cere-
bellum. Their floor keeps on thicken-
ing, and. thus the striate bodies become
greatly enlarged, and project upward into
the lateral ventricles, giving these cav-
ities their arched form.
The following table, exhibits the rela-
tions, with respect to their development, in which the different
parts of the brain stand to its fundamental rudiments :
tricle
grow
Fig.
of
— Brain and Spinal Cord
Fcetiis, four months old.
(KOlliker.) h, hemispheres of
the cerebrum; m, corpora quad-
rigemina (or mesencephalon) ;
c, cerebellum; too, medulla ob-
longata ; S.9, spinal cord with
its brachial and crural enlarge-
ments.
f 1. Prosencephalon,
I Fore-brain.
I. Anterior prima- j
xy vesicle.
1 2. Tlialamencephalon,
1^ Inter-brain.
II. Middle primary J 3. Mesencephalon,
vesicle. | Mid-brain.
4. Epe ncephalon,
J Hind-brain.
I 5. Metencephalon,
1^ After-brain.
III. Posterior prima-
ry vesicle.
f Cerebral Hemispheres. Cor-
! pora Striata, Corpus Callo-
j sum. Fornix, Lateral Ven-
[ tricles, Olfactory bulbs,
f Thalami Optici, Pineal gland,
J Pituitary body, Third Ven-
[ tricle, Optic nerve (prima-
I rily).
f Corpora quadrigemina. Crura
) Cerebri, Aqueduct of Syl-
) vius. Optic nerve (secon-
l darily).
' Cerebellum, Pons Varolii;
anterior part of the Fourth
Ventricle
j Medulla Oblongata, Fourth
( Ventricle, Auditory nerve.
^ Taken from Quain's Anatomy (Ninth Edition), II.
14
p. 828.
210
EMBKTONIC LIFE OF MAW.
Fissura parieto-
Fig. 81. — Brain of a Six-months Human Embryo. Natural size,
(Kolliker.) ol, olfactory bulb ; /«, fissure of Sylvius ; c, cere-
bellum ; p, pons Varolii ; /, flocculus ; o, olive.
The more important convolutions and sulci of the cerebral hemi-
spheres (those called "primitive ") result from the folding of the
whole substance of
the wall of the hemi-
sphere ; the less im-
portant (the so-called
"secondary") consist
merely of depressions
and elevations of its
more superficial por-
tion. The former ap-
pear earlier — the first
of the primitive sulci
being the fissure of
Sylvius, which is visi-
ble before the end of
the third month. By
the end of the seventh
month almost all the principal features of the cerebral hemispheres,
both convolutions and sulci, are already fixed.
§ 16. The nervous parts of the eye are differentiations of certain
lateral growths of the germinal brain-buds, called the "optic
vesicles." The optic vesicles are outgrowths from the sides of the
first cerebral vesicle, and are originally connected with it by short
and wide stalks ; at first they stand out at nearly right angles to
the axis of the embryo. The stalks soon become narrower and thus
form the rudiments of the
optic nerves ; ' at the same
time the rudiments of the
retina are formed from the
vesicles themselves. The
bulb of the optic vesicle is
made into a cup with two
walls by doubling it upon
itself ; thus a second optic
vesicle or "optic cup" is
produced, as distinguished
from the original one. The
lens of the eye is made by
thickening some of the superficial epiblast and involuting it in-
ward over the front of the optic cup, or secondary optic vesicle.
' But His and Kclliker suppose these nerves to be formed by secondary em-
anation from tlie chiasm or nervous centre.
Fig. 82. — LouKitudinal Sections of the Eye of an Embryo,
in three stages. (From Remak.) 1, commencement
of the formation of the lens, I, by rlepression of a part
of h, the corneous layer ; u. r, the primitive ocular vesi-
cle is doubled back on itself by the depression of the
commencing lens. 2. the depression for the lens is now
encloscil, with the lens beginnine' to be formed on tho
inner side: the optic vesicle is more folded back. 3,
a third stage, in which the secondary ojjtic ve.sicle, g I,
begins to be formed.
. DEVELOPMENT OF EYE AISTD EAR. 211
This involution has at first the form of a pit, then of a closed
sac with, thick walls, then of a solid mass. The cavity between
the two walls of the optic cup is closed up by bringing the walls
into contact. The subsequent development of the different parts
of the eye is conditioned upon the fact that the walls of the
optic cup grow more rapidly than does the lens, and that their
growth, does not take place equally in all portions of the cup. It
is by changes in the surrounding mesoblast, which takes on the
character of an investment, that the outline of the eyeball is defi-
nitely formed (the choroid and sclerotic). The vitreous humor
also is a mesoblastic product which is supposed to originate as a
kind of transudation through the so-called choroid slit. Of the
two walls, the inner or anterior is originally somewhat thicker ;
and since, in most parts of the cup it grows more rapidly, it con-
stantly increases in relative thickness. But just in front of a line
which afterward becomes the ora serrata, both layers soon cease
to thicken and then completely coalesce ; thus the hind portion or
true retina becomes marked off from the ciliary ridges and the iris,
while the wide opening of the optic cup is narrowed into a smaller
orifice that constitutes the pupil. By differentiations of the inner
or anterior wall of the hind portion of the optic cup — its cells mul-
tiplying rapidly and undergoing morphological changes while the
wall is thickening — the different layers of the retina are formed. It
is a significant fact that in its early stage this wall resembles the
brain in its structure, and may be considered as a part of that organ.
It is not necessary to enter into a more detailed description of the
development of the different parts of the eye.
§ 17. The ear originally appears on either side of the hind-brain
as an involution of the external epiblast, sunk in a mass of the
mesoblast. It is then simply a shallow pit with a wide-open
mouth. The mouth closes up and the pit then becomes a closed
vesicle (the otic vesicle) which is lined with epiblast and sur-
rounded by mesoblast. As the walls of this vesicle thicken, its
cavity enlarges. The shape of the vesicle is at first nearly spheri-
cal, but it soon becomes triangulai', with the apes of the triangle
directed inward and downward. It is by elongating this aj)ex that
the rudiment of the cochlear canal is formed. Part of the vesicle
becomes stretched into a long, narrow, hollow process (the recess us
vestibidi), and from the outer wall of the main body two pi-otube-
rances grow, which are the rudiments of the vertical semicircular
canals. These parts of the auditory labyrinth are soon more clearly
defined. The cochlear canal is further elongated and curved ; the
recess us is also stretched out more ; and from a new protuberance
212 EMBRYONIC LIFE OF MAIT.
tlie horizontal canal is developed. Another protuberance, which
becomes apparent at the inner commencement of the cochlear
canal, is converted into the sacculus by being constricted on either
side. The rest of the cavity, into which all the other parts open,
may now be called the utricidus. Dilatations of the semicircular
canals form the ampullae. When the cochlear canal has reached two
and a half coils, the thickened epithelium of its lower surface
forms a double ridge, from which the organ of Corti is developed.
For the details of the structure of the labyrinth we refer to the
previous description of this end-organ of sense.
§ 18. All the coarser differentiations of structure to which refer-
ence has thus far been made are only the expression — as it were — •
of certain histogenetic changes which have been secretly taking
place. The laj'ing down of delicate threads of nervous tissue, the
proliferation of nerve-cells along definite lines of movement, have
resulted in combining these elements by a living process into the
organs of the neiwous mechanism. The white matter of the cord
is supposed to result from a difierentiation of the outer parts of its
superficial cells into longitudinal nerve-fibres ; the latter remain,
however, for a considerable time without their medullary sheath.
The white matter first appears in four patches at the front and
back of either side, in which the individual fibres seem like smaU
dots. The gray matter of the cord is formed by a differentiation
of the principal mass of the Avails of the medullary canal. The
outer cells first lose their epithehal-like arrangement, and then
become converted into true nerve-cells, with prolongations that
constitute nerve-fibres. The early histological character of the
parts of the brain which lie back of the cerebral hemispheres is
very similar to that of the spinal cord. In the floor of the hind-
brain and mid-brain a superficial layer of delicate nerve-fibres is
early formed. The cells internal to the nerve-fibres give rise to
the epithelial layer which lines the cavities of the ventricles and to
an outer layer of gray matter. In the fore-brain the walls of the
hemispheres become divided into two la3'ers, between which the
fibres of the crura cerebri interpose themselves. The inner layer
unites with these fibres to give rise to most of the white matter of
the hemispheres ; the outer layer of rounded cells becomes further
differentiated into the outer part of the gray matter, which has
comparatively few cells, and a deeper layer with numerous cells,
the latter forming the principal mass of the gray matter of the
cortex.
§ 19. The preceding description of the outlines of the develop-
ment of the human nervous mechanism is derived for the mosi
MECHAlSriCAL THEORY OF THE EMBRYO. 213
part, from 'the study of other embryos than those of the human
species. It is probably, however, substantially true for the latter
also. It is valuable for the purposes of Physiological Psychology,
chiefly as emphasizing vphat has already been said concerning the
structure and functions of this mechanism in its developed form.
The nature of the process by which the nervous system is devel-
oped, as well as the nature of the developed structure and its func-
tions, as far as physical science can go at all, leads us in the direc-
tion of a mechanical theory. But in respect to both, such a theory
is at present in an exceedingly fragmentary and uncertain condition.
Further investigations may largely remove the present limitations.
But the most complete theory possible can hardly be more than
a statement of the order and extent of physical changes, the real
causes and meaning of which it lies beyond the power of a mechani-
cal theory to give.
The impregnated ovum does, indeed, become converted into the
developed organism by an evolution that, at every step in its course,
appears as an alteration in the arrangement of material molecules,
under conditions derived from the original nature of the molecules
themselves, from their necessary relations to each other, and from
the action of their total environment. By division of that which
was single into several parts, by bending of that which was straight,
by stretching in one direction and compressing elsewhere, by swell-
ing and dilating in the various outlines under the influence of press-
ure, by folding and tucking in so as to close up an opening here
and form another there, by laying down cells of the same kind in
right lines or grouping them in masses, etc. — in brief, by motion
of pai'ticles of matter in such way that the motion of each is con-
ditioned upon that of the others, the nervous mechanism is built
up. What it can accomplish in the way of further molecular mo-
tion, after it is thus built up, depends of course in large measure
"Upon what it is made to be by the very process of building. Bow
far it is possible even to propound a mechanical theory of the build-
ing process belongs to the speculations of embryologists to con-
sidei*. It is our next problem to consider as a whole the few data
upon which it has been thought possible to base a mechanical
theory of the behavior of the nervous system after it has once beea
constructed as a result of the embryonic process.
CHAPTER YII.
MECHANICAL THEOEY OF THE NEEVOUS SYSTEM.
§ 1. The macliine-like nature of much of tlie structure and move-
ment of the human body does not escape the most ordinary obser-
vation. When this body, either as a whole or with respect to some
of its parts, changes its position in space, its various masses sup-
port and act upon each other in essentially the same manner as
the masses of matter which compose the parts of any machine con-
structed by human skill. Such movement is possible for it, because
its framework of boues has a rigidity sufficient to sustain the other
less rigid organs ; and because the bones are so divided, and yet
articulated, that they can assume different relations toward one an-
other in accordance with the simplest principles of mechanics.
The laws of the lever, of the pulley, the ball-and-socket joint, etc.,
need no modification when applied to this particular machine of the
human body.
The action of certain other of its parts, which do not belong
to the bony framework but which are of muscular or epithelial
stnicture, is also plainly of the same machine-like character. The
movement of the heart, for example, is in part to be explained as
that of a pump with chambers and valves ; and the flow of the
blood thi'oug-h the arteries as that of a fluid pumped through con-
duits, of unlike and changeable sizes. So, too, the lungs may be,
with considerable propriety, compared to bellows which alternately
suck in and expel the surrounding atmosphere. The optics of the
eye and the acoustics of the ear are special only so far as the stnict-
ure of the organs makes necessary a special application of the gen-
eral laws of those sciences. Moreover, the distribution of the
fluids among the tissues of the body takes place under the laws
which govern the distribution of fluids generally when separated by
membranes which they can permeate. Nor is the chemistry of the
same tissues and fluids by any means wholly unlike that with which
the experiments of the laboratory make us familiar. When, how-
ever, we begin to speak of those changes of relative position which
take place at extremely minute distances among the molecvdar ele-
MACHIJSrE AND MECHAIVTISM. 215
ments of which the larger masses of the body are composed, we
seem compelled to drop the conception of a machine and to seek
both another conception and another title.
The very attempt, then, to explain the motion of the more purely
machine-like parts of the human body, leads us to consider certain
activities of other parts for which the word "mechanism " is more
appropriate. The movement of none of the more or less rigid or-
gans of the body originates within these organs themselves. The
changes of relative position in the parts, with which the ordinary
laws of mechanics deal, imply antecedent molecular changes in
other parts with which these laws cannot deal. The motion which
finds its final expression in the swing of the arm, or of the leg, in
the lifting of a weight, and even in the contraction of the heart, or
in the rising and falling of the chest, does not begin in arm, or leg,
or ribs, or diaphragm, or cardiac muscles. The change of position
of so considerable masses of matter is but the summing-up of in-
numerable minute molecular changes which began within the body,
but outside of the masses themselves. If, for example, we inquire
as to what causes the bones to move — however strictly their mo-
tion, once begun, may follow the laws of mechanics — the answer is
to be found in the pull of the tendons, or cord-like structures,
which are attached to them. And if we then inquire, What causes
the tendons to pull upon the bones by means of their attachment ?
the answer must be, That it is the contraction of the muscles which
pulls upon the tendons.
The next step in following this chain of causes, however, intro-
duces us to a different class of considerations from any of the fore-
going. For we cannot say that the contraction of the muscles is
caused by the pull of the nerves upon them. The movement of
muscular fibre in contraction is an altogether dififerent affair from
the movement of the bones as they are pulled by the muscles ; nor
do the nerves act upon the muscles as the muscles act upon the
tendons. The elasticity of the muscles is, indeed, a mechanical
quality, like that of which we avail ourselves in the construction of
machines. But the quality of elasticity does not fully explain the
behavior of the so-called muscle-nerve machine when its muscular
tissue is contracting or relaxing. Yet the Hving muscle, in itself
considered, may certainly be looked upon as a molecular mechan-
ism. It is a system of minute particles of matter which act upon
each other at indefinitely small distances ; and which, when any
motion is set up at one part of it, propagates such motion accord-
ing to laws that are given in the very constitution and arrangement
of the particles themselves. This is precisely what we understand
216 THE ISTEEVOUS SYSTEM A MECilANISM.
by a pbj-sical molecular mechanism. The office of the nerve with
respect to the muscle is simply, as we know, to start that molecular
activity which it is the function of the irritated muscle itself to ex-
ercise. The nerve, however, cannot perform its office of irritating
the muscle without being in a state of molecular commotion called
the " excitement " of the nerve. And, further, this excited condition
of that jDart of the nerve which is in immediate contact with the
muscle is itself a state of the nerve which has been propagated from
a distant point of the nervous matter. All the machine-like move-
ments of the masses of the body require us, therefore, to look for
their origin in minute molecular changes that originate in its ner-
vous elements. And for the further account of these neural molec-
ular changes we are to look to a mechanical theory of the nervous
s^'stem.
§ 2. The basis for a general view of the nervous system as a
mechanism has been laid in all the preceding examination ; and
it cannot be denied that the results of this examination are such
as to dispose us favorably toward the attempt to develop such a
view into a complete mechanical theory. Physical science, as a
matter of course, strives to establish such a theory. It knows no
other way of considering any group of phenomena when brought
before it for examination. To deny totally the application of the
conception of a mechanism to the action of the nervous system
would be to refuse to apply to its phenomena the same scientific
treatment which we apply to all other physical phenomena. To
limit, a priori, such application would be to restrict improjperly, on
merely theoretical grounds, the area of the phenomena with which
such science is entitled to deal. The fact that molecular changes
here are correlated with another class of phenomena which we call
" mental," in no wise destroys the propriety of pushing our physical
science of the nervous system to its furthest possible limits. The
movements of all material bodies, whether in the elemental shape
of the molecules, or in the shape of the same molecules when aggre-
gated into masses, as well as the laws under which such bodies in
movement act and react upon each other, constitute the legitimate
sphere of physical science. But it is to a system of interacting
molecules that the conception of mechanism especially ajDplies.
The aim of physical research with regard to any given system of
this kind is, therefore, not accomplished until all the movements
of its different parts are explained in the light of a consistent
mechanical theory. This general principle of all physical science
neither needs nor permits a special exception in the case of the
human nerves, organs of sense, and brain.
. THE CONSTITtTTIOlSr MECHATSTICAL. 217
On the other hand, the very unsatisfactoiy condition of the data
for a mechanical theory of the human nervous system has been im-
plied in each of the preceding chapters. It -will appear all the
more plainly now as we present briefly a statement of two or three
such theories in the form in which it has been found possible for
different investigators to state and to defend them. Nor can we
express much confidence that physics and physiology combined
will ever be able to point to a complete theory of so intricate and
delicate a mechanism as this nervous system. Moreover, we do not
by any means affirm that a purely mechanical treatment, however
complete, would of itself suffice to furnish a satisfactory understand-
ing of all the phenomena ; or even that the phenomena in general
could by any possibility be brought solely under the terms of such
treatment. We only affirm the unrestricted right of jDhysical sci-
ence to attempt, in the light of the conception of mechanism, an ex-
planation of the nervous system as well as of all other physical
subjects ; and also its right to its ^Dersistent faith that — So far as
■physical science can explain any such subject, all the s^Decial difficul-
ties of the nervous system can be fitly considered only in this way.
§ 3. The chemical constitution and structural form of the ele-
ments of nervous matter require that the system which they com-
pose should be regarded in the light of the concej)tiou of mechan-
ism. It is true that physical science cannot give an accurate descrip-
tion of the chemical processes which take place in the formation of
the nerve-fibres and nerve-cells, or during their functional activity ;
it cannot do so much as this for the living tissues generally. But
it finds here the same chemical elements which exist elsewhere
in nature, esj)ecially the four elements, oxygen, hydrogen, nitrogen,
and carbon. It nowhere finds these elements behaving differently
in the nervous system from the way in which it is their nature to
behave elsewhere, under similar circumstances. And the fact that
precisely similar circumstances do not occur to induce the same
combination and interaction of these elements outside of the ner-
vous sj'stem, is traced back to its causes in a succession of occur-
rences that all have the character belonging to the chemistry of
living tissues. We know of no sap which is suitable for forming-
organisms in general, but which is itself a perfectly homogeneous
fluid. Nucleated granules in the very chemical constituents which
give conditions to all the subsequent activity of the molecules, are
revealed by microscopic examination of those cells from which the
whole body springs. This fact, together with the character of the
subsequent process, may lead some to insist that a certain special
form of energy (called "vital force," or by some less obnoxious
218 THE NERVOUS SYSTEM A MECHANISM.
title), is marslialling the minute particles under its superior control
But such way of considering the phenomena — whether admissible
or inadmissible — does not at all help us to dispense with the purely
mechanical point of view. In the original living germ with which
the organism began, and in all its subsequent development, every
chemical change in nervous matter is nothing more than a move-
ment of physical molecules, strictly under the conditions furnished
by their constitution and previous arrangement.
The general significance of the chemical constitution of ner-
vous matter, with reference to a mechanical theory of the nervous
system, is by no means wholly obscure. It is obvious that all the
energy expended in the movement of the body as a whole, or of its
larger masses, originates in minute molecular changes. The latter
changes have, of course, a direct relation to the chemical constitu-
tion of the tissues in which they occur. The muscular fibre can
contract because its molecules admit of that rearrangement in
which the contraction essentially consists ; for doing the amount of
work implied in such rearrangement, this fibre is, of course, depen-
dent upon its own chemical constitution. But the source of the
excitation of the muscle is to be found in antecedent molecular
changes within the nervous system ; indeed, all the changes that
are to be summed up in the work done by and within the rigid
masses of the body have their origin here. It accords, then, with
the mechanical conception of the nervous system that its chemistry
should be just such as we have seen that it actually is. Nervous
matter holds in store a large amount of energy that is easily dis-
posable ; of energy that will be yielded freely and rapidly if any-
thing occurs to start the process within the system of molecules
of which such matter is composed. For the molecules are of such
kind as readily break up and recombine their elements in simpler
forms ; in doing this they render kinetic a large amount of energy
which they have previously held latent.
No mechanical theory of the nervous system can explain the
meaning of all the various structural forms which the elements of
this system assume. It cannot be told, for example, what pecuUar
place in the mechanism belongs to the different shapes of nerve-
cells, bipolar, multipolar, stellate, etc. Nor can a complete picture
be drawn of the dift'erences in character which the nerve-commotion
takes as it passes from the nerve-fibres to the nerve-cells, or from
one nerve-cell to another. We can only insist upon the undoubted
general fact that all these structural forms have whatever signifi-
cance belongs to them, because they are themselves molecular
structures, capable of undergoing, in relation to each other, those
, THE AERANGEMENT MECHANICAL. 219
very changes in which the functional activity of the nervous system
consists.
§ 4. There can be no doubt that the arrangement of the nervous
elements into a system corresponds to the conception of mechanism.
A certain work of "concatenating" the different physical systems of
the body, and of adjusting its relations to the changes in its
environment, requires to be accomplished. This problem demands
a three-fold exercise of function ; it is a problem in the construction
of a mechanism. The nervous system actually is of threefold con-
struction ; its threefold construction is the answer which it prac-
tically makes to the above-mentioned problem. One part of the
complex problem consists in the conversion of certain of those
molecular motions which take place in nature outside of the living-
organism into molecular motion within the tissues of such organism.
The solution of this part of the problem is furnished by the end-
organs of the nervous system. The end-organs are those special
mechanisms which are adaj)ted to convert the molecular motions
called stimuli into the molecular motions called neural excitation.
That by far the larger portion of the eye and ear, for example, acts
in a purely mechanical way, there is no doubt. It is the office of
the great mass of the eye to transmit and refract the rays of light ;
of the ear to transmit and condense the acoustic waves. But when
the nervous elements of the retina and of the organ of Corti re-
ceive the physical processes transmitted to them, they transmute
these physical processes into physiological neural processes ; in
doing this they act as special molecular mechanisms.
The second j)art of the complex problem before the nervous sys-
tem consists iu the conduction in all necessary directions of these
neural processes ; only on this condition can distant parts of the
nervous system act, as it were, in view of each other, and thus the
whole body be bound into a living unity under the influence of
changes in its environment, and iu the ideas and impulses of the
mind. The nerve-fibres solve this part of the problem. This they
do by acting as mechanisms, which have such a molecular constitu-
tion and function that a commotion, started at any point in tbe
physical elements of the system, spreads from molecule to molecule,
in accordance with the laws of the system.
The third part of the same complex problem requires for its solu-
tion structures and functions still more intricate and inexplicable.
Incoming molecular disturbances must be modified and redistributed
so as to give rise to outgoing molecular disturbances along definite
tracts, in order that definite groups of muscles may be made to con-
tract. Only in this way can the whole physical organism, by a so-
220 THE NERVOUS SYSTEM A MECHANISM.
called reflex activity, adjast its condition, in view of the presence of
given kinds and degrees of stimuli. Moreover, the vital functions —
the movements that control respiration, digestion, circulation of the
blood and of other fluids, etc. — must be united so as to work to a
common end, and with the modified forms and degrees of their re-
spective energies, which the changing circumstances require. Still
further, not only must the neural processes set up by the end-or-
gans and conducted inward by the afferent nerves have a place of
meeting in j)i'oximity with the centres of origin for the correspond-
ing efferent impulses ; but all the neural processes in this place of
meeting must also be so modified and made mutually dependent
that they can be correlated, under psycho-physical laws, with the
processes of mind. It is the central organs which alone possess
the molecular construction and functions necessary for such won-
derful reflex and automatic activities. In their highest form — the
hemispheres of the human brain — they solve the problem of pro-
viding a system of molecules, whose constitution and changes may
be immediately related with the phenomena of mind. These central
organs are extremely intricate physical structures. It cannot be
pretended that even a beginning has been made toward a satisfac-
tory theory of their functional activity considered as a special case
in molecular physics. But this fact does not affect the confidence
which is based upon what is known of physical structures in gen-
eral, that in these organs, the changes wliich take place are essen-
tially of the same order as are those with which the science of mo-
lecular physics has elsewhere to deal. They are modes of motion in
which the behavior of each molecule, regarded as a constituent
element of the system, is conditioned upon the constitution and
behavior of the other members of the same system. That is to
say, the central organs must be regarded in the light of the con-
ception of mechanism.
§ 5. The general office of the nervous system may, then, be de-
scribed in somewhat the following manner. The development of a
rich and varied life, both animal and intellectual, requires a great
store of sensations and of motions. Tlie sensations are jDrimarily
designed to serve as signs of changes in the environment of the
animal to \^hich his condition must be adapted by movement of
his l)odily parts ; but they are also to serve as a basis for intel-
lectual attainment and development. The forces of external nature
continually storm the peripheral parts of the animal's body. In
order that any of these forces may act as the stimuli of sensations,
they must be converted into molecular motions within the tissues
of this body. In order, further, that the masses of the body may
. THE EQUILIBKATING MECHAlSriCAL. 221
constantly be readjusted to tlie external changes of which the sen-
sations are signs, the molecular motions must, in turn, be converted
into movements of these masses. In other words, a process of con-
stant interchange must take j)lace between the animal organism
and external nature.
Disturbances in one part of the body, by the play upon it of nat-
ure's energ}', instead of becoming injurious or destructive, are
thus made serviceable through inducing the needed disturbances
of other j^arts of the same body. The equilibrium on which life
depends is maintained. Moreover, the material necessary for self-
conscious development, for a growing knowledge of the so-called
outside world, is furnished through the conduction of these dis-
turbances to their common meeting-places iii the central organs.
To accomplish the general work of equilibrating the interaction
of the different jjarts of the body, of readjusting its condition to
the changing condition of its surroundings, some special construc-
tion and arrangement of material molecules is necessary. If the
work is to be done in a highly elaborate way, a very intricate ar-
rangement of an indefinitely great number of chemically complex
molecules is necessary. Such an an-angement is the human ner-
vous system. But just because its arrangement and function are
of this kind, it is a " mechanism." As a highly complex molecular
mechanism it utilizes the disturbances which arise from the en-
vironment. It binds together all the other systems of the body in
living reciprocity of energies and. functions. Its superficial parts
are so constructed that they can be set in motion by various forms
of physical energy — by light, heat, sound, chemical change, etc. ;
they are also adapted, fitly to modify the impressions thus received.
The molecules of its conducting nerves are so constituted and ar-
ranged that they can indicate the path along which the disturbance
thus occasioned must pass ; they can dictate the conditions and
laws under which its course must be completed. The molecules of
its central organs are capable of assuming inconceivably varied re-
lations to each other, of thus transmuting and redistributing the
nerve-commotions which reach them along the incoming tracts, and
even (it would seem) of starting automatically outgoing disturb-
ances in response to self-conscious sensations and ideas.
But all the foregoing offices of the nervous system are nothing
but the jnovements of physical elements, in constant reciprocal de-
pendence upon each other, though in response to excitations lying
outside of the system itself. To move thus is the function of a
molecular mechanism. So far as science can control the different
parts of the nervous system for experimental purposes, it finds
222 THE NERVOUS SYSTEM A MECHANISM.
them behaving in such a manner as to make a plain demand for a
physical and mechanical theory in explanation of their behavior.
§ 6. The foregoing description of the nervous system as a mech-
anism, like all similar descriptions, undoubtedly lacks scientific
quality. It is neither exact nor in such form as to admit of ex-
l^erimental verification. It is largely based upon conjectures, full
of gaps and assumptions ; and were it pressed at every point for
proof, it would be obliged to rely much upon general principles in
mechanics (the special applications of which to the case in hand are
by no means certain or obvious), and even to indulge in hopes and
promises with reference to the future, rather than present demon-
stration. May we not know more precisely the nature of the mo-
lecular changes which constitute the functions of nerve-fibres and
nerve-cells ? Cannot physical science help us to complete these be-
ginnings of a theory ?
In answer to the question just raised we have already seen how
little satisfaction is afforded on applying to the science of chemistry.
On general principles of physical science there can be little doubt
that the excitation and conduction of nerve-commotion is dependent
upon a chemical change in the nervous tissue itself. Moreover, we
know that the j)rocess of conduction in the nerve requires each of
its molecules to act upon the neighboring elements as the condition
of the process continuing. Nor can this process itself be a mere
impartation of motion, from molecule to molecule ; on the contrary,
the phenomena of electrotonus seem to show that it must also con-
sist in the setting free of energy which exists latent within the
molecules of the nerve-substance. These molecules contain, then,
by virtue of their constitution, stored or potential energy which is
converted into kinetic energy in the propagation of the process of
excitation, and which is expended, in part, in either inhibiting or
increasing the energy of that process. Such potential energy can
scarcely be other than chemical.
Accordingly, we should be tempted to describe the process of
progressive excitation of the nerve somewhat as follows : Every
element of the nerve, by reason of its highly complex and unstable
chemical constitution, contains a large store of energy ; the excite-
ment of the nerve consists in the explosive decomposition succes-
sively of these elements of the nerve ; and the result of the decom-
position is the setting free of the stored energy to be expended in
part in the excitation of the next adjoining elements. The process,
then, is not altogether unlike the burning of a line of powder
grains. Such an hypothesis, however, would at once have to answer
several difficult questions. "Why does not the whole of the exjilosive
INTERFERENCES OF NERVE-COMMOTION. 223
substance burn up, instead of only an amount of it approximately
proportional to the strength of the stimulus which sets the process
ao-oing ? Analogies may indeed be found in the union of chlorine
and hydrogen under the action of light. What checks the process
in the nerve as a whole, and what limits it quantitatively in a differ-
ent way at different points in its course, so as to give the phenomena
of anelectrotonus and catelectrotonus ? (comp., Chap. III., § 19 f.).
Moreover, direct observation has as yet discovered no indisputable
evidence of functional chemical changes in the nerve-fibres. If
such changes exist at all they are exceedingly small.
§ 7. Allusion has been made (p. 119 f.) to the fact that the effect
of several excitations of a nerve-stretch is compounded, as it were,
in the action of the attached muscle. That is to say, excitations
which are simultaneous, or which follow each other with sufficient
and not too great rapidity, are summed up in the nerve, like mo-
lecular waves of nerve-commotion piled upon each other. Besides
such phenomena of " summation," there exist analagous phe-
nomena of so-called " interference ; " and, further, of the facilitat-
ing effect which one excitation has upon others following it along
the same paths of conduction, especially in the central organs.
These and similar phenomena tempt us to consider the activity of
the nervous substance in terms of an exceedingly complex sum in
the addition and subtraction of molecular disturbances of a wave-
like character. Elaborate experiments have been made to deter-
mine the laws under which such summation or interference of
electrical excitations takes place. Thus G. Valentin' assumes that
the case of the nerves comes under the general theory of molecular
waves that may either be piled upon each other, or may interfere
with each other. The interferences he calls " positive " when the
currents are moving in the same direction, " negative " when they
are moving in opposite directions ; and such currents may, of
course, be either ascending or descending. The character of the
interferences is to be defined by the way in which the nerve-muscle
machine responds to these four kinds of interference. The inter-
ference has a heightening effect (is erhohende) when the result
indicated by the behavior of the muscle is greater than the sum of
two single effects from the partial excitations that are compounded ;
a depressing effect when the result is less than this sum. If the
effect of the interference is such as to reduce the result to zero,
it is called inhibitory. Valentin concludes that, in case of inter-
ferences of excitations from one and the same current (with respect
' In PfliJger s Archiv, vii. (1873), pp. 458-496, article on the Interfer-
ences of Electrical Excitations.
224 THE NERVOUS SYSTEM A MECHAISTISM.
to degree, direction, etc.), the character of the effects produced
depends upon the original molecular constitution of the nerve.
Just as its constitution is decisive with regard to the nature of the
muscular contractions that follow a single excitation of the nerve,
so is it also decisive with regard to the results of interference.
These results, moreover, conform to the same laws after decapita-
tion or poisoning as before. And further, the same rules govern
in the case of interferences of two currents, if both the currents
are of about the same degree of strength. Finally, according to
Valentin, the same rules belong to the interferences that occur in
cases of reflex action, or of the stimulation of motor nerves through
the sensory, as those which apply to the direct stimulation of the
motor nerves. It is apparent that the only net gain from the fore-
going experiments consists in the information that the molecular
constitution of the nerves themselves determines all the variable
elements in the results of exciting them. But this would be an
assumption fairly made by every attempt at a physical science of the
nervous functions. And inasmuch as we can make no such veri-
fiable statements concerning the nature of this molecular constitu-
tion as will serve the purposes of a precise mechanical theory, it is
hard to see what advance has been gained toward the construction
of such a theory.
The jDhenomena caused by the reciprocal action of different ex-
citations within the central nervous system are, of course, much
more complex and difficult to bring under a theory of molecular
wave-like impulses, than are the phenomena of the comparatively
simple nerve-muscle machine. A fortiori, molecular physics is
unable to propose a satisfactory theory for the central organs.
According to, Exner,' many of the phenomena are covered by the
general principle that one excitation acts io facilitate or, as it were,
smooth the path for others passing, after only a brief interval, along
the same course. This principle he distinguishes from that of
''summation," when applied to reflex action. The latter term Exner
applies to the accumulation in the central organ of excitations
which, taken singly, are too weak to produce any reflex motion, but
which by their combined strength do produce such motion. The
principle of "facilitation," however, refers to the condition of the
central parts after the passage through them of a stimulus which
has already called forth some reflex action. Exner's experiments
led him to conclude that the motor excitation of some one ex-
tremity from the brain (that is, by stimulating, in the brain, the
so-called motor area of the extremity) facilitates the subsequent pas-
' Article in PflLiger's ArcLiv., xxviii., pp. 487 ff.
'PHYSICS OF THE CENTRAL ORGANS. 225
sage of reflex stimulus affecting the same extremity ; and, con-
versely, stimulating an extremity reflexly facilitates the passage of
a subsequent motor excitation from the area of the bi'ain to the
same extremity. Thus, for example, the reflex motions of the fore-
leg of a rabbit, produced by stimulating the toes of that leg, were
found to be increased in intensity if the so-called cerebral motor
centre of the fore-leg was also stimulated. Different reflex excita-
tions also may facilitate each other's effect in the same way. For
example, the sensory stimulation of the left foot has the effect of
facilitating the reflex act which, as it might appear, would relate
only to the right foot and its motor area in the central organ ; and
such reflex action of the right foot facilitates the contraction set
fz'ee in the same foot by stimulating the left-foot section of the spi-
nal cord. Exner was unable, however, to obtain any inhibitory
effect upon the motion of the extremities by stimulating various
other places of the cortex of the cerebrum, or by stimulating the
cerebellum. He also found that when one side of the cortex of the
cerebrum is stimulated by electricity so as to produce a condition
of tetanus in one extremity of the animal, the results of two excita-
tions— one as a reflex from the foot and one directly from the same
side of the brain — are compounded in a way which seems incom-
patible with any known form of the summation and interference
of molecular wave-like disturbances.
Indeed (to return to the simpler case), Griitzner ' seems justified
in saying that, strictly speaking, we cannot without qualification
even represent what takes place when two currents of electricity
act in combination upon a nerve, as though it were a matter of the
addition or subti'action of their separate effects. For it is possible
that an electrical current of an intensity equal to the d,mount of the
natural nerve-current (current of rest = a) and the current used as
stimulus (current of action = b), taken together (a + b), will not ex-
cite a nerve that shows no current at all, although the latter (b)
alone will excite the nerve if just previously the former {a) was
present in the nerve. The currents already existing in the nerve,
when the exciting current is applied, are, therefore, not simply
added to or subtracted from the latter ; but they produce molecu-
lar changes of an unknown kind which tend to induce the origina-
tion of so-called " cathodic " and "anodic" places in the nerve —
that is, places of exalted and places of depressed excitability.
Thus a weaker current will excite the nerve when it is in a condi-
tion of exalted excitability , a stronger current may fail to excite
the nerve when in a condition of depressed excitability.
' See Pfliiger's Arcliiv, xsviii., p. 144 f.
15
226 THE ELECTRICAL THEORIES.
How obscure and complicated are the molecular conditions con-
nected with the excitation of the nerve is further shown by the
effect of giving different treatments to the cross-section of the nerve.
If the nerve is simply cut, its behavior under stimulation is differ-
ent from that which occurs when it has been bound before the
cross-section is made. Binding the nerve produces, for some min-
utes after cross-section, a large increase of its excitability in the
immediate neighborhood of the injui-ed place ; this is true for all
kinds of stimuli, including the electric current in both directions.
From five to ten minutes subsequently, however, the making of the
current in the opposite direction to the current induced by cross-
section has frequently a diminished rather than an increased effect.
§ 8. On the whole, it would appear, then, that the ability to lay
even a basis for a strictly scientific molecular theory of the nervous
mechanism depends upon the ability satisfactorily to explain the
electrical process in the nerves and their consequent behavior under
electrical stimulation. It would by no means follow that a com-
plete theory for the comparatively simple phenomena of the nerve-
muscle machine would furnish the sure clew, not to say the full
explanation, of all the activities of the nervous system. On the
contrary, the evidence is overwhelming that the working of the
complete nervous mechanism involves other principles than those
which may be deemed sufficient for the case of the single nerve
and muscle when under electrical stimulation. But, plainly, the
more complex case cannot be solved without fii'st solving the far
less complex one. And yet the simplest possible case of nervous
molecular mechanism — the case that can be brought under the
most favorable experimental conditions — has thus far proved to
lie beyond oui" power to find a satisfactory scientific solution.
The two most important principles which must enter into any
mechanical theory for explaining the behavior of nerves in relation
to electricity are, according to Hermann : ' (1) the law of electrical
excitation, and (2) the law of the so-called current of action. The
phenomena upon which these laws are themselves based are chiefly
the phenomena of electrotonus and the phenomena of negative
variation.
It is a fact (see p. 114 f.) that the passage of the electrical current
through a nerve-stretch produces in the nerve a changed condi-
tion of excitabilit}^ called electrotonic. This condition is, however,
different for different parts of the nerve-stretch. It is dependent
upon the nearness of each part to the electrodes, it being greatest
in their vicinity. It is dependent on the strength of the polarizing
' Handb. d. Physiol., II., i., p. 193.
TIIEOJJY OF DU BOIS-EEYMOND. 227
current and on the length of the stretch through which it flows.
Its intensity is greater on the side of the anode than on the side
of the cathode. The condition may be said to be one of increased
excitabihty in the region of the cathode, of diminished excitabihty
in the region of the anode. Helmholtz found that the time of the
development of the electrotonic condition is not perceptibly later
than that of the electrical current which excites it ; the condition
originates at the moment of making, and ceases at the moment of
breaking, the polarizing current. Du Bois-Reymond concludes,
thereupon, that the electrotonic condition is spread over the nerve
with a speed equal to that of the process of excitation.
It is also a fact (see p. 117 f.) that, in the case of the nerve-stretch
as well as in that of the muscle, the galvanometer shows the pas-
sage of a current when one of the electrodes is placed at its cut
end and the other at its equator. It is a fact that this so-called
natural current, or current of rest, is diminished by the stimula-
tion of the nerve with an interrupted current, or by other means
of exciting it — the diminution being shown by the return of the
needle of the galvanometer toward the zero-point (the so-called
" vegative variation ").
§ 9. The two principal theories which have hitherto attempted
to account for the above-mentioned facts are the theoi'ies of du
Bois-Reymond and of Hermann. Du Bois-Reymond ' assumes
that in the substance of the nerve there exists an arrangement of
electro-motive molecules embedded in an imperfectly conducting
medium. Each molecule is like a minute battery with positive and
negative poles ; and the molecules present their positive surfaces to
the longitudinal surface of the nerve, their negative surfaces to the
cut ends or transverse sections of the nerve. The presence of these
molecules gives rise to currents in the medium which surrounds
them. Owing to the imperfect conductivity of the medium, such
currents flow in more or less concentric lines at some distance
from each molecule. The current which exists in the nerves
(exists, according to du Bois-Reymond, as natural to the nerve and
previous to its injury by cross-section), and which is made obvious
by the deflection of the needle of the attached galvanometer, may
therefore be regarded as the resultant of the numerous unobserv-
able currents belonging to the several molecules. In this way the
so-called " cui'rent of rest " is to be explained. Du Bois-Reymond
is forced to account for the fact that such natural currents are
' The views of du Bois-Reymond are to be fouud in his Untersuchungen
liber thierische Electricitat, 1848-49, and Gesammelte Abhaudluugen, etc.,
1875-77.
THE ELECTRICAL THEORIES.
either exceedingly small or wholly wanting in an uninjured mus-
cle by a very artificial hypothesis as to a so-called parelectronomic
region at the place where the ends of the muscle come into contact
with the tendons. His theory of electrotonus and of the negative
variation of the nerve-current is too complicated and doubtful to
be even stated here ; it is enough to say that his assumptions as to
"peripolar" and "bipolar" molecules, and the efiect of the elec-
trical current in reversing the molecules, etc., have little to com-
mend them to the practical workers in modern physics.
§ 10. The theory which Hermann,' and those who agree with
him, would substitute for the theory of du Bois-Reymond takes
its point of starting from a discovery made by Matteucci some
years ago. In 1863 this truly great investigator noticed phenom-
ena similar to those of the electrotonic condition of the nerves in
over-spun wires moistened with a conducting fluid. If an electri-
cal current is conducted to the moist covering of such a wire, the
needle of the galvanometer shows along every part of the wire the
presence of a current in the same direction with the primary cur-
rent, but with the strength of the former diminishing as the dis-
tance increases fi'om the points where the latter is applied to the
wire. No such cun-ent arises, however, if the wire is made of amal-
gamated zinc and its covering is moistened with a solution of sul-
phate of zinc. It appears, then, that the electrical condition of the
wire, when a current is conducted to it, depends upon the limiting
surfaces of its metal centre and of its moistened covering being po-
larizable. Very recently ^ Hermann has, as he thinks, still further
shown the possibility of explaining all the electrotonic properties
of the nerves after the analogy of Matteucci's discovery. A con-
ductor consisting of a central and a covering substance, with polar-
izable hmiting surfaces, as soon as a momentary electiic current is
conducted through any portion of it begins successively to exhibit
a current of the same kind at every other place in it ; the more
• distant the place from the one to which the cui-rent is applied the
later its appearance there, so that at the most distant places such
current may begin after it has for some time ceased at the primary
place. Now, in an analogous manner, every nerve-fibre may be as-
sumed to consist of a centre and covering substance, with polarizable
limiting surfaces. In the nerve-fibre the limiting surfaces needed
for the theory are j)erhaps actually to be found between the axis-
' The views of Hermann may be found in liis Untersucliungen znr Physiol-
ogie d. Muskeln u. Nerven, 1867-68, and in numerous later papers in PfliigerV
Archiv.
^ Pfliiger's Arcliiv, 1885, xxxv., p. 23 f.
THE THEORY OF HERM AISTIST. 229
cylinder and the medullary sheatli. Griinliagen,' however, affirms
that the polarization of the limiting surfaces of the nerve-fibre is a
consequence rather than a cause of the current in electrotonus.
The first and fundamental cause of this current he considers to be
the characteristic difference in the resistance, as conductors, of the
kernel and the covering of the nerve-stretch.
The so-called " natural current," or " current of rest," Hermann
does not consider it necessary to explain. What appears to be a
natural current Hermann holds to be in all cases the result of in-
jury. It is to be considered, then, as due to the peculiar molecu-
lar condition into w^hich certain parts of a nerve-stretch are thrown
by their mechanical or chemical destruction. In fact, whenever a
nerve is cut across, or any of its fibres are injured, the molecules
thus disturbed begin at once to die ; they then become negative to-
ward the other uninjured parts of the nerve. It is because of this
change in the dying molecules that the electrical current is devel-
oped. But all the parts of a wholly untouched and unexcited nerve
are, according to Hermann, " isoelectric." It is not necessary to
give the experimental evidence by which this investigator strives
to prove his opinion ; it is enough to say that this evidence is
strong, and nearly, if not quite, conclusive.
Accordingly', Hermann regards the negative variation as not due
to the diminution of any current previously existing, but rather as
a manifestation of the electro-motive forces which come into opera-
tion at the moment, and at the seat, of excitation. This current is,
therefore, the only true " current of action." Its rise and flow are
explained by the fact that every excited part of a nerve-stretch be-
comes negative toward all the other parts. As this wave passes
along the nerve-fibre, each minute portion becomes first negative
and then positive toward the adjoining minute portions ; and hence
the so-called "ad-terminal" and "ab-terminal currents" appear
along the nerve-stretch as fast as successive parts of its substance
reach their maximum of negativity. The excess of the ab-terminal
over the ad-terminal current manifests itself as the so-called '^'■neg-
ative variation."
The phenomena of electrotonus Hermann explains, as has already
been said, upon the basis of Matteucci's experiments. An inner
polarization, such as takes place between the wire and its moist-
ened covering, takes place between the substance which constitutes
the core of the nerve and one of its sheaths. The electrotonic cur-
rent is, therefore, simply due to an escape of the polarizing cur-
rent. It is wanting in the dead nerve, because the inner polariza-
' Pfliiger's Archiv, xxxv., p. 534 f.
2S0 THE ELECTEICAL THEORIES.
tion belongs only to the nerve in its living state ; it is stopped bj
ligature or by crusbing, because the nervous substance is thus
made into dead, indifferent substance, and the functional continu-
ity of the nervous core is destroyed. His detailed explanation of
" tetanic action-currents " and " phasic action-currents," and of the
jDhysiological phenomena of electrotonus and catelectrotonus, need
not be repeated. The one principle to which Hermann -would re-
duce all the electrical j)henomena derived from the cut nerve-
stretch is this : All excitable j^^otoplasm, when dying or irritated,
becomes negative toward its own univjured and unirritated parts.
Such is the nature of its electro-motive reaction.
§ 11. Objections have been made to the theory of Hermann, but
they can scarcely be said to be so formidable as those which he
brings against the theory of du Bois-Keymond. The most forcible of
them is, perhaps, the following : If the so-called currents of rest were
due solely to the negativity of the dying jjortion of the substance,
we should not expect that the current from the equator to the cross-
section would be greater than the current from a point nearer the
cross- section, seeing that the resistance is greater in the former case.
Hermann is himself ready to admit,' however, that no simple
scheme of polarization will fully satisfy the conditions of the prob-
lem offered by the behavior of the nerve-muscle machine under
electrical stimulation. " The platinum wire, with its moist sheaths,
is no model of the irritable nerve ; it is only a model of its elec-
trotonic properties." We must, therefore, after the discussion of
all analogies resort again to the unknown molecular constitution
and properties of the substance of the nerve, as being sui generis,
for oui' explanation of its peculiar physiological properties. Its
functions are a species of molecular change, connected, to be sure,
both with chemical changes and with other mechanical changes of
a wave-like character, and yet unlike them all ; and these molecular
changes, when the nerve is excited, ai^e propagated from point to
point along its course with a speed and according to laws which
have already been stated (see Chapter IH.). But further than this
we cannot as yet go with confidence in af&rming a mechanical the-
ory of even that simplest element of the nervous mechanism for ex-
perimental purposes — namely, the nerve attached to the muscle
and constituting the nerve-muscle machine.^
' See Handb. d. Physiol., II., i., p. 195 f.
- Further information upon the two theories of Hermann and du Bois-Rey-
mond may be found in Foster's Text-book of Physiology, pp. 101 ff. See, also,
a brief statement of Hermann's theory in the Journal of Physiology, I., pp,
196-213.
THE THEORY OF WUISTDT. 231
§ 12. A confession of ignorance might fitly close the entire dis-
cussion as to the possibility at present of a precise mechanical
theory of the nervous system. For on resuming the larger and
more Complicated inquiry, as to how the physiological functions of
all the nervous organs in their mutual relations may be explained
according to any known laws of molecular science, we are obliged
to approach this inquiry with an acknowledged inability to deal
satisfactorily even with the much simpler case of one of the ele-
ments of this system. The peculiar forms and laws of the molec-
ular activity of the entire nervous mechanism certainly cannot be
understood until we are able to describe and explain the molecu-
lar activity of a single nerve-muscle machine. A statement of an
elaborate theory, framed with a view to meet the whole case, by a
distinguished authority, cannot fail, however, to possess a certain
interest and value. Accordingly, we shall refer briefly to the
theory of Wundt.^
Wundt begins his discussion of the mechanics (or molecular
physics) of nervous substance by stating two possible ways of ap-
proaching the subject. It is conceivable that we might directly
investigate the chemical and physical constitution of the nervous
elements, and the changes they undergo in the exercise of their
physiological functions, with a view to construct a theory of so-
called nerve-force by induction from such investigation. But the
preferable — because the much more promising — way of procedure
is to assume that the processes which take place in the nervous
system are modes of molecular motion connected with each other,
and with the forces of external nature, under the general principles
of molecular physics ; and then, arguing deductively^ to make such
a combination and application of these principles as will serve to
meet all the demands of the case. It scarcely need be said that
Wundt adopts the latter method.
Assuming, then, the general principles of molecular physics, and
especially the lav/ of the conservation of energy, it is possible to
show how living beings may be brought under the control of these
principles. Such beings, through the regularity with which the
making and breaking of chemical combinations goes on within
them, take a noteworthy part in the continuous process of inter-
changing potential and kinetic (inner and external) energy. It is
the nervous system, in all the animals that have one, from which
'To be found, in part, in his Untersuchungen zur Mechanik der Nerven,
and in later and more complete form in the chapter (vi., Part I.) " Physio-
logische Mechanik der Nervensubstanz," in his Grundziige der physioiogi-
schen Psychologie. Leipzig, 1880.
232 THEORY OF MOLECULAR ENERGIES.
this process is controlled. The process itself is a species of com-
bustion ; the nervous system keeps going those functions which
effect the process, regulates the setting free and distributing of
the heat, and determines the muscles to movement. The source
of the special activities of the nervous system itself lies in the nat-
ure of the chemical combinations which compose it.
The nervous system regarded as unaffected by stimuli — that is,
as unexcited — may be theoretically compared to a fluid in a condi-
tion of equilibrium. But, in fact, the nervous system is never in a
condition of perfect equilibrium. For, not only is there a ceaseless
play of energy internal to this system, in which the atoms separate
from the old combinations as nervous substance to form new com-
binations as the same substance ; but a continuous process also
goes on by which the molecules of the nervous substance are broken
up to form less complex but more stable compounds. Moreover,
the building of the nervous substance itself out of the nourishment
brought tc it is a process the reverse of that last mentioned ; it
is a process, that is to say, in which the more stable chemical com-
pounds of other substance are broken up and their atoms used to
form the more complex but more unstable molecules of the nervous
substance. The process of change from the less stable to the more
stable combinations represents the setting-free of stored or poten-
tial energy ; the reverse j)rocess represents the storing of energy
and the vanishing of kinetic or actual energy. That energy which
is made apparent by the former process Wundt calls "positive;"
that which is stored xip, when the more stable combination disap-
pears, he calls "negative." Positive molecular energy of the ner-
vous system is recognized as heat set free, as contraction of the
muscles, etc. ; its negative molecular energy exists in the form of
heat becoming latent, or of inhibitory action upon the course of
excitation in the nerves, etc.
In accordance with the foregoing theory of positive and negative
molecular energy, as due to the chemical activity of the nervous
substance, Wundt would explain the process of excitation and con-
duction in the nerve-fibres. No simple conduction of motion, of
course, takes place in the nerve ; but certain molecular processes,
peculiar to the constitution of the nerve, are set up at one point by
the stimulus, and are then conducted successively to other points
along its stretch. In all cases when a nerve is irritated two classes
of opjDosed effects are set up in its substance ; the one is directed
toward the production of external energy (seci'etion, stimulation of
the gaijglion-cells, movement of the muscles, etc.), the other toward
the control of the energy thus set free. The former is positive,
' POSITIVE AND NEGATIVE ENERGY. 233
the latter negative or inhibitory. The general law for all excita-
tion of the nerves is, that by the application of stimulus the posi-
tive as well as the negative molecular energy of the nervous sub-
stance is increased. Stimulating the nei've accelerates both the
recombination of the atoms of its highly complex molecules in
less complex but more stable forms, and also the escape of the
atoms from these forms and their return to the more complex and
less stable combinations. The i*enewal of the nerve depends upon
the i-estitution of the more complex molecules ; but the work
which the nerve does external to itself depends upon that process
of combustion in which the complex molecules break up and pass
into more stable but less complex forms. The latter process
involves, of course, the exhaustion of the nerve. External energy
(work done outside of the nerve) can then only take place in case
the positive molecular energy is more accelerated than the negative,
by the application of the stimulus.
The entire sum of positive molecular energy which is set free
when a nerve is ii'ritated may be reckoned as distributed in three
directions : a part is spent in the continuous excitation of the
nerve ; another part becomes heat ; still another part is converted
into negative molecular energy. In this way the peculiar molec-
ular condition which the nerve-fibre leading from the peripheral
region assumes, when it is irritated, is imparted to the central re-
gion of the nerve-cell.
§ 13. The application of the foregoing theory to the central
organs of the nervous mechanism requires us to take account of
the fact that a greater intensity of the stimulus is needed to move
a muscle through a collection of ganglion-cells than directly by
stimulating the nerve-fibre connected with the muscle. We are to
conclude, then, that the nervous substance of the central parts
offers a far greater resistance to the conduction of the jDi'ocess of
excitation than is offered by the nerves themselves. On the other
hand, the central organs are in a condition to develop within them-
selves a far greater amount of work ; that is, to convert into
kinetic form a vast sum of energy stored in their chemical con-
stitution. The proofs which "Wundt brings forward for this view
are derived from the phenomena of summation of inhibition, and
of so-called "reflex-poisons," etc. A detailed discussion of such
phenomena leads to the conclusion that, when " summation " (com-
pare pp. 223 ff.) takes place, the several excitations along the cen-
tripetal tracts have been conducted to different sensory central
regions, and have then passed from them, as a result of their being
simultaneously excited, over into the same motor elements of the
234 THEORY OF MOLECtJLAE ENEEGIES.
central organ; but when "inhibition" takes place, such excitations
have been conducted so as to come together and counteract each
other in the same sensory central region. The external conditions
of those relations which obtain among the different senses and
sensations are to be found, partly in the constitution of the organs
of sense, and partly in the nature of their respective stimuli.
When speculating as to the molecular changes, with respect both
to positive and also to negative energy, which take place in the
central organs, our point of starting must be taken from a condition
of equilibrium assumed to exist in their ganglion-cells. Excitation
of the central organs, like irritation of the nerves, increases both
kinds of nervous energy. But the positive molecular energy of the
central organs is relatively little increased by a momentary excita-
tion. The result of repeated excitation, however, is to make the
positive condition largely predominate in the whole central region.
An excited ganglion-cell is in a condition analogous to that of the
nerve-stretch at the anode when a constant current is passing
through it. In the nerve, as a rule, the nervous substance is used
up, and the process of storing energy goes on in only a very par-
tial manner. In the cells the production of the complex molecules
in which energy is stored predominates, as a rule.
The fundamental properties of nervous matter — mechanically
considered — are (1) to receive external impressions in order by
them to be determined in its own molecular condition ; and (2) to
transform potential energy into kinetic, partly under the immedi-
ate, and partly under the progressive, influence of these impres-
sions.
Wundt also proposes an elaborate and highly speculative view
of the molecular constitution and functions of the ganglion-cells.
Every such cell possesses, he thinks, two regions (although the
word " regions " is not to be interpreted locally). These regions
are called "peripheral " and "central," because the former is as-
sumed to stand in more intimate x-elations to the peripheral ner-
vous substance, with respect to its own reactions under stimula-
tion. Excitations which reach the central region of a ganglion-cell
induce a propagation of the processes set up in this region to the
other or peripheral region. In the same way do excitations which
first touch the peripheral region necessitate the spreading of the
form of molecular energy set free here over into the central region.
When a process of excitation is frequently conducted in a definite
direction through some ganglion-cell, such direction is favorably
disposed toward the conduction of future excitations which may
reach the same cell. Whether the excitation of any particular
'ACTIOT^ DEPENDENT ON STRUCTURE. 235
nerve-fibre connected with a ganglion-cell results in an excitatory or
an inhibitory effect depends upon the nature of its connection with
the cell.
But we refrain from further statement of a theory so largely con-
jectural. Nothing i-emains but to repeat a confession of igno-
rance and of inability even to suggest a satisfactory solution for so
complex a problem in molecular physics as is offered by the human
nervous system.
§ 14 A review of various molecular theories proj)osed to account
for the nervous mechanism, either as a whole or in any of its parts,
makes plain the important fact that such theories are all obliged
to assume the origin and continuance of a peculiar molecular
structure for this mechanism. In other words, no attempt to
explain how the nervous system acts can avoid the conclusion that
the determining factor in the explanation must be found in what
the nervous system is. The physiological functions of the nerve
depart when the nerve dies. The nerve dies when it is severed
from the ganglion-cell. Both cell and nerve must, therefore, con-
stitute a living molecular unity, in order that their normal physio-
logical functions may be performed. The explanation of these
functions assumes the molecular constitution of the organs them-
selves. But how shall we explain, in accordance with the known
laws of molecular physics, the origin and preservation of such a mo-
lecular constitution ? It is the business of biology rather than of
physiology to attempt an answer to this question. But the question
itself asks from science the performance of a task no smaller than
that of framing a mechanical theory of life. Biological science can,
as yet, do little toward framing such a theory. Throughout our en-
tire discussion of the nervous mechanism we have carefully avoided
raising an inquiry as to the nature of life, as to the source and con-
ditions of that very molecular constitution which determines the
nature and working of this mechanism. We have simply assumed
and argued that, taking the nervous system for what it really is
and really does, its structure and functions admit of scientific ex-
planation, so far as such explanation is possible at all, only when
they are regarded as belonging to a molecular mechanism. The
question of a mechanical theory for the origin and constitution of
living organisms in general lies outside of the inquiries of Physio-
logical Psychology.
§ 15. One other important question has also thus far been
avoided. What is the relation of the mind to the working of the
nervous mechanism ? Can the mind set this molecular mechanism
at work, or can it in any way determine the character of its func-
236 THEOEY OF MOLECULAE ENEEGIES.
tions ? As far as our consideration of the nervous system has gone
hitherto, all might very well have been the same without the exist-
ence of a single act of conscious thought or feeling occurring in
any relation whatever to this system. Given the molecular mechan-
ism as it is constituted and conserved by the forces which control
as long as life continues ; and given the necessary impact of out-
side forces ujDon the end-organs, and the projDer changes of blood
within the central organs ; and it has been assumed that this mech-
anism would exercise its functions in ways thus far described.
But the consideration of another class of phenomena is now to be
introduced ; these are the phenomena of human consciousness, the
phenomena of 3Iind. The question whether such phenomena can
be true causes of any of the changes in the molecular mechanism
is a part of the general question as to the correlations that exist
between two classes of facts. The answer to such general question
belongs to the following divisions of our work.
PART SECOND.
CORRELATIONS OF THE NERVOUS
MECHANISM AND THE MIND.
CHAPTER I.
THE LOCALIZATION OF CEEEBEAL FUNCTION.
§ 1. Ordinaey observation recognizes the fact that the phenomena
of consciousness are more or less definitely correlated with the
condition of the body. Certain alterations in our mental states, on
account of the injury of any of its masses, as well as a constant de-
pendence of those states upon the way some of the masses stand
related to each other and to the outside world, impress the fact upon
our daily experience. It is by no means so obvious that the ner-
vous substance has any peculiar relation to the thoughts and feelings
of the mind. For the functions of the nervous system are not ex-
ercised in giving information as to itself, its own condition and
changes. By aid of these functions we have presented in con-
sciousness a more or less clear picture of the condition and changes
of the superficial parts of the body. In the same way a knowledge
is gained of the successive states of tension belonging to the
muscles in movement, and even — though rather obscurely — of the
place and condition of the internal organs. But as long as they
are healthy and excited with only a moderate intensity of their
stimuli, the nerves do not even reveal their own existence ; and
when they are injured or unduly excited, the notice they furnish
of the fact comes in the form of painful feeling which we have
learned to localize, not in the nervous substance itself but in the
adjacent parts of muscle and skin. Attention may be called, how-
ever, to the peripheral nerves by the accident or the dissecting-
knife which exposes them to sight. In the case of the central
nervous organs, and especially in the case of the brain, there is little
in ordinary experience which leads to a suspicion of their signifi-
cance or even of their existence.
It is not very strange, then, that no general recognition of the
supreme importance of the brain, in relation to the phenomena of
consciousness, is to be found in early history. It is true that
Plutarch ' and Theophrastus " inform us of the opinion of the
' DePlacitis Philosophorum, IV., 17, 1.
' De Sensu, § 35 f.
240 GENERAL FUNCTIOlSr OF THE BRAIlsr.
pliysieian Alcmaeon, who is said to have been a younger contem-
porary of Pythagoras, and who regarded the brain as the common
meeting-place of the senses. The same view is also ascribed to the
celebrated Hippocrates. Later on Plato accepted it. But Aris-
totle,' the greatest of all thinkers in antiquit}', the son of a phy-
sician, especially educated in physical science, and well acquainted
for the time in the dissection of animals, regarded the brain as a
lump of cold substance, quite unfit to be the seat and organ of the
sensus communis. This important office he ascribed rather to the
heart. The brain he considered to be chiefly useful as the source
of fluid for lubricating the eyes, etc.
§ 2. The opinion of Exner," however, who supposes that feeling
in no way immediately informs us that we think with the head,
still less with the brain or the cortex of the cerebrum, seems some-
what extreme. Concerning the contents oi the cranial cavity, indeed,
we get no direct information from the feelings connected with
the exercise of its functions. But we certainly localize in the head
certain phenomena of consciousness that are inextricably inter-
woven with the processes of thought. The act of attention results
in feelings which indicate that the muscles of the eye are being in-
nervated ; or in the more indefinite and diffused sense of strain
produced by contracting the skin of the forehead and adjacent
parts of the face. The special sensations of hearing, smelling, and
tasting, which impress so strongl}^ our conscious life, are frequently
referred to the head. The same thing is true of many of the sen-
sations of sight — particularly of such as appear when the eyes are
closed, in the form of after-images, or spectra, or indefinite and
changing color-spots, seated in the upper front part of the face.
Moreover, that inchoate and sometimes half-articulated language,
with which we support our ti'ains of thought, even when we are not
conscious of resortiog to the expedient of " talking to ourselves," is
felt to be going on within the head. When one has been engaged
for some time in intense thought, or in eager and concentrated
observation, one is suddenly made aware of more or less painful
feelings which are somewhat indefinitely ascribed to the same
cerebral region. Men commonly lean the head upon the hand
in supporting meditation ; or rub it vigorously to awaken
the powers of memory and reasoning ; or stroke it to relieve the
disagreeable sensations which follow severe mental excitement.
Headache, of more or less intensity, thus becomes associated with
1 See De Partibiis Animalium, 052. b. 5; (II., 7); 656, b. 22 (II., 10); De
Juvent. , 4(!7, b. 28 ; and De Anima. III., 1 and 2.
' See Hermann's Haudb. d. Physiol., II., ii., p. 193.
NEED OF AETERIAL BLOOD. 241
"active exercise of the intellect. The head is wearied with thought ;
and not only so, but also with intense physical exercise. The dis-
comfort which bodily strain produces in the hinder regions of the
head are an indication, although of only a very general kind, that
processes have gone on in that locality which are of great impor-
tance to the succeeding states of consciousness. All this apparent
testimony of immediate feeling is, doubtless, somewhat exaggerated
in an age so distinctively " nervous" as our own ; and this fact may,
perhaps, account in part for the inclination of the ancients to em-
phasize the more obvious connection of mental jDhenomena with the
heart, and other lower visceral organs, to the neglect of all connection
of these phenomena with the brain. But it cannot well be doubted
that a certain amount of testimony from immediate feeling as to the
important relation which exists between the state of mind and the
contents of the cranial cavity, belongs to all human experience.
However uncertain the witness of immediate feeling upon the
point in question may be, very little observation of others is needed
to amplify and confirm its witness. We are not infrequently led to
notice how quickly and profoundly the states of consciousness are
changed by injuries to the brain. The effect of a blow upon the
head in suspending consciousness is decisive of this question. The
intimate local connection between the organs of sense and the
brain leads naturally to the conclusion that the avenues of sensa-
tion and of perception have in the latter a kind of gathering-j)lace,
as it were. It is but a step from this conclusion to a recognition
of the truth that the physiological significance of the contents of
the cranial cavity consists in their afibrding a field upon which all
the impressions of sense can meet together, and so furnish the basis
and material of comparative thought. Indeed, it was this line of in-
quiry which probably led certain ancient anatomists, like Herophilus
and Galen, to locate the soul, or psychical principle, in the brain,
§ 3. A great multitude of physical considerations, advanced by
modern science, place beyond doubt the supreme importance of
the brain in its influence upon the phenomena of consciousness.
It has already been stated (Part I., Chapter HI., § 7) that the free
circulation of arterial blood, with its supjDly of oxygen, is a
necessary condition for the fulfilment of the functions of all the
central organs ; this necessity is especially marked in the case of
the brain. The stoppage of one of the great arteries leading to
this organ, either by compression in the neck, or by embolism at
some point along its course, at once produces profound dis-
turbances and even complete cessation of consciousness. It has
been calculated that, while the weight of the entire encephalon is
16
242 GENERAL FUISrCTION OF THE BRAIN".
only about one-forty-fifth of that of the body, the supply of blood
used uj) there is not less than about one-eighth of the whole supply.
This expenditure is indicative of the large amount of work done
by the intercranial organs.
More delicate measurements seem to show that the temperature
rises and falls in the whole cerebral area, or at particular cir-
cumscribed regions of the cortex, in close connection with the
psychical activities. Thus Dr. Lombard found, by measurements
with exact thermo-electric apparatus, that the temperature of the
head during waking hours varies rapidly, though slightly (less
than y^^° C.) ; and that these variations " appear to be connected
with different degrees of cerebral activity. . . . Every cause
that attracts the attention — -a noise, or the sight of some person or
other object — produces elevation of temperature. An elevation of
temperature also occurs under the influence of an emotion, or
during an interesting reading aloud." Similar examinations have
been carried still further by Schiff,' who has appUed extremely del-
icate thermoscopic instruments directly to the cerebral substance
of certain animals (comp. Part I., Chapter III, § 21). He finds
that the arrival of sensorial impressions is followed by a rise of
temperature, in certain special areas of the cortical substance, where
— as he supposes— these impressions are diffused; he also con-
cludes that any resulting psychical activity is itself connected with
a still further rise of temperature than that which the sensorial
impressions alone engender. Schiff 's conclusions, therefore, point
not only to the localization in the entire brain of functions connected
with the phenomena of conscious psychical life, but also to some
distribution of such functions among its various areas. In the
same general direction are the conclusions of Byasson" and others,
as to an increase of waste in the tissues of this organ, which
corresponds, to some extent, at least, with the amount of thought
accomplished. This investigator found that the quantity of sul-
phates and phosphates excreted, in comparison with the quantity
estimated as entering into his diet, was notably increased in pro-
portion to the amount of his mental work. That is to say, in con-
nection with an increase in the number and intensity of the
psychical operations stands an increase in the functional activity of
the cerebral cells, as shown by the expenditure of their phos-
phorized constituents.^
' Archives de Physiologie, 1870, p. 451.
'' In the Jour, d, Anat. de Robin, 1869, p. 557 f.
'■' See the chapter of Luys on tlie Physico-chemical Phenomena of Cere-
bral Activity ; The Brain and its Functions.
RELATIVE WEIGHT OF BllATN".
243
§ 4. Comparative anatomy also indicates the importance of the re-
lation between the size, structure, and functions of the intercranial
nervous mass and the jDhenomena of mind. It shows, first of all, a
general but indefinite correspondence betvs^een the size and weight
of the brain of any species of animal, as compared with the weight
of its entire mass, and the place of the same species in the scale of
intelligence. This fact is roughly exhibited by the following com-
parative table : ^
RELATIOiSr OF THE WEIGHT OF THE BRAIN TO THE WEIGHT OF THE BODY.
Tunny-fish . . .
Land tortoise.
Shad
Tadpole
Elephant . . . .
Salamander . .
Sheep
1
37,440
1
2,240
1
1,837
1
720
1
500
1
380
1
351
Finch 1
Eagle 1
Pigeon 1
Rat 1
Gibbon 1
Young cat 1
Sai — ape 1
231
160
104
82
48
39
25
Doubtless other tables might be compiled which would lead to
less satisfactory conclusions than the one given above. Even in
this table we note that the elephant stands lower than the sala-
mander or the sheep, both of which animals are, in fact, far in-
ferior to the elephant in intelligence. Large allowance must also
be made in certain cases for peculiarities of physical structure ; for
example, the tortoise is rated lower than he would be were it not
for his heavy shell. The law itself is confessedly subject to re-
markable and unexplained exceptions ; at best it holds good only
in a very general way. For example, the relative weight of the
brain is not greatly different in the dolphin, in the baboon, and in
man. It is much greater in the infancy and youth of the human
species than in middle life or old age. In the male child at birth
it is about as one to six or seven (according to Tiedemann, 1 to
5.85 in the male, and 1 to 6.5 in the female). The brain grows with
great rapidity for the first few years — the increase during the first
year being estimated at about one cubic centimeter daily. But the
rest of the body increases so much more rapidly that by the end of
the second year it is about 1:14 ; by the end of the third year, 1:18.
It increases in absolute weight until well on into middle life, and
then after middle life diminishes at about the average rate of one
' Taken from Hermann's Handb. d. Physiol., XL, ii., p. 193. as compiled by
Exner on the basis o£ the works, in part of Carus, and in part of J. Miiller.
The figures of comparative weight between the brain and the body are some,
what differently given by other authorities.
244 GENERAL FUNCTIOjST OF THE BRAIaST.
ounce in a decade. The average relative weight of the adult brain
is one-fortieth or one-fiftieth. Tiedemann found that the relative
weight of the brain is dependent upon the absolute weight of the
body, and is relatively greatest with light persons. The human
brain is, however, absolutely heavier than that of any of the ani-
mals except the elephant (8-10 lbs.) and the whale (5-6 lbs.).
Much pains has been taken, by actually weighing diiferent
human brains, or by calculating their weight on the basis of careful
cranial measurements, to establish a law connecting the amount of
the iutercranial nervous mass with the comparative intelligence of
races and of individuals.' The average weight of the brain of the
adult European is, for the male, fi'om 46 to 52 ounces ; for the fe-
male, from 42 to 46 ounces. Boyd gives the average weight of the
brain of the male, at the period of life when it is most developed
(twenty-five to forty years of age), as 46.8 ounces (1,321 grams, 91
centigrams). This difference between the sexes is not wholl}' de-
pendent on difference in bulk of body, but is an important sexual
distinction. The brain of man is on the average ten per cent, above
that of woman ; the difference in average stature is about eight per
cent. Many human brains rise above the upper average ranges ;
others fall below the lower average ranges ; and yet no marked
peculiarities of mental development are necessarily connected with
these variations. Considerable quantities of the substance of the
brain may be lost (at any rate from some areas of the cortical sur-
face) without perceptibly changing the mental life. In 278 cases
of males, the maximum weight of brain was found to be 65 ounces,
the minimum 34 ounces ; in 191 cases of females, the maximum
was 56 ounces, the minimum 31 ounces.' Numerous instances of
large excess in the average weight of brain-mass by individuals
eminent for intelligence are on record : for example, Byron scarcely
under 79 ounces ; Cromwell, only 77 grains less, or 78.8 ounces
(although Vulpian thinks that the national spirit has exaggerated
both these instances) ; Cuvier, 64.5 ounces ; Abercrombie, 63
ounces ; Spurzheim, 55 ounces ; Sir J. Y. Simpson, 54 ounces ; Web-
ster, 53.5 ounces ; Agassiz, 53.4 ounces ; Chalmers, 53 ounces.
Other persons? of eminence, however, have had brains of only aver-
age, or of under average weight ; thus C. F. Hermann, 46.5 ounces,
and J. F. L. Hausmann, 43.3 ounces. Moreover, brains of high
weight not infrequently occur without evidence of unusual mental
capacity, or even in the case of those mentally inferior. Kecord is
' On the relations of the Brain witli respect to weight and mass, see Schwalbe,
Lehrb. d. Neurologie. ii., pp HSO ff. Erlangen, 1881.
-Results obtained by Sims, Clendinning, Tiedemann, and J. Reid.
BRAIlSrS OF DIFFERENT RACES. 245
made of four male brains, beloBging to persons of no repute for in-
tellectual ability, which ranged from 62.75 ounces to 61 ounces ; of
another such, which weighed 60.75 ounces ; of the brain of a boy
of fourteen which weighed 60 ounces. In the West Riding Asy-
lum ' for the Insane, out of 375 males examined, the weight of the
bi*ain in 30 cases was 55 ounces or upward ; out of 300 females
examined, in 26 cases it was 50 ounces or upward. Several persons
afflicted with dementia were found to have brains weighing more
than 60 ounces. On the contrary, idiots, almost without exception^
have brains far below the average in weight ; as a rule, the brain
of such an unfortunate does not weigh so much as 30 ounces.
Cases of microcephalous idiots are on record whose brains weighed
only 10.5, or even 8.05 ounces. Here, again, however, singular ex-
ceptions must be admitted ; for in a few cases the brains of idiots
have reached the average weight, and have even, in rare cases, con-
siderably surpassed it.
Although the data adduced to show that the average weight of
brain in the more highly civilized races is greater than in the savage
races, are by no means abundant or conclusive, yet they are suffi-
cient to create a reasonably strong presumption in favor of this
view. Calculating from the size of the cranial cavity, as ascertained
by measurement of a large number of skulls, it is inferred that the
average weight of brain in the African, Australian, and Oceanic
races generally, falls from 1 to 4 ounces below that of the more
highly civilized European. It is further noted that there is almost
a complete absence of cases rising above the higher ranges — above
54 ounces, for example ; and that there is not the same difference
between the two sexes in the uncultivated as in the cultivated,
peoples. Davis calculated the average weight of brain among the
Chinese to be about equal to that of the Caucasian race in Europe ;
among the Sandwich Islanders to be some thirty grams less. The
surpi'isingly low weight of the brain of the Hindus is in part a
function of their smaller weight and bulk of body. It ma}' fairly
be urged in objection, that by the method of measuring skulls
taken somewhat at random we should be likely to find a note-
worthy absence of such exceptional cases in certain quarters
among the European races ; and that the relative increase in size
of the female brain among uneducated peoples is probably, in part
at least, the result of the response of the nervous system to the
demand made upon it for the hard labor performed by the women
among such peoples.
Any law which refers the intensity and range of the mental
^ For these facts see the Encyclopsedia Britaunica, uiuth ed., I., p. 879 f.
246 GENERAL FUNCTION OF THE BRAIN.
activities directly to the size and weight of the nervous mass of the
brain must, therefore, be held only very loosely. It is to be ex-
pected that many unexplained exceptions will meet us, whether we
compare men with the other animals, or certain races of men
with others, or individual men with one another. No intelligent
physiologist would now think of making mere mass the test of
mental capacity.
§ 5. A more intimate relation of dependence exists between the
amount of intelligence and the complex structure of the brain as
arising to a large extent from the development of the cerebral
hemispheres — that is, from their relative size and esjDause, and
from the number and depth of their convolutions. In other
words, wealth of expanded and convoluted cerebral hemispheres
is, in some general way, a measure of the richness and intensity of
mental life. This conviction becomes stronger the more carefully
the comparative anatomy of the cerebi^um, and the development of
the cerebral hemispheres in the human embryo, are examined.
The forms of brain found permanently in fishes, amphibians,
reptiles, birds, and the lower mammals, are extremely similiar to
those shown in succession by the developing brain of the higher
mammals, and especially of man. The most distinctive feature of
man's superior brain is the marked development in the size, num-
ber, and depth of the convolutions of the hemispheres. In fishes
generally, both cerebrum and cerebellum are very small ; but the
ganglia connected with the organs of sense, especially of vision, are
relatively large. In amphibia the cerebral hemispheres are rel-
ativel}' enlarged ; are advanced backward still farther in reptiles ;
while in birds the vesicles of the mid-brain are partially hidden by
the development of the hemispheres. In the lower mammals the
enlargement of these same organs by growth backward continues,
and their two parts become connected by a commissure ; but they
still remain comparatively meagre in size and simple in structure,
without much distinction of lobes or division into convolutions. It
is only in the most elaborately developed brains of the higher
mammals that the occipital lobe enlarges backward so as to cover
mid-brain, cerebellum, and medulla oblongata ; and that the frontal
lobe spreads forward over the nasal cavities so as to constitute a
development of forehead. Meantime the convolutions apparent on
the cerebral surface increase in number and depth.
The theory suggested by comparative anatoniy is confirmed by
the probable view of Meynert, that the whole of this cortical I'egion
of the cerebrum is a great "projection-field" on which the sensory
impulses are marshalled and systematically ordered (to serve, as it
THE MEASUREMENTS OF WAGNER. 247
Tvere, for the physical bans of mental phenomena), as they arrive
from the peripheral regions and are distributed over the outgoing
motor tracts. Certain striking exceptions to the principle of this
theory must, however, be acknowledged. Within each great group
of animals considerable variations occur in the degree of cerebral
convolution, such that it cannot be said accui-ately to measure the
degree of intelligence. For example, among mammals the in-
sectivora have brains "poorest" in convolutions, the herbivora
are "richest," and the carnivora stand between; the ruminants,
although rather dull and incapable of being taught, have numer-
ous and deep convolutions enough to rank them much higher than
their real intelligence deserves. The marmoset, on the other hand,
the relative weight of whose brain is as 1 to 18, shows a compara-
tively smooth and non-convoluted surface, in striking contrast with
that of other monkeys.
Trustworthy data are as yet wanting to place beyond doubt the
probable opinion that the brains of less highly civilized races and
less highly intellectual individuals are relatively poor in develop-
ment of the cerebral hemispheres. The human embryo is, indeed,
an illustration in miniature of the truth of this opinion ; the older
it becomes the more distinctly marked are the lobes of the cere-
bral hemispheres, and the more numerous and deep are their con-
volutions. The brains of idiots are said, as a rule, to be jjoor in
convolutions ; this fact is doubtless connected with the embryonic
condition in which many of them have remained through arrested
development. Hermann Wagner,' on the basis of measurements
made by his father, undertook to estimate the comparative total
siu'face of the cei'ebral hemispheres of four brains, viz.: of two
males of noteworthy intelligence (Gauss, the mathematician, and
Fuchs, the physician), of a male laborer (Krebs), and of a female
in middle life. By weighing carefully the amount of gold-foil laid
on uniformly, which was required completely and closely to en-
velop all the convolutions of these brains, Wagner concluded that
the area of concealed surface was, in each case, approximately
equal to that exposed. The total surfaces of the four brains were
thus found to measure — of Gauss, 2,196 square centimeters; of
Fuchs, 2,210 ; of the woman, 2,041 ; of Krebs, 1,877. It is a tempt-
ing but rather insecure generalization which concludes from so
sew cases that the richness of the cerebral convolutions (the total
surface, both that exposed and that concealed by the sulci), is a
general direct measure of the intelligence.
§ 6. Other interesting attempts have been made to measure the
1 Maassbestimmuiigen d. Oberflaclie d. grossen Geliiriis. Cassel, 1864.
248 GENERAL FUNCTIOlSr OF THE BEAIlSr.
intelligence of the animal by the relative size and structure of
the iutercranial nervous mass, and so, definitely, to establish a dii^ect
relation between the two ; we notice especially those of J. Miiller,'
and of Meynert.^ The great physiologist, Miiller, held that the
position of an animal in the scale of intelligence may be estimated
by comparing the hemispheres of his bi'ain with the corpus quad-
rigeminum. According as the latter organ is relatively large, and
lies behind the hemisi^heres, uncovered by them, the animal is low
in the scale of intelligence ; according as the hemispheres increase
in size, and so envelop and bury beneath them the relatively small
corpora quadrigemina, the animal stands high in that scale. This
statement, however, scarcely covers anything more explicit than
the general fact that relative increase of the cerebral hemispheres
is indicative of progressive mental life. Meynert has pointed out
other important relations between parts of the brain, by which he
proposes to measure the intelligence. In the entire mass of the
crura cerebri we may recognize two parts, an upper (tegmentum),
which stands in direct connection with the optic thalami and the
corpora quadrigemina, and a lower (crusla), which is connected
through the lenticular nuclei of the striate bodies with the cere-
brum. Now the greater the hemispheres are in comparison with the
corpora quadrigemina, the greater must the mass of the crusta be iu
comparison with that of the tegmentum. The development of the
pons Varolii is also essentially dependent on that of the crusta, for
the fibres of the latter enter into the former ; the arching of the
pons is therefore connected with the development of the hemi-
spheres. In general, then, the relative development of the entire
tract represented by the crusta, or lower jDart of the crura cerebri,
and the nucleus lenticularis, the fibres of which expand in the cere-
brum, is — according to Meynert — a measure of an animal's intelli-
gence. In man the mass of the crusta on the level of the corpora
quadrigemina exceeds that of the tegmentum ; in the other mam-
mals the reverse is true.^
§ 7. The above-mentioned facts of comparative anatomy, with
many others similar, show plainly the unique significance which the
masses of the brain, and especially the cerebral hemispheres, have,
as related to the phenomena of self-conscious mind. They may be
supplemented and confirmed through other facts furnished by
physiology, esjDecially of the experimental kind. Upon this point,
' Handb. d. Physiol, d. Meiisclieii, 1844, I., p. 702 f.
^Sitzgsber. d. Wiener Acad., LX., iii. (1869), pp. 447-462.
^For a brief but judicious discussion of this subject, see Briicke, Vorles'
ungen iiber Physiologie, 1884, II., pp. 52 ff.
FUNCTIOlSr OF CEREBRAL HEMISPHERES. 249
for the present, reference is simply made to the results of inves-
tigation as already set forth in Part I. (see especially Chapter
IV.). Physiology demonstrates that the nervous impulses, so far as
they I'esult in sensation, pass along centripetal tracts which con-
verge from every portion of the periphery toward the brain ; and
that, so far as they x'esult in motion following upon idea and voli-
tion, they pass along centrifugal tracts diverging from the same
central masses. It thus confirms the same theory which studies of
the anatomical structure of the nervous system suggest, namely,
that in these masses, and especially upon the cortex of the cere-
brum, is the common meeting-place of both kinds of impulses. The
section or injury of any nerve-tract, even in the spinal cord, apart
from indirect and secondary influences, does not affect the psychical
functions. In such an event, the parts of the body lying j)eriphe-
rally from the point of interruption are simjDly withdi'awn from all
direct connection with sensations or volitions. Sensory impulses,
then, no longer occasion sensations ; ideas of motion and volitions
to motion, of the parts thus disconnected, become of no effect in
producing the customary result. It has also been made obvious
that, in proportion as the masses of an animal's bi-ain are removed
or incajDacitated from performing their functions, the evidences of a
varied and complex mental experience are diminished. The simple
spinal cord of a frog, acting as a nervous mechanism, will perform
a few wonderful feats ; joined with the medulla oblongata, optic
lobes, and other lower parts of the brain, it will give largely in-
creased signs of psychical phenomena ; it would not be claimed,
however, that the cerebral hemispheres of this animal — relatively
insignificant as they are when compared with those of the higher
animals — are of no special importance for its highest psychical life.
Essentially the same thing, though in more emphatic form, is true
of all animals of a higher grade of intelligence.
§ 8. In the case of man, the cerebral hemispheres are, aj^par-
ently, the only portions of the nervous system, between the size,
condition, and molecular activity of which and the phenomena of
consciousness there is a direct correlation. If, then, we are to speak
of mental activities as " localized " at all, the locality must be in
the cortex of the cerebrum. The position that, in the case of man,
the spinal cord and all the intercranial organs below the cerebral
hemispheres, are incapable of acting as the immediate physical
basis of mental states, is confirmed even by those experiments upon
other animals, which seem at first sight to discredit it. The hypoth-
esis that consciousness has a seat in the spinal cord of the frog ;
that, in fact, we may properly speak of the decapitated animal as
250 GENERAL FUNCTIOlSr OF THE BRAIJST.
having a soul — has been urged by eminent j)hysiologists (Pflnger,
for example). That the cord alone is capable of various purpose-
ful activities, such as serve, under certain circumstances, as signs
of a psychical experience, may be demonstrated by experiment
(comp. Part I., Chapter IV., §§ 4 ff.). But unless one is prepared
to maintain that all purposeful activity, as resulting from excited ner-
vous substance, must be correlated with phenomena of conscious
sensation and volition, one can scarcely assume with confidence
that such phenomena accompany the movements of the decapitated
frog.
"What the nervous mechanism will do, when set agoing by the
appropriate stimuli, depends not only on its oi'iginal structure, but
also on its acquired habits of action. That this law holds good
even for the mechanism of the hemispheres of the brain is obvious
from various facts. Stimulating those regions of the cerebral cor-
tex which are connected with definite groups of muscles, in the case
of the adult animal (for example, a dog), does not call out the same
responses in the animal newly born (that is, under nine or ten days
old). The case of the bird which has lost its cerebral hemispheres,
and which executes motions by means of the lower basal ganglia,
that seem to indicate a complex psychical life (comp. Part I.,
Chapter IV., § 20) is less easy of solution. Are we to consider
such an animal still capable of "sensation," " perception," and "vo-
lition ? " If this question means whether any phenomena continue
to occur such as correspond to those conscious experiences of our
own to which we apply the above-mentioned words, then we must
confess our inability to answer it.
In general, we know extremely little of the conscious mental life
of the lower animals. What we conjecture is wholly dependent on
the interpretation, given in terms of our human consciousness, to
motions of their bodies resembling those which express definite
conscious states in ourselves. But a large part of our own
bodily activity is ordinarily not definitely correlated with any con-
scious mental activity ; for example, breathing, winking, swallow-
ing, changing the posture of the body in sleep and in states of
jDrofound meditation, and especially the very complex operations
involved in walking, singing, playing on musical instruments, or
handling a tool, etc. In all these and similar cases, we find that
the intricate and purposeful play of the mechanism is by no means
necessarily connected with a corresponding series of conscious sen-
sations and volitions. But in proportion as the hemispheres of an
animal's brain become relatively developed, not only their abso-
lute but also their relative significance is increased. The influence
LOSS OF THE CEREBRAL HEMISPHERES. 251
of the brain proper upon the voluntary movements of an animal
is greatei', the higher the animal stands in the scale of cerebral
development and of intelligence. A frog, or a fowl, deprived of
its hemispheres, can do what is quite impossible for a dog or an
ape in the same condition. If, theu, man's nervous mechanism,
especially in case it has been trained to elaborate co-ordinated func-
tions, can, without any corresponding accompaniment of mental
phenomena, accomplish so much which ajppears significant of the
most elaborate psychical activities ; a fortiori, it is likely that we
may make this mechanism, working without consciousness, account
for most of what is done by the hen or pigeon without its cerebral
hemispheres. Moreover, experimental physiology undoubtedly
tends toward accounting more and more fully for the most com-
plex bodily motions under the tei-ms of physical mechanism.
The most marked result of an animal's loss of the cerebral
hemispheres is the sudden and great, or total departure of its
intelligence. This fact is, of course, confirmatory of the impres-
sion that the functions of these hemispheres, and of them alone,
constitute the physical basis of its intelligence. We confess,
however, our inability to affirm that the " psychical life " of every
animal is inseparably bound to its continued possession of these
organs. There may possibly be a varied psychical life of animals
that have no brain. Yet in the case of the higher mammals, and
especially in the case of man, we need not hesitate to affirm the
probability of such an inseparable connection. The physical basis
of the phenomena of human consciousness is pre-eminently, if not
exclusively, the convoluted cortex of the cerebrum.
§ 9. It is impossible, accordingly, to avoid raising the inquiry
whether some more definite scheme of the localization of cerebral
functions may not be discovered. The cerebral cortex is itself a
very complex organ, or system of organs. Its different regions
are marked by comparatively slight, and yet not insignificant, dif-
ferences of structure ; they stand in different local relations and
nervous connections with one another and with the ganglia lying
below. This outlying rind of gray nervous matter is, of course,
not a homogeneous mass. It is made up of innumerable nervous
elements combined in various ways and multiform connections.
It may be regarded, then, as a complex of organs. The question
therefore arises : Have the different members of this complex of
organs different relations to definite motor activities in the pe-
ripheral regions, and to the various phenomena of conscious men-
tal life ? or, in other words : Have different parts of the cere-
bral hemispheres all the same office and value in relation to the life
252 EVIDENCE FOR LOCALIZATIOlSr.
of sensation and voluntary motion ? This is the question generally
understood under the term — "the localization of cerebral func-
tion. "
§ 10. Most of our definite knowledge concerning the functions
of the other parts of the nervous mechanism creates a presumption
in favor of some localization of cerebral functions. All the different
parts of this mechanism are, indeed, constructed by combining
variously a few elements of essentially the same structure ; all of
them likewise are capable of exercising essentially the same neural
functions. But each part of this mechanism has also its special
functions. Thus we found that the different nerves become classi-
fied functionally ; some are motor, voluntary or involuntary, some
inhibitory, some secretory, some sensory, etc. Hints of a certain
kind of classification may be discovered for the smaller ganglia or col-
lections of nerve-cells. In making transverse sections of the cord,
different regions with different functions appear. Considered lon-
gitudinally, the cord is capable of being more or less definitely
divided into several so-called centres, with specifically different
functions. Localized centres, where specific kinds of reflex-motor
activity have their particular seats, are fairly crowded together in
the medulla oblongata. All the lower parts of the encephalon
appear subject, in a measure, to the principle of localization. Shall
we, then, stop short in our attempts at differencing the functions of
the locally separate parts of the nervous system just at the point
where we reach the most complex and extended organ, or I'ather
collection of organs, which this system contains ?
§ 11. Notwitlistanding the strong presumption in favor of the
localization of cerebral function, the beginnings of a successful
attempt to establish this theory are only about fifteen years old.
The doctrines of Gall, Spurzheim, and others in the older school
of phrenologists, proved so inconclusive as to bring contempt
ujDon subsequent attempts to divide the hemispheres of the brain
into different functional areas. Moreover, certain indisputable facts
seemed to render impossible the assured beginnings of a theory
of cerebral localization. Considerable portions of the human brain,
it was found, might be lost without destroying any one sensory or
motor function. Moreover, the gray matter of the cerebral hemi-
spheres, it was then thought, could not be directly excited by elec-
tricity or by other forms of stimuli. The greatest experimenters
in i)hysiology, such as Longet, Magendie, Flourens, Matteucci, van
Deen, Budge, and Schiff, declared against the localizing of cerebral
function. In 1842 Longet ' afiS,rmed that he had experimented upon
' Anatomic et physiologie du sjsteme nerveux, etc., Paris, 1842, i., p. 644 f.
EXPERIMENTS OF FRITSCH A-KD HITZIG. 253
the cortical substance of dogs, rabbits, and kids, had irritated it me-
chanically, cauterized it with potash, nitric acid, etc., and had passed
galvanic currents through it in different directions, without obtaining
any sign whatever of resulting muscular contraction. In the same
year Flourens ' asserted, on the basis of numerous experiments in
extirpation, that the lobes of the cerebrum perform their functions
with their whole mass ; that there is no special seat for any of the
cerebral activities ; and that even a small remnant of the hemi-
spheres can serve all the uses of their collective functions.
So great was the authority of the distinguished names just men-
tioned, that their confident opinions gained general credence. The
evidence brought forward by Broca and others seemed, however,
to show some special connection between a single convolution of
the frontal lobe and the complex activities of articulate speech ;
and the anatomist, Meynert, held the opinion that the structure
and connections of the cerebrum show its anterior poi'tion to be
in general used for motor, its posterior for sensory functions. In
1867 Eckhard repeated the significant observation which had been
made by Haller and Zinn more than a century before : namely,
that, on removing parts of the cortical substance of an animal's
brain, convulsive movements occur in its extremities.
§ 12. It was not until 1870 that the "epoch-making" experi-
ments of Fritsch and Hitzig " began the modern era of investiga-
tion into this subject. These observers announced the fact that the
cerebral cortex of dogs is, at least in certain minute areas of it, ex-
citable by electricity. They pointed out the further fact that, while
some parts of the convexity of the cerebrum ai'e capable of motor
excitation and others not, the motor parts lie in general to the
front, the non-motor to the rear of this convexity'. By stimulating
with an electrical current the so-called motor parts, co-ordinated
contractions of the muscles in the opposite half of the body are
obtained. Of such so-called "motor centres" they indicated, in
their first announcement, the following five : One for the muscles
of the neck, another for the extension and adduction of the fore-
limb, another for the bending and rotation of the same limb,
another for the hind-limb, and lastly one for the face. From such
facts they drew the conclusion that the principle announced by
' Recherclies experimentales sur les proprietes et les fonctions du systeme
nerveux, etc., p. 99 f.
^See the article by G. Fritsch and E. Hitzig in the Archiv f. Anat., Phy-
siol., etc., 1870, pp. 300-332 ; and subsequent articles by Hitzig in the same
Archiv, 1871, 1873, 1874, 1875, 1876 ; also his work, Untersuchungeu iiber
das Gehirn, Berlin, 1874.
2j4 evidence for localization.
Flourens is demonstrably false. We must rather admit, say they
that " certainly several psychical functions, and probably all, are
shown to have their point of entrance into matter or of origin from
it at circumscribed centres of the cerebral cortex." ' The same
principle was subsequently defended at length by Hitzig, and the
number of so-called cerebral centres increased. The most note-
worthy facts which these experimenters first made clear and de-
monstrable have since been verified by many investigators. Many
of these facts may, with care and skill, be verified by any observer.
Dr. Terrier in particular has used the method of Fritsch and Hitzig
to map out the hemispheres of the brain of the monkey into no
fewer than fifteen kinds of centres. The testimony of human pa-
thology, and the evidence of comparative anatomy and of histology,
have also been largely drawn upon either to confirm or to confute
the conclusions originally based on experiments with animals. Be-
fore considering the conclusions themselves, it is necessary to
understand the true nature and extent of the various kinds of evi-
dence.
§ 13. Exner has well said that " a physiology of the cerebral cortex,
in the sense in which there is a physiology of the muscle, etc., scarcely
exists at the present time." The reasons for such a deficiency lie
partly in the very nature of this organ and the place it holds with-
in the animal economy ; as well as partly, perhaps, in certain prej-
udices which have hindered the physical theory of a material struct-
ure so intimately related to the action of the mind. The cerebral
cortex of the animals is exjDerim en tally approached only by over-
coming immense difficulties. Moreover, those physical and chemi-
cal processes of the cerebral substances, to which we must look for
any strictly scientific understanding of its physiology, are placed
almost utterly beyond reach of investigation. Seasoning must fill
up with conjecture the great gaps that lie between a very complex
series of physical occurrences, only a part of Avhich are observable,
on the one side, and on the other, an equally complex group of
psychical occurrences. The latter belong to a different order of
phenomena from the former ; and, moreover, in the case of the
lower animals — which must be selected almost exclusively for ex-
periment— we know nothing of these psychical occurrences except
through physical signs that are peculiarly liable to misinterpreta-
tion. The result is that our conclusions on the localization of cere-
bral function must be reached by considering a great multitude of
complicated facts, many of which appear to take sides with contend-
' Archiv. f. Anat, Physiol., etc., 1870, p 332.
*See Hermanns Handb d. Physiol., II., ii., p. 189.
STIMULATIOISr AND EXTIEPATION. 255
ing cliampions of dijBferent theories who ahke appeal to them. It
is only by observing the du'ections in which the different Hnes of
evidence seem to point in common, that we can reach even a prob-
able opinion upon a few points.
§ 14. Three great lines of evidence, leading from three great
groups of facts, must be considered. These are the evidence from
exjDerimentation, the evidence from pathology, and the evidence
from histology and comparative anatomy. Each of the three has
its peculiar advantages and value ; each also its peculiar difficulties
and dangers. It is only by regarding the combined testimony of
the three that the highest probability at present possible can be at-
tained.
Experimentation with a view to discover the localized functions
of the cerebral cortex is of two kinds, stimulation and extirpation.
Here, too, what has already been said (Parti., chap. IV., § 14) con-
cerning the difficulties of the same mode of investigation in the
sub-cerebral regions of the encephalon must be recalled and made
more emphatic. All experiment by stimulation of certain areas of
the hemispheres of the brain relies, of course, upon the argument
that those areas whose stimulation is followed by tlie movement of
definite groups of muscles are especially connected with such groups
of muscles. The further assumption is likely to be made that these
areas constitute the special organs which Lave control, as it were,
of the same muscles. Since it seems to be a general princij)le that
the sensory and motor nerve-tracts distributed to any region of the
periphery come into tolerably close local relations to each other
somewhere within the entire field of the cerebrum, it would seem to
follow that some special connection exists between certain classes
of sensations and volitions and the circumscribed areas of cortical
substance pointed out by experiment. It should not be forgotten,
however, that the excitation of any group of muscles, by applying
stimulus to some area of the cerebral cortex, proves only that this
area is somehow connected with such group of muscles. It still
remains to be shown that sensory impulses, on arriving from such a
peripheral portion of the body, serve as the physical basis for the
psychical phenomena of sensation solely within this circumscribed
central area ; or that conscious volitions, in order to be followed
by motion in this peripheral portion, must give rise to the mole-
cular commotion of the same area.
§ 15. By far the most efficient and manageable stimulus for ex-
perimenting upon the localization of cerebral function is the electrical
current. Mechanical or chemical irritation may, however, be em-
ployed in certain cases. The use of the electrical current incurs,
256 EVIDENCE FOR LOCALIZATION.
of course, tlie danger of its diffusion. Important objections, based
upon this fact and upon other grounds connected with the use of
electricity, have been raised to the conclusions of Hitzig.' To
Hitzig's claim that the electrical currents which excite the so-called
motor areas are "very weak," and therefore unable, at a very slight
distance from the place of the application of the electrodes, to affect
the nervous substance, Hermann replies that, on the contrary, con-
sidering the effect antecedently to be expected, these currents are
" surprisingly strong," and that the brain, in diffusing the currents,
must act like any other substance {e.g., a mass of copper) of similar
form — that is to say, the distribution of such a cuiTent in the sub-
stance of the brain is a purely geometrical function of the form of
this substance and of the position of the electrodes. Moreover, it
is found that increasing the strength of the current ajDplied to a
so-called "motor area" invariably increases the size of the cortical
region thrown into activity. That extra-polar conduction actually
takes place in the substance of the brain has been shown by Dupuy,
and by Carville and Duret ; contraction of the muscle of the rheo-
scopic frog and deflection of the needle of the galvanometer, at re-
mote distances from the electrodes, prove that the current passes
along the whole extent of the cerebral hemisphere. The excitability
of the cortical substance continues for hours after its exposure to the
air, or after acids have completely destroyed its external third por-
tion. If the cortical area be separated by a circular cut from all
connection with the nervous substance below, it is still excitable with
only a slight increase in the strength of the stimulus applied. Or
if the gray substance of the surface be wholly removed, and the
electrodes plunged in the blood of the cavity of one of these so-
called motor areas, the customary results follow. Still further, the
size of the circle within which the minimum amount of stimulus,
when applied to certain gyri, will serve to excite the hind-limb of
the animal, remains about the same whether the amount of cortical
surface contained in the circle be largely increased by a sulcus
crossing it, or not.
From facts like the foregoing it is argued that, while beyond
question the application of a given amount of stimulus to certain
gyri of the cortical surface will produce definite motor results, we
cannot ajBSrm those gyri to be the true cortical centres of such
motion. Such gyri have accordingly been regarded by some as
merely connected with the excitation of motion in a mechanical
1 See especially the article of Hermann describing investigations under-
taken by him in company with von Borosnyai, Luchsinger, and others,
Pfluger's Archiv (1875), x., pp. 77 fE.
EFFECTS OF ELECTRICAL STIMULATION. 257
way, through their service in conducting the electrical stimulus to
other regions of the brain, especially to the basal ganglia. The
ai'gument for the theory of localization would need to show, how-
ever, that the electrical current stimulates these areas immediately
to the exercise of their central nervous functions, and does not
simply pass through them to excite other nervous matter lying
beneath.
To the foregoing objections the advocates of the theory of locali-
zation make the following among other replies : " The effect of irri-
tation of the basal ganglia is capable of exact estimation ; " ' and
definite localized contraction of single groups of muscles, such as
comes from stimulating certain areas of the cortical surface, does
not follow from irritating the basal ganglia. Stimulation of other
areas of the cortical surface which lie nearer to the basal ganglia —
for example, of the island of Reil, which immediately overlies the
corpus striatum — causes no movements. On the contrary, it was
found by Carville and Duret that the phenomena evoked by stimu-
lating the motor areas persist, even after the destruction of the
corpus striatum. Moreover, when the animal is deeply etherized,
the excitability of the cortical regions is partially or wholly lost.^
Since the physical conductivity of the gray nervous substance is
not impaired by the anaesthesia, the loss of function must be due
to the functional condition of this substance. More conclusive do
the facts appear to be, which show that the nature of the motor
reaction following upon the application of stimulus to the cortical
substance is peculiar. Many observers have found that a stronger
stimulation is necessary to bring about the same motor results
after the cortical surface is removed ; this is what we should expect
on the theory of localization, but the reverse of what would be
true if the effect of the current was transmitted unchanofed through
this surface. Then, too, Franck and Pitres' have shown that the
effect of the electrical current is retarded in the gray matter ; the
difference of time, as dependent upon whether the stimulus is
applied to the gray matter or to the white lying beneath, being
about 0.015 second. This interval must be spent in evolving,
under the influence of the stimulus, the distinct neural function
which belongs to the gray matter. Finally, the excitation is appar-
ently reinforced in strength by the functional activity of the cor-
tical substance, since — as we have just seen — a stronger stimulation
is needed to produce the same result after this substance is re-
1 Ferrier, The Functions of the Brain, London, 1876, p. 133 f.
2 See Hitzig in Archiv f. Anat., PliysioL, etc., 1873, p. 403.
2 Archives de physiologie, 1875.
2oS EVIDElSrCE FOR LOCALIZATIOX.
moved ; such reinforcement is the peculiar property of the central
organs.
It seems obvious, therefore, that experiments with electrical
stimulation of the cortical surface demonstrate a special connection
between certain more or less definitely circumscribed areas of
that surface and definite groups of muscles ; they also create a
strong jDresumption that this connection is not merely anatomical
or structural, but also functional.
§ 16. The second kind of direct experimental evidence is de-
rived from observing the effects of extirjoation. It is natural to
arsrue that those areas of the brain, the loss of which is followed
by the loss or disturbance of motion in definite groups of muscles,
or by the loss or disturbance of any class of sensory impressions,
are functionally related in a peculiar way to such muscles or organs
of sense. But the application of this argument is encompassed
with many difficulties. In the first place, it is impossible at
each stage of the experiment — which often includes several days
or months of observation — to know precisely what the condition
of the brain is. Post-mortem examination of the brain reveals only
what was the final effect of the experiment in destroying its
tissues. The rise and fall of local or extensive inflammations, the
progress of degeneration in the nerve-tracts and of abscesses result-
ing from the primary lesions, etc., cannot be followed by the ex-
perimenter in detail. Nor can he directly observe the formation
and education of the tissue as it is called upon for an increase in
the amount of its former functions, or perhaps for the discharge of
functions partially new. As a rule, then, it is found that the
effects of extirpation change from time to time ; some of them are
of first importance and cannot well be overlooked, and others are
so delicate and minute as almost wholly to escape observation ;
some speedily pass away, others more slowly, still others perhaps
not at all. The difficulties are, of course, especially great when
we try to deal with effects upon the animal's sensory apparatus and
his psychical world of sensations and perceptions. To tell whether
an animal sees, hears, feels, smells, and tastes, or not ; and to tell
precisely in what sense it exercises these functions — whether, for
example, its deficiency is " soul-blindness " in any of its various
degrees — are not tasks which it is easy to perform, or about the
coiTCct pei'formance of which one can indulge in a boundless
confidence.
The demonstrative value of both kinds of experimental evidence
— electrization and extirpation — is much lessened by the fact that
it is almost wholly derived fx'om the lower animals. Ethical con-
FACTS OF HXJMAI^ PATHOLOGY. 259
siderations, which few investigators dare even occasionally to dis-
regard, forbid that the living human brain should be made the
subject of similar experiment. In ordei', then, to draw any safe
conclusions from this evidence, it is necessary not only that the
application of the principle of localization in general should be as-
sumed, but also that some right should be gained to transfer to
the human brain from the map of the cortical surface of the ani-
mal's brain, the so-called motor and sensory areas which have been
determined by experiment. But it is not even in all cases clear,
jDrecisely what convolutions or parts of convolutions of the human
cerebrum correspond to those previously marked out on the brain
of the animal. Moreover, in the effort to make any such transfer-
ence of the argument from the animals to man, we meet again with
the insuperable difficulty of forming a correct mental picture of
the psychical life of the animals.
§ 17. The evidence from human pathology for the localization of
cerebral function has a peculiar value ; but it has also its peculiar
puzzles and dangers. Such evidence is free, indeed, from the ob-
jections which arise against all attempts to carry the argument over
from the cerebral hemispheres of the lower animals directly to
those of man. Nature and human intercourse are less kind to this
wonderful mass of nerve-cells and nerve-fibres than the electrodes
and knife of the physiologist are compelled to be. Accident and
disease destroy, either suddenly or progressively, the different
areas of the cortical substance of the human brain. They have, in
various cases, made such a variety of attacks upon it as to cover all
the areas of both hemispheres. If, then, we had a large collection
of cases in which the lesions were definitely circumscribed, or the
progress made by the destruction of tissue Avas accurately recorded
for every stage ; and if we had also a correspondingly definite and
accurate description of the motor and sensory disturbances occa-
sioned by these lesions, we might perhaps be able to make a toler-
ably conclusive induction. But losses of brain-tissue, when caused
by accident and disease, have not the same circumscribed limits
which can be observed by the knife or corroding acid of the physi-
ologist. Lesions of the cortical areas entirely free from complica-
tion with lesions in the sensory and motor tracts below are compar-
atively infrequent. Cases of total destruction of any so-called "area "
on both hemispheres, and of such area alone, rarely or never occur.
Furthermore, it is only by careful post-mortem examination that
the precise extent of the pathological changes can be known ; this
examination, at best, reveals simply the last state of the case.
The reports oi post-mortem examinations are also, as a rule, lacking
260 EVIDElSrCE FOR LOCALIZATION.
, in precision. On the other hand, the symptoms of motor or sensory
disturbance are rarely described, from beginning to end, with suffi-
cient accuracy of detail to be of great service. Many large losses
of cerebral substance are followed by no sensory or motor disturb-
ances which can be distinctly traced. In large numbers of cases
where such disturbances arise, they in time pass almost or quite
wholly away. For these and other reasons the best evidence at-
tainable from pathological cases, when collected and sifted, appears
surprisingly confusing and self-contradictory. Pathology has, there-
fore, furnished the common fund of cases from which the most di-
verse and even contradictory theories have drawn at sight their stock
of so-called proof. It has been used as the careless and false witness
upon which either party, and all parties to the suit, could call for
precisely the testimony desired. An increase of information and
care on the part of those who have opportunity for ante- and post-
mortem observation of such cases will doubtless, in time, cause
pathology to yield much more assured results.
§ 18. The third kind of evidence to which the principle of the
localization of cerebral function may appeal comes from compara-
tive anatomy and histology. Comparative anatomy, however, gives
us evidence of only the most genei'al kind. Combined with exper-
iment by electrical excitation, it shows that, on the whole, the
higher the structure and intelligence of the animal, the more nu-
merous and moi'e definitely marked are the " excito-motor areas "
which may be discovered on the hemispheres of its brain. Only
traces, as it were, of such areas can be found upon the cerebral
hemispheres of the frog or the pigeon ; only a few areas can be
doubtfully pointed out for the i-at or guinea-pig. The indications
are clearer and more numerous of localized cerebral function in
definite centres of the brains of the rabbit and the sheep. But it
is in dealing with the cerebral convolutions of the more highly
specialized brains of the dog, and particularly of the monkey or the
man-like ape, that the proofs of the theory become most abundant.
While, then, the argument from all the other animals to man is
uncertain and should be used only with great caution, the general
drift of comparative anatomy encourages us to place the greater
confidence in it, the more nearly the bi-ain of the particular animal
from whose case we wish to draw the inference resembles the
brain of man. At the same time, the rash confidence with which
the brain of the monkey has been mapped out in detail, and human
pathology thereupon ransacked with the purpose of finding some
warrant for copying this map upon the brain of the human species,
cannot be too carefully avoided.
THE EVIDENCE OF HISTOLOGY. 261
Histology supplements and confirms the other evidence by show-
ing that the structure and connections of different parts of the
cerebrum are such as we should expect them to be, in case the
functions of the parts were such as experimentation and pathology
seem to have discovered. The modern arts of microscopy and
photography have made possible an increasingly accurate knowledge
of the intimate structure of the brain. Many great difficulties,
however, still remain in the way of such perfection of this knowl-
edge as will make it available as a secure foundation for a theory
of the localization of cerebral function. At present the histology
of the human cerebral hemispheres is not in a condition to take
the place of a leader of physiological experiment and pathological
observations. Its office is still rather that of rendering supple-
mentary evidence in correction or confirmation of the evidence
from the other two sources. Thus, for example, if Gliky's belief
that he traced the nerve-tracts from the so-called motor centres of
the cerebral hemispheres as they bend around the striate bodies
and run into the crusta of the crura cerebri should be demon-
strated, this fact would constitute an item of confirmatory evidence
furnished by histology to experimental physiology and pathology,
in favor of their general theory.
§ 19. According to the foregoing view of the nature of the three
kinds of evidence available, it would seem that, in collating and
estimating the combined proofs from them all, the following course
of inquiry should be pursued. The indications of experiment upon
the cerebral hemispheres of the animals— especially of those most
closely allied to man in their cerebral structure — by the two
methods of stimulation and extirpation, must first be gathered and
carefully weighed. Only those conclusions upon which the two
methods are found to yield substantially the same results should be
selected for further testing. The instances of localization of cere-
bral function thus detected in the other higher mammals must
then be allowed to suggest to pathology the questions it should
undertake to answer with reference to man. In other words, ex-
perimentation with the other animals suggests and strengthens the
hypothesis which human pathology must try to satisfy. But in
undertaking to test such hypothesis, pathology must be both fair
and comprehensive in its observations. All the accessible patho-
logical cases must be sifted and those only selected to bring for-
ward as evidence which have the definite nature, and have received
the careful examination recorded in detail, that are necessary to
make them of real value. The corrective or confirmatoiy evidence
of histology must then, so far as possible, be summoned to aid in
262 EVIDENCE FOU LOCALIZATION.
forming our final conclusions. It is not until all the kinds of proof
unite with a large and substantial agreement, if not with an abso-
lute uniformity, that we can feel the utmost confidence attainable
in our results. If it be found that certain regions of the cerebral
hemispheres of the higher animals are the only ones to respond
when stimulated with movements in definite peripheral parts of the
body, and that the injury of those same central regions alone, or
chiefly, causes motor and sensory disturbances in the same periph-
eral parts ; if it also be found that lesions of the corresponding-
regions of the human brain are alone, or chiefly, followed by similar
motor and sensory disturbances, and that lesions of other regions
alone are rarely or never followed by these same disturbances ; and,
finally, if it be found that these same cortical regions have in the
human body a special anatomical connection with these same pe-
ripheral parts ; then we have reached the most conclusive evidence
attainable for a theory that the cerebral functions are localized in
the case of man. But precisely what is meant by such " localiza-
tion " may still remain more or less a matter of dispute. We con-
sider now a summary of the evidence according to the foregoing
principles.
CIIAPTEE II.
THE LOCALIZATION OF CEEEBEAL FUNCTION. [Continueb.]
§ 1. On attempting to make an induction from all the three kinds
of evidence which may be adduced in answer to the question,
whether the different functions of the cerebral cortex have special
relations to its different localities, no other difficulties are on the
whole so great as those which come from so-called "negative cases."
These negative cases force the inquirer to undertake a detailed ex-
perimental and pathological examination. " That the cortex of the
cerebrum, the undoubted material substratum of our mental opera-
tions," says Ecker,' "is not a single organ, which is brought into
play as a whole in the exercise of each and every psychical function,
but consists rather of a multitude of mental organs, each of which
is subservient to certain intellectual processes, is a conviction which
forces itself upon us almost with the necessity of a claim of reason."
But even the proposition that the brain is the "material substratum
of our mental operations," is very far indeed from having the char-
acter of a rational necessity. The further proposition that the cor-
tex of the cerebrum " consists of a multitude of mental organs," is
an inadequate statement of a conclusion which, at the very best,
we can adopt only as the result of a long series of complex and con-
flicting researches. Li fact, considerable areas of the cortical sur-
face appear, at first, not to have any immediate relation to any psy-
chical function whatever.
The first general principle to be admitted in all attempts at a
theory of the localization of cerebral function is, then, of a nega-
tive character. This principle is based upon the negative results
of physiological inquiry. Considerable areas of the cortical sur-
face do not respond with motor activities when stimulated. Con-
siderable portions of the cortical substance may be extirpated or
lost by disease without the destruction or appreciable disturbance
of any motor, sensory, or more purely intellectual functions. To
such an astonishing extent is this true as to throw temporary doubt
not only over the whole theory of the localization of cerebral func-
■ The Convolutions of the Human Brain, p. 1. London, 1873.
264 STIMULATION AND EXTIRPATION.
tion, but even over tlie statement that the cerebral cortex, as a whole,
is the only " material substratum " of mental operations.
§ 2. Attention has already been called (Chap. L, § 11) to the fact
that Longet, Flourens, and other great physiologists, considered
the cerebral hemispheres to be active as a whole in all their func-
tions, and this, partly, because they found them not irritable by the
electi'ical current. The discovery of Fritsch and Hitzig in 1870 de-
monstrated that a part of the hemispheres of the dog, and a part
only, gives signs of being excited by the application of stimulus.
This part they called " motor," and located, in general, in the fore
part of the hemispheres ; behind lay the region called " non-mo-
tor," because it gave no response on being stimulated.' Even with-
in this so-called "motor" region the early reseai'ches of these in-
vestigators pointed out only five spots of a small fraction of an inch
in diameter (the electrodes were, as a rule, separated not more than
2-3 mm.) that could be more definitely related to the movement of
certain groups of muscles ; between and around these spots lay the
much larger areas of negative resrdt. Subsequent experiments
added a few more such irritable areas to the map of the cerebral
hemispheres of the dog. A large number of so-called centres, cover-
ing an increased amount of the cortical surface, have been pointed
out by Ferrier and others on the cerebral hemispheres of the mon-
key. Fully half of this number, however, cannot be regarded as
having anything like a demonstrable character ; and much fault has
justly been found ^ with many operators upon the brains both of
monkeys and of dogs, for their lack of precision in experiment, and
haste in drawing conclusions.
Experiments in extirpation also show that considerable areas
of the cortical substance may be removed without perceptibly im-
paiiing any of the motor or sensory functions of the animal. In-
deed, even when the loss of the cortical substance, thus artificially
produced, extends over almost an entire hemisphere, or over a large
portion of both hemispheres, the operation may not result (in the
case of the dog, ordinarily does not result), in the pervmnent and
complete loss of any siDecific function, motor or sensory. So true is
this that one eminent observer, Goltz, has maintained, on the basis
' Archiv f. Anat., Physiol., etc., 1870, p. 311.
^ See, for example, Munk s strictures of Ferrier, Ueber d. Functionen d.
Grosshirnrinde, Berlin, 1881. pp. 14 fE. (also p. G f. ; 36 f. — " roh w<ir operirt,
roh beohachtet, roh geschlossen ''''). On the other hand, the charge of careless-
ness in experiment, and of illogical conclusions is freely made against Munk
himself, both by advocates of rival theories of localization, like Dr. Yeo and
others, and also by opponents of all theories of localization, like Goltz, Lob,
and others.
EVIDENCE FROM NEGATIVE CASES. 265
of many experiments in extirpation, that it is chiefly the quantity of
the cerebral substance destroyed, in large measure irrespective of
the locality, which determines the nature and extent of the result-
ing psychical disturbances. The arguments of Goltz (as he him-
self admits) do not answer those urged for a certain kind and de-
gTee of the localization of cerebral function. But his experiments
furnish a large number of facts which emphasize' the negative char-
acter of many of the results of experiment. This fact is in itself
undeniably unfavorable to any theory which would map out the en-
tire cortical surface into so-called centres or areas, to be considered
as separate organs of particular psychical processes.
§ 3. The negative evidence from certain cases in human pa-
thology is yet more astonishing and perplexing. At first sight it
seems to suggest the conclusion that the mind can dispense, with-
out impairment, with a considerable mass of brain-substance, no
matter from what region it be subtracted. Many cases of large le-
sions of the cerebral hemispheres in man, with no resulting disturb-
ance of the psychical functions, are recorded.'
Berenger de Carpi tells of a young man who had a foreign body
of four fingers' breadth square driven into the substance of bis
brain until it was buried. Much of this substance was lost when
the foreign body was removed, and more yet some thirteen days
later. Nevertheless, the patient lived for a long time in the enjoy-
ment of all his faculties.
Longet was acquainted with an army ofiicer who had lost, by a
wound in the parietal region, a large quantity of brain-substance ;
yet he remained mentally vivacious and showed no other result of
the lesion than a tendency to grow tired easily. The same authority
communicates ^ the case of an Italian whose skull was crushed in
the right parietal region by a stone. So much of the substance of
the brain was lost on the wound being dressed, and subsequently
through a fall from his bed (on the eighteenth day) and through
intoxication (on the thirty-fifth day), that the attendant physician
calculated the lesion must have reached down nearly to the corpus
callosum. The man, however, lived without any apparent impair-
ment of psychical functions ; but we note in this case a permanent
laming of the limbs of the left side.
' See the list of such cases in Ferrier, the Localization of Cerebral Disease,
London, 1878, pp. 25 ff.; Hermann, Handb. d. Physiol., II., ii., pp. 333 ff.;
Briicke, Vorlesungen liber Physiol., II., p. 57 f. Wien, 1884; and the works
cited by the two former, especially Pitres, Lesions du centre ovale, Paxis,
1877.
^ Recorded, however, by Quesnay.
2Q6 STIMULATION AND EXTIRPATION.
A remarkable case is narrated by Brticke, " on the authority ol
a certain Dr. Kratter. By a blow from a stone on the parietal
region of the skull, one Ivan Mussuhn was thrown to the ground ;
but within two hours he recovered so that he himself went to
the " praetor " and entered complaint against his assailant. For
twenty days he hved in apparently full possession of his powers
of motion, sensation, and intelligence ; on the twenty-first day he
suddenly died. The entire left cerebral hemisphere was found on
examination to be a disorganized mass. It is to be noticed, how-
ever, that the autopsy did not take place until some eighteen hours
after death, and that we have no good means of judging what the
condition of the injured hemisphere was during the twenty days
preceding his sudden death.
Remarkable instances of defective brains are also on record ; for
example, the case which Lallemand nari'ates of a person of normal
psychical constitution in whose cerebrum the entire place of the
right hemisphere was, after death, unexpectedly found to have
been filled with a serous fluid. Here again, however, there had
been lameness of the left side of the body from birth.
Extensive lesions without marked motor or sensory disturbances
occur by far most frequently in the frontal lobes of the cerebral
hemispheres. Yet similar negative cases are by no means infre-
quent also in the occipital and temporo-sphenoidal lobes. Trous-
seau narrates the case of an officer who was shot through the head
in the middle of the frontal lobes, and who showed until death,
which occurred from inflammation, no signs of. any kind of paral-
ysis. The work of M. Pitres ^ contains a large collection of cases,
in which the frontal lobes have been the seat of extensive disease,
of softening, or of abscess, without any symptoms of laming what-
ever ; in most of which, also, no disturbance of psychical con-
dition was observed. That sudden extensive lesions may occur in
this region without inducing sensory or motor paralysis, is shown
in a marked way by the celebrated "American crowbar case." ^
By prematui'e discharge of blasting powder an iron bar, three feet
seven inches in length and one and one-fourth inch in diameter,
was driven through the brain of a young man. The missile en-
tered at the left angle of the jaw, and passed through the top of the
head near the sagittal suture in the frontal region ; it was picked
up at some distance off, covered with blood and brains. The pa-
' Vorlesungen iiber Physiol., 11., p. 57.
'^ Lesions du centre ovale.
" See the paper in the Am Journal for Med Sciences, by Dr. Bigelow, July,
1850, and the one read before the Masa. Med. So. by Dr. Harlow, June, 1868,
GENEKAL MOTOR EEGION. 267
tient, although, for the moment stunned, recovered in a few min-
utes so as to ascend a flight of stairs and give to the surgeon an
intelhgible account of his injury. He Hved twelve and a half years
afterward, with no noticeable impairment of his sensory-motor
powers. Examination of the skull showed that the substance de-
stroyed by the bar must have been confined to the frontal region,
with the possible exception of the tip of the temporo-sphenoidal
lobe.
Boyer narrates the case of an epileptic child, that showed, how-
ever, no other abnormal nervous phenomena, whose entire temporal
lobe on the left side was found to have been destroyed. Instances
of extensive lesions in the occipital lobes, without any resulting
sensory or motor disturbances, might also be given.
§ 4. It must be confessed, in the words of Exner,' that the
understanding of cases of this sort "is made more difficult rather
than easier by recent researches." Nevertheless, a large amount
of concurrent testimony from all three main sources of evidence
proves that some theory may be framed in acknowledgment of a
more definite localization of cerebral function. Such theory can
be most clearly established Avith respect to the cerebral region
esj)ecially concerned in the motor functions. This region is the
one Ijing about the great central fissure, or fissure of Rolando ;
more precisely still, it embraces the gyrus centralis anterior, the
gyrus centralis posterior, and the prolongation of the two on the
median surface of the brain in the lohulus paracentralis. (Comp.
Figs. 87 and 88). More definite localizations still, of smaller re-
gions within the larger one — e. g., for the upper limbs, for the lower
limbs, for the separate fingers, etc. — are more doubtful ; they can
by no means appeal to the same amount of evidence as that at com-
mand of the more genei-al induction.
§ 5. The evidence from experiments in stimulation indicates that
we are to look for the so-called ^^ motor areas'" in the above-mentioned
convolutions about the fissure of Rolando. The original experi-
ments of Fritsch and Hitzig ^ located the five motor areas as fol-
lows : The centre for the muscles of the neck (marked A in the
figure) in the middle of the pree-frontal gyrus at the spot where its
surface falls off steep ; the centre for the extensor and adductor of
the fore-limb, at the outermost end of the post-frontal gj^rus in the
region near the end of the frontal fissure (-1^ in the figure) ; the
^ 111 Hermann's Handb. d. Physiol., II., ii., p. 834.
» See Archiv f. Anat, Physiol., etc., 1870, p. 312 f . ; comp. Taf. IX B. by
Hitzig in the same Archiv for 1873, from which the accompanying figure is
taken.
268
STIMULATION AND EXTIRPATION".
centre for the bending and rotation of the same limb, a little
farther back (+ in the figure); the centre for the hind-limb, in
the post- frontal gyrus but to-
ward the median line of the
^ hemisphere and back of the
* preceding two centres (4^ iu
f the figure) ; the facial centre,
# in the middle part of the
0 gyrus lying above the fissure
of Sylvius (4~0 in the figure).
** These experimenters found
■^ also that the muscles of the
o back, tail, and abdomen, were
excited to contraction by
stimulating points lying be-
'*' tween those marked as above ;
but they could not definitely
circumscribe the cortical areas
Fig. 83.— Hitzig's Motor Areas on the Cortex of the -^Jiich WCre to be aSSiffUed tO
Dog. The left hemisphere belongs to one animal, °
the right to another; o, the mlmis cruciatUH, tlieSC mUSclcS.
around which the gyrus sigmoideus bends ; oooo, i. i.i i, i.
area for the face. The other symbols are explained J3y retercnce tO tUe CUart
*'' *''^ ^''^- of the numerous " centres of
electrical irritation " Avhich Terrier ' claims to have discovered on the
cerebral hemispheres of the monkey, it will be seen that they are set
close together in the two
central convolutions
{gyri centrales, called
by Ferrier the " ascend-
ing frontal" and "as-
cending parietal ") and
in the immediately ad-
joining parts of the
frontal and temporo-
sphenoidal convolu-
tions. Thus, the cen-
tres (2, in part), (3), (4,
in part), (5, in part),
(6), (7), (8), (9), and
(10), are located in the
anterior central (" ascending frontal ") convolution ; (2, in part),
(4, in part), (11, in part), and (a), (b), (c), (d), are placed on the poste-
' See The Functions of the Brain, pp. 141 fE. , 149 f. , and 305 f . London, 1876,
In the second edition (1886), pp. 240 ff.
Pig. 84.— Areas on the Left Hemisphere of the Monkey, by
stimulating which Ferrier obtains motion in definite groups
of muscles.
EFFECT OF ELECTRICAL STIMULUS. 269
rior central (" ascending parietal ") convolution ; the centres (12) and
(5, in part) are situated on parts of the superior and middle frontal
convolutions adjacent to the anterior central ; and (14) on the su-
perior temporo-sphenoidal convolution.
Further and more recent information seems to render the experi-
ments in the electrization of the cerebral areas of animals more
available for use in confirming the general argument in behalf of
some kind of localization of cerebral function in the case of man.
Luciani and Tamburini, as well as other experimenters, have agreed
with Hitzig and Terrier in finding small, circumscribed motor cen-
tres on the cortex of the dog, monkey, rabbit, and other animals.
Some experimenters (Bochefontaine and Vulpian, e.g.) claim to
have discovered that the minute areas, at first excitable, after a
time cease to be so ; and that other areas, at first not excitable,
afterward become excitable — that is, a displacement of the excit-
able points takes place.
More recently still, it has apparently been discovered ' that Ex-
ner's view (to be explained subsequently) of the existence of " ab-
solute " and " relative " motor fields in the case of man is probably
applicable to the animals also. Paneth found that a number of
minute areas (or spots) for each one of the several groups of muscles
could be detected as lying in the larger " excitable zone " of the
cortex. These areas, vmlike the immediately surrounding ones,
could be excited when cut around, but not when cut heneMh ; the
fibres whose function it is to bring a definite group of muscles to
contraction seem then to proceed directly from these cortical spots
to the lower parts of the brain. A number of such belong to each
muscle excitable ; but only two general " fields " are distinguish-
able, within which all the isolated motor spots are located ; one
field is for the extremities, the other for the orbicularis palpebrarum.
The former is situated in the posterior division of the gijrus sig-
moideus. The minute areas for the different muscles of the ex-
tremities are sharply limited ; they do not wholly cover each other ;
and those for any special muscle (the extensor digitorum of the fore-
foot, etc.) are of small extent in comparison with the field or zone
which may be looked on as common to all the extremities. The
excitability of the different muscles is not all alike ; this Paneth ex-
plains by assuming that the number of nerve-elements assigned to
each is not alike.
§ 6. Experiments in extirpation confirm, at least in a general way,
' See the art. of J. Panetli, "Ueber Lage, Ausdehnung, \ind Bedeutung der
absoluten motorisclieu Felder," etc., in Pfliiger's Archiv, xxxvii. (1«85) pp.
530 fE.
270 STIMLTLATION AND EXTIRPATION.
the above-mentioned results of experiments in stimulation. The
destruction of the substance of those cortical areas which respond
to the current of electricity with the co-ordinated movement of def-
inite groups of muscles, causes a temporary or permanent impair-
ment of the functions connected with the same groups of muscles.
In their first report Fritsch and Hitzig called attention to certain
experiments of their own in removing from the cerebral hemispheres
of two dogs the nervous substance of the centre which had already
been fixed upon by them as that for the " right fore extremity "
of the animal. These experiments they found confirmatory of the
views derived from stimulation. The animals operated upon,
when sitting or standing or running, used the right fore-leg un-
skilfully ; this part of the body, however, showed no marked dimi-
nution of sensibility under hard pressure. Other observers have
since performed many similar experiments ; — especially Ferrier on
monkeys, and Goltz and Munli on dogs. Among them all no oth-
ers are so carefully refined as are those of Munk." But the very
refinement of these experiments subjects them to more of distrust,
in certain particulars.
§ 7. The earlier experiments of Munk were confined to the convex
surfaces of the parietal, occipital, and temporal lobes of dogs ; they
consisted in removing clean-cut circular bits of the cerebral sub-
stance about three-fifths of an inch in diameter and one-twelfth of an
inch thick — sometimes simultaneously, from the symmetrical areas
of the two hemispheres, and sometimes with an interval between the
two operations. Munk's general conclusion is stated as follows :
If a line be drawn from the terminal point of the fissure of
Sylvius vertically toward the falx cerebri, it will mai'k, approxi-
imately, the limits of two spheres that are sharply distinguished
experimentally — namely, an anterior motor and a posterior sensory
sphere." Extirpations in front of this line always occasion dis-
turbances of motion, those back of it never so. More precisely,
the cerebral convolutions of the dog may, according to Munk, be
mapped out into the several spheres and regions indicated in the ac-
companying figure (Fig. 85). It will be noticed that three of these
regions (namely, C for the hind leg, D for the fore leg, and E for
the head) correspond pretty accurately to the centres of stimulation
fixed upon by Fritsch and Hitzig. Extirpations of the cortical sub-
stance in these i-egions, of only a few millimetres broad and not
more than two deep, are regularly followed by definitely localized
' See his Gesammelte Mittheilungen aus d. Jaliren 1877-80, in the book,
Ueber d. Functionen d. Grosshiruriude. Berhu, 1881.
2 Munk, ibid., p. 11.
MOTOR AREAS ' OF THE DOG.
271
distiu'bance of motion. For example, let the region (Z)) be removed
from the left cerebral hemisphere of a dog. At the end of from three
to five days and after the fever from the operation has subsided,
abnormal phenomena connected with the fore-leg of the opposite
side will be observed. If any other limb of the animal than the
right fore-leg be touched lightly, the dog will look quickly around ;
Fig. 85.— Areas on the Brain of the Dop. (According to Munt.) A, centre of the Bye ; B, of
the Ear ; C, of the sensations of the hind Leg- ; D, of the fore Log ; E, of the Head ; F, of the
Apparatus for protecting the Eye ; G, of the Region of the Ear ; H, of the Neck : J, of the
Rump.
and if of a bad temper will try to bite the offending hand. He
will also quickly withdraw any other limb when it is subjected to
even very slight pressure. But hard pressure and pinching or
sticking of the right fore-leg is either followed by no result, or else
by mere withdrawal of the limb, as though in reflex motion, without
any attention being paid to the attack. Moreover, this particular
limb, unlike all the others, can be put into unnatural and uncom-
fortable positions — can be bent, stretched, set on the ground with
272 STIMULATION AND EXTIEPATION.
the back of the foot down, etc. — without any resistance on the
animal's part or any apparent disposition to remove it to the
normal and comfortable position. According to Munk, the animal
has apparently lost all mental picture of this one limb, and there-
fore all power to move it intelligently and voluntarily. If he has
been accustomed, on call, to put the right leg into his master's hand,
he will now respond with the left instead of the right foot to the
same call. The dog no longer handles his food with the right
foot. In running he slips on that foot. If he is drawn to the
edge of a table and the right leg forcibly stretched out over it, he
will allow the leg to hang down thus, although evidently aware of
the dangerous position in which this places him. Such an animal
can, however, still walk and run, using all four limbs. The " gross
mechanism " of motion — to borrow Munk's phrase ' — still acts as it
did before; but the so-called "cerebral" or intelligent quality in
the management of this particular limb has been lost.
Gradually the phenomena which indicate impairment of cerebral
function as related to the movement of the foi-e-leg diminish in
magnitude. Less pressure is then necessary to secure the with-
drawal of the injured limb ; the dog is less surprisingly unskilful
in its use. At the end of four or five weeks the moi-e marked
symptoms of his loss of function have probably disappeared ; at the
end of eight or ten weeks it may be difficult or impossible to dis-
tinguish his movements from those of a perfectly sound animal.
If, however, the size of the pieces of cerebral substance taken from
any of the so-called " motor regions " be somewhat larger than that
indicated above, recovery is slower and more imperfect. In the
opinion of Munk, if the extirpations are considerably enlarged the
restitution of function is never complete.
§ 8. That explanation of the phenomena which regards the va-
rious cerebral regions, that seem somehow specially connected with
motor activities, as true " motor centres," — that is, as areas of the
cerebral cortex that have for their peculiar function the initiating
of definite motor impulse on occasion of the idea and volition to
move definite portions of the peripheiy of the body, — is rejected
by Munk. All the regions marked G — J, belong rather to what he
calls the "feeling-sphere" of the cerebral hemispheres. It is an
undoubted fact that the definite co-ordination of the limbs, from the
higher cerebral centres, depends upon feelings of contact and press-
ui'e of the skin, and upon muscular feelings or so-called feelings of
innervation. The effects of extirpating centres like (C), (D), and
(E), is due, therefore, first to the sudden loss, and subsequently to
' Ueber d, Functionen d. Grosshinirinde, p. 47.
MOTOR AREAS" OF THE MOl^iKEY.
273
the gradual restitution of these feelings, and of their correspond-
ing mental representations, with respect to given groups of mus-
cles.
Schiff ' agrees with Munk in the view that the real loss of function
due to the extirpation of the above-mentioned cerebral regions is
sensory rather than motor ; he considers that the imj)airment of the
power of moving these parts is only an expression of the loss of the
sense of touch in the same parts ; in other words, it is tactile an-
aesthesia. He calls attention to the significant fact that an animal
thus operated upon will freely allow parasites and insects to gather
on that surface of the skin whose corresponding cortical area has
been removed. Schiff also finds that the use w^hich the higher apes
Fig. i
-Areas on the Brain of the Monkey. (According to Munk.) The letters have the same
reference as in tho preceding figure.
make of their limbs for grasping the rounds of a trellis or ladder
is not permanently impaired by removing to considerable depth
the convolutions about the central sulcus, unless the trellis or ladder
be turned at an angle of 60'' to 70°, so as to convert the animal's
walking into climbing. Apparently the animal cannot climb be-
cause he is unable to form a mental picture of the next round so
as to i-each out and grasp it. Schiff therefore concludes, that " all
motions are suppressed (by extirpating the cerebral substance)
which, on being excited by the higher senses, receive a special
supervision on the side of cerebral sense, in relation to direction,
extent, and succession." He also asserts, in opposition to the
conclusions of Goltz, that the injured animal never recovers the
1 See Pfliiger's Archiv, xxx. (1883), pp. 313 flf.
18
274 STiMULATioisr AjStd extirpation.
powers it has once really lost ; in other words, it is not possible to
extir^Date any of the centres, excitation of which produces a given
motion, without effecting some permanent result.
§ 9. The conclusions of Munh and Schiff undoubtedly have cer-
tain facts of experiment in theu" favor, but they can scarcely be said
either to cover all the facts or to be wholly consistent with certain
pai'ticular ones. Goltz ' agTces substantially with Munk in finding
that destruction of the cerebral substance of the frontal lobe causes
the animal to execute movements of the limbs of the opposite side
in a coarse and unskilful manner. He also finds that the tactile
sense is temporarily impaired, although by giving increased atten-
tion the animal is able to feel the slightest touch on any area of
the skin. Indeed, deep and extensive lesions in this region may
be followed by hj^DcrEesthesia. The muscular sense, on the other
hand, seems permanently to suffer. Goltz's conclusions are squarely
contradictory of all those which find any permanent laming of any
muscle as the result of even the most extensive destruction of the
cortical substance in the so-called "motor field." His theory lays
more emphasis on the general impairment of intelligence which re-
sults fi'om removing any considerable amount of the substance of
the brain, from whatever region it may be taken.
A still more recent investigator^ calls attention anew to the facts
that an animal deprived of the " motor sphere " cannot use the ex-
tremities as hands ; cannot hold the foot out on call, or push away
the hand by which its chin is grasped, or stretch out the limb so
as to grasp the dish containing its food. These phenomena imply,
he thinks, some severance between the organ of will and the nerves
which execute the will. The motor centres are to be limited, it is
claimed, almost exclusively to the gyrus sigmoideus, and those for
feelings of the skin and muscles to the region lying above the fis-
sure of Sylvius.
On attempting to reconcile all the results of experiment upon
the animals with one another, and with the facts of human pathol-
ogy, it must be admitted that great difficulty is experienced ; and
even more difficult}'^ when the effort is made to frame a consistent
theory which shall cover them all. On the whole, however, it
seems obvious that a certain region or sphere of the cortex of the
brains of the higher animals is entitled to be called " motor" in a
special sense ; and that this region corresponds in a general way to
' See his article in Pfli'ger's Archiv, xxxiv. (1884). pp. 450 fP.
" Bechterew, art. " Wie siiid die Ersclieiuiuigen zu verstelien die nach
Zerstorimg des motorischeu Riudeufeldes an Thiereu auftreteu ; " Pfliiger,
XXXV. (1885), pp. 137 tf.
FROM AlSriMAtS TO MAN. 275
that which (as we shall soon see) pathology indicates as specially
motor in the case of man. Stimulation of various minute areas in
this region is followed by the movement of definite muscles of the
body ; extirpation of this region in its entirety, or in part, is fol-
lowed by special disturbances of the motor functions of the animal.
These disturbances are not of the kind which indicates so much
a laming of any particular muscle, as a loss of cerebral, and so in-
telligent, quality in respect to the handling of the extremities.
They probably imply more or less of all those various kinds of psychi-
cal disturbances and impairments of function, by some one of which
exclusively the different investigators are wrongly inclined to ac-
count for the phenomena which they observe. Extensive lofeses of
cerebral substance in the motor region result in the loss of those
tactile sensations and muscular sensations, by means of which the
animal localizes and interprets the meaning of objects, and adapts
the finer movements of its limbs accordingly. They also impair
the power to express the volition of the animal by motor impulses
started, in accordance with the sensations and images of motion, in
the appropriate area of the brain. Moreover, such loss of the
powers of sensation, sense-perception, and skilful motion, neces-
sarily implies more or less of loss of intelligence.
§ 10. It will always be difficult to designate precisely what fac-
tors in the animal's complex sensory-motor activities drop out as the
result of the removal of a certain area of cortical substance from the
brain of a dog or monkey ; and whether these factors are exclusively
sensory or exclusively motor, rather than both sensory and motor.
It is doubtful if enough can ever be known, concerning the mental
life of the dog or the monkey, to determine confidently in this way
the question of the localization of psycho-physical functions. The
phenomena of human pathological cases indicate, however, that in
man the corresponding general area of the cerebrum — that is, the
convolutions on both sides of the central fissure and the lobulus
paracentralis — is especially concerned in both sensory and motor fac-
tors for co-ordinated action of the limbs. Without adducing further
confirmatory evidence from experiment upon other animals, we
pass to the consideration of the evidence from human pathology.
The results of experiments in stimulation and extirpation upon the
lower animals are not to be transferred in toto, as a matter of
course, to the human cerebrum ; they are rather to be consulted
as indicating the precise nature of the questions to be proposed to
pathology, and of the answers to these questions which are antece-
dently probable.
From this point onward our chief reliance must be placed upon
276
HUMAN PATHOLOGICAL CASES.
Exner's ' careful and scientifically classified investigations. The
method pursued by this investigator is described at length by him-
self. ° Exner began, with true German thoroughness, by reading
several thousand cases of cerebral disease which had been followed
by post-mortem examination ; the catalogue of works thus consulted
by him occupies more than twenty pages. From all these cases he
Fig. 87. — Lateral View of the Human Brain. (Schematic, Ecker.) F, frontal, P, parietal, O,
occipital, and T, temporo-sphenoidal lobes. S, fiBsure of Sylvius, with S'. the horizontal, and
8", the ascending ramus ; C, sulcus centralis ; A, anterior, and B, posterior, central convolu-
tions ; Fl, ra, F8, superior, middle, and inferior frontal convolutions ; fl, superior, f2, infe-
rior frontal sulci; f3, sulcus praeceiiiralis; PI, superior, and P2, inferior parietal lobule; the
latter, the gyrus supra marginalis, and P9', the gyrus angularis ; ip, sulcus interpiirietalis : cm,
end of calloso-margii'al fissure ; Ol. 02, 08, occipital convolutions ; po, parietooccipital fissure ;
o, transverse, and o2, inferior longitudinal sulcus; Tl, T2, T3, tempore sphenoidal convolu-
tions; and tl, t2, tempero sptienoldal fissures.
then made a collection of such only as could safely form the basis
of a scientific induction. The conditions of admittance into this
collection were as follows : Both the history of the disease and the
description of the post-moi'tem condition must be trustworthy, full,
' Untersuchnngen iiher d. Localisation d. Functionen in d. Grossliirnriude
d. Menscheii. Wien, 1881.
•' Ibid, p. G f.
THE METHODS OF KECKONING.
277
and unambiguous ; and there must have been no other lesion than
the one in the cerebral cortex, either elsewhere in the brain or in
the spinal cord, to complicate the legitimate inferences. Only two
exceptions to the latter rule were, for reasons peculiar to themselves,
admitted. Nearly all cases in which symptoms indicative of diffuse
meningitis occurred were also excluded. In this cautious way one
Fig. 88. — View of the Human Brain from Above. (Schematic, Ecker.) The letters have the
same reference as in the preceding figure.
hundred and sixty-nine test-cases were secured from the thousands
recorded. These test-cases were then tabulated on three sets of
maps, according to the following methods of induction : (1) The
method of negative cases, (2) the method of "reckoning per cent.,"
(3) the method of positive cases.
The method of negative cases (if the number of such cases were
large enough) would result in showing what regions of the cerebral
hemispheres, if any, are not necessarily connected with motor or
278
HUMAN PATHOLOGICAL CASES.
sensory functions — both, or either one respectively. The charts
constracted by this method would, accordingly, have only those
convolutions and parts of convolutions left blank, or unmarked,
in which no lesion had occurred that was not followed by some
given kind of motor or sensory disturbances. The method of per-
centage was designed to show the amount of probability that a
given small area of the cerebral cortex will be hit by disease, as
it were, in case the lesion has been followed by a given kind of
motor or sensory disturbance. For this purpose the entire sur-
face of one hemisphere was mapped out into three hundred and
A 9
Fig. 89. — Median Aspect of the Right Hemisphere. (Schematic, Ecker.) CO, corpus callosum.
G-yri : G-f, fornicatns ; H, hippocampi (with its sulcus, h), and TJ, uncinatus : PI', praecuneus;
Oz, cuneus ; oc, calcarine fissure, with its two rami, oc' and oc'' ; D, gyrus descendens ; T4, the
lateral, and T5, the medial, gyrus occipito-iemporal.R.
sixty-seven quadrilateral areas, all small and yet of somewhat dif-
fei'ent sizes. As the different selected cases were recorded by
painting the area of the lesions on this set of maps, the intensity of
the color used would, of course, deepen in proportion to the cer-
tainty of a connection between that particular area and some par-
ticular sensory or motor function. Thus a joerfect black would
indicate one hundred per cent, of cases in which a given quadri-
lateral was hit when a given disturbance of function had followed ;
pure white, nought per cent, of such cases. The third method (that of
positive cases) is the one usually relied upon to prove (?) the theory
of localization of cerebral function from pathology ; it is justly re-
garded by Exner as the least conclusive, as never of itself forming
FIELD OF LATENT LESIOISTS. 279
a basis for anything beyond conjecture. Its principle is the as-
sumption that the region where the lesions connected with certain
disturbances are most thickly crowded together, is the required
cortical area with its specific function.
§ 11. The result of Exner's comprehensive induction from patho-
logical cases, as based on all three of the methods just described,
fixes almost beyond doubt the so-called "motor areas" of the hu-
man cerebrum. [For understanding Exner's induction, consulta-
tion of Ecker's charts, found on p. 276f., figs. 87, 88, and 89, will be
found helpful.] The field of wholly ^'latent lesions" — that is, of le-
sions which are not necessarily followed by any disturbances of
either sense or motion — covers a large part of the surfaces of both
hemispheres ; it is not, however, precisely the same for them both.
While Exner's collection of cases comprised 67 lesions of the right
hemisphere, and 101 of the left, the absolute number of latent
lesions was the same (namely, 20) for both hemispheres. The
chances that a lesion of the right hemisphere will not be followed
by any disturbance of function are, therefore, about fifty per cent,
greater than the chances that the same thing will occur in the left
hemisphere. On the right hemisphere the entire surface, with the
exception of the two gyri centrales, the lobidus paracentralis, and
certain small portions on the convex and inferior surfaces of the
occipital lobe is latent. On the left hemisphere the latent region
is of less extent. This result may be regarded as a restatement,
on a basis of scientific induction, of the well-known fact that ex-
tensive lesions can occur in the frontal, temporal, and occipital
lobes, without being followed by any sensory or motor disturb-
ances. But it also confirms the impression that the portions of
the cerebral cortex lying about the fissure of Rolando are entitled
to be called " the exquisitely motor parts of the cortex."
Yet more precisely, the motor region on either hemisphere may
be, according to Exner, marked out by the method of negative
eases, and by the method of percentage of cases. The former meth-
od shows that, for the upper extremities, the corresponding cortical
region on the right hemisphere is the lobulus paracentralis, the gyrus
centralis anterior (with the exception of a small part of its lower
end) and the upper half of the gyrus centralis posterior. The latter
method further confirms the foregoing conclusion. It shows that
the "absolute field" for the upper extremities — the field, that is,
within which lesions are always followed by impaired motion of
these extremities — covers quite completely the same parts of cere-
bral convolutions ; while the " I'elative field," or portion in which
more than fifty per cent, of cases of lesions are followed by similar
280 HUMATq" PATHOLOGICAL CASES.
disturbances, extends over the remaining half of the gyrus centralis
posterior, the posterior third or half of the three frontal convolu-
tions, the anterior half of the parietal lobe, and more of the neighbor-
ing median surface. Corresponding to the better motor education
of the right arm is the fact that its motor region on the left hemi-
sphere is more extended. Here the absolute field comprises the
lobulus paracentralis, the three upper quarters of both gyri centrales,
and the greater part of the upper parietal lobe. Portions of the
median surface of the occipital lobe may also belong to this field.
The relative field for the upper extremity on the left hemisphere
includes the posterior half of the gyrus frontalis superior, almost
the entire convex surface of the other frontal gyri, the parietal lobe
at large, and the upper part of the occipital lobe.
More specific localization of cerebral areas, corresponding to the
different parts of the upper extremities, can as yet be accomphshed
only with much less confidence and in a conjectural way. The
method of positive cases seems to designate the gyrus centralis an-
terior as the special cortical area for the hand ; with a probability
that the area for the extensors of the hand lies in its middle part,
and the area of the thumb somewhat below in the same gyrus.
§ 12. Exner's collection contained 75 cases of disturbances of
motion in the loiver extremities ; 26 lesions being on the right, 49
on the left hemisphere. The methods both of negative cases and
of percentage agree in indicating that the " absolute " cortical field of
the left leg comprises the lobulus paracentralis, the uppermost third
(as far as the lower end of the sulcus frontalis superior) of the
gyrus centralis anterior, portions of the corresponding third of the
gyrus centralis posterior, and some small areas behind and below on
the lobulus quadratus, — all, of course, in the right hemisphere. The
" relative field " of the same limb on the same cerebral hemisphere
includes both lower thirds of the central convolutions, the back
parts of the frontal convolutions, the parietal lobules, and the up-
per portion of the occipital lobe. On the median surface of the
brain, the posterior part of the gyrus frontalis superior and the
anterior half of the lobulus quadratus belong to this field. On the
left hemisphere the absolute cortical field for the right leg includes
the lobulus paracentralis, the upper half of the gyrus centralis pos-
terior, and most of the upper portion of the parietal lobe. A small
lateral part of this lobe, and on the median surface the lobulus
quadratus, and perhaps the cuneus, must be added to complete the
relative field of this lower extremity. Exner does not consider it
possible, as yet, to be more precise in designating the cerebral fields
for the lower limbs of man.
FIELDS OF FACE, TOJSTGUE, A]S^D NECK. 281
§ 13. On comparing with each other the foregoing conclusions,
it is apparent that the absolute field for the upper extremities en-
tirely covers the corresponding field for the lower extremities ; but
the gyrus centralis anterior and lower half of the gyrus centralis
posterior belong only to this field for the upper extremities. The
relative fields, too, for both arms and legs, have a similar relation in
extent and intensity. There is considerably greater probability,
therefore, that a lesion of a given size in the motor region will af-
fect the arms than that it will affect the legs ; indeed, the collection
of Exner shows but one case in which the motions of the legs were
disturbed and not those of the arms. This greater " sensitiveness "
— if we may so speak — of the cortical region of the upper extrem-
ities, corresponds to the fact that their motion is more distinc-
tively cerebral and intelligent than that of the lower extremities.
§ 14. In this same " exquisitely motor " region of the cerebral
cortex, and in the most nearly adjacent regions of the frontal and
parietal lobes, certain other cerebral fields corresponding to definite
muscles or groups of muscles may be localized, conjecturally. By
the method of percentage the cerebral area for those muscles to
which the facial nerve is distributed may be rather indefinitely in-
dicated as lying in the lower half of the gyrus centralis anterior, and
lower third of the gyrus centralis posterior, on the right hemisphere ;
while, on the left hemisphere, it appears to be moi'e definitely fixed
at a small strip that belongs to the gyrus centralis anterior, and lies
between the places where the inferior and superior frontal gyri
spring from this central gyrus, but nearer the first of the two.
Both methods of induction apparently unite in indicating the
cortical region for the tongue as lying where the middle and lower
frontal gyri meet with the anterior central gyrus. In the nine cases
of the collection in which the muscles of head and neck were af-
fected, the lesions were all situated in one of the central convolu-
tions ; but a more definite localization within the limits of these
convolutions does not apjjear to be possible. As to the localization
also of the cerebral field for the muscles of the eyeball, including
that for raising the upper lid, pathology is able only to say in a
general way that this field appears to fall within the general motor
area as thus far pointed out. Exner thinks it certain that the
rectus internus muscle of one side, and the rectus externus of the
other side, are innervated from the same hemisphere of the brain.
This we should also argue from their ordinary physiological func-
tion.
§ 15. Positive cases of a nature to strengthen the foregoing in-
duction as to the cerebral areas especially connected with the upper
282 HUMAN PATHOLOGICAL CASES.
and lower extremities might be indefinitely multiplied. Especially
interesting are those where disuse, through accident or disease, of
one of these extremities has been found, post-mortem, to have re-
sulted in atrophy of the corresponding cortical fields. That is to
say, the cortical region, being unused on account of the loss of
function in the peripheral member, has itself paid the penalty of
all failure to exercise the normal functions ; it has lost in size and
strength. For example, atrophy of the upper end of the gyrus
centralis anterior of the right hemisphere, and of its prolongation
in the lohulus paracenlralis, was in one case found to have resulted
from the amputation of the left leg twenty years before death.
§ 16. The conclusions of other authorities as to the motor re-
gions of the cerebral cortex in man — especially of Lepine,' and of
Charcot and Pitres'^ — as based on pathology, confirm those of Exner
in the main, as well as also in some interesting particulars ; any di-
vergences arise almost wholly from the effort to make distinctions
more nicely than the present condition of the facts will warrant.
The most general conclusions of these investigators may be summed
up as follows : ^ " The cortex of the cerebral hemispheres in man
may be divided, functionally, into two parts ; motor and non-motor,
according as destructive lesions do or do not cause permanent par-
alysis of the opposite side of the body." . . " The motor zone in-
cludes only the ascending frontal and ascending parietal convolutions
and the paracentral lobule." It may be concluded then, as a well-es-
tablished induction, that the convolutions on either side of the fissure
of Rolando (the gyri centrales anterior and posterior) and the con-
nected lobule on the median surface of the brain (lohulus paracen-
tralis) are in the highest degree especially connected with the mo-
tion of the extremities of the body ; that adjacent parts of the
frontal and parietal lobes are thus connected in a less degree ; that
the cortical region for the arms lies, on the whole, anterior to that
of the legs ; and that, probably, the region for the hand is near the
middle part of the front central convolution, and that for the tongue
where the middle and lower frontal convolutions meet the front
central. More precise localization of the motor functions of man
must as yet be made with a lower degree of confidence. Beyond
these general statements lies the undefined field of conjecture.
§ 17. It cannot be said that histology and comparative anatomy
' Localisation dans les maladies cerebrales. Paris, 1875.
^ Localisation dans les maladies du cerveau, Paris, 1876; Revne mensuelle
de Med. et de Chir.. 1877-1879; Etude critique et clinique de la doctrine
dans I'ecorce des hemispheres cerebraux de I'homme, Paris, 1883.
'' See Brain, July, 1884, p. 270 f.
TESTIMONY OF HISTOLOGY.
much affect the strength of the argument for the localization of the
cerebral motor regions, as derived from experimentation and pa-
thology ; whatever evidence they do furnish, however, is confirma-
tory of the conclusions reached above. In this connection refer-
ence maybe made to the conclusion of Meynert,' that the paths
of the sensory nerves run more toward the occipital, and those of
the motor nerves toward the frontal region of the cerebrum. The
existence of nerve-cells of gigantic size, resembling those found in
the motor region of the spinal cord, which Betz discovered in the
motor regions of the cerebrum of the dog, the monkey, and of man,
is an indication in the same direction. It should also be mentioned
that the pathological researches of Pitres ^ into the results of lesions
in the medullary substance lying between the cerebral cortex and
the basal ganglia, seem to show that such as occur in the fronto-
parietal portion of this substance cause paralysis of motion and de-
generation of the motor tracts. Finally, the general structure of the
cerebrum and the courses of its nerve-tracts, as already considered
(Part I., Chapters 11. and IH.), are, in the main, accordant with
the facts of experimentation and pathology.
§ 18. The remarkable degree of coincidence in locality which
obtains among those circles whose extirjDation is followed by dis-
turbances of motion (disturbances due, in the opinion of Hitzig,
to destruction of the physical basis of the animal's control over its
limbs, but, in the opinion of Schiff, rather due to tactile anaesthe-
sia) suggests the following question : Is not the cortical field of
tactile sensation in the extremities of man coincident, in the main,
or even in particular, with the field for the motion of the same ex-
tremities? An affirmative answer to this question woiild seem
reasonable, even prior to experimental and pathological evidence.
The sensory and motor mechanisms are, of necessity, most inti-
mately connected, locally, in all the central organs. This state-
ment is certainly true of the spinal cord and of the inferior parts
of the braiu. Moreover, in consciousness the sensations which
guide the volitions in all the finer uses of the peripheral parts of the
body are very promptly, and even almost inextricabl}', interwoven
with the volitions. In walking, talking, handling a tool, or playing
a musical instrument, to be unable to experience certain delicate
sensations is to be unable to will the execution of corresponding
nicely adjusted motions ; whereas the appearance of the associated
sensations may instantaneously call forth the requisite volitions.
It would seem, then, that the cerebral mechanism for both the
* Sitzgsbr. d. Wiener Acad., LX., heft iii., p. 455 f.
^ Lesions du centre ovale. Paris, 1877.
284 HUMAN PATHOLOGICAL CASES.
sensory and the voluntary motor factors of these complex functions
must be composed of elements having the closest local connection.
Certain indisputable facts of pathology form, however, a strong
objection to such an identification of the cerebral fields of motor
function and tactile sensory function. Many cases of motor dis-
turbance occur without the disturbance of sensation in the same ex-
tremity ; and cases of sensory disturbance withoiit corresponding
motor disturbance, although much less frequent, are by no means
very rare. How, then, can these facts of pathology be reconciled
with any hypothesis which locates in the same cerebral region the
so-called " fields " for both classes of function ?
The answer which Exner gives to the foregoing question is per-
tinent, but not wholly conclusive. No absolute cortical field for
disturbances of tactile sensation in the extremities of the body can,
indeed, be pointed out ; that is to say, there is no portion of the
cerebral cortex, lesions of which are invariably and necessarily fol-
lowed by tactile anaesthesia, hyperaesthesia, etc., in definite parts of
the periphery. But that the entire relative field of sensations of touch
in the extremities corresponds with that of the motor activities, is
made highly probable by the method of positive cases. After ex-
cluding doubtful cases — in which the patient comjplained rather in-
definitely of a feeling of " heaviness" or " numbness," etc., in some
area of muscle or skin — Exner's collection was found to contain
22 cases where marked disturbances of tactile sensations seemed
clearly made out. Of these 22 cases no fewer than 16 were located
wholly in the two central convolutions ; and 3 of the remaining 6
extended for several millimetres into the same convolutions. Of
those still remaining, the one farthest removed from the " exquisitely
motor " region was in the gyrus angularis, and therefore in a portion
of the relative motor field which has a considerable per cent, of in-
tensity.
On the basis of so complete an agreement of the positive
cases, Exner feels warranted in affirming that "the tactile cortical
fields for the different divisions of the body coincide in general
with their motor cortical fields." It is to be noted, moreover, that
the percentage of the cases of disturbance of tactile sensations
occurring on the right hemisphere is more than twice as large as
that of the left. Sensibility seems, then, to be the predominating
function of the right hemisphere, as motion is of the left. This
fact, when taken in connection with the greater liability of the left
hemisphere to be the seat of cerebral disease, accounts in part for
the less frequent occurrence of sensory disturbances following le-
sions in this general area. Moreover, we are warranted in assum-
THE CONCLUSIONS OF LUCIANI. 285
ing that the cortical fields, in which the nervous impulses occasion-
ing tactile sensations are projected, are connected with each other,
and with the ascending sensory tracts, in a very complicated way.
The manner of this connection is doubtless different for the different
areas of muscle and skin. Nor does it appear that the sensory areas
are so well differentiated as the corresponding motor areas ; although
one case, at least, can be pointed out in which loss of sensation in
the thumb and index-finger was the definite result of a lesion of
the very limited cortical region already conjecturally assigned to
these members. Finally, it must be remembered that those descrip-
tions of pathological cases on which all our inductions have hitherto
been based, are very liable to be faulty with respect to slight dis-
turbances of sensibility.
It is a general conclusion, then, which is entitled to a large de-
gree of confidence, that both the gyri centrales, the lobulus para-
centralis, and the most nearly adjacent parts of the frontal and
parietal convolutions, constitute a cortical region especially related
to both the motor and the sensory functions of the extremities of
the body.
The view of Exner concerning the nature of the motor area in
man is, on the whole, greatly strengthened by the most recent con-
clusions of Luciani. This experimenter finds ' that total or partial
extirpation of the " motor zone " in the dog and the monkey is
uniformly followed, not only by motor paralysis, but also by cuta-
neous and muscular anaesthesia. The " motor " sphere and the
" tactile " sphere are largely coincident in these animals ; and " in
all experiments upon the tactile sphere there was a manifest and
constant crossing of the relations between the peripheral sensory
fibres and their respective cortical centres." "What one calls
'motor zone ' is the central focus of the large portion of the senso-
rial sphere visible on the external aspect of the hemisphere."
§ 19. The testimony of the facts upon which reliance must be
placed in the effort to localize the cerebral field for sensations of sight
and hearing in man is by no means so satisfactory as the foregoing.
Experiment upon animals by stimulation is of no direct value ; it
could at most only discover the cortical regions especially related
to some of the motions of the eye or ear and their surrounding
parts. Our conclusions from the method of extirpation also must
always be somewhat uncertain, since we infer the sensations of the
animal only by interpreting his motions into terms of our own seK-
consciousness. It is not strange, then, that the leading experi-
menters differ irreconcilably in certain of their conclusions. There
' See au abstract of liis results, in Brain, July, 1884, pp. 145 ff.
286 CEREBRAL FIELDS OF SENSATIOIT. '
is pretty general agreement at present, however, as to the localiza*
tion of sight somewhere in the occipital lobe. Hitzig ' found that
the removal of certain gyri in the posterior lobes of the dog pro-
duced blindness of the opposite eye, combined with a paralytic
dilatation of its pupil ; stimulation of the same gyri produced con-
traction of the pu j)il. Ferrier ^ claims that destruction (by cauter-
ization chiefly) of the gyrus angularis of apes produces blindness of
the opj)osite eye, and this loss of function alone ; stimulation of the
same region causes movements of the eye. He therefore considers
this convolution as pre-eminently the cortical centre of sight. But
Munk, after numerous experiments upon dogs, and some upon
monkeys, locates the centre of sight above and behind the place
assigned it bj' Ferrier — namely, in the upper and hinder part of the
occipital lobe ; the gyrus angularis, on the contrary, he makes the
cortical region for the tactile sensations of the eye. Munk's ex-
pei'iments are so minute in carefulness, and his conclusions so
based upon detailed analysis of the phenomena, that they perhaps
deserve to suggest to pathology the exact form in which to put its
inquiry. They are, undoubtedly, excessive, however, in the refine-
ment to which they would carry the principle of localization.
§ 20. Munk details the following among other phenomena which
result from extirpating the region marked A^ (see Fig. 85) from the
brain of a dog. The animal thus operated upon is in a condition
to Avhich the name of " psychical blindness " (Seelenhlindheit) is
given ; but it has suffered no other obvious impairment of its sen-
sor}^ or motor functions. By " jDsychical blindness " is meant the
inability of the dog to form those visual mental images or ideas
which give it the meaning or interpretation, as it were, of its visual
imjDressions. This includes the loss of the use of that portion of
the retina which is necessary for distinct vision, and of the immedi-
ately surrounding retinal parts. If the region Aj be removed from
both hemispheres of the brain, when the animal has recovered from
the inflammatory reaction, it will still move about freely, guiding
itself by sight even under difficult circumstances. But it does not
recognize by sight the dish from which it has been accustomed to
take food or water, the companions with which it has formerly
played, the man who has been its keeper, the threatening hand or
1 Centralb. f. d. med. Wissenschaft, 1874, p. 548.
2 The Functions of the Brain, p. 164 f. In the second edition (p. 271 f.)
Ferrier acknowledges that he was in error in localizing the visual centres in
this gyrus to the exclusion of the occipital lobes. For a very telling criticism
of this position of Ferrier, see Munk, Ueber d. Functionen d. Grosshirurinde,
p. 14 1
THE SIGHT- CEISTTEE OF MUNK. 287
whip, the burning coal held before its face. It still retains its gen-
eral intelligence and makes constant and diligent investigation into
the objects by which it is surrounded. As time passes, it gradually
learns to recognize again all these visual objects. The more com-
plex and infrequent of the objects are the last in the process of re-
covery to receive interpretation. At the end of three to five weeks
after the operation, the injured animal may be said to have recov-
ered ; its restlessness and curiosity have subsided in proportion to
the progress made in the knowledge of visual impressions ; it ^.s
itself at last, its " soul-blindness " having departed. It may be
shown, moreover, that this recovery consists in learning anew the
meaning of visual impressions ; or, in other words, in acquiring
anew the stock of visual ideas that has been blotted out of the ani-
mal's mind by extirpating the cortical centre of sight. For if the
dog be carefully kept, for a long time, fi'om any given kind of ex-
perience— for example, from being struck with a Avhip or biu-ned
with a coal — it will give no sign of " psychical sight " in relation to
these particular objects. More remarkable still is the fact that,
according to Munk,' in certain cases, after the extii'pation of Aj, a
single visual image or two — for example, the motion of the hand
commanding the dog to hold out the foot — may be retained. Ex-
tirpations of the cortical surface on the occipital lobe in the regions
marked A — that is, before, beneath, or in front and above, the sight-
centre A, — cause disturbances of sight in a less degree. Such phe-
nomena Munk considers explicable by the hypothesis that, while a
large part of the area of the occipital lobe is the seat of the percep-
tions (?) of sight, the visual images of memory are especially con-
nected with the so-called sight-centre A^. "When, then, all, or nearly
all, of the field of sight, in the widest sense, is extirpated from both
hemispheres, complete and permanent " soul-blindness " results.
The cortical projection-field corresponding to the entire retinas of
both eyes, its accumulations of old visual ideas, and capacity for
receiving new ones, has been wiped out.
Munk endeavors to establish a still more minute differentiation
of function in the cortical field of sight as corresponding to the ret-
inal field of sight. ^ Each retina, he holds, stands for the most part
in connection with the visual sphere of the cortex of the opposite side
of the brain ; only a small part — namely, the extreme lateral por-
tion of the retina — is in connection with the cortical sphere of the
same side. This lateral poi-tion of the retina seems to be of differ-
ent dimensions in different races of dogs. Further, the retina ia
' Die Functionen d. Grosshirnrinde, pp. 23, 34, 119 f.
* See the " Fuufte Mittheiluug " of his Work, as cited before.
288 CEEEBEAL FIELDS OF SENSATION.
projected, as it were, on the cortical field of vision in and about Aj,
in such manner that its lateral area corresponds to the lateral area
of the cortical sphere on the same side ; its inner area to the median
area of the cortical sphere on the opposite side. ; its upper area to
the front area of the cortical sphere on the opposite side ; its lower
area to the hinder area of the cortical sphere on the opjDosite side.
In monkeys, as well as dogs, Munk finds that the sight-centre is
not, as Ferrier at first supposed, the gyrus angularis, but rather the
convex surface of the i^osterior lobes. Small circular extirpations,
of not more than two-fifths or three-fifths of an inch in diameter,
from this region are followed by disturbances of vision, and by these
alone. If the whole convex surface of one lobe is extirpated, the
animal has cortical blindness for those halves of both retinas that
are on the same side as the lesion. If the convex surfaces of both
posterior lobes are destroyed, the animal becomes entirely blind ;
no restoration of cerebral function subsequently takes place, unless
some considerable parts of the edges on the upper surface of at
least one lobe have escaped destruction. The cortical projection-
field for the visual impressions of the monkey differs from that of
the dog simply in having the lateral part of the retina, which cor-
resjDonds to the cortical area of the same side, much more extended.
Accordingly, extirpation of the lateral half of the left cortical sight-
centre, and of the median half of the right cortical sight-centre,
produces in the monkey total cortical blindness of the left eye.
§ 21. The searching examination which the views of Munk have
received has resulted in throwing doubt over some of his alleged
facts, and in discrediting several most important points in his hy-
pothesis. This is true especially of the work of Lob and Luciani,
both of whom have gone thoroughly over the ground covered by
Munk and come to conclusions dissenting from him. The former '
has minutely investigated the effects of destroying Munk's visual
centre A^, and even his entire visual sphere in the case of dogs.
He finds, contrary to Munk, that no blindness of the clear spot of
vision in the opposite eye is produced even by the most extensive
lesion of this area ; that losses of the cortical substance in the
area bordering on the lateral part of the visual sphere {i.e., in
Munk's auditory sphere) also produce disturbances of vision ; that
other disturbances of motion and intelligence also follow destruc-
tion of this area ; and that disturbances of sight may follow lesions
in other than the occipital lobes, especially in the frontal lobes.
This last conclusion agrees with the results obtained by other ob-
sei"vers (Ki'iwotorow, Luciani and Tamburini, and especially Goltz),
' See articles in Pfliiger's Arcliiv, xxxiv. , pp. 67 ff.
VIEWS OF LOB, AND OTHERS. - 289
and must be accepted as correct. The more permanent disturb-
ances which undoubtedly do follow injury of the occipital lobes
are thought by Lob to be due to what is called a " homonymous
lateral hemiamhlyopia " (or weakness of the corresponding lateral
half of the eye) on the opposite side. Munk's whole theory of
" psychical blindness " as due to the extirpation of visual percep-
tions and images, and of recovery from such blindness as due to
special education of the animal in forming new mental images, is
rejected by Lob.
The admirable observations of Luciani also tend to disprove
many of the particular conclusions of Munk, while at the same
time showing how relatively important are the occijntal lobes in re-
spect to the cerebral and psj'chical elements of vision. These lobes,
together with the angular gyrus, are in a peculiar degree the re-
gion on which the animals are dependent for " psychical " vision
— that is, for "discernment of things, and a right judgment con-
cerning their properties and their nature," by sight.
The foregoing general conclusions from experiment with the ani-
mals as to the especial importance of the occipital lobes for intelli-
gent (or " psychical ") vision are, on the whole, in accordance with
the indications from human pathology. Even Lob testifies that
after extirpating part of the occipital lobes he has never observed
a ?7iere motor disturbance without one of vision also ; whereas after
extirpating part of the parietal lobes he has never observed a dis-
turbance of vision loithout a motor disturbance.
§ 22. The answer of pathology to the question, whether the cere-
bral field especially connected with visual sensations and ideas is
the same in man as in the dog and the monkey, is not unambigu-
ous. The method of negative cases, according to Exner,' yields no
certain results; no "absolute field" for vision can as yet be indi-
cated on the cerebral cortex. The methods of percentage and of
positive cases, however, point clearly to the occipital lobe as the
visual field, and to the upper end of the first gyrus occipitalis (01, in
Ecker's charts ; see p. 276 f.) as its most intensive portion. Li six out
of seven cases of disturbances of vision due to cortical lesion the seat
of the lesion was here. The region of less intensity extends over
both the first and second occipital convolutions, the cuneus, and
the adjacent part of the lobulus quadratus. Confirmatory evidence
may be found in the cases of several persons for a long time blind,
whose brains have been found on post-mortem to be atrophied
above the place where the parieto-occipital fissure emerges from
the median surface upon the convex surface of the occipital lobe.
' Untersucliungen iiber d. Localisation, etc., p. 60.
19
290 CEREBRAL FIELDS OF SENSATION.
It should be said, on the other hand, that lesions of the occipital
lobes are very frequently latent, and that extensive injuries of this
cortical field in man are recorded which v^^ere followed by no
marked disturbance of sight.
§ 23. Histology also has some evidence to contribute regarding
the nervous connections of the retinas of the eyes with the cerebral
cortex. The amount of crossing which the fibres of the ojDtic nerve
undergo in the optic chiasm has been the subject of much debate.
It undoubtedly differs in different animals, and depends uj^on the
structures of both retina and brain, and upon the relations of the
two. The researches of von Gudden ' and others have tended to
show that each optic nerve contains both a bundle of nerve-fibres
that is crossed and one that is uncrossed, in the optic chiasm or
beyond it, towai'd the cerebral connections of the nerve ; and that
the former bundle increases and the latter diminishes in size, on
the whole, in the higher orders of animals as compared with the
lower. Biesiadeclii and others claim, on the contrary', that there
is total decussation of the otitic nerves in the monkey and in man,
as well as the lower animals. Charcot ° has propounded a yet more
elaborate scheme of decussation. In the case of man there is still
doubt, therefore, how far — if at all — the retina of each eye is repre-
sented on the cortical surface of both hemispheres of the brain.
That the cortical region especially concerned in the sensations,
perceptions, and images of sight is in the occipital lobe, and es-
pecially on its upper convex surface, is a highly probable conject-
ure. But for the settlement of further details we must await the
development of the evidence. In the work of this develoj^ment,
experiment with aiaimals can only suggest the question which a
more careful collation of a growing number of cases in human
pathology will perhaps finally answer ; meanwhile the evidence of
histology may be used to confirm or modify the conclusions estab-
lished, more or less conjecturally, on the basis of pathology.^
§ 24. The localization of other sensory functions in so-called
" fields " or " centres " on the hemispheres of man's brain — of hear-
ing, taste, and smell — is even more doubtful. Little confidence can
be placed in any conjectures thus far put forwai'd. The tempta-
tion is naturally strong to suspect that those regions of the cortex
unoccupied by such motor and sensory functions as we are able to
' Grafe's Archiv f , Ophthalmologie, 1874, Abth. ii. ; 1875, Abth. iii. ; 1879,
Abth. i.
- Le Progri's Medical, August, 1875.
■'For a further description of plienomena and cases, and for a defence of his
own views, see Ferrier, The Localization of Cerebral Disease, pp. 110 fiE.
CElVfTEES OF SMELL AND TASTE. 291
locate should have the other mental phenomena assigned to them.
In this way the entire brain appears to be made of some definite
value and use. Convolutions which are located where they are
unapproachable for purposes of experiment, and in which compar-
atively few cases of lesion occur, are peculiarly provocative of con-
jecture. In such Jields of the cerebral cortex, theories of localiza-
tion may roam at will. The auditor^' centre is assigned by Terrier '
to the superior temporo-sphenoidal convolution ; but the evidence
adduced in proof — such as the pricking-ujD of the animal's ears,
etc, — is highly unsatisfactory. The same centre is located by
Munk '^ at the region Bl, for its greatest intensity, and with less
intensity in the adjacent regions marked B ; but since the entire
region on both hemispheres must be extirpated (an almost certain-
ly deadly operation) in order that the animal may become wholly
" soul-deaf," and since we have no sure means for ascertaininsr
precisely to what deficiency we should ascribe the failure of the
animal to respond intelligently to sounds, Munk's experimental
proof is likewise unconvincing. Luciani, with much more proba-
bility, considers the " auditory sphere " to extend over the whole
cortical area of the temporo-sphenoidal lobe, and probably also the
cormi ammonis.
The centres of smell and taste are located by Ferrier close to-
gether in the subicidum and neighboring parts of the lower temporo-
sphenoidal convolutions ; the centre of touch in the gyrus hijjpo-
campi and hippocampus major. Munk,^ however, regards these
centres of Fei'rier as " phantasms." He is strongly inclined, on the
basis chiefly of one well-differentiated case, to localize smell in the
gyrus JdiopocampL It is difficult to see how anything sufficiently
definite for scientific purposes can be known as to distui-bances of
taste in a dog or a monkey. No adequate evidence is j)rocurable as
yet for an induction from human pathological cases in regard to
the cortical fields of any of these so-called lower senses.
§ 25. To the foregoing remark a possible exception must be
allowed for the sense of hearing. In. this connection belongs the
noteworthy localization of the cerebral functions concerned in the
utterance and interpretation of articulate speech. The various de-
ficiencies in the power of producing and interpreting articulate
sounds, whether as spoken or written, which are due to lesions of
the cerebral cortex, may be grouped together under the general
' The Functions of the Brain, p. 171 f. ; comp. The Localization of Cerebral
Disease p. 132 f.
- Ueber d. Functionen d. Grosshirnrinde, p. 23 f . ; 40 f.
3 Ibid., p. 129.
292 DISTURBAISrCES OF SPEECH.
term "aphasia." For about a decade previous to the discoveries
of Fritsch and Hitzig, in 1870, the facts Avhich seemed definitely to
connect the loss of speech with a certain region of the left cere-
bral hemisphere were nearly all to which any advocate of the local-
ization of cerebral function could confidently appeal in behalf of
his theory. As long ago as 1825, Boillaud located the articulation
of words in the frontal lobes. Subsequently (1836) M. Dax main-
tained the proposition that " lesions of the left half of the enceph-
alon are coincident with forgetfulness of ^the symbols of thought."
In treatises of the years 1861-1865, Broca first announced the
substantially true discovery that the gyrus frontalis inferior on the
left side of the cerebrum is especially concerned in using the pow-
er of siDcech. This circumstance he connected with the fact that
men generally use the left hemisphere more than the right for the
expression of thought with the I'ight hand and arm, whether in
writing or in the mechanical arts. The literal meaning of the
statements made hj Broca — such as that this part of the brain is
"the seat of the faculty of articulate language " ' — is, however, not
simply inappropriate to the facts ; it is even absurd. There is no
one " faculty " of language which can, in any possible meaning of
the word, be regarded as having its "seat " or locality confined to
some particular region of the brain. Speech involves, in a very
complicated and large way, all the faculties ; strictly speaking, then,
it cannot be located, with all its attendant operations of self-con-
scious, rational mind, in any one cerebral area. But that the
phenomena of aphasia show some special connection of certain
cerebral centres with the complex process of apprehending and ex-
pressing articulate language, seems entitled to credit as an induc-
tion based upon a wide range of facts. Of course, in this particu-
lar attempt at localization of function, no real help can be derived
from experiments upon the lower animals.
§ 26. The jDhenomena of various classes, among which the truly
aphasic cases must be discriminated, vary all the way from those
resembling the results of momentary inattention — such as that of
the German professor who certified in writing, "A. B. has attended
my remarkable lectures in chemistry with inorganic assiduity "■ — to
the impairment and utter loss of speech in progressive paralysis
with dementia." A few of the more curious and instructive in-
' Sur le siege de la faculte du langage articnle, etc., Bull, de la Soc. anat..
August, 1861 ; Du siege de la faculte du langage articule dans I'hemisphere
gauche du cerveau. Bull, de la Soc. d'anthropol. , June, 18(55.
'For the whole subject, see the great monograph of Kussraaul, in Ziemssen'a
Cyclopaedia, xiv., pp. 581-875.
THE KINDS OF APHASIA. 293
stances furnish facts like the following : The aphasic patient may
be entirely speechless, and yet understand what is said to him, and
be able to write his wishes down on paper. Some thus afflicted re-
tain the power to pronounce words of one syllable, but are obliged
to resort to writing in order to communicate anything fm-ther. Oth-
ers possess a small stock of words, which they make more serviceable
with expressive gestures. Others, still, are simply able to speak " a
few senseless, and often very extraordinary, syllables and words."
Among the surprising phenomena of the disease of aphasia,
none are perhaps more so than those occasioned by the ability
to utter certain syllables or words, when accompanied by an utter
inability to put the same letters into slightly different combination.
One patient, who could say "Bonjour, monsieur," tolerably well,
could not pronounce the word "bonbon" at all. Another, whose
vocabulary was almost entirely limited to the meaningless syllables,
" cousisi," was quite unable to utter either " coucon " or "sisi."
The celebrated case of the aphasic Le Long, reported by Broca,
was that of a man confined to five words for his entire vocabulary.
These words were, " oui, non, tois instead of trois, toujours, and
Le Lo instead of Le Long." The first two and the last were used
with their appropriate meaning; "tois" indicated all ideas of
number whatever ; and " toujours" was the word used when the
patient could not express his meaning by gestures and the other
four words. It appears, then, that Le Long could pronounce the
r in " toujours," but not in " trois," and the nasal sound in " non,"
but not in his own name. In another class of cases, the aphasic
person can utter only a few or no words spontaneously and cor-
rectly, but can repeat and write without difficulty words that are
spoken before him. Such inability is sometimes called "simple
aphasia of recollection." Different classes of words, as a rule, slip
fi-om the memory in succession, as it were. Proper names are
most frequently forgotten ; then substantives generally, and some-
times verbs, adjectives, pronouns, and all other parts of speech.
"The more concrete the idea," says Kussmaul,' "the more readily
the word to designate it is forgotten, when the memory fails."
Many cases of disease occur where the patient has lost the power
mentally to find the appropriate words, although his power of ar-
ticulation is unimpaired. Such disturbances of speech may, or may
not, be accompanied by a corresponding impairment of general in-
telligence. This complication increases the difficulty of studying
the phases of this disease.
Aphasia may also be accompanied by so-called "word-deafness"
' Ziemsseu's Cyclopaedia, xiv. , p. 759.
294: DISTURBANCES OF SPEECH.
and "word-blindness." Persons thus afllicted hear words as con-
fused nmrmurings, or see them as bluri'ed images. The individ-
ual letters may be intelligently heard or read, but their combina-
tion has become unintelligible. The same thing sometimes happens
with figures ; as in the case of the accountant who could read the
sum 7G6, figure for figure, but did not know what the figure 7
meant as placed before the two 6's. At other times the disturb-
ance of speech takes the form of grammatical ataxy, as it were, or
of verbal delirium — a medley of words, partly in themselves signifi-
cant and partly unmeaning.
The agraphia, or inability to express thought in written language,
which not infrequently accompanies aphasia, may be incomplete,
or absolute and literal. Some patients, who have formerly been
highly cultivated, become unable to produce a single letter with
the pen. Others can write long rows of letters, but arrange them
for the most pai't in meaningless fashion, with an intelligible word
occurring here and there. In brief, the phenomena more or less
closely connected with the disturbance called aphasia are exceed-
ingly complex and various.
§ 27. In the effort to classify so many complicated facts, and to
distinguish among them such as are of truly cerebral origin, Ex-
ner' makes the following distinctions: First, there are cases
where the understanding of the words is affected ; and such loss
may constitute the chief or the entire part of the aphasia. The
patient can then hear and articulate, but the "acoustic image" of
the word as the symbol of an idea has jDcrished. In a second form
of aphasia, the inability concerns the clothing of the result of
thought (the idea) in words — whether for purposes of spoken or of
written expression. In most such cases it is simjDly the appro-
priate word which is forgotten. In the third class of cases, the
aphasic person can foi'm the idea and select the word approj)i'iate
to express it, but cannot bring about those processes of central in-
nervation which are necessary to initiate the expression. All these
three forms may combine variously, and all may be connected with
disturbances of speech which are not to be localized in the cerebral
cortex, but which have their origin at some point in the extra-cor-
tical nerve-tracts concerned in speech. The very elaborate analysis
of Kussmaul leads him to make the following statement: "All
disturbances of speech can be brought under two great classes^
according as the connection between the conception and the word
is impeded in the direction from the former to the latter or, vice
versa, from the latter to the former. When the first happens, the
' In Hermaun's Handb. d. Physiol. , II., ii., p. 343 f.
CORTICAL AREAS OF APHASIA. 295
expression suffers; when the second, the understanding." By the
1 ist word, however, we must naean the " understanding " as apphed
especially to articulate speech. For aphasic persons are often very
intelligent in carrying on the trains of thought necessary to suc-
cess in games of skill, or in the expression of feeling in music ; and
if we accept, even with considerable allowances, the intelligent
testimony of Lordat concerning his own mental condition when
aphasic, they sometimes exercise the mind in abstract reasoning
of a high order, even when unable to recall a single word appro-
priate for the expression of their thoughts.
In all true aphasia, then, the connection between ideas and ar-
ticulate language is interrupted within the cerebral cortex. Is it
possible to indicate any region of this cortex, lesions in which are
regularly accompanied by aphasic symptoms ? or, in other woi'ds,
Can the function of articulate speech, so far as this consists in the
ability to apprehend and successfully to will its acoustic and visual
symbols, be localized in the cerebral hemispheres ? In answer to
this question it must be admitted that no absolute field for aphasia
can be pointed out ; that is, besides the region where lesions are
connected in by far the greater number of cases with aphasic dis-
turbances, other regions of the cerebral hemispheres only some-
limes thus connected may be pointed out.
§ 28. In a large percentage of cases of disturbance of speech due
to cerebral lesions, the posterior third of the third frontal convolu-
tion and the other regions bordering on the fissure of Sylvius
(island of Eeil, and immediately adjacent parts of the parietal and
temporal lobes) are the seat of the lesions. Aphasia is far more
frequently due to changes in the left than in the right hemisphere
of the brain. Dr. Seguin, out of 260 cases, calculated the propor-
tion of aphasias due to lesions on the left side, as compared with
those due to lesions on the right, to be as 243 : 17 or 14.3 : 1. Such
disparity is far too great to be attributed to the comparative fre-
quency with which the left hemisphere in general is the seat of
lesions. In Exner's ' collection of cases, out of 81 lesions resulting
in aphasia, all but one were on the left hemisphere (in three cases,
however, the right was also involved), and in that one the trouble
was only temporary. Such facts have led to the theory that, in all
but left-handed men, speech, like other motor functions, is chiefly
left-brained ; remarkable cases of left-handed people who have be-
come aphasic through lesions on the right hemisphere are actually
recorded.^
' Functionen in d. Grossliirnrinde, p 51 f.
^ See Kussmaul and his citations, p. 739 f.
296 DISTURBANCES OF SPEECH.
Of the left hemisphere, the gyruii centralis anterior and the
adjacent convokitions of the frontal lobe, but especially the pos-
terior part of the third (lower) convolution, have much the highest
intensity as seats of aphasia lesions. In 53 carefully collected
cases by Lohmeyer,' 60 were on the left hemisphere, 24 in the
lower frontal convolution, 34 in this convolution and neighboi-ing
parts, 13 in the island and adjacent parts, 6 in the island alone.
Exner's collection, however, did not show that the "intensity" of
the lower is any greater than that of the middle frontal convolution,
or of the two upper temporal convolutions. This collection con-
tained, moreover, five cases in which lesions were seated in the
lower left frontal convolution loithout any resulting aphasia. Exner
therefore justly concludes that the " cortical field " of speech, like
the corresponding fields of all the motor functions, is really much
more extended than has generally been supposed. He is himself,
nevertheless, inclined to localize, yet more definitely, so-called
"ataxic aphasia" in the third frontal convolution, "word-deaf-
ness" in the middle gyrus temporalis, and agraphia in the lower and
front part of the parietal lobe ; that is, in the neighborhood of
the motor region for the upper extremities. So specific localiza-
tion can hardly, however, be safely based on the restricted number
of cases which Exner considered.
Lohmeyer gives 2 cases of aphasia following lesions in the an-
terior portion of the frontal, 3 in the parietal, and 4 in the occipital
lobe, Exner gives 3 cases in which the central convolutions were
alone the seat of disease ; 2 in which the temporal and parietal
lobes were alone affected ; 1 in which the only lesion was in the oc-
cipital lobe. In the only sense in which the brain can be spoken
of as the " seat of the faculty of articulate language," we must ad-
mit that the evidence confirms the following assumption of Kuss-
maul : " It is, a liriori, probable that an enormous association-tract
in the cortex has been assigned to speech, even though the key-
board of sound may be confined to the anterior cortical regions."
§ 29. The moi'e ardent and positive advocates of the theory
of locally specific cerebral functions find it exceedingly difiicult to
refrain from seating general intelligence, or the powers of percep-
tion, memor}^, comparison, etc., as applied to all the objects of
cognition, in some particular so-called "field "or "area "of the
brain. At present the frontal lobes offer themselves as the most
convenient region for such pre-empting of the cerebral domain.
The general propriety of considering the connection which un-
doubtedly exists between the central nervous mechanism and men-
' Arcliiv f. Klin. Cliirurgie, XIII., p. 309, as cited in Kussmaul.
IMPAIEMENT OF I]SrTELLIGE]S"CE. 297
tal phenomena, under any spatial terms whatever, will occupy our
attention later on. It is enough at present to say that the experi-
mental and pathological evidence do not warrant us in assigning
such pre-eminence to the frontal lobes. Extensive lesions may oc-
cur in these lobes with little or no diminution of so-called general
intelligence. On the other hand, small lesions in other regions of
the brain are not infrequently productive of comparatively profound
mental derangement or loss of function. Moreover, lesions localized
in those areas of the cerebral cortex which have thus far been con-
sidered—namely, the parietal, occipital, and temporo-sphenoidal
lobes— are, of necessity, connected with more or less impairment
of intelligence.
There can be no doubt that the mental processes which we describe
by the word "intelligence " are all closely related to the basic sensory
and motor activities that are chiefly localized elsewhere than in the
frontal lobes. An animal that is " soul-deaf " or " soul-blind " has,
so far forth, an impaired intelhgence. The same thing is eminently
true of the man afflicted with aphasia in any of its severer forms.
The loss of intelligence is not necessarily (or even probably) due to
the partial destruction of that functioning of the hemispheres in
general which results in intelligence ; it is rather due to the fact
that the support which all ideation receives from the audible and
visible symbols of the idea— whether chiefly as respects its forma-
tion or as respects its expression — has become impossible. The
impairment of any considerable area of tactile sensations, especially
as localized in those parts of the body which are most used in per-
ception through such sensations {e.g., the hand), also occasions a
certain loss of intelligence. The restrictions which cerebral disease
introduces into the number and nicety of the sensory and motor
functions are, of course, much less important when they come upon
minds already /»rni67ierf, as we say, " with a stock of ideas." Still,
even in such cases a basis of sensations and volitions constantly
underlies, as it were, all the higher and pre-eminently intellectual
mental processes.
§ 30. In spite of the evidence adduced, a few experimenters still
either wholly reject the principle of the localization of cerebral
function, or else urge arguments against carrying it out even with
the limitations which the foregoing conclusions have observed.
Among such experimenters the most prominent is perhajDS Goltz. '
The method of extirpation practised by Goltz was that of wash-
ing away the substance of the cerebrum by streams of water sent
' See especially liis treatises as collected in the book, Ueber d. Verriclitungen
d. Grosshiriis, Boun, 1881 ; and Pfliiger's Arcbiv for 1876, 1877, and 1879.
298 SUMMA-ET OF RESULTS.
through orifices broken at selected places in the skulls of dogs.
This metbocl has the advantage of saving bleeding ; it has the dis-
advantage of not definitely localizing the injuiy. Its author has
applied it with great care and skill to a large number of animals,
many of which he has succeeded in keeping alive for months, even
after the removal of considerable areas from both hemispheres
(in one instance tbe brain-substance, calculated to have weighed
originall}' 93 grammes, had been reduced to 13). The principal
conclusions drawn from his expei'iments by Goltz are adverse
to the theories of localization held by Ferrier, Munk, Luciani, and
others.
Goltz's conclusions may be summarized as follows. No impair-
ment of intelligence follows the loss of a large amount of cortical
substance from one side of the brain ; but loss of any considerable
amount of substance from both sides — whether in the frontal,
posterior, or temporal lobes — produces a permanent impairment of
all the functions, which corresponds in a general way to the amount
of the loss. Every sense, and the inteUigence of every sense, is
thus weakened ; for tlie cerebral elements of sense are impaired or
destroyed [Hirnsehschwache, etc.). For example, a dog which has
been trained to give his paw on command loses the power to do so
in consequence of such loss of brain-substance, and never regains it.
It is not possible, by extirpating any amount of the substance of
the cortex on either side or on both sides, to produce a permanent
laming of any muscle of the body, or a total loss of sensibility in
any of its parts. It is, however, possible, according to Goltz, by
repeated removal of the cerebral substance on both sides, gi-adually
to reduce an animal to a condition of almost complete idiocy — to
an elaborate eating, drinking, and walking "reflex-machine." The
removal of as much as 4 grammes from each hemisphere produces,
as he calculates, a considerable degree of idiocy. No part of the
cortex of the brain can, then, be called the exclusive organ or centre
of intelligence or feeling ; but the psychical functions of sensation,
volition, ideation, and thought are connected with all of its parts.
The quantity of the cerebral substance i-emoved determines the
amount of the general impairment of mental powers, instead of the
locality from which the removal is made fixing the quality of mental
impairment.
It must be admitted that the facts discovered by Goltz, and the
conclusions which he reaches, seem at first strongly opposed to all
localization of cerebral function. But they are not really so ; nor
is it quite coi-rect even to say, as Foster ' does, that Goltz's results
' A Text-book of Physiology, p. 649. New York, 1880.
THE VIEWS OF GOLTZ. 299
are "absolutely opposed" to tliose of Munk. In fact, Goltz' him-
self asserts that destruction of the parietal lobes produces a greater
permanent disturbance of feeling, and destruction of the occipital
lobes a greater permanent disturbance of sight. In general, an
animal operated upon in the two hind-quarters of the cerebrum is
more stupid than one which has suffered loss of the fore-quarters ;
the former is duller of sight, hearing, smell, and taste ; the latter is
duller in respect to skin-sensations. The effect of injury to the
posterior parts of the brain is therefore much more marked in de-
pressing the intelligence of the animal (as shown in sense-percep-
tion). Moreover, Goltz ^ claims that he has never rejected the
possibility of a localization of the functions of the brain. He con-
firms ^ the conclusions of Fritsch and Hitzig, by saying that he has
often seen mechanical excitation of the parietal lobes j^roduce mo-
tions in the limbs of the opposite side. His facts and arguments
are rather directed against tliat form of the hypothesis of localiza-
tion which seats the different functions in small circumscribed
areas ^ and then, w^hen forced by facts, conceives of them as also ca-
pable of hopping about from one of these areas to another, like a
bird from twig to twig in the branches of a tree. Furthermore, a
detailed comparison of the experiments of Goltz with those even
of Munk shows that the results of the two are in the main recon-
cilable ; if only it be remembered that the former has not always
precisely defined the areas of brain-substance removed, nor suffi-
ciently taken into account the undoubted results obtained by others
from definitely circumscribed lesions ; and that the latter has, cer-
tainly, in many cases been more precise and confident than a fair
view of all the facts will warrant.
§ 31. Three principles may be laid down as summing up the
results reached by inference upon the basis of experiment with
respect to the localization of function in the cerebral cortex. '" The
first principle is to be accepted in the form of a general postulate
derived from a study of the other parts of the nervous system, and
confirmed on attempting to apply it to the cerebral hemispheres.
It may be stated as follows : the different elementally parts of the
nervous system are all capable of performing its different sj^ecific
functions when, and only when, they have been brought into the
proper connections and have been exercised in the performance of
' Verrichtungen d. Grossliirns, pp. 114 f. and loO f. ; and art. in Pfliigers
Archiv. xxxiv., pp 450 ff.
^ Verrichtungen d. Grossliirns, p. 163. ^Ibid., p. 165. *Ibid.. p. 169.
' Compare the five general laws o£ central functions given by Wundt,
Grundzuge d. pliysiolog. Psycliologie, i., p. 224 f.
300 sujVimakt of results.
tliose functions. This principle includes two important laws which,
we know, hold good throughout the whole nervous mechanism, and
which he at the physical basis of important psychical facts and laws ;
they are the law of Specific Energy and the law of Habit. Different
combinations of the elementary parts of the nervous system, form-
ing composite parts or organs, have different values and functions
in the general economy of the system. Every nerve-fibre, every ele-
ment of an end-organ, or of a central organ, may be said to have a
specific function, and to discharge that function in the exercise of
a specific energy. As to how far the capacity for this specific energy
is dependent upon the specific molecular structure of the element-
ary parts, we are only able to conjecture ; but about its depend-
ence upon the connections in which the elementary parts stand with
each other, there can be no doubt.
Moreover, the elementary parts of the nervous system, inasmuch
as they have the general adaptation necessary to the performance
of nervous functions, can " learn " (so to speak) to perform the
more specific of these functions — but only in case they stand in
appropriate connections. The repeated action of the nervous ele-
ments in specific functions fits them the better to act in the same
functions. The effect of the exercise of any function in the past
may be " stored uj) " so as to increase the facility of the nervous
structure to exercise again every similar function. Thus, different
elementary parts of the nervous system, if at first forced by circum-
stances to become active in a given way, may by repeating the
activity gain a position of facility and value like that belonging to
other parts whose so-called normal action lies in this particular
way. This law of habit in the nervous system explains much of
the behavior of the nerve-muscle machine, or of the decapitated
frog, etc., under artificial stimuli ; it also underlies the theory of the
sensory-motor effects attributed to centres in the spinal cord and
basal ganglia ; it throws light upon the physical basis of our ex-
perience in learning to walk, talk, play upon musical instruments,
or handle tools, as well as upon the transmission from generation
to generation of minute bodily characteristics. Both the law of
specific energy and the law of habit undoubtedly apj^ly to the func-
tions of the cerebral cortex.
The remaining two of the three principles alluded to above may
be said to follow from the first ; they are the princij)le of localized
function and the principle of siibstitulion. The former asserts
that, in the normal condition of the nervous system, all jjarts have
not the same definite functions. Inasmuch as the functions of the
different elementary parts necessarily depend upon the manner
NATURE OF THE CEREBRAL " FIELDS." 301
in whicli tliey are combined and connected, the composite parts
or organs thus formed must also have certain normal functions.
But such composite parts or organs have, of course, a definite local-
ity ; hence the functions of the nervous mechanism must be more
or less definitely localized. Nor can the principle be suspected
of a disposition to stop short off and abdicate its authority, when
we reach the region of the cerebral cortex. There is nothing in
the structure of the cortex to show why the general law of differen-
tiation of function should be inapplicable there. On the contrary,
everything in both its anatomy and physiology indicates that the
principle of localized function does apply, in some sort, to the cere-
bral hemispheres.
So-called "centres," or "areas," or "fields," of the cerebrum are
in no case, however, to be regarded as portions of its nervous sub-
stance that can be marked oft' by fixed lines for the confinement
of definite functions within rigid limits. These areas are some-
what different for different brains of the same species ; the}' widen
when a heightened energy is demanded of them ; their centres
are neither mathematical points nor very minute collections of
cells. They are not composed of elements which have, each one,
a fixed and unchangeable value, and a definite function, as though
the number of mental operations assigned to a locality needed to
be jDrecisely matched by the separate nerve-fibi'es and nerve-cells of
the locality. Nor are these areas perfectly isolated localities ; on
the contrary, they obviously overlap each other in certain cases.
According to the true statement of Luciani, "the single centres
in the sensory-motor zone are so completely bound up with, and,
so to speak, let into one another, that it is not possible to divide
them with a clear and definite line, such as is the case when the
cortex is incised and removed ; so that in destroying a centre one
necessarily eliminates a portion of the neighboring centres." Nev-
ertheless, there is no doubt that the cerebral functions connected
with the different sensations and motions of the peripheral parts of
the body are not all alike exercised by all parts of the cerebrum.
They are assigned specifically to those regions which alone have the
proper structure and stand in the proper relations.
Furthermore, the functions of the cerebrum are not absolutely
confined to those centres with which, under ordinary circumstances,
they are chiefly or wholly connected ; in which, that is to say, they
are localized. If such centres, for any reason, become incapacitated
or relatively unfitted to perform their normal functions, the same
functions may be performed by other areas of the cerebral cortex,
provided these areas also stand in the proper connections. This
302 SUMMARY OF RESULTS.
is the principle of substitution. It is clue to its working that
animals subjected to exj)eriments in extirpation, as a rule, so
largely recover the powers of sensation or motion which they have
temporarily lost. It is on this class of phenomena that Goltz rests
much of his argument. In the cerebral hemispheres, however, the
principle of substitution does not overstep all limits, nor does it
operate arbitrarily. The portions of the same hemisphere that
are just adjacent to the so-called centres — the larger areas sur-
rounding or contiguous to the smallei' — and, on account of its bi-
lateral structure, the corresponding portions of the other hemi-
sphere, are in general those best capable of exercising such substi-
tutive functions. It may be doubted whether these portions do
not, in all ordinary cases, cover the entire limits within which the
principle of substitution can act. Such substitutive functions im-
prove under the law of habit to which the organs of the cerebral
cortex are subjected.
The connections between the different cerebral areas and their
functions are so complex and subtile that physiological science wiU
need a long time to disentangle them ; it may be doubted whether
it will ever succeed in doing this completely. The connections
among the phenomena of conscious sensation, volition, ideation,
and thought are at least equally subtile and complex. Will psy-
chology ever disentangle these connections ?
The bearing of the subject on our conclusions concerning the
nature of the mind and its connection with the body will be con-
sidered elsewhere.
CHAPTER III.
THE QUALITY OF SENSATIONS.
§ 1. The world of ordinary experience consists of a great number
of so-called '•' things " that are known to us by their distinguishing
qualities. Although each one of these things is believed to be a
separate existence, they are all perceived as having certain common
characteristics, and as standing in certain relations to each other,
of space, time, and action. It is with the things, their common
qualities and mutual relations, that unreflecting practical life is
chiefly concerned. But even without special reflection, everyone
learns that his knowledge of such external objects dejDends upon
the kind and degree of the effect they exercise upon his conscious-
ness through the senses. Attention is thus turned from the things
themselves to the sensations produced in us by their action. The
variety of such sensations, at first bewilderingly great, is soon re-
duced to some order by a classification referring them to the dif-
ferent organs through which they come. Thus, certain sensations
are received through the nose, others through the mouth, the ear,
the eye, or the skin — especially as covering that part of the body
(the hand) which is most active in touch. Smell, taste, hearing,
sight, and touch are the five classes of sensation, as the grouping
is made by the unprejudiced judgment of all.
A further rough and scientifically inadequate classification takes
place among the sensations of the same sense. Those of smell, in-
deed, defy classification, whether popular or scientific. Among
tastes, the most familiar are easily distinguished ; such are the
sweet, the sour, and the bitter. The two principal classes of sensa-
tions of sound are easily discriminated, as either noises or musical
tones ; the former are further classified as respects the character of
the feeling which accompanies them, and the latter as high or low
in pitch. The different more prominent colors — including black
and Avhite— are recognized by all persons of normal vision as
modes of the sensations of sight ; hence the colors commonly
named, and the various so-called "shades" of these colors. That
more than one class of sensations arise through the skin is shown
304 THE KINDS OF SENSATIOIST.
by the popular use of the word to "feel." Things /eeZ hard and
soft, smooth and rough, as weU as warm and cold. But things are
also said to feel heavy or light. The feeling by which their weight
is estimated, however, is only ascribed in a very indefinite way to
the parts of the body that are chiefly concerned in passively sup-
porting, or actively lifting, or pushing against their weight. The
particular use of tactual feeling, as well as the general use of the
muscular sense, in gaining this class of sensations is little noticed
by ordinary reflection.
§ 2. All the sensations are also regarded as having some place
in a scale of degrees of sensation ; they are either strong or faint,
or else He somewhere between the two extremes. They are also
habitually thought of as related in time, and as being connected
with the motion in space of the objects that occasion them. Of
the molecular action of their stimuli upon the end-organs of special
sense ; of the hidden chemical, electrical, or other processes con-
nected with the activity of the peripheral and central nervous sys-
tem ; of the physiological, psycho-physical, and psychological laws
under which the mind reacts in the form of simple sensations, and
combines these sensations into the composite objects of sense ; of
all these and other similar matters, the unreflecting conception of
sensation takes no account.
§ 3. It is obvious that the analysis of sense-percepts which suf-
fices for working-day life will in no respect answer the demands of
science. Its " common-sense " character is a distinct mark of its
inadequacy. An adequate scientific treatment of this branch of
Physiological Psychology requires at least four things : (1) to dis-
tinguish the simple sensations from those complex objects of experi-
ence with which alone our adult consciousness is familiar ; (2) to
point out the varieties of quality and degrees of quantity which be-
long to these sensations, and to discover the laws which relate them
to changes in the form and intensity of their stimuli ; (3) to show
how the simple sensations are constructed by the mind into the so-
called "presentations of sense" under mental laws of time-form
and space-form ; and (4) to indicate how far, if at all, the higher
mental activities of association, memory, will, and judgment, may
be brought under laws similar to those upon which the formation
of these presentations of sense depends. It is upon these four
heads of inquiry that modern psychology, as studied from the
psycho-physical point of view, has expended most of its painstak-
ing researches. Its success has been by no means complete. All
these fields of inquiry still include many unanswered questions ; all
of them present the results of researches that seem in various re-
THE ANALYSIS OF SENSATIONS. 305
spects conflicting. Yet it is precisely in these fields that modern
psychology has achieved its most brilliant successes. It has thrown
a flood of new light upon the essential nature and growth of hu-
man experience. It has profoundly influenced the current views
on metaphysics. It has contributed important factors toward tlie
solution of certain questions of interest to ethics and religion. It
has given us a new jDoint of view for I'enewiug the ancient debate
between Materialism and Spiritualism.
§ 4. The distinctions with which scientific analysis begins are to
a large extent received from ordinary experience. Some of the
most essential of the distinctions are confirmed by the results of
this analysis. They all, however, require to be carried farther and
to be fixed with much more of accuracy than belongs to the im-
pressions of common life. New distinctions also have to be intro-
duced. For example, scientific investigation maintains the differ-
ence between sensations of smell and sensations of taste ; but it
points out what is not ordinarily apparent — namely, that certain
results commonly referred to the latter sense really belong to the
former. It also adds the sensations of the muscular sense to the
classes popularly described ; and it discriminates more clearly be-
tween two distinct kinds of sensation that have the skin for their
organ — namely, temperature and pressure.
Psycho-physical science, moreover, accepts the common distinc-
tion between the quality and the quantity of the different sensa-
tions. But it describes with all possible accuracy the limits Avithin
which alone this distinction can be carried out. It shows that the
quality and quantity of sensation are inseparably connected ; that,
as Lotze held (a view confirmed by von Kries and others), changes
in quality can be distinguished from changes in intensity, with
perfect confidence, only in the case of sensations of hearing. It is
possible that even here the distinction is largely made on the basis
of complex experience. Very intense sensations of heat and cold so
far change their specific character as to tend to pass into each other,
or, perhaps, to become submerged in a common tone of painful
feeling. Minimum sensations of heat and pressure are difficult to
distinguish from each other ; maximum sensations of pressure are
likely to lose the characteristic quality of touch and be displaced
by sensations of pain. To treat scientifically of the quality of
sensations requires, then, a large amount of the most careful
analysis.
§ 5. It is essential, in the first place, to distinguish " simple
sensations" from " presentations of sense," or those complex ob-
jects of consciousness which result from an act of mental synthesis
20
306 THE KINDS OF SENSATION.
on the basis of several simultaneous affections of sense. As respects
developed experience, the simple sensation is a necessary fiction of
psycho-physical science. Consciousness is scarcely more able di-
rectly to analyze a presentation of sense into those factors out of
which it originated than it is to analyze a drop of water into its
component oxygen and hydrogen gases. Simple sensations, there-
fore, are not objects which can be examined in the direct light of
introspection. Yet they are factors which, as scientific analysis
shows, actually enter into all such objects as can properly be sjDoken
of under the term "presentations of sense." Any sensation which
is absolutely unanalyzable with respect to distinctions of quality',
and which, therefore, cannot be considered as consisting of com-
ponent parts, is called simple. It is distinguished as a sensation
from all other elementary forms of feeling or knowledge, by the
relation which it sustains to the jDresentations of sense. A sensa-
tion, unlike the feeling of grief, of desire, or of weariness, etc., is a
potential factor of a material object. Through the senses we know
"things;" not, indeed, as though they apj^eared before the mind
by immediate apprehension in the form of exact copies of extra-
mental realities. But every sensation is an affection of the mind
recognized as connected with an extra-mental reality, through the
activity of the senses. Simple sensations are those elementary
factors, themselves indecomposable, out of which the presentations
of sense are composed. The objects of sense, however, do not have
the character of mere compounds of simjDle sensations. Sensations
must not only be associated and compounded, but also localized
and projected without (that is, set in systematic relations of sj)ace-
form), in order to constitute the objects of sense.
§ 6. The foregoing remai'ks suffice to indicate, in a preliminary
way, what is the nature and value of the psycho-phj'sical investi-
gation of sensation. We inquire, in the next two chapters, as to
the Quality of Sensations. The inquiry, when conducted from the
psycho-physical point of view, involves an answer to three questions :
(1) What is the precise locality in the organism where the specific
excitation which occasions each kind of sensation originates ; and
what is the natui-e of the action of the stimulus in producing such
excitation? (2) What are the kinds of sensations which appear in
consciousness as the result of the various excitations? (3) What are
the laws by which the quality of the sensations is related to the
kinds of excitation? Neither of these three questions can be
answered completel}'. The investigation of the first is much re-
stricted by our almost complete ignorance of those processes in
the central organs that are in all cases the proximate internal
SPECIFIC ENEKGY OF JSTERVES. 307
stimuli or immediate antecedents of the sensations. Moreover, our
knowledge of the intimate structure of the end-organs of sense,
and of the nature of the physical processes which excite them, is
still very incomplete. The detection of obscure but important dif-
ferences in the qualities of conscious states of sensation is by no
means easy ; it requires great skill, strict and trained attention,
and unwearied rej)etition of experiment. But these conditions of
success have a great effect in altering the quality of the sensations
themselves. Besides all this, remarkable idiosyncrasies not infre-
quently appear ; and language can only imperfectly describe even
the most common factors of the varied and living experiences wdth
which science tries to deal.
In investigating the laws that define the relations between our
subjective experience, called sensation, and objective phenomena
in the shape of physical energy acting uj^on the nervous mechanism,
there is often the greatest doubt as to what manner of laws are be-
ing investigated. They may be considered as purely physiological,
or as psycho-physical, or as purely psychological. It is not strange,
therefore, that different theories exist for accounting for all the
more important groups of facts, deijending uj^on the emphasis laid
by different investigators upon the value of each of the three possi-
ble modes of explanation. The truth is, that each sensation is sepa-
rated by a series of intricate j)hysiological and psychical processes
from the application of the stimulus in the gross, as it were, to the
end-organ of sense.
§ 7. The authority of one great law is involved, as a silent
assumption, in all discussion of the quality of sensations. This law
is known as the law of the Specific Energy of the Nerves. It has
already been shown (Part I., chap. I., § 35) that any such dis-
tinction of the kinds of nerve-fibres as denies their possession of
common functions cannot be maintained. But the phenomena
of sensation cannot be explained without a much more extended
application of this law than has thus far been found necessary.
Distinctions of quality in sensation depend upon the excitation of
specific corresponding elements of the nervous system. That only
the optic nerve is capable, when excited, of exercising the physio-
logical function upon which sensations of light and color depend,
does not admit of doubt ; the same specific quality cannot be
denied to the functional activity of the nerves of smell, taste, hear-
ing, and touch. Moreover, in the end-organs of each of these
senses, provision must be made for a further differentiation of
function. What is the nature of the evidence, and what conclu-
sions must be drawn from it, will be best appreciated at a later pe-
308 SENSATIONS OF SMELL AND TASTE.
riod in the discussion. Meantime we find ourselves obliged to as-
sume the existence of some law of the specific euex-gy of the nervea
of special sense.
§ 8. Little of a scientific character is known concerning Sensa-
tiona of Smell, considered as respects their qualit}'. Anatomy,
chemistry, and physics fail to furnish definite information on this
point ; experimental physiology as aj)plied to the lower animals is,
of course, unsatisfactory ; and the appeal to human consciousness
asks for an anatysis of which it is incapable. It has already been
shown (Part I., Chap. V.) that the part of the mucous membrane
of the nasal passages known as regio olfactoria contains the end-
organs of smell ; the specific stimulus of the organs in this region
is applied as borne thither by the current of air, and almost, if not
quite, exclusively in the act of inspiration. In order that any sub-
stance may act through the end- organs on the nerve (olfaclorius)
which is spread out in this region, it must either exist in gaseous
form or else be vaporizable under given conditions of temperature.
The degree of temperature at which different substances become
odorous therefore varies according to their i^hysical characteristics.
For example, arsenic, which at ordinary temperatures is inodorous,
when raised to a dark-red heat is vaporized and the vapor excites
an intense sensation of smell. Fluid bodies which give off an
odorous i-eek, when brought in fluid form into contact with the
mucous membrane of the regio olfactoria have no smell ; if this
membrane is soaked in fluid of any kind whatever, it loses for a
time the capacity to be excited witli olfactory impressions. E. H.
Weber ' discovered that if the head be placed with the nostrils
pointing upward, and the nasal jDassages be then filled with pure
water, sweetened water, or a mixture of water and eau de Cologne,
after these passages are emptied the sense of smell is, in all cases,
temporarily lost ; even when Cologne is used, with the exception
of the instant at which the fluid is poured in, no odor can be per-
ceived. Subsequent observers have confirmed the experiments of
Weber. One investigator ^ lost all sense of smell, even for acetic
acid and ammonia, for a period of half a minute ; another for five
minutes, and the sense in its full acuteness did not return for nearly
half an hour. Whether this effect of the fluid is due to impair-
ment of the end-apparatus of smell by soaking it (so Valentin), or
to the mechanical barrier which the layer of foreign substances
interposes between the odorous particles and this apparatus (so
FrohHch), we cannot say ; it may be due to both causes. Contrary
1 See Archiv f. Anat , Physiol., etc.. 1847, p. 257.
sprolilicli, in Sitzgsber. d. Wiener Acad., 1851, VI., p. 322.
THE STIMULUS OF SMELL. 309
to the assertion of Wundt,' that probably no gases or vapors, except
atmospheric air and its constituents, are absolutely inodorous, so
far as we have present information a number of gaseous and va-
porizable substances are so ; and no reason is known for such
apparent exceptions to the rule.
§ 9. The stimulus of smell is supposed to consist in certain ex-
ceedingly minute particles contained in the odorous gas or vapor
which is drawn in with the current of air over the mucous mem-
brane of the regio olfactoria. The question is as yet scarcely de-
cided, whether other forms of stimulus, besides these odorous
particles — mechanical, electrical, thermic, or so-called subjective —
can excite the sensation of smell. Tlie older experimenters (Volta,
Pfaff, Fowler, and Humboldt) failed to obtain any certain proof
that the electrical current is an excitant of this sense. In one place,
however, Pfaff speaks of a sensation resembling the smell of sul-
phur as caused by the apj)lication of electricity to the sensory pas-
sages of the nose. Ritter (in 1798) experimented by using bits of
graphite and zinc thrust into these passages, and also by holding
one pole of a battery in the hand and placing the other in the nos-
tril. In the latter way he thought that he excited a genuine sj)e-
cific sensation of this sense. He describes the positive pole in the
nostril as producing an inclination to sneeze and a trace of a smell
like that of "ammonia ; " the negative pole placed there does away
with this inclination and produces a kind of " sour " smell. Such
phenomena are probably, however, all to be assigned to the nerves
of taste, touch, and common feeling. More recent investigations
have done little to remove the reasons for doubt." The smell of
phosphorus which is developed by the action of the electrical ma-
chine is probably due to the ozone set free ; it is not a case, then,
of the direct excitation by electricity of the sensation of smell.
Some physiologists (notably Valentin) have observed that this sen-
sation may be awakened by mechanical stimulation, such as strong
vibi'ation of the nostrils, violent sneezing, etc. ; others have failed
to produce this specific sensory effect in such ways. It does not
appear that thermic stimulation will excite the sensation of smeU.
Experiments to prove that subjective sensations of smell may be
produced b}' injecting odorous substances into the veins of animals
are very uncertain. Human pathological cases, in spite of the cus-
tomary indefiniteness of the patient's testimony as to the nature of
his sensory affection, show that compression of the olfactory nerve
' Gruiidziige d. physiolog. Psycliologie, i. , 384; comp von Vintschgau, in
Hermann's Kandb d. Physiol., HI., ii., p 261 f.
^See Roaeutiial, iu Archiv f. Auat., Physiol., etc., 1860, pp. 217 ff.
310 SENSATIONS or SMELL AND TASTE.
by tumors, etc., may produce sensations of smell. Disturbances of
the central organs, such as occur in certain cases of insanity, may
doubtless have the same result. The powerful effect which some
odors have upon the brains of certain persons, so that nausea, gid-
diness, and other disturbances of feeling result, scarcely needs
mention ; it cannot all be resolved into mental associations con-
nected with the sense-impressions.
§ 10. No approach can be made toward a scientific classification
of the kinds of smells.' This specific sensation must, however, be
carefully distinguished from the other forms of feeling with which
it is most closely allied. Many supposed sensations of taste are
really sensations of smell. Substances like ammonia and acetic
acid powerfully excite the sensations of touch and common feeling
through their action on the trigeminus as well as the olfactory
nerve. Other sensations of touch and of the muscular sense are
reflesly occasioned in such cases, and blend with the specific sensa-
tions of smell in the total mental result. But of all the attempts to
classify the qualitatively jDure sensations of this sense, none can be
said to have any scientific value. The division into pleasant and
unpleasant smells depends upon the idiosyncrasies of individuals ;
to some the smell of burning feathers, of assafoetida, of valerian, or
of rank cheese, is pleasant. Frohlich's " classification into those
which excite merely the olfactory nerve, and those which call out
other sensations reflexfy through their action on the trigeminus, is
purely physiological and not psycho-physical ; moreover, it does
not apply to sensations of smell, as such. When we classify the sen-
sations according to the objects which produce them — as j)ractieally
we are obliged to do — we are not distinguishing the qualities of
our feeling ; the smell of a rose does not belong to a class of sen-
sations as does a sour taste or the color red. No known principle
will bring order out of the bewildering complexity of this sense.
Sensations of smell cannot, like those of pressure, hearing, and
sight, be schematized or represented as standing in any definite
local or mathematical relations to each other. Smells cannot be con-
ceived of as having a scale of pitch, or triangle of color-tones. As
Wundt ' declares, the sensations of smell form " a discrete mani-
foldness Avhich has an unknown arrangement."
§ 11. The properties which any substance must j)ossess in order
to be odorous, and the nature of the action of the odorous particles
' For the entire subject, see von Vintschgau, in Hermann's Handb. 4
Physiol., IIL, il, p. 2G6 f.
•^Sitzgsber. d. Wiener Acad., 1851, VI., p. 322 f.
^Physiolog. Psychologie, i , p. 386.
NATUEE OF ODOROUS SUBSTANCES. 311
upon the end-organ of smell, are wholly unknown — as much so
now as when, more than a half-century since, Cloquet confessed the
complete ignorance of the scientific world on these matters. A
great variety'' of phenomena appear, but no known laAV has control
of them. Some plants are odorous by day alone, others by night
alone ; still others only in the morning. Some plants have a smell
when dried ; others give off only a weak odor when dry, but a
stronger one when moistened. Of course, the effect of any odorous
substance depends upon the ease wdth which it may be vaporized,
and the speed and extent of its diffusion through the atmosphere.
Camphor, musk, and other similar substances are distinguished for
their long-continued and far-reaching effects.
The discovery of Eomieu, in 1756, that small bits of camphor on
the surface of water have a rotary motion, has called out various
investigations in the line suggested by this fact. Provost subse-
quently (1799) observed that other odorous bodies have a similar
motion on the surface of water, and that a very thin layer of water
on a perfectly clear plate or glass withdraws itself as soon as jduI-
verized camphor is laid upon it. More recently still, Liegeois has
noticed the same phenomena, wholly or in part, exhibited by some
two hundred odorous substances of either vegetable or animal struct-
ure. Minerals, according to this observer, do not behave in the
same way. Some of these odorous substances seem to inhibit or
check the rotar}^ motion in others. He concludes that we are jus-
tified in believing odorous substances to have the power, especially
when in contact with water, of setting up a motion of these outside
particles which distributes them through the atmosphere so that
they reach the mucous membrane of the nasal passages. Just how
they act upon the end-apparatus there it is impossible to say. The
researches of Tyndall ' and others as to the influence which odorous
particles of different substances have upon the capacity of the air
to absorb heat may possibly be combined with the foregoing re-
searches in a way to suggest some tenable hj-pothesis touching the
nature and action of the stimuli of this sense ; but thus far, as has
been said, we cannot go beyond a confession of ignorance.
§ 12. The condition of scientific attainment as to sensations of
taste and their stimuli is only little better than that as to the allied
sense of smell. The adeqnate specific stimulus for the nerves of
this sense consists in certain tastable substances ; such substances,
however, do not excite the end-apparatus unless they act upon it
under definite conditions. Only fluid bodies, or such as are at
least to some small degree soluble in a fluid or menstruum, excite
' Heat as a Mode of Motion, pp. 341 ff. New York, 1868.
312 SENSATIONS OF SMELL AND TASTE.
sensations of taste ; absolutely insoluble bodies are, without excep-
tion, tasteless. This fact may be due to the concealed position of the
inner cells of the gustatory flasks, which is such that they cannot be
reached by substances undissolved. By no means all soluble sub-
stances have a taste. No known law regulates the relation between
the solubility of bodies and their power to excite sensations of this
class. It is disputed whether any of the gases are direct excitants
of the end-organs of taste. The monograph of A. Stick ' maintains
the tastable character of certain gases, on the ground that a stream
of them, let fall upon the tongue when dry (so that they cannot well
be absorbed by the saliva), produces the peculiar sensations of
taste which these gases are known to possess. A stream of car-
bonic-acid gas, for example, when acting on the dry edge of the
tongue, has a taste which is described as sweetish sour. It is diffi-
cult, however, to secure such a degree of dryness of the tongue as
will not leave a moist capillary layer ; diflficult, also, to exclude all
the connected sensations of smell and common feeling.''
It is doubtful whether the sensation of taste can be excited by
mechanical means ; and there is no j)roof that heat can irritate the
gustatory nerves. Certain authorities of the first rank have indeed
described specific sensations of taste as mingled with the feelings
which follow rubbing, pricking, and pressing the tongue. Henle
observed a saltish taste to be excited by passing a current of air
over the tongue ; Wagner a bitter taste by pressing down the base
of the tongue with the dry finger ; Dr. Baly an acid or a saltish
taste by repeatedly and lightly tapj)ing the end of the tongue.
The long-debated question as to the electrical stimulation of this
sense seems now to be decided affiinnatively.^ It was discovered in
1752 that the application of two different metals to the tongue is
followed by a peculiar sensation of taste. Volta recognized the
fact that the effect of the metals is due to the electrical current
called out between them. If the cathode is laid upon the upper
surface of the tip of the tongue, a sensation is produced by the cur-
rent passing out which is variously described as metallic, acid and
metallic, or bitter and metallic, etc. ; but if the anode is applied to
the same spot, the sensation produced by the entering current is
described as acid, or acid and metallic, or bitter and metallic. In
the former case, not infrequently, a strong cuxTent is needed to pro-
'Ueber d. Schmeckbarkeit d. Gase, Berlin, 1857; article in Annalen des
Charite-Krankenhanses.
■•* See von Vintschgau, in Hermann's Handb. d. Physiol., III., ii., p. 19G f.
^ The whole question is discussed by von Vintschgau, ibid., p. 181 f.; and
Pfluger's Archiv, xx., pp. 81 ff.
ELECTRICAL STIMULUS OF TASTE. 313
duce any sensation at all. Since the discovery of electrolysis, it
has been objected that these effects are due to the decomposition
of the fluids of the mouth and the consequent accumulation of free
acid at the positive and free alkali at the negative pole ; the}' are
therefore not to be ascribed to the direct action of the electrical
cui-rent on the end-apparatus of sense. Experiments by du Bois-
Eeymond, Rosenthal, ' and others have been directed toward an-
swering this objection. The former showed that when a chain of
four persons is arranged in such manner as to send a current of
electricity through the tongue of one, the eyeball of another, and
the muscles of a frog-preparation held by two of the four, the same
current will cause simultaneously an acid taste, a flash of light, and
a movement of the animal's muscles, Rosenthal discovered that,
if two persons touch the tips of each other's tongues while one
holds in a moist hand the positive and the other the negative pole,
an electric current Avill cause the first person to have an alkaline and
the second an acid taste. Still other experiments confirm the
opinion that sensations of this sense may be directlj' due to elec-
trical stimulation. Attempts have been made to prove the possi-
bility of exciting subjective sensations of taste by injecting tasta-
ble substances into the veins of animals ; but the psychology of
the subject has reaped no results from these attempts. Most of
the alleged cases of such subjective origin are probably due to
substances really brought to the tongue in the saliva. It is worth
remarking here that sensations of taste rarely or never mingle in
our dreams.
§ 13. The question whether atastable substance excites precisely
the same sensation when applied to all portions of the organs of taste
is a difficult one to answer satisfactorily (see Part I, Chap. V., §
6). The tabulated results of different experimenters upon this
question disagree considerably. Such disagreement is suggestive
of idiosyncrasies of taste, and of doubt whether the different shades
of the same class of sensations are either nicely discriminated or
uniformly described by most persons. Descriptions which speak
of the sensations aspi'ickly, piquant, cooling, etc., show, of course, a
combination of sensations of common feeling with those of special
sense. The minor varieties of taste may be occasioned in a manner
similar to that of the less important shades of color-sensations. It
seems tolerably well established that sweet and sour are tasted
chiefly with the tip of the tongue ; bitter and alkaline with its roots.
The experiments of two of the principal observers, Horn and Picht,
agree in the conclusion that nearly all substances (even sugar) call
' Ueber d. elektrischen Geschmack ; Archiv f. Anat., Physiol., 1860, p. 217 f.
314 SENSATioisrs or smell and taste.
out a bitterish taste when applied solely to the papilloe circum-
vallatce.
§ 14. Most of the different kinds of tastes admit of being con-
sidered as compounds of a few simple sensations of this sense with
each other and with sensations of smell, touch, common feeling, and
muscular sense. Many so-called tastes are really chiefly smells.
Physiologists generally distinguish four principal classes of tastes —
sweet, bitter, salt, and sour. Wundt ' adds to these four the alka-
line and the metallic. But possibly the alkahne may be considered as
a modification of the salt ; and the metallic is probably a compound
taste, although its analysis is by no means easy. The attempt has
been made by Valentin and others to reduce this number to two —
the sweet and the bitter. The sour is thus considered as not a pure
sensation of taste, but as predominatingly a sensation of touch.
Acids in concentrated form certainly bring into action the nerves of
feehng ; but in very dilute form they seem to excite purely the sensa-
tion of taste. The same thing is true of saltish substances. The
bitter and the sweet are agreed by all to have the character of pure
sensations of this sjDecific sense. Powerful reflex sensations of the
muscular sense are occasioned by strong stimulation of the nerves
of the tongue, and these sensations blend with the specific sensa-
tions of taste. There is no satisfactory reason to be given for
classing the sensation of nausea under the sense of taste.
The primary forms of taste are combined, in the greatest variety,
with an indefinite number of shades under each of them. The
hypothesis of four or more specifically different forms of the end-
apparatus corresponding to the primary forms of sensation — for
example, "bitter-tasting" nerve-fibres, "sweet-tasting" nerve-
fibres, etc. — offers, under the law of the specific energy of the
nerves, an opportunity for explaining all the phenomena of this
sense somewhat similar to that embraced by the so-called Young-
Helmholtz theory of color-sensations.
§ 15. Concei'ning that in tastable substances which fits them to
excite the end-apparatus of the gustatory nerves, or concerning the
molecular action of such substances, we have no information what-
ever. No scale of stimuli, considered as differing in the rapidity of
their vibration and corresponding to a scale of resulting sensations
differing in pitch or tone, can be made out for sensations of taste.
The great difficulties which accompany experiments uj)on this
sense, and the fact that the most fundamental questions concerning
its activities are still unanswered, place it in an unsatisfactory posi-
tion only less hopeless than that occupied by the kindred sense of
' Playsiolog. Psycliologie, i., p. 382.
SUBJECTIVE CHARACTER OF SOUND. 315
smell. We have in the case of taste, however, the very great ad-
vantage of being able, at least loosely, to classify the sensations
Avhose quality we are considering.
§ 16. On passing to the consideration of sensatiojis of sound much
more help is received from the science of physics. But modern in-
vestigations, in the form in which they concern us, do not go back
of the great work of Helmholtz,' who made the entire field peculi-
arly his own. Since the first appearance of this work, the subject
has also been greatly enriched by the original researches of Oetting-
en,^ Mach,' Preyer,* Hensen,' Stumpf," and others. In speaking
of the stimuli of these sensations, we are still comj)elled to refer
chiefly to the vibrations of air, which are only remote excitants of
the end-organs of this sense. Neither physics nor physiology has
yet been able to fix the precise locality in the organism (the ner-
vous structure of the cochlea) where the immediate stimulation of
the end-apparatus takes place ; or to tell what is the exact nature
of its action. We are obliged, then, to confine ourselves in the
main to considering a relation between the vibratory energy of the
air and certain states of consciousness, without attempting to ex-
plain the many intermediate links.
All sensations which arise in the mind by means of the irritation
of the auditory nerve are called sensations of sound. The word
" sound " is thus used by psychology for a wholly subjective affair,
which has no more resemblance to those vibrations which physics
designates by the same word than has the taste sweet to the un-
known physical properties that produce it. The trained mind, or
"trained ear," as we say, has indeed the power du-ectly to analyze
a compound musical sound into its constituent elements. But each
of these elements is purely a sensation, a subjective affair. It car-
ries in itself no token that it has been produced by vibrations of
any kind ; or that it sustains any numerical relation whatever to
the vibrations of which some other sensation of sound is composed.
We know nothing directly, through sensations, either of the struct-
1 Die Lelire von d. Tonempfindungen als pliysiolog. Grundlage f. d. Tlieorie
d. Musik, Braunschweig, 1st edition, 1863; 2d edition, 1865; 3d edition,
1870 ; 4th edition, 1878.
'^ Harmoniesystem in dualer Entwicklung, 1866.
^ Various contributions in the Archiv f. Ohrenheilkunde and elsewhere
(especially the Sitzgsber. d. Wiener Acad.).
■* Ueber d. Grenzen d. Tonwahrnehmung, 1876 ; Sitzgsber. d. Jen. Ge-
sellsch. f. Med., 1878 ; Akustische Untersuchungen, 1879.
5 In Hermann's Handb. d. Physiol. , III. , il. , pp. 3-142, and works by the
same autlior there referred to.
" Toupsychologie, Leipzig, 1883 (Vol I. only).
316 SENSATIONS OF SOUND.
ure of the ear or of vibrating strings and particles of air, or of the
mathematics and physics of music.
Sounds are of two classes — tones, or musical sounds, and noises.
The former are due to periodic motions of sonorous bodies ; the
latter to non-periodic. Noises are those sounds which, objectively
considered, are wanting in tlie periodic regularity of stimulation
which characterizes all musical sounds, and, subjectively considered,
in the peculiar, pleasant modification of consciousness which the
latter produce. But noises accompany almost all tones ; and, con-
versely, tones may be detected by the trained ear as mingled with
the noises of every-day life. No plaj'er of the violin avoids all noise
of scraping from the bow ; no stroke of a workman's hammer, or
slamming of a door, that does not start and catch up into itself
some trace of musical tone. The interest of science has hitherto
been almost wholly concentrated upon musical sounds, and little
has been done by either phj'sics or physiology toward tlie analysis
of noises. It is characteristic of a noise, according to Helmholtz,*
that there is a quick and irregular alternation of different kinds of
sensation of sound. This distinctive character can generally be
detected " by attentive aural observation without artificial assist-
ance." "We can compound noises out of musical tones ; as, for ex-
ample, by striking together all the keys of an octave on the piano.
Hensen'"' distinguishes three " categories of unmixed noises " — the
" beats " or pulsations which disturb the purity of musical tones ;
the crackle, crack, or crash ; and hissing sounds. These three shade
into each other, and, when mixed with different kinds and quantities
of musical sounds, make up the noises which we hear on every hand.
§ 17. Musical sounds differ, not only in quality, but also in
quantity or intensity of sensation as dependent upon the ampli-
tude of the vibrations which produce them. With respect to their
qualitij they are distinguished as either simple or complex, accord-
ing as they result from one set of regularly recurrent (periodic) vi-
brations of a given number in a given unit of time, or result from
a combination of two or more sets of such vibrations. The musi-
cal sounds of ordinary experience are complex. The blending of
the simple tones into the complex tone is not so complete, however,
that it cannot be at least partially analyzed directly by a trained
ear. The complex sound, which results from this compounding
of the contrasts or coincidences of several simple musical sounds,
may be called by the term " clang " — in this meaning borrowed
from the usage of the German. The quality of tones considered as
1 The Sensations of Tone, etc., p. 11 f. London, 1875.
2 Hermann's Handb. d. Pliysiol., Ill, ii., p. 17.
THE LIMITS OF PITCH. 317
simple sensations is their pitch, which varies according to a scale of
states of consciousness that are immediately apprehended and com-
pared with each other, and that are discovered by objective meth-
ods to correspond to a scale of changes in the number of the vi-
brations of the waves which occasion them. The pitch of tones is
therefore spoken of as "high" or "low," according to the place
which we assign to the resulting sensations in this scale. Such
place in the scale may be considered either with respect to the re-
lation of any particular tone to the upper or lower limits of the
scale, or with respect to the relation of the different tones to one
another. " Clangs," or complex tones — the musical sounds with
which we are made acquainted by all ordinary experience — have
also a variable quality called timbre, or " color-tone ; " the timbre
of the clang is dependent upon the pitch, number, and relative in-
tensity of the simple tones which compose it. Thus a note having
the same place in the musical scale (for example, a of the once-
marked octave — 440 vibrations) sounds differently, as we say, on
the piano, violin, cornet, or when sung hy the human voice. The
pitch of the tone as produced by all these different methods is the
same ; but its color-tone is determined by the character of the
over-tones which are blended with the fundamental tone.
§ 18. Tlh.Q pilch of tones depends npon the rapidity of the peri-
odic vibrations (the number in a given unit of time — usually one
second) wliich occasion them, or — what is the same thing — upon
the length of the sound-waves. This class of sensations, however,
has both an upper and a lower limit ; that is to say, vibrations ei-
ther below or above a certain number per second, or — what is the
same thing — -wave-lengths that are either shorter or longer than a
given limit, produce no sensations of musical sound. The difficulty
of determining these limits is great, because the intensity of ex-
tremely low or high tones has to be enormously increased in order
that the}^ may be heard at all ; because the perceptions of the
acoustic sense are so very blunt near the limits that the different
sensations are almost certain to be confused ; because distracting
sensations of common feeling mingle in these ranges of tone with
the sensations of sound, and because near the lower limits the
over-tones — especially the octave above — become so strong as to be
mistaken for the fundamental tones. On account of these diffi-
culties the older investigators made numerous mistakes. Indi-
vidual j)eculiarities are also very important in determining sensa-
tions of pitch. Some persons can hear tones below or above those
audible to most others. Helmholtz ' thought that sensations of
' The Sensations of Tone, p. 268. London, 1875.
318
SENSATIONS OF SOUND.
tone begin to cease when the vibrations fall below 34 per second ;
some tuning-forks of great size, which vibrated only 28 times per
second, seemed to him, however, to have a trace of tone in the form
of a "weak drone." Preyer ' found that while 14 vibrations pro-
duced no tone that he could hear, at 16 vibrations he was able to
hear a tone ; others could distinguish a musical sound only at 19
or 23 vibrations. The same observer experienced as a sensation of
musical sound more than 40,000 vibrations per second ; Turnbull
found that the majority of those with whom he experimented
could not hear more than about 20,000 to 22,500 vibrations per sec-
ond, and only one — a musician — heai'd 30,000 ; Despretz succeeded
in producing with tuning-forks audible tones that had 32,000 vi-
brations. Blake thinks that persons with defective ear-drums are
able to hear tones of higher pitch, reaching even 50,000 vibrations.
Vibrations slower than 28 to 30 per second produce in most ears
only a buzzing or groaning sound ; the more acute tones are unpleas-
ant, or even painful, and finally inaudible to all ears. These results
cannot be considered as very concordant or precise. They show,
however, that the range of the average human ear is rather more
than nine octaves, reaching from about A„_ of the sub'contra octave
(27-j vibrations per second) to above c' of the seven-times-marked
octave (16,896 vibrations per second).
The following table " gives the pitch of all the musical tones audi-
ble to the human ear, in the key of C major, on a scale in which
a' is fixed at 440 vibrations. Only about seven of the rather more
than eleven octaves of the table are, however, usable in music ;
these seven reach upward from C ^ of the contra, or fz-om A„ of the
subcontra octave, to 6^ — namely, the seven or seven and a half
octaves of the modern piano.
c
D
E
B
Subcontra octave
Contra octave
Great octave
Small octave
Once-marked octave
Twice-marked octave
Thrice-marked octave
Four-times marked octave
Five-times-marked octave .
Six-timt-s-marked octave ..
Sevcii-timcs-marked octave
Eight-times-iiiarked octave
33
6H
132
2(i4
528
1.056
2,112
4.224
8.44S
16,S9fi
33,792
18% 6
3T'^
74 J:^
1481^
297
594
1,188
2,376
4,752
9,504
19,(108
38,016
20%
41 H
S2M
16>
330
660
1,320
2,640
5.280
10.560
21,1-iO
42,240
22
24i'i
27^
44
49j<r
55
88
99
110 ,
176
198
220
352
396
440 !
704
792
880 i
1,408
1,584
1,760 '
2.816
3,168
3,520 ;
.'5.6.32
6,336
7,040
11,264
12.672
14.080
22.528
25,344
28.160
.3015/,, Cj
fil^ C,
123?^ ; c.
2473<? : c,
495 c',
990 c2
1,980 cs
3,960 o^.
7,920 c6,
15,840 c6,
31.680 c'i
, T>2, etc.
, Dj, etc.
D, etc.
(i, etc.
, d', etc.
, d2, etc.
, d'i, etc.
d", etc.
, d^, etc.
d^, etc.
. d^, etc.
' Grenzen d Tonwahrnehmiiiig, p. 23 f.
- Taken from Stumpf, Tonpsychologie, I., p. xiv. , and giving the German
scale ; tlie Frencli fixes a' at 435 vibrations ; the theoretical pitch in England
gives 512 for c'K
SENSITIVENESS TO PITCH. 319
§ 19. The sensitiveness of the ear to differences of pitch varies
greatly with different individuals, and for the different octaves of
the musical scale. Preyer found that unpractised persons, within
the octaves from c to c^ (132-1,056 ^dbrations by the table, but
128-1,024 by the scale adopted for his experiments), distinguish
a difference of from 8 to 16 vibrations as producing a distinct dif-
ference in the sensation of pitch. Extreme cases of deafness to
differences in pitch are recorded ; as, for example, that of the man'
who, in the middle part of the scale, could not distinguish an in-
terval of less than a third, and, in the higher and lower parts, of
less than a seventh.^ Persons insensitive to differences of a tone or
half-tone, who are sometimes said "not to know one note from
another," are by no means infrequently met with. Differences of
the two ears of the same person, in the fineness of this kind of per-
ception, are common enough ; in certain cases the difference may
amount to a half-tone or more. Sensitiveness to pitch is generally
capable of rapid cultivation, and may reach a high degree of per-
fection in persons Avho have what is called " a good natural ear" for
musical tones, if the ear be also highly trained. Such persons may
become able to discriminate differences in the sensations caused by
changing the number of vibrations not more than a third of a single
vibration per second, in the region of the scale between a' and c'.
In the octave from 6' to h' more than 200 tones are distinguish-
able. But above and below this region the distinctions jDos-sible
are less fine ; above c^ even well-trained ears commit errors in iden-
tifying two notes that differ by 100 or even by 1,000 vibrations. It
appears, then, that not only the musical quality of tones, but also
the power of distinguishing differences in them, diminishes rapidly
as we approach the upper and lower limits of the scale.
The fineness of the possible distinctions of purity of interval also
differs for different individuals and for different intervals. The
following table is compiled by Hensen ^ from data drawn from
Preyer 's investigations. The bracketed numbers of the first column
indicate the proportion in which the vibrations of the different
intervals stand to those of the fundamental tone ; the quotient
n : n = i, the variation from the pure interval which was fovind
detectable in each case ; V = the number of vibrations off from the
pure interval which is the least distinguishable ; and aS" is the de-
1 Reported by Grant Allen, in Mind, 1878, p. 157 f.
^ Comp the lengthy and interesting discussion on "Individualitat des Sin-
nes und Gedachtnisses fiir Tonqualitaten," in Stumpf, Tonpsychologie, I., pp.
263 ff.
''See Hermann's Handb. d. Physiol., III., ii., p. 114.
320
SENSATIONS OF SOUND.
nominator of the fraction which indicates the sensitiveness of the
ear to the purity of each interval.
rNTERVAL.
Fourth (1.333)
Fifth (1.5)
Minor Sixth (1.6)
Major Third (1.25) j
Minor Third (1.20) ,
Octave (2.0)
V/holeTone (1.125)
n.
n' .
i.
1.3396
V.
187.58
251.23
1.02
167.68
251.23
1.4983
0.23
143.06
231.41
1.6108
1.19
139.60
163.68
1.2437
0.73
139.62
175.53
1.2572
0.89
207.54
251.23
1.2102
1.90
500.40
1,001
2.0004
0.13
215.15
243.51
1.1291
0.85
211
822
148
198
193
117
5,000
274
Immediate judgment of abf;ohUe tone (as the «' carried in mind
by musicians) is possible ; judgment between two tones as to
which is higher or lower in pitch is also immediate, and may be
exercised independently of everything except the two sensations
themselves. The latter judgment is the common power of mind
belonging to this sense ; the former is, as a rule, exercised only by
skilled persons, and by them only very imperfectly. Experiments
of Stumpf,' upon himself and three other musicians, showed that
the mistakes in judgment of absolute tone amounted, in the lower
region of the scale (from G^ to B^), to 15^-100^ of the trials ; in
the middle region (from a-cj\ or from g-e'), to Qfo-lQ'fo ; in the
ujjper region (from g'^-f'^, or from/^-a^), to 7^-80^^. Only-one of
the four persons experimented upon seemed to approach the point
of infallibility. Judgment of absolute tone is, therefore, a different
matter from that which makes distinctions in intervals or in the
least observable differences of pitch, and is much more precarious.
§ 20. Those psychologists appear to be in the right who claim
that some power of the mind immediately to judge differences of
quality in pitch, purely as such, must be assumed in order to ac-
count for the foregoing phenomena." Such judgment, however,
may be, and ordinarily is, much assisted by auxiliary discrimina-
tions of other sensations which blend with those of musical tone.
Among such secondary helps the most important are the muscular
sensations which accompany the innervation of the larynx and other
organs used in producing musical tones. For we ordinarily inner-
' Ton p.sychol ogle, I., pp. 305 ff.
s On tin's Rubiect. comp. Lotze, Medicin. Psychologie, pp. 265 ff., 480 f. ;
Strieker, Studien iiber d, Association d. Vorstellungen, 1883. p. 2 1; G. E.
Miiller, Zur Grundlftcung d. Psycho-physik, Berlin, 1878, pp. 276 ff.; and
Stumpf, Toupsychologie, I., pp. 134 ff.
THE JUDGMENT OF TONES. 321
vate these organs (at least in an inchoate and partial way) — that is,
"we sound the note to ourselves — when trying carefully to judge of
its pitch. But the niceness of these muscular sensations is not
great enough, even when most highly trained, to account for the
discriminations of the " good ear." The trained musician can de-
tect by ear a difference in quality between two tones of 400 and
400^ vibrations per second ; but the most skilful singer — Jenny
Lind, for example — scarcely succeeds in singing in quarter-tones.
Moreover, the relative powers of larynx and ear by no means keep
pace with each other in the same person. It should also be re-
membered that all our ordinary discriminations of musical sound
apply to composite tones, or " clangs ; " in discriminating these we
are aided by the color-tone, or tone-feeling, which belongs to each
note as sounded by some sonorous body with whose peculiarities
we are previously more or less acquainted.
It follows, then, that the judgment is supplied, by the. varying
qualities of musical tones, with the means for arranging them in a
continuous series which may be symbolized by different positions
assigned along an uninterrupted straight line. Of any three un-
like tones, one must be, and only one can be, arranged as respects
pitch between the other two. And whenever any two tones, as m
and n, are given, another sliding tone, which begins with m and
ends with «, is possible. Moreover, within the bounds of our ex-
perience of tones, as we advance along the scale toward either the
upper or the lower limit, we see no tendency in the qualities of
the sensations to approach each other. In this respect the scale
of sound-tones is wholly different from that of color-tones. There
are not two ways, for example, of getting from a' to c^ (one
through b\ c^ etc., and the other through g\ f, etc., around to
e\ d,^ and then c"), as there are two ways of going from yellow to
blue (i.e., through green and blue-green, or through violet, red,
and orange). We speak, then, of the series of tones as a constant
and infinite series ; although, of course, no series of states of con-
sciousness is really infinite, and although the upper and lower
limits of the musical scale, as well as the limits of the least ob-
servable differences between two tones, are not constant but vari-
able for different individuals.
The symbolism taken from relations of space, which we employ
when we speak of certain acoustic sensations as " high " and of
others as "low" in pitch, or when we distinguish so-called "in-
tervals " between the tones as large and small, is strictly applicable
only to the complex tactual, visual, and muscular sensations that
accompany the acoustic. In sounding the lower tones with the
31
322 SENSATIONS OF SOUND.
voice the organs are depressed ; in sounding the higher, they are
elevated. Low notes have a certain breadth and gravity which
corresponds to the foundations of a spatial structure ; as sensations
they require more time to come into and depart from conscious-
ness, as it were. A great intensity and slower tempo belong to the
bass-viol than to the violin. We read iqj for the notes of highest
pitch, and doivn for those of lowest pitch, in the written musical scale.
§ 21. We have seen that tones, like rays of light, come to us as
compounded into "clangs;" these really composite tones being
esteemed as single notes in ordinary experience. The nature of
such composition determines the so-called "timbre," or "color-
tone," of the notes. Each sensation of a clang is a summing-up in
consciousness of several absolute qualities of musical sound ; the
stimulus which occasions this complex subjective state is a complex
sound-wave made up of the contrasts and coincidences of several
single waves that have the character of simple pendulum vibrations.
The quality of each clang depends upon the form of this complex
sound-wave. We need not consider in detail the physics and
mathematics of such complex waves. It is enough to observe that
those single tones whose vibrations stand in simple mathematical
relations to each other, when combined into a clang, cause a pe-
culiarly pleasant sensation ; those whose vibrations stand in com-
plex mathematical relations make, when combined, an unpleasant
sensation. In an octave of the musical scale the eight different
notes stand in the following ratios to each other.'
D : E
9 . 5.
¥ • 4
9 : 10
F
101
G
: A
: B
: C
3
2"
. .5
• 3
¥-
2
12
^.\^
15
16
That is to say, while the tone G makes one vibration, D makes
nine-eighths, and E makes five-fourths, etc. ; or while G makes 8
vibrations D makes 9, E makes 10, etc. Of these relations in the
number of vibrations the simplest is, of course, that of the octave,
1 : 2. The acoustic waves which constitute the stimuli of each
complex sensation called a " clang," accordingly, also permit of
being regarded as the summing-up of the waves of a fundamental
tone and of certain partial tones belonging to the fundamental
tone. These partial tones, or "over-tones," are called "the har-
monics" of the " clang," or single compound tone.
§ 22. When two or more "clangs "are sounded together, the re-
sult is what is called either a "chord " or a " discord." The former
1 For the mathematics and physics of tones, see Hensen, in Hermann's
Handb. d. Physiol., III., ii , pp. 4fE.
CONSONANCE AND DISSONANCE. 323
is a pleasant, tlie latter an unpleasant, complex of sensations ; con-
sonance and dissonance are thus spoken of as qualities of sensations
of musical sound. Thus, if c and c' are struck together upon a
weil-tuued piano, the combination of clangs is a chord, or harmo-
nious musical sound ; but if c and d, or c and c sharp, or c and
its seventh, h above, are simultaneously sounded, then the com-
bination of tones is unpleasant. Cases of consonance and disso-
nance differ from those just considered under the term "clang"
only with respect to the relative strength of the partial tones as
compared with the fundamental tones : in the clang the over-tones
are weak as compared with the one fundamental tone ; but in the
chord or discord the fundamental tones of the other clangs are, of
course, strong, and stand in powerful relations of consonance or
dissonance both toward the fundamental tone of the lowest clang
and toward its partial tones. All the partial tones of the different
combined clangs enter into the formation of the total result pro-
duced. According to the table already given (p. 322), the Octave
is the most perfect possible consonance (1 : 2); then the Twelfth
(1 : 3), the Fifth (2 : 3), the Fourth (3 : 4), the Sixth (3 : 5), the ma-
jor Third {4 : 5), the minor Third (5 : G). With the relation of the
Third we come upon the borders of dissonance ; indeed, the ancient
Greeks and Komans considered the Third a dissonance, and avoided
it in singing, because, as Helmholtz supposes, their ears were more
sensitive to "beats " than ours. The consonance of the Sixth and that
of the Fourth have also been much disputed. The major Sixth
and major Third are called by Helmholtz " medial consonances ; "
the minor Third and minor Sixth, "imperfect consonances."
An analysis of the harmonics of these consonances yields the fol-
lowing results,' which show the amount of coincidence belonging
to the acoustic waves of the different tones when combined in a
chord with a fundamental tone.
Octave j"'g'"'"'g'^^°"'
( c' I c'^ g' c'^
Twelfth ]«l-^:il^l^V^^!^li!.
Fifth j
Fourth
Major Third | °
( e
c' g' c- e-
gi d'^
ci g' c' e^
c^ g' c'^
b' e'^
The major Sixth is similar in the form of its harmonics to- the
major Third.
' Conap. Helmholtz, The Sensations of Tone, p. 281 f.
324 SENSATIONS OF SOUND,
Two psycho-physical causes for the characteristic feelings which
belong to sensations of consonance and dissonance, respectively,
may be assigned with more or less of probability. The first is that
proposed by Helmholtz.' The feeling of dissonance which is pro-
duced by sounding together two notes that differ only by a semi-
tone is found to be increased when the difference in the pitch of
the notes is still further diminished. Successive shocks called
"beats " occur, less frequently but more decidedly and unpleasantly,
as the pitch of the notes becomes more nearly the same. The feel-
ing of dissonance is found to reach its height when the number of
beats is about 30 per second. For example, if 6' (495 vibrations)
and c^ (528 vibrations) are struck together, the number of beats
is 33 (528 — 495=33), and the dissonance is very strongly marked.
In all marked dissonances such beats occur at the rate of from 20
to 40 in a second. The unpleasant effect in consciousness is an-
alogous to that produced by all sudden and rapid intermission of
stimulation ; as, for example, the flickering of light or the scraping
of uneven surfaces over the skin. The feeling of consonance is due
to the absence of beats. In addition to Helmholtz's negative reason,
Oettingen has jDroposed the positive one, that the pleasantness of
harmony is due to what he calls the " tonicity " and " phonicity "
of certain intervals and combined notes. " Tonicity " is the prop-
erty of being recognized as a constituent of a single fundamental
tone which is designated by the name "tonic." "Phonicity" is
that property of a chord or interval which consists in the possession
of certain partial tones that are common to all tones. The first of
these qualities of harmony seems to ally the pleasure it yields to
that which follows even the obscure and only half-conscious per-
ception, as it were, of all relations, as such, between our sensa-
tions.
§ 23. In order that the physical apparatus of hearing may act
as the organ of those wonderfully fine discriminations which belong
to the most analytic of all the senses, it would seem that it must
possess an outfit of end-organs with structure sufficiently minute
to serve as a basis for a satisfactory development of "local signs."
The number of the cells of Corti, and of their separate terminal
auditory nerves, has been calculated by Hensen '^ at about 16,400 ;
by Waldeyer ' at 20,000. It is doubtful, howevei^ whether even
this large number will suffice to account for that niceness of audi-
tory discriminatioDS which we have seen to be possible.
' The Sensations of Tone, p. 255 f.
■^ In Hermann's Handb d. Physiol, III., ii., p. 115.
^ Strieker s Gev,ebelehre, II., p. 954.
CHAPTEE lY.
THE QUALITY OF SENSATIONS. [Continiied.]
§ 1. The analysis of the qualities of different Sensations of Sight
is much more intricate than that of any of the other senses. They
may all be described as sensations of color and light ; but an in-
definite number of colors is known to experience, and as many
grades of the sensation of light. Moreover, the quantity of the
white light which acts as stimulus upon the eye has an important
effect upon the quality of the resulting color-sensation ; in other
words, the tone of the color is dependent upon the amount of white
light which is mixed with the " saturated " spectral color. The size of
the colored object and the resulting breadth of the sensation, as
well as the intensity of the stimulus and the time during which it
acts, also affect the quality of the sensation. Still further, the same
stimulus produces different sensations as it falls upon different por-
tions of a normal retina ; while a considerable class of persons are
color-blind, or incapable of certain kinds of color-sensations. The
previous condition of the retina, and the relations between the con-
tiguous portions when any considerable area of it is under stimu-
lation, must also be taken into account. The fundamental laws
governing sensations of sight can, therefore, be discovei'ed only by
excluding for the time many of those variable elements which, in
fact, always enter into the determination of the exact quality of
such sensations. Thus defining the first problem before us, we
find that it may be stated in the following terms. What sensations
result from the stimulation of a sufficiently small, but not too small,
area of the most central part of a normal retina, for a given time,
when it is not fatigued and the eye is at rest, and with neither too
great nor too small intensity of a given kind of light? Such sen-
sations may be called (though somewhat ineptly) normal sensations
of color. When the foregoing question is answered we may go
on to consider the most important variations possible on account
of various forms of departure from the so-called normal conditions
of sensation.
§ 2. The ordinary stimulus, the application of which to the eye
gives rise to the sensations of sight, is light — or certain exceedingly
326 SENSATIONS OF SIGHT.
rapid oscillations of luminiferous ether. Some forms of mechani-
cal and electrical stimuli also produce the same sensations. Any
violent shock to the eye, such as a blow upon the back of the head,
maj^ fill the whole field of vision with an intense light. The action
of mechanical pi*essure of moderate intensity upon a limited j^art
of the retinal elements may be studied by rolling the eyeball in-
ward and using the fingernail, or a small, blunted stick, upon the
outer surface of the closed lids. By such stimulation disks of
light (called 2^hosphenes), with darkly colored edges, are produced
in the field of vision of the closed eye. Some observers have
claimed that very strenuous exertion of the apparatus for accom-
modation occasioned in their eyes similar phenomena ("phos-
phenes of accommodation "). On making or breaking a weak elec-
trical current sent through the eye, the entire field of vision is
lighted up ; the constant current also seems to excite the optic
nerve. The quality of the sensations thus excited is found to de-
pend upon the direction of the current through the nerve. When
the current is ascending, the place where the nerve enters the ret-
ina appears as a dark disk upon a field of vision that is bright-
er than it, and of pale violet-color ; when it is descending, as a
bright bluish disk on a field of dark or reddish-yellow color. The
retina has also a " light of its own " {Eigenlicht) ; for its nervous
elements are rarely or never inactive, but have a continuous tonic
excitation. Hence the most gorgeous and varied coloring is often
seen when the eyes are closed in a darkened room. This normal
light of the retina is not constant either in degree or in quality ;
both the form and the color of the different minute parts of the
field of vision, as lighted by it, are very changeable. It may be
said to have the rhythmic movement of all tonic excitation. Such
excitation is supposed to be due to chemical effects, wrought by
the changing supply of blood, upon the nervous elements of the
retina and (perhaps, also) of the central organs of the brain. The
peculiar action of the ascending and descending electrical current
has been thought by some ' to be due to its catelectrotonic or
anelectrotonic effect upon the central organs by way of the optic
nerve. Aubert has estimated the retina's own light to be about
equal (in his case) to half the brightness of a sheet of white pajier
when seen in the full light of the planet Venus.
§ 3. The place where the light acts (and here, as is supposed, only
indirectly through photo-chemical— and perhaps electro-motive —
changes in the pigments of the eye) upon the end-organs of vision
' See Fick, Physiolog. Optik, iu Hermann's Handb. d. Physiol., III., i. , p
230.
THE FINElSrESS OF VISION.
327
must be located at the back of the retina in the rods and cones
(see Part I., Chap. V., §§ 18-22). The argument b}' which we have
connected the analytic power of vision with the structure of this
nervous layer ma}' be carried yet further into details. It appears
likely that each element of the structure — at least in some parts of
the retina — should be regarded as an isolated sensitive spot, which
corresponds on the one side to definite excitations from the appro-
priate stimuli, and on the other side to the smallest localized sen-
sations of color and light. In order that two visual sensations
may be seen as separate, yet side by side, in an object, two neigh-
boring retinal elements must be excited by the stimulus. This
implies that the breadth of retinal surface stimulated must be, at
least, about that of the distance between two such elements. With
this hypothesis the facts of histology and exi^erimental physiology
agree fairly well.
The degree of accuracy which sight can attain is dependent
upon the size of the retinal elements directly affected by the
light. ' Hooke observed that no one can distinguish two stars as
two, unless they are apart at least 30" ; few, indeed, can distin-
guish them when less distant from each other than 60'. E. H.
Weber could not perceive as separate two lines whose distance
did not cover at least 73" of the angle of vision ; Helmholtz puts
the limit of his sharpness of vision at 64". The numbers 60",
64", and 73", in the angle of vision, correspond to a size of the
retinal elements varying from 0.00438 mm. to 0.00526 mm.; and
this agrees very closely with the
calculated breadth (by Kolliker)
of the thickness of the cones in
the yellow-spot — namely, 0.0045
mm. to 0.0055 mm. (0.000177 in.
to 0.0002165 in.}. If white lines
be drawn on a dark ground so
closely together as to approximate
this limit of vision, they will ap-
pear, not straight, but knotted and
nicked. This fact is due to the
action of the stimulus on the mo-
saic of rods and cones, as seen by the accompanying figure (No. 90).
The diminishing sharpness of vision as we move away on the sur-
face of the retina from its most central area corresponds to the
' See Helmholtz, Handb. d. Physiolog. Optik, Leipzig. 1867, p. 215 ft.;
Fick, in Hermann's Handb. d. PhjsioL, HI., i., p. 152 f.; von Kries, ArcMv
f. Anat. u. Physiol., Physiolog. Abth., 1883 (Appendix), p. 24 f.
Fig. 90. — A shows the appearance of lines
drawn veiy clopely together, which is sup-
posed to be due to their falling upon the
nervous elements of the retina in the man-
ner shown by B.
328 SENSATIONS OF SIGHT.
comparative paucity of the nervous elements which enter into the
structure of the peripheral parts.
§ 4. Excluding consideration of those changes in the quantity,
as such, of visual sensations which are produced by changes in in-
tensity of the light, and confining our attention to what has already
been defined as the normal action of the eye (comp. p. 325), we treat
scientifically all the different sensations of sight when we describe
(1) the wave-lengths of the different kinds of colored light, or pure
color-tones, and (2) the relations in which the different colors
stand with respect to the amounts of white (or colorless light) and
saturated light (or light of pure color-tone) which enter into them.
The foregoing distinctions in the quality of our color-sensations
may be confirmed by an appeal to experience. Eed is unlike yellow
in "color-tone," and both are unlike blue ; but orange is more like
either red or yellow than it is like blue, while violet is more like
blue than it is like either yellow or red. Yet we distinguish colors
of the same class (red, green, or violet) as being like or unlike
with respect to their " brightness ; " and in resj)ect of brightness, a
certain shade of red may differ more from another shade of red than
it differs from some shade of yellow, green, or blue. The bright-
ness of a color is, scientifically speaking, dependent both upon
the degree of saturation which the color possesses and upon the
total intensity of the light.
§ 5. A color-tone is said to be " pure " or " saturated " when it is
free from all admixture of other color-tones. Pure or saturated
color-tones can be obtained only by use of the spectrum, which,
on account of the different refrangibility of the different colored
rays that compose it, analyzes the compound ray of white light into
its constituent color-tones. By stimulating with different simple
rays those nervous elements which have the same local situation
at, or very near, the pole of the eye, we test the question whether
each special color-sensation corresj)onds to a special physical con-
struction of the stimulus. It is thus discovered that the compound
ray of sunlight, so far as it stimulates the human eye, is made up
of components formed by oscillations varying all the way between
about three hundred and seventy billions and about nine hundred
billions per second ; and that the color-tone of the sensation changes
as the number of these oscillations changes. The following table '
exhibits these facts on the scale of Fraunhofer's lines, which mark
those portions of the spectrum where its principal colors appear
most obvious to the normal eye.
' Taken from Fick, Physiolog. Optik, iu Hermann's Handb. d. Physiolog.,
Ill, i., p. 173.
COLOE-TONES OF THE SPECTRUM.
329
Name of the line.
Number of vibra-
tions per second.
Wave-length in the air.
B
Billions.
450
472
526
589
640
722
790
Millimeters.
0.0006878
C
0 0006564
D
0.0005888
E
0 0005260
F
0 0004843
G
0.0004291
H
0 0003928
Rays of light which have a number of oscillations less than four
hundred and seventy billions |Der second, so far as they affect the
retina at all, occasion the sensation of Red ; and this sensation does
not vary essentially in quality when the oscillations are four hundred
and forty to four hundred and sixty billions. But when their number
increases beyond four hundred and seventy billions (C) the quahty
of the sensation changes rapidly, takes on a yellow tone (Orange-
yellow), and finally, at about five hundred and twenty-six billions
(D), corresponds to what we definitely call Yellow. This yellow
becomes greenish as the oscillations increase in number, until they
reach about five hundred and eighty -nine billions (E), when Green
appears. (Changes from yellow to green occupy only a small zone
in the spectrum.) The green in turn becomes bluish ; at six hun-
dred and forty billions (F) Blue begins to appear. From this point
to seven hundi-ed and twenty-two billions (F-G) the color-tones
that lie between blue and violet are run through ; beyond the latter
number Violet comes to view.
The color-tones of the spectrum are, therefore, not sharply sepa-
rated, but pass gTadually into each other. The nearer together two
colors are situated in the spectrum, the more nearly do they corre-
spond in the quality of their sensations. Nor has the spectrum any
sharply defined limit at either end, but passes gradually into black
— more gradually at the violet than at the red end. The energy
of the ultra-red rays, as measured by their physical and chemical
action, is greater than that of the more highly refrangible rays.
The fact that these rays do not excite visual sensations must, then,
be due to the structure of the retina. The ul(ra-\iolei end of the
spectrum has been made visible for a certain extent by experiment ; '
it produces the sensation of a glimmer of lavender-gray color. Our
inability to perceive these ultra-red and wZ^ra-violet rays is not to
be considered an imperfection of the eye, as Tyndall thought. It
is rather purposeful, and of the greatest importance for vision ;
since, if these ultra rays were visible, the clearness of objects would
'- See Helmholtz, Physiolog. Optik, p. 232 f.
330 SENSATIONS OF SIGHT.
be much disturbed by tbe chromatic aberration of the refracting
appai'atus of the eye.'
§ 6. Besides the foregoing distinctions of color-tones, the im-
pression made by the green-yellow of the spectrum (D-E, and im-
mediately about D) is by far the strongest ; or, as we should say,
this color is naturally the "brightest " of the spectral colors. From
the region immediately around D, the brightness of the color-tones
diminishes toward both the red and the violet ends of the spectrum
— at first quickly, then more slowlj', and then more quickly again.
Such a relation cannot be due to the spectrum as an objective
affair ; for if we measure by other physical means the amount of
energy belonging to its different regions, we find that of the red
rays (which are by no means brightest) to be strongest. "We must.
Fig. 91. — (From Fick.) The letters on the horizontal line stand for Fraunhofer's lines. The
ordinates of the interrupted curved line show the brightness of rays as seen ; the ordinates of
the dark curved line, the intensity of the rays as measured by calorific effect.
then, seek an explanation in the structure of the retina, and conclude
that it is peculiarly sensitive to stimulations by oscillations of about
five hundred and fifty billions per second. The sensitiveness of the
retina to slight variations in color-tone, as dependent upon differ-
ences in the wavelengths of the stimulus, is also different at different
portions of the spectrum. It is greatest in the green and blue-
green regions (D and F).
The following table represents both the foregoing laws. The
numbers of the second and third columns show the relative bright-
ness with which the different colors of the spectrum appear to the
eye, as calculated by different methods and by two observers. It
will be seen that the results agree substantially, though by no
means perfectly. In the last two columns the letter sstand for
Fraunhofer's lines, and the figures give the fractional variation in
the wave-lengths which produces an observable variation in the
color-tone for different regions of the spectrum.''
' See Fick, Compendium d. Physiologie, 2d edition, p. 181 f • ; and Her-
mann's Handb. d. Physiol., III., i., p. 181 f.
■■* See Helmholtz's Physiolog. Optik, p. 317 f.; von Kries, in Archiv f. Anat.
u. Physiol., Physiolog. Abth., 1882 (Appendix), pp. 56-76 ; Fick, in Hermann's
Handb. d. Physiol, III., i., p. 174 f. ; MandelstammandDobrowolsky, in Aichiv
f. Ophthalmologie, XIII., ii., p. 899, and XVIII., i , p. 66.
MIXED COLOE-IMPRESSIONS.
331
Fraunhofer.
Vierordt.
33
22
94
128
640
780
1,000
1,000
480
870
170
128
31
8
5.6
0.7
Mandelstamm and Dobrowolsky.
Red, B
Orange, C
Reddish -yellow, D
Yellow, D-E
Green. E
Blue-green, F
Blue. G
Violet, H
B ..
C...
C-D
D..
D-E
E ..
E-F
F...
G...
H..
1 1 5
id I
340
dl7
Y7^
— L-^
- § 7. The colors of every-day experience, like its musical tones, are
not simple and pure color-tones, such as are obtained by spectral
analysis ; they are composite. Inquiry must therefore be raised as
to the effect produced in sensation from the co-working of two
homogeneous ra^'s of light upon the same elements of the retina
under all the normal conditions to which reference was previously
made. In pursuing this inquiry no direct assistance can be ob-
tained from the discriminations of consciousness ; for sensations of
color, unlike those of musical clang, cannot be mentally analyzed
into their constituent elements. The science of optics makes us
acquainted, however, with the following facts : When the wave-
lengths of the two colors mixed vary but slightly (a few billions of
oscillations in a second) from each other, the color resulting from
the mixture lies between, and may be recognized as a " shade " of,
the colors mixed. By selecting for mixture color-tones that lie
apart at all possible distances along the spectrum, an indefinite
number of impressions of color may be obtained, which all differ
from those obtained by the homogeneous colors. These mixed
color-impreHHions, however, are not all different from each other ;
so that the number of the qualities of resulting sensations is far less
than that of the compound physical processes which stimulate the
retina. Their character depends both upon the place of the spec-
trum from which the simple color-tones are selected for mixture,
and also upon the relative intensity of the ones selected. For ex-
ample, if a ray of four hundred and fifty billions of oscillations per
second (red) be mixed with one of seven hundred and ninety billions
(violet), anew series of impressions of color (the purples) is attained
by varying the intensities of the two. These impressions are more
or less like red or like violet, according to the relative amounts of
the rays of four hundred and fifty billions and of seven hundi-ed and
ninety billions which enter into the mixture. Moreover, there are
found to be two ways of advancing by this process of mixing color*
332
SENSATIONS OF SIGHT.
tones toward any one of the composite colors. Thus, we may pass
from yellow to blue either through green-yellow, green, and blue-
green, or through orange, red, purple, and violet. The following
table ' is of interest in this connection. Where two colors are given
as resulting from the mixture, the variation is to be understood as
dependent upon the prevailing intensity of one of the two compo-
nents.
Components.
Red and Yellow
Orange and Yellow-green
Yellow and Green
Yellow-green and Blue-green . .
Green and Cyanic Blue
Blue-green and Indigo
Cyanic Blue and Violet
Red and Yellow-green
Red and Green
Violet and Blue-green
Violet and Green
Violet and Orange
Red and Cyanic Blue
Red and Indigo
Tone of the color obtained by mixture.
Orange
Yellow
Yellow-green
Green
Blue-green
Cyanic Blue
Indigo
Orange or Yellow
Orange or Yellow or Yellow-green. . . .
Indigo or Cyanic Bine
Indigo or Cyanic Blue or Blue-green.
Red
Indigo or Violet
Violet
Degree of
saturation.
Spectral.
Spectral.
Whitish.
Very whitish.
Whitish.
Spectral.
Spectrid.
Spectral.
Whitish.
Spectral.
Whitish.
Whitish.
Whitish.
Slightly whitish.
§ 8. The number of colors distinguishable by the human eye is
not easily stated with accuracy ; like the number of musical tones,
it varies with different individuals. The usual number of seven
fundamental colors, as fixed by Newton, with the intent of forming
an octave in the scale of color-tones, has no sufficient claim to
acceptance. Six of the seven — namely, red, orange, yellow, green,
blue, violet — are indeed names in common use. But indigo, as an
intermediate tone, or kind of semitone, between blue and violet,
has perhaps no more real right to recognition than various other
intermediate color-tones. Bonders " puts the number of color-tones
distinguishable in oil-colors at one hundred ; von Kries ' the rec-
oo-nizable number of spectral tints at about two hundred and
thirt}'. But each of these yields different sensations of color ac-
cording to the degree of its saturation or purity, due to freedom
from admixture of white light. Another series of variations of sen-
sation must be allowed for, which are due to differences in " bright-
ness " or intensity. Introducing these two variable elements, von
Kries calculates the number of distinctions of color-sensations,
possible for all degrees of purity of tone and intensity of light, at
' Made according to investigations by J. J. Miiller, and taken from Tick, in
Hermann's Handb. d. Physiol., III., i., p. 190.
'^ Archiv f. Ophtbalmologie, XXVII.
2 Arcbiv f. Auat. u. Physiol., Physiolog. Abth., 1882 (Appendix), p. 58 f.
THE COMPLEMENTARY COLORS.
333
about five hundred thousand to six hundred thousand. This num-
ber stands midway between the " many milHons " of which Au-
bert speaks and the five thousand allowed by Douders. Herschel
thought that the workers on the mosaics of the Vatican must have
distinguished at least thirty thousand different colors.
§ 9. Experiment also shows that if certain color-tones with a
given intensity are united on the retina, the result is a sensation
unlike that of any other of the colors, whether pure or mixed.
This sensation we call "white," and the two colors which by their
admixture produce it are called " complementary." Complementary
colors may be mixed upon the retina in various ways ; either by al-
lowing two spectral rays properly selected to be superimposed at
the same spot, or by blending the reflected images of two colored
wafers, or by blending the du'ect visual impressions of colored
surfaces on a swiftly revolving top or wheel, etc. But however
mixed, the resultant sensation is that of a so-called " white " color
in which all trace of the constituent elements is lost. Following is
a table of complementary colors : '
Color.
Wave-len^h.
Complementary
color.
Wave-length.
Relation of
wave-lengths.
Red
2,425
2,244
2,162
2,120
2,095
2,085
2,082
Green-blue . . .
Blue
1,818
1,809
1,793
1,781
1,716
1,706
1,600 {^i
1,384
Orange
1,240
1,206
Gold-yellow .. .
Gold-yellow. . .
Yellow
Yellow
Green-yellow. .
Blue
Blue
1,190
Indigo blue. . .
Indigo-blue. . .
Violet
1,221
1,222
1,301
§ 10. If the foregoing facts and laws are held to be true of the
" normal " connection between light and visual sensations, then
various classes of circumstances must be taken account of as "ab-
normal," which, nevertheless, enter into all our daily experience
with this sense. Indeed, the connection between stimulus and
sensation is not the same for different individuals who possess sub-
stantially the same color-sensations ; frequently the complementary
colors for two different indi%T.duals are not precisely the same.
Even the two eyes of the same individual often differ percejDtibly
in this regard. Important changes in the quality of the sensations,
other than those directly ascribable to changes in the wave-lengths
of Hght, take place when the intensity of the light approaches ei-
' Taken from Helmlioltz, Pliysiolog. Optik, p. 277. The numbers are given
in hundred milliontlis of a Parisian inch, and may be reduced to millimetres
by multiplying by 27.07.
334 SENSATIONS OF SIGHT.
tliei- a masimum or a minimum. At the maximum intensities of
the stimulus all sensations of color-tone cease, and even homoge-
neous rays appear white. Previous to reaching this maximum,
red and green pass over into yellow. At the mininium intensities
of light every color-tone except the pure red of spectral saturation
appears colorless when seen alone on a perfectly black ground.
The different colors appear and disajjpear, as such, at different
degrees of intensity of the stimulus — green, among them all, re-
maining visible in the weakest light. They all also change their
tone as the light which falls on them diminishes ; but it is scarcely
possible to describe the law of this change, on account of the great
difficulty of distinguishing color- tones in very weak light.
§ 11. Changes of color also take place when the time of the
action of the light is reduced to a minimum. Sensations of satu-
rated color can be produced by instantaneous illumination of the
spectrum with the electrical spark. More time is needed, however,
to produce these sensations with smaller intensities of the light.
The different colors, even when of the same brightness, appear to re-
quire different amounts of time in order to reach the maximum of
their effect— red, 0.0573; blue, 0.0913 ; green, 0.133 of a second.'
The tone of the color varies with the duration of the impression as
well as with the intensity of the Hght. Very minute objects, too,
appear of a different color on account of their size. In general, the
larger the surface, the less the intensity of the light necessary to
produce the sensation of any particular color-tone ; the greater the
intensity of the light, the smaller the surface which will suffice for .
such sensation. Fick '' has shown that the color-sensations derived
from small dislinct points support each other, as it were, in the
same way as the contiguous points of a colored surface. For if we
make with a fine needle a single hole (of about 0.6 mm. in diameter)
in a sheet of paper and look through it at colored paper distant
some six and a half metres, the color of the paper cannot be dis-
ting-uished. But if the number of holes be as many as sixteen,
the color can be distinguished at the same distance, even when the
holes through which we look are smaller. Subsequent experiment^
has shown that the smaller the distance between the single perfo-
rations, the greater the distance at which the eye can recognize
colors through them. In general, then, two weak sensations, each
of which belongs to one eye, may fuse together into one strong
one.
' According to Kunkel, in Pfluger's Archiv, ix. , p. 207.
* Pfluger's Archiv, xvii., p. 152.
* See Dobrowolsky, in Pfluger's Archiv, xxxv., p. 536 f.
KINDS OF COLOR-BLIlSrDISrESS. 335
§ 12. Very important changes in the visual sensations occur as
dependent on the place of the retina which is stimulated. In this
respect a great difference exists between the central and the pe-
ripheral parts. The entire field of this organ may be somewhat
indefinitely divided into three zones — a central or polar, a middle,
and an outer or peripheral. It is probably true that the periph-
eral parts of the retina produce no sensations which cannot be
produced by stimulating the central zone.' But it is equally true
that, under the same circumstances, the same stimulus produces
a markedly different effect upon sensation when applied to differ-
ent localities of the retina. Rays which, falling on the polar zone,
produce the impression of red, yellow, or green, all make an im-
pression of yellow when they fall on the surrounding zone (a few
millimetres from the fovea centralis) ; and this yellow is so much
the paler, the greener the impression on the polar zone. Rays
which make on the polar zone the impression of blue or violet make
on the outer zone the impression of blue ; and this blue is so
much the paler, the nearer the imi:)ression on the polar zone is to
green. It follows, then, that whereas thei'e is at the central zone
an indefinite number of color-tones possible, this number is re-
duced to comparatively few impressions at the middle zone ; while
all color-tones gradually become indistinguishable and are lost on
passing through the outer zone. These great changes in sensi-
tiveness to color are not accompanied by similar changes iii sen-
sitiveness to colorless light ; it even appears that regions of the
retina distant about 30° from its centre are more sensitive to light
than is the polar zone.
A certain proportion of persons (perhaps one-twentieth or more)
appear to have a defective structure of the retina, which may be
described as corresponding in the polar zone to that of the normal
retina in the middle or even the outer zone. Such persons are said
to be "color-blind." The farther outward this imperfect condition
of the retina extends, the nearer does the defect approach to total
color-blindness.'' In most cases of this defect there is a partial or
complete insensitiveness to the red rays ; these rays are especially
liable to be confused with the dark-green or the yellow. The spec-
trum is thus shortened at the red end. Cases of so-called violet-
blindness, as reported by Donders and Stilling, are much more rare
and doubtful. In total color-blindness only shades of gray from
' See von Kries, Archiv f. Anat. ix. Physiol., Physiolog. Abth., 1883 (Ap-
pendix), p. 90.
'^ See Fick, Zur Tlieorie d. Farbenblindbeit, p. 213 f. ; and in Hermann's
Handb. d. Phyfaiol., III., i., p. 206 f.
336 SENSATioisrs of sight.
white to black are visible. In general, the attempts to make out a
spectrum for the color-blind are unsatisfactory, since we can only
be sure as to what color-tones appear like or unlike to them ; we
cannot, on the contrary, be sure that their abnormal sensations are
like any of our normal sensations — in other words, that what they see
when red light falls on the retina corresponds to any of our color-
tones. The three or four cases reported where one eye of a person
has been normal and the other color-blind are, of course, especially
valuable ; since they offer an opportunity to compare immediately
the sensations of the normal with those of the pathological eye.
These cases, according to von Kries ' show that the two funda-
mental colors to which the color-blind are reduced may be con-
sidered as either red and blue-green or greenish-yellow and blue-
violet.
§ 13. Important modifications of the normal action of the eye are
also caused by the previous coj^cZiiion of the retina, or by the contem-
poraneous condition of parts of it contiguous to those on which the
light falls. The former fact explains the phenomena of " inertia "
and " exhaustion ; " the latter, the phenomena of " contrast." The
reaction of the sense of sight is relatively very sluggish ; or — in
other words — the inertia of the eye is relatively great. This fact
is undoubtedly due to the chemical nature of the stimulus which
acts directly upon its end-organs. The light requires time in order
to effect those photo-chemical changes on whose action upon the
nervous elements of the retina our sensations of light and color
depend. On the other hand, if we close the eyes after looking
intently upon any bright object, the image of this object remains
for some time, and only slowly fades out of sight. Such an image
is called a "positive after-image," because its bright and dark lines
and surfaces correspond to those of the original object. The delay
which the sensations undergo, both in forming and in fading away,
is said to be due to the inertia of the retinal structure. It is, of
course, a law of all nervous excitation and action that it requires a
certain amount of time for beginning and for changing its char-
acter.
White positive after-images (as Fechner, Helmholtz, and oth-
ers have shown) pass quickly through greenish-blue to indigo-
blue and then to violet or rose-color. But "negative after-images "
are due to the exhaustion of the retina. If the eye be intently
fixed for some time on a small square of black lying upon a sheet
of white paper, and then suddenly turned upon the white surface,
a bright square appears, moves about with the eye, and slowly
' ArcLiv f. Anat. ij.. Physiol., Physiolog. Abth., 1883 (Appendix), p. 153 £
PHENOMElSrA OF CONTRAST. 337
fades away. If wg look for a long time at a green surface and then
direct the eye upon'a white one, the latter appears for a moment to
be of a red color. In general, the color of the negative after-image
is such that, when combined with the color of the object, the two will
produce white. In other words, the color of such an image is " com-
plementary " of the color of the object. Such facts as the foregoing
must in some manner be brought under the law which applies to all
the elements of the nervous system, but especially to the end-organs
and the central organs ; these organs become wearied by continuous
use, and require time for recovery of their suspended or diminished
functions. Precisely how the application is to be made lo the case
of the retina is, however, a matter of the general physiological the-
ory of vision which cannot as yet be stated with perfect certainty.
The phenomena of exhaustion are among the most important for
the formation of such a theory. Investigations in this direction
have led to the discovery that none even of the spectral colors are
perfectly saturated, since each of them can be made to appear more
so by looking at it with an eye wearied by the complementary
color. ' Red is most nearly saturated, blue and yellow next, and
green least of all.
§ 14. The different ]3arts of the retina are interdependent in the
production of sensation ; or — to employ the statement of Wundt ^
— " The sensation which arises through the stimulation of any given
point of the retina is also a function of the state of other immedi-
ately contiguous points." Hence arise, in part at least, the phe-
nomena of contrast, which are of two kiiads — contrast of bright-
ness and contrast of color-tone. The fundamental fact in the first
class of contrasts is this : every bright object appears brighter with
surroundings darker than itself, and darker with surroundings
brighter than itself. These phenomena are explained by Helm-
holtz ^ as deceptions of judgment, such as we are accustomed to in
our estimates of distances. To this explanation, however, Fick,*
Hering,^ and others oppose strong and apparently conclusive ob-
jections. They would explain the same phenomena by the modify-
ing influence of the excitation of one part of the retina upon the
excitation of contiguous parts. Such influence does not always
^ Comp. Helmlioltz, Physiolog. Optik, p. 279 f. ; Exner, in Pfliiger's Archiv,
i., p. 389; and see, especially, von Kries, Archiv f. Auat. u. Physiol., Phy-
siolog. Abth., 1882 (Appendix), p. 115.
- Physiolog. Psychologie, i., p. 439.
3 Physiolog. Optik, pp. 388 ff.
* In Hermann's Handb. d Physiol., III., i., p. 231 f.
^ Sitzgsber. d Wiener Acad, June, 1872, and December, 1873.
22
338 SENSATIONS OF SIGHT.
take the form of depressing the excitabihty of the contiguous
parts ; on the contrary, stimulating certain elements for some time
may finally involve contiguous ones in a secondary way. This fact
they consider to be the true explanation of the spreading of a
bright object on a dark background, whose after-image becomes a
clear band of light around the dark image of the bright object.
When colored instead of white light is used in experimenting under
the law of conti'ast, phenomena similar to those of complementary
colors are obtained.' A small square of white on a surface of green,
when covered with a transparent sheet of tissue-paper, appears as
red on a surrounding surface of a whitish hue ; on a red ground it
appears as green, on a blue ground as yellow, and vice ver'sa. There
is the same dispute over these as over the other phenomena of
contrast. Shall they be considered as cases of deception of judg-
ment, or do they admit of a physiological explanation ? Mere
cases of deception they cannot well be. The theory which ascribes
to each part of the retina an influence upon other contiguous parts
is the most satisfactory form of a physiological explanation. But
such physiological explanation seems to need supplementing by
reference to induced conditions of the central organs, concei'ning
the nature of which we ai'e thus far almost entirely ignoi'ant.
§ 15. It will readily be seen that a theory which shall satisfac-
torily account for the complicated phenomena of visual sensations
is difficult to establish. Physiological optics will probably never
be able to explain in detail the individual sensations of light and
color. But each claimant to present such theory must, as Wundt '
maintains, account for the following- four main classes of facts : (1)
The subjective i-elations of the color-tones, and the fact that they
may all be graded downward, as it were, into colorless light ; (2)
the law of the mixing of all the colors from three (or more) funda-
mental color-tones ; (3) the phenomena of after-images ; and (4)
the phenomena of contrast. Among all the hypotheses hitherto
proposed to account for the quality of visual sensations, that brought
forward by Young, and elaborated and applied b}' Helmholtz, is by
far the most prominent. This hypothesis takes its point of start-
in<T from the undoubted fact that, by admixture of a few so-called
fundamental color-tones, we can produce all the other colors, as
well as the sensation called "white." There are said to be /Aree
such color-tones, because this is the smallest number which will
account for the facts. Of these three, green must be one, since, in
the spectrum of colors, this tone has no complementary color. Green
' See Helmlioltz, Physiolog, Optik, pp. 388 E.
^ Physiolog. Psycliologie, i , p. 450.
THE YOUT^G-HELMHOLTZ THEOEY.
339
being fixed, the other two color-tones must be chosen from near the
ends of the spectrum, and in such a way that, when combined with
spectral green, they will produce white. Ked (carmine-red, ac-
cording to Fick) and either violet (so Young and Helmholtz) or blue
(indigo-blue, Fick) best fulfil the required conditions. It is, then,
assumed, by the Young-Helmholtz theory, that in every portion
of the retina which is susceptible to color there exist three kinds
of nervous elements, the excitation of which separately would pro-
duce three distinct kinds of sensations ; and that each kind of ele-
ment is capable of producing only that kind of sensation which is
peculiar to itself. It apparently follows that each of these three
kinds of nervous elements has its special form of end-apparatus, the
excitability of which differs from that of the others ; that is to say,
Fig. 92. — Diagram from Fick, illustrating the Young-Helmholtz Theory. (For explanation, see
the text. )
there are fibres of red color-sensation, whose end-apparatus responds
specifically to rays of small refrangibility ; fibres of green color-
sensation, whose end-appai*atus responds to rays of medium re-
frangibility : and fibres of violet or blue color-sensations, whose
end-apparatus responds to rays of great refrangibility. We must
suppose, however, since we cannot directly analyze into their com-
ponents the sensations which appear in consciousness, that no one
of the three kinds of elements is ordinarily excited alone. Every
actual sensation of color is therefore a complex affair, whose char-
acter is determined by the relations in which each one of the three
intensities of excitation stands to both the others. In explanation
of this assumption the following diagram is proposed.' (See Fig.
92.) The curved lines E, G, and B represent the three kinds of
' Taken from Fick's Physiolog. Optik, in Hermann s Handb. d. Physiol.,
III., i., p. 198; comp. Helmholtz, Physiolog. Optik^ p. 291.
340 SENSATIONS OF SIGHT.
nerves sensitive to the three fundamental color-tones — K to red, G to
green, B to blue (indigo). The curves described by them show the
strength of the excitation exercised by the stimulus, corresponding
to the colors of the spectrum, upon each kind of nerves. The per-
pendicular lines indicate the colors of the spectrum ; and the waj
these lines cut the curves shows the relative strength of the excita-
tion of each kind of nerves w^hich is combined to produce these
colors.
It should be gratefully acknowledged that the Young-Helmholtz
theory affords a brilliant explanation of a great many of the phe-
nomena of sensations of light and color. It is most successful with
those that relate to the mixijig of colors and to complementary
color. The hypothesis cannot be said, however, to be wholly ade-
quate and satisfactory. One of its most intelligent advocates (Fick)
admits that it cannot explain the following cardinal fact : Every
ray of light which, so long as it is confined to a moderate extent of
the polar zone, makes the impression of a saturated color produces
a whitish impression, almost devoid of color-tone, as soon as it is
limited to an extremely minute portion of the retina. This is the
very opposite of what the hj'pothesis would lead us to expect ; for,
according to it, extremely minute impressions on the retina ought
to isolate the particular kind of fibres, and so yield tlie purest
possible color-tone. The facts of histology seem rather adverse
than favorable to the theory, although not much stress can be laid
upon them alone. Moreover, it does not satisfactorily explain the
facts of contrast of colors and of color-blindness. The most re-
cent investigations seem to indicate that cases of color-blindness
cannot be accounted for by dropping out one fundamental kind of
nerve-fibres, as the Young-Helmholtz theory supposes.' Various
other important objections are raised by its opponents (especially
by Hering, Wundt, and others).
§ 16. In order to supply the alleged defects of the Young-Helm-
holtz theory of color- sensations, several other theories have been
devised — notably those of Hering and of Wundt. The former*
differs from most other investigators in his view of the nature of
the changes of sensation which take place as we, in experience,
run through all the different shades of gray from white to black.
All such changes Hering considers analogous to those alterations
in the quality of our sensations that would be produced by jpassing
' See von Kries, Archiv f. Anat. u. Physiol., Physiolog. Abth., 1882 (Ap-
pendix), pp. 1 84-153.
^ B. Hering, Zur Lehre vom Lichtsinne, Sitzgsber. d. Wiener Acad., 6 papers,
1872-74.
wutstdt's theoey of coloes. 341
the eye over a surface on which the different color-tones almost
insensibly shaded into each other. Hering, therefore, proposes six
(or three pairs instead of three single ones) fundamental color-
tones — namely, black and white, green and red, blue and yellow.
The changes which give rise to sensations of black, green, and blue
are ascribed to the process of "construction " of a so-called visual
substance ; those which give rise to white, red, and yellow are as-
scribed to the "destruction" of such visual substance. The three
pairs of color-tones are thus made antagonistic rather than com-
plementary. But the hypothesis of Hering appears to involve more
uncertain assumptions, and to explain fewer facts, than the one it
would displace. Moreover, the assumption that white, and its shades
down to black, may be considered as color-tones, instead of altera-
tions in the brightness of the true color-tones, is generally denied.
The theory of Wundt ' emphasizes the difference in processes
rather than in the kinds of retinal elements. It involves the fol-
lowing principles : (1) In every excitation of the retina two dif-
ferent processes are set up, the variations of which follow differ-
ent laws ; one of these is a " chromatic " process (which gives us
color-tones), and is a function of the length of the waves of light ;
the other is "achromatic," and is also dependent upon the wave-
lengths, but varies only in intensity and remains in character the
same. (2) The achromatic excitation consists in a "uniform pho-
to-chemical process," which reaches its maximum at yellow and
falls off toward both ends of the spectrum. (3) The chromatic
excitation is a "polyforra photo-chemical pi'ocess," which changes
continuously with the wave-lengths of light. The extreme differ-
ences of this length are such as to produce effects that approximate
each other ; while the effects of certain different intervening wave-
lengths are related in such a way that opposed phases of one and
the same movement equalize each other perfectly. (4) Evei'y pro-
cess of excitation of the retina outlasts the stimulation for a certain
time, and exhausts the sensibility of the nerve-substance for that
particular form of stimulation. The positive after-images are to be
explained by the persistence of the retinal excitation, the negative
by exhaustion. (5) The difficult phenomena of contrast are to be
explained by the general principle that all impressions of light and
color are experienced in relation to each other. In other words,
they fall under the general law of relativity.
§ 17. Von Kries'' has subjected all the principal theories of color-
' See Physiolog. Psychologie, i. , pp. 450 if.
- See Arcliiv f. Anat. u. Physiol., Physiolog. Abth., 1883, Appendix, pp.
1-178.
342
SENSATIONS or SIGHT.
sensations to a most searching criticism as considered in the light
of all the facts. He naturally finds serious defects in them all, but
arrives at the following highly important conclusions. The photo-
chemical facts concerned in vision compel us to adopt a theory of
component elements rather than one of changes qualitatively alike
and arranged in a continuous series. This would seem decisive
against the theory of Wundt, Only by the aid of assuming the
varied combination of such elements can we explain the phenomena
sm
W
^%^
PURPLE
^XG
Fig. 93. — Color-Triangle, from Fick. (For explanation see text.)
of exhaustion. Three series of components are apparently requisite :
one for the bright and dark, but colorless, sensations, and two
color-tone series — a red-green series, and a yellow-blue series.
White is, nevertheless, not to be considered as belonging to the
three, since it corresponds to all the color-tones whenever they
reach a minimum of saturation. The processes corresponding to
these three series of components ma}' be located at dilferent places
in the nervous apparatus of vision — either more centrally or more
SYMBOLISM OF COLOE-TOTs^ES. 343
peripherally. The articulation and adjustment, as it were, of the
three processes von Kries would assign to the central organs. And
here we reach the extreme limits, not only of our assured knowl-
edge, but also of our power to frame a plausible theory ; for it ap-
pears that all theories must either leave certain important facts un-
explained, or else make further assumptions concerning nervous
processes — especially in the central organs of vision — of the exist-
ence and influence of which upon the sensations there can be no
doubt, but of the precise natui-e of which we are completely ig-
norant.
§ 18. Much ingenuity and painstaking have been expended in de-
vising some form of si/inbolism which should represent to the ej'ein
geometrical relations the laws of the sensations of light and color.
Obviousl}' the sensations of this sense cannot, like those of hearing,
be symbolized by the relations of points along a straight line.
Color-tones, unlike musical tones, form a series of qualitatively differ-
ent sensations that, at certain places in the scale, separate from each
other with varying degrees of rapidity, and then toward the broken
ends, as it were, of this scale, tend to approach each other again.
Such relations are most successfully set forth by a triangle, which
maybe constructed as in the foregoing figure ' (93). In this triangle
the different color-tones may be regarded as tying together along
the cuiwed line, from red to violet, and the difference in any two
color- tones as measiu'ed by the angle which two lines make when
drawn from the point W through the
points occupied on the curve by the
two color-tones. For example, the
difference between red and violet is
less than that between red and green,
as is indicated by the fact tbat the
angle B TF//is smaller than the an-
gle EWG.
By Fig. 94 " the relations of the
color-tones as contrasting with, and
complementary of, each other are rep-
l-esented. Of the two concentric Fig. 94.— scheme for showing the Rela-
circles, each color in one corresponds *^°''' °^ Coior-tone (see text).
to the complementary color of the other. If the color inducing
the contrast is represented by a segment of the inner circle, the
coincident segments of the two circles represent the direction in
which the induced change is moA-ing, as it were. For example,
' Taken from Fick, in Hermann's Ilandb. d. Plij'siol., III., i., p. 184.
■•^ Taken from Wundt, Physiolog. Psycliologie, i., p. 442.
344 SENSATIONS OF THE SKIN.
since the segment green coincides with purple, and red coincides
with blue-green, green on a red ground is modified as it would be
if blue-green were mixed with it ; and red, as it would be if purple
were mixed with it.
§ 19. At least two specifically different forms of sensation — namely,
Pressure and Temperature — have generally been admitted to have
their organ in the skin. ' The claims of various other kindred forms
of feeling to be considered as primitive factors of our sense-percep-
tions, arising from the activity of the skin as an end-organ of sense,
are more doubtful. Sensations of motion, of innervation and weari-
ness of the muscles, the so-called " common sensations " (or sensa-
tions of the sensus communis), the sensations of pain or pleasure, and
those delicate shadings of sensation, as it were, which constitute
the " local coloring " of all the feelings to which we assign a definite
place in the fields of sight and touch, are all closely allied to sensa-
tions of pressure and temperature. But some of these forms of
feeling — as, for example, the so-called sensations of motion and of the
sensus communis— oxe undoubtedly complex modifications of certain
simpler states of consciousness ; others of them, as the sensations,
of muscular weariness, of pain, of innervation, and " local coloring,"
may possibly have, in jDart, a central origin. As a rule, they lack
the characteristic quality of being components of the " presenta-
tions of sense," as this quality belongs to all genuine sensations.
Sensations of "local coloring" have, indeed, a most important part
to take in the formation of the " presentations of sense ; " but they
are, in the realm of touch and of muscular feeling, as infinitely and
delicately varied (and even more difficult of description) as are the
finest shadings of musical tones or color-tones.
§ 20. A sixth sense, however, and a sixth organ of sensations
must doubtless be recognized as constituted by the muscles and
the various kinds of feeling which their action occasions. These
muscular sensations, when combined with those of the skin, give
certain complex feelings of motion on which the adjustment of the
body to its environment is so dependent. The long-continued dis-
pute concerning the presence of sensory nerve-fibrils in the muscles
may be said to be settled affirmatively. '^ Certain subjective phe-
nomena cannot be accounted for by ascribing the so-called muscular
sensations to feelings of central innervation, or by identifying them
' On the physiology of the skin, see Goldscheider, art. Neue Thatsachen
liber die Hautsinnesnerven, Archiv f. Anat. u. Physiol., Physiolog. Abth.,
Supplement-Band, pp. 1-104.
^ See, especially, Sachs, iu Archiv f. Anat. u. Physiol., 1874, pp. 175 f., 491
f . , and 645 f .
THE FEELING OF PRESSURE. 345
with the sensations of pressure through the skin. ' Bernhardt " found
that the degree of sensitiveness to different weights, when lifted by
the foot or the finger, was little or not at all diminished by exclud-
ing all central innervation of the muscles through an act of will.
The discrimination of differences of weight was not greatly impaired
when the limb was bent by an induction -shock sent through the
muscles instead of by motor impulses arising in the brain. The
muscular sensations cannot, therefore, be due to such central activ-
ity. Investigation also shows that the muscular sensations sup-
plement those of pressure in the skin in all our estimates of the
position and motion of the limbs ; these two are, therefore, not
identical. Moreover, without assuming the existence and aid of
such sensations we cannot account for that nice control of the mus-
cles which, especially in the case of the eye, is so indispensable a
prerequisite, not only for adjusting their action to the ends desired,
but also for gaining an exact knowledge of the position and motion
of objects in the outside world. The precise manner, however, in
which the muscular sensations originate, through that stimulation
of the sensory nerves which the contraction of the muscular fibre
occasions, is as yet unknown. Nor can they easily be separated
and classified into kinds, apart from the sensations of pressure with
which they are in actual experience constantly allied. Their chief
interest to psychology centres in the help which they furnish to the
mind in forming itfe " presentations of sense."
§ 21, Sensations of Pressure are dependent upon the excitation
of the sensory nerves of the skin through their appropriate end-
orgfins. The excitation of the trunk of any of these nerves at some
point along its course may produce the feeling of pain, but does not
produce those definite sensations of pressure which we are able to
localize so accurately and discriminate so nicely as to their degree.
Precisely which of these end-organs are specifically related to sen-
sations of pressure neither histology nor experimental physiology
has thus far been able to determine (see Part I., chap. V., § 10),
The ordinary stimulus of the end-organs of the skin active in these
sensations consists in their compression or expansion by contact
with some external object which either rests upon them or upoa
which they rest, or which is moved over or against them, or over or
against which they are moved. Such stimulus may, of course, vary
both in form and in degree. The quantity and succession of the
sensations of pressure, as well as the manner in which they com-
bine with one another and with sensations of the muscular sense,
' Comp. Funke, in Hermann's Handb. d. Physiol., III., ii, , p. 359 f.
2 Archiv f . Psychiatrie, III. , p. 627.
346 SENSATiOTsrs or the skin.
have a marked effect in determining their characteristic "tone"
of feeling. In respect to quality pure and simple, sensations of
pressure scarcely admit of a scientific classification. We localize
them in the field of touch ; we make an important use of them in
connection with sensations of muscular origin, for constructing the
field of vision and for giving to different objects their respective
places in this field ; but in ordinary experience we do not directly
recognize kinds of the simple sensations of pressure as we do of
tastes, smells, tones, and colors. A distinction is sometimes made
between " light touch," or touch proper, and sensations of press-
ure or weight. But the distinction, so far as it leaves out of ac-
count the muscular sensations, has hitherto been one only of de-
gree and not of kind.
The more recent and thorough investigations of Goldscheider *
have led him to distinguish two si^ecifically different sensations
which enter into what is ordinarily called the feeling of pressure.
This distinction is based upon facts experimentally ascertained. If
a very fine point of metal, wood, or cork, be touched lightly to the
skin, it will be found to awaken a definite sensation, such as is en-
titled to be called a" sensation of pressure," only at certain minute
spots in any given area of the skin. This sensation, when the
pressure is very light, is described as lively and delicate, often
accompanied by the feeling of being tickled. On increasing the
pressure upon these same spots the sensations change their char-
acter somewhat, and become as though some small, hard kernel
were pressed uj)on the skin (" Kdrniges Gefnhl "). Between these
distinctively "pressure-spots" it is not possible to excite by i^ress-
ure the same characteristic sensation. Stimulation of the inter-
mediate spots, on the contrary, produces a dull, indefinable, "con-
tent-less " sensation ; and when the pressure is increased, a sense
of being pricked or stuck. Both of these kinds of sensation, when
the pressure is still further increased, pass over into painful feeling ;
but the character of the pain in the two is different.
The arrangement of the " pressure-spots " is analogous to that of
the temperature-spots (to be described subsequently). They occur
much more frequently in certain areas of the body than in others.
They are placed in chains, as it were, sometimes more and some-
times less thickly set. These chains ordinarily radiate from a kind
of central point, and run in such directions as to form either circu-
lar, longitudinal, or pyramidal figures. Their direction is seldom
identical with that of the temperature-spots. In tlie opinion of
' Archiv f. Anat, u, Physiol., 1885, Pliysiolog. Abth., Supplement-Band, pp.
76 fE.
ARRANGEMENT OF PRESSURE-SPOTS.
347
Goldscheider the spots of both kinds correspond to the terminal
points of the nerve-fibres of two specifically different kinds of nerves
distributed over the skin. But whereas aU the area of the skin is
well covered with such nerves as give us the general dull and in-
definite feeling of contact, the nerves of the sensation of pressure
are much more unevenly distributed. It need scarcely be said
that, other things being equal, they are most numerous in the areas
of the skin most sensitive to touch. The different pressure-spots
themselves differ in sensitiveness ; some are much more easily ex-
cited than others. The sensations themselves come under the
.'^jmm-
Fig. 95.— Arrangement of Pressure- spots (Goldscheicler). A, dorsal and radial surface of the
first phalanx of the Index fioger ; B, membrane between thumb and index finger; 0, dorsal
surface of forearm ; D, back ; B, inner surface of forearm ; F, back of hand.
general laws of exhaustion, practice, etc., as these laws apply to
the whole mechanism of sense.
The attempt has been made, on the other hand, to identify, in
kind, sensations of pressure (especially those of light touch) and
sensations of temperature.' E. H. Weber observed that cold bodies
resting on the skin appear heavier, and warm lighter, than they
really are. A single silver dollar of the temperature of 25°-19.5°
Fahr. appeared to be of the same weight as two dollars of the tem-
perature of 98.5°-100.5° Fahr. Wunderli also argues the identity
of these two classes of sensations on the ground that, if certain parts
of the skin are lightly touched with cotton or slightly warmed by
approaching a heated surface to them, through a square opening in
' For a discussion of this qiiestion, see Funke, in Hermann's Handb. d.
Physiol., III., ii., p. B20 f.
348 SENSATIONS OF THE SKIN.
a piece of paper laid upon the skin, the two sensations thus occa-
sioned are frequently mistaken for each other. But Szabadfoldi
has much Aveakened the force of Weber's experiment by showing
that small wooden disks when heated to 122° Fahr. often feel
heavier than those which are really larger but are not thus warmed.
And Wunderli's observation at best holds good only for compara-
tively obtuse parts of the skin, especially the back. Moreover, if
the same stimuli should serve to excite both the pressure-spots
and the temperature-spots, this would not prove the identity of the
two sensations.
Finally, the physiology of the sense of temperature re-enforces
the indubitable testimony of consciousness, and leads us to the con-
clusion that from beginning to end — in the character of their stimuli,
of their nervous processes, and of the resulting modifications of
feeling — the sensations of pressure and the sensations of tempera-
ture are qualitatively distinct. They have in common only the
organ in which their apparatus is located, and the fact that both
kinds of sensations are constantly associated most intimately in
time and space.
§ 22. Sensations of Temperature, therefore, form a second dis-
tinct species which have their origin in the excitation of the nervous
end-apparatus of the skin. Whether their end-apparatus is locally
the same as that upon the excitation of which the sensations of
pressure are dependent, it has seemed rmtil very lately impossible
to say. But recent investigations (especially of Blix,' Goldscheider,''
and Donaldson') point unequivocally to the conclusion that certain
definite spots of the skin, and these only, are susceptible to irrita-
tions of a kind to result in sensations of temperature. Such spots
are insensible to pain (even the pain of temperature), and a needle
can be run into them without being felt ; they are probably also in-
sensible to pressure. What is more remarkable still, the existence
of " heat-spots " and " cold-spots " — or minute localities of the skin
sensitive to heat but not to cold, and conversely — seems demon-
strable. By using a machine which locates the stimulus micro-
metrically, the topography of the skin may be mapped out, and
extremely minute spots indicated which respond to irritation with
sensations of pain, of pressure, of cold, and of heat — respectively.
These different kinds of sensation-spots appear never to be super-
' Zeitschrift f. Biol., 1884, XX., pp. 141 ff.
^ Moiiatshefte f. prakt. Dermatol., 1884, III., Nos. 7, 9, 10 ; 1885, IV., No. 1 ;
and art. in Archiv f. Anat. u. Pliysiol., 1885, Physiolog. Abtli., Supplement-
Band.
^ Reseai'ch on the Temperature-sense, reprinted from Mind, No. XXXIX.
AKRAiSGEMENT OF TEMPERATUEE-SPOTS. 349
imposed. They are not located alike on the symmetrical parts oi
the same individual, or on the corresponding parts of different in-
dividuals. An accurate mapping out of the different areas of the
skin, with respect to their temperatui'e-spots, is difficult ; since ex-
periment soon blunts the sense, and even the approach of a heated
or cooled point raises or lowers the temperature over a considerable
area. But, in general, such spots occur in lines that radiate from
centres generally coincident with the roots of the hairs, in those
Fig. 9C.— Arrangement of Temperature-spots. A, heat-spots ; and B, cold- spots— from the palm
of the left hand (GoMsoheider).
regions of the skin where such appendages are found. These lines
often run so as to cross each other, forming figures of various shapes,
— triangles with rounded corners, etc. Heat-spots are, on the
whole, less abundant than cold-spots ; but inpartsof the body where
the skin is most sensitive to either heat or cold the corresponding
class of sjDots is relatively frequent. Temperature-spots may be
divided into first-class and second-class (so Goldscheider) according
to the strength with which they react on moderate stimulation.
Some spots are roused only by excessive temperatures. The same
object feels cool to one spot, ice-cold to another.
The electrical current when applied to these spots is thought to
call out the corresponding specific sensations. Goldscheider con-
siders that he has succeeded in exciting definite temperature-sensa-
tions by applying electricity to the trunks of the nerv'es distributed
to certain areas of the skin. This would appear to be almost a
demonstration that the nerves of this sense are specific, and of
two kinds — nerves of heat-sensation and nerves of cold-sensation.
Puncturing a temperature-spot also gives rise to temperature-sen-
sations. The discriminative sensibility of the temperature-spots
is found to be much finer than that of the tactile sensations.
Everything which produces a change in the temperature of the
skin acts, of course, as a stimulus for the sensations of heat and
cold.
§ 23. The above-mentioned discoveries as to the specific energy
of the nerves and end-apparatus of the skin, interesting as they are.
350 SENSATIONS OF THE SKIN.
have not yet been completely brougiit into rational connection with
our experience of temperature-sensations and our knowledge of
the general laws of nervous action. It is obvious, however, "^iat
the principles of contrast, of relativity, and of exhaustion, must
bear a large part in the explanation of all these sensations. Sen-
sations of temperature have apparently a certain dependence on
the temperature of the thermic apparatus itself. This law has been
elaborated and defended in detail by Hering,' in the following
form : " As often as the thermic apparatus at any spot in the
skin has a temperature which lies above its own zero-point we
have a sensation of heat ; in the contrary case, a sensation of cold.
Either sensation is so much the more marked, or stronger, the
more the temperature of the thermic appai-atus at the time varies
from the temperature of its own zero-point." By the "zero-point"
of any part of the skin is meant the exact objective temperature
which at that part will produce no sensation of either heat or cold.
Such zero-point is, of course, different for different parts of the
body, according as they are or are not exposed, and are or are not
well supplied with arterial blood, etc. It also changes in connection
with changes in the temperature of the surrounding air or of the
bodies with which the skin is in contact. By this principle a great
number of our ordinary sensations of temperature are explained
by Hering. The finger and the nose are colder than the inside
of the mouth, because they are exposed to radiation of their heat.
On passing from a room of a given temperature into one of either
higher or lower temperature we experience at first certain sensa-
tions of temperature while the zero-point of the thermic apparatus
is becoming adjusted to its new surroundings. After such adjust-
ment has taken place these sensations may cease — to be renewed
in the revei'se direction, however, on a return to the former sur-
roundings. This adjustment has its limits ; it is dependent chiefly
upon the evaporation of the skin and upon the circulation of the
blood.
If the surroundings are more than so hot or so cold, they may
excite constant sensations of temperature. Among the induce-
ments to sensations of heat at any locality of the skin, Hering men-
tions the following as prominent in our ordinary experience : All
checking of the radiation of heat, while the blood-supply remains
unaltered ; all contact with a medium or object of higher tem-
perature— and this according to the ease with which such medium
or object parts with its heat ; and all increase of heat in the skin
' In Hermann's Haiidb. d. Physiol., III., ii., p. 419 f . ; and Sitzgsber. d. Wie-
ner Acad., LXXV., Abth. 3, p. 101 f.
DETERMINATION OF THE ZERO-POINT. 351
coming from the interior of the body, as in the sudden hj'pergemia
which takes place in blushing. Inducements to sensations of cold
are as foUows : Increased convection of the heat of the skin by the
suiTounding medium, while the blood-supply remains unchanged
(as when the wind blows over the hand or face, esj)ecially if the
skin be moist) ; contact with objects which have the same (or even
slightly higher) objective temperature as the surrounding air, but
convey the heat from the skin more rapidly than it ; contact with
or j)roximity to objects colder than the skin ; lessening of the
interior warmth of the body — for example, by contraction of the
blood-vessels which supply a given portion of the skin. Ordinary
experience makes us famihar with many of the phenomena which
come under all these cases.
The determination of the e'K^act zero-point of different parts of the
body is a matter of great difficulty. The rise and fall of the tem-
perature of the thermic apparatus, in connection with that principle
of exhaustion which aj^plies to all the nervous mechanism, and es-
pecially to certain of the end-organs of sense, doubtless account
(at least partially) in some way for the well-known phenomena of
contrast in temperature-sensations. "Weber showed that if the
hand be held for a minute in water of the temperature 54.5°
Fahr., and then in water of 64.4" Fahi*., a sensation of heat will be
felt for a few seconds, although the latter would have felt cold to
the hand if placed in it at first. Moreover, if we hold one hand in
moderately cold water, and dip the other repeatedly in the same
water, the sensation of cold is stronger in the latter, although the
temperature of the hand held in the water is really lower. But,
according to an experiment of Goldscheider's, if one hand be left
for ten seconds in water of the temperature of 104° Fahr., and then
both hands immersed in cold water, the warmed hand will feel the
cold less distinctly than the other. This latter investigator, how-
ever, is inclined to dissent from Hering's theory, and retui-n to the
theory of E. H. Weber. "Weber held that the rising of the tem-
perature of the skin is felt as heat, and its sinking as cold.
After-images of temperature-sensations seem also to exist. But
when a surface of the skin has been warmed or cooled, and the
after-image has faded quite away, it is said that it can be called
back b}' light mechanical irritation ; this is especially true of sen-
sations of cold. The phenomena of exhaustion are noticed in sen-
sations of tempei'ature. Our perception of the absolute degree of
temperature, and of minute variations in its degree, is most acute
for places in the scale lying close to the normal temperature of the
skin. It would seem, on the whole, as though the phenomena
352 SENSATIONS OF THE SKIN.
of contrast of sensations of temperature, as well as of color, require
for their satisfactory explanation a knowledge (possibly of the
action of the central organs of the nervous system) which we do
not yet possess.
E. H. Weber also showed that the amount of the skin which is
stimulated has a marked influence on the quality of the resulting
sensation. The temperature of the same fluid does not feel pre-
cisely the same to a single finger and to the entire hand. This
experience is similar to that which has already been described in
the case of sensations of color. It appears explicable in the case
of the skin from what is now known about the existence of a cer-
tain variable number of heat-sjDots and cold-spots. In the same
way, in part, may we explain the fact that smooth objects, which
therefore come into contact with a larger portion of the skin — like
leather, paper, wood, glass, and porcelain — appear colder to the
whole hand even when they have the same objective temperature
with it.
§ 24. Nothing whatever is known as to the exact manner in which
changes of temperature act upon the thermic apparatus to excite
it ; the recent discoveries ajDpear to make such action all the more
difficult of conception and description. Since the terms " hot "
and " cold " are in physics only relative, it is hard to see why ab-
solutely different apparatus, with a distinct local position, should
be used (as Goldscheider's discoveries indicate) for the sensations
corresponding to each. Moreover, on Hering's hypothesis, how
are we to account for the fact that heat-spots and cold-spots are in
turn stimulated by the same objective temperature according to
the rise and fall of the zero-point of tbe entire region of the skin ?
Possibly it may be found that certain chemical or electrical changes,
dependent upon the increase or decrease of that mode of molecular
motion which jDhysics calls " heat," are the proximate stimuli of
the two classes of end-organs of the temperature-sense. Gold-
scheider supposes that the difference in sensitiveness of different
areas of the skin to temperature must be ascribed to the anatomi-
cal distribution of the heat- sensitive and cold-sensitive fibres, re-
spectively. But he does not show us what kind of nervous con-
trivance would satisfy all the conditions which are imposed by the
complicated facts of experience.
A- Herzen ' considers himself to have demonstrated, by patho-
logical cases and experiment upon animals, that sensory impulses
of cold, like those of touch, pass along the posterior strands of the
spinal cord ; and that the sanje region of the brain {Gyrus sigmot-
' See Pfliiger's Archiv, 1885, pp. 93 fE.
'SPECIFIC ENERGY OF THE NERVES. 353
deus) is the " centre " for both. Sensitiveness to heat can be re-
tained, it would seem, after sensitiveness to cold has been lost.
§25. In closing the subject treated in the last two chapters,
attention is again called to the large amount and cumulative char-
acter of the evidence afforded by the special sensations, considered
as respects their quality, for the law of the Specific Energy of the
Nerves. It is impossible to account for the above-mentioned phe-
nomena without carrying this law to a great length in its applica-
tion to the special senses. We may not be able to affirm — as does
Fick,' for example — that two sensations are distinguishable as re-
spects quality only in case they are occasioned by two individually
different elements of the nervous system. For we have seen that
the quality of sensations depends upon their quantity, upon their
relation to preceding and contemporaneous sensations, and upon
considerations other than merely the one of what particular nerve-
fibre or element of the end-apparatus was acted upon by the stim-
ulus. Moreover, there is no warrant for saying that identically the
same nervous apparatus cannot be excited variously according to
the nature of the stimulus which acts upon it, or according to the
combination with other parts of the system into which it enters for
the time. It is obvious, however, that the differentiation of func-
tion, and the assignment to specifically distinct apparatus of par-
ticular nervous impressions corresponding to particular mental
states, is carried to a great length in the special senses. In this
differentiation of function it is not wholly or chiefly the nerve-
fibres, as such, which should be taken into account ; it is also the
minute subdivisions of the eud-organsof sense, and the connections
set up within the corresponding regions of the central organs. In
accounting for those complex sensations which appear in ordinary
consciousness, the law of permutations and combinations has, of
course, to be considered. A vast variety of such sensations maybe
made up by changing the relations to each other of comparatively
few simple elements. But in each of the senses our analysis, when
carried to its utmost limit, leaves a number — in some of the senses
very large — of simple sensations, which apparently must have their
physical basis in the excitation of specifically distinct elements of
the nervous mechanism.
The sense of smell apparently requires that the law of the specific
energy of the nerves should be carried to such a length as almost
to reduce it to an absurdity. Histology has discovered only one
essential kind of olfactory end-organ, and that of comparatively
simple structure ; and yet experience gives, as the result of its ex-
1 In Hermanns Handb. d. Physiol., III., ii., p. 166.
23
354 SENSATIONS OF THE SKIN".
citation, a bewildering variety of sensations so specifically different
as to baffle all our attempts to classify them. From the case of
this sense an argument may then be derived which leads in ei-
ther direction. It may be objected to the law that it is absurd to
sup23ose a complexity of the end-organs of smell such as to corre-
spond to each specific kind of olfactory stimulus with a specific sen-
sation— for example, the smell of musk, or of sulphuretted hydro-
gen. It may be replied to the objection that, in the case of the
ear, there are at least 16,000 or 20,000 distinct forms of auditory
end-apparatus corresponding to the different musical tones ; and
it is therefore by no means impossible that the entire regio ol-
factoria may contain enough siDecifically different forms of its own
peculiar end-apparatus to suffice for all the simple sensations of
smell.
The sense of taste does not occasion so many difficulties in rela-
tion to the law of the specific energy of the nerves. It is thought
possible by most physiologists to reduce all the sensations of taste
to four, or at most six, different species. It is easy to suppose
as many specifically different forms of the nervous apparatus cor-
responding to the different classes of sensations — sweet and sour,
salt and bitter, alkaline and metallic. In spite of the fact that
such a classification appears satisfactory to most authorities, experi-
ence is reluctant to confirm it. Many of the complex tastes, even
when separated from their accompanying sensations of smell, are
scarcely resolvable into combinations of the above-mentioned
simple tastes. Into which of the six, for example, would experi-
ment resolve the gustatory sensations which come from chewing a
bit of chocolate, or of a nut from a black-walnut tree ?
The strongest defence of the most extreme form of the theory of
the specific energy of the nerves has hitherto been found in sensa-
tions of musical sound. Here we undoubtedly have a wide range
of qualitatively distinct states of consciousness which are ap-
parently dependent ujDon the excitation of a correspondingly large
number of distinct nervous elements. From sensations of sight,
although many points of the prevalent theory are still obscure and
unsatisfactory, a considerable force of evidence bearing in the same
direction may be obtained. It seems almost certain that the
numerous states of consciousness which result from stimulating
the different nervous elements of the retina are due to combina-
tions of a comparatively few kinds of such elements, each of which
responds in a specific way to a special order of stimulus. Yet this
is not precisely what the theory of specific energy seems to de-
mand. For the different color-sensations all appear as simple and
• SPECIFIC ENERGY OF THE NERVES. 355
unanalyzable states of consciousness. None of them are twofold, as
sensations. We are at a loss to say why, according to the theory
of specific energy, each sensation should not result from the ex-
citation of one, and only one, kind of nervous elements.
The recent discoveries as to the existence of pressure-spots,
heat-spots, and cold-spots in the skin add important evidence to
that ah-eady existing in favor of the law under discussion. It will
further appear, when we consider the process of locaKzation in the
so-called " geometrical senses " of the eye and the skin, that the
very possibility of such a process demands a strict and far-reaching
application of the law of the specific energy of the nerves. Pre-
cisely how we are to state and limit this law, neither its opponents
nor its advocates have as yet been able satisfactorily to show. The
exact expression of the theory waits for further evidence from
experiment, although there can be little doubt that in its main
features it is already secure.
CHAPTER Y.
THE QUANTITY OF SENSATIONS.
§ 1. By an act of mental analysis, which all men readily perform,
changes in the amount of sensation are distinguished from changes
in its quality. This distinction obviously requires for its perform-
ance nothing beyond what is immediately given in consciousness.
All sensations appear there as differing among themselves, not only
with respect to the nature of the impression which serves to classify
them into groups (as sensations of sight, sound, etc.), but also with
respect to the degree in which each particular impression possesses
the sphere of conscious attention and feeling. The best illustra-
tion of an alteration in the intensity of sensation, while its charac-
teristic quality remains unaltered, may be derived from musical
tones. The dying-out of a single note when the bow is drawn
with decreasing force across the string of a violin, or a single
key of the piano is struck and the pedal held, may be considered
as a change in the quantity of sensation, while its quality is un-
changed. A more complex case is the experience we have when
approaching to, or receding from, a bell that is sounding or a
steam-whistle that is blowing. Noises of a certain complex quality
— such as slamming, hissing, grating, etc. — are continually de-
scribed as very loud, moderately loud, or of weak intensity. So,
too, when approaching a white or colored light, with our attention
fixed upon it, we generally disregard almost wholly the changes
in its color-tone which take place, and consider chiefly the changes
in its intensity and apparent size. The pressure of diffei'ent
weights upon different parts of our skin is ordinarily regarded as
the same in quality and as varying only in amount and locality.
The same thing is true, in almost precisely the same way, with
sensations of temperature. The thing we touch is called slightly
cold or very cold, somewhat warm or hot, our attention being
directed chiefly to the quantum of sensation which it calls forth.
In other words, it is generally the same kind of pressure and tem-
perature, with a varying degree of intensity, of which we are
conscious.
QUAISTTITY ATSTD QUALITY. 357
It Is more difficult, however, even in the most indefinite way, to
separate the quantities of our sensations of smell and taste from
the changes in quality of the same sensations. A concentrated
sweet or acid so strongly excites a variet}^ of forms of feeling which
mingle indistinguishably with the specific sensations of taste that
we are compelled to attend to the very decided qualitative changes
which are taking place. The increased intensity of the sweet or
sour we may indeed speak of as "very" much of the same sensa-
tion which was excited in less degree by the diluted form of the
stimulus ; but we are more likely to regard it as constituting a
complete change in the kind of taste. In the same manner, atten-
tion is forcibly directed toward the kind of sensation which results
from increasing the quantity of any specific sensation of smell.
It is further obvious that the distinction which we make between
changes in the quantity and changes in the quality of our sensa-
tions is to some extent applicable for comparing the sensations of
different senses. And here the distinction, when applied to sub-
species under certain specific forms of sensation, affords us a
means of transition for such comparisons. Some yellows are
bright and others dull ; and the same thing is true of the reds and
the blues. The sours, the sweets, the bitters, may be compared
with each other as respects the degree of intensity which they pos-
sess. We may next, in a very indefinite way, compare the quantities
of the sensations of the different senses as they appear side by side,
or successively, in consciousness. We are ordinarily satisfied,
however, with simply describing the varying degrees of intensity
possessed by our different sensations as " weak " or " strong " (with
or without the emphatic " very "), or as only " moderate." Thus
we may judge that both the light which we see and the tone which
we hear (either simultaneously or one immediately after the other)
are, or are not, to be classed together under the same one of these
three grades of intensity.
§ 2. That changes in the intensity of our sensations are not, in
fact, independent of changes in their specific nature has already
been proved (Chap. TV"., § 4). Only in the case of musical tones
are we able at the same time to attend carefully to both the quan-
tity and quality of our' sensations, and so discover with perfect
confidence that the former is changing while the latter remains un-
changed. Even in this case, since the tones which we ordinarily
hear are composite, any considerable alteration of their intensity
changes also their tone-coloring, through the alteration which it
produces in the comparative intensities of the overtones. Any in-
crease iu the brightness of a particular color invariably changes its
358 MEASUKEMENT OF SENSATIOTSTS.
characteristic color-tone. A white of less intensity is not merely
less white, but becomes a gray ; and by constantly diminishing its
intensity white can be shaded through the different grays toward
black, which is certainly not a feebler degree of the sensation of
white. The same dependence of quality on quantity is true in all
sensations of smell, taste, pressure, and temperature. It would be
a mistake, however, on this account to consider " quantity " of sen-
sations as only another name for shades of quality, or to deny that
we can apply terms of measurement to these reactions of the mind
upon the excitation of the nervous apparatus of sense.' Scientific
analysis confirms the distinction made by ordinary experience be-
tween "the way" we feel and "how much" we feel in any particular
way.
§ 3. All descriptions of the changing intensities of sensations,
when made on the basis of ordinary experience solely, leave the
subject in a very indefinite and unscientific form. That a certain
noise is louder or weaker than another of precisely the same kind,
one may be quite ready to afiirm ; one may even be ready to say
that one judges this noise to be about twice or three times as loud
as the other. But when more precise estimates are demanded, one
is obliged to hesitate before giving them. Is this musical tone ten
(or a hundred) times as loud as the other ; or is it only nine and
nine-tenths (or ninety-nine and nine-tenths) as loud ? Few would
venture so nice an estimate with any confidence. Yet the case of
sound is much more favorable than that of most of the senses for
forming an exact judgment as to its intensity. It would be difficult
under the most favorable circumstances to affirm that the sensa-
tion of the light a is twice or three times as bright as that of the
light h ; or that of the shadow x one-half or one-third as bright as
y. The comparative intensities of different color-tones are yet more
difficult to fix subjectively — even in the most indefinite way. This
particular yellow may seem about as bright a color, of its kind, as
does the red near it, of its kind. But the precise moment could
not readily be told when the blue of the sky appears exactly
twice as intense as the green of the grass. Still further, all esti-
mates of the quantity of sensation approach the point at which
they lose their meaning and tend to become absurd, when we com-
pare, for example, sensations of smell or taste with those of press-
ure, temperature, or sight. We never say : The rose smells as
sweet as it looks red ; or the lemon is twice as sour as the sky is
blue. And yet each qualitatively different sensation is assumed to
have its place somewhere in that scale of intensities through which
' Comp. Ktumi)i', Ton psychologic, I., p. 347 f.
PEOBLEMS OF QUANTITY. 359
the different qualities may run ; each may, therefore, be compared
with every other, with respect to the general position which it oc-
cupies in its characteristic scale.
§ 4. All things to which terms of quantity apply admit of some
kind of measurement and comparison with respect to their quantity.
Sensations, to be sure, are not "things," but rather modes of the ac-
tivity of mind, excited through the nervous mechanism of sense.
Nevertheless, since, like material things, they admit of some appli-
cation to themselves of the terms of quantity ; and since they vary
in their absolute and relative degrees of quantity, it is not strange
that experimental science has endeavored to measure sensations,
and to state laws for their comparison and mutual relations. The
general question of the quantity of sensation involves an answer to
two subordinate inquiries. Of these two the first concerns the
limits within which the different sensations may vaiy in quantity,
and yet remain sensations of the same sense ; the second concerns
the law of the relation which is maintained within the limits among
the various sensations compared. But neither of these questions
can be answered directly. Sensations cannot be kept constant in
quantit}-, and measured by the direct application of physical stand-
ards, whether with a view to fix their absolute or their relative
magnitude. They are all, however, under ordinary circumstances,
connected with the action of different forms of physical energy
upon the nervous system ; that is to say, they are caused by the
application of stimuli to the nerves, and the changes in the amount
of the sensations are dependent upon changes in the intensity of
the stimuli which occasion them. These stimuli admit of changes
in quantity, which, theoretically at least, are measurable objectively,
with more or less exactness. Resulting changes in consciousness
can only be measured by attentive judgment, which directly dis-
criminates the sensations as varying in intensity, and as being
greater or less, one than the other, in the scale of impressions
which experience has framed.
The problems of the measurement of sensation may then be
stated as follows : (1) To determine how little and how much of each
kind of stimulus will produce respectively the least and the
greatest quantity of each kind of sensation of which the mind is
capable, or to find the quantitative limits within which sensations of
each sense are possible ; and (2) to determine the law of the relation
under which changes in the intensity of sensations, as estimated
in consciousness, are dependent upon changes in the intensity of
the stimuli.
§ 5. Unexpected and insuperable difficulties, however, stand in
360 MEASUREMENT OF SENSATIOJ^S.
the -way of a direct solution of either of the two above-mentioned
problems, even in the modified form in which they were last stated.
For, in the first place, it is only with respect to sensations of press-
ure and of the muscular sense that we can measure objectively the
physical energies which act on the nervous end-organs, with much
approach to perfect exactness.' The amplitude of the acoustic waves
in the air which originate from a given source would indeed admit
of exact measurement ; but the modifications which these waves
undergo before they reach the nerve-cells and nerve-fibres of the
inner ear are so complicated as to make it impossible to calculate
accurately the amount of the physical stimulus which is directly
applied to the end-organs of healing. The photo-chemical and
thermic effects of light may be measured objectively. But this
light is not the direct physical stimulus for the fibres of the oj)tic
nerve, or even for the end-organs of the retina ; and we have no
sufficient means for estimating the amount of those chemical changes
in the visual substances, or pigments of the eye, which are supposed
to be the immediate excitants of the terminal apparatus of vision.
The case is yet more hopeless with respect to the senses of taste
and smell ; inasmuch as we do not even know what pi'operties smell-
able and tastable substances must possess in order to influence the
nerves of those senses. The objective measurement of the stimulus
for sensations of temperature also is made difficult by the fact that
its amount is dependent upon the zero-point of the skin itself,
since this point is different at different times and for different
areas of the entire surface, and is always difficult of precise deter-
mination.
Moreover, could we measure with perfect exactness the intensity
of the stimulus as it is applied directly to the appropriate end-
organs of sense, our knowledge of the intensity of the necessary
physical antecedents of the resulting sensations would be far
enough from complete. How do the end-organs modify the quan-
tities of the stimuli before they transmit their effect to the conduct-
ing nerve-fibres ? Precisely how much further modffication do
these quantities receive in transmission to the central organs, at
the hands of the conducting nerve-tracts ? What are the laws which
control the reception, diffusion, and modification of the different
intensities of the transmitted nerve-commotions, within those parts
of the nervous mechanism (the central organs), where they become
the immediate occasions of the rise and change of sensations in the
mind ? These are questions to which we are absolutely unable to
give any satisfactory answer.
' Comp. Wuudt, Philosopliische Studien, 1883, II., hefti., pp. 10 ff.
LEAST OBSERVABLE DIFFERElSrCE. 361
§ 6. But if an exact objective measurement of the physical stim-
uli is intrinsically difficult, an exact subjective measurement of the
sensations themselves is inherently impossible. Such subjective
measurement can exist at all only in the form of a judgment which
compares two or more sensations with a view to pronounce whether
they are equal in intensity ; or, if unequal, which is the greater and
which the less of the two. But we have seen that the ordinary
estimate of the absolute strength of a sensation is able simply to
assign to it an indefinite position in the scale of its kind. With
certain exceptions, scientific analysis can do little to exclude the
uncertainties of the ordinary estimate. These exceptions are all of
the following kind : Where two sensations of the same quality are
produced, either simultaneously on difierent corresponding areas of
the same organ or successively (with the most favorable interval be-
tween) upon the same area, by amounts of stimulation that are very
nearly or precisely equal, the attentive mind can discriminate the
minute differences, or exact equality, of the intensities of these two
sensations, with a great degree of nicety. The problem of meas-
uring the quantity of sensations depends, therefore, upon obtaining
the least observable differences in intensity for each kind of sensa-
tions, and for every point along the scale of degrees of intensity.
But in this connection another occasion for doubt and debate
arises. Is "the least observable difference" of two sensations it-
self a constant quantity ? The affirmative answer to this question
is assumed by Fechner ' and all strenuous advocates of the law
which he defends. It has even been argued that to hold another
than the affirmative view involves a contradiction in terms." What
can be meant, it is asked, by a "least obsei'vable difference " in in-
tensity between two sensations, unless it be that this difference is
a constant unit for the measurement of those sensations of the
same kind which lie near the same point in the scale ? If the dif-
ference is more than just observable, then of course it is not the
least observable ; if it is less, then it is not observable at all — that
is to say, there is no change in sensation. But to this argument
the following reply is pertinent : The "least observable difference "
is not itself a mental entity or a mental state, that can be measured
and used as a unit for measuring the quantity of other mental
states. For example, if the addition of n to the stimulus *S^ is the
smallest amount that will produce such a change in the mental
state X as to cause it to pass over into x\ which the mind recog-
' Elemente d. Psychophysik (1860\ i., p. 54 f. ; In Sachen d. Psychophysik
(1877\ p. 45 f. ; Revision d. Hanptpunkte d. Psychophysik (1882), p. 18 f.
■ Comp. the first edition of Wundt's Physiolog. Psychologie, p. 294.
362 MEASUEEMENT OF SENSATION'S.
nizes as having a greater quantity of sensation than x, such fact is
to be stated and accepted as a mere fact ; it does not follow, how-
ever, that we may conclude that x' — x = A, and that this A is en-
titled to a name (" least observable difference ") and a rank among
the mind's experiences by way of sensation. There are no seiisa-
tl07^s (whatever physical occasions of sensations may exist) except
those that appear in consciousness ; ex hypothesi, there appear in
consciousness only x and x', and no sensation whatever Ijing be-
tween the two in intensity. We judge, indeed, that the intensity
of x', now present in experience, is greater than was the intensity of
X, now remembered as an image of past experience ; but A (or x' — x)
is a mere abstraction, a figment of the experimenter's brain, and not
a real experience of the person with whom he is experimenting.
Moi'eover, if A were capable in any case of being regarded as a
unit of subjective measurement, it would by no means follow that
its mental value is a constant. That n, or the amount of stimulus
which must be added to S in order to produce an observable change
in the quantity of sensation, is not constant we know beyond doubt.
For the different senses, for different individuals, for different de-
grees of the absolute stimulus {i.e., value of S), for different con-
ditions of the organs of sense, this amount n is constantly varying.
The amount of A may also be held to vary, according to psycho-
logical changes in the means and power of mental discrimination,
such as we have no way of measuring objectively. For we must
again insist upon the fact that the real quantity of a sensation is
not the same thing as the estimated quantity of the same sensation.
The " least observable difference " would not, therefore, necessarily
be the same as the least real difference, between two sensations.'
It is not the mind's custom to attend accurately to the changes in
quantity of its sensations as such. Properly speaking, many con-
siderable changes in our sensations, as we may judge by the guid-
ance they give to the bodily motions and the mental train, do not
appear in consciousness with a label of exact quantitative measiire-
ment, as it were, attached to them.
It is therefore obvious, from the great difficulties which belong
inseparably both to the objective measurement of the stimuli of
sensation, and to the subjective measurement of the resulting sen-
sations, that any law of their relation can have only an indefinite
statement and a secondary value.
§ 7. Two methods of determining the lower limit, or minimum
of stimulus producing a sensation, are possible. In the use of one
method, a weak stimulus, but somewhat above the amount needed
' Comp. Stumpf, Tonpsychologie, I., p. 51 f.
DETERMINING THE LIMIT. 363
to produce a sensation is applied ; its intensity is then diminished
by minute gradations until the exact point is readied and noted at
■which it ceases to produce any sensation at all. In the use of the
other method a stimulus too weak to produce any sensation is first
applied ; its intensity is then very gradually increased until it
begins to produce the smallest observable sensation. Both ways
may be combined, and thus the " sensitiveness " of each organ of
sense, and of each part of each organ, may be determined. Such
sensitiveness increases, of course, in inverse ratio to the amount of
stimulus necessary for producing any sensation at all, or for pro-
ducing a sensation estimated as having a definite degree of energy.
The effort to determine the lower limit of sensations of sight and of
sound is embarrassed by the facts that the retina is always under
excitation from the chemical changes going on in its pigments, and
therefore has a certain quantum of so-called " light of its own,"
and that such a thing as " absolute stillness " cannot probably be
secured for the ear. Total absence of sensation in the ear, could
it be secured, would not be comparable to the black which we see
with the eyes closed.'
The upper limit, or maximum amount of stimulus which the ner-
vous organism can receive, cannot be determined experimentally.
The use of excessive quantities of stimulus is not only too fatigu-
ing but also too dangerous to the structure of this organism (for
example, of blinding light upon the eye, stunning noise in the ear,
etc.) to admit of successful experiment in this dii-ection. Moreover,
the application calls out so much of those varied forms of feeling
which are allied with all the specific sensations as to overwhelm
the latter with the former. Very concentrated, sour, or bitter solu-
tions, or very intense odors, are not simply tasted and smelled ; they
are oho felt with aU the adjoining parts of the body. Very strong-
light and very loud noise do not simply heighten the specific sensa-
tions of sight and hearing, they rather destroy them in a flood of pain-
ful feeUng. We may affirm in general, however, that the " capacity "
of each sense varies directly as the amount of stimulus which it can
receive. The " circuit " or range of the sensations of each sense
C 1
may then be said to be — where _ stands for the measure of the
sensitiveness, and C for the measure of the capacity, of each sense."
^ On the question whether absolute stillness is possible, and whether the ear
has any sensation comparable to the black of the eye, see Lotze, Medicinische
Psychologie, p. 218 ; Volkmauu von Volkmar, Lehrbuch d. Psychologie,
1884, I., p. 273 ; and Stumpf, Tonpsychologie, I., p. 380 f.
2 See Wundt, Physiol og. Psychologie, i. , p. 324.
364 MEASUEEMENT OF SENSATIOl^TS.
§ 8. There are tliree methods of determining experimentally tke
least observable differences in sensations. These are called, (1) the
method of least observable difference ; (2) the method of average
errors ; (3) the method of correct and mistaken cases. Of the
three methods, the first bears the name which suggests the real
subject of investigation in them all. This method is divided by
Wundt ' and others into two — namely, the method of mean grada-
tions of sensation, and the method of minimum changes of sensation.
Bat these are really only two modes of applying one method. In the
one case an attempt is made to form a scale of stimuli whose intervals
correspond to equally large intervals in our estimate of the resulting
sensations, by judging what amount of the stimulus produces a sensa-
tion (M) that lies exactly midway between two other sensations (A and
O) separated by a clearly perceptible interval (hence A : M : : M : 0).
Between A and M another middle terra, the sensation of magnitude K,
may then be sought and found ; and so on until the limit of observ-
able differences is reached. This mode is, however, less comprehen-
sive and fruitful than the second mode of applying the same principle.
The " method of minimum changes in sensation " seeks directly to
establish, all along the scale of intensities of the stimuli, that change
in their strength which is just enough (and no more than enough)
to produce a minimum change in sensation. Such minimum
change may be conceived of as standing just on the ''threshold"
of our power to make distinctions in the degrees of strength with
which our sensations are apprehended in consciousness.^
The " method of average errors" (2) begins by fixing upon some
given sensation which is known to bo caused by a given intensity
of stimulus ; the attempt is then made also to fix upon another
stimulus, by means of the sensation it produces, as being exactly
equal to the former. The trial results in a number of guesses that
are more or less out of the way. By averaging all the cases of trial,
the degree of sensitiveness to distinctions is discovered. In other
words, the method attempts to determine, at each point along the
scale and for each kind of stimulus, the differences in the strength
of stimuli that are just below the amount necessary to make an ob-
servable difference in the resulting sensations.
In the " method of correct and mistaken cases " (3) minute ad-
ditions or subtractions of the amount of stimulus are made, with
the intent of seeing how many cases of right and how many of
' See Wundt Pliysiolog. rsycliologie. i. , p. 325 f., and comp. his Philosoph-
ische Studien, 1881, p. 8 f.
-Called "Unterschiedsschwelle" by Fechuer, Elemented. Psychophysik,
i.,p. 242.
CORRECT AND MISTAKEN GUESSES. 365
wrong guessing, respectively, will result for each of the different
positions in the scale of the stimuli, and for each kind of stimulus.
If, then, the proportion of the number of correct to mistaken guesses
is kept the same for all points of the scale, the amount of change
in the stimulus necessary for this may be held to measure the sen-
sitiveness to differences which belongs to each of these points.
Thus, let n = the whole number of guesses, and r — the number
/'
of right guesses ; then — = the sensitiveness to differences. But
?i
the positive value of this quotient being kept unchanged, the
amount of stimulus added to or subtracted from the original
amount will measure the sensitiveness to differences for all points of
the scale. Tiiis method has been largely used and warmly defended
by Fechner ' in experimenting with sensations of pressure. Much
doubt has, however, been thrown upon the use made of it by this
observer ; and especiall}'' upon the propriety of reckoning the doubt-
ful cases one-half to the right and one-half to the wrong guesses.^
A comparison of the above-mentioned methods shows that they
ai'e all simply different ways of measuring the sensitiveness of the
mind to minute differences in the quantity of its sensations as de-
pendent upon changes in the intensity of the stimuli. They should
never be employed, therefore, without taking into account the
fact that various other causes, besides such objective changes in
the stimuli, always co-operate to determine the degree of this
mental sensitiveness. To eliminate these other factors from the
calculation is by no means easy.
§ 9. The one law which claims to be a scientific expression of the
relations between changes in the intensity of stimuli and changes
in the quantity of the resulting sensations is that known by the
name of E. H. Weber. This observer originally used the method
of least observable differences as applied to sensations of pressure
and to the measurement of lines by the eye.' " Weber's law " has
been elaborated, confirmed by a vast amount of espei"iment, and
defended as a psycho-physical pi'inciple of the widest application,
by Fechner (in the works referred to, note, p. 361). The significant
addition which' Fechner has made to Weber's law consists in the
assumption that all just observable differences are equally great. ^
' Elemente d. Psychophysik, i., pp. 98-120.
" On this point see, especially, G. E. Miiller, Grundlegung d. Psychophy-
sik, p. 36 f. ; and Wundt, Physiolog. Psychologie, i. , p. 330 f.
^ Especially in articles on the sense of toiich, in R. Wagner's Handworterb.
d. Physiologie, III., ii. ; and Archiv. f. Anat, Physiol., etc., 1835, pp. 153 ff.
* On this point comp. Funke, in Hermann's Handb. d. Physiol. , III. , ii. , p.
349 f. ; and Wundt, Philosophische Studien, II., Ileft 1, p. G f.
366 THE LAW OF WEBEE.
It is therefore also called " Fechner's law." As an empirical law
it attemjDts to put into scientific form, on the basis of experimen-
tal investigation, the truth of ordinary experience — namely, our
estimate of the difference in amount between two sensations is
not directly proportioned to the real difference in their stimuli,
but the latter must increase faster than does the former. For ex-
ample, the difference in the intensity of the shadows cast by one
and by two wax tapers is very perceptible in a dimly lighted room,
but is altogether unobservable in open sunlight ; or the strength
with which two clocks tick can be discriminated with much nicety,
but not the amount of noise made by two successive discharges of a
cannon.
In other words, if we assume that the least observable difference
in sensations may be regarded as a constant quantity, then, in
order to produce this increase or decrease in the amount of sen-
sation, the addition or subtraction of a much greater amount of
stimulus is needed for the higher than for the lower portions of the
scale. Weber's law undertakes to tell us how much greater such
required amount of stimiilus must be. It admits of statement in
the several following ways : The difference between any two stimuli
is experienced as of equal magnitude in case the mathematical re-
lation of those stimuli remains unaltered ; or, If the intensity of
the sensations is to increase by equal absolute magnitudes, then
the relative increase of the stimulus must remain constant ; or. The
strength of the stimulus must ascend in a geometrical proportion
in case the strength of the sensation is to increase in an arith-
metical proportion.*
1 See Wundt, Physiolog. Psychologie, i., p. 335. For the detailed mathe-
matical discussion and expression of Weber's law the reader is referred to
the technical works, especially of Fechner and G. E. Miiller. A simple state-
ment of Weber's principle may be given as follows : Let H= the intensity of
the light of one-half of a white field ; j-^ = the smallest fraction of stimulus
added to H that will produce an observable increase in this intensity ; and
JET H — ~ = the intensity of the other half of the same field. Then let 8 =
the sensation produced by II; S + s = the sensation produced by 11+ 77777.
and s will, of course, represent the so-called least observable difference at this
point in the scale. We have, then, H produces S; H + 77577, or |{ji ZT, pro-
duces S + s; lolf £[+ LP." ^ , or igi-ISr) H, produces 8 + s +s; and so on.
That is to say, if s is to be kept of the same magnitude, then i/must be mul-
tiplied by the same magnitude {{f,}-,)-
The three fundamental formulas which Fechner has employed to state and
demonstrate the law are the following : Let 8 be the magnitude of the sensa-
tion caused by the stimulus 2, and AS a just observable increase in this sen-
'QUANTITY OF TACTUAL SENSATIONS. 367
The empirical data upon which the advocates of Weber's law rely
are very numerous, but their value and trustworthiness are often
much diminished by the fact that most experimenters have failed
to isolate sufficiently the exact problem which it was desired to
solve. Nevertheless, the data show that the law summarizes many
facts reasonably well within a certain range of sensations lying near
the middle of the scale of quantity. Near both the upper and the
lower limits the law fails to prove applicable ; even in the regions
and under the circumstances which are most favorable it is only
approximately true. Many fluctuations of unknown significance
and origin occur in all the senses.
§ 10. In determining the least observable sensations of touch,
the result is largely dependent upon the presence of muscular sen-
sations also. It further depends upon the method in which the
comparison is made ; for, as Weber discovered, an actually present
sensation can be compared with the remembered image of one just
past better than two present sensations can be compared. The in-
terval of time and the locality of the organ have also a great influ-
ence. Most persons observe a stronger sensation of pressure when
the weight is laid on the left than when it is laid on the symmetri-
cal place of the right side. The same amount of surface must be
covered, and the objects compared must have the same temperature,
in order to secure trustworthy results of experiment. Weber
found that, when the interval was fifteen to thirty seconds, under
the most favorable circumstances, 14|- could be distinguished from
15 grammes, or 14^ from 15 ounces. That is, some persons can
distinguish weights which differ as 29 : 30, by the sensations of
pressure they occasion, when laid on the volar side of the last
phalanges. By raising the weights the nicety of discrimination can
be increased so as to be represented by the proportion 39 : 40.
sation wliicli is caused by an increase of the stimulus = A2. Let (7 be a con-
slant dependent on tbe values chosen for ;!? and 2. Then AiS = -^. Let it
be further assumed that A/S remains constant whatever valiies for 8 and A2
are assumed; then dS = 0 -^, and by integration S=C log. 2, which is
Fechner's "fundamental formula." But if the stimulus is just belotcthe least
observable amount, and be = 2% then substituting in the above formula we
have 0 = C log. 2' ; from which Fechner derives formula No. 2 (the formula
of measurement), namely, 8 =^ C log. — , which means that the magnitude of
the sensation is " negative,^'' in case the stimulus sinks below the least observ-
able = 2'. If two sensations {8 and 8) are observably different, then 6' — 8'
= C (log. 2— log. 2') ; this is called the "formula of difference," and means
that the difference in the intensity of two sensations is proportional to the
logarithm of the quotient of the magnitudes of their stimuli.
368 THE LAW OF WEBER.
By an extended series of experiments with weights ranging from
300 to 3,000 grammes Fechner ' emploj^ed the method of correct
and mistaken cases to confirm Weber's law as applied to combined
sensations of pressure and of the muscular sense. Some experi-
ments were made with both hands ; others with the right or left
separately. The weight used to add or subtract was either 0.04 or
0.08 of the absolute weight. The results showed that the law held
only approximately for all the series of experiments, and not abso-
lutely for any one series. As calculated by G. E. Miiller ° they
give, instead of a constant quotient to express the degree of sensi-
tiveness (as Weber's law requires), a quotient varying from ^j-^vg- for
•weights of 300 grammes to ^^ for weights of 3,000 grammes. Nor
can Fechner's effort to correct the variation, by introducing after-
ward a conjectural allowance for the weight of the arm itself, be
considered successful.^ Biedermann and Lowit, by the method of
just observable differences, obtained results departing widely from
Weber's law.* By experimenting with weights varying from 10 to
500 grammes they found that the sensitiveness to pressure rose
with the increase of the weights from 10 to 400 grammes, and then
fell off rapidly, as the following table will show :
Quotient of sensitiveness.
.1.
2.9
-4^
The trustworthiness of these results is impaired, however, by the
fact that no method, except the doubtful one of directing "atten-
tion " exclusively to the sensations of pressure, was employed to
exclude the disturbing effect of the muscular sensations. The
same observers concluded, also, that the fineness of the muscular
sense, when isolated, does not vary according to Weber's law. They
fixed it at ^\ for weights of 250 grammes, j{j for weights of 2,500
grammes, -^^ for weights of 2,750 grammes.
That Weber's law does not hold good, near the lower limits, for
1 Elemente d. Psjcliopliysik, i,, p. 183 f.
^ Zixr Grundlegung d. Psychopliysik, p. 197.
^ In Sauhen d. Psychopliysik, p. 198.
* See Heriiig, Sitzgsber. d. Wiener Acad., LXXIL, Abth. iii., p. 343 f.
solute weight.
Least observable diflference.
Grammes.
Grammes.
10
0.7
50
1.7
100
2.4
200
3.6
300
46
400
5.2
450
6.5
500
25.5
QUANTITY OF TEMPERATURE-SEISrSATIOlSrS. 369
sensations of pressure, and of muscular innervation and movement,
is admitted by all. The absolute sensitiveness of these sensations
differs greatly, as has been shown (p. 346 f.), for different localities
on the surface of the body. Aubert and Kammler found the light-
est weight which produced a sensation of touch to be 0.002 gramme
on the forehead, temples, and dorsal side of the forearm and hands ;
0.003 gramme for the volar side of the forearm ; 0.005 gramme
for the nose, lips, chin, eyelids, and skin of abdomen ; 0.005-0.015
gramme for the volar side of the fingers ; and 1 gramme for the
fingernails and skin of the heel. This kind of sensitiveness has
been thought to be chiefly dependent upon the number of the
nervous elements present in the skin, its thickness, the character
of its tension over the underlying parts, etc. ; but its variations are
by no means parallel with those of the sharpness of the sense of
locality. The foregoing and similar conclusions all need to be re-
vised in the light of Goldscheider's determinations of the pressure-
spots.
§ 11. Extraordinary difficulties accompany the attempt to apply
Weber's law to sensations of temperature. As has alread}^ been seen
(p. 350 f.), we do not know exactly what to measure — whether the
rising and falling of the thermic apparatus, or its actual tempera-
ture in relation to its own zero-point ' — as constituting the quanti-
tative changes in the stimuli. Even Fechner admits that Weber's
law does not apply to the sensitiveness of the hand to changes in
temperature when it is itself cooling off; but he thinks the law
holds good approximately for degrees of warmth varying between
25° and 37.5° C. (77°-99.5° Fahr.), if 18.71° C. (65.66° Fahr.) be
taken as the zero-point. The assumption of this zero-point is,
however, arbitrary. No general rule for the quantity of sensations
of temperature can well be given except this : the akin is most
sensitive to changes which lie near its oion zero-point. In compar-
ing two temperatures it is most favorable to nice discrimination
that one should lie slightly above, the other slightly below, this
point. The degrees of the thermometer between which the maxi-
mum of sensitiveness is attainable are given differently by differ-
ent observers: By Nothnagel, 27^-33° C. (80.6°-91.4° Fahr.) ; by
Lindemann, 26°-39° C; by Alsberg, 35°-39° C; by Fechner, 12°-
25° C. — where it is so great as not to be easily measurable by a
good quicksilver thermometer (about \° Fahr.). Cold and heat alike,
when applied for some time, reduce greatly the sensitiveness of
the skin to minute changes of temperature ; by heat it can be so
dulled as not to distinguish alterations of less than ^° or f° Fahr.;
' So Heriug, see Hermann's Handb. d. Physiol., III., ii., p. 430.
24
370 THE LAW OF WEBER.
bj cold it can be rendered insensible to changes measuring from
2^ to 5i-=.
We have already seen (comp. p. 348 f.) that the sense of tempera-
ture depends for its fineness upon the extent and locality of the sur-
face excited. Weber found that water at 29^-° E., in which the
Avhole hand was immersed, seemed warmer than that at 32^ R., to a
single finger. Nothnagel placed the following values upon the fine-
ness of discrimination, for minute variations in temperature, of dif-
ferent parts of the body : Middle breast, 0.6° C; sides of the same,
0.4°; middle of the back, 1.2°; sides of the same, 0.9°; hollow of the
hand, 0.5°-0.4°; back of the same, 0.3°; partsof upper and lower arm,
0.2°; cheeks, 0.4°-0.2°; temples, 0.4°-0.3°. More recent investiga-
tions have shown that the table of sensitiveness for the different parts
of the body must take account of the division of the tempei'ature-
sense into two species, and of the locality of the heat-spots and
cold-spots in all such different parts. On the basis of experiment
with areas of the skin whose topography with respect to the tem-
perature-sense had previously been investigated, Goldscheider has
given a lengthy statement ' of the sensitiveness of different parts
of the body.
Thus he finds that the skin of the head is, in general, little
developed for the sense of cold, and only in a few places for the
sense of heat. The sensitiveness of the forehead to cold is intense,
but to heat only moderate ; that of the breast to cold moderate
along the sternum, and elsewhere very intense, while to heat it is
only moderate except near the uiiDj^les ; that of the back everywhere
very intense to cold, and only moderate to heat ; while in all parts
of the hand the intensity of sensitiveness to both cold and heat
is alike.
In general, the skin in the median line of the body seems much
less sensitive to changes in temperature than at its sides ; and the
number of thermic elements (according to Goldscheider, the dis-
tributory fibrils of the temperature-nerves), the thickness of the skin,
etc., are determining factors.
§ 12. The possibility of executing or appreciating a musical
passage in which the intensity of the successive notes is brought
to a certain standard of memory, or in which these notes are nicely
shaded so as to constitute a crescendo or a diminuendo, ajDpears to
depend upon appljdng to sensations of sound some law resembling
that of Weber. It is partly by comparing such sensations with
their images in memory that the singer or player reproduces certain
' See the Arcliiv f. Auat. u. Physiol., Physiolog. Abth., 1885, Supplement-
Band, pp. GO If.
MEASUREMENT OF SOUND. 371
notes previously executed, with about the same stress of tone.*
Moreover, in order to shade the relative intensities of successive
tones, our appreciation of their differences needs to be much greater
for those that have a low degree of intensity. Many obstacles,
however, stand in the way of determining either the lower limit
or the least observable difference for sensations of sound. The
general dif3S.culty which belongs to investigating the intensity of
sensations, even under the most favorable circumstances, is here
enhanced by the facts, that the pitch and timbre of each clang have
much to do with our judgment of its strength ; that different ears
differ so widely in their organic susceptibility, while the mind is
peculiarly sensitive to changes of feeling and judgment connect-
ed with sensations of sound, and thus very weak sensations are
vacillating and unsteady in consciousness, and sounds appear and
disappear in the ear while the degree of stimulus and of attention
are unchanged ; that the reflection and interference of the acoustic
nerves, their distance and direction, and the absence or presence of
" entotic " sounds, are so influential ; and, finally, that it is impossi-
ble to discover a sounding apparatus of definitely ascertainable and
uniform intensity of action.
§ 13. None of the means employed for determining the amount
of stimulus necessary to produce the weakest sensations of sound,
or the least observable differences in such sensations, are entirely
satisfactory. The method of listening to noises made by falling
weights is rendered uncertain by the fact that the character, both of
the weight an'd of the surface on which it strikes, has so much in-
fluence. Moreover, it is a matter of dispute whether the intensity
of the stimulus is to be measured by the product of the mass into
the height from which the body falls (m x h) or into the square-
root of that height (in x Vh). It is possible that neither of these
measurements is exact. ^ Assuming the former to be correct (noise
= m X h), by using a sound-pendulum A. W. Volkmann found that
differences in intensity are observable when they stand in the pro-
portion 3 : 4. Vierordt, on the other hand, concluded that the latter
measurement (noise =. m-^h) is more nearly correct; and by assum-
ing Vierordt's view, and using iron balls that fell vertically on a vi-
bx'ating plate, Norr ^ attempted to fix a unit of measurement. This
unit h& made = 1,500 milligramme-millimetres vsdth the ear distant
50 ctm. from the soiu'ce of the sound. Experimenting with sounds
' Comp. Stumpf, Tonpsychologie, I., p. 345 f.
''■ Comp. Wundt, Physiolog. Psycliologie, i., p. 341 and note ; and E. Tiscber,
in Philosophische Studien, I., heft 4, p. 543 f.
- Zeitschrift f. Biologic, 1879, XV., p. 297 f.
372 THE LAW OF WEBER.
ranging in intensity from those a little above the least observable to
those of unpleasant strength (1.71-524167.8 times the unit), and
dividing the entire scale into 7 groups, w^ithin each of which about
1,000 experiments were conducted, he found that the proportion of
right guesses to the entire number made ( — ) remained approxi-
mately constant — that is, that Weber's law holds for sounds of vary-
ing iutensit}'. A large allowance, however, had to be made for
relations of time ; the percentage of correct guesses being about 8.7
larger when the sound of greater intensity followed that of less
intensity.
More recently, E. Tischer ' has apjDarently added some evidence
to the validity of Weber's law by experimenting with an improved
form of the method of Vierordt and Norr. Keeping one of the two
sounds to be compared at a constant intensity, he increased or
diminished the other until from 4 to 6 successive correct guesses
as to their relative value were obtained. But the fact that, when
the second stimulus was diminished until certainty of judgment
was obtained, very considerable unexplained variations from the
results expected by Weber's law occurred leaves much doubt still
hanging over the matter. In order to harmonize the conflicting-
results, the proposal has been made to introduce another function
into the formula, noise = m h or my/h. All the investigations,
therefore, still leave the question of the applicability of Weber's
law to sensations of sound in a rather uncertain condition.
Little or nothing has been accomplished by expetiment to de-
termine whether the same law applies to the intensity of musical
tones. Among the various factors which enter into our judgment
of the intensity of tones, the " color-clang " is especially influential."
Absolute pitch and intervals of pitch are also very important. In
general, tones and noises of a higher pitch, with an equal objective
intensity of stimulus, are judged to be louder than those of a lower
pitch. Konig showed that a tuning-fork of the pitch c must have
about four times the amplitude of vibration required by one of the
pitch C, in order to produce upon the ear the same effect from the
same distance.
§ 14. The various attempts to determine the lower limit of sound
for the human ear have not resulted in any precise statement.
Schafhiiutl, after experiments in as near perfect stillness as possi-
ble, at midnight, fixed the limit at the noise made by a cork ball of
1 milUgrarame weight (about 0.0154 gr.) falling from a height of 1
' Wundt's Philosophisclie Studien, 1883, I., heft 4, pp. 495 fE.
'■'Comp. Stumpf, Toiipsychologie, I., p. 364 f.
LOWER LIMIT OF SOUND. 373
millimetre (0.03937 inch). Boltzmann and Topler have reached
results which Hensen' considers to be as accurate as possible. By
measuring the compression of the air at the end of an organ-pipe of
181 vibrations per second, they calculated that, even under circum-
stances not as favorable as possible, the ear responds with sensation
to an amphtude in the vibration of the molecules of the au' not more
than 0.00004 mm. at the ear, or about j\ the wave-length of green
light. The mechanical work done upon the ear-drum in a single
vibration of such small intensity is reckoned at not more than j^-g
billionth kilogrammetre ; or only about J^ of that done upon the
same surface of the pupils of the eye by a single candle at the
same distance. These calculations indicate that the motions in
the cochlea which excite the end-organs of sense are astonishingl}'
minute — far too minute to be observed even by the microscoioe.
Yet the sharpness of hearing maybe enormously increased by dis-
ease.
§ 15. Judgments of the intensity of sounds are dependent also
upon practice, and upon other psycho-physical conditions such as
determine the nicety of all judgments of quality. Small impres-
sions of noise are apt to have their intensity underestimated ; the
inclination to do this has been attributed to the influence of our
custom of withdrawing attention from them altogether under ordi-
nary circumstances.^ The fact that sounds to which we become
accustomed lose most of their intensity in consciousness must be
explained chiefly under the same law of mental habit ; it cannot, on
the other hand, be largely due to the physiological law of exhaus-
tion.
§ 16. Attention was early called to the law of judgment in esti-
mating the quantitative relations of sensations of sight, on account
of its connection with astronomical observation. In the preceding
century French physicists had already begun to investigate the
sensitiveness of the eye to varying intensities of light. Bouguer, in
answer to the question, What force must a light have in order to
make a more feeble one disappear? placed the fraction of least
observable difference in the intensities of two shadows at gJj. That
the magnitudes of the stars are not to be classified according to
their absolute brightness as determined by photometric observa-
tions was, of course, assumed by Sir John Herschel when he made
the latter vary in the series 1 : ^ : |- : J^, while the former vary in
the series 1:2:3:4. That the least observable difference in the
intensity of two sensations of sight is absolutely much smaller for
' See Hermann's Handb. d. Physiol.. III., ii , p. 117 f.
^ So Stumpf, Tonpsychologie, I., p. 388.
374 THE LAW OF WEBEE.
those of the lowest grade of intensity is a truth needed to explain
many every-day experiences. For example, the finer gradations of
shade in a lithograph or photograph are not lost when we take it
from the open sunlight into a rather dimly lighted room ; we can
also observe them through smoked glass, if it be not too black.
Through the same media we can measure rather delicate shades of
brightness on the clouds. We observe, however, that in all such
cases either too great or too weak intensity of the light destroys
our power to distinguish the finest gradations of its intensity.
§ 17. It has already been shown (p. 326) that the retina is never
free from light of its own which has a varying intensity ; this fact
greatlj' increases the difficulty of fixing accurately either the lower
limit or the least observable difference of visual sensations. lu the
effort to apply Weber's law to sensations of color, the laws of change
in the quality operate to obscure the laws of change in the quantity
of the sensations. Experiments with shadows for the sake of testing
Weber's law were first conducted by A. W. Volkmann and others,
under the direction of Fechuer.' By measuring the distance to
which a candle must be removed from an object in order that the
shadow produced by its light might disappear in that of another
candle of like intensity situated at a fixed near distance from the ob-
ject, the quotient for the least observable difference was found to be
y-J-y. This quotient was also found to remain nearly constant for
absolute intensities varying from 1 to 38.79. If, however, the light
of the background diminished to 0.36 in intensity, marked varia-
tions in the law occxuTed ; the difference in the brightness of the two
shadows had then to be greater than yj-o to be observable. Later
experiments of the same observer yielded results less favorable to
Weber's law.^ The quotient was found to vary from j^ for weak
intensities of light to j^^j for stronger intensities.
By using rotating disks and comparing the grayish circles made
upon them when revolving rapidly, through the admixture of small
black stripes with the white of their surfaces ("Masson's Disks"),
Helmholtz ^ found the medium value of the quotient of least observ-
able difference to be y^^ ; this quotient is not constant, however, and
increases, especially for sensations near the upper or the lower limit.
By changing the method somewhat, Aubert obtained a variation
of yJ-^ to yI-o i^ the degree of sensitiveness to differences in the
brightness of lights, even when not going above the middle of the
scale of intensity. Experiments with such intensities as lie nearest
' See Elemente d. Psychophysik, p. 148 f.
* A. W. Volkmann, Physiolog. Untersuchungen, I., p. 56 f.
^ Physiologisclie Optik, p. 315 f.
INTEXSITT OF COLOK-TOXES. 375
the limits showed much greater dej^artures from Weber's law. Just
above the lower limit, au addition of even :^ to ^ to the stimulus
might be necessary in order to produce an observable difference
in the resulting sensation. Similar results have been obtained by
Delboeuf, but, on the whole, more favorable to Weber's law than
the results of Aubert.
A more accurate and carefully guarded series of experiments
than any of the foregoing is recently reported by Dr. Emil Kj-ae-
pelin.' This experimenter used the method of just observable dif-
ferences as applied to Masson's disks when looked at through gxay
glasses of varying intensity. The utmost care seems to have been
taken to exclude disturbances from changes iu the adjustment of
the eye, retinal exhaustion, reflection of light from surrounding-
objects, etc. Three groups of experiments were conducted — one
by daylight, one by candlelight, one by lamplight. Both eyes
were experimented upon ; and both directions of alteration in the
intensity of the stimulus (stronger following weaker, and vice versa)
were employed. Kraepelin concludes that for the unexhausted eye,
with a good power of accommodation, the fraction which gives the
least obseiwable difference remains constant, while the intensity of
the light varies between values of 1,000 and 9.61 of absolute inten-
sity as fixed for his experiments. That is, within these limits the
law of Weber holds good as expressing with closely approximating
accuracy the results of experiment.
The experiments of Dobrowolsky ^ and Lamansky ^ with light of
the different spectral color-tones shows that, with these sensations
also, Weber's law holds approximately good for moderate intensi-
ties, but is subject to considerable variations a3 we approach the
upper and the lower limits. The former used the method of com-
paring a white surface with one in which colored light had been
mixed with the white. On changing the absolute intensity of the
light between values of 1 and 0.0302, only a slight variation in the
quotient indicating the least observable difference of intensity ap-
peared for the color red. This quotient was found, by the same
observer,^ however, to be very different for different color-tones : thus
for red, -^^j ; yellow, J^- ; green, -^^ ; blue, y^^ ; violet, j^. Laman-
sky and others have made the sensitiveness to changes in the inten-
sity of color-tones greatest for green instead of violet ; and have ob-
tained other results different from those obtained by Dobrowolsky.
§ 18. The minimum of the intensity of light ajDpreciable by the
1 In Wundt's Philosopliisclie Studien, 1884, II., lieft 2, pp. 306 ff.
^ Pfluger"s Arcliiv. xii . p. 441 f.
3 Arcliiv f. Ophthalmologie, XVII., i., p. 123 f. ■* Ibid., XVIII., i., p. 74 f.
376 THE LAW OF WEBER.
eve under the most favorable circumstances was fixed by Aubert at
^^ of that reflected from white paper in the light of the full-moon.
This result can only be considered as approximate. The individ-
ual factor in all such calculations must be held to be very large and
variable ; especially, perhaps, if we admit that there is a class of
so-called " sensitives " to whom the ends of an electro-magnet
when excited appear luminous, as Eeichenbach's experiments seem
to show. Weber applied his own law to so-called extensive sensa-
tions of sight. He showed that in judging of the comparative
length of lines the least observable difference is, for each person, a
tolerably constant fraction of the absolute length of the line with
which the comparison is made. This fraction is different for differ-
ent persons ; and has a range from J-^ to j^. Fechner ' defends
the validity of the law for lines of lengths varying between 10 and
240 mm. (| to 9^ in.), with the eye removed from 1 ft. to 800 mm.
(12-32 in.). The lower limit for such cases has been fixed by A. W.
Volkmann at lines of length from 0.2 to 3.6 mm. It is obvious,
however, that we are here not dealing with pure quantity of visual
sensations, but with judgments of local relation which, in case the
eyes are moved, have their basis, at least partly, in our power to dis-
criminate minute differences in the sensations of the muscular* sense
connected with such movements.
§ 19. The law of Weber can, of course, derive little or no sup-
port from sensations of taste and smell. In the case of these two
senses our knowledge of both series of quantities — of the intensity
of the stimulus and of the amount of specific sensation which re-
sults from its application — is altogether too inadequate to admit
of trustworthy comparison. We cannot measure forms of energy
like those by which smellable particles and tastable solutions act
on the end-organs of sense, until we have a unit of measurement and
some information as to what the object is to which the standard
should be applied. Nor can we compare amounts of sensations
that are so largely matters of indiridual origin and capricious
change, and that are so overlaid with other forms of feeling, as are
the sensations of these senses. Moreover, the element of time — both
as respects the interval elapsing between the two sensations com-
pared and also the order in which the sensations follow each other
— is here a very important influence.
The irdensl.ty of taste depends upon a variety of circumstances
besides the objective quantity of the stimulus. Among these cir-
cumstances is the extent of surface excited. Camerer ^ found by
' Elemente d. Psychophysik, i , p 211 f.
- See Zeitschr. f. Biologie, 1870, VI., p. 440 f.
MEASUREMENT OF TASTE. 377
experimenting with common salt in solutions of different degrees
of concentration that the number of correct guesses inci-eased almost
in exact proportion to the number of gustatory papillse upon which
the solutions were placed. Certain mechanical and thermic con-
ditions also have a great influence. Substances even in fluid form,
when quickly swallowed, have little taste ; pressing and rubbing
against the gustatory organs, movement of the tastable matter in
the mouth, increase the excitatory effect of the stimuli. It is
doubtful whether this effect is due solely to the mechanical result
of spreading the stimulus over the surface and urging it into the
pores against the end-orgaus of the sense, or in part also to some
direct physiological cause. The influence of temperature on the
intensity of sensations of taste is well known. Weber showed that
if the tongue is held for |- to 1 minute in very cold water, or in wa-
ter of about 125° Fahr., the sweet taste of sugar can no longer
be perceived. Cold also destroys for a time the susceptibility to
bitter tastes. Keppler '• endeavored to test Weber's law by deter-
mining the sensitiveness to minute changes in the four principal
kinds of taste ; and arrived at a negative result. Fechner, how-
ever, considers that Keppler's experiments with common salt confirm
Weber's law, and that his other experiments were not adapted to
yield any assured result. We can only repeat the statement that
other causes than mere increase in the quantity of the stimulus so
largely determine the intensity of the resulting sensations as to
discredit any arguments from the experiments either for or against
applying Weber's law to sensations of taste.
§ 20. The exj)eriments of Valentin' and others, to determine how
weak solutions of various substances will excite the end-organs of
taste, are chiefly valuable as gratifying our curiosity. The figures
are not to be accepted as exact, but as showing in general the ex-
treme fineness of this sense, and the great difference of different
substances in their power to excite it. Valentin found, for exam-
ple, that 0.24 gramme of a solution containing 1.2 per cent, of cane-
sugar excited the sensation of sweet ; a solution containing j|-g-
part of common salt was scarcely detectable ; of sulphuric acid
To oVo'o' could be discerned, yro ottotf ^°^ '■> extract of aloes contain-
i^^o g'o oVTro could be distinguished from distilled water ; -33^0
of sulphate of quinine was plainly observable, and the observer
thought he could detect a slight trace of bitter when the solution
was diluted to foTr^oin) o^ ^^i^ substance. In general, a smaller
absolute quantity of stimulus, when in a relatively concentrated
' Pfluger's Archiv, 1869, ii., p. 449 f.
"^ In his Lehrb. d. Physiol, d. Menscheu, 2 ed., Abth. 2.
378 THE LAW OF WEBER.
solution, will suffice to excite tlie end-organs of taste.' It will
readily be seen that the minimum of some of these substances
which will give rise to a sensation under the most favorable cir-
cumstances is exceedingly small.
§ 21. The intensity of sensations of smell is also largely depend-
ent on other causes than changes in the quantity of the stimuli.
The amount of sensation appears to be largely governed by the
extent of surface excited ; since it is greater when we smell with
both nostrils, and with the current of inspiration which carries the
exciting particles over more of the sensitive membrane. No as-
siu'ed results on this point, however, have yet been reached. Val-
entin supposes that a smaller number of odorous particles will
excite sensation if presented in a concentrated rather than a dilute
form. When the intensity of the stimulus increases beyond a cer-
tain point, the character of the resulting sensation changes — often-
times from a pleasant to an unpleasant tone of feeling. All are
familiar with the fact that a large increase of some smells — for
example, musk — does not give the same kind of sensation. This
sense has a great degree of "sharpness," or power to be excited
by small quantities of stimulus, as distinguished from "fineness,"
or power to distinguish minute variations in the sensations. It is
undoubtedly different in different species of animals, as dependent
upon unknown differences in their psycho-physical constitution ;
but it is tolerably uniform among men where there is the same
cultivation of it, and the same concentration of attention. It is
well known that certain animals have an astonishing fineness of
smell, and are able by it even to detect the individual variations
that are quite imperceptible to man. Little value can be attached
to the results reached by experiments to fix the least number of
smellable substances which can excite the human end-organs of
this sense. In general, we can say that incredibly small quanti-
ties of some substances will suffice. Valentin found that a curx'ent
of air containing -g-oiiVoTr of vapor of bromine excited a strong un-
pleasant sensation. Atmosphere polluted with even jYiyl-u-o-Tr ^^
sulphuretted hydrogen could be detected. It was calculated by
this observer that -jo"o J-oo u "^^ ^ milligramme of alcoholic extract of
musk is about as little as can be perceived. The effect of constant
over-excitement of the organs of this sense, in deadening their sen-
sibility, is too well known to require illustration. No argument
for or against Weber's law can safely be drawn from sensations of
smell.
§ 22. A review of the preceding facts confirms what was previ-
' See Camerer's table in Pflijger's Archiv, ii. , p. 322.
INTEllPEETATION OF THE LAW. 379
ously said as to the unsatisfactory nature of tlie evidence adduced
in proof of the principle which is thought to control the quantita-
tive relations of our sensations and their stimuli. At best, Weber's
law is only an approximately correct statement of what holds true
of the relative intensity of certain sensations of sight and hearing,
and, less exactly, of pressure and the muscular sense, when these
sensations are of moderate strength, and other causes for variations
in their intensity, besides objective changes in the amount of the
stimulus, are as far as possible excluded. In general, it is true that
the amount of matter pressing on the skin, or lifted by moving the
arm or leg, as well as the intensity of the waves of light and sound
acting on eye and ear, must increase much more rapidly than does
the intensity of the resulting sensations, as estimated by comparing
them with each other in consciousness. Within certain limits for
the above-mentioned four kinds of sensation, the latter scale of
quantities is ordinarily related to the former about as an arithmet-
ical to a geometrical series. But other conditions than mere increase
in the objective quantity of the stimulus largely determine its
effect upon the resulting amount of sensation. Stimuli and sensa-
tions are not connected quantitatively in such a simple manner that we
can measure one off in terms of the otJier ; so much feeling for so
much amplitude of wave-lengths, or work done on the end-organs
by mechanical pressure. Numerous factors, some of which are
individual and extremely obscure and variable, constantly mix
with the piu'ely quantitative relations between sensations and their
stimuli.
§ 23. The value of Weber's law is so restricted, even as stating
a general fact of expeiience, that it would seem scarcely necessary
to discuss at length its higher significance. Three possible modes
of explanation have all had their defenders ; these are the physio-
logical, the psycho-j^hysical, and the psychological. The first of
the three assumes that the physical construction of the nervous
sj^stem, including chiefly the end-organs of sense and their central
representatives and connections, is such as to supply the reason
for this relation between the intensity of sensations and that of
their stimuli. And certainly, if we were to make any assumption,
it would be that the quantitative relation between the last ante-
cedent molecular changes in the brain and the mental changes to
which they give rise, is one of simple proportion ; the more work
done by means of the excitation in the appropriate cerebral centres,
the more of physical basis laid, as it were, for a resulting quantity
of psychical movement.
If, then, the sensations vary in quantity in an arithmetical pro-
380 THE LAW OF WEBER.
portion, wliile their external stimuli vary in a geometrical propor-
tion, the explanation of the fact must be found somewhere in the
chain of events between the external stimuli and the nerve-commo-
tions set up as a result in the appropriate centres of the brain. And
without doubt the explanation of so much as is true of Weber's law
lies largely in physiological causes ; but our knowledge of the struct-
ure and function of the end-organs of sense, and especially of their
cerebral representative elements, is so incomplete that no satisfac-
tory statements can be made on this point. In all of the senses, the
end-organs profoundly modify the intensity of the stimulus they re-
ceive. In the so-called chemical senses (smell, taste, sight) a pro-
found quantitative modification takes place, even before the stimu-
lus reaches the fibrils of the sensory nerve. In the case of the
mechanical sense of hearing we cannot say how naucli of the efifect
stated in Weber's law may not have been gained even before the
acoustic waves set agoing the nervous elements of the organ of
Corti. As to profounder modifications in the same direction by
reason of the interaction of different nerve-elements in the brain we
are yet more ignorant. And although we can have little confidence
in Wundt's ' theory of an " apperception-centre " and its influence
in accounting for Weber's law, we cannot deny the general assump-
tion on which that theory is based.
Tlie psycho -physical explanation of Weber's law is that adopted
by Fechuer. This explanation insists upon making the law one of
the utmost generality and of the highest import as stating the re-
lations between organic and spiritual activities. Although Fech-
ner's view confessedly grew out of his speculation that body and
mind are only two phenomenal aspects, as it were, of one and the
same underlying reality,^ it has been defended by him with a great
amount of mathematical science and experimental research. No
other form of explanation, howevei', takes us so much into the
regions of utter obscurity. Why the quantitative relations of body
and mind should be such, and such only, that a geometrical series
of changes in the one should invariably be represented by an arith-
metical series of changes in the other, must indeed remain an ulti-
mate mystery. And the experimental proof of Weber's law is as
yet much too incomplete to make us ready to accept it as an ulti-
mate psycho-physical principle.
The psychological explanation of Weber's law resolves it into a
special case under the greater law of the relativity of our inner
* Comp. his Physiol. Psychologie, i. , p 351 f . , and ii. , p. 207 f . ; also
Philosophische Studien, 1883, II., heft 1, p. 31 f.
' Id proof, see his Revision d. Hauptpuncte d. Psychophysik, p. 13 f.
THE LAW OF EELATIVITT. 381
states. It is not so much, then, a law of the absokite quantity of
sensations as dependent on stimuli, but rather a law of our ap-
prehension in consciousness of the relation of our own feelings. In
general, it may be said that every mental state has its value de-
tfrmined, both as respects its quahty and its so-called quantity, by
its relation to other states. It is the amount of change rather than
the absolute amount of feeling which the mental apperception esti-
mates. That the psychological explanation is needed to account
for the facts there can be no doubt when we consider how impor-
tant are the elements of attention, mental habit, power of acute
discrimination, etc., in determining our estimates of the quanti-
tative relations of our sensations. Estimates — that is, acts of the
comparing judgment, are involved in the experience upon which
reliance is placed for a demonstration of Weber's law. Further
discussion of the significance and extent in application of the men-
tal law of relativity will appear in other connections. The subject
of the quantity of sensation as a matter of psycho-physical investi-
gation is fitly closed with the following quotation from Wundt : '
"In the imperfect condition of cerebral physiology, we are not
seldom in a position to recognize the psychological formulating of
certain laws, the physiological meaning of which still lies in ob-
scurity or belongs to the domain of hypothesis."
1 Physiol. Psychologie, i., p. 353.
CHAPTER VI.
THE PEESENTATIONS OF SENSE.
§ 1. Sensations are, primarily consiclerecl, modes of our being
affected ; but the objects of sense are known as real beings, which
are assumed to exist independent of the affections of our minds,
and to have their inherent quahties disclosed to us through the
operation of the senses. There is a wide interval," however, between
our consciousness of being ourselves affected and the perception
of " things " as having qualities resembling our mental states or re-
vealed by them. This interval is filled, in nature, by the develop-
ment of mind as conditioned upon its environment of sense-stimuli;
it must be filled in psychological theory, by a description of the
process of development. Physiological Psychology constructs such
theory as much as possible on a basis of experiment to determine
how the various steps in the mental development are related to the
changes which the stimuli jDroduce in the nervous system, espe-
cially, of course, in the organs of sense. Upon this work of con-
struction it has expended its choicest resources and utmost ingenu-
ity. Its efforts are yet far from being completely successful. Many
of the secondary jDrinciples, and even questions of fact, are still un-
settled ; no theor}' of perception that will account satisfactorily for
all the admitted truths has hitherto been discovered. Nor is this
lack of complete success surprising, when we consider how rapid
and complex are the processes which combine to form the world of
sensible objects ; as well as how entire is the loss suffered by memory
and consciousness of those details which served as a basis for the
earlier and most significant stages of the development.
Nor should we fail to take account of the fact that the mechan-
ism of both nervous system and mind operates as rendered native
to the individual by his inheriting the results of many ages of an-
cestral experience. The psychologist does not remember by what
stages he first learned to see or feel the extended and external ob-
jects of sense. The child cannot describe the process to the psy-
chologist ; the child is farther from his own infantile experience in
this regard than the philosopher is from that of the child. It is
eOMMOW-SEFSE VIEW OF PERCEPTIOlSr. 383
not even likely that, if the infant were endowed with the developed
power of searching his own consciousness, and of describing its
contents, he could discover and impart what is needed in order to
explain the process of his own mental development. In all stages
of human growth the analyzable contents of consciousness represent
only very imperfectly the nature of the basis upon which they rest.
§ 2. Scientific analysis of the process of perception corrects in
many particulars the so-called "common-sense" view. The convic-
tion which everyone has on opening the eyes upon a landscape, for
example, is undoubtedly that of being immediately impressed with
a faithful copy of extra-mental reahty. Some of the objects are seen
as larger, others smaller, some in the foreground near by, and others
more remote ; but all have that solid, substantial character which
makes them things as distinguished from the images of revery or
dreaming. But it is precisely the acquired power thus to construct
the landscape which psychological science tries to explain. The ordi-
nary conviction accepts the aj^parent fact of an immediate and certain
knowledge of these things through the eyes, as though it were matter-
of-course and needed no explanation. We must begin by removing
certain assumptions obviously involved in the ordinary conviction.
The forms of being and happening in the world, outside of the
body, furnish in themselves no explanation whatever of the presen-
tations of sense. ' This is as true of the colored or smooth extension
of an object as it is of its sweet taste or disagreeable smell. "What-
ever exists (?.x^ra-mentally, so far as its pure existence goes, is of no
account to the mind. It is only as so-called "things " act upon us,
or — in other words — get themselves exjjressed within the mind, by
causing changes in our mental states, that any theory of knowledge
by the senses can make use of them. Centuries ago the popular
feeling was framed into a doctrine that semi-spiritualized copies
of the material realities enter the body through the senses and meet
the mind somewhere within ; or, that the mind itself, passing out
through the openings of sense in semi-materialized form, embraces
and so knows these realities. The time for all similar crude theo-
ries of knowledge by the senses ought, however, to have long gone
by. And yet fragments or suggestions of essentially the same
assumptions are still frequent enough.
What is true of all that exists and happens outside of the body
is just as true of all the bodily conditions and processes. Strictly
speaking, they can in themselves furnish no explanation for the rise
and development of the presentations of sense. Only mental factors
' Comp. Volkmann von Volkmar, Lehrbucli d. Psycliologie, Cothen, 1885,
II.. p. 1 f . ; and Lotze, Medicinische Psycliologie, Leipzig, 1852, p. 325 f.
384 THE SYNTHESIS OF SENSATIO]S"S.
can be built into mental products. The simple sensations are in
themselves always psychical phenomena, and are to be referred, as
modes of its being and action, to the subject called " mind." It is
only when considered in this way that they afford, by their charac-
teristic qualities and modes of combination, any explanation of the
resulting knowledge of things. The image on the retina, for exam-
ple, is a necessary jDhysieal condition of the clear vision of outside
objects ; it may also become an object for the inspection of another
observer. But the retinal image never becomes a kind of inner
object for one's own brain or mind. Nothing in its construction,
in itself considered — that is, as independent of the system of local-
ized sensations which result on the other or psychical side of the
transaction — helps to explain the act of vision. What is true of the
peripheral is also true of the central organs of sense. There is no
image in the brain transmitted in exact copy from the retina by
the optic nerve to its central nerve-fibres and nerve-cells ; if there
were such a brain-image, we should need another eye connected
with a second brain and mind to read it. The mind is never to be
conceived of as contemplating a spatial picture of its object formed
somewhere within the cerebral substance.
Even more obvious is the worthlessness, for purposes of strictly
psychological analysis, of all theory as to the precise spatial arrange-
ment of the fibrils of sensory nerves within the shin or muscular
fibre. That such fibrils exist in the muscles has apparently been de-
monstrated by Sachs and others (comp. Chap. IV., § 20) ; the nervous
impulses occasioned in them, when conveyed to the central organs,
are probably one main physical basis of those feelings of innerva-
tion, of being in the body, etc., which enter as essential factors into
the spatial perception -field of our own periphery.' But it is the
muscular sensations, as modes of the affection of mind, which per-
form this ofl&ce. We have nothing approaching an immediate cog-
nition of the extended net-work of sensory fibrils in the skin or
muscles ; much less of the extended muscle or area of the skin.
No copy in space-form of the various simultaneous or successive
rubbings and stretchings of these peripheral fibrils is propagated
to the brain ; and if it were, the mind could not be regarded as
taking account of any of these neural processes.
A fui'ther negative statement may be made wdth entire confidence.
The place at which each organ of sense is found in the periphery of
the body, or the place at which any such organ is acted on by the
stimulus, cannot of itself furnish a reason for the spatial perception
of such place and for distinguishing it from other places near or
' See an article in Mind, by G. Stanley Hall, III. (1878), pp. 433 ff.
TOUCHING AND BEING TOUCHED. 401
tions are localized ; we see some of the same parts as projected in
space before our eyes. Objects that are not a part of ourselves are
given to us as projected eccentrically, either by touch through their
being in contact vpith the skin and occasioning sensations of mus-
cular exertion, or by sight as having distance in its field of vision.
Localization and projection are not to be regarded as two phases of
one and the same process ; we do not first have the presentations
of sense as parts of the periphery of our bodies, and then, on further
experience, push them beyond this perij)hery, either to an infini-
tesimal distance or to one remote. Localization and eccentric pro-
jection are rather two processes, largely unlike, which go on con-
temjDoraneously and are set up chiefly on the basis of different
classes of sensations.
Where two j)arts of the sensitive skin of our own bodies come
together the conditions for both of the above-mentioned processes
are fulfilled. Accoi-dingly, one part has localized in it those com-
plex sensations which make us aware that this joart of our body is
touching something ; the other has localized in it those sensations
which make us aware that this part is being touched by something.
Which of the two j)arts shall be regarded as touching, and which as
being touched, depends on various considerations. Those mem-
bers of the body which are most used in active touch are generally
known as touching, and the less active parts as being touched. For
example, if with closed eyes the forehead be moved across the sta-
tionary tip of a finger, the latter will appear to be the active organ
of touch. Comparatively insensitive areas of the skin are less likely
to be presented to the mind as touching other more sensitive parts ;
callous spots, indurated surfaces, etc., seem, as a rule, to be touched.
Parts of the body which lose all sensitiveness come to be regarded
as external things. If the tip of a finger of normal sensitiveness be
brought into contact with the callous tip of the corresponding fin-
ger of the other hand, the former will be known as touching and
the latter as being touched. The direction of attention often deter-
mines the strife, as it were, between the motifs to localization and
those to eccentric projection. We ordinarily strive to gain knowl-
edge of the qualities of some outside object, rather than of the con-
dition of our own peripher}^ with respect to the sensations localized
in it ; the attention is therefore directed to those series of sensations
which form the basis of eccentric projection, even when some part
of our own sensitive organism is the object known. But sensations
which ai'e accompanied by obtrusive feeling of some kind furnish
superior grounds for localization. We locate pains, pricks, severe
pressure, sensations of creeping, and tickling, in the body. Li gen-
26
402 PEECEPTIONS OF THE LOWER SENSES.
eral, then, a strong tone of feeling with the sensation favors the
process of localizing ; tonelessness of sensation favors the jDrocess
of objectifying.'
A system of localized sensations, gained chiefly by pressure of
the skin and muscles, and accompanied by a strong tone of feeling,
gives us the primary field of the body as known to touch. Certain
points of starting, as it were, must first be fixed in the process of
localizing ; this process then goes on by relating all other localized
sensations to these points of starting. But by eccentric projection,
the system of muscular sensations of movement and the system of
visual sensations are combined to develoj) our perceptions of ob-
jective space ■with its three dimensions. The sensations of touch
are subsequently projected into a space thus originally constituted
by combined muscular sensations and visual sensations. The eye
and hand in motion, therefore, project their extended objects into
a space which they develop themselves ; while the ear and the nose
project their perceptions into a space which they are compelled to
assume on the authority of the other senses.
The foregoing principles must now be illustrated and confirmed
by a brief statement of facts which relate to the formation and de-
velopment of presentations of sense by a synthesis of simple sen-
sations. Attention will, for obvious reasons, be directed almost
exclusively to those presentations of sense which come through the
eye and skin, including in both the influence of muscular sensa-
tions.
§ 17. Perceptions of Smell differ only in fineness, duration, and ac-
companying tone of feeling ; they have no size or shape, no spatial
properties of any kind. They cannot even be said to be localized.
Fineness of smell, or power to make minute distinctions in quality,
and so infer the presence or direction of an object previously known
to excite such quality of sensations, diffei'S greatly in different spe-
cies of animals and in different individuals of the same species.
The exploits of some animals give ground for the conjecture that
every species, and even every individual, has an odor of its own.'^
The direction and nature of the object which causes the sensations
are judged by variations of intensity on turning the head, or on
approaching or receding from the object. Sensations of smell are
known to come through the nose, by localizing there the accom-
' Compare Volkmann von Volkmar, Lehrbucli der Psycliologie, II., p.
12G f.
- See the articles of Donhoff, in Archiv f. Anat., Physiol., etc., Physiolog.
Abth , p. 750 f. (1874) ; and Jiiger, in Zeitschr. f. wissensch. Zool., xxvii., p.
319 f. (1876).
TASTE AND HEAEING. 403
panying muscular and tactual sensations with their strong tone of
feeling. This is readily done, since we draw the air through the
nostrils and feel its double effects in producing the two classes of
sensations. As to the simultaneous influence of two smells, little
is known beyond the statement of Valentin, that the stronger
overwhelms the weaker. The power of discrimination may, of
course, be cultivated in this sense as in every other.'
§ 18. Most of the remarks just made as to perceptions of smell
apply also to Perceptions of Taste. Sensations of taste, however, are
much more closely connected with those of touch ; since the tongue
is a chief organ of active touch. It is the tactual and muscular
sensations, and not the purely qualitative affections of taste, which
are localized in the mouth. Concerning contrast and comjDensation
of tastes, little is known which does not belong to ordinary experi-
ence. Valentin " alleges that when a sour mass is laid on one half,
and a bitter mass on the other half, of the root of the tongue, the
predominating taste may sometimes be determined by our choice.
It is well known that certain tastes compensate each other, as it
were, in experience, without any chemical equivalence of their prop-
erties. The sugar neutralizes the acid of the lemonade, not in the
vessel that contains the mixture, but in the nervous system of him
who drinks it Brilcke holds ^ that the neutralizing of one sensa-
tion of taste by the other takes place in the brain. The sensation
of bitter is es^Decially difficult to cover or neutralize.
§19. Perceptions of Hearing n&x.i demand consideration. More
difficulty accompanies the effort to establish the proposition that
sensations of sound are not directly localized, but are projected
in a space constituted chiefly by the eye and the hand, through
complicated indirect inferences. Such a proposition is, however,
undoubtedly true. The locahzing of the area of the body which
serves as the organ of the sensations of sound, the knowledge that
we hear loith the ear, is accomplished chiefly through those sen-
sations of shock to the muscles and skin of the region which come
from loud and massive or piercing sounds. Sensations of sound
originating through excitement within or very near to the ear itself
are called "entotic." A great part of such sounds, if not all of them,
are transmitted through the tympanum. Perceptions combined of
such sensations may be located either within the ear or at some dis-
' On the whole subject see von Vintschgau' s monograph, in Hermann, Handb.
d. Physiol., III., ii., pp. 225 ff.
^ Lehrbuch der Physiol, d. Menschen, etc., Abth. ii., p. 308 (second edi-
tion).
^ Vorlesungen liber Physiol, (ed. 1884), ii. , p. 262.
404 PERCEPTIOiSrS OF THE LOWER SEN"SES.
tance from the bod}', according to previous associations and oppor-
tunities for judgment. The sound produced by the vibration of the
adjoining muscles, and heard as a low musical tone when the fin-
gers are pressed in the ears (especially if the teeth are tightly set
together), is located in the head by the help of its accompanying
sensations of other kinds. The same thing is true of the crackling
noise sometimes produced by yawning, or of the whirring occasioned
by the passing of the blood through the neighboring large blood-
vessels. In the same way we learn to hear the beating of our own
hearts, or the noise of air in our respiration. But the click of the
valves of the internal organ may, when experience gained through
tactual and muscular sensation fails us, be located in the watch
under our pillow; just as the singing or ringing "in the ears"
produced by quinine, or cerebral excitement otherwise occasioned,
may be located in a cricket supposed to be upon the sill of the open
window. Li certain pathological cases the power to distinguish
between entotic sounds and those having an external origin is al-
most wholly lost.
§ 20. We can orientate ourselves in space with reference to ex-
ternal sounds with great speed and considerable precision, but as
an acquired art difFering in different individuals and dependent
upon attention and previous experience. E. H. Weber thought
that we tell the direction of sounds by the help of the feeling of
the swing of the ear-drum ; and instanced, in proof, that this
eccentric projection is hindered by filling the external passage
of the ear with water. When using both ears and moving the
head freely in space, we undoubtedly determine the direction of
sounds by differences in the intensity of the sensation dependent
upon changes in the relative position of both ears. Kayleigh '
found that, in a quiet place under favorable circumstances, the
direction of a word or letter uttered in a natural voice could be
given with considerable accuracy ; that of a musical tone much
less accurately. The direction of a sound from a tuning-fork
could not be given when it was held either behind or before, but
could be given if the fork was held to the right or to the left. It
is said that the conducting of an intermitting cui'rent from a tele-
phone through both ears causes a perception of tone localized in the
median plane of the head.
Such facts as the foregoing introduce us to the theory of "acous-
tic shadows," or of the amount of "covering" power which the
sound produced by the waves of a given intensity entering one
ear would have upon the sound produced by waves of a difterent
'Nature, XIV., p. 33.
THE EXPERIMENTS OF WEBER. 405
intensity entering the other ear. It does not appear to Hensen/
however, that the prompt and accurate locahzation of direction
possible to some ears can be wholly accounted for by the theory of
acoustic shadows. Some other form of feeling, possibly connected
with the remarkable arrangement of the semicircular canals, may
blend with the estimate of differences in intensity to form a basis for
judgment. Von Kries and Auerbach found that the promptness
with which the direction of the noise from an electric spark can be
localized depends upon its relation to the circuit of the head.^
Our perceptions of the absolute distance of sounding objects are
entirely dependent upon our knowledge of the quality and quantity
of the sounds ordinarily proceeding from them ; they are, that is
to say, not presentations of sense, but indirect estimates as to the
objective cause of the sensations immediately experienced. It has
been claimed that a change in the relation of the partial tones to
the fundamental tone, dependent upon the remoteness of the place
of origin of the compound clang, aids our estimate of distance by
sound.
§ 21. An account of the process by which a Field of Touch is con-
structed, and extended objects are known as in contact with the
skin at definite points or areas of it, must begin by enumerating the
data which the mind has for such activity. The most important of
these data are indicated by certain facts as to the fineness of the
so-called " sense of locality " belonging to the skin. E. H. Weber
first estabhshed a rule for measuring the degree of this fineness ac-
curately ; he also mapped out the entire field of the surface of the
body into areas differing greatly in their fineness.^ For a measur-
ing instrument he used the two points of a pair of dividers, blunted
so as to prevent the sensation of being pricked ; the princijDle of
measurement was that the minimum distance apart at which the
two points, when touching the skin of any region, are felt as two local-
ized sensations is the measure of the sensitiveness to local distinction
of that region. The following table gives some of the results of
Weber's experiments ; the figures indicate the number of milli-
meters ■" apart which the points of the dividers were when the given
area of the organ was just able to distinguish them :
' In Hermann's Handb. d. Physiol., III., ii., p. 136.
2 Archiv f. Anat. u. Physiol., Physiolog. Abth , 1877, p. 331 f.
^ Annot. Anatom., vii., p. 4 f. ; Wagner's Handworterb. d. Physiol., HI.,
Abth. ii. , p. 529 f .
^ The numbers were given by Weber in Parisian lines ; in the table they are
taken from Wundt, Physiolog. Psychologie, ii., p. 7, who has reduced them to
even millimeters.
406 THE FIELD OF TOUCH.
Tip of the tongue ■ 1
Volar side of the last phalanx of the finger 2
Red part of the lips 5
Volar side of the second and dorsal side of the third phalanx of the finger . 7
White of the lips, and metacarpus of the thumb 9
Cheek, and plantar side of the last phalanx of the great-toe 11
Dorsal side of the first phalanx of the finger 16
Skin on the back part of cheek-bone, and forehead 23
Back of the hand 31
Knee-pan, and surrounding region 86
Forearm, lower leg, back of the foot near the toes 40
Skin of the nape, and of the back in the five upper cervical vertebrae 54
Skin of the middle of the back, and of the upper arm and leg 68
"Weber also found that the fineness of the sense of loeaHty is
greater in a transverse than in a longitudinal direction, on both arms
and legs. On these surfaces of the skin the " sensation-circles," or
areas within which the minimum distances of the dividers' points
are felt as two points, have an elliptical shape, with their long axes
up and down. That the size of the sensation-circles, or the fineness
of the sense of locality, largely forms the basis for our judgments
of the position, number, and magnitude of the localized sensations
in the field of touch may be shown by a simple experiment. If
the points of the dividers be separated somewhat less than is neces-
sary in order to distinguish them as two on the cheek just in front
of the ear, and then (the distance apart of the points remaining un-
changed) be slowly moved until one point rests upon the upper and
the other upon the lower lip, to a person blindfold, and unpreju-
diced by knowing what is to take place, the point first felt as one
will appear to become two, and then the two recede from each
other continually as the parts with a finer sense of locality are trav-
ersed. The same experiment may be tried upon any other part
of the body. It appears, therefore, that the mental rejDresentation
of the magnitude of the distance between two impressions varies in
inverse proportion to the real magnitude of the smallest perceiv-
able distance, on any given area of the skin. The same principle
holds good when all the space between the impressions is filled up,
as it were, so as to make a continuum of localized sensations. Thus
Weber found that the circular form of a tube of only 1^ Parisian
line in diameter could be recognized by pressure on the tip of the
tongue ; while on the skin of the abdomen the diameter of the tube
must x'each 3f inch before its form was recognizable. Our estimate
of the length of lines of pressure marked out by laying rods upon
the skin follows the same principle.
§ 22. Other important discoveries as to the skin's so-called
NATURE OF SENSATIOIST-CIRCLES. 407
" sense of locality " have been made since those of Weber. Valen-
tin has called attention to the fact that enormous individual differ-
ences exist in the fineness of this kind of perception ; some per-
sons are not more than one-fourth as sensitive as are some others.
The relative degree of fineness belonging to different areas of the
skin remains, however, approximately the same in different persons.
A. "W. Volkmann ' showed the remarkable effect of exercise upon the
cultivation of the sense of locality. After fixing the value of the
least perceivable differences of locality for a number of small areas
in the field of touch, Volkmann found that each successive series of
experiments with each area increased its fineness of perception,
until within a few hours twice the original degree of fineness could
be reached. The growth in perceptive skill of the skin was slower
at first for areas not ordinarily used for touch ; quicker for those
accustomed to daily use. The improvement ceased at a certain
limit, and was soon lost by disuse, so that a few months out of
practice served to reduce the acquired tact of any area to its origi-
nal condition. A most surprising discovery of this experimenter
was, that the practice exclusively of a member of the body on one
side resulted in improving the fineness of touch of the correspond-
ing member of the other side. Thus, if the smallest perceivable
distance for the tip of a left finger was, to begin with, 0.75 line,
and that of the corresponding place on the right finger, 0.85, prac-
tice with the left finger exclusively reduced the distance for both
fingers — for the left to 0.45 line, and for the right to 0.4.
It is well known that the blind, who have no spatial series of
sensations or presentations of extended objects by the eye, attain by
exercise a high degree of fineness for certain space-perceptions of
the skin.^ In the case of those who have sight, the most movable
and discriminating organs of the skin — such as the tips of the fin- ,
gers — are capable of being cultivated to great delicacy of touch ;
but Funke ^ did not succeed, even by an education lasting an en-
tire month, in reducing the obtuseness of the skin of the back be-
tween the shoulder-blades and in the lumbar region more than by
about one-fourth.
§ 23. The explanation of Weber's " sensation-circles " of the skin
has been the subject of much debate. It is natural at first to as-
sume that each entire circle is provided with one and only one
nerve-fibre, whose terminal expansion covers the circle, and whose
excitation is represented in consciousness by a sensation of a spe-
' Berichte d. Sachsischen Gesellschaft d. Wissenschaften, 1858, p. 38 f.
'^ Comp. Czermak, Sitzgsber. d. Wiener Acad., XVII., Abth. ii., p. 563 f.
** See Hermauu's Haudb. d. Physiol., III., ii., p. 383.
408 THE FIELD OF TOUCH.
cific value. Doubtless certain anatomical differences in the nerve-
fibres of tlie skin, and certain corresponding physiological differ-
ences in their function, must be assumed as the basis of every the-
ory to account for the skin's sense of locality. But Goldscheider's
experiments show that a number of pressure-spots must be recog-
nized within each sensation-circle, and each pressure-spot at least
should have a sensory fibre. Moreover, every point within each
sensation-circle is itself sensitive (however large the circle may be),
and the limits of none of the circles are fixed as would be the ex-
panse of a single nerve-fibre distributed over them. Still further,
different individuals differ greatly in the size of these circles (and
we cannot well suppose a corresponding difference in the number
of sensory nerves of the skin), and practice suddenly and greatly
diminishes the area covered by a single circle. It must at least be
admitted that " the smallest perceivable distance is not a direct
measure for the diameter of the sensation-circle." '
Weber himself assumed that sensation-circles always contain a
number of isolated nerve-fibres ; and that, in order to have the im-
pression of two localized sensations, several unexcited fibres must
exist between the two excited. The number of these unexcited fibres
serves the mind as a kind of means for the approximate measure-
ment of distances on the skin. Other advocates of Weber's ex-
planation have spoken as though the brain could somehow become
conscious of the unexcited fibres lying between the two excited
ones, and so derive a support for its judgment from their num-
ber.'' Of course, all attempts to explanation which assume the
mind's knowledge of the condition of the minute subdivisions of
the nervous elements are AvhoUy futile and illusory. Wundt ^ cor-
rectly calls attention to the fact that the diflerences in the so-called
sensation-circles of the skin are simply a special case under the
general jjsychological laws of the least observable differences in
sensations ; only in this case the differences are not pure differences
in intensity, but rather differences in the complex color-tone of the
quality of sensation. In other words, the sensation-circles represent
the local difference between the points at which stimulus must be
applied to the skin in order to produce enough of difference in the
color-tone of the resulting sensations to make them observable by
the mind. These local signs of the skin, as the organ of touch
proper, like all local signs, are complex mixtures of feeling belong-
ing to different localities ; as such they are dependent, not only
' So Funke, in Hermann's Handb. d. Physiol., HI., ii., p. 392 f.
^ Comp. Bernstein, The Five Senses of Man, p. 31 f. New York, 1876.
^ Physiolog. Psychologie, ii , p. 10.
THE THEORY OF VIERORDT. 409
upon original, anatomical, and physiological diflferences, but also
upon other peculiarities of the individual, upon habit, and upon
association with each other and with other spatial series of sensa-
tions of the skin.
§ 24. Difficulty has been found in assigning a conclusive reason
why the different areas of the skin should differ so greatly in the
fineness of their capacity for making local distinctions. In the view
of Lotze,' this difference is chiefly due to the varying character of
the areas of the skin, with respect to richness in nerve-fibres, thick-
ness and so sensitiveness, support and tension according as the
skin is stretched over underlying soft or hard parts — fat, muscle,
tendon, bone, etc. Doubtless all such influences enter into the
determination of that mixture of feeling which characterizes the lo-
cal signs of the skin. The theory suggested by Vierordt,^ on the
basis of experiments made by himself and his pupils, should also
be mentioned. This investigator concluded that the fineness of
the sense of locality belonging to any area of the skin increases
in direct proportion with the distance of that area from the axes
about which it is rotated. The relative fineness of the organ's local
sense is a function of its mobility. Thus an uninterrupted increase
of the power of localization exists in the arm from the acromion
to the tips of the fingers ; an increase of its movableness, on the
whole, also exists. If a value of 100 be assigned to the power of
discrimination exercised at the acromion, 151 will represent that of
the upper arm, 272 that of the lower arm, 659 of the hand, 2,417
of the thumb, and 2,582 of the tips of the fingers. In estimating
the relative movableness of these different pai-ts, it should be re-
membered that they not only all move in an enlarging circuit from
the shoulder- joint downward, but that each of them from the el-
bow-joint downward has its special increased circuit and more
numerous forms of motion.
But even if Vierordt's law could be strictly demonstrated for
every portion of the body, its meaning would have to be translated
into other terms in order to be of any real service to psychology.
It is therefore suggested by Fuuke ^ that the increased power of
discrimination which belongs to the more movable areas of the
skin is really due to the superior facility which they thus have for
exercise ; it therefore falls under the law of habit. Furthermore
— as we have occasion to remark concerning many similar functions
' See Medicin.'Psychologie, p. 405 f.
2 Pfluger's Archiv, 1869, ii., pp. 297 ff. ; and Zeitsclir. f. Biologie, VI., VII.,
IX,X.,XL
" Hermann's Handb. d. Physiol. , III , ii , p. 384.
410 THE FIELD OF TOUCH.
of the mind in correlation with the nervous mechanism — -the effect
of acquired habit is not Hmited to the experience of the individual ;
it belongs also to the race. The superior fineness of local sense in
some parts of the body may therefore be regarded as largely na-
tive to the individual.
§ 25. The view which must be taken of Weber's " sensation-cir-
cles," and of the entire subject of the localization of areas of press-
ure on the skin, has been largely changed by the recent experi-
ments of Goldscheider ' and others. "We have already seen (p.
346 f.) that this experimenter distinguishes, more carefully than has
hitherto been done, the sensations of pressure from other closely
allied sensations coming through the same organ. The finest point,
when it touches a " pressure-spot," produces a sensation of pressure,
and not one of being pricked ; but touching other spots does not
produce a sensation of pressure at all. It must be held, then, that
the sensations produced by laying a single blunted dividers' point
upon the skin, as in Weber's classical experiment, are really very
complex, and are composed of the sensations from several pressure-
spots blended with other sensations from the rest of the same area
not covered by the pressure-spots. The fineness of discrimination
possible in any area of the skin depends, then, upon how all the
points irritated stand related to the specific pressure-spots. Gold-
scheider finds that only when two irritating points touch two press-
ure-spots are thej/elt as two. But when one of the points touches
a pressure-spot, and the other touches some place in the contiguous
area of skin which is free from such spots, the two points are not
both felt ; in this case only the one resting on the pressure-spot is
felt.
Moreover, the impression of being doubly touched may be ex-
cited by the points when lying much nearer together, in case they
rest upon pressure-spots that belong to two different chains of
such spots than when both spots belong to the same chain. This
is to say, pressure-spots thus located have a high degree of sensitive-
ness. Still further, the minimum distance required to produce a
sensation of being touched twice is surprisingly small, when one of
the touching points rests upon a pressure-spot from which the
chain radiates or at which it makes a sharp bend.
The table of minimum distances at which two points can be felt
as two, when the exact nature of the area of the skin on which we
are experimenting is known, and everything made as favorable as
' On this subject, see Goldscheider, Archiv f. Aiiat. u. Physiol., Physiolog
Abth., IbbS, Supplemeut-Band, pp. 1-104; especially, p. 84 f.
DIRECTION OF THE PRESSURE-SPOTS.
411
possible, consists of numbers very much reduced from those oi
Weber. Following? are some citations from Goldscheider's table :
Part of the bodj\ mm.
Back 4-6
Breast 0.8
Forehead 0.5-1.0
Cheek 0.4-0.6
Nose and chin 0.3
Upper and lower arm 0 5-1.0
Part of the body. mm.
Back of hand 0.3-0.6
I. and II. phalanges (volar). . 0.2-0.4
I. and II. phalanges (dorsal).. 0.4-0.8
Upper leg 3.0
Lower leg 0.8-2.0
Back, and sole of foot 0.8-1.0
From the foregoing data it would seem to follow that, as the con-
struction and relation of the chains of pressure-spots differ in the
different areas of the body, so will our sense of locality change.
The number, sensitiveness, and direction in the chains of these
spots determine the sensitiveness of a given area. Moreover, our
perception of the size and shape of objects in contact with the skin
depends upon the same conditions. This can be shown in an as-
tonishing way by comparing the apparent direction which the out-
lines of any small body moved across the skin seem to assume with
the way the pressure-spots are located in the different areas through
which it is moved. If the curve of the chain of pressure-spots, for
example, bends in the reverse direction from that of the outline of
the body moved, the effect may be to make this outline curve ir-
regularly or even straighten it out.
It need scarcely be said that Goldscheider regards the true ex-
planation of these phenomena to lie in the anatomical distribution of
the specific nerves of sense in the different areas of the skin. How-
ever this may be, it is certain that our sensations of pressure are
primarily "punctiform," and afterward massed into a tactual continue
um ; and that what we primarily know is not the extended object aa
such, but our sensations of pressure which are afterward objectified.
§ 26. Closely connected with the foregoing is the difference in
power of different parts of the skin in giving to the mind data for
discriminating the fact, the amount, and the direction of motion
in contact with the body. Upon this point the experiments of G.
Stanley Hall ' are of special interest. These experiments seem to
show that we are more likely, when in doubt, to judge motion on
the surface of the limbs to be up rather than down their axis ; on
the breast, the shoulder-blades, and the back, the tendency is to
judge motion to be toward the head. The discriminative sensi-
bility of the skin for motion is much greater than that for sepa-
rate touch, as determined by Weber's experiments. Thus, while at
' Motor Sensations on the Skin, by Professor G. S. Hall and Dr. H. H
Donaldson, in Mind, October, 1885, pp. 557 ff.
412 THE FIELD OF TOUCH.
least a distance of 25 mm. between the dividers* points was needed
on the volar surface of the right arm, in order to perceive them
as two points, both the fact and the direction of motion could be
discriminated at an average distance of between 6 and 7 mm. In
judging the rate and distance of motion over the skin the liabil-
ity to error is always great ; but, as a rule, distances rapidly trav-
ersed are judged to be relatively shorter than the same distances
more slowly traversed. Inasmuch, however, as the judgment of
motion on the left arm was expressed by reproducing the rate
and distance with the right hand,' we have a double liability to
en'or involved in regulating the muscular movenient of this hand
by means of its series of muscular and tactual sensations.
Hall found the motor sensibility of different parts of the surface
of the skin to be different ; but the differences do not appear to
correspond to those belonging to Weber's sensation -circles. The
average distance, in millimeters, which a metallic point of 12 mm.
in diameter could move over the skin at a rate of 2 mm. per second
before a judgment of direction could be formed was found, for one
subject of experiment, as follow^s : forehead, 0.20; upper arm, 0.40;
forearm, 0.44 ; shin, 0.60; palm, 0.74; back, 0.85. Motion can be
produced so slowly as not to be discriminated at all, even when the
body in contact has really moved from 6 to 12 centimeters. It can
also be jjroduced so rapidly as to make it impossible to tell when it
begins and when ends. Heavy weights seem to move faster than
light ones going at the same rate ; but here other sensations are
called out by the deep pressure, and combined with those of con-
tact. Hall concludes that heat-spots and cold-sjjots traversed by
the moving body are of great service in judging motion and its di-
rection on the skin ; the cold-spots more than the heat spots, "be-
cause of the fainter sensation and wider irradiation " of the latter.
Further experiments with a travelling metallic point that carried
the stimulus of an electrical current over the surface of the skin
showed an astonishing diversity of sensations developed at different
points of the area thus traversed. Points of cutting pain, " thrill-
points," "tickle-points," " acceleration-points " (or places where the
rate of motion seems suddenly to increase without any real change
in the speed of the moving metal), " blind-points " (or spots where
all impression of contact is momentarily lost), are all to be differen-
tiated. Yet the sharp differentiation of these sensations is ren-
dered difficult by the fact that the various kinds are so impacted
and run together, in a tayigle of sensation. The experimenters also
speak as though many dermal sensations may thus be j)artially dis-
' Mind, October, 1885, p. 564 f.
nXEXSSS OF TZ.UPEI^iTUnE-GENSE.
413
entangled, for the description of whicli language furnishes no ade-
quate terms. All these facts agree exceedingly well with the theory
of local signs already proposed. These dermal signs are complex
"mixtures" of feeling, which give to each discernible locahty a
characteristic local stamp. The fact that our sensibility to motion
is so much greater in each area of the skin than our susceptibility
to the distance of stationary points accords with the same theory.
Our ability to localize the dermal sensations is dependent upon the
degree and rate of the changes in the color-tone of these sensations.
Hall is undoubtedly right in holding that, by moving the touching-
surface over the surface touched, we do not simply multiply, but
also diversify, our data for filling up the dermal blind-spots and
judging the nature of impressions.
§ 27. The localizing of sensations of temperature in the skin is,
in principle, the same as that of sensations of light-pressure or of
motion. The former, however, are in all our ordinary experience
interwoven with' the latter ; they therefore have the helj) of the lat-
ter in getting a place assigned to them in the periphery of the
body. Kecent researches, already referred to (Chap. IV., § 22), dem-
onstrate the fact that the relative number and arrangement of
heat-spots and cold-spots is different for different areas of the skin.
Goldscheider ' has experimented to determine how far apart the
heat-spots and cold-spots must be, respectively, in order that two
of them, when stimulated, may he felt as two. Both kinds of sen-
sations are localized, not as points, but as minute warm or cold
drops in contact with the skin. By the following table, which
gives the minimum distances for different areas of the body, it ap-
pears that the sense of locality connected with the cold-spots is
about twice as fine, as a rule, as that connected with the heat-spots.
The distances are given in millimeters.
Part of the body.
Cold-spots.
Heat-spots.
Foreliead clieek, and cliin
0.8
2.0
1-2
1.5-2.0
1.5-2.0
2-3
0.8
2-3
3-5
Breast
4-5
Abdomen
4-6
Back
4-6
Upper arm
2-3
Lower arm .
2-3
Hollow of the hand .
2.0
3-4
' Archiv f. Anat. u. Physiol., Physiolog. Abth., 1885, Supplement-Band, pp.
70 fE.
414 THE FIELD OF TOUCH.
Some basis seems to be laid in the foregoing facts for a system
of local signs of the skin, that consist in a mixture of color-tones of
temperature-sensations. Yet sensations of heat or cold, in them-
selves considered, differ chiefly, if not wholly, in intensity. In them-
selves, therefore, they are not well fitted to constitute a so-called
" spatial series " of sensations. If, for example, a certain area of
the skin be stimulated simultaneously by both heat and cold, at
points too near together to be distinguished by touch, the result is
neither a modification of one sensation by the other nor a localizing
of the two sensations as Ij'ing closely side by side.' A wavering of
perception rather takes place, similar to the strife of colors in vi-
sion ; the experience is as though the skin were being touched with
a single body alternately hot and cold. Klug also found that the
least observable distance between two points touching the skin at
the same time depends upon their temperature relative to that of
the skin. The medium value of this distance "is reached when these
points have a temperature of 20°-40° C. (68^-104° Fahr.) ; it dimin-
ishes on either raising or depressing their temperature greatly
above or below the zero-point of the skin. The fineness of our
sense of locality, as well as of our sensitiveness to motion (comp.
§ 25), is increased by exciting sensations of temperature up to the
point where pain intervenes. But the localizing of these sensations
is primarily dependent, to a great extent, uj)on their connection
with localized sensations of touch. If we bring two parts of the
skin, that differ considerably in temperature, into contact — for ex-
ample, a cool hand and warm forehead, or a cool hand and a warm
one — it is often difficult by strict attention to the sensations of tem-
]Derature -alone to tell which part is cooler, which warmer. The
difficulty is doubtless largely due to the fact that each part which
feels the temperature of the other is also changing its own tem-
perature in the direction of the temperature of the othei\ It is
therefore induced to feel itself, as it were, as being of the tempera-
ture of that other, A confusion of the data for judgment, accord-
ingly, takes place. Any localization of the sensations which occurs
under such circumstances is largely dependent upon secondary con-
siderations, and especially upon the direction of the attention.
We judge of depth by sensations of temperature, indirectly, and
through our ability to remove or change the intensity and locality
of these sensations by changing the position of the body in space
as related to what we know to be hot and cold bodies or surround-
ing media.
' See Czermak, Sitzgsber. d. Wiener Acad., March, 1855, p. 500; confirmed
by Klug and otliers.
ISTATUKE OP THE MUSCULAR SEISTSE. 415
§ 28. The specific sensations of the muscular sense constitute
another spatial series which combines with the foregoing in the
localizing of areas at the periphery, and of external objects as
projected in space and yet known as in contact with the body. In-
deed, it is upon this particular system of local signs that the mind
is chiefly dependent for its data — other than the visual — in the
synthetic construction of its presentations of bodies that stand re-
lated to each other in three dimensions in objective space. Three
principal theories have been held as to the nature of the so-called
muscular sensations : (1) So far as they are not tactual, they are to
be resolved into " central feelings of innervation," which differ only
in intensity and not in specific quality, and which result from the
changes, initiating movement of the bodily organs, that take place
in the brain as correlated with impulses of the will (so Wundt, and
others) ; (2) they are not specific sensations, but are due to interpre-
tations of those feelings in the skin which originate on account of
its changes of position, tension, etc., as the underlying muscles are
moved (so Schiff, and others) ; (3) they are specific sensations de-
pendent on a specific nerve-apparatus of sense, which has its end^
organs in the muscle-fibre, and which is excited by the contraction
of the latter in a manner dependent upon the kind, ainount, and
direction of the muscular movement taking place (so Bell, Weber,
Funke, and others).
We have already given certain reasons for rejecting the first
two and accepting the last of the foregoing views (see p. 344 f.) ;
other reasons will be mentioned subsequently in discussing the
so-called "feeling of innervation" or of "active energy." The
muscular sense, like all the other senses which contribute to our
presentations of objects extended in space, appears to have its own
system of local signs. The muscular sensations are qualitatively
(and not merely quantitatively) different, according to the combi-
nation of the muscles moved, and according to the extension over
the muscular area of the stimulus imparted to the sensory nerve-
fibres situated in the muscle by the changing condition of the
latter as it contracts and relaxes. The series of sensations — with
all the qualities of rapid and nice gradations which belong to
"spatial series" of sensations — called out by moving one limb dif-
fers from that called out by moving another limb. At each step in
the flexing of the leg — for example — the color-tone of the muscular
sensations has a specific quality and value as a local sign, in our
consciousness, of the position of the member. The same thing is
true of the bending arm, back, or single toe or finger. These sen-
sations are intimately, and even inextricably, combined with the
416 THE FIELD OF TOUCH.
spatial series of specifically dermal sensations ; but in themselves
tliey have a different quality, and ai-e not localized simply at the
surface of the body. As the extent of the circuit of motion gone
through by any limb increases, or the intensity of the strain be-
comes greater, the quality of the mass of resulting muscular sensa-
tions is perpetually changing. These sensations are, accordingly,
localized over a broader area of the body and deeper in its sub-
stance, as it were. Everyone knows what new mixtures of sensa-
tion are produced in consciousness by calling into vigorous exer-
cise the unused more deeply lying muscles of the body. Bain' has
discussed these sensations at great length and with commenda-
ble acuteness. But the apparent assumption that these particu-
lar sensations can, by being associated, acquire of themselves the
quality of extension in space, and the accounting for all our other
perceptions of sjDatial qualities and relations as merely secondary
and symbolic of the associated muscular sensations, are in plain
contradiction of established psychological facts and principles.
The muscular sensations also assist the more strictly tactual in
discriminating locality for all cases where the pressure upon the
sliin exceeds a certain small degree of intensity. In strong contact
or heavy pressure the sensory nerves of the underlying muscle are
excited; we have the feeling, not simply of being touched, but also
of being pressed. The combination of these two spatial series
gives to the mind a doubly constituted system of local signs ; hence,
as the experiments of G. Stanley Hall ^ show, our judgment of di-
rection of motion is quicker as the weight resting on the skin is
increased np to the limit where other disturbing sensations inter-
vene. The superior discriminating power which any member of
the body has when permitted to move — that is, to call forth fa-
miliar series of muscular sensations — is largely due to the help
which the local signs of this system render to the mind. When
the particular member (the hand) which is capable of the nicest
tactual discrimination is also permitted to move over an object
freely, and to acquire abundant data from all the sources described
above, we have fulfilled the most advantageous conditions for the
utmost nicety of knowledge possible to " touch," in the widest
meaning of the word.
§ 29. It is unnecessary to illustrate in further detail the process
by which the mind, with its native synthetic activity, and with
the help of qualitatively different sensations, constructs its field of
' The Senses and the Intellect, especially pp. 57-100, 336-348, and 364-
398.
2 Mind, October, 1885, p. 567.
TOUCHIlSrG AND BEIISTG TOUCHED. 401
tions are localized ; we see some of the same parts as projected in
space before our eyes. Objects that are not a part of ourselves are
given to us as projected eccentrically, either by touch through their
being in contact with the skin and occasioning sensations of mus-
cular exertion, or by sight as having distance in its field of vision.
Localization and projection are not to be regarded as two phases of
one and the same process ; we do not first have the presentations
of sense as pai'ts of the periphery of our bodies, and then, on further
experience, push them beyond this periphery, either to an infini-
tesimal distance or to one remote. Localization and eccentric pro-
jection are rather two processes, largely unlike, which go on con-
temporaneously and are set up chiefly on the basis of different
classes of sensations.
Where two parts of the sensitive skin of our own bodies come
together the conditions for both of the above-mentioned processes
are fulfilled. Accordingly, one part has localized in it those com-
plex sensations which make us aware that this part of our body is
touching something ; the other has localized in it those sensations
which make us aware that this part is being toadied by something.
Which of the two parts shall be regarded as touching, and which as
being touched, depends on various considerations. Those mem-
bers of the body which are most used in active touch are generally
known as touching, and the less active parts as being touched. For
example, if -with closed eyes the forehead be moved across the sta-
tionary tip of a finger, the latter will appear to be the active organ
of touch. Comparatively insensitive areas of the skin are less likely
to be presented to the mind as touching other more sensitive parts ;
callous spots, indurated surfaces, etc., seem, as a rule, to be touched.
Parts of the body which lose all sensitiveness come to be regarded
as external things. If the tip of a finger of normal sensitiveness be
brought into contact with the callous tip of the corresponding fin-
ger of the other hand, the former will be known as touching and
the latter as being touched. The direction of attention often deter-
mines the strife, as it were, between the motifs to localization and
those to eccentric projection. We ordinarily strive to ga,in knowl-
edge of the qualities of some outside object, rather than of the con-
dition of our own periphery with respect to the sensations localized
in it ; the attention is therefore directed to those series of sensations
which form the basis of eccentric projection, even when some part
of our own sensitive organism is the object known. But sensations
which are accompanied by obtrusive feeling of some kind furnish
superior grounds for localization. We locate pains, pricks, severe
pressure, sensations of creeping, and tickling, in the body. In gen-
26
402 PEECEPTIOlSrS OF THE LOWEE SENSES.
eral, then, a strong tone of feeling with the sensation favors the
process of localizing ; tonelessness of sensation favors the process
of objectifying.'
A system of localized sensations, gained chiefly by pressure of
the skin and muscles, and accompanied by a strong tone of feeling,
gives us the primary field of the body as known to touch. Certain
points of starting, as it were, must first be fixed in the process of
locahzing ; this process then goes on by relating all other localized
sensations to these points of starting. But by eccentric projection,
the system of muscular sensations of movement and the system of
visual sensations are combined to develop our perceptions of ob-
jective space with its three dimensions. The sensations of touch
are subsequently projected into a space thus originally constituted
by combined muscular sensations and visual sensations. The eye
and hand in motion, therefore, project their extended objects into
a space which they develop themselves ; while the ear and the nose
project their perceptions into a space which they are compelled to
assume on the authority of the other senses.
The foregoing principles must now be illustrated and confirmed
by a brief statement of facts which relate to the formation and de-
velopment of presentations of sense by a synthesis of simple sen-
sations. Attention will, for obvious reasons, be directed almost
exclusively to those presentations of sense which come through the
eye and skin, including in both the influence of muscular sensa-
tions.
§ 17. Perceptions of Smell differ only in fineness, duration, and ac-
companying tone of feeling ; they have no size or shape, no spatial
properties of any kind. They cannot even be said to be localized.
Fineness of smell, or power to make minute distinctions in quality,
and so infer the presence or direction of an object previously known
to excite such quality of sensations, differs greatly in different spe-
cies of animals and in different individuals of the same species.
The exploits of some animals give ground for the conjecture that
every species, and even every individual, has an odor of its own.'^
The direction and nature of the object which causes the sensations
are judged by variations of intensity on turning the head, or on
approaching or receding from the object. Sensations of smell are
known to come through the nose, by localizing there the accom-
' Compare Volkmann von Volkmar, Lehrbuch der Psycliologie, II., p.
126 f.
■^ See the articles of Donhoff, in Archiv f. Anat., Physiol., etc., Physiolog.
Abth , p. 750 f. (1874) ; and Jiiger, in Zeitschr. f. wissensch. Zool., xxvii., p.
319 f. (1876).
TASTE AND HEARING. 403
panying muscular and tactual sensations with their strong tone of
feeling. This is readily done, since we draw the air through the
nostrils and feel its double effects in producing the two classes of
sensations. As to the simultaneous influence of two smells, little
is known beyond the statement of Valentin, that the stronger
overwhelms the weaker. The power of discrimination may, of
course, be cultivated in this sense as in every other.'
§ 18. Most of the remarks just made as to perceptions of smell
apply also to Perceptions of Taste. Sensations of taste, however, are
much more closely connected with those of touch ; since the tongue
is a chief organ of active touch. It is the tactual and muscular
sensations, and not the purely qualitative affections of taste, which
are localized in the mouth. Concerning contrast and compensation
of tastes, little is known which does not belong to ordinary experi-
ence. Valentin ^ alleges that when a sour mass is laid on one half,
and a bitter mass on the other half, of the root of the tongue, the
predominating taste may sometimes be determined by our choice.
It is well known that certain tastes compensate each other, as it
were, in experience, without any chemical equivalence of their prop-
erties. The sugar neutralizes the acid of the lemonade, not in the
vessel that contains the mixture, but in the nervous system of him
who drinks ih Briicke holds ^ that the neutralizing of one sensa-
tion of taste by the other takes place in the brain. The sensation
of bitter is esj^ecially difficult to cover or neutralize.
§19. Perceptions of Hearing ne^i demand consideration. More
difficulty accompanies the effort to establish the proposition that
sensations of sound are not directly localized, but are projected
in a space constituted chiefly by the eye and the hand, through
complicated indii'ect inferences. Such a proposition is, however,
undoubtedly true. The localizing of the area of the body which
serves as the organ of the sensations of sound, the knowledge that
we hear iDith the ear, is accomplished chiefly through those sen-
sations of shock to the muscles and skin of the region which come
from loud and massive or piercing sounds. Sensations of sound
originating through excitement within or very near to the ear itself
are called " entotic." A great part of such sounds, if not all of them,
are transmitted through the tympanum. Perceptions combined of
such sensations may be located either within the ear or at some dis-
' On the whole subject see von Vintscligaus monograph in Hermann, Handb:
d. Physiol., HI., ii., pp. 225 ff.
^ Lehrbuch der Physiol, d. Menschen, etc., Abth. ii., p. 308 (second edi-
tion).
^ Vorlesungen ilber Physiol, (ed. 1884), ii., p. 263.
404 PERCEPTIOlSrS OF THE LOWER SEISTSES.
tance from the body, according to previous associations and oppor-
tunities for judgment. The sound produced by the vibration of the
adjoining muscles, and heard as a low musical tone when the fin-
gers are pressed in the ears (especially if the teeth are tightly set
together), is located in the head by the help of its accompanying
sensations of other kinds. The same thing is true of the crackling
noise sometimes produced by yawning, or of the whirring occasioned
by the passing of the blood through the neighboring large blood-
vessels. In the same way we learn to hear the beating of oiir own
hearts, or the noise of air in our respiration. But the click of the
valves of the internal organ may, when experience gained through
tactual and muscular sensation fails us, be located in the watch
under our pillow; just as the singing or ringing "in the ears"
produced by quinine, or cerebral excitement otherwise occasioned,
may be located in a cricket supposed to be upon the sill of the open
window. In certain pathological cases the power to distinguish
between entotic sounds and those having an external origin is al-
most wholh' lost.
§ 20. We can orientate ourselves in space with reference to ex-
ternal sounds with great speed and considerable precision, but as
an acquired art differing in different individuals and dependent
upon attention and previous experience. E. H. Weber thought
that we tell the direction of sounds by ihe help of the feeling of
the swing of the ear-drum ; and instanced, in proof, that this
eccentric projection is hindered by filling the external jD^ssage
of the ear with water. When using both ears and moving the
head freely in space, we undoubtedly determine the direction of
sounds by differences in the intensity of the sensation dependent
upon changes in the relative position of both ears. Rayleigh '
found that, in a quiet place under favorable circumstances, the
direction of a word or letter uttered in a natural voice could be
given with considerable accuracy ; that of a musical tone much
less accurately. The direction of a sound from a tuning-fork
could not be given when it was held either behind or before, but
could be given if the fork was held to the right or to the left. It
is said that the conducting of an intermitting current from a tele-
phone through both ears causes a perception of tone localized in the
median plane of the head.
Such facts as the foregoing introduce us to the theory of "acous-
tic shadows," or of the amount of " covering " power which the
sound produced by the waves of a given intensity entering one
ear would have upon the sound produced by waves of a different
' Nature, XIV., p. 32.
THE EXPERIMENTS OF WEBER. 405
intensity entering the other ear. It does not appear to Hensen,'
however, that the prompt and accui-ate locaHzatiou of direction
possible to some ears can be wholly accounted for by the theory of
acoustic shadows. Some other form of feeling, possibly connected
with the remarkable arrangement of the semicircular canals, may
blend with the estimate of differences in intensity to form a basis f or
judgment. Von Kries and Auerbach found that the jDromptness
with which the direction of the noise from an electric spark can be
localized depends upon its relation to the circuit of the head."
Our perceptions of the absolute distance of sounding objects are
entirely dependent upon our knowledge of the quality and quantity
of the sounds ordinarily proceeding from them ; they are, that is
to say, not presentations of sense, but indirect estimates as to the
objective cause of the sensations immediately experienced. It has
been claimed that a change in the relation of the partial tones to
the fundamental tone, dependent upon the remoteness of the place
of origin of the compound clang, aids our estimate of distance by
sound.
§ 21. An account of the process by which a Field of Touch is con-
structed, and extended objects are known as iu contact with the
skin at definite points or areas of it, must begin by enumerating the
data which the mind has for such activity. The most important of
these data are indicated by certain facts as to the fineness of the
so-called " sense of locality " belonging to the skin. E. H. Weber
first estabHshed a rule for measuring the degree of this fineness ac-
curately ; he also mapped out the entire field of the surface of the
body into areas differing greatly in their fineness.^ For a measur-
ing instrument he used the two points of a pair of dividers, blunted
so as to prevent the sensation of being pricked ; the princi^Dle of
measurement was that the minimum distance apart at which the
two points, when touching the skin of any region, are felt as tivo local-
ized sensations is the measure of the sensitiveness to local distinction
of that region. The following table gives some of the results of
Weber's experiments ; the figures indicate the number of milli-
meters * apart which the points of the dividers were when the given
area of the organ was just able to distinguish them ;
' In Hermann's Handb. d. Physiol., III., ii., p. 136.
2 Archiv 1 Anat. u. PliysioL, Physiolog. Abth , 1877, p. 331 f.
^ Annot. Anatom., vii., p. 4 f. ; Wagner's Handworterb. d. Physiol., III.,
Abth ii., p. 529 f.
^ The numbers were given by Weber in Parisian lines ; in the table they are
taken f rom Wundt, Physiolog. Psychologie, ii., p. 7, who has reduced them to
even millimeters.
406 THE FIELD OF TOUCH.
Tip of the tongue .- 1
Volar side of the last phalanx of the finger 2
Red part of the lips 5
Volar side of the second and dorsal side of the third phalanx of the finger . 7
White of the lips, and metacarpus of the thumb 9
Cheek, and plantar side of the last phalanx of the great-toe 11
Dorsal side of the first phalanx of the finger 16
Skin on the back part of cheek-bone, and forehead 23
Back of the hand 31
Knee-pan, and surrounding region 36
Forearm, lower leg, back of the foot near the toes 40
Skin of the nape, and of the back in the five upper cervical vertebrae 54
Skin of the middle of the back, and of the upper arm and leg 68
Weber also found that the fineness of the sense of locality is
greater in a transverse than in a longitudinal direction, on both arms
and legs. On these surfaces of the skin the " sensation-circles," or
areas within which the minimum distances of the dividers' points
are felt as two points, have an elliptical shape, with their long axes
up and down. That the size of the sensation-circles, or the fineness
of the sense of localit}', largely forms the basis for our judgments
of the position, number, and magnitude of the localized sensations
in the field of touch may be shown by a simple experiment. If
the points of the dividers be separated somewhat less than is neces-
sary in order to distinguish them as two on the cheek just in front
of the ear, and then (the distance apart of the points remaining un-
changed) be slowl}^ moved until one point rests upon the upper and
the other upon the lower lip, to a person blindfold, and unpreju-
diced by knowing what is to take place, the point first felt as one
will appear to become two, and then the two recede from each
other continually as the parts with a finer sense of locality are trav-
ersed. The same experiment may be tried upon any other part
of the body. It appears, therefore, that the mental representation
of the magnitude of the distance between two impressions varies in
inverse proportion to the real magnitude of the smallest perceiv-
able distance, on any given area of the skin. The same principle
holds good when all the space between the impressions is filled up,
as it were, so as to make a continuum of localized sensations. Thus
Weber found that the circular form of a tube of only It} Parisian
line in diameter could be recognized by pressure on the tip of the
tongue ; while on the skin of the abdomen the diameter of the tube
must reach 3f inch before its form was recognizable. Our estimate
of the length of lines of pressure marked out by laying rods upon
the skin follows the same principle.
§ 22. Other important discoveries as to the skin's so-called
NATURE OF SENSATION-CIRCLES. 407
" sense of locality " have been made since those of Weber. Valen-
tin has called attention to the fact that enormous individual differ-
ences exist in the fineness of this kind of perception ; some per-
sons are not more than one-fourth as sensitive as are some others.
The relative degree of fineness belonging to different areas of the
skin remains, however, approximately the same in different persons.
A. W. Volkmann ' showed the remarkable effect of exercise upon the
cultivation of the sense of localit}'. After fixing the value of the
least perceivable differences of locality for a number of small areas
in the field of touch, Volkmann found that each successive series of
experiments with each area increased its fineness of perception,
until within a few hours twice the original degree of fineness could
be reached. The growth in perceptive skill of the skin was slower
at first for areas not ordinarily used for touch ; quicker for those
accustomed to daily use. The improvement ceased at a certain
limit, and was soon lost by disuse, so that a few months out of
practice served to reduce the acquii-ed tact of any area to its origi-
nal condition. A most surprising discovery of this experimenter
was, that the practice exclusively of a member of the body on one
side resulted in improving the fineness of touch of the correspond-
ing member of the other side. Thus, if the smallest perceivable
distance for the tip of a left finger was, to begin with, 0.75 line,
and that of the corresponding place on the right finger, 0.85, prac-
tice with the left finger exclusively reduced the distance for both
fingers — for the left to 0.45 line, and for the right to 0.4.
It is well known that the blind, who have no spatial series of
sensations or presentations of extended objects by the eye, attain by
exercise a high degree of fineness for certain space-perceptions of
the skin.^ In the case of those who have sight, the most movable
and discriminating organs of the skin — such as the tips of the fin-
gers— are capable of being cultivated to great delicacy of touch ;
but Funke ^ did not succeed, even by an education lasting an en-
tire month, in reducing the obtuseness of the skin of the back be-
tween the shoulder-blades and in the lumbar region more than by
about one -fourth.
§ 23. The explanation of Weber's " sensation-cii'cles " of the skin
has been the subject of much debate. It is natural at first to as-
sume that each entire circle is provided with one and only one
nerve-fibre, whose terminal expansion covers the circle, and whose
excitation is represented in consciousness by a sensation of a spe-
' Bericlite d. Sachsischen Gesellschaft d. Wissenscliaften, 1858, p. 38 f.
^ Comp. Czermak, Sitzgsber. d. Wiener Acad., XVII., Abth. ii., p. 563 f.
^ See Hermann's Handb. d. Physiol., III., ii., p. 383.
408 THE FIELD OF TOUCH.
cific value. Doubtless certain anatomical differences in the nerve-
fibres of the skin, and certain corresponding physiological differ-
ences in their function, must be assumed as the basis of every the-
ory to account for the skin's sense of locality. But Goldscheider's
experiments show that a number of pressure- spots must be recog-
nized within each sensation-circle, and each pressure-spot at least
should have a sensory fibre. Moreover, every point within each
sensation-circle is itself sensitive (however large the circle may be),
and the limits of none of the circles are fixed as would be the ex-
panse of a single nerve-fibre distributed over them. Still further,
different individuals differ greatly in the size of these circles (and
we cannot well suppose a corresponding difference in the number
of sensory nerves of the skin), and practice suddenly and greatly
diminishes the area covered by a single circle. It must at least be
admitted that " the smallest perceivable distance is not a direct
measure for the diameter of the sensation-circle." '
Weber himself assumed that sensation-circles always contain a
number of isolated nerve-fibres ; and that, in order to have the im-
pression of two localized sensations, several unexcited fibres must
exist between the two excited. The number of these unexcited fibres
serves the mind as a kind of means for the approximate measure-
ment of distances on the skin. Other advocates of Weber's ex-
planation have spoken as though the brain could somehow become
conscious of the unexcited fibres lying between the two excited
ones, and so derive a support for its judgment from their num-
ber.'' Of course, all attempts to explanation which assume the
mind's knowledge of the condition of the minute subdivisions of
the nervous elements are wholly futile and illusory. Wundt ^ cor-
rectly calls attention to the fact that the diflerences in the so-called
sensation-circles of the skin are simply a special case under the
general psychological laws of the least observable differences in
sensations ; oidy in this case the differences are not pure differences
in intensity, but rather differences in the complex color-tone of the
quality of sensation. In other words, the sensation-circles represent
the local difference between the points at which stimulus must be
applied to the skin in order to produce enough of difference in the
color-tone of the resulting sensations to make them observable by
the mind. These local signs of the skin, as the organ of touch
proper, like all local signs, are complex mixtures of feeling belong-
ing to different localities ; as such they are dependent, not only
' So Funke, in Hermann's Handb. d. Physiol., HI., ii., p. 392 f.
'^ Comp. Bernstein, The Five Senses of Man, p. 31 f. New York, 1876.
^ Physiolog. Psychologic, ii , p. 10.
THE THEORY OF VIEP^ORDT. 409
upon original, anatomical, and physiological differences, but also
upon other peculiarities of the individual, upon habit, and upon
association with each other and with other spatial series of sensa-
tions of the skin.
§ 24. Difficulty has been found in assigning a conclusive reason
why the different areas of the skin should differ so greatly in the
fineness of their capacity for making local distinctions. In the view
of Lotze, ' this difference is chiefly due to the varying character of
the areas of the skin, with respect to richness in nerve-fibres, thick-
ness and so sensitiveness, support and tension according as the
skin is stretched over underlying soft or hard parts — fat, muscle,
tendon, bone, etc. Doubtless all such influences enter into the
determination of that mixture of feeling which characterizes the lo-
cal signs of the skin. The theory suggested by Vierordt,^ on the
basis of experiments made by himself and his pupils, should also
be mentioned. This investigator concluded that the fineness of
the sense of locality belonging to any area of the skin increases
in direct proportion with the distance of that area from the axes
about which it is rotated. The relative fineness of the organ's local
sense is a function of its mobility. Thus an uninterrupted increase
of the power of localization exists in the arm from the acromion
to the tips of the fingers ; an increase of its movableness, on the
whole, also exists. If a value of 100 be assigned to the power of
discrimination exercised at the acromion, 151 will represent that of
the upper arm, 272 that of the lower arm, G59 of the hand, 2,417
of the thumb, and 2,582 of the tips of the fingers. In estimating
the relative movableness of these different parts, it should be re-
membered that they not only all move in an enlarging circuit from
the shoulder- joint downward, but that each of them from the el-
bow-joint downward has its special increased circuit and more
numerous forms of motion.
But even if Vierordt's law could be strictly demonstrated for
every portion of the body, its meaning would have to be translated
into other terms in order to be of any real service to psychology.
It is therefore suggested by Funke ^ that the increased power of
discrimination which belongs to the more movable areas of the
skin is really due to the superior facility which they thus have for
exercise ; it therefore falls under the law of habit. Furthermore
— as we have occasion to remark concerning many similar functions
' See Medicin. Psychologie, p. 405 f.
•2 Pflager's Archiv, 1869, ii., pp. 297 ff. ; aud Zeitschr. f. Biologie, VI., VII.,
IX , X. . XI.
^ Hermann's Handb. d. Physiol. , III , ii , p. 384.
410 THE FIELD OF TOUCH.
of tlie mincT in correlation with the nervous mechanism — the effect
of acquired habit is not Umited to the experience of the individual ;
it belongs also to the race. The superior fineness of local sense in
some parts of the body may therefore be regarded as largely na-
tive to the individual.
§ 25. The view which must be taken of Weber's " sensation-cir-
cles," and of the entire subject of the localization of areas of press-
ure on the skin, has been largely changed by the recent experi-
ments of Goldscheider ' and others. We have already seen (p.
346 f.) that this experimenter distinguishes, more carefully than has
hitherto been done, the sensations of pressure from other closely
allied sensations coming through the same organ. The finest point,
when it touches a "pressure-spot," produces a sensation of pressure,
and not one of being pricked ; but touching other spots does not
produce a sensation of pressure at all. It must be held, then, that
the sensations produced by laying a single blunted dividers' point
upon the skin, as in Weber's classical experiment, are really very
complex, and are composed of the sensations from several pressure-
spots blended with other sensations from the rest of the same area
not covered by the pressure-spots. The fineness of discrimination
possible in any area of the skin depends, then, upon how all the
points irritated stand related to the specific j)ressure-spots. Gold-
scheider finds that only when two irritating points touch two press-
ure-spots are thejfelt as two. But when one of the points touches
a pressure-spot, and the other touches some place in the contiguous
area of skin which is free from such spots, the two points are not
both felt ; in this case only the one resting on the pressure-spot is
felt.
Moreover, the impression of being doubly touched may be ex-
cited by the points when lying much nearer together, in case they
rest upon pressure-spots that belong to two different chains of
such spots than when both spots belong to the same chain. This
is to say, pressure-spots thus located have a high degree of sensitive-
ness. Still further, the minimum distance required to produce a
sensation of being touched twice is surprisingly small, when one of
the touching points rests upon a pressure-spot from which the
chain radiates or at which it makes a sharp bend.
The table of minimum distances at which two points can be felt
as two, when the exact nature of the area of the skin on which we
are experimenting is known, and everything made as favorable as
' On this STibject, see Goldscheider, Arcliiv f. Anat. u. Physiol., Physiolog.
Abth., 1885, Supplement-Band, pp. 1-104; especially, p. 841
DIEECTIOJSr OF THE PRESSURE-SPOTS.
411
possible, consists of numbers very much reduced from those of
Weber. Following are some citations from Goldscheider's table :
Part of the bodj-. mm.
Back 4-6
Breast 0.8
Forehead 0.5-1.0
Cheek 0.4-0.6
Nose and chin 0.3
Upper and lower arm 0.5-1.0
Part of the body. mm.
Back of hand 0.3-0.6
I. and II. phalanges (volar). . 0.2-0.4
I. and II. phalanges (dorsal).. 0.4-0.8
Upper leg 3.0
Lower leg 0.8-2.0
Backj and sole of foot 0.8-1.0
From the foregoing data it would seem to follow that, as the con-
struction and relation of the chains of pressure-spots differ in the
different areas of the body, so will our sense of locahty change.
The number, sensitiveness, and direction in the chains of these
spots determine the sensitiveness of a given area. Moreover, our
perception of the size and shape of objects in contact with the skin
depends upon the same conditions. This can be shown in an as-
tonishing way by comparing the apparent direction which the out-
lines of any small body moved across the skin seem to assume with
the way the pressure-spots are located in the different areas through
which it is moved. If the curve of the chain of pressure-spots, for
example, bends in the reverse direction from that of the outline of
the body moved, the eff'ect may be to make this outline curve ir-
regularly or even straighten it out.
It need scarcely be said that Goldscheider regards the true ex-
planation of these phenomena to lie in the anatomical distribution of
the specific nerves of sense in the different areas of the skin. How-
ever this may be, it is certain that our sensations of pressure are
primarily "punctiform," and afterward massed into a tactual continu-,
urn ; and that what we primaril}^ know is not the extended object aa
such, but our sensations of pressure which are afterward objectified.
§ 26. Closely connected with the foregoing is the difference in
power of different parts of the skin in giving to the mind data for
discriminating the fact, the amount, and the direction of motion
in contact with the body. Upon this point the experiments of G.
Stanley Hall ' are of special interest. These experiments seem to
show that we are more likel}', when in doubt, to judge motion on
the surface of the limbs to be up rather than down their axis ; on
the breast, the shoulder-blades, and the back, the tendency is to
judge motion to be toward the head. The discriminative sensi-
bility of the skin for motion is much greater than that for sepa-
rate touch, as determined by Weber's experiments. Thus, while at
' Motor Sensations on the Skin, by Professor G. S. Hall and Dr. H. H
Donaldson, in Mind, October, 1885, pp. 557 S.
412 THE FIELD OF TOUCH.
least a distance of 25 mm. between the dividers' points was needed
on the volar surface of the right arm, in oi'der to perceive them
as two points, both the fact and the direction of motion could be
discriminated at an average distance of between 6 and 7 mm. In
judging the rate and distance of motion over the skin the liabil-
ity to error is always great ; but, as a rule, distances rapidly trav-
ersed are judged to be relatively shorter than the same distances
more slowly traversed. Inasmuch, however, as the judgment of
motion on the left arm was expressed by reproducing the rate
and distance with the right hand,' we have a double liability to
error involved in regulating the muscular movement of this hand
by means of its series of muscular and tactual sensations.
Hall found the motor sensibility of different parts of the surface
of the skin to be different ; but the differences do not appear to
correspond to those belonging to Weber's sensation -circles. The
average distance, in millimeters, which a metallic point of 12 mm.
in diameter could move over the skin at a rate of 2 mm. per second
before a judgment of direction could be formed was found, for one
subject of experiment, as follows: forehead, 0.20; upper arm, 0.40;
forearm, 0.44; shin, 0.60; ]Dalm, 0.74; back, 0.85. Motion can be
produced so slowly as not to be discriminated at all, even when the
body in contact has really moved from 6 to 12 centimeters. It can
also be produced so rapidly as to make it impossible to tell when it
begins and when ends. Heavy weights seem to move faster than
light ones going at the same rate ; but here other sensations are
called out by the deep pressure, and combined with those of con-
tact. Hall concludes that heat-spots and cold-spots traversed by
the moving body are of great service in judging motion and its di-
rection on the skin ; the cold-spots more than the heat spots, "be-
cause of the fainter sensation and wider irradiation " of the latter.
Further experiments with a travelling metallic point that carried
the stimulus of an electrical current over the surface of the skin
showed an astonishing diversity of sensations developed at different
points of the area thus traversed. Points of cutting pain, " thrill-
points," " tickle-points," " acceleration-points " (or places where the
rate of motion seems suddenly to increase without any real change
in the speed of the moving metal), " blind-points " (or spots where
all impression of contact is momentarily lost), are all to be differen-
tiated. Yet the sharp differentiation of these sensations is ren-
dered difficult by the fact that the various kinds are so impacted
and run together, in a tangle of sensation. The experimenters also
speak as though many dermal sensations may thus be partially dis-
' Miud, October, 1885, p. 564 f.
nxEXESS OF te:.ipe::atui^3-3ense.
413
entangled, for the description of whicli language furnishes no ade-
quate terms. All these facts agree exceedingly well with the theory
of local signs already proposed. These dermal signs are complex
"mixtures" of feeling, which give to each discernible locahty a
characteristic local stamp. The fact that our sensibility to motion
is so much greater in each area of the skin than our susceptibility
to the distance of stationary points accords with the same theory.
Our ability to localize the dermal sensations is dependent upon the
degree and I'ate of the changes in the color-tone of these sensations.
Hall is undoubtedly right in holding that, by moving the touching
surface over the surface touched, we do not simply multiply, but
also diversify, our data for filling up the dermal blind-spots and
judging the nature of impressions.
§ 27. The localizing of sensations of temperature in the skin is,
in principle, the same as that of sensations of light-pressure or of
motion. The former, however, are in all our ordinary experience
interwoven with the latter ; they therefore have the help of the lat-
ter in getting a place assigned to them in the periphery of the
body. Recent researches, akeady referred to (Chap. IV., § 22), dem-
onstrate the fact, that the relative number and arrangement of
heat-spots and cold-spots is different for different areas of the skin.
Goldscheider ' has ex]3erimented to determine how far apart the
heat-spots and cold-spots must be, respectively, in oixler that two
of them, when stimulated, may he felt as two. Both kinds of sen-
sations ai'e localized, not as points, but as minute warm or cold
drops in contact Avith the skin. By the following table, which
gives the minimum distances for different areas of the body, it ap-
pears that the sense of locality connected with the cold-spots is
about twice as fine, as a rule, as that connected with the heat-spots.
The distances are given in millimeters.
Part of the body.
Cold-spots.
Heat-spots.
Forehead, cheek, and chin
0.8
3.0
1-3
1.5-3.0
1.5-3.0
3-3
0.8
3-3
3-5
Breast
4^5
Abdomen
4-6
Back
4-6
Upper arm
3-3
Lower arm ... .
3-3
Hollovv of the hand -
3.0
Back of the hand, and upper and
lower \e
s. . . .
3^
' Archiv f . Auat. u. Physiol. , Physiolog.
70flE.
Abth.
1885,
Supplemen
t-Band, pp.
414 THE FIELD OF TOUCH.
Some basis seems to be laid in the foregoing facts for a system
of local signs of the skin, that consist in a mixture of color-tones of
temj)erature-sensations. Yet sensations of heat or cold, in them-
selves considered, differ chiefly, if not wholly, in intensity. In them-
selves, therefore, they are not vs^ell fitted to constitute a so-called
" spatial series " of sensations. If, for example, a certain area of
the skin be stimulated simultaneously by both heat and cold, at
points too near together to be distinguished by touch, the result is
neither a modification of one sensation by the other nor a localizing
of the two sensations as lying closely side by side,' A wavering of
perception rather takes place, similar to the strife of coloi'S in vi-
sion ; the experience is as though the skin were being touched with
a single body alternately hot and cold. Klug also found that the
least observable distance between two points touching the skin at
the same time depends upon their temperature relative to that of
the skin. The medium value of this distance is reached when these
points have a temperature of 20°-40° C. (68°-104° Fahr.) ; it dimin-
ishes on either raising or depressing their temperature greatly
above or below the zero-point of the skin. The fineness of our
sense of locality, as well as of our sensitiveness to motion (comp.
§ 25), is increased by exciting sensations of temperature up to the
point where pain intervenes. But the localizing of these sensations
is primarily dependent, to a great extent, upon their connection
with localized sensations of touch. If we bring two parts of the
skin, that differ considerably in temperature, into contact — for ex-
ample, a cool hand and warm forehead, or a cool hand and a warm
one — it is often difficult by strict attention to the sensations of tem-
perature alone to tell which part is cooler, which warmer. The
difficulty is doubtless largely due to the fact that each part which
feels the temperature of the other is also changing its own tem-
perature in the direction of the temperature of the other. It is
therefore induced to feel itself, as it were, as being of the tempera-
ture of that other. A confusion of the data for judgment, accord-
ingly, takes place. Any localization of the sensations which occurs
under such circumstances is largely dej^endent upon secondary con-
siderations, and especially upon the direction of tbe attention.
We judge of depth by sensations of temperature, indirectly, and
through our ability to remove or change the intensity and locality
of these sensations by changing the position of the body in space
as related to what we know to be hot and cold bodies or surround-
ing media.
' See Czermak, Sitzgsber. d. Wiener Acad. , March, 1855, p. 500; confirmed
by Klug and others.
' nSTATUEE OF THE MUSCULAE SEISTSE. 415
§ 28. The specific sensations of the viuscular sense constitute
another spatial series which combines with the foregoing in the
localizing of areas at the periphery, and of external objects as
projected in space and yet known as in contact with the body. In- ,
deed, it is upon this particular system of local signs that the mind
is chiefly dependent for its data — other than the visual — in the
synthetic construction of its presentations of bodies that stand re-
lated to each other in three dimensions in objective space. Three
principal theories have been held as to the nature of the so-called
muscular sensations : (1) So far as they are not tactual, they are to
be resolved into " central feelings of innervation," which differ only
in intensity and not in specific quality, and which result from the
changes, initiating movement of the bodily organs, that take place
in the brain as correlated with impulses of the will (so Wundt, and
others) ; (2) they are not specific sensations, but are due to interj)re-
tations of those feelings in the skin which originate on account of
its changes of position, tension, etc., as the underlying muscles are
moved (so Schiff, and others) ; (3) they are specific sensations de-
pendent on a specific nerve-apparatus of sense, which has its end-
organs in the muscle-fibre, and which is excited by the contraction
of the latter in a manner dependent upon the kind, amount, and
direction of the muscular movement taking place (so Bell, Weber,
Funke, and others).
We have already given certain reasons for rejecting the first
two and accepting the last of the foregoing views (see p. 344 f.) ;
other reasons will be mentioned subsequently in discussing the
so-called "feeling of innervation" or of "active energy." The
muscular sense, like all the other senses which contribute to our
presentations of objects extended in space, appears to have its own
system of local signs. The muscular sensations are qualitatively
(and not merely quantitatively) different, according to the combi-
nation of the muscles moved, and according to the extension over
the muscular area of the stimulus imparted to the sensory nerve-
fibres situated in the muscle by the changing condition of the
latter as it contracts and relaxes. The series of sensations— with
all the qualities of rapid and nice gradations which belong to
"spatial series" of sensations — called out by moving one limb dif-
fers from that called out by moving another limb. At each step in
the flexing of the leg — for example — the color- tone of the muscular
sensations has a specific quality and value as a local sign, in our
consciousness, of the position of the member. The same thing is
true of the bending arm, back, or single toe or finger. These sen-
sations are intimately, and even inextricably, combined with the
416 THE FIELD OF TOUCH.
spatial series of specifically dermal sensations ; but in tliemselvea
they have a different quality, and are not localized simply at the
surface of the body. As the extent of the circuit of motion gone
through by any limb increases, or the intensity of the strain be-
comes greater, the quality of the mass of resulting muscular sensa-
tions is perpetually changing. These sensations are, accordingly,
localized over a broader area of the body and deeper in its sub-
stance, as it were. Everyone knows Avhat new mixtures of sensa-
tion are produced in consciousness by calling into vigorous exer-
cise the unused more deeply lying muscles of the body. Bain' has
discussed these sensations at great length and with commenda-
ble acuteness. But the apparent assumption that these particu-
lar sensations can, by being associated, acquire of themselves the
quality of extension in space, and the accounting for all our other
perceptions of spatial qualities and relations as merely secondary
and symbolic of the associated muscular sensations, are in plain
contradiction of established psychological facts and principles.
The muscular sensations also assist the more strictly tactual in
discriminating locality for all cases where the pressure upon the
skin exceeds a certain small degree of intensity. In strong contact
or heavy pressure the sensory nerves of the underlying muscle are
excited ; we have the feeling, not simply of being touched, but also
of being pressed. The combination of these two spatial series
gives to the mind a doubly constituted system of local signs ; hence,
as the experiments of G. Stanley Hall ^ show, our judgment of di-
rection of motion is quicker as the weight resting on the skin is
increased up to the limit where other disturbing sensations inter-
vene. The sui^erior discriminating power which any member of
the body has when permitted to move — that is, to call forth fa-
miliar series of muscular sensations — is largely due to the help
which the local signs of this system render to the mind. When
the particular member (the hand) which is capable of the nicest
tactual discrimination is also permitted to move over an object
freely, and to acquire abundant data from all the sources described
above, we have fulfilled the most advantageous conditions for the
utmost nicety of knowledge possible to " touch," in the Avidest
meaning of the word.
§ 29. It is unnecessary to illustrate in further detail the process
by which the mind, with its native synthetic activity, and with
the help of qualitatively different sensations, constructs its field of
' The Senses and the Intellect, especially pp. 57-100, 336-348, and 364-
398.
2 Mind, October, 1885, p. 567.
RELATIOIS^S OF EYE AND HAND. 417
touch. To multiply instances would neither explain the ultimate
mystery which enters into the processes of " localization " and " ec-
centric projection " by touch, nor add materially to our compre-
hension of known psycho-physical principles. The muscular sense
may pi'obably be said to have the leading position in the develop-
ment of the perception of spatial objects and relations, so far as
attainable without the aid of sight. Perceptions of the magnitude,
distance, and primary spatial qualities — such as the extension and
inertia — of material things are largely dependent upon associated
sensations of the muscular sense, although these perceptions cannot
be said to be mere compounds of such sensations with secondary
and symbolic sensations of other kinds added to them. The activ-
ity of the hand, as it moves over various surfaces of the body, either
touching them itself or carrying with it something with which these
surfaces are touched, early combines with the different series of
muscular sensations other spatial series of tactual sensations.
The localization of certain points in the area of the body which
are of marked local characteristics, and frequently recurrent in ex-
jDerience, is the first achievement in constructing the field of touch.
To these landmarks, as it were, other points or areas, subsequently
discovered, are referred. One hand learns to know the other ; the
right hand chiefly exjDlores the left arm and side and the upper right
leg ; the left hand, the right arm and side and the upper left leg*.
The finger-tips, especially of the right hand, have an office similar
to that performed by the yellow-spot of the retina ; they are the
centre or hearth of clear perceptions of touch. But in order to
bring them to their object they must be moved ; through this mo-
tion fresh combinations of muscular and tactual sensations result.
§ 30. But long before the entire field of touch has been con-
structed with any considerable appi'oach to comj)leteness, the eye
has already explored those parts of the body which are open to its
inspection. It learns first to know the hand, which nature keeps
constantly in motion before it. As objects rest on the hand, it
notes the place where they rest ; with its perceptions of sight cer-
tain combinations of tactual sensations thus become associated. As
the hand moves over other objects, or especially over the other parts
of the body, the eye marks its successive progress ; combined sen-
sations of muscular and tactual kind are thus associated with each
position of the hand and with each area of the body which it touches.
Very early in the development of a normal experience the eye comes
to be the leader and critic of the discriminations connected with
the muscular and tactual sensations. Its power of rapid movement
over its total field, and its delicate judgment on account of the
27
418 THE FIELD OF TOUCH.
finely sliadecT complex local signs which it calls forth with a com-
prehensive simultaneousness, give a great superiority to the organ
of vision as a geometrical sense. The results of such superiority it
constantly places at the disposal of the more slowly moving and
less delicate sense of touch. For this reason, one born blind can
never attain the same quality (of " comprehensive simultaneous-
ness ") for his sj)atial intuitions and ideas of spatial relations ; even
the field of touch, in spite of the greater refinement which the
muscular and tactual sensations of such an unfortunate person ac-
quire through use, cannot possess this quality as it is imparted by
the eye.
The familiar experiments of trying to estimate the size, shape,
and relation of objects, the amount and direction of motion, etc.,
when blindfold, show our dependence upon the organ of sight. It
must not be forgotten, however, that the discriminations possible
through the muscular and tactual sensations alone are wonderfully
exact ; and that in certain circumstances touch has sight at a dis-
advantage, as it were. Thus the player on the violin who should
adjust his spacing of the strings by the sensations of the eye, with
the unaccustomed and unfavorable perspective made necessary by
its position in relation to the left hand, would not attain the art of
making true and pure tones.
§ 31. Among the most complex perceptions of which the skin
and muscles by their combined action are capable are the so-called
"feelings of double contact." It is largely by means of these feel-
ings that skill is acquired in the use of tools, weapons, and musi-
cal instruments. In these cases the process of projection goes so
far that we seem to feel the object with which the implement is in
contact, not so much in the hand (the feelings of contact being
located there), by the external means of the implement, but rather
as ourselves being in the implement and using it as a sentient part
of the organism. The carver in wood feels his chisel move through
the stuff he is shaping, and guides it as unerringly as he would his
finger, so as to lay it with a given degree of pressure upon a given
spot. We are all familiar with the experience of feeling the ground
we are about to tread, with a cane or other stick. If the fingers be
lightly brushed over the hair when it stands out from the head, it
will be difficult to localize the sensations of pressure at the scalp
rather than in the hair. We feel the touch of our finger at the end
of the tooth, where the contact takes place, instead of where the
sensory nerves really receive the stimulus and convert it into a
nerve-commotion
The management of the implement is, of course, really made
FEELINGS OF DOUBLE CONTACT. 419
possible by delicate changes in the shades of feeling called out by
its changing pressure upon the nerves terminating in the skin and
muscles of the hand, and by the accompanying feelings of strain
and of effort that result from the movement of the arm which
carries the hand. These feelings are aroused by the end of the
implement which is in contact with the body, and are primarily
localized in that pai't of the body ; but they are felt through a
more artificial and elaborate process of localization, as though di-
rectly dependent upon the other end of the implement. Upon the
aesthetic and pleasurable uses of these feelings of double contact
Lotze ' has remarked at length.
At this point the further discussion of the development of our
presentations of sense in general must be arrested, in order to con-
sider more in detail the activities of the other great " geometrical
sense."
' See Microcosmus, i., pp. 586 ff. Edinburgh, 1885.
CHAPTEE YII.
THE PEESENTATIONS OF SENSE. [Continued.]
§ 1. The application of the general princij)les which control the
development of our presentations of sense to the particular case
of the eye has many peculiar difficulties. The physiological psy-
chology of visual perception is, therefore, a much controverted and
very obscure domain. This fact is doubtless in part due to the
amount of experimenting and speculating which has been be-
stowed upon it. For here, as elsewhere in scientific research, one
chief result of extended examination is to raise unanswered in-
quiries. Peculiar difficulties, however, are intrinsic in the case of
the eye. These are due to the great complexity of its native
activities, and to the speed with which it reaches a generous
maturity of development. Nature has equipped this organ with
superior means for furnishing to the mind a variety of data, as
respects both quantity and quality, for the nicest discriminations ;
it has also provided it with such constant stimulation as to cause
it to acquire an incomparable facility. But the character of its
structure, functions, and development is such as to make experi-
ment difficult in a way to disentangle the simple factors from those
complex forms into which the synthetic activity of the miud has
constructed them.
§ 2. It is affirmed by one authority ' that no less than eight
different data, or motifs, are used in monocular vision by the
adult for perceiving the third dimension of space and of visual
objects in space. These are the changes with respect to (1) extent
and (2) clearness, of the complex of the sensations of color and
light, as dependent on distance ; (3) the perspective elevation of
the bottom of distant objects above the horizon ; (4) the covering
of known distant objects by those placed nearer ; (5) the alter-
ations of light and shadow on the curved surfaces of the object,
according as they are nearer or more remote ; (6) the perspective
contraction of the retinal image ; (7) the change of the visor angle
in proportion to the distance of the object ; (8) the muscular sen-
' Volkmann vou Volkmar, Lehrb. d. Psychologies II., p. 84.
PKOBLEM OF VISUAL PERCEPTION-. 421
sations of the accommodation of the eye. To these eight data, two
others at least must be added for binocular vision ; namely (9), the
stereoscopic double images, and (10) the sensations arising from
convergence of the axes. These ten sets of variable experiences may
be combined, of course, in an almost infinite variety of proportions.
Moreover, it is not improbable that we shall have to admit still
other data as entering into the complex perceptions of sight. The
tactual, as well as muscular, sensations which accompany the move-
ment of the eyeballs in their sockets are not ineffective in giving
grounds for judgment in certain cases. The question must also
be raised : Do not the visual sensations themselves have a certain
local coloring directly dependent upon the nervous elements of
the retina which are excited by the stimuli ? If we answer this
question affirmatively, we shall have a system of local retinal signs
as constituting one of the most primary of the spatial series of
sensations entering into the space-perceptions of this sense. And
after all this cataloguing of data, the dispute as to the existence of
series of sensations of innervation that have a central origin and
differ only in intensity as directly dependent upon so-called acts of
will (so Wundt) remains unsettled.
Several of the data just enumerated, however, are plainly of only
secondary rank and value ; they do not necessarily enter into every
preception of a visual object as such. What does seem necessary
to the most elementary form of visual perception may be stated as
follows : Sensations of light and color, differing in intensity and qual-
ity, hut simultaneously present in consciousness, must be systematically
arranged with reference to each other by being localized with the help
of retinal signs, and associated with other spatial series of muscular
sensations that arise from accommodation of the eye and from its
motion. The complexity of the combinations arising in the normal
use of the organ of vision is, of course, increased by the fact that
there are two eyes, and, therefore, two retinas with their systems
of retinal signs, two images of each object, and two sets of motions.
But the two eyes are (as we shall see subsequently) in a certain
sense to be regarded as one eye — certainly as constituting one
organ of vision. So that, even when one eye is closed, the other
does not see what it sees without being influenced by the closed
and relatively inoperative part of the one organ. The constancy
with which the eyes act together explains, in part, why they are one
organ as the two hands are not ; but the frequency with which avb
voluntarily suppress the activity of one eye by closing it explains,
in part, why they are not one organ as are the two nostrils or the
two ears.
422 DATA OR MOTI"FS OF VISION.
§ 3. Could we select an adult human being who had never seen,
and proceed to develop his visual perceptions, experimentally, in
the direct order of their complexity, we might possibly rely upon
his description of his experience to solve certain problems that now
seem unsolvable. We should wish, before either eye had been
moved when open, to excite the nervous elements of a small area of
one stationary retina, and to ascertain how far the sensations of light
and color thus excited could be said to have any strictly "local"
ari'angement with reference to each other. We should then wish
to try the effect of combining with these sensations other spatial
series, consisting of muscular sensations and arising from the ac-
commodation and motion in its orbit of the same eye. Finally, the
intricate process of putting the two eyes together — both open and
both moving — might be studied in detail. At present, however,
it is quite impossible to say what the experience of the subject of
such experiments would be. The testimony of the few blind per-
sons whose eyes have been couched is so meagre and unsatisfac-
tory, on account of its failure to comply with the conditions of
scientific investigation, that it can be used only to confirm con-
clusions arrived at on other grounds. Nothing remains, then, but
to employ the data which physiological optics has secured, in order
to make a theoi'etic reconstruction (confessedly imperfect and doubt-
ful) of the process that nature is all the while successfully com-
pleting. In this effort we naturally follow the order of nature, so
far as possible ; we begin with the simplest conceivable case, and
proceed f I'om it to the explanation of the amazing complexity which
really belongs to our apparently simple daily experience of vision
with two trained eyes. This is substantially the course followed
by Wundt,' who finds three things to be considered in explaining
the develoj)ed perceptions of sight : (1) The retinal image of the
eye at rest, and the motifs which it furnishes ; (2) the single eye
as moved, and the influence of these movements ; (3) the conditions
furnished by the existence and relations of the two eyes exercis-
ing their functions in common. But, in reality, from the very be-
ginning of its activity the eye is in motion, and acts as a double
organ.
Corresponding to the three sets of considerations just mentioned,
we may speak of three fields of vision which are to be constructed
in the order of their complexity. They may be called, resi^ectively,
the retinal field of vision, the field of monocular vision, and the
field of binocular vision. In the "retinal field of vision " we mean
to include only such a percejotion — or mental spatial arrangement
' Pliysiolog. Psychologie, ii. , p. 63.
NATURE OF THE EETIISTAL FIELD. 423
of sensations of color and light as points lying side by side — as
would be presented through the excited expanse of nervous ele-
ments constituting the retina of one motionless eye, in case there
had been no previous vision with both eyes in motion. The field
of monocular vision, when completely constructed, includes all that
can be seen with one eye as the result of its experience, devel-
oped, but unaided by the other eye. The field of binocular vision
includes all that can be seen by both eyes. The first two so-
called " fields of vision " are, strictly speaking, fictitious and theo-
retically constructed in order to explain the process by which the
mind reaches the construction of the third and last. Indeed, the
question may be pressed, whether we can speak of a purely " retinal
field of vision," and whether the excited mosaic of nervous elements
on which the image is formed, without aid from muscular sensations
of the eje, could furnish any presentations of sight.
§ 4 The most nearly original experience of sensations of light
and color which can be easily produced for adult observation is
gained by closing and blindfolding both eyes, and then keeping
them as motionless as possible. Let time enough be allowed for
all the after-images, both positive and negative, to die wholly away.
Nothing is then seen but a small and undefined expanse or massive
aggregate of related color-sensations, which we will call the " ret-
inal field ; " it might almost be said that this is felt rather than
seen. Such " vision " (?) of a certain continuum of sensations can-
not be said to be either localized or j^rojected in space, as a whole,
and by the eye alone. When we speak of it, for example, as " in
front of " the upper part of the body, we introduce terms that are
derived from experiences of touch. Now, without moving or un-
covering the eyes, let the head be turned to the right or to the
left, and the expanse of color-sensations will move in the same
direction ; or, if we turn the face upward, the retinal field seems
above us ; if downward, then it seems to sink toward our feet. But
each position of this field, as a whole, is entirely determined by the
fact that the customary muscular and tactual sensations assure us
of the posture of the head with reference to the rest of the body.
Such localization is accomplished chiefly by sensations in the neck.
So far as sight alone is concerned, the entire expanse of color-sen-
sations cannot be said to be perceived as anywhere in space.
The "retinal field" has no clearly defined limits, or boundary-
lines ; it may be described rather as having its expanse of sensa-
tions distinguished by a shifting, graded transition into a region of
no-sensations. This fact is, of course, due to the constantly chang-
ing activity of the nervous elements of the retina. Yet the sensa-
424 DATA OR MOTIFS OF VISION.
tious which are massed in the foregoing experience constitute a
true spatial expanse ; they are not simply recognized as differing
in color-tone, or brightness or intensity of effect, but as having true
local distinctions, and as being aiTanged into a system of points of
color and light lying side by side. In other words, the different
sensations do not fall together in consciousness so as to resemble
the one sensation of smell produced by irritating simultaneously a
number of fibres of the olfactory nerve ; nor are they simply ana-
lyzable into several qualitatively different factors, as is the com-
plex sensation of a musical clacg. They are presented as spatially
systematized, as a true perception of an extended object. The " ret-
inal field " may, then, be said to be extended in two dimensions ;
and the minima visibilia which compose it all have local relations
to each other. It cannot properly be said, however, to have depth
(as Stumpf ' and Hering ' hold that it does) ; for the different col-
ored points are not projected as different in distance, nor can we
be said to look into the colored space thus presented before the
mind. It is true that the expanse of the retinal field is not like
that of a darkly colored wall or curtain placed in front of the eye.
But the quasi-appearance of depth is due to constant change in
color-tone and brightness of the minute portions of the field,
which has an effect somewhat like that we get on looking at a very
dense mist of particles differently colored and drifting. In other
words, the secondary and derived data give to it an ajDpearance
which we have learned to associate with the perception of depth.
§5. Further experiment, however, with this so-called "I'etinal
field " serves to show how complicated its apparently simple char-
acter really is. In the first place, even this field is the result of
the combined action of the two retinas. If, with both eyes closed,
a "phosphene " (see p. 195 f.) be produced in either eye by pressing
upon its ball, the colored circle will be located in the correspond-
ing part of the field ; but the character of the entire field, as formed
by the activity of both retinas, wiU be changed. It is, of course,
impossible to suppress the action of one retina, and thus exam-
ine a monocular " retinal field," as it were. But it may easily
be shown that, even in vision with one eye open and in motion,
the character of the whole field of vision is under the influence
of the retinal activity of the closed eye. Let one of the eyes — both
hitherto closed and motionless — now be opened. Immediately a
' Ueber d. physiolog. Ursprung d. Raumvorstellurig. Leipzig, 1873. Stumpf
liolds that "Space is just as originally and directly perceived as quality" (p-
115).
2 In Hermann's Handb. d. Pliysiol, III., 1., p. 572 f.
NATURE OF THE RETINAL FIELD. 425
picture of all the objects falling within the field of monocular vision
appears before us ; each object seen with its position, magnitude,
and spatial relations determined according to the laws of visual
perception. This monocular field seems bounded on one side (the
left side if the right eye is opened, the right side if the left) by
the rather dim outline of the nose and lower line of the forehead.
What has become of the retinal field of* the closed eye ? It has
been submerged or overwhelmed by the field of the open eye, on
account of the latter's stationary and clearly defined images and
strong arrest and fixation of attention. But if a character to arrest
and fix the attention be given to the field of the closed eye, it may
be made in turn to overwhelm that of the open eje. This can be
accomplished by producing strong " phosphenes " in the former. On
pressing the closed eye brightly colored circles are presented in
the corresponding part of the field ; and by using sufficient press-
ure the objects seen as projected in space by the open eye are
drowned in a shower of minute, vivid sparks.
The " retinal field " has its character determined also by as-
sociated muscular sensations dependent upon the movement of
both eyes. It will be found impossible to make any definite area
of this retinal field, which lies much to the right or left, to the
upper or lower part, of its centre, a matter of regard without
detecting slight movements of the eyes according to the direc-
tion in which the attention is to be fixed. The value of muscular
movements in this case cannot consist in their enabling a clear
image of objects situated in different relations to the eye to be
formed on its retina ; for with closed eyes no change is occasioned
in the retinal images by motion of the eyes. The conclusion, then,
is, that certain muscular sensations constitute an indispensable
part of the data for localizing objects even in the retinal field — at
least such as are only a slight distance from its centre. Moreover,
it will be found that the extent of this entire field and its pro-
longation, as it were, in any given direction are dependent upon
the accommodation and motion of the eyes. The explanation of
this fact can be found only in the same truth, namely : The per-
ception of localized areas in the tivo-dimensioned " retinal field " of the
closed eyes is dependent upon the revival of associated muscular sen-
sations.
§ 6. The foregoing facts undeniably afford considerable support
to the " empiristic " theory of visual perception ; but they do not
show that the considerations it brings forward are entirely con-
clusive. They do not even prove the truth of Wundt's statement : '
' Physiolog. Psychologie, ii., p. 69.
426 DATA OR MOTIFS OF VISION.
" Our sensations of light do not immediately possess spatial form."
After excluding all the factors wliich combine into our ordinary
presentations of sight — such as double images, accommodation,
convergence of the axes of the eyes, and secondary helps by way
of shadows, perspective, elevation, etc. — a certain spatial quality
still remains to the simplest sensations of color and light which
we are able to reproduce. It will naturally be objected that these
sensations are the reactions of a mind that has had a long pre-
vious experience in localizing visual sensations by means of just
such heljDS as the foregoing. The question then recurs : Is the
fact that the sensations of light and color, which are produced by
the simultaneous excitation of many nervous elements of the ret-
ina, appear as locally distinct (even when the eyes are closed and
motionless) an otherwise unexplained datum due to an original
activity of the mind under the law of the specific energy of these
nervous elements ; or is it a result of acquired experience, to be
explained by the revival of images of previously associated impres-
sions obtained when the eyes were both open and moving ? To
take the former position is to adopt, so far forth, the nativistic
theory of visual perception ; to take the latter is to espouse the
empiristic opinion. Either position has its difficulties. The for-
mer seems to us, however, nearer to the ultimate truth.
§ 7. That the sensations of light and color occasioned by stimu-
lating different elements of the retina have a different value in
consciousness, and that the recognition of this value, and the pres-
entation of the sensations as locally separate and arranged into
a spatial system, is native to the mind, may be argued from the
following among other reasons : The peculiar mosaic structure of
the retina is obviously the fundamental cause for the pre-eminence
of the eye as a " geometrical sense." It has already been shown
(Chap. IV., § 3) that each element of this structure maybe regarded
as an isolated sensitive spot, which corresponds, on the one side, to
individual irritations from the stimuli, and, on the other, to the
smallest localized sensations of light and color. But the latter part
of this statement could not be true unless each of the elements in
this nervous mosaic had a certain peculiar representative value in
consciousness. In other words, sensations of light and color are
localized in part, at least, by means of the specific local quality
which belongs to the result of the different points in the retina
being simultaneously irritated. The very construction of this or-
gan, as well as the correspondence between its construction and the
nicety attained in its use for local distinctions, indicates that the spa-
tial quality of our visual percepts depends upon its specific functions.
NATURE OF THE RETHSTAL IMAGE. 427
Moreover, unless the series of light- and color-sensations had an
original spatial character, it is difficult to see how they could com-
bine with the other sj)atial series of the eye into percejDtions of ex-
tended colored objects. It is difficult to see what advantage they
would then have over the series of musical tones varying in pitch.
Still further, it is as impossible to prove exj)erimentally as it is to
make seem true to consciousness that the arrangement of the points
of light and color which ajppears before us with closed and motionless
eyes is only the residuum, as it were, of past sensations of a muscu-
lar kind. Such an appeal to consciousness could not be made, in-
deed, with any confidence, if scientific analysis were able to show
that the color-sensations can be perceived simultaneously, as a sys-
tem of points lying side by side, without having the characteristics
of a spatial series. But in view of our inability to do this, we only
account for the facts of consciousness by admitting what the very
structure of the organ suggests, and what general psychological
theory seems to confirm, when we hold that spatial perception, at
least in germinal form, is native to the mind as a synthesis of the
qualitatively different sensations which result from stimulating simul-
taneously the retinal mosaic of nervous elements.
The foregoing view is very different from that which assumes
that we have an immediate knowledge of the retinal image ; or
that a knowledge of the direction from which the Hght falls upon
the retina is an unresolvable intuition of the mind. ' To such mis-
taken statements it is a sufficient reply to show that the subjective
image (or mental presentation) of the object does not correspond
either to the image on the retina or to the real object as it is other-
wise known to exist in space. The mental presentation, for exam-
ple, has no blind-spot ; it is a different representation of the real
object from that offered by the retinal image, with more inaccu-
racies than belong to the latter as seen by an observer looking
at it from without.^ To the question, then, whether sensations of
light and color would have space-form if they came only from an
excited but motionless retina, and were uncombined with other
sensations of a spatial series, we can give only a tentative and par-
tial answer. Doubtless the "presentations of sense" formed by
combining such sensations alone would be indescribably different
from those to which we now ascribe visual space-form. An animal
with a single immovable expanse of nervous elements susceptible
' See Le Conte, Sight, pp. 85 f. and 105. IS'ew York, 1881. Le Conte is
obliged to admit, however, that this " law of direction " is sometimes opposed
to the "law of corresponding points " (p. 258).
'^ See Wundt, Physiolog. Psychologie, ii., p. 68.
428 DATA OR MOTIFS OF VISIOTST.
to irritations from ligM could not be said to have what we call
" vision." But, on the other hand, the spatial quality which be-
longs to the visual sensations of man cannot be all resolved into
muscular and tactual sensations of eye and hand ; these sensations,
quoad sensations of light and color, do have the quality which in-
sures their arrangement in consciousness in spatial order. This
fact is due to the working of the law of the specific energy of the
nervous retinal elements in connection with the native activity of
mind in synthesizing these sensations. The law as applied to the
eye is essentially the same as that already demonstrated for the
skin ; the activity assumed as native to man is not essentially dif-
ferent from that ascribed to the lower animals in the use of their
senses. That this tact for the individual has been largely won by
the development of the race is a proposition to which our attitude
is determined by more general conclusions. But physiological op-
tics cannot account for the phenomena of vision without assum-
ing both the original exercise of this tact and the theory of local
retinal signs as data hitherto uni'esolvable by its analysis.
§ 8. Whatever may be thought of the foregoing assumptions, it
is certain that ordinary adult visual perception involves the motion
of the open eye — monocular vision of one eye and binocular of
both. The sensations which accompany such motion must be com-
bined with sensations of light and color to make the complete pres-
entations of sight. The consideration of the simplest case requires
that we should recur to the physiology of the eye. Only one small
spot in the retina (the so-called "fovea centralis," see p. 183), is
capable of giving a perfectly clear image of an object. When, then,
we desire to see an object clearly, we bring its image upon this
spot and fixate it there. That point of the object to which the
centre of the retinal area of clearest vision corresponds is called
the "point of regard" (or "fixation-point"). In ordinary vision,
then, the eye constantly changes its point of regard, and so brings
successively upon its most sensitive area the images of the different
points of its object.
The different changes of position in the point of regard are
accompanied by sensations of motion and strain ; they are accom-
plished by the six muscles of the eyeball. This wandering of
the point of regard over an object may be considered as accom-
plished by rotating the eye vipon a pivotal point, or " centre of
rotation," by motions that have different axes of rotation. The
centre of rotation is, however, only theoretically a point, but is
really an interaxial space. It has been variously located for normal
eyes at about 13.45-13.73 mm. behind the cornea, and 1.24-1.77
PRIMARY POSITIOIir OF THE EYE.
429
pbl.:,SUp.
mm. behind the middle of the optical axes. Of such axes of rota-
tion, three are especially to be distinguished — an antero-posterior,
a vertical, and a ti-ansverse. A line drawn from the centre of
rotation to the point of regard
is called the "line of regard;"
since each eye has its own cen-
tre of rotation, there are, in vi-
sion with both eyes, two lines of
regard. A plane passing through
these two lines is called " the
plane of regard " (or " plane of
vision").' In the " primary posi-
tion " the head is erect and the
line of regard directed toward
the distant horizon. The plane
jDassing througli the lines of re-
gard of both eyes in this position
is the " primary plane of vision."
In this position for most eyes,
however, the line of vision is in-
clined somewhat below the hori-
zontal plane.
Starting from the primary po-
sition, one set of positions are suc-
cessively assumed by moving the eye upon its transverse and verti-
cal axes. When the eve rotates round the former, the line of regard
is displaced either above or below ; it thus makes a varying angle
with the line corresponding to its first direction, and this is called
the " angle of vertical displacement " (so Helmholtz), or the " ascen-
sional angle." When it moves about the vertical axis, the line of
regard is displaced from side to side, and forms with the median
plane of the eye a varying angle called "the angle of lateral dis-
placement." In passing from the primary position to the foregoing
secondary position no rotation of the axis itself occurs. Another
order of positions is assumed by an apparent rotation on the antero-
posterior axis, combined with lateral or vertical displacements ; this
movement results in bringing the eye to an oblique position, and is
really a torsion of the eye. The angle which the plane of regard
makes with the transverse plane measures the amount of torsion,
and is called the " angle of torsion."
' For the detailed theory of the movements of the eye, see Hering, in Her-
manns Handb. d. Physiol., III., i., chaps. 9-11 ; Helmholtz, Physiolog. Op-
tik, §g 27-30 ; and Wuudt, Physiolog. Psychologic, ii., p. 72 f.
r>ext; r. inf. r. int;
Fig. 97.— Diaprram of the Attachments of the
Muscles of the Eye, and of their Ajxes of Ro-
tation— the latter being shown by clotted
lines. The axis of rotation of the rectus,
externus, and internus, being perpendicular
to the plane of the paper, cannot be shown.
430
DATA OR MOTIFS OF VISION.
§ 9. The various movements possible for the eye in all the direc-
tions just described are accomplished by the combined pull of the
muscles of the eye as summarized in the following table ' (for the
muscles and their position, see Fig. 49 f., p. 174) :
Number of muscles active.
Direction of line of regard.
Muscles acting..
n-no
5 Inward
Internal rectus.
( Outward
External rectus.
( Upward
j Superior rectus.
Two
{ Downward
' Inward and upward ....
Inward and downward . .
-
Outward and upward . .
Outward and downward.
I Inferior oblique.
Three
j Inferior rectus.
I Superior oblique,
I Internal rectus.
•< Superior rectus.
( Inferior oblique.
( Internal rectus.
< Inferior rectus.
( Superior oblique.
i External rectus.
-| Superior rectus.
( Inferior oblique.
i External rectus.
■| Inferior rectus.
( Superior oblique.
§ 10. The law which seems to govern all the eye's movements of
torsion — or combined movements sideways, and either up or down
—was conjectured by Listing, whose name it bears, and elaborated
by Helmholtz. Listing's law is stated by Helmholtz * in the fol-
lowing terms : " When the line of regard passes from its primary
position into any other position, the torsion of the eye (as meas-
ured by the angle of torsion) in the second position is the same as
if the eye were turned about a fixed axis standing perjDendicular to
both the first and the second positions of the line of regard." The
same principle is stated in different language by Wundt : ^ " All
movements of the eye from its primary position take place about
fixed axes, each of which at the point of rotation stands at right
angles to the plane which is described by revolving the line of re-
gard ; and all of these axes lie in a single plane, at right angles to
the primary position of the line of regard, at its point of rotation."
The orientating of the eye, then, for every possible position of the
line of regard, may be referred to a constant standard. Concerning
one important matter in the carrying out of Listing's law, thei-e is
a direct conflict of view between authorities. According to Helm-
' Given by Beaunis, and to be found in the Encyclopaedia Britannica,
ninth ed., VIII., p. 825.
2 Physiolog. Optik, p. 466. ^ Physiolog. Psychologie, ii., p. 79 f.
THE EFFECT OF ROTATIOlSr. 431
holtz,' when the plane of vision is raised, lateral displacements to
the right produce rotation of the eye to the left, and lateral dis-
placements to the left produce rotation to the right ; when the
plane of vision is depressed, lateral displacements to the right pro-
duce rotation to the right, and vice versa. But according to Le
Conte,' in elevation of the visual plane the eyes both move and ro-
tate to the right or to the left ; in depression of this plane, motion
of the eyes to the light is accompanied with rotation to the left,
and motion to the left with rotation to the right.
More detailed statement of the laws of the eye's motion in vi=
sion is not necessary for the purposes of physiological psychology.
It need only be noted that the construction of the field of monocular
or binocular vision is a synthetic mental achievement dejoendent upon
the varying sensations which result from the wandering of the point of
regard over the outline of an object. Starting from its primary posi-
tion, the eye may come around, as it were, by a variety of circui-
tous paths, to the fixation of any particular point of its object. In
the pursuit of these paths it develops various series of muscular
sensations that have spatial qualities and are fitted to combine with
the spatial series of light and color sensations. Thus the field of
vision necessarily has the same form as the surface over which the
point of regard can be made to wander. Its construction is a pro-
gressive synthesis of the mind, stimulated and guided by means which
consist in varying states of consciousness, chiefly dependent upon
the local coloring of the two sets of sensations thus far described.
§ 11. Certain important consequences follow as to the relation
between the lines of the extended and objective " thing " and the
lines of the retinal image, as affording the mind data for the spatial
ordering of the sensations that arise from stimulating the nervous
retinal elements and nerve-fibres of the muscles of the eye. Both
the general form of the field of vision and the relative position of
the objects in it are determined by the movements of the eye. The
rule is, that only those objects which ai-e seen by direct vision (their
images lying in the line of regard when the eye is in its primary
position) appear in their actual place ; objects indirectly seen ap-
pear in the place which they would assume if their retinal images
were transposed to the point of regard and its immediately sur-
rounding points.^ It follows, furthei', that all lines lying outside
of the vertical and horizontal meridians of the retina, in order to be
seen straight, must be really bent ; and all really straight lines in
' Physiolog. Optik., p. 463,
'•* Sight, pp. 173 fE. ; and American Journal of Science and Arts, xx. (1880),
pp. 83 ff. ^ Comp. Wundt, Physiolog. Psjchologie, ii., p. 90 f.
432 DATA OR MOTIFS OF VISION.
such positions are seen bent. This fact may be proved in varioua
ways. If a sheet of white paper, having a black dot in its centre
to serve as a point of regard, be held at right angles to the line of
vision, with the eye in its primary position and constantly fixed
upon this point, thin, straight slits of black jDaper outside of the two
meridians will appear bent. Or if the after-images left on these
meridians of the retina by light falling through narrow and straight
slits be studied when torsion of the eye takes place, these after-im-
e| ]e
Fig. 98 (From HerinR. after Helmholtz).— With the eye at the distance e-e, and fixated upon the
centre, the hyperbolic lines which limit the black and white surfaces show the so-called "right
lines " of the field of vision.
ages will themselves be found to suffer torsion.' Such images, re-
ceived upon the vertical meridian of the eye when it is in its pri-
mary position, lean to the right, thus / , when the visual plane is
elevated and the eye moved to the right ; but when, with this
plane elevated, the eye is moved to the left, the vertical image in-
clines to the left, thus \ . With depression of the visual plane,
the inclination of the after-image is reversed. The image of a
perfect rectangular cross is distorted as follows by different torsions
> See Le Conte, Sight, pp. 164 fE.
SENSATIOlSrS OF ACCOMMODATION. 433
of the eye : "Upward and to the right, ,J^^ ; upward and to
the left, "^"v, ; downward and to the right, ^-«\^ ; down-
ward and to the left, .^4'^ », The connected results of all the
possible torsions of the eyes in curving the lines of the field of vis-
ion is . illustrated by the accompanying figure (98)' ; the study of
this figure, as it appears at various distances, from arm's length to
contact with the nose and forehead, is an instructive exercise. The
dependence of the field of vision upon the positions and motions
of the eye is one principal source of the errors of this sense.
§ 12. Besides the help from muscular sensations due to move-
ments of the eye in fixing its point of regard, account must be taken
of those which result from accommodation of the eye (for the
mechanism of accommodation, see p. 177 f.). As says Helmholtz : "
" There can be no doubt that anyone who has much observed his
own changes of accommodation and knows the muscular feeling
of the effort belonging to them, is in a condition to tell whether,
when he fixates an object or an optical image, he is accommodating
for a great or small distance." There is scarcely greater doubt that
the significance of this change of muscular feeling would not be
realized as indicating a third dimension of space, were it not com-
bined with sensations belonging to the use of both eyes in conjunc-
tion with the organs of touch. Even adult judgment of distance,
by accommodation alone, is extremely imperfect. Wundt ^ experi-
mented to determine the niceness of this judgment by regarding a
black thread, stretched vertically against a white background, with
one eye through an aperture in a shield. He found that almost
nothing could be told in this way as to the absolute distance of the
thread. Its relative position, however, could be discriminated with
considerable accuracy by changes in accommodation ; and, as might
be expected, with more accuracy when the apparatus was called
into more active operation by approach of the object toward the
eye. Helmholtz * found that he required a stronger accommoda-
tion to see a red stripe clearly through a tube than was necessary
to see one of blue.
' Taken from Hering (after Helmlioltz), in Hermann's Handb. d. Physiol.,
ni., i., p. 537.
? Physiolog. Optik, p. 633.
^ Beitrage zur Theorie d. SiuneswahrnelLmung, 1863, pp. 105-118.
4 Ibid., p. 634.
28
434
BINOCULAR FIELD OF SIGHT.
§ 13. But all tlie achievements possible to a single eye, when open
and in motion, would not avail to produce the presentations of
sight as our ordinary experience is familiar with them. Strictly
monocular vision is for the most part a fiction of science. What
we can see with one eye, after experience in binocular vision, de-
pends upon what we have been accustomed to see with both eyes.
Indeed, what we see at any instant with one open eye depends, in
part, upon the position, motion, and retinal condition, of the other
and closed eye. A theory of hinocular vision, however, requires the
consideration of two sets of data in addition to those already enumer-
ated. These are the existence and relations of the two retinal images,
and the relations and laws of the binocular movements of the eyes.
The fact that two eyes are ordinarily active, and that there are,
therefore, two images of the object, is a fact of the first importance
for the theory of visual percej^tion. Each eye is in itself, indeed,
a complete optical instrument ; each has its own point, line, and
plane of regard, and movements of rotation, torsion, and accom-
modation. The two eyes, however, act normally as one instrument ;
and yet they cannot be regarded as mere duplicates. The theory
of binocular vision, then, considers the two eyes acting as one. For
the purposes of such theoz-y it is not important what shape the two
retinas are regarded as having ;
they are usually taken as surfaces
with the curvature of the inside
of a sphere whose centre lies at a
point where all the lines of direc-
tion intersect. ' It may be assumed,
to begin with, that this point of in-
tersection is the same for accom-
modation to all distances of the
object. If the two retinas were
perfectly symmetrical all the ner-
vous elements which compose the
mosaic of each one might be re-
garded as situated at points identi-
cal with those occupied by the ner-
vous elements of the other. In
other words, the surfaces of the
two retinas might be regarded as capable of being perfectly super-
imposed. Upon such retinas, when the eyes Avere parallel, each sin-
gle point of an object would have its image formed upon two " iden-
^ See Hering, Plijsiolog. Optik, in Hermann's Handb. d, Physiol. , IH., 1., p.
349 f.
Fig. 99. — Diagram to illustrate the theory
of corrosponding retinal points. The im-
ages rif objects at a" or b" or c" will fall
on forrfsponding points of the retina—
a and a', b and b', c and c' — and be seen
Bingle.
IDE]^TICAL AND CORRESPONDING POINTS. 435
tical " points of the two retinas — upon points, that is, wliose position
would be mathematically the same with relation to the centre of
each retina.
But the retinas are not symmetrical, and the physiological centre
is not the true mathematical centre ; moreover, the eyes, to be of use,
must act together in other positions than that called " primary." A
distinction must then be made between corresponding points and
identical points ; the former are such as are found by experiment
actually, as a rule, to act together and to combine their images
when simultaneously stimulated. If the eyes be fixated upon any
very remote object without apparent magnitude — for example, a
star— the points of two retinas upon which its image falls when it
is seen as single are " corresj)onding." One image then exactly
covers the other. But in certain cases the j)oints of the retinas
which customarily act together do not so act ; points not exactly
corresponding sometimes cover each other, and points usually cor-
responding sometimes fail to cover each other. Hence, a distinc-
tion may be made between corresponding points and " covering
points ; " the latter term being used for those points whose im-
pressions, in each individual case of seeing, are actually referred to
one and the same point of the object' The two points of regard of
the two eyes are in all cases identical, corresponding, and cocering.
Scarcely more than a reference to previous elaborate attempts to
determine the corresponding points of the two retinas is necessary
for our purpose.'^ Experiment shows that considerable reciprocal
substitution takes place among the diffei'ent points of both retinas.
The eyes of most persons, if not of all, are both structural!}' and
functionally incongruous. When the lines of regard lie parallel in
the plane of the horizontal meridian of the two retinas, the verti-
cal meridians do not correspond. A vertical meridian of the left
eye, with its upper end inclined to the left, may be conjoined with
a vertical meridian of the right eye that has its upper end inclined
at about the same angle to the right. The image of a line which
lies on these meridians thus inclined, appears in the vertical horizon
of the field of vision and divides it into a right and a left half.
§ 14. That objects are ordinarily seen as single when their images
are formed on corresponding points of the retinas, and otherwise as
double, may be shown by many familiar experiments.'' If we hold
'By Wundt, Physiolog. Psycliologie, ii., p. 122 f.
^Here see Hering, in Hermann's Handb. d. Physiol., III., i., pp. 355 ff. ;
and Helmlioltz, Physiolog. Optik, pp. 695 ff.
•'See, especially, the ones described by Le Conte (Sight, pp. 92 fp.), from
which the immediately foUowiug are taken.
436
BINOCULAR FIELD OF SIGHT.
a finger before the eyes and look, not at it, but at the wall or the
sky ; or if- we point it at some distant object, and keep ovir eyes
steadily fixed on the object — tAvo trans-
parent images of the finger, rather than
one solid finger, will be seen. Many
persons may have difficulty in seeing
the two images, but none will fail to lao-
tice their transparent character. Under
these circumstances the wall, sky, or
distant object, may readily be seen
through the finger. By experimental
methods the images of a siugle object
may be dissociated, and Avhat is really
one be seen as two ; on the other hand,
images coming from two objects may
be combined upon corresponding points,
and thus what is really two be seen as
one. It needs only a little skilful press-
ure upon one eyeball to create for us
the double of each one of a group of
Fig. 100. — Diagram to illustrate phe-
nomena of double vision. If the
imase of the point 6 fall in one eye <• ■ -, n , in j • ti
on 6, and in the other on 7, the dis- tneuds, and to See oue body jDartially
tance of the two images seen will ,i „i i.i,„ j.„„ „„j. ; ^ „ .„ £
equal that between 6 and 7. If th., through the transparent nnage of an-
image of a fall on 5 and 5. it will be ^fl-,Q-|» Tf
Been single, but if the image of 6 f nil ^ ^^^•'- • -'■■'■
on the left eye at 6, and on the right
eye at 4, it will appear double.
two objects very similar —
for example, the two forefingers — be
held a little way apart at about a foot
distant and against a clear sky, three like objects, one solid and two
transparent, may be made to appear by combining the two middle
images and dissociating the two on the outside. Two systems of
regularly recurring similar objects — such as a regular small pattern
of carpet or wall-paper, or the diamond-shaped spaces of a wire-
grating— may have all their images combined by slipping them, as
it were, simultaneously to one side. There is, then, a double-seeing
of what is really single and a single-seeing of what is really double ;
but the latter is much rarer than the former, and seldom occurs
except when brought about for purposes of experiment.
§ 15. It is obvious that the relations of the two images of an ob-
ject cannot remain unchanged when the ej'es are moved from their
primary position. When the eyes are converged upon an object,
the images which are formed on the central sj)ots of the two retinas,
by rays coming from the point of regard, are exactly identical and
corresponding ; the object in this case is therefore seen absolutely sin -
gle. Points of the object lying near to the jioint of regard in any di-
rection, and thus having their images formed close to the centres of
CALCULATION OF THE HOROPTER.
4G7
the two retinas, are also seen single. For the points of the retinas
on which the images are then formed, although not strictly identi-
cal, are corresponding ; that
is, they have habitually act-
ed together in seeing ob-
jects single by binocular
vision, and the sHght incon-
gruousness of the two sets
of images is disregarded, as
it were, by the mind. But
all objects lying nearer or
Jaaore remote than the point
fixated by the eyes are liable
to be seen double ; for their
images do not fall on corre-
sponding points of the re-
tinas. Objects lying below
or above, or to one side or
the other, of the point of
regard, do not, as a rule,
have their images formed on
corresponding points ; they
may, therefore, also be seen
double. Some of these
points, however, which oc-
cupy positions below or
above, to the one side or the other, of the point of regard, are seen
single. The sum of all the points which are seen single while the
point of regard remains the same is called the horopter.
There has been a great amount of calculation, experiment, and
discussion, to determine the exact nature of the horopter. It has
been held to be a surface (plane or curved), a circle, a line, a num-
ber of disconnected points. Its calculation as a matter of mathe-
matics is unsatisfactory, for the really corresponding points of any
two retinas are not to be determined by mathematics. Experiment
is made exceedingly difficult by the indistinctness with which we
see objects that do not lie near the point of regard. No conclusions
regarding the nature of the horopter are, perhaps, on the whole,
more trustworthy than Meissner's.' They are thus summarized by
Le Conte.'^ With the eyes in the primary position, the horoj)teris
' Beitrage zur Physiologie d. Seliorgans, Leipzig, 1874 ; and Arcliives des
Sciences, iii. (1858), p. 160 f.
2 Sight, p. 204.
Fig. 101 (From Hering).— //, the sash of the window,
and p the black spot fixated. On the left line of
vision I b lies a distant object, and on the right line
r e another object. The images of 6 and e, as well
as the image of ?J, fall on the place of direct vision
and, therefore, on corresponding points of the two
retinas.
438 BIlSrOCULAK FIELD OF SIGHT.
a plane perpendicular to the median line of sight. For all nearer
points in the primary plane, it is a line which dips toward the ob-
server with an inchnation to the visual plane, increasing with the
nearness of the point of regard. When the plane of vision is turned
upward, the inclination of the horopteric line increases ; when the
plane is turned downward, the inclination of the line decreases
until it becomes zero at 45°, and the line expands into a plane.
The plane of the horopter, then, passes through the point of regard
perpendicular to the median visual line. With these conclusions
the careful experiments of Le Conte himself correspond in the
main ; but Le Conte considers that the inchnation of the horopteric
ILae remains constant, and that its surface, when the horopter be-
comes a surface, is curved instead of a plane.
§ 16. The existence and relation of the two images in binocular
vision is of the greatest importance for all perception of solid
objects set at varying distances from each other. It is largely by
their help that binocular perspective and stereoscopic vision are
explicable. But all such elaborate and complex presentations of
visual sense require for understanding them certain considerations
concerning binocular movements of the eyes. In binocular move-
ments the laws of parallel motion hold good only for the case when
the eyes, being in the primary position, are both turned equally in
the same direction. But in fixating the point of regard for the two
eyes for a near object the eyes move in opposite directions, so that
the lines of vision may converge upon the object. In convergence
the eyes rotate on the optic axis in opposite dii-ections. ' Since
divei-gence of the eyes in visual activity is, in all ordinary cases,
impossible, there ai-e three customary indissoluble conjunctions of
motion which belong to the eyes as under control from the central
nervous organism ; these are, right and left together, up and down
together, or turning symmetrically inward. In lowering the plane
of vision, as well as in fixating the point of regard upon near
objects, convergence naturally takes place ; in elevating this plane
or in looking upon distant objects, the converging Hues of regard
diverge toward a parallel position. Convergence may be " sym-
metrical" or " asymmetrical ;" in the former case the two lines of
regard are turned inward at equal angles and the point of regard
is kept in the median plane of vision ; in the latter case the point
of regard is outside of the median plane, and either the two eyes are
turned at unequal angles inward, or else one is turned inward, and
the other, at a smaller angle, outward. Both kinds of convergence
are possible at different angles of the elevation of the plane of visio/x
> See Le Conte, Sight, p. 178 f.
THE USTFLUENCE OF ATTENTION. 439
Listing's law does not hold for movements of the eyes in conver-
gence. ' The principal points at which this law is abrogated for
converging motion of the eyes are stated thus by Le Conte :^
When the right eye moves to the left in convergence, it rotates to
the right instead of to the left as in parallel motion ; so the left eye
rotates to the left when turning inward. Whereas in parallel mo-
tion the torsion of the eye increases with the angle of the depres-
sion of the plane of vision, in convergent motion it decreases to
zero at 45°. These facts doubtless result in imparting variety of
local coloring to those sensations of strain, etc., which are produced
in the two kinds of motion of the eyes, and which serve the mind
as local signs in its synthesis of extended visual objects.
Changes of accommodation naturally accompany the changing
convergence of the eyes for near objects, and the resulting sensa-
tions enter into the spatial series out of which the presentations of
visual sense are constructed. In the alteration of the indices of re-
fraction, and in the contraction of the pupils, the ej'es act together
under the influence of motor impulses from the central nervous
organs.
§ 17. An effort to see, and a corresponding fixation of the atten-
tion upon the object lying at the point of regard, are implied in
the convergence of the eyes. The eyes of new-born children and
eyes that are recently couched after long-continued blindness move,
as a rule, in parallel lines. ^ . Ai-rest of attention brings the two
eyes into use as one organ, and this necessitates the turning of the
lines of vision of both so that they shall meet at a common point
where lies their common object. It follows, also, that the sensa-
tions accompanying innervation of their muscles so as to produce
convergence are of capital importance in the construction of the
most elaborate and intelligent visual presentations. According to
Wundt, these " feelings of innervation " are the direct expression
in consciousness of the cerebral changes that accompany the initiat-
ing of motor impulses in the central organs. They differ only in
intensity or amount. It is by the " feeling " of this amount, as it
were, that our knowledge of the size and distance of the object
seen in convergence is obtained. Wundt's view* of the nature and
origin of the feelings of innervation, however, is unsatisfactory.
In the opinion of Hering,^ the innervation of both eyes is equal,
^ Comp. Hering, in Hermann's Handb. d. Physiol., III., i., p. 497 1; and
Le Conte, Sight, pp. 177 ff. * Sight, p. 190.
^ Comp. Bonders in Pfliiger's Archiv, xiii., p. 383.
* See Physiolog. Psychologie, ii., p. 118 f.
" Phvsiolog. Optik, Hermann's Handb. d. Physiol., III., i., p. 519 f.
440 BTNOCULAH FIELD OF SIGHT.
however they are moved with relation to each other. Even when
the movements of the two are unequal, the law holds ; for each eye
is then under the influence of two innervations, one of which is
directed toward turning both eyes right or left, and the other
toward turning them inward or outward. As a result, in one eye
the two innervations would support, and in the other eye oppose,
each other — thus bringing about a compensation. In this way the
will guides its pair of borses in either direction by a pull upon one
rein. The innervation for accommodation is also supposed to be in
like manner bilateral and uniform. Whatever view may be taken
of the foregoing theories as to the distribution of central innerva-
tion to the two eyes and as to the origin of so-called "feelings of
innervation," there can be no doubt that the mental representatives
of the different areas passed over and positions reached, in both
parallel and converging motions, are important factors in construct-
ing the presentations of sight.
§ 18. By the various helps already described, stereoscopic vision
and the seeing of things in perspective are made possible. To one
eye acting alone and without previous experience, only one of the
spatial series possible could, in any event, serve as a suggestion of
depth ; this is the series of muscular sensations accompanying the
accommodation of the eye to near distances. How little such sen-
sations of themselves can accomplish, even at the end of years of
experience in binocular vision, the experiments of Wundt make
obvious (already alluded to, p. 433). Our localization of objects
by one eye, with respect to the third dimension of space, is con-
fessedly very imperfect even under the best of circumstances. It
is probable, then, that the field of monocular vision is directly
known only as a plane, and that all immediate perception of depth
depends upon the existence of double images and muscular sen-
sations derived from the movements, especially in convergence, of
the two eyes.
The stereoscopic and perspective vision which takes place, with
apparent immediateness, even when one eye is closed, is therefore
really mediate and indirect ; it is accomplished solely by second-
ary means of varying intensities of light and color, changes in
apparent magnitude, etc., on the basis of associations gained by
using both eyes and the hand. Accordingly, it is easy to reduce
all the objects seen in the field of monocular vision to one depth —
to flatness outlined on the same plane — by cutting off these
secondary helps and withdrawing attention as much as possible
from the influence of judgment based on experience. By nearly
closing one eye while the other is wholly shut, objects really
THE PERCEPTION OF DISTANCE. 441
situated at different distances from the head may easily be made
to appear as patches of Hght and color blended, indistinguishably
to the visual perception, with other patches of the retina's own
light. That is to say, when the results of experience in interjiret-
ing the secondary signs of the third dimension are Avithdrawn, the
field of monocular vision becomes as purely two-dimensioned as is
the "retinal field."
§ 19. There is no doubt that the double images, and the muscu-
lar sensations resulting from binocular movement, furnish motifs
for the immediate perception of the distance and solidity of ob-
\ects. In other words, these two spatial series are most important
data for constructing visual presentations of objects having the
♦hird dimension. It is more doubtful just how this service is
rendered. Stereoscoj^y has made the fact familiar, that the two
images of each object are different as furnished by the two eyes.'
The right eye sees the object farther around on its right side, the
left eye on its left. Every small portion of a solid object, as seen
in binocular vision, provided it lies a little way out of the point of
regard, instead of consisting of two exactly similar sets of lines
which might be superimposed, consists of two sets of minute
curves that are partial images of its lines and are different for each
eye. The constant and uniform objects of sense which appear
through the use of both eyes result, therefore, from uniting a great
number of varying partial images of these objects due to simul-
taneous excitation of both retinas. In some manner or other the
perception of solidity is substantially aided by the combination of
these partial images.
Furthermore, in ordinary binocular vision, our perception of the
solidity and distance of objects is accomplished largely by motion
of the eyes which successively unites and separates the double im-
ages of the objects seen. In viewing all objects of any size, whether
near or distant, we may readily become conscious of the fact that
we are engaged in sweeping over the field of vision with a moving-
point of regard. Even when we suppose the eye to be looking at a
single point, with a perfectly fixed regard, it is actually making
short and rapid excursions in one direction and another around
this point. How difficult it is to keep the organ of vision perfectly
motionless, anyone knows who has tried to hold steady one of the
floating specks {musccB volitantes) situated in, and projected in the
1 For the study of the theory of stereoscopy as a matter of optics, the reader
is referred to treatises on this science ; a brief allusion to the fact is enough
for our purpose, which primarily is, of course, to illustrate the psychology of
visual perception.
442 BINOCULAE FIELD OF SIGHT.
air before, this organ. Such facts strengthen the theory of Briicke ^
and others, that we gain our perception of depth by running the
point of regard back and forth with a varying degree of convei'-
gence to the axes, and so combining successively the different parts
of the two pictui-es as seen by the two eyes.
But that motion is not necessary for stereoscopic vision with
adult eyes is proved by what is known as " Dove's experiment."
A field composed of different solid objects stationed at different
distances in space, or of two stereoscopic pictures, may be seen in
perspective when illuminated by the light of an electric spark.
Since the duration of this spark is perhaps not more than jjiluJ
sec, it is plain that no change of convergence, or running back and
forth of the point of regard, has time to take place. It is asserted
by Le Conte ^ that the interpretation of the double images depends
upon the fact that such images of any object are different according
as the object lies nearer or more remote than the point of regard.
In the latter case, the double images are called "homonymous,"
and are united by less convergence ; in the former case they are
called " heteronymous," and are united by greater^ convergence of
the optic axes. Now the observer knows, "instinctively and xvithout
trial" whether greater or less optic convergence will be necessary
to unite the double images ; and accordingly refers the homony-
mous images to objects beyond, the heteronymous images to objects
this side of, the point of regard. But the question arises, Hoio does
this so-called " instinctive " knowledge come ? It can scarcely be
by way of a native insight into the distinction between homony-
mous and heteronymous images, as such ; or through any seeing of
both retinal images by the mind's eye,' as it were. Since what is
needed to unite the images is motion of the eye, and since the
mind has always been accustomed to associate sensations of motion
with the double images of binocular vision, it is impossible to avoid
the conclusion that instantaneous binocular vision, like monocular
vision, of solidity and distance, is secondary and wholly dependent
ui^on previous experience acquired with both eyes in motion.
§ 20. Localizing of the third dimension is, accordingly, much
more secure in binocular than in monocular vision ; and judgments
of distance are assisted greatly by movements of both eyes. If
' Archives des Sciences, iii. (1858), p. 142.
2 Sight, p. 151 ; and Am. Journal of Science and Arts, ii., 1871, p. 425.
^ To say that "each eye, as it were, knows its own image, although such
knowledge does not emerge into distinct consciousness," is in plain contradic-
tion with all the fundamental laws which psychology has to propound con-
cerning the nature of visual perception.
INTERPEETATIOlSr OF DOUBLE IMAGES. 443
no other motif iov seeing depth of space is present, according to
Hering ' the following law seems to hold : All the lines or points
whose images lie, with a given position of the point of regard, in the
vertical horopter, appear clearly defined on a surface which is either
plane or slightl}' cylindrical, and all the lines or points Ijing this
side of the surface of the vertical horopter and whose images have
a " crossed disparateness" (that is, the left one of the double im-
ages belongs to the right eye, and the right one to the left eye —
making them " heteronymous "), appear in front of the surface ;
while those lying beyond the horopter and whose images have an
" uncrossed disparateness " (that is, the right image belongs to the
right eye, and the left image to the left eye — making them " hom-
onymous "), appear behind the surface on which whatever lies iu
the horopter is seen. But, as we have already learned, interjDreta-
tion of the double images for the stationary eyes is an acquired art,
which is dependent upon previous association of the retinal signs
of both eyes with muscular sensations arising from the innervation
and movement of the eyes. It is also in perfection of practice de-
pendent, as all stereoscopic vision is, upon the so-called "second-
ary " means of such vision.
§ 21. All stereoscopic vision, or vision of perspective for remote
objects, requires, in order to secure any considerable accuracy, the
larger use of " secondary helps." Five or more classes of such helps
may be mentioned. Vision, as accomplished by such means, is
often called judgment in distinction from immediate percej^tion.
This should not be held to imply that activity of the mind in as-
sociation and discernment is not involved iu all the jDresentations of
sense. The distinction lies between such a synthesis of the sensa-
tions into objects of sense as is inseparably connected with all nor-
mal binocular vision, and such other seeing (or judging) of the spa-
tial properties and relations of remote objects as depends for its
accuracy upon changing aspects of these objects. The increased
necessity for secondary helps when the objects of vision are remote
arises largely from the fact that the mind loses the data (or motifs)
that accompany strong convergence and accommodation of the nor-
mal eye for near objects. Changes in the tone and intensity of the
muscular sensations are comparatively slight on passing from vision
of objects 20 40 feet distant to vision at infinite distance. On the
contrary, such changes are relatively great on converging the eyes
to alter the point of regard from a distance of 20-40 feet to one
of 5-6 inches ; still greater on increasing the convei'gence for still
nearer vision. Hence the increased necessity, iu vision of distant
' Physiolog. Optik, Hermanns Handb. d. Physiol., III., i., 400 f.
444
BINOCULAR FIELD OF SIGHT.
objects, for other secondary lielps to take the place, as it were, of
the diminished value of the primary data or mot 'fa of the eye.
§ 22. The principal secondary helps of stereoscopic vision and
vision of perspective are the following : ' The course of the Jimitivg
lines of the objects in the field of vision determines our perception
of their distance and form as lying in the third dimension of space.
In looking at a building, we connect together into vertical, horizon-
tal, or curved wholes, the successive fragments of the images of its
lines as the eyes are swept along in the requisite directions. If
these lines become confused in distinctness, or changed into direc-
tions that are contrary to our previous experience of how the
parts of a building appear to the eye, we are liable to errors in per-
ception. "When the bottom lines of a distant object are covered,
its distance and shape in the third dimension become uncertain to
the eye. Mountains that tower behind each other seem to lie in
one surface, provided the presence of other secondary helps, such
as atmospheric j^erspective, etc., is excluded. The parts of un-
shaded geometrical figures drawn on a plane where the course of
their outlines does not define the matter to us as fixed in one way,
may often receive two or more interpretations ; they may thus
actually appear as subject to change from a nearer to a more I'e-
mote place in space. The same arrangement of lines may appear
either as a staircase or a
portion of an overhang-
ing wall (see Fig. 102).
The same angle of a poly-
gon may be made to seem
either the nearest or the
most remote. Indeed,
the whole stereoscopy of
certain figures may thus
easily be reversed. But
if the course of the limit-
ing lines of an object for-
bids moi'e than one interpretation of the relations of its parts in
the third dimension of space, then the object must be seen as in-
terpreted in that one way. Objects of known size and shape are
seen as nearer or remote, according to the manner in which the
parts cover each other and are covered by each other. The con-
tour of an object, then, is one determining factor of its stereoscopic
appearance (see Fig. 103).
' Comp. Wundt, Pliysiolog-. Psycliologie, ii., p. 145 f. ; and Helmholtz, Phys-
iolog. Optik, pp. 623 ff. and 766 ff.
/ /
(5
b
^
0
y^
a
y^
a
^
_/
Pig. 102 (From Wundt). — a can be made to apprar either
nearer or farther off than 6.
i:NFLlTE]SrCE OF SECOISTDAEY HELPS.
445
Mathematical perspective, or the size of the angle of vision which
is covered by near and far objects respectively, is one of the most
important secondary helps of stereoscopic vision and vision of per-
spective. In this way objects of known size are seen as placed at
a distance necessary to give them their apparent size. The street
ajipears narrower and more distant, the houses lower and more re-
mote, in the upper part of its visual picture. Parallel lines, like
the tracks of a railway, appear to converge from us more and more
toward a point ; the same thing is true of the sides of the table or
box at one end of which we are standing, or of the walls of the
Fig. 103 (From TVundt).— The two rings A and B may be stereoscopioally combinprl in either of
the following ways— according as the vertical or horizontal contours prevail.
room. For although the perspective of visual experience is very
different from true " mathematical perspective," the latter affords
to the former one of the secondary helps.
More distant objects are also, on account of the amount of atmos-
phere through which the rays of light reflected from them have to
pass, more dim in outline and of changed shades of color. Such
alterations in the character of the image furnish another of the
secondary helps of our vision of perspective. Accordingly, things
are seen nearer in a clear atmosphere, more distant in one less
clear. This is sometimes called "aerial perspective,"
The size and direction of the shadows also fui'nish data for the
446 BIXOCULAIl FIELD OF SIGHT.
perception of the distance and shape in the third dimensions of vis-
ual objects. In the morning and evening light, when all shadows
are lengthened, the objects of the landscape appear more distant
from us and from each other. The direction of the shadows of
different objects with relation to each other and to the source from
which the light comes is also an aid to vision of perspective. The
arrangement of the lights and shadows is by far the most impor-
tant means for determining the relative position in space of differ-
ent parts of objects like intaglios or medallions. A change of the
arrangement of the lights and shadows of such an object, so as to
substitute the one for the other throughout, converts an intaglio
into a medallion or bas-relief, and vice versa. A medallion, placed
near a window, but shielded from its direct light, and lighted from
the other side by reflection from a mirror, has its relief reversed.
§ 23. Other secondary helps to stereoscopic vision and vision of
perspective are derived from experience in a still more indirect
way. Within certain hmits we see what we know to be in the
field of vision ; but, on the other hand, we are not infrequently
compelled to see what we know cannot be there. The account of
such phenomena depends upon laws of association and reproduc-
tion, the physical basis for which is exceedingly obscure. Since
the ultimate psycho-physical processes take place in the brain ;
and since the central processes come under the law of habit and
are in part determined by the tendencies embedded, as it were, in
the structure and customary functions of the central mechanism ;
the influence of changes in the peripheral organs of vision, the
shape and clearness of the retinal image, etc., cannot always deter-
mine just what the presentation of sight
will be. Many retinal images admit of
two or more interpretations — which in-
terpretation will be chosen depends
upon a variety of circumstances that
perhaps cannot all be accurately defined.
The few lines drawn upon the black-
board, or employed by the skilful etch-
er, cause us to see Avhat is not, but
rather ougld to be, in the image formed
Pio. i04.-First one, thenThe other upou the retina. Anyone accustomed
corner of the figure may be drawn ^.^ gtudviuCf the effect of the Colored
forward, partly at will. J o • ji_
points and outlines which appear m the
image seen with closed eyes by the retina's own light, knows how
apparently lawless is the interpretation given to this image. This
is especially true when attention is somewhat relaxed — as, for exam-
INFLUENCE OF EXPERIENCE. 447
pie, on sinking into re very or sleep. Much of the "stuff" out of
which the usual phenomena of dreams are made, may be suggested
and controlled by the condition of the "retinal field." In all these
cases, only a sharper attention and more objective view of things is
needed to dispel the illusion and make us aware how scanty is the
schema, as it were, out of which, by association and reproduction, we
have constructed our presentations of sense. Similar experiences not
infrequently occur even with open eyes by day, in the dimly lighted
room, or in the obscurer nooks and recesses of vision on the street.
In this way numberless ghosts and apparitions have been most per-
spicuously seen. The face of a friend whom we know to be thou-
sands of miles distant may look at us from the window of a house ;
it is only after persistently trying to interpret the appearance in ac-
cordance with our knowledge that we finally succeed in resolving
the face into some chance combination of lights and shadows, of
window-sash, curtain, or other objects.
§ 24. Phenomena like the foregoing recall once more the gen-
eral office of experience in determining the existence and character
of particular presentations of visual sense. We have seen that the
strife between the two rival theories of the oi-igin and development
of sense-perception concerns the relative amount of what is to be
counted "native," on the one hand, or accredited to a process of
" learning " how to perceive on the other hand.
The analysis of the mind's data or motifs has made it apparent
that the influence of experience through the association and repro-
duction of its past forms is very great over the presentations of
sense.' The mind sees, not simply according to the objective
character of so-called " things," nor siinply according to the retinal
images as connected with sensations of motions, but also accord-
ing to its custom in seeing. When, therefore, its habits are broken
up for the time, its interpretation of the sensations, as well as its
synthesis of them into recognized objects of sense, is liable to be
disturbed. Various experiments impress this truth in a vivid way.
For example, let one regard, with one eye, the reversed picture of
a landscape or the photograph of a friend turned upside down
after covering up nearly all of it except the face. The effect of the
pseudoscope, or optical instrument, which, by exchanging the two
stereoscopic pictures, changes convex into concave, and vice versa,
when applied to a complicated scene of landscape, streets, etc., is
very bewildering. The data with which the mind has been wont
' Comp. the chapter, Der Einfluss der Erfahrungsmotive auf die Localisi-
rung, in Hering's Physiolog. Optik, Hermann's Handb. d. Physiol., III., i. , pp
564 fE.
448 BINOCULAR FIELD OF SIGHT.
to deal may all be given, and the sensations localized according to
the laws of stereoscopic vision, but the relation of the parts is in-
exj)licable out of any previous experience. Similar effects are pro-
duced by the telestereoscope,^ or optical instrument which enables
us to see a larger portion of a distant object than is possible with
two ordinary eyes, after the fashion of a pair of optical organs in
the sides of a gigantic head. Individual peculiarities of localizing,
such as are acquired by the practice of some trade or art, are also
accounted for under the princqile of irijluence from experience over
those elements of reproduction that determine what object of sense
shall be constructed out of the various sensational data at command.
Indeed, all our estimates of visual size, shape, and distance, as well
as our " errors of sense," can be understood only in the light of
this same general principle.
§ 25. Not only what we know, but what we choose, has an influ-
ence— often a determining one — upon what we see. This is true,
not simply because we can at will, within certain limits, decide the
area of the field of vision over which the point of regard shall move,
as well as the parts of this area upon which it shall be fixated, but
also because we can regulate the amount of attention which shall
be given to visual impressions and the manner of the distribution
of attention over the various parts of these impressions. Further-
more, it often lies with us to say how we will interpret the data,
and so see the complex product resulting from the act of mental
synthesis. This is especially true of geometrical figures in outline,
as in the cases already referred to under another head (§ 22).
§ 26. With the use of the foregoing data, and under the guidance
of past experience, we judge of the spatial extension and relations
of lines, angles, and solid bodies, of their shape, size, distance, and
relative situation. The position of lines and angles affects our es-
timate of their magnitude ; under this principle many errors of sense
originate. Distance and size are, of course, so related that they vary
inversely, and when one is known the other is immediately or readily
judged on the basis of such knowledge. But the size of the visual
object is measured by the magnitude of the visor angle covered by
its image, or the relative extent of the retinal surface simultaneously
excited by the rays of light reflected from the object. This is called
its " apparent magnitude." The real magnitude of any object is its
size as related to certain fixed standards of measurement formed on
the basis of generalizations from the use of both eye and hand. Dis-
tance, apparent magnitude, and real magnitude, are therefore con-
' See Helmholtz, Pliysiolog. Optik, p. 646 f., for an account of these two in-
struments.
INFLUENCE OF INTENSITY. 449
nected as three factors of one problem proposed by each presentation
of sight. Given the apparent magnitude and the real magnitvide of
an object, we judge of the distance according to our experience of
how large an object of such size appears at an assumed distance.
The remote spot on which a human figure is standing seems nearer
or farther away according as we know the figure to be that of a
man or that of a boy. Distance and apparent magnitude being
given, the real magnitude of the object is judged as that which it
would need to have in order to appear so large at the given dis-
tance. When one of the two necessary data is lacking, no judg-
ment can be formed except upon the basis of other secondary helps,
such as aerial perspective, etc. Thus, no common standard for es-
timating the distance of the sun or moon being given, their size ap-
pears different according to the place whei-e different observers are
inclined to locate them, or according to the standard of comparison
made necessary for the time by their position. These bodies ordi-
narily appear to some persons no larger than a saucer, to others
larger than a large cart-wheel. "When the sun sets behind a tree,
the size of the spreading of whose branches is fairly well known, it
may be enormously magnified by being seen to fill its branches en-
tirely.
§ 27. When the eye is in motion, as in all ordinary vision of ob-
jects not very minute and very near, the number, duration, and in-
tensity of the spatial series of sensations called forth by the motion
determine our estimate of the outline-form, magnitude, and dis-
tance of the objects.' Every spatial series of sensations contrib-
utes the lai'ger magnitude to the object the greater the number of
members which enter into the series. For this reason the same
extension of a line or surface when broken up into parts by inter-
secting lines appears larger than when perceived as an uninter-
rupted whole. The repetition of similar figures in architecture,
upon walls, columns, etc., takes advantage of this effect.
The intensity of the sensations of a spatial series, and of the act
of attention necessary to comprehend them in one whole as a pres-
entation of sense, also has an influence on the size of the object.
When the movements of the eyes are made with lamed or tired
muscles, the size of the thing perceived by them is increased.
When the function of one of the muscles (for example, the rectus
externus) is impaired, so that the circuit of the eye in a given direc-
tion is shortened, objects lying at any position in the field of vi-
sion, as seen by the eye moving in the shortened circuit, are located
where they would have been if the same intensity of muscular sen-
' Comp. Volkmann von Volkmar, Lehrb. d. Psychologie, 1885, II., pp. 99 fif.
29
450 BINOCULAR FIELD OF SIGHT.
sation had been necessary to bring them to this position with a
normal function of the muscles. A patient with paralysis which
prevents turniug the eye more than 20"" will locate an object
actually lying only 20° from the median plane much farther to
one side. Such a patient will reach beyond when he tries to grasp
the visual object. The increased size which is given to objects
that are parti-colored or mottled, and so have an interrupted sur-
face and furnish greater difficulty to perception of them as wholes,
may be due to both the foregoing causes. Volkmann von Volk-
mar ' calls attention to the fact that both monotony and variety
may, under the working of these principles, be productive of the
same effect in magnifying the size of an object. For the size of
any visual surface is usually estimated by the application of some
standard of measurement selected from the field of vision. The
frequent repetition of this standard creates the impression of vast-
ness ; and the absence of any standard to apply, or a vague, unsuc-
cessful effort to find a standard, may produce the same impression.
Monotonous areas of unbroken snow, and stretches of streets
crowded with forms of men and animals, both seem of great ex-
tent.
The amount of time through which the spatial series of sensa-
tions endure has also an influence on the magnitude of the objects
perceived through those sensations. It is as enduring in time that
the changing qualities and quantities of sensation which belong-
to the perception of any complex object are expressed. The length
of the time-course, as well as the degree of the intensity of the spa-
tial series of sensations, may be interpreted as extensive magnitude
of the perceived object.
8 28. The laws which control our estimates of visual magnitudes
are psychological, and apply to all the action of the mind in con-
structing its sense-data into the presentations of sense. Yet more
elaborate mental activities, such as take place when the distance,
size, and contour of visual objects are deliberately estimated and
expressed in terms of an accepted standard, of course imply more
of dependence upon skill acquired through experience.
The degree of fineness with which differences of distance and
maernitude can be seen, under the most favorable circumstances, is
limited by the least observable differences in the members of the
spatial series of sensations which compose the visual objects. Of
such series, those most capable of exceedingly fine differentiation
are the local retinal signs and the muscular sensations accompany-
ing convergence of the eyes for near distances. It is difficult
' Lehrb. d. Psycliologie, II., p. 101 f.
MEASURING POWER OF THE EYE. 451
to assign the exact proportion of help which these two series ren-
der in making the finest possible distinctions of visual magnitude.
Heriug ' denies that any help is obtained from muscular sensations,
or "feelings of innervation," in comparing the size of two miniite
objects near bj", and assigns all the work of furnishing such data to
the "spatial sense of the retina." Lotze," who admitted the as-
sistance of muscular sensations, nevertheless held that the fineness
of the distinctions possible among them is not sufficient to support
our ordinary- judgments of the size, distance, and direction of ob-
jects. Wuudt ' and others claim that it is by gradations in the so-
called " feelings of innervation " alone that we make the most accu-
rate of these estimates ; they deny that any " spatial sense " (in
Hering's meaning of the words) belongs to the retina. The evi-
dence seems to favor the view that both the muscular sensations and
the local retinal signs furnish data for all nice discrimination of
visual extension.
The particular degree of accuracy with which minute differences
in the distance and magnitude of visual objects can be perceived
varies gi-eatly, according to different positions of the eyes and the
object, the amount of light, practice, etc. — and all these, as con-
nected with individual peculiarities of structure and previous func-
tion of the organs of sense. That such estimates fall to some extent
under Weber's law — in other words, that the least observable dif-
ference in the length of visual lines and surfaces is relative and
not absolute — has already been shown (Chap. V., § 18). Chodin
found the relative value of the least observable difference, with a
variation of the absolute vertical distance from 2.5 to 160 mm., to
be as follows when the lines lie in the same direction :
Absolute distance. . 2.5 5 10 20 40 80 160 mm.
Fraction of observ- ( j i_ _i i i _i i_ j. i_ i i i i j.
able difference, f '^ ^^ ^y—'ji 37"— 45' '5i~ of 44 i6 iS~'j2 4a~3u
The fineness of ocular judgment is greater for horizontal dis-
tances.
The measuring power of the eye is much less accurate when the
distances compared lie in different directions. In particular, points
lying at a vertical distance of 20 mm. are estimated as equally far
away with those lying at a horizontal distance of 25 mm.'' Most
estimates of direction and distance are comparatively inaccurate
when only one eye is used. A vertical line drawn at right angles to
' Hermann's Handb. d. Physiol., III., 1 , p. 533 f.
^ Medicin. Psychologie, 3b4 f.
^Physiolog. Psychologie, ii., pp. 85 fif. ; comp. 1., pp. 875 S,
- So "Wundt found, Physiolog. Psychologie, ii, , p. 96.
452 BiJsrocuLAE field of sight.
a horizontal appears bent to monocular vision ; its apparent inclina-
tion is variable, and was found by Bonders ' to vary between 1° and
3° of the angle within a short time.
Helmholtz '^ experimented to determine the accuracy of the bi-
nocular perception of depth by trying how small a deviation from a
perfectly straight line could be detected in a wire bent atone point
so that its two halves formed an extremely obtuse angle, when the
wire was looked at both in and out of the horoiDteric line ; he also
employed for the same purpose three nails, the heads of which could
be very slightly displaced from a straight line. Under the most
favorable circumstances, he found that a displacement of a nail by
a change of its distance corresponding to 60|- seconds of the angle
of vision, or 0.0044 mm. variation in the position of the retinal
image, could be detected. The latter distance corresponds so well
to the calculated size of the retinal elements (see p. 327) as to form
an argument in favor of the theory that estimates of size and dis-
tance are dependent upon the local signs attached to the excitation
of these elements.
But, on the other hand, it is claimed that Weber ^ showed the
muscular sense of the eye to be' one of the finest of micrometric
apparatuses, since a distinct muscular sensation is attached to a
displacement of the most sensitive spot of the retina of not more
than j^2j of a Parisian line. By experimenting with a black thread
stretched over against a white Avail and moved in the median jDlane
toward and from both eyes, which looked at it through a horizon-
tal slit in an upright board, it was found j^ossible to detect changes
in distance of 3.5 ctm. at an absolute distance of 180 ctm., and
changes of 1 ctm. at an absolute distance of 60 ctm/
§ 29. The data or motifs already described are the foundation,
also, of our perceptions of motion, and of our estimates of its di-
rection, speed, and extent. It need scarcely be said that all such
perceptions and estimates are relative ; they imply the existence of
some point which may be regarded as fixed, and the application of
a standard of measurement. For j)erceptions of motion by the eye,
the point of regard when the organ is in the primary position
furnishes the means of orientating ourselves and of placing the dif-
ferent things of vision in their right relations to us and to each
other. Sujopose the body and head to be erect, and the eyes motion-
1 Archiv f. Oiihthalmologie, XXI., iii., p. 100 f.
2 See Pliysiolog. Optik, p. 644 f.
^ In the Ber. d. sachs Gesells. , etc. , for 1852, p. 130; cited by Volkmann
von Volkmar, Lelirb. d. Psychologie., II., p. 56.
^ See Wuudt, Physiolog. Psychologie, ii., 94 f., and the reference there.
THE PERCEPTIOlSr OF MOTION. 453
less and looking into the distance with the Hnes of vision parallel ;
the perception of motion may then arise in either one of two ways.
Of these, by far the most frequent is the change of relative position
of an object in the field of vision which is occasioned by its move-
ment. What is necessary, however, is simply the successive stimu-
lation of continuous points or areas of the retina with images that
are sufficiently similar to be perceived as one object. The percep-
tion of motion may also be produced by the successive stimulation
of the same points or areas of the retina with images that are too
dissimilar to be regarded as one object. One may thus see motion
when neither the eyes nor any external objects are really moved.
It is in the latter way that the colored points of the images formed
by the retina's own light, when the eyes are closed and motionless,
seem to be in constant motion.
The direction and amount of motion perceived with the ej-es is
measured off upon the entire field of vision in accordance with pre-
vious experience and by means of the data already described. With
the eyes at rest, the retinal local signs, or space-values belonging
to the retinal elements, furnish the only primary data ; secondary
helps, and associated ideas of muscular sensations which have been
by experience found necessar'y to follow objects in motion, complete
the perception.
It is assumed, in cases like the foregoing, that no sensations in-
dicating motion of either the organ of vision, or the head, or the
whole body, complicate the pi'oblem. But ordinary perceptions of
motion are gained with the eyes in motion out of the primary
position. When the eye and the object both move in such a way
that the point of regard remains fixed on the object, our percep-
tions of motion, and estimates of its direction and magnitude are
dependent upon muscular and tactual sensations occasioned by the
eye's changes of position. We know from experience what kinds
and intensities of sensations are produced by keeping the point of
regard fixed on an object which is moving at about a given rate in
a given direction. If any of the links ordinarily belonging to this
chain of conscious experiences drop out, our measuring instru-
ment fails us either partially or completely. The head, too, is in-
variably turned when we are watching an object that is moving in
any direction other than straight forward or away from us along the
line of regard. The sensations originating in the action of the
muscles and skin of the head and neck thus enter into our compu-
tation ; they must have such a value in consciousness as to inform
us about how far the head has gone from the position with which
it started, in order to fixate the moving object. According to
454 BINOCULAR FIELD OF SIGHT.
Eelmholtz/ the ordinary movements of the head in vision follo^v
the same principle as that followed by the eyes in movement ; that
is to saj', the head turns fi'om its primary position on an axis that
is approximately parallel to the axis of the simultaneous rotation
of the eyes. But Hering " asserts that a difference between the laws
of the motion of head and eyes is of essential significance for our
perception of space. However this may be, it is certain that the
position and motion of the head, as known by its muscular and
tactual sensations, must be taken account of in all ordinary visual
perception of motion. The same thing is true of the j)osition and
motion of the entire body. Many of our errors of sense, or false
perceptions of motion — its existence, direction, rate, and amount —
are dependent upon the principles of judgment governing such
data of sensations. AYe are peculiarly liable to error in all cases
where the motions of our own bodily organs are passive ; in such
cases we do not have the ordinary motifs, or data, at our command.
Objects are perceived at rest, either when, our organs of vision
being themselves at rest, the images of the objects do not change
their position in the field of vision, or when sensations of motion
occasioned by moving these organs are such and so great as we
know by experience correspond to (or compensate for) the changes
in the position of their images which are occasioned by their actu-
ally remaining at rest. But whenever we look with moving eyes
upon a number of objects arranged in fixed position with relation to
each other, a conflict between two sets of data i-eally takes place.
The result with respect to our perceptions of motion may depend
upon which of the two is chiefly effective in arresting attention.
When the eyes are brought from the parallel position, which they
assume in vision of remote objects, to convergence upon some near
object, the two fields of view belonging to the two eyes rotate in
opposite directions, while the middle visual line maintains its posi-
tion in the median plane. ^ Ordinarily we do not perceive this
rotary motion of the two fields of vision, but consider the field as
one and stationary and ourselves as changing our point of regard in
it. By attention, however, we may see that the external objects,
although they really continue at rest, appear to move as the rela-
tions of their double images are changed. So, also, when the eye
or head or body turns in either direction, in order that a new ob-
ject may be brought under regard, it is possible either to perceive
or -not to perceive the entire field of objects sweeping by ; which
J Physiolog. Optik. p. 486.
■^ In Hermann's Handb. d. Physiol., III., i., p. 495.
^ See Le Coute, Siglit, p. 229.
VISIOlSr AS INTEEPRETATIOlSr. 455
of the two happens depends upon the dii'ection in which attention
is drawn. When strictly attending to the phenomena, we cannot
well fail to regard everything as moving in the opposite direc-
tion from that in which we know the organ of vision to be turn-
ing.
§ 30. The principles already laid down also suffice to explain
most of the ordinary " errors of sense," as well as certain extraor-
dinary experiences of a somewhat different kind. The right to
speak of errors of sense has been questioned. It has been claimed
that such errors belong rather to judgment, and that sense pure
and simple cannot err. The claim is based upon a misunderstand-
ing of the nature of perception. A very obvious difference exists,
indeed, between a mistaken estimate of the distance of a mountain
through extraordinary clearness of atmosphere and the seeing of a
square of white paper as green on a red ground, or as yellow
on a blue ground. Bat the latter is surely an " en*or of sense," or
sensation, in as pure form as such error is conceivable. That sense
cannot err is true only in case we speak of unlocalized and unpro-
jected sensation, regarded as not predicating anything beyond itself.
In all presentations of sense a certain psychological judgment is
involved ; for all such presentations imply association of impres-
sions discriminated as similar or dissimilar, and a mental synthesis
which is dependent upon attention and the interpretation of certain
motifs or data according to past experiences. Clear vision is always
mental interpretation.
The attempt to assign the relative amount of blame to sense and
to intellect, in cases where our presentations of sense do not rep-
I'esent objective relations of things, assumes an ability to make dis-
tinctions which we do not possess. Moreover, the distinction, when
made as the objection would have it, will not hold. Innumerable
experiences contradict the statement that immediate sense-percep-
tion cannot err. When one sees (with no power to see otherwise)
a gigantic human form through the fog, or projected against the
scenery of a stage, and yet judges that this form is only of usual
size, the error is not one of judgment, but just the reverse. Errors
of sense are only special instances where the mind makes its syn-
thesis unfortunately, as it were, out of incomplete data, instantane-
ously and inevitably interpreting them in accordance with the laws
which have regulated all its experience. As Lotze has remarked,
" The whole of our apprehension of the world by the senses is
one great and prolonged deception." Objects of sense are in no
case exact copies of ready-made things which exist extra-mentally
just as they are afterward perceived, and which get themselves
456 EKEORS OF VISUAL PERCEPTION.
copied off in the mind by making so-called impressions upon it ;
they are mental constructions. In the special case of sight we have
seen that, in every particular — in its elements, its mode of con-
struction, its laws of change — the field of vision is a subjective af-
fair. The case is in no respect essentially different, whether our
presentations of sense are so-called errors or true images of things.
In both cases the same data and laws of the use of these data main-
tain themselves. Errors of sense, however, are distinguished from
hallucinations, because the former result from the activity of an
organism which is normal in structure and function, while the lat-
ter do not.
§ 31. The errors of visual perception are almost innumerable ;
they may be classified in part, however, according as they fall under
some one or other of the before-mentioned princij^les. Such errors
may be called " normal," because they are committed in accordance
with principles which regulate the ordinary activity of the mind in
making its synthesis by the help of the sense-data or motifs fur-
nished to it through the excitement of the organism. Deceptions
of this class really result, then, from the fidelity of both mind and
nervous system. Certain errors of sense, for example, are special
examples of the working of the laws which regulate the correspond-
ence of the two images in binocular vision. Thus, near objects
erroneously appear double when the eye is adjusted for distant
vision, distant objects when it is adjusted for near vision ; solid
things are seen through other solid things ; relations in space in
general are perceived different from the reality ; and all according
to the law of the correspondence and non-correspondence of the
two retinal images. Accordingly, the inquiry, Why is vision single
when it is performed with two eyes ? can demand and receive only
one answer. A chief condition of the single vision of solid objects
is that they shall he seen with two eyes. Whether anything what-
ever is seen as two or one does not depend, primarily, upon its
really being either two or one, or upon the existence of one or two
retinal images of it (as though such images were directly perceived) ;
it rather depends upon tlie appropriate data of sensations being
furnished to the mind for completing its mental synthesis of the
object. The two eyes being simultaneously affected in a certain
way, these data are supplied. What is one is seen as one, and
what is two is seen as one, and what is one is seen as two — all in
essentially the same way.
A still larger class of errors of the visual sense falls under the
laws which regulate the smallest observable differences in the
muscular sensations as related to the mathematical perspective of
COMEAEISON OF MAGNITUDES.
457
lines, angles, and surfaces/ Keference has already been made to
the working of this principle in our ordinary perceptions of the
visual magnitude, contour, and distance of objects.
Vertical distances are regularly perceived as larger ' fiTTob '
than equally large horizontal distances. On trying
to draw a cross with limbs of equal
i 1 1 1 1 J 1 I 1 ] I length one is apt to get the vertical
dimension too small ; exact squares
are likely to appear higher than their
Fig. 106.
breadth. When comparing magnitudes in
the upper part of the field of vision with
those in its lower part, one is likely to over-
estimate the former. The upper and lower
half of a letter " S " or a figure " 8 " appear
of nearly the same size ; but when they are
inverted (" g " and " g ") the difference in the
size of the two halves becomes magnified.
Under the same prin-
ciple— in part at least — may those errors be brought which are
Fig. 108.
determined by the way in which the field of vision is filled up. If
"the horizontal distance between two points be exactly half filled
with a line, this line will ap- a\
pear longer than the remain- \ | — . \
ing empty space. A square \ \
intersected by parallel hori-
zontal lines appears elongat-
ed upward, but one intersect-
ed by parallel vertical lines
appears elongated sidewaj'S.
If one of the two right angles
formed by drawing a vertical
perpendicular to a horizontal
line be filled with several lines diverging from the point of the an-
' Comp. Wundt's discussion of such cases, Physiolog. Psycliologie, II., pp
92 ff.
Fig. 109.
\
LiU^
458
ERRORS OF VISUAL PERCEPTIOIST.
gle, the angle thus filled will appear the larger and the perpendic-
ular will seem bent. For essentially the same reason, when two
unequal angles together make 180°, the obtuse angle appears rela-
FlCr. 111.
Fig. 112.
tively too small, and the acute angle relatively too large. Many
surprising errors of sense result from the varied applications of this
principle. (See the Figs, on p. 457 f.)
THE ILLUSION'S OF AET.
459
Fig. 113.
§ 32. The influence of experience, which often corrects what
would otherwise be an instinctive interpretation of the data fur-
nished to the mind, is at
other times the cause of
errors. If the data will at
all permit it, we incline to
perceive any object as we
know that similar objects
are usually perceived. Such
errors of sense as result
from the vision of distant
objects through secondary
helps are too well known
and frequently remarked
upon to require extended
treatment. All the pleasant
illusions of art — in archi-
tecture, drawing, and paint-
ing— are obliged constantly
to take them into account. The very relations of light and shade,
the conjunction, separation, and covering of lines and surfaces, upon
which reliance is ordinarily placed for perception of fact, may be
employed by either nature or art to compel us to perceive what is
contrary to fact. Painting is successful according to the skill it
displays in furnishing to the eye its customary data so as to entice
it to regard things as other than they really are. That its success
is so good need not siu'prise us, when we remember that the mind
has never anything more than these same data out of which to
construct its objects of sense and to make its various judgments
concerning them. The man}' errors in our perceptions of motion
may, for the most part, be explained in the same way. It matters
not whether the data for such perceptions are furnished by actual
changes in the relative position of things in external space, or
whether the same sensations arise through changes confined to the
oi'gans of sense. Past experience has great influence in all this
domain. We incHne for this reason, when two objects are chang-
ing their relative jDosition, to perceive the smaller of them as in
motion ; we also over-estimate the speed of small bodies in motion,
and under-estimate that of large bodies.
§ 33. Some errors of visual perception differ from the foregoing
in that their explanation seems to be due to cerebral activity under
other laws as yet unknown to us. We have alread}' seen (Chap.
IV., § IJ:) that the phenomena of contrast of colors must be referred
460 ERRORS OF VISUAL PERCEPTION".
to certain inexplicable activities of the central organs as related to
our sensations or states of consciousness. The same thing is ap-
parently true of those errors of sense which occur in connection
with the strife and prevalence of contours, and the binocular mixing
and contrast of colors. If a well-defined image of some contour,
such as a sharp-marked limit between two differently colored sur-
faces, be formed on one retina, and on the corresponding points of
the other the image of a uniform-colored background, then only the
former will be visible. This is called the " prevalence of contours."
But if the contours of the images of two differently colored objects
run on the retina so as to cross only in one place, then sometimes
one color and sometimes the other will prevail and get itself per-
ceived at that j)lace. This is called "the strife of contours." If
two squares of red paper and two of blue, all of equal size and bright-
ness and without any distinguishing marks, be laid side by side at
equal distances, and their images then combined, the color of the
middle one of the binocular images will at first be sometimes red-
der and sometimes bluer than that of the two side images, but in
no case exactly like either of them. By steady looking it is said to
be j)ossible to mix the colors of the two objects in a binocular
image which is reddish blue (or violet).' This is called "the bi-
nocular mixing of colors." If such a deception can be secured, it is
manifest that the mixing of colors on which it depends must take
jDlace in the brain, and not upon the retinas of the two eyes. If a
white stripe be placed upon a black surface and divided into two
images, the right one of which is formed by looking at one half
through blue glass, the left by looking through gray glass, then
the right image will be seen blue, but the left will be seen yellow.
This is called " binocular conti-ast of colors."
The peculiar perception of luminosity is due to a struggle be-
tween the two fields of vision which results, not in combining the
black images of one field with the white images of the other so as
to produce an equal tint of gray, but in a rapid alternation of the
two. Very smooth bodies, when they reflect the light perfectly,
do not appear luminous. But when the surface of such bodies —
as, for example, the surface of a sheet of water — becomes ruffled
by ripples, it becomes luminous. The perception of luminosity
may be produced by combining two stereoscopic pictures of an
object which are alike in contour, but one of which is black with
white hnes where the other is white with black lines. Two such
pictures not combining to produce an equal tint of gray over the
' So Hering asserts, Physiolog. Optik, in Hermann's Handb. d. Physiol.,
III. , i. , p. 592. Binocular mixing of colors lias been denied by some authoritiea
LAWS OF CEREBRAL ACTIOIST. 461
whole surface, the images of the separate points on the two retinas
enter into a struggle with each other ; and the rapid alternation of
the prevalence, first of one and then of the other, gives rise to the
appearance of luminosity.
Such phenomena as the foregoing seem to require a reference to
certain unknown processes in the central organs as a physical basis
for the psychical experience. Some experimenters claim that in
these cases of contrast they are able to see either color at will by
giving attention, first to the image on one retina, and then to that
on the other. The words in which this claim is couched, however,
afford no explanation of the phenomena ; for, we repeat again, the
mind does not see the image on the retina, and cannot direct spe-
cial attentioii^ to it. It can only attend to this or that feature of
the "presentation of sense," which is in every case a subjective
affair. But the very question that we are unable to answer con-
cerns the reason why the presentations of sense are constructed as
they are in such cases ; the reply, so far as any reply can be given,
must be, that such data or motifs furnished by the spatial series of
sensations as we cannot connect with known laws of the peripheral
organs of sense must be referred to unknown laws of the central or-
gans of the same sense. Apparently this truth holds good of certain
optical illusions of motion. The fact that a steady succession of im-
ages (as in the case of watching a fall of water), passing over a partic-
ular region of the retina for a long time, sometimes ceases to be per-
ceived as a motion, and that the image of a stationary body on the
same retinal region may appear to be moving in the opposite direc-
tion, has been explained by "Thomson's law." This law refers the
phenomena to the principle of fatigue. Recent investigations, how-
ever, seem to show that the explanation is incorrect. They bring
out the remarkable result that the same elements of the retina,
when stimulated simultaneously, may give rise to imjDressions both
of motion and of rest. For this result some unknown law of cere-
bral action would seem to afford the only possible explanation.'
§ 34. The fact that things are seen upright and in correct relations
horizontalh', by means of data furnished through inverted retinal
images, as well as all illusions and errors that are connected with
this normal fact, imjjlies yet more maturity of experience. Why do
we see the upper part of the object by means of the lower part of the
retinal image, and vice versa ? and why do we see the right side of
the object by means of the left side of the retinal image, and vice
versa ? Such questions have often been propounded as psycho-
logical puzzles of special difficulty. The only answer possible fol-
' See Journal of Physiology, iii. , p. 399 f .
462 DEVELOPMENT OF VISUAL PERCEPTION'.
lows, obviously, from the foregoing principles. Strictly speaking,
we neither see the external object nor the retinal iruage ; the field
of vision is a subjective affair, and is like neither of these two. The
presentation of visual sense is normally dependent upon the retinal
image for the data from which it is constructed ; the image is
dependent upon the external object for its formation by rays of
light reflected from the object and converged upon the nervous
elements of the retina. The different parts of the object as seen
are primarily localized simply with reference to each other by
means of local retinal signs and of muscular sensations produce,d
by motion of the eyes. But as yet the field of vision has no locality
in objective space ; no part of it can be said to be either up or
down, either right or left. The use of such tenns of position
impliea an association of localized sensations of sight with those of
touch and of the muscular sense, in giving us a j)icture of the
relation of the diffei'ent parts of the body to each other, and of the
entire body to the ground, the sky, and the various parts of sur-
rounding objects. When the eyes are moved downward, the lower
parts of the body and objects situated on the ground successively
come into the field of vision ; when the eyes are moved upward,
the near ground and lower parts of objects successively disappear
from the field of vision, and remoter or higher objects come to
view. Seeing objects to the right or to the left is accomplished by
motion of the eyes in the corresponding direction. Eight is the
direction in which the right hand is placed from the middle of the
body ; left is the direction in which the left hand is found. The
massive feelings of touch and muscular sensation keep us informed
of the general relation of our bodies to the earth and to objects on
its surface. The head is the upper part, or part farthest away from
the ground ; the feet are the lower part, or members of the body in
contact with the ground. Thus we come to use terms for localized
sensations of sight which, in this use of them, have no primary
reference whatever to the field of vision in itself considered.
§ 35. The nature of the " sense-data" which the mind has at its
disposal for constructing its presentations of sense, and the psycho-
physical laws which are followed in the process of construction,
have been explained in such detail that little need be added con-
cerning the development of visual j)erception. Visual space pre-
sents itself to us as a coherent complex of sensations of light and
color systematically arranged. The arrangement implies certain
native activities of the mind in connection with and dependence
upon the action of the nervous organism ; but it also implies an
immense influence from experience. It is extremely difficult, if not
LEARNING TO LOCALIZE. 463
•wholly impossible, to distinguish with confidence the limits which
must be drawn between what is native and what is learned. The
seeing of colors is undoubtedly a far more simple and primary act
than the seeing of colored objects as situated in relation to each
other in objective space. A colored surface, or a system of color-
sensations related to each other as side by side in space-form, re-
sults in experience from the weaving together of several spatial
series of sensations. Such a surface may theoretically be conceived
of as presented to the mind through the activity of the nervous
elements belonging to the retina of a single motionless eye. The
motifs or data which the mind would have for constructing such a
surface must be found in the sei-ies of sensations of light and color
as varpng in intensity and quality according to the locally distinct
nervous elements which are simultaneously excited. The evidence
seems, on the whole, favorable to the assumption that some indefi-
nite picture of visual space might be gained wholly through the
excitation of a motionless nervous mosaic (Hke the retina) sensitive
to light.
But visual space, as experience makes it known to us, requires
binocular Adsion with moving eyes. The firm spatial connection of
all the parts requires that a system of lines of direction should be
fixed, prescribing the objective points at which the sensations pro-
duced by exciting together the difierent paii's of the covering i^oints
of the retina must appear in visual space. To establish such spatial
connection, both eyes must move in their conjoined action as a
single organ of vision. By this action the field of binocular vision
is built up in an order of experience which, on the whole, consists
in the successive mastery of more and more complex problems.
For the process of learning to localize, the one centre — the point
of starting and the goal of return — is the spot of clearest vision of
the retina (the yellow- spot), to which the point of regard in the ob-
ject corresponds. With the point of regard fixed in the primary
position of the eye, the first and most essential means is gained for
orientating objects in the field of vision. The meridians, horizontal
and vertical, and the locations of different points in the surface of
the field of vision thus presented to the mind, afford the compara-
tively simple problems furnished by the primary position. In this
way a central point, determining lines, and finally a continuous sur-
face are fixed, to which may be referred all the directions and loca-
tions of the binocular points and lines of regard in the secondary
positions of the eye.
The motifs or data which give to the mind its guidance in
achieving its more difficult tasks are the spatial series of muscular
464 DEVELOPMENT OF PERCEPTION.
and tactual sensations which are caused by the motions of the eye
for parallel turning, for accommodation, and for convergence in
near vision. The general principle is, that by motion the relative
space-values of the retinal elements are not changed ; hut their ab-
solute values — that is, the complex which is formed by combining
all these muscular and tactual sensations with the local signs of the
retina — are changed in equal sense and measure. What moving the
eyes does for the retinal images, moving the head and body does
for the presentations of sense as constructed in binocular vision ;
it alters the absolute values of the complex of sensation as related
to objective space, while keeping the relative values belonging to
the different positions of the eyes unchanged.
The visual perception of depth involves a later and more complex
training from experience than the perception of two-dimensioned
extension. To solve the problem of depth, binocular vision with
moving eyes, and its resulting combination and separation of the
double images of objects, seems necessary. The existence and as-
sistance of those secondary helps, which are so important in per-
ceiving the solidity and distance of objects, imply a further devel-
opment of experience. In all these advances, however, the coirrse
of acquisition is not in separate straight lines that run parallel or
converge, as it were. More complex experience, when obtained,
modifies what is really more simple and primary. What we see in
monocular vision with an open eye, and even what we see with both
eyes closed and motionless, depends upon what we have learned to
see with both eyes in varied movement and availing themselves of
all possible secondary helps. It also depends upon what we have
learned to know of the nature and probable position and shape of
manifold objects of which the eye has already attained the mastery.
§ 36. Finally, brief mention must be made of the connections
which are constituted, in the development of our perception of ob-
jects as having the qualities and relations of space-form, by the
joint action and mutual assistance of eye and hand. With the
sense-presentations of one of these senses the images of objects as
known by the other become most intimately related. It is a misuse
of terms, however, and involves the entire subject in confusion, to
speak of this joint product as a " sense-perception." It is rather to
be spoken of as a mental image or concept. The visual presenta-
tion of an object — as, for example, a ball, a pen, a table — may re-
call its tactual presentation. We readily interpret one into terms
of the other — sight into terms of touch, and touch into terms of
sight. But all the perceptions, as such, of spatial proiDerties and
relations, whether gained by eye or hand, are kept quite distinct
TEANSLATION OF PERCEPTIOlSrS. 465
and separable in the mind. No such synthesis takes place between
the spatial series of the one sense and the spatial series of the other
sense as takes place between the spatial series of the same sense.
And aU the properties and relations of bodies as known in space-
form are given by each of these senses. The view which makes the
sense of sight dependent upon the sense of touch and the muscu-
lar sense for the construction of its spatial objects is erroneous.
While feehng the pen, we can image how it would look ; when
seeing it, how it would feel. We can image how much exertion
would be required to reach a mountain which appears to the eye so
far away, or how a mountain would look at a distance of so many
miles as measured by the exertion required to walk there. But the
true presentations of the visual objects and tactual objects do not
mix in one combined perception. They unite only in one image or
idea of the object.
§ 37. Interesting experiments have been conducted to determine
the degree of accuracy with which perceptions of distance by sight
can be translated, as it were, into terms of the tactual and mus-
cular sense. Some of these experiments show the amount of har-
mony which can be obtained between optical localizing and localiz-
ing with the finger. Helmholtz * made use of a vertical thread
which he tried to locate, as seen in monocular vision, by hitting it
with a pencil's point ; Donders,^ of a very small induction-spark,
which was to be touched with the index-finger. The result of 50
experiments, made for distances along the same line of regard vary-
ing between 60 and 610 mm., when only the spark itself was seen in
perfectly dark surroundings, showed that the distance was over-
estimated 34 times, under-estimated 12, estimated right 4 times.
The greatest errors were +35 and —34 mm. ; the mean error
10.6 mm. When the suiToundings were visible and the electrodes
seen with open eyes, the eyes then closed, and the finger reached
to the estimated distance, the greatest errors were -1-30 and —12
mm., and the mean variable error 9.8 mm., for distances from 80 to
630 mm. The exact localizing of the point of regai'd in terms of
touch is more difficult the farther the object is removed and the
less assistance is had from secondary helps. Locahzing in the
same way when the object lies out of the line of regard is still more
inaccurate. In 29 experiments, where the spark to be localized
was flashed at a distance of 210-600 mm. to one side of this line,
the greatest errors were +120 and —68 mm., with a mean error
of about 34 mm.
' Physiolog. Optik, p. 650.
2 Archiv f. Ophtlialmologie, XVII., ii., p. 55.
30
466 DEVELOPMENT OF PERCEPTIOlSr.
The problem of comparing tlie judgments of linear extension
made by the eye, the hand, and the arm, and of determining their
relative accuracy, has recently been examined, experimentally, at
considerable length by J. Jastrow.' His method was to present a
definite length, varying from 5 mm. to 120 mm., to the retina, the
skin (by application of a pair of points, or by motion of a single
point), to the forefinger and thumb (by being held between the
two), or to the arm when in free movement and guiding a pencil to
express its estimate. The subject of experiment was required to
get a clear perception of the given distance by one of these organs
(called, in such case, the " receiving sense "), and then either si-
multaneously or successively exj)ress this perception through the
same or some other one of these organs (the " expressing sense ").
In this manner it was discovered that, if the eye is both receiving
and expressing sense, small lengths will be under-estimated and
large lengths exaggerated, the point where no error is made being
at about 38 mm. ; whereas, if the hand is both receiving and ex-
pressing, small lengths will be exaggerated and large lengths un-
der-estimated, the "indifference-point" being at about 50 mm. ;
but the arm exaggerates all lengths within the limits of the experi-
ments. When, however, the eye expresses and the other organs
receive the impression, all lengths are greatly under-estimated ; but
if the hand is the expressing sense, all lengths are greatly exagger-
ated. The arm as expressing sense exaggerates all lengths received
by the eye, and under-estimates all received by the hand.
The relative accuracy of the three senses, whether receiving or
expressing, or both, stands in the order of eye, hand, arm — the hand
being only slightly better than the arm. The degree of confidence
felt in the estimate made is naturally greatest where the accuracy
is greatest. Inasmuch as " the expressing sense gives the charac-
teristic properties to the curve of error, '"^ the question arises
whether all the phenomena cannot be accounted for by a special
application of the law of habit in connection with the normal action
of the sensory apparatus. Each sense, when expressing the esti-
mate, tends to approximate it in size toward those dimensions which
it is most accustomed to judge accurately.
All the foregoing results show plainly that the interpretation of
visual distance in terms of the tactual and muscular sense is a mat-
ter of complex experience, and is not usually more than very im-
perfectly attained. It bears little comparison with the nicety of
' Art. on The Perception of Space by Disparate Senses, in Mind, October,
1886. pp. 539-554.
= Ibid., p. 549.
MIND AS PSYCHICAL SUBJECT. 467
the spatial perceptions belonging to each one of the two senses
concerned when interpreting its own specific data in corresponding
terms, as it were.
§ 38. In closing this subject, the one psychological truth of pre-
eminent value which has been most obviously demonstrated should
be stated again. Perception is the result of an extremely complex
activity of the psychical subject, Mind; it involves the synthesis of
a number of sense-data according to laws that are not deducible
from the nature of the external objects, or of the physiological ac-
tion of the end-organs and central organs of sense. An analysis of
these data themselves is not sufficient to explain perception. The
descriptions of Physiological Psychology can do no more than
enumerate these data, show their dependence on external stimuli,
and the value which they have as motifs for the perceiving subject ;
and then understand the laws of this synthesis as the permanent
modes of the behavior of the psychical subject. The object of
sense-perception, the presentation of sense, is not an extra-VLXQnisl
entity made up outside of the mind and borne into or impressed
upon it thi'ough the avenues of sense. It is a mental construction.
The field of vision is a subjective affair, and so is the field of touch.
The same psychical subject which reacts upon the stimulation of
the nervous organs of sense in the form of sensations, by its activity
in' synthesizing these sensations, constructs the objects of sense.
The fundamental fact is the presence and activity of the subject,
known as Mind.
CHAPTER VIII.
TIME-EELATIONS OF MENTAL PHENOMENA.
§ 1. " Pkesentations of sense " appear in consciousness, not only
as having spatial qualities and relations, but also as occurring either
simultaneously or successively as respects Time-form. The clear-
est expeiience of the manner in which our sensations are located in
this framework of time, as it were, is gained by attention to the
successive notes of a melody, or to the rhythm of visual or mus-
cular impressions which accompanies a regularly recurrent motion
of some member of the body. What is true of the presentations
of sense is also true of all mental phenomena, of the reproduced
images of sense, of pure creations of fancy, and of thoughts. All
have that form of occurrence and relation which we call " Time."
Physiological Psychology, however, can no more give an ultimate
explanation of this time-form which belongs to all mental phenom-
ena than of the space-form which objects of sense acquire as the
result of a mental synthesis. Experimental science cannot explain
"time." Nothing is accomplished toward comprehending the ori-
gin of the mental representation of time by indicating the speed,
number, and order of the various series of conscious experiences.
Successive presentations of sense or successive ideas do not of
themselves constitute a mental presentation or idea of succession.
The idea that a follows or precedes h is not the idea of a nor the
idea of h ; neither is it the idea of a -f 6 or of a — h. Experimental
science can explain the order of succession ; but in doing this it
imphes the idea of succession, and this idea is not itself a succes-
sion, or an order of succession, or a compound of successive ideas.'
Many thousands of experiments have been made (since the work
of Donders in 1868), with the use of the most comiDlicated and deli-
cate machinery, in order to fix the amount of time required for the
various processes, both nervous and mental, which are the condi-
tions of our conscious life. These experiments have succeeded in
bringing many interesting facts to light. But the laws thus estab-
lished beyond all reasonable question are remarkably few ; more-
' Comp. Volkmann von Volkmar, Lelirb. d. Psychologic, II., p. 11 f.
METHODS OF MEASUEEMENT. 469
over, they are nearly all merely restatements in more definite form
of familiar generalizations. That a kind of sluggishness or inertia,
which the stimulus must overcome, belongs to all the senses, and
that they often continue to act, when once roused, after the excit-
ing cause is withdrawn ; that different sensations following each
other too quickly tend to confuse or destroy each other ; that no
one can see or think more than about so rapidly, but that this rate
varies with different individuals and with the same individual at
different times ; that it takes more time to perceive or think where
the objects are complex, and are either too small or too large or
too closely alike ; that it takes time to will or choose, less time to
act when we know what to expect, and more time to move, in re-
sponse to a particular sensation, some part of the body which we
are not accustomed to connect with that sensation ; that practice
increases the speed of our mental and bodily action, and that fatigue
and certain drugs diminish it>— ail these statements are matters of
common observation.
§ 2. It is not necessary to describe the construction of the
machines which have been used in experimenting upon the time-
relations of mental phenomena, or the methods of using them em-
ployed and commended by different observers. The general prob-
lem is in all cases essentially the same — namely, to produce certain
definite impressions upon the organs of sense, to secure a definite
result in the form of motion of some part of the body as a sign
that the impressions have been received (aud, perhaps, interpreted
and mentally combined), and to measure with extreme accuracy the
interval between peripheral stimulation and resulting motion.
The electrical current is ordinarily used to mark both the in-
stant when the external sense-stimulus acts on the organ and that
when the resulting motion occurs. The stimulus may consist in
the flash or crackle of an electric spark, the appearance of one
or more colors or figures, or letters or words, the sounding of a
bell or a falhng ball, etc. ; the motion may be with the finger
pressing a key, or the foot or hand closing or breaking a circuit,
or the vocal organs calling into a tube, etc. The one difficult
matter which marks the success or the comparative failure of any
series of observations is the arrangement of the experiments and
their tabulated results so as to analyze the difterent elements of the
complex process involved. Such experiments need to be repeated
many times upon the same individual, so as to eliminate the vari-
able factors of bodily condition, attention or distraction of mind,
practice, etc. ; they need also to be repeated vdth. many individuals,
so as to calculate upon the so-called personal equation.
470 THE FIXING OF EEACTION-TIME.
§ 3. The interval between the instant when the external stimulus
begins to act ujDon the end-organ of sense and the resulting move-
ment of some member of the body has been called " physiological
time" by Hirsch and others, and "reaction-time" by Exner. The
latter term is preferable. Reaction- time is " simple " when all the
elements which tend to complicate the processes involved in the re-
action, and so to lengthen the time required by it, have been as far
as possible ehminated. Reaction obtained in response to a single
sensation of known quality, the instant of whose appearance is ex-
pected, by executing a single natui-al and easy motion, best fulfils
the conditions of simphcity. It is therefore requisite, for all ex-
periments of this sort, that the average simple reaction-time of each
individual experimented upon shall be determined ; and also the
effect of practice, exhaustion, and other influences ujDon this inter-
val. But even the simplest reaction-time is, of course, a very com-
plex affair.
Donders ' distinguished no less than twelve different processes
as entering into "physiological time" (or simple reaction-time)—
and this without interpolating any purel}^ psychical elements, as
occupying separate periods, into the entire interval. The analysis
of Exner '^ is more pertinent to our purpose. Exner finds seven
elements in all reaction-time : (1) An action of the stimulus on the
end-organ of sense preparatory to excitation of the sensory nerve ;
(2) centripetal conduction in this nerve ; (3) centripetal conduction
in the spinal cord or lower parts of the brain ; (4) transformation
of the sensory into the motor impulse ; (5) centrifugal conduction
of the impulse in the spinal cord ; (6) centrifugal conduction in
the motor nerve ; (7) setting-free of the muscular motion. Of
these seven factors, however, the fourth is most interesting to psy-
chology. It may properly be called " psycho-physical " as distin-
guished from more purely physiological time. The other six ele-
ments (with the exception of the first, on account of difficulties
inherent in the experiments) have been determined with some de-
gree of definiteness (see Part I., chap, iii., on the speed of nervous
processes). It is, then, theoretically possible to ascertain the amount
of these six and subtract them from the entire reaction-time ; the
remainder would be the interval occupied by the central cerebral
processes (that is, by No. 4). Thus Exner ^ assumes 62 meters
per second as the probable rate of conduction in both sensory
and motor nerves ; and in the spinal cord, 8 for the sensory and
' Archiv f. Anat. , Physiol., etc., 1868, p. 664.
^ See Hermann's Handb. d. Physiol., II., ii., p. 271.
3 Ibid., p. 272 f.
ELEMENTS OF PSYCHO-PHYSICAL TIME. 471
11-12 for the motor process. He thus calculates that about 0.0828
sec. is the "reduced reaction-time," or interval occupied within
the cerebral centres in transforming the sensoiy into motor im-
pulses— in the special case of reaction from hand to hand, where
the whole reaction-time is 0.1337 sec. The uncertainties of all
such calculation, however, occasion the demand for other methods
of determining the strictly " psycho-physical " portion of reaction-
time.
§ 4. "Psycho-physical time" (No. 4 of Exner's seven processes)
is analyzed by Wundt ' into three psycho-physical processes : (1)
Entrance into the y'lsnal field of consciousness, or simple perception ;
(2) entrance into the point of clear vision with attention, or apper-
ception (attentive and discerning perception) ; (3) the excitation of
the will, which sets free in the central organ the registrating mo-
tion. Obviously, the mental processes are here all conceived of
after the analogy of sight. Consciousness is regarded as a field of
vision ; objects enter it and are at first only obscurely and indefi-
nitety perceived, as are those visual objects whose images enter the
field of the eye at the sides of the retina. Time is required for the
objects to arrive at the spot of clear vision — the fovea centraliH of
consciousuess [Blickpunkt) — where discerning attention is bestowed
upon them and they are opperceived. "When they are apperceived,
further time is required to get up the corresponding molecular mo-
tion in the motor areas of the brain. All three foregoing processes
are psj'cho-physical — that is, they comprise physiological processes
in the central organs and simultaneous corresponding changes of
consciousness occurring in time-form. There is no good reason to
suppose that the mind occupies time for its own processes which is
separate from and — as it were — thrown in between the physio-
logical processes. Indeed, all the evidence is contrary to such an
hypothesis.
Wundt has made an elaborate defence of his positions with re-
gard to the nature of psycho-physical time. He and his pupils
have attempted more definitely to characterize the cerebral changes
which correspond to each of the mental elements of (1) perception,
(2) apperception, and (3) wall. His figure of speech, which likens
all changes of conscious states to those produced by moving an
image over the retina to the spot of clear vision, may be accepted
as helpful to the imagination ; it must not be forgotten, however,
that it is still a figure of speech. The fact of which it takes account
is, that all changes of consciousness require tim.e in order to define
themselves with their maximum of clearness and intensity. The
' Physiolog. Psychologie, ii., pp. 330 fE.
472 THE FIXIIS^G OF EEACTIOIST-TIME.
position that the mental forms of perception, apperception, and
will, are exactly simultaneous with corresjooncling cerebral processes,
and that mental states are not to be regarded as forming them-
selves in a separate time, as it were, on top of these processes, may
also be admitted in a provisional way. It is probable theory, how-
ever, rather than demonstrated fact. Accordingly, the first problem
of psychometry is, to determine the simple reaction-time, and from
it to find the three factors of psycho-physical time — namely, per-
ception-time, apperception-time (or discernment-time), and will-
time.
§ 5. Any psycho-physical theory of the time-relations of mental
phenomena requires that account should be taken of the inertia
of the nervous system. As composed of moving molecules, it ne-
cessarily requires some time to be started by the action of a given
stimulus, then reach its maximum of activity in a particular direc-
tion, then subside into a negative condition with respect to this
direction (called "Anklingen" and "Abklingen" of the nervous
excitement, by the German investigators). This statement follows
as a necessary assumption from the physical nature of the nerve-
fibres and nerve-cells, since iuertia is a propei-ty of every material
mechanism. It is difficult, however, to justify the assumption
experimentally, or to fix the exact amount of time consumed by
the inertia of different parts of the nervous system. Experiment
demonstrates no stadium of latent excitation for the motor nerve,
such as is about yig- sec. for the muscle when electricity is used.
The case is different, however, Avith the end-organs of sense. They
do exhibit a certain sluggishness, and this is one reason why only
so many sensations in a given unit of time can be produced by
their successive irritation.
The result of the inertia of the end-organs, as determining the
number of separate excitations of which they are capable in a
second, varies for the different senses. The nerve-endings of touch
probably exceed all others in the promptness with vdiich they re-
sjiond to stimulus and then return to a relative equilibrium. But
the number of separate sensations of this sense which can be pro-
duced during a given interval depends in a remarkable way upon
the quality and intensity of the stimulus, the place where it is ap-
plied, etc. The' results of different experimenters therefore differ
widely. Preyer thought that 27.6-36.8 nervous shocks (per sec-
ond) of the skin fused into one continuous sensation ; but Valentin
put the limit at 480-640, and von Wittich ' succeeded in distinguish-
' For his remarks on Preyer' s experiments, see tlie article in Pfliiger's Archiv,
ii., pp. 329 ff.
STATEMENT OF TALBOT'S PRINCIPLE. 473
ing about 1,000 separate excitations in this unit of time. Hearing
can receive nearly as many separate sensations in a second as can
touch. The noise of the electric spark has been heard with one ear
only, as separate sensations, at intervals of 0.00205 sec; but hardly
or not at all at intervals of 0.00198 sec. The number of possible
sensations of sound may then be placed at about 500 per second.
Mach, ' however, by using the click from a revolving toothed- wheel,
claims to have reduced the interval to 0.016 sec. The interval
is increased to about 0.064 sec. when the same auditory impres-
sions are heard by both ears. E. H. Weber noticed that we can
tell whether two watches are ticking exactly together mucli better
when both are held near the same ear than when one is held at
each ear. Far fewer musical tones than noises can be heard in a
second ; and, indeed, a number of vibi'ations, occupying a consider-
able fraction of a second, must be secured before the sensation of
tone is established, as it were.
The smallest interval for sensations of sight, when the two stimuli
act on the same place of the retina, is still greater. In ordinary
daylight, rotating disks whose surface is part white and part black
become gray (that is, the sensations fuse) when they attain a motion
of about 24 per second. It can be told which of two images of elec-
tric sparks that are 0.011 mm. apart on the retina occurs first, if
the difference in the time of their occurrence is 0.044 sec. If the
two sparks are seen as one with an apparent motion, its direction
can be distinguished when the two ends of the Une of motion are
only 0.014-0.015 sec. apart. But if one stimulus strikes the fovea
centralis and the other a point of the retina 6 mm. off, the smallest
interval for distinct perception is increased to 0.076 sec." Within
certain limits these intervals are independent of the intensity of the
light, when it falls on the retina near its centime ; but (comp. p. 334)
the intensity and quality of the sensations are connected with the
time during which the stimulus acts. The law for the " time-
course " of such retinal excitations has been stated and defended by
Fick,^ as known by the name of " Talbot's principle :" If any place
of the retina is periodically excited with light of given intensity, for
a certain time a, and then left unexcited for a time h, and if the
time (2 -f 6 is less than about 0.04 sec, then the sensation becomes
continuous, with a strength corresponding to the excitation — — -7-
' Sitzgsber. d. Wiener Acad., LI., p. 142.
^ Comp. Exner, in Hermann's Handb. d. Physiol., II., ii. , p. 256 f. ; and
Sitzgsber. d. Wiener Acad., LXXII., fi. 156 f.
2 Archiv f. Anat., Physiol., 1863, p. 739 f. ; and Hermann's Handb. d. Pby
siol., IIL, i., p. 212 f.
474 THE FIXING OF EEACTION-TIME.
If the inertia of the eye for the different color-sensations were
greatly different, we would see objects differently colored accord-
ing to the time that the rays from them were acting on the retina.
That the different parts of the spectrum do actually require slightly
different intervals of time to reach the maximum of their excitation
has been shown by Kunkel. ' Equally bright light, as before stated
(p. 334), attains its maximum effect, for red rays in about 0.0573
sec, for green in 0.133 sec, for blue in 0.0916 sec. With the same
color-tone, the greater the brightness the quicker the maximum
effect is reached. Thus for three degrees of brightness the time for
red rays is 0.0573-0.071 sec ; for green, 0.0699-0.133 sec ; for blue,
0.0916-0.102 sec. Accordingly, the spectrum may be reduced in
size and number of color-tones by diminishing the duration of the
action of the light which forms it.
The measurement of the smallest intei'val for sensations of smell
and taste cannot be made with satisfactory exactness on account of
the nature of the stimuli of these senses. Little is known which
goes beyond ordinary experience concerning after-tastes analogous
to the after-images of the eye. One experimenter (Bidder) thought
that the sensation continued after the tongue had been so carefully
dried off that no particles of thetastable substance were left remain-
ing ; but of this we can scarcely be sure. It may be that certain
substances leave their after-taste because their tastable particles are
dissolved later ; or because their effect, being weaker, is at first
suppressed by particles of stronger quality.^
§ 6. When the successive sensations are of different senses, the
" smallest interval " between them, and so the number j^ossible in
a second, varies still more. The following table ^ exhibits the re-
sults obtained by several different observers :
Sec.
Between two sensations of sound (electrical sparks) 0.002
Between two sensations of liglit (direct electrical excitation of same
retinal spot) 0.017
Between two sensations of toucli (impact on finger — Macli) 0.0277
Between two sensations of light {a,i fovea centralis, by optical images). . 0.044
Between two sensations of light (at periphery of retina, by optical images) 0. 049
Between sensation of sight and sensation of touch (sight following) . . . 0.05
Between sensation of sight and sensation of hearing (sight following). . 0.06
Between two sensations of noises (each heard by one ear) 0.064
Between sensation of sight and sensation of touch (sight preceding) . . . 0.071
Between two sensations of light, one at the periphery and the other at
the centre of retina 0. 076
Between sensation of sight and sensation of hearing (sight preceding) ... 0. 16
^ Pflliger's Archiv, ix. , p. 206 f.
^ Comp. von Vintschga>i, in Hermann's Handb. d. Physiol., III., ii. , p. 221
^ By Exner, in Hermann's Handb. d. Physiol., II., ii., p. 262.
EEACTION FROM HAND TO HAND.
475
Fig. 114. — Curves showing the Rise and Fall of
the Intensity of Sensations of Light — ihe ab-
cissas measured along a-d representing the
time.
§ 7. The way that the intensity of sensations of light rises to a
maximum, continues there, and then falls off through exhaustion
of the retina, in time, has been
represented by Fick ' with the
use of the accompanying figure
(No. 114).
§ 8. The point of starting for
determining experimentally all
the jDroblems which concern the
durations and relations in time
of mental phenomena is gained
by fixing the " simple reaction-
time. " This is found to vary for
different persons, for the differ-
ent senses, and under different conditions of expectation, attention,
habit, etc. In its very simplest form, the question may be stated as
follows : How long an interval will elapse, under the most favorable
cu'cumstances, between the instant when some end-organ of sense is
stimulated and the instant when motion follows as the result of rec-
ognizing the fact, in consciousness, that such stimulation has taken
place ? In this form the three elements of psycho-physical time
(perception, discernment or apperception, and choice) are sup-
posed to be reducible to one — namely, to simple perception. This
supposition is, of course, true only in case that, by practice in react-
ing upon an expected sensation in one definite way, the cerebral
sensory-motor processes have attained the highest possible rate of
speed, and the time ordinarily occupied in deciding what to do, and
in starting the voluntary motor mechanism, has been reduced al-
most, or quite, to zero.^ The entire process then becomes reflex,
simply the sensory central part of it being represented by a con-
scious act of perception. To shorten the reaction-time as much
as possible, the subject of the experiment must know what place of
the sensory organism is to be hit by the stimulus, and about when
to look out for it ; he must also be called upon to react, in one and
the same easy and natural way, in aU cases, as soon as he knows
that he is hit at all.
The following table ' gives the mean values of the reaction-time
"from hand to hand " (one hand being hit by the electrical cui-rent
I Hermann's Haudb. d. Physiol. HI., i., p. 216.
^ Comp. Wundt, Physiolog. Psychologie, ii., p. 226 f.
3 Taken from Exner, in Hermann's Handb. d. Physiol., II., 11., p 263; the
two sets of numbers indicate values which were found iu two series of exper-
iments.
476 THE FIXING OF EEACTIOlSr-TIME.
and the other reacting, for example, to press a key), as determined
by various observers :
,^. , ^ , , . Von Ti Von Von Kries and
Helmholtz. Hirsch. Kohlrausch. -^ittich. ^^^ier. vintschgau. Auerbach.
0.12776 sec. I 0.1733 sec. ) n ifiQ7 =«^ I 0-153 sec. ) 0.1376 sec. ) 0. 1087 sec. I 0.117 sec.
0.12495 sec. \ 0.1911 sec. \ "-^"^' ^^°- f 0.166 sec. J 0.1283 sec. ( 0.1860 sec. j 0.146 sec.
The last two experimenters developed certain interesting results.
They found the reaction-time, when the stimulus was applied to
the middle finger, to be for Kries 0.117 sec. and for Auerbach 0.146
sec. ; but when applied to the back of the hand, to be for Kries
0.119 sec. and for Auerbach 0.147 sec. But the hand being about
16 ctm. nearer the brain than the middle finger, its reaction-time
should have been some 0.004 sec. shorter instead of longer, as a
matter of physiological time. Esner found that the reaction-time,
when the forehead is stimulated, is greater than when the stimulus
is applied to the hand. Bloch found the same thing true when the
nose is stimulated. The intercerehral relations, taken in connection
with the law of habit, probably account for the foregoing facts.
The value of the reaction-time also changes when the character
of the stimulus is changed on which the subject of experiment re-
acts. This fact is made apparent by the following table : '
Observer. Optical stimulus. Acoustic stimulus. Stimulus of touch.
Sec. Sec. Sec.
Hirscli 0.200 0.149 0.182 (hand).
Hankel 0.225 0.151 0.155
Bonders 0.188 0.180 0.154 (neck).
Von Wittich 0.194 0.182 0.130 (forehead).
Wuudt 0.175 0.128 0.188
Exner 0.1506 0.1360 0.1276 (hand).
Auerbach 0.191 0.122 0.146
VonKries 0.193 0.120 0.117
We conclude, then, that under the most favorable circumstances
the reaction-time can scarcely be reduced to y^o" o^ ^ second, while
it rarely rises much above y\ of a second.
§ 9. It has been argued that the apparent difference in the reac-
tion-times of different senses is due to difference in the intensity of
the stimuli applied. Increasing the strength of the stimulus de-
creases the reaction-time in all the senses ; but we have no veiy
good means of measuring stimuli of one sense in terms of another
sense. It has been proposed ^ to reduce them to a common standard
by referring the sensations to the point where they barely reach
the " threshold of excitation " (Heizschivelle) ; that is, where they
' Taken from the article of von Kries and Auerbach, Archiv f. Anat. u. Phy-
siol., Physiol og. Abth., 1877, p. 359 f.
'^ By Wundt, Physiolog. Psychologic, ii., p. 223 f.
EFFECT OF INCliEASED INTENSITY.
477
are just perceptible in consciousness. In this way the mean result
for sound (0.337), light (0.381), and touch (0.327) are found to be
almost exactly the same. It has further been argued that the
speed of perception and the duration of psycho-physical time are
the same for all the senses. On the contrary, there seems good
reason to suppose that the reaction-time of sight is necessarily
longer than that of hearing or touch, on account of the photo-
chemical natui'e of its more immediate stimulus. One observer
(von Wittich) has even gone so far as to conjecture that the speed
of conduction in the optic nerve is less than that of the other
nerves of sense ; it is rather to be concluded, however, that the la-
tent time of the sensory end -apparatus, and of the cerebral pro-
cesses by which sensory impulses pass over into motor impulses,*
is different.
§ 10. The effect of increasing the intensity of the stimulus, in di-
minishing the reaction-time, has been studied by Wundt for sen-
sations of sound occasioned by the fall of a hammer or ball — with
the following' result :
Height of hammer. Reaction-time.
Sec.
1 millimeter 0.217
4 millimeters 0.146
8 millimeters 0.132
16 millimeters 0.135
Height of ball. Eeaction-time.
Sec.
2 centimeters 0. 161
5 centimeters 0.176
25 centimeters 0.159
55 centimeters 0.094
This effect is obtained, of course, only within certain limits ; for
the sound must not be so loud as to startle and confuse. Thus,
also, when the length of the electric spark which stimulates the
retina is increased the reaction-time is diminished. Exner " found
that, while it was 0.1581-0.1502 sec. for sparks 0.5-1 mm. in length,
it was 0.1479-0.1384 sec. for those 2-5 mm. long, and diminished
to 0.1229 sec. for those of 7 mm.
The reaction-time is also diminished by indicating the instant
at about which the sensation may be expected, through some pre-
ceding signal. The interval for the sound caused by a ball falling
25 ctm., which without signal was 0.253 sec, was reduced by a
signal to 0.076 sec. ; and when the fall was 5 ctm. the interval was
reduced by the signal from 0.266-0.175 sec.° In order to secure
this effect, however, the interval between signal and impression
should be nearly constant, and not so long as to overstrain atten-
' Comp. von Kries and Auerbach, Arcliiv f. Anat. u. Physiol., Physiolog.
Abth. . 1877, p. 359 f.
- Hermann's Handb. d. Physiol., II., ii., p. 269 f.
3 See Wundt, Pliysiolog. Physiol., ii., p. 238.
478
THE FIXIKG OF EEACTION-TIME.
tion or prevent the carrying of a definite mental image of this in-
terval.
The detailed investigations of Berger,' recently published, an-
nounce the following conclusions : (1) The reaction-time increases
in inverse ratio to the intensity of the stimulus, and so much the
faster the nearer we approach the " threshold " (or lower limit) of
the stimulus ; (2) discernment-time is related to alterations in the
intensity of the stimulus in the same way as simple reaction-time ;
and (3) will-time is independent of the intensity of the stimulus.
§ 11. When the quality of the impression to be expected is
known, but its intensity is unknown, the reaction-time is increased.
The increase is greater if the alternation of intensities is very irreg-
ular. This fact is exhibited by the following table : ^
I. Uniform change of intensity.
Sec.
Loud sound 0. 116
Feeble sound 0.127
II. Irregular change of intensity.
Sec.
Loud sound 0.189
Feeble sound 0.298
By suddenly intercalating a feeble sound in a series of loud noises
the reaction-time may be prolonged to 0.4 or 0.5 sec. It is also
greatly lengthened when the impression is wholly unexpected by
the subject of the experiment being taken off guard, as it were ; in
such a case, also, it may reach 0.5 sec. As might be expected, it
takes longer to react in an unnatural and unaccustomed way. It
requires more time to react with the foot than with the hand ; a
mean reaction-time from eye to foot was found by Exner to be
0.1840 sec.
§ 12. The reaction-time for the sense of taste varies in depend-
ence upon the part of the tongue to which the stimulus is applied,
and upon the character of the gustable substance. It also varies
greatly with different persons. Von Wittich fixed it at 0.167 sec.
from tongue to hand, by using the sour taste which the electrical
current excites. The reaction-time for sugar on the tip of the
tongue varied, for three different persons, from 0.1639 to 0.3502
sec. ; and for quinine, for two persons, from 0.2196 to 0.993 sec.
For the root of the tongue, it was found to be 0.552 sec. for sugar,
and 0.502 sec. for quinine.^ Little has been done to determine the
reaction-time of smell. Some have maintained that it must be much
longer than the reaction-time of sight and hearing, and even reach
several seconds ; others have held that, although slower than these
» Wundt's Philosoph. Studien, 1885, III., heft i., pp. 38 fE.
'^ Wundt, Physiolog. Psychologie, ii., p. 241 f.
3 Von Vintschgau and Honigschmied, in Pfliiger's Arcliiv, x., 1; xii., 2;
xiv., 3.
THE METHOD OF DON'DERS. 479
senses, smell lias probably a reaction-time of only a fraction of a
second. The latter view seems more recently to have been con-
firmed by the experiments of Moldenhauer/ who obtained the fol-
lowing among other figures : Oil of mentha, 0.203-0.362 sec. ; oil
of bergamot, 0.212-0.374 sec. ; camphor, 0.226-0.492 sec. ; musk,
0.319 sec. Taste and smell are much more subject to change in
the length of the reaction-time through individual peculiarities
of the exciting substances and of the subjects of experiment, than
are the senses of hearing, sight, and touch.
§ 13. Having obtained the mean reaction-time for the different
senses under varying circumstances, the method of investigation
requires that it should be determined how much the reaction-time
is increased by increasing and complicating the psycho-physical
elements. One principal question to be answered by this method
is the following : How much time is required for " apperception" ov
clear discernment of perceived objects in the central point of con-
sciousness under different conditions ? This question has been veiy
patiently and fully investigated, at first by Donders, and since by
many observers, especially by von Kries and Auerbach."
Donders ^ and his pupils were the first to examine in detail the
speed of psychical processes, with a view to determine how long it
takes to recognize one of two or more different presentations of
sense ; and also how long to solve the dilemma of choosing one
of two means for making the reaction. For example, in one series
of exj)eriments the eye was suddenly stimulated with either red or
white light (the subject of the experiment not knowing which to
expect), the signal for the former to be given with the right hand,
the signal for the latter with the left. In another series of experi-
ments, the quality of the light or sound was to be recognized before
reaction, but reaction was to take place only in case a particular
one of the two sensations was recognized ; in case the other sensa-
tion appeared in consciousness, no reaction was to take place. In
other words, discernment of the presentation of sense was to be
followed by the choice between reacting in a prescribed way and re-
fraining from reacting at all. In still other experiments the stimulus
consisted of a "vocal clang "called into a "phonautograph" by one
person, and the reaction consisted of the same clang repeated by
another person ; or, again, the recognition of one or more letters
seen was signalled by a movement of the hand. By such methods
' Wundt's Philosoph. Studien, I., heft iv., p. 606 f.
2 See their article in Archiv f. Anat. u. Physiol., Physiolog. Abth., 1877, pp.
297-378.
3 Archiv f. Auat, Physiol., etc., 1868, pp. 657-675.
480 APPEKCEPTION AND WILL TIME.
Donders made the mean reaction-time of five persons, for dis-
cernment between red and white Hght, with choice of the hand by
which to react, to be 0.154 sec; the minimum, 0.122 sec; the
maximum, 0.184. The mean reaction-time for two letters, with
discernment and signal by calUng them out, was found to be 0.166
sec; when the number of letters was increased to five, the mean
reaction-time rose to 0.170. It took 0.180 sec. to discern and
repeat a vocal clang when known, 0.268 sec. when unknown. With
the method of reacting only on one clang and keeping silent when
others were heard, the mean I'eaction-time varied from 0.201 to
0.284 sec. The investigations of Donders made obvious the fact
already stated (p. 475 f.), that the natural connection between the
sensation and the peculiar means chosen for reaction is of in-
fluence in detei-mining the interval. Donders assigned 0.039 sec.
to the psychical process of the development of a presentation of
sound in his own case, and a little less to the formation of a
decision of will.
§ 14. Another and ingenious method of determining the time
required for " apperception " was proi^osed by Baxt ;' it was based
upon the principle of the inei'tia of the senses, especially of sight.
Suppose the question raised, How long must an image act on the
optical apparatus in order to occasion a clear presentation of sense ?
It may be answered by discovering how quickly after a given im-
pression another stronger one must follow in order that the latter
may overtake the former, and quench it — as it were — before it
reaches the focus of apperception. Let then some image which
requires discernment to interpret it — as the image of several letters,
or of a simple geometrical figure — be thrown upon the retina, and
let this image be succeeded after a brief interval by the image of a
bright white disk ; then, if the interval be less than a certain time,
apperception (or clear vision, with discernment of the significance of
the image) will not take place at all. Baxt found that the time ne-
cessary under these circumstances for a presentation of visual sense
depends upon the intensity of the second excitation ; it increases
as this intensity increases. It depends also upon the complexity of
the apperception required ; to recognize three letters required only
about half the time necessary to recognize five or six. With an
interval of 0.0048 sec. between the two excitations, the first ap-
peared as scarcely a trace of a weak shimmer ; with an interval of
0.0096 sec, letters appeared in the shimmer — one or two of which
could be partially recognized when the interval increased to 0.0144
sec. When the interval was made 0.0192 sec, the objects were a
' See Pfliiger's Archiv, iv. , pp. 325 ff.
CONCLUSION'S OF KRIES AND AUERBACH.
481
little more clearly discerned; at 0.0336 sec. four letters could be
well recognized ; at 0.04:32 sec, five letters ; and at 0.0528 sec. all
the letters could be read.
§ 15. The method of Baxt was rejected by von Kries and Auer-
bach' as unsuitable to answer the question most interesting to
psycho-physical researches ; because it includes as an inextricable
factor the time used ujd in the peripheral nerves. Besides, we
have no means of estimating just to what stadium a psycho-physi-
cal process must have advanced when it becomes impossible for a
strong succeeding sensation to overwhelm it. These observers pre-
ferred, therefore, the method employed by Donders, and especially
in the form (called " Danders' G-method ") in which the subject of ex-
periment reacts in one prescribed way or else refrains from reacting
at all. By this method they endeavored to answer the questions :
" How long time passes after the occurrence of a stimulus of sight
before I know what color it has ; and how long before I know at
what place in the field of sight I experience it," etc. ? Their results
may be summed up in the following table.^ [The numbers give
the time assigned by them to the discernment involved in the va-
rious processes performed — that is, the psycho-physical time exclu-
sive of all solution of a dilemma by the will. This time is found
by subtracting the simple reaction-time, or time necessary for re-
acting when no discernment is required, from the whole time re-
quired for the process including such discernment.]
Discernment of the direction of light
Discernment between two colors
Localization of sound (minimum)
Discernment of tone when higher
Localization of sensations of touch
Localization of distance by sight
Discernment between tone and noise
Judgment of intensity of sensations of touch (strong)
Discernment of tone when lower
Judgment of intensity of sensations of touch (weak).
Localization of sound (maximum)
Auerbach.
Von Kries.
Sec.
Sec.
0.011
0.017
0.012
0 034
0.015
0.032
0.019
0.049
0 021
0.036
0.022
0.030
0.022
0.046
0.023
0.061
0.034
0.054
0.053
0.105
0.062
0.077
§ 16. Various interesting discoveries were made during the course
of the experiments which resulted in preparing the foi-egoing table.
For example, it was found that the simple reaction-time for A.
(Auerbach), when stimulus was applied to the middle finger or
1 See Archiv f. Anat. u. Physiol., 1877, Physiolog. Abth., p. 298.
5 Ibid. , p. 346 f .
31
482 APPERCEPTIOlSr AND WILL TIME.
back of tlie hand, was 0.146-0.147 sec; and for K (Kries\
0.117-0.119 sec. But, as the table shows, when discerament wag
required of the two observers, the reaction-time of K. was relative-
ly so much increased as to make his discernment-time greater than
that of A. The result of practice in discernment was found to hold
good for other areas of the skin than those in experimenting upon
which the practice was gained. For discernment among three
places (middle finger, back of hand, and middle of lower arm), the
order being unknown and only one to be reacted on — the mean in-
terval required was for A. 0.028 sec, and for K. 0.050 sec. ; fur-
ther practice, however, reduced this interval to about the same as
that required for two places.
Discernment between two intensities of the sensation of touch was
found to be very uncertain and difficult. Many more false reactions
followed the attempt to tell whether the dorsal side of the last of
the phalanges of the middle finger was being hit with the weaker
or the stronger of two stimuli than occurred in the attempts to
localize tactile sensations. The discernment-time, when reaction
followed the stronger stimulus, was 0.016-0.034 sec. for A, and
0.05-0.07 for K. ; when reaction followed the weaker stimulus, the
discernment-time was 0.035-0.069 sec. for A, and 0.089-0.114 forK.
The character of our judgments of intensity is, perhaps, dependent
on the steepness, as it were, with which the curve rises in consci-
ousness ; but, however this may be, it appears that we discern how
and where we are affected with a sensation more promptly than
about how much we are affected.
When discernment between two simple tones of different pitch is
required, the reaction follows the one of higher pitch more promptly.
Thus the discernment-time, under such circumstances, was for A,
0.015-0.044 sec, and for K, 0,043-0,11 ; but, if reaction followed
the tone of lower pitch, the discernment-time for A, was 0.03-0.059
sec, and for K, 0.045-0,092. To discern tone from noise, when re-
action followed the tone, A. required 0.015-0.023 sec, and K 0.036
-0.055 ; when reaction followed the noise, A's discernment-time was
0.017-0.025 sec, and K's, 0.045-0,047. The reaction-time dimin-
ishes as the pitch rises ; for very high notes it nearly reaches the
limit required for hearing the noise of the electric spark. The ex-
planation for these experiences requires reference again to the fact
that some 15-20 vibrations are necessary to start the organ so that
the sensation of musical tone can be received at all.
The simple reaction-time for sensations of sound remains nearly
the same for all changes in the angle by which the locality of the
sound diverges from the median plane between the two ears. But
THE EXPERIMENTS OF WUNDT.
483
the time required for discerning the locality of the sound varies
greatly for the different sizes of this angle. Thus the discernment-
time for locality, as to right or left, varied for Auerbach and Kries
as follows :
Angle ISC-SS".
Angle 35°-2G<'.
Angle 26°-ll».
A
Sec.
0.020
0.013
Sec.
0.033
0.122
Sec.
0 120
K
0 153
The discernment-time required for localizing the direction of a
spark by direct vision varied for A. from 0.005 to 0.025 sec, and for
K. from 0.006 to 0.029 sec. ; by indirect vision, for A. from 0.008
to 0.028 sec, and for K from 0.007 to 0.028 sec For locaUzing
distance, A. required 0.019 to 0.027 sec. of discernment-time, when
the object arose in front of the fixation-point, and K. 0.027 to 0.035
sec ; but A. required 0.019 to 0.029 sec, and K. 0.021 to 0.036 sec,
when the object arose behind this point.
§ 17, Various strong objections have been raised to the validity
of the results reached by the observers last mentioned. For ex-
ample, Richet' thinks that an interval so small as their " discern-
ment-time" (about 0.03 sec.) is below the limit of the experimental
error. But the constancy of the results obtained by such a large
number of experiments with reference to the mental peculiarities
of the two subjects of experiment, and to the different kinds of men-
tal processes involved (discernment of locality, quaUty, quantity,
etc.), is too great to allow of the results being summarily rejected.
The criticism of "Wundt ^ as applied to the method employed (the
so-called "Bonders' C-method") is much more pertinent. This
veteran experimenter considers that the psycho-physical time re-
quired to discriminate between two or more possible presentations
of sense, and then react only in case one of them is apperceived,
cannot all be allotted to discernment-time. For an element of vo-
lition, or will -time, is as truly involved in the decision whether to react
or not to react as in the decision between two modes of reaction.
With a view, then, to analj'ze these elements more perfectly, and
so determine the exact duration of "apperception," in the sense
in which the word is used by Wundt, another method of experiment
has been employed by Friedrich.^ In this method the subject of
experiment is warned ichen to expect one of two or more colors
' See Revue philosophique, VI., p. 395.
^ Physiolog. Psycliologie, ii. , p. 251 f.
3 See Wundt's Philosoph. Studien, II., heft i., pp. 39 S.
484
APPERCEPTION AND WILL TIME.
to be discerned, but does not know which one to expect ; only one
way of reaction is employed for all cases ; and the judgment of the
subject is left to determine just when he clearly discerns, or " apper-
ceives," the object. The time of apperception is then found by sub-
tracting the simple reaction-time (or time necessary to announce the
sensation without discernment) from the entu'e reaction-time thus
obtained. In this way the interval for apperception was fixed at
0.030 to 0.185 sec. for white, in the case of Wundt, and 0.044 to
0.146 for black ; in the case of Tischer, 0.046 to 0.112 sec. for white,
and 0.021 to 0.061 for black ; and in the case of Friedrich himself,
0.042 to 0.084 sec. for white, and 0.019 to 0.064 for black. The mean
duration o:^ apperception, as derived from all the experiments with
two color-sensations, was 0.086 sec. for W., 0.047 for T., 0.050 for F.
§ 18. The time required for discernment increases, of course,
when the other conditions are kept as nearly as possible the same,
but the number of objects is increased among which the discern-
ment is required. For example, Friedi'ich found that when four
(instead of two) colors — black, white, green, and red — were inter-
changed in an unknown order, both the reaction-time as a whole
and the duration of apperception were increased. The latter for
black as one of four colors was, when averaged for several series of
experiments, 0.081 to 0.141 in Wundt's case, 0.021 to 0.105 in Tisch-
er's, 0.076 to 0.197 in his own. With red as one of four colors the
duration of apperception was 0.049 to 0.247 for W., 0.024 to 0.124 for
T., and 0.066 to 0.234 for F. Experiments were also instituted with
a view to determine how long it takes to discern composite percep-
tions of sight.' For this purpose printed figures of 6 mm. high
and 3.8 mm. broad were employed, ranging from one to six places —
the reaction being in the form of calling the number constituted by
the figures as arranged when displayed. The mean time required
for apperception by the three subjects of experiment is shown by
the following table : [The figures at the head of the columns indi-
cate the number of places which the numbers had in the different
series of experiments ; the letters, the subjects of experiment ; the
figures under the head, the seconds of apperception-time.]
1.
2.
3.
4.
5.
6.
w
Sec.
0.344
0.290
0.820
Sec.
0.361
0.380
0.346
Sec.
0.354
0.493
0.344
Sec.
0.459
0.709
0.481
Sec.
0.573
0.849
0.670
Sec.
0.817
T
1.197
F
1.043
' Wuudt's Philosopli. Studieu, I., lieft i. , p. 53 f.
THE HEADING OF NUMBEilS. 485
It will be noticed that the reaction time for numbers of three
places is not much greater than that for numbers of one place ; but
when the complexity is increased to four places, the reaction-time
is suddenly and largely increased. This fact is probably due in
part to the habit of grasping numbers mentally in periods of three
places each. It is not certain, however, that the apperception-time
as calculated by this method is trustworthy ; for, although the sub-
ject of experiment reacts, and then notifies the number discerned,
the act of discernment may really be completed after the reaction
has taken place. Moreover, a certain time for accommodating the
eye must be allowed ; especially in the case of numbers of five or
six figures each. This time, in the opinion of one critic, may be
placed at 0.166 to 0.186 sec. A more recent investigator^ concludes
that the true discernment-time in a composite perception is possibly
so short as to occupy only a few hundredths of a second. For
numbers of one to three places the interval between perception and
apperception is 0.015 to 0.035 sec. This conclusion accords with
and enforces that arrived at by the careful experiments of von Kries
and Auerbach.
Cattell ° — by assuming that perception-time and will-time are
about equal, and thus dividing into two parts the remainder ob-
tained by subtracting the simple reaction-time from the whole time
including both discernment and choice — estimated the perception-
time for light, of B. at 0.030 sec, and of himself at 0.050. It took
longer, of course, to discern between two colors. Between red and
blue discernment required about 0.038 sec. for B., and 0.054 for C.
If one color among ten was to be discerned, the time rose to 0. 105
for B., and 0.117 for C. The time required to discern one letter
from all the others was found to vary somewhat for the different
letters ; but the legibility, or comparative accuracy of the quick
discernment, varied still more. In this sense the letter W is about
four times as " legible " as E. The discernment-time for a simple
picture of a familiar object was found to be about the same as that
for a color, and shorter than that for a letter or a word.
§ 19. We have already seen (p. 480) that Donders assigned a
little less time (0.036 sec.) to the operation of will in setting free
the required impulse when a dilemma was presented to it than is
required for discernment between two objects of the visual sense.
The duration of " ivill-time" (the third element of psycho-physical
time) has since been investigated at greater length by Friedrich.
Buccola, Merkel, and others. The first of these experimenters
1 Tigerstedt, in Zeitsclirift f. Biologie, 1883, XIX., p. 43 f.
2 See Mind, July, 1886.
4SG APPEllCEPTION AND WILL TIME.
determiued the time required for simple choice by finding how
much the reaction-time is increased when the subject of experiment
must decide whether to react or not. ' For example, let the sensa-
tions of black and white follow each other in unknown order, it be-
ing understood that only white is to be followed by reaction. The
interval for simple choice was thus found by Friedrich to have a
mean value of 0.152 sec. for W., 0.184 for T., and 0.183 for him-
self ; it lay, therefore, between \ and \ sec. If choice was re-
quired, however, between the two hands — reaction with one hand
being the sequence of the appearance of one color, and with the
other hand of the appearance of the other color — the interval
assigned to this element of psycho-physical time increased to 0.188
sec. for W., 0.330 for T., and 0.287 for F.^
Merkel ' has perhaps investigated most thoroughly the time-
relations of activities of the Avill. The question he proposes for
answer is the following : How long does it take, under different
circumstances, to set free a voluntary impulse? He assumes that,
in all cases where reaction follows disceinment between two or
more impressions, some "will-time" is present, although the
amount of this time may become so minute as to escape detection.
The method of Merkel was suggested by Wundt. The simple
reaction-time (E), or time requii'ed when the nature of the stimulus
is known and the mode of reaction fixed the same for all cases, is
first found. The reaction-time x*equired to discern clearly one of
two or more impressions, and announce the fact in some one way
previously determined upon (R d), is next found. Finally, the I'e-
action-time is found for cases where there is involved, in addition
to discernment, a choice between one or more ways of reacting, or
between reacting and not reacting [R d w). The difference lid— li is
then held to give the " discernment-time ; " the difference II d iv — li d
is held to give the " will-time." It is with the latter that we are
now concerned. For his experiments Merkel used figui'es of about
13 mm. altitude placed 250 mm. distant from the eye. To deter-
mine the reaction-time, including discernment (R d), but not includ-
ing choice, reaction is ordered invariably with the same finger. To
determine reaction-time, including choice {R d ?o), reaction is ordered
with some one finger of either hand previously assigned to each
number. Will-time is then found by subtracting the reaction-
time in the former case from that in tbe latter (R dio—JR d). The
' Friedrich, in Wundt's Philosoph. Studien, I., heft 1. , p. 57 f.
'^ Only a few experiments of this kind were tried ; the numhers are those
given by Merkel in his article.
^ Article in Wundt's Philosoph. Studien, II., heft i. , pp. 73-127.
DIFFEREXGES OF INDIVIDUALS. 487
results showed that ^vhile the simple reaction-time for the different
fingers of both hands does not differ gi'eatly, the difference in will-
time for the different fingers is much more marked. The latter
difterence is greater among the fingers of the right than of the left
hand. For ten persons experimented upon, the mean inteiTal
required for setting free a definite reaction, ^vith a choice between
two possible courses, varied from 0.02-t to 0.155 sec. This inter-
val increases for every additional course possible until, in case the
subject of the experiment is required to select one of his ten fingers
with which to react on receiving an impression corresponding to
that fiDger, the will-time becomes 0.298 to 0.448 sec.
Yery interesting individual differences in the speed of decision
attained under different conditions of complexity are brought out
by Merkel's experiments. This fact may be shown by plotting the
curve of the will-time of each individual. In general, it was found
that the individual differences increased as the complexity of the
choice required was increased from one to five places, and that they
then fell off", being least at nine or ten places. That is to say, different
individuals differ much more markedly in the speed with which they
can choose one of two or five than one of nine or ten different pos-
sible ways of reaction. Merkel's value for will-time when the choice
lies between two courses [R 2r=0.024: to 0.155 sec.) may profitably be
compared with that given by Buccola for choice between motion and
rest with discernment of color-tone and locality (0.028 sec. and 0.066
see. respectively), or Avith that given by Tischer ' for choice between
motion and rest (for nine persons, 0.052 to 0.179 sec.) or for choice
between two symmetrical motions (0.033 to 0.179 sec).
§ 20. A careful survey of the statistics and discussions furnished
by different exj)erimenters shows that it is not as yet possible to
analyze with perfect confidence the different elements of psycho-
physical time. Wundt seems justified in holding that will-tin:e is
necessarily involved in the choice between motion and rest. But,
on the other hand, von Kries and Auerbach appear to have reduced
this time almost or quite to zero, by practice and by arranging
their experiments under the most favorable conditions. By elimi-
nating will-time they have, perhaps, found about what is the least
possible interval required for simjDle acts of discernment. There is
other evidence (fi'om the phenomena of rhythm, etc.), however, to
indicate that successive acts of discernment may attain a higher
rate of speed than is possible for successive acts of will.
§ 21. Investigation has also been dii'ected toward determining
how far series of events in consciousness correspond, as regai'ds
' See Wuudt's Pliilosopli. Studien, I., heft iv. , p. 533 f.
488 APPEECEPTIOlSr AND WILL TIME.
time, to the series of excitations which occasion them. Something
may thus be accomphshed toward fixing the time-rate of conscious-
ness, as well as the interval which it is possible for the mind to ap-
preciate with the nearest approach to perfect accuracy. In all the
preceding experiments the subject of them is uniformly aware that
a pause, as it were, takes place between the excitation and the re-
action ; this pause he is able to estimate with much accuracy, and
so to tell whether his effort to react promptly has been more or less
successful. Exner ' states that in 39 cases of reaction from eye to
foot, which had a mean of 0.184 sec, the reaction was always felt
(with a single exception) to be " too slow " when it reached 0.1994
sec, and pronounced " very good " when it fell below 0.1781 sec;
its time was therefore estimated Avithin about 0.01 sec. There is
abundant proof, however, that the speed and duration of our sensa-
tions, as estimated in consciousness, do not precisely correspond
with the series of stimulations of the organ of sense. Indeed,
under certain circumstances very remarkable errors may occur in
our estimate of both the rate and the interval of our mental acts.
To show the fact and amount of the error which takes place when
we are called to intercalate an excitation of any kind in a series of
impressions, Wundt * devised the following exj)eriment : An indi-
cator is kept moving at a uniform rate over a graduated scale, and
so situated that the place of the needle can be clearly seen at each
instant of time. The action of the same clock which moves the
needle causes a sound at any moment, but in such a way that the
subject of experiment does not know when to expect it. With
what position of the needle, now, will the sensation of sound be
combined? Will the sound be heard exactly when it occurs as
indicated by the needle; or later than its real time (" positive "
lengthening) ; or earlier than its real time (" negative " lengthen-
ing) ? The result shows that one rarely hears the sound without
either positive or negative displacement of it ; but most frequently
the lengthening is negative — that is, one believes one hears the
sound before it really occurs as measured by the indicator.
§ 22. Vierordt,^ after experimenting upon our power to repro-
duce the interval as heard between two sensations of noise, con-
cluded that very small intervals are regularly overestimated and
greater ones underestimated. The minimum of error in estimating
intervals — the duration that corresponds most perfectly in our con-
sciousness to the real duration as measured by objective methods
! Hermann's Handb. d. Physiol., II., ii., p. 273 f.
^ Physiolog. Psychologie, ii., p. 264 f.
^ Der Zeitsinn. Tiibiugen, 1868.
INTERVAL OF MINIMUM ERROE. 489
— he placed at 1-1.5 sec. More recently (1881) KoUert ' published
the results of experiments instituted with a view to determine the
accuracy of our sense of time. Suppose that one metronome is
marking off time, by the sound it makes, with a normal interval
= t. Another metronome is at the same time at work with an in-
terval = S, that may be made to vary with different experiments,
and that is set as either equal to or sUghtly greater or less than t.
Let T = the time in our consciousness which is equivalent to t, and
A — a constant representing the mean error which is made in es-
timating the relations of the two intervals (t and 3) ; that is, A =
t — ^. Let 3^ = the intervals of consciousness just observably
smaller, and 3^ = those just observably greater, than the normal
time (t). Then the following table shows how A varies as t varies;
dj giving the experiments in which the interval of the variable
metronome was smaller, and d^ those in which it was greater, than
t (^^ - t = d,, and », - t = dj.
t=
d,=
d,=
A=
0.4
-0.018
+0.090
+0.036
0.5
0.044
0.098
0.026
0.7
0.044 •
0.055
0.005
0.8
0.073
0.060
-0.006
1.0
0.107
0.063
0.022
1.2
0.206
0.074
0.066
It will be noticed that, according to these results, our sensitive-
ness to minute differences of time varies for different intervals so
that it is greatest at 0.7-0.8 sec. (A = o at about 0.755 sec.) ; while
it falls off quickly for intervals less than this, and more slowly for
intervals longer than this. Kollert confirms Vierordt's statement
that times above this most favorable time are estimated too small,
and those below too large. He also concludes that, as the normal
time increases, our sensitiveness to minute differences of diminution
is lessened, while our sensitiveness to minute differences of increase
grows greater.
The same method as that employed by Kollert has been applied
by another observer ^ to intervals longer than 0.4-1.5 sec. Using
intervals of 1.8-8.0 sec. for the normal time, the sensitiveness of
our estimate of minute differences was still found to diminish as
the normal time increases ; thus the mean error of all the individ-
uals engaged in the experiments (A m) increased from 0.0792-
0.0879 sec. for intervals of 1.8-2.0 sec. to 0.5988 sec. for intervals
' Wundt's Philosoph. Studien, I., heft i, pp. 78 ff.
« Estel, iu Wundt's Philosopli. Studien, II., heft i., pp. 37 ff.
490 COMPLEX EEACTIOE" TIME.
of 8.0 sec.'' Estel reaches the conclusion that "our ideas of time,
like our other sensations and ideas, are essentially conditioned upon
past impressions belonging to the same domain of sense ; and a
short time makes the one next succeeding appear longer, while a
long time shortens still more the succeeding shorter time." A
more recent investigator ^ places the interval which can be repro-
duced with greatest accuracy at 0.53-0.87 sec. ; but reaches the
conclusion that, with all other intervals, an error is made which is
plus for those above, and minus for those below, this so-called in-
difference-point. This conclusion would seem to need re-examina-
tion, since it is exactly the opposite of that of preceding investi-
gators. The difference in result may, however, be due to difference
in the method of experiment, which in the one case consisted in
noticing the least observable difference in two series of intervals,
and in the other consisted in catching, mentally, a given interval,
retaining and reproducing it.
§ 23. In this connection should be mentioned the results of in-
teresting " studies of rhythm " undertaken by G. Stanley Hall and
J. Jastrow.^ These observers experimented to find the degree of
accuracy with which successive clicks having a constant interval
can be counted. It was found that persons most successful were
able to count 2-4 clicks with perfect accuracy, when the interval be-
tween them was 0.0895 sec; but if this interval was diminished to
0.0523 sec, they could not be sure of more than two clicks. When
the number of clicks was increased to 45, with the longer of these
intervals, the most successful estimates were 42 and 43 ; with the
shorter interval, for the same actual number, the best estimate was
32 and the worst was 17. The conclusion is thus reached that " count-
ing requires a series of innervations, if not of actual muscular
contractions," and that " attention discriminates sensation much
more rapidly than the will can generate impulses." If, then, the
interval between the acoustic sensations is less than the reduced
reaction-interval (or time necessary for starting successive impulses
of innervation) between ear and tongue, some of the sensations will
drop out of consciousness as a result of the blending, as it were,
of the later afferent with the earlier efferent stage of the complex
process. The time-sense for series of mental phenomena is then
different for different classes of these phenomena. The rate of
sensation may considerably surpass the rate of motor impulses ;
" we do not realize how far the fastest counting falls short of the
1 Estel, in Wundt's Philosoph. Studien, II., heft i., p. 43.
« L. T. Stevens, in Mind, October, 1886, pp. 393-408.
2 Mind, January, 1880, pp. 55 fE.
eeproductiojST of compositp: images. 491
fastest hearing." The same observers found that the most rapid
possible rate of pronouncing the names of letters was gi'eater than
that of counting them ; the former being 0.248 sec. per letter for
50 letters, and the latter 0.283 sec. The reasons for this dif-
ference are apparently to be found in the fact that counting in-
volves a severer sti-ain on the attention and more complex processes
of association and discernment in order to give to each number its
right name and place in a series of numbers.
§ 24. We are thus led to consider certain researches for deter-
mining the reaction-time of yet more complex mental processes,
such as involve reproduction of composite images of memory and
the association of ideas. The mean duration of association — that
is, " of the time which is required for the reproduction of an image
of memory by some apperceived presentation of sense " — has been
investigated at great length by Trautscholdt ^ under the direction
of Wundt. For purposes of experiment the following elaborate
classification of the possible kinds of association was adopted. All
associations are either (I.) External or indirect, or else (11.) Inter-
nal or direct. The former are such as are induced by the habit
of perceiving objects together— simultaneously or successively — in
space or time, without any interior relation between them ; the
latter are such as imply kinship in common properties or other in-
herent relations. External associations may, then, be either simul-
taneous, as in the case of the parts of a single presentation of sense
or of the coexistence of independent presentations ; or they may be
successive, as in the case of repeated impressions of sound, of sight,
and of the other senses. Internal associations may either be such
as involve the relation of ranking one mental object below or above
another in terms of genus and species ; or they may follow relations
of co-ordination, as similar or contrasted ; or they may follow rela-
tions of dependence, as of cause and effect, means and end. To de-
termine the time required for a " word-reaction " ( Wr), the experi-
menter spoke aloud some word at the instant that he pressed down
his key ; and the person reacting indicated the instant at which he
apprehended the word. The time required for such reaction was
found to have the following mean value for the four persons ex-
perimented upon : For W., 0.303 sec; for B., 0.285 ; for H., 0 280 ;
and for T., 0.173.^ The time required for the discernment of a single
word is obtained by subtracting from these numbers the simple
reaction-time {R) for each individual {Wr—R). The result obtained
^ Experimentelle Untersuchungen iiber d. Association d. Vorstellungen, in
Wundt's Philosoph. Studien, I., heft ii.. pp. 213-250.
■^ Philosopli. Studien, I., heft ii. , p. 236.
492
COMPLEX REACTION-TIME.
gave, for W., a "discernment-time" of 0. 107 sec; for B., of 0.177; for
H., of 0,137 ; and for T., of 0.057. In experiments to determine the
duration of association, the person reacting does not pi-ess his key
until the instant when the reproduction of some idea called forth
by liearing the word spoken has fully taken place. For example,
on hearing the word "zero" the idea of "infinity" may arise in
the mind ; or "market-place" as associated with "market/' "port-
folio " with " letter," etc. The mean reaction-time for such as-
sociation, both before and after subtracting the time for word-
reaction alone, was as follows :
Association-reaction (Ar). . .
Association- time {Ar— Wr). .
W.
Sec.
1.009
0.706
Sec.
1.037
0.753
H.
Sec.
1.154
0.874
Sec.
0.896
0.723
The mean duration of association for all the subjects of experi-
ment (excluding one for special reasons) is, therefore, placed at
0.727 sec. It takes, that is to say, about f of a second of psycho-
physical time to recall a familiar idea associated with a word we
hear. This association-time was most prolonged in certain cases
where the result may be looked upon as odd and unexpected, or
where a pause would seem to have taken place through hesitation
between several ideas simultaneously suggested. For example, the
association-time which elapsed between the word "pious" and the
idea " God-fearing " was 1.132 sec; between " throne " and " king,"
1.437 ; between the German word " Sieg " and " a person of this
name," 1.626 ; between "Karl "and "August," 1.662. The mini-
mum of association-time was reached with ordinary words where
the associated ideas were such as all individuals are likely to have in
common. Thus, from " gold " to " silver" required only 0.402 sec;
from "storm" to "wind," 0.368 ; from "clear" to "dark," 0.507;
from "north"to "south," 0.502; from"duty"to "right," 0.415; etc
§ 25. Trautscholdt ' also found — as we should expect — that
judgments involving subsumption, or the definition of the word
heard, required moi"e time than mere association, when they were
at all complex. But when very simple, the minimum time for such
judgments was about that of association ; and the mean value of
" subsumption-time " (0.766) differed but very little from the mean
value of "association-time." Thus it required 1.403 sec. to judge
that a " ray " is a "form of the motion of light ; " 2.023 to judge
■ Philosoph. Studien, I., heft ii., p. 345 f.
MCJLTIPLIC AXIOMS' OF TWO ^STUMBERS. 493
that " fame " is a " form of the ascription of praise ; " and 1.899 to
judge that " art " is an " aesthetic activity " of man ; but only 0.391
sec. to recognize a "mast "as a "part of a ship," and 0.469 to
identify "egg" and "cell."
The time necessary for multiplying, in the head, tioo numbers of
one figure each has also been investigated by von Vintschgau. '
The psycho-physical processes involved in this achievement are
necessarily somewhat complex. The influence of association must
vary largely, according to the number of times we have previously
made the same or any very similar calculation. For example, the
whole process involved in answering the question, How much is
1x1? is different from that involved when the numbers are 8x12;
much more different when they are quite unfamiliar— as, e.g.,
76 X 89. The order of the numbers is not indifferent ; as a rule,
reaction is quicker and more correct when the smaller number pre-
cedes. The mean reaction-time for multiplying two numbers (1 to
10) was 0.211 sec. for L., 0.207 for P., and 0.259 for V., when repro-
duction was with the finger; and 0.200 for L., 0.252 for P., 0.248
for v., when reproduction was with the lip. Of this, 0.049 for L.
reproducing with the finger, and 0.096 with the lip ; 0.051 for P.
with the finger, and 0.082 with the lip ; and 0.098 for V. with the
finger, and 0.087 with the lip — are calculated to have been due to
the cerebral processes involved in the calculation. As might be
expected, any great increase in the speed was found to be accom-
panied by an increase in the number of mistakes.
Cattell,'^ after objecting on good grounds that the results of
the laboratory are always too artificial and often too incorrect to
" give the time it takes a man to perceive, to will, and to think,"
attempted to do away with "involved methods and complicated
apparatus," and in simpler fashion determine the time Ave usually
require to see and name an object, such as a letter or a color. He
concludes that to see and name letters requires from ^ to \ sec.
for each letter, and to see and name words that do not make sen-
tences requires \io ^ sec. When the words are connected into sen-
tences it requires only about one-half as much time to name them
— the rate at which one can read varying from 0.138 to 0.484 sec.
for each word, according to one's degree of familiarity with the
language. Single letters can be named more rapidly when several
are in view at the same time ; nearly all persons are helped by hav-
ing as many as three, and most persons by having as many as four
^ See Pfliiger's Archiv, xxxvii., pp. 127 ff.
' See Mind, January, 1886, p. 63 f.; and Wundt's Philosoph. Studien, II.,
heft iv., pp. 635 fE.
494: COMPLEX REACTIOISr-TIME.
or five, letters in view at the same time. That is to say (using
Wundt's figure of speech), the time of perception, or field of con-
sciousness, covers the time of apperception, or clear spot of con-
sciousness ; while one presentation of sense is at the focus of
consciousness, several others may be coming toward the focus
from the background of consciousness. The second letter in view
shortens the time of apperception about j^g ; the third, gJ^ ; the fourth,
Y-^u ; the fifth, ^^-^ sec.
§ 26. Finally, the closing remark of the foregoing paragraph in-
troduces the inquiry into the "circuit of consciousness" — that is,
the number of impressions which can exist within the field of con-
scious perception at any one time ? This question has been much
debated on abstract or metaphysical grounds touching the nature
of the soul. Since the soul is one and simjDle — it has been claimed —
there can be before it but one object at the same instant of time ;
but since all its knowledge is relative, the claim has also been
made that at least two impressions are always contemporaneous in
consciousness. Hamilton,' on the contrary, concluded, from ob-
serving his own mental activities, that the circuit of consciousness
could embrace as many as six or seven distinct simultaneous im-
pressions. It is evident that only an appeal to facts can decide
such a dispute ; it is also evident that the manner of appeal should
be more precise and scientific than the one proposed by Hamilton.
Experiments have therefore been instituted to determine the
" circuit of consciousness,'"' by finding how many regularly'recurrent
successive impressions of sound, for example, can be so far united
into one mental image as to have their likeness or unlikeness to
another similar series clearly discerned. The method of experi-
ment employed by Dietze " was the following : The stroke of a pen-
dulum, heard at regular iuteiwals, was employed as the stimulus.
After a single stroke as a warning, a series of successive strokes
was given, which was begun and ended by the sounding of a clock-
bell simultaneously with a stroke of the pendulum. Another series
of strokes of the pendulum followed immediately upon the sound
which announced that the first series was closed. The second se-
ries was ended by simply stopping the pendulum. A fixed number
of strokes constituted the first series ; a variable number (either one
more or one less than the first series) constituted the second. The
question projDosed for answer Avas : How man}' impressions of sound
can be received in the first series and the relation of the second
series to the first (as equal, greater, or less) be accurately discerned
' Lectures on Metaphysics, p. 165. f. , and elsewhere Boston, I860,
^ Article in Philosoph., Studien, II., heft iii., pp. 362 fE.
'effects of practice and ATTENTION". 495
without counting ? The effect upon the subject of such an experi-
ment may be described as that of sending through the focus of con-
sciousness a train of impressions, in regular succession, from the
obscure regions of perception at which they enter to the obscure
regions at which they depart from the field of consciousness. An
image of the whole field of consciousness, with the line of march of
the impressions, must be formed in order accurately to compare two
series like those described. The result of such experiments showed
that the number of successive impressions which can be comprised
within the circuit of consciousness depends upon the rate with
which they succeed each other. The most favorable interval was
found to be 0.2-0.3 sec. ; with this interval most of the subjects of
experiment attained a high degree of accuracy for even as many as
ten or twelve impressions.' Individual difierences were marked,
however; thus, for one subject, the time of 0.21 sec. interval was
too great for the maximum of accuracy, and 2.0 sec. was so lai'ge
as to prevent his having any satisfactory apperception of even a
single impression. The manner of uniting the impressions was
also found to have a great effect upon the circuit of consciousness.
When the process of apprehension was allowed to have a rhythmic
form of grouping the impressions, the number possible in a single
field of consciousness was increased. Without grouping, 16 was
the maximum even number, 15 the maximum odd number, at-
tained. Rhythmic grouping raised this number to 40, or a little
more, as the maximum even number, and to 35; 37, and 39 as the
maximum odd numbers. It is possible, then, to apprehend a larger
even number than odd number of impressions in a siugie circuit
of consciousness. Certain numbers, perhaps those most familiarly
grouped in experience, seem also to have the jDreference over
others.
§ 27. In all experiments to determine the time-relations of mental
phenomena, the effects of practice and attention in diminishing
psycho-physical, time, and oi fatigue to increase it, are made ap-
parent. Certain special experiments have also been instituted to
show how illness, old age, and drugs operate upon the speed of
psycho-physical time. Thus MerkeP found that the will-time ne-
cessary- for choice between two motions was reduced by practice, for
three subjects of experiment, from 0.080 sec. to 0.050, from 0.097
to 0.0535, and from 0.098 to 0.062, respectively. For choice among
' See Dietze's statement. Pliilosopli. Stiidien, III., lieftiii., p. 386, and a
note, p. 384, correcting the erronous conclusion drawn by M. Ribot (German
Psychology of To-day, p. 278, New York. 1886 j.
■' Wuudt's Philosoph. Studien, II., heft i., p. 110 f.
496 COMPLEX EEACTION-TIME.
five and ten possible motions, the effect of practice was yet more
marked : thus, with five possible choices, the will-time of one per-
son was reduced by practice from 0.239 sec. to 0.083 ; and of an-
other, with ten possible choices, fi'om 0.358 to 0.094. For each
single day's series of experiments, the time diminished faster at first
than subsequently ; but, in many cases, more distinctly on the second
than on the first day of experiment. Ivries and Auerbach ' discov-
ered that, after a short time, further practice has no influence on sim-
ple reaction-time ; but some practice is necessary to give any reliable
value to such time. The effect of practice on discernment- time is
very different. In the experiments upon the localization of tactile sen-
sations, the discernment-time for A. was at first as great as 0.064 sec,
or even 0.117, but afterwai-d fell to a mean of 0.021. Discernment-
time continues to decrease by practice, after all diminution of sim-
ple reaction-time has ceased ; it is also transferable to other regions
of the same sense. Trautscholdt ^ found that practice for fourteen
days reduced the "word-reaction-time" of one subject from 0.309
sec. to 0.149 ; association-time was found to be sensitive to practice
in a much smaller degree. The effect of attention must also al-
ways be taken into account. It was, ajDparently, by guarding this
carefully, and by practice, that Kries and Auerbach succeeded in
obtaining such small values for discernment-time. The effect of
distracting the attention was observed by Wundt,^ who introduced
disturbing sensations of the same or of a different sense into series
of regularly recurring impressions. Thus, the mean reaction-time
for a weak impression of sound was lengthened from 0.189 to 0.313
sec, by a disturbing noise ; and for a strong impression of sound,
from 0,158 to 0.203 sec. The mean reaction-time for sight of an
electric spark was increased from 0.222 to 0.300 by a disturbing
noise occurring simultaneously.
All the experiments also make obvious the great influence of
individual peculiarities. But this influence may not be in the di-
rection in which it would most readily be supposed to lie. For
example, Exner " found that, of two young men, one of whom had a
very lively temperament and the other not, the former had much the
longer simple reaction-time (0.3311 sec. as compared with 0.1337).
The reaction-time of a man of seventy-seven, taken from the alms-
house, was at first 0.9952 sec. ; this was, however, reduced by practice
to 0.1866 sec. The enervation produced by a hot summer's day, or
' Archiv f. Anat. u. Physiol., Physiolog. Abth., 1877, p 361 f.
* Wundt's Philosoph. Studien, I., heft ii., p 237 f.
^ Physiolog. Psychologie, ii. , p. 243.
* Hermanri's Handb. d, Physiol., II., ii., p. 268.
THE RESULTS OF EXPERIMENT. 497
the exhaustion of a sleepless night, or bad news, etc., increases the
reaction-time. A small quantity of wine, slowly drunk, decreased
the reaction-time ; but a larger quantity increased it from 0. 1904
sec. to 0.2969, although the subject of the experiment considered
himself to be reacting more promptly than usual. Coffee begins to
decrease the reaction-time at 20-25 minutes after it is taken, and
continues this effect for about 2 hours. Subcutaneous injections
of morphine delay ' it ; but this effect does not last long unless the
injection is repeated. Obersteiner found that a subject whose re-
action-time in the first stage of paralysis was 0.166 sec, gradually
lost control of himself until, in the last stages when experiment was
possible, the interval was 0.281-0.753. Buccola, who has experi-
mented upon idiots, imbeciles, epileptics, etc., finds that the dura-
tion of perception is lengthened in all these cases, with the exception
of some forms of abnormal excitement.
§ 28. On summing up the results of all the experiments hitherto
made in psychometry, we can only reiterate what we began by say-
ing: Experimental research does not explain the origin or nature
of our idea of time and its relations, nor has it succeeded in estab-
lishing many new principles of great moment for psychology. It
is, however, a vigorous and promising branch of psycho-physical
study. It has placed upoii a scientific basis, and defined in accurate
mathematical terms, many of our ordinary impressions as to the
time-relations of mental phenomena. The attempt to analyze psy-
cho-physical time seems to show thai its various elements of simple
perception, apperception, or clear discernment, and volition, occur in
the order named, and yet ordinarily overlap each other, as it were.
Practice and attention, under the most favorable circumstances, may
reduce either one nearly to zero. In this way, simple reaction-time
becomes most nearly equal to purely physiological or reflex time ;
reaction-time, with discernment, is almost reduced to simple per-
ception-time ; and the duration required by will-time for solving a
dilemma is wellnigh eliminated.
Conclusions as to the existence and intercerebral relations of
nervous centres of apperception and volition would be premature,
and probablj'' misleading, in the present state of this science. Nor
have we as large hopes as to its ability " to solve many of the old
problems " in the future as have been expressed by some of its
enthusiastic students.
' See von Vintschgau and Dietl, in Pfliiger's Archiv, xvL, pp. 316 ff ; and
Exner, in Hermann's Handb. d. Physiol., XL, ii., p. 270 f.
32
CHAPTEE IX.
FEELINGS AND MOTIONS.
§ 1. From tliis point onward the study of Physiological Psychol*
ogy is compelled to content itself with opinions much more in-
definite and uncertain even than those to which we have already
become accustomed. Theories of the localization of cerebral func-
tion, of the quantity and quality of sensations and their combina-
tion into presentations of sense, and of the time-relations of mental
phenomena, admit to a considei'able extent of experimental tests.
But the feehngs and their physical basis elude the efforts made to
subject them to the conditions of a strictly scientific investigation.
The same complaint may be justified concerning all opinions as
to the physical basis of the higher intellectual operations, and as
to the effect of age, temperament, sex, and race, upon the character
and development of the mind. No attempt whatever will be made
to conceal the meagre, obscure, and doubtful character of the evi-
dence upon which our conjectures must be based. Indeed, on
these matters nothing but the greatest caution is fitted to inspire
confidence ; the supreme wisdom is not infrequently a frank con-
fession of ignorance or uncertainty.
About our "Feelings" so-called — their nature, origin, relation
to a physical basis and to sensations and ideas — we know remark-
ably little. Nor has any classification of the feelings hitherto been
made which is entitled to command general assent. The reason
for this fact is not difficult to discover. By their very nature, the
phenomena are obscure, indefinite, and 3'et extremely variable and
multiform. They are also connected with our sensations and ideas
in such a way as to make all separation in fact quite impossible.
The psychology of the feelings, as studied from the introspective
point of view, has therefore always been peculiarly unproductive
of assured results. The fact that their physiological conditions
are laid so largely in obscure, rapid, and infinitely varied changes
within the central organs, such as cannot be either directly ob-
served or indirectly subjected to experimentation, increases the
difficulties of the subject. What is the nature of feeling ? How do
DIFFERENT THEORIES OF FEELING. 499
the different feelings differ, and what elements have they in com-
mon ? Under what conditions do we have sensiious feelings ; and
tinder what conditions are these feelings pleasant or unpleasant ?
Is feeling ever perfectly indifferent ; is there a zero-point of feel-
ing ? How are the feelings related to the quality and intensity of
physical stimuli ? What is the physiological basis (if any exist) of
the higher sesthetic, moral, and religious feelings ? ' These and
other similar questions may be asked of psycho-physical science
with little satisfactory result,
§ 2. Many diverse views have been held as to the essential na-
ture of. feeling. These views may, for the most part, however, be
classified under two heads : They are either such as emphasize the
dependence of the feelings on bodily conditions, and so resort to
physiological explanation of their origin and nature ; or else they
are such as emphasize their dependence upon relations that obtain
among the so-called " ideas," or purely mental states and products
of the mind. The extreme form of one of these two theories holds
that feeling is always merely a consciousness of a certain condition
of the nervous elements. The extreme form of the other leads to
the position from which all feeling is regarded as a sort of sec-
ondary consciousness of the " furtherance "or " hindrance " of one
idea by another. The principal real ground for the former theory
lies in the fact that certain conditions of the nervous elements under
stimulation are, as a rule, followed by painful, and certain others by
pleasurable, feeling. The latter theory is based solely upon the truth
that certain mental states called "ideas " are, as a rule, accompanied
or followed by corresponding modes of being affected which have
the characteristic tone of all feeling — that is, are either agreeable or
disagreeable. Neither of these views, however, serves to define the
essential nature of feeling, since to feel is as simple and funda-
mental an operation of mind as it is to know. Feeling can never
be stated in terms of knowledge. Inasmuch, then, as all definition
is only the expression of an elaborate and complex form of knowl-
edge, the nature of feeling is not capable of being defined ; it
must he felt. When, then, this nature is defined as consisting in
some relation to physical sensation or to mental images, it is de-
prived of the very characteristic which makes it to he feeling rather
than sensation or idea. Both theories, however, have succeeded in
stating certain conditions or antecedents of the reaction of mind in
the way of feeling.
§ 3. The foundations for a physiological theory of the feelings
' Comp. Horwicz, Psycliologische Analysen, i. , p. 21 f.
500 NATUKE AISTD KINDS OF FEELING.
were laid by Lotze, ' with that blending of scientific caution and psy-
chological insight which characterize most of his work. ■ He distin-
guished the feelings, as mental conditions of pain or pleasure, from
sensations as indifferent elements of our percejDts of things. Yet,
in fact, sensations are always, or usually, colored wdth feeling ; and
analysis is therefore obliged here to distinguish in theory what co-
exists in fact. Feelings are of two hinds : " sensuous," as coming
from bodily impressions ; and " intellectual," as flowing from the
relations of ideas. Pleasurable feelings always arise from the co-
incidence, and painful from the opposition, between the effects of
the stimulus and any one of those conditions to which the regular
expression of the bodily or spiritual life is attached. Yet even this
statement is not true without making further explanations and
Umitations. For something bitter may be harmless, or even bene-
ficial ; and acetate of lead may be sweet and pleasant, but deadly.
More precisely, then, "feeling is, in general, only the measure of
the partial and momentary concord between the effect of the stimu-
lus and the conditions of vital activity."" Lotze was far too keen
a psychologist, however, to suppose that in laying down this law
he was explaining the nature of feeling as a secondary and derived
form of consciousness. He has himself vindicated its right to be
regarded as primitive, and not deducible from either sensations or
ideas.^ But even in the way in which he understood his own
theory, much doubt may be thrown upon its truth.
It is admitted by all that certain intensities of nearly all forms of
stimuli are both productive of painful feeling and also antagonistic
to the vital conditions of the organism. Undoubtedly, also, suffering
is both an indication and a cause of abnormal and injurious action of
the nervous mechanism. But that the feeling of jDain measures the
degree of this antagonism, or that everything found at the time dis-
agreeable is in any degree demonstrably opposed to the vital wel-
fare of the organism, cannot be assumed; and the alleged law even
seems incompatible with the individual peculiarities which charac-
tex'ize what is agreeable or disagreeable to the senses of different
persons. The excessive stimulus of the surgeon's knife is not .ren-
dered any more really in accord with the conditions of the vital
activity of the organ to which it is applied by the fact that anaes-
thetics prevent the pain which would otherwise result. An exces-
sive and immediately injurious stimulation of considerable portions
of the body may be accompanied by a large amount of positive
' Medicin. Psychologie, pp. 233 ff. - Ibid.
•'See Metaphysic, p. 474, Oxford, 1884; and Microcosmus, i. p. 177 1,
Edinburgh, 1885.
PHYSIOLOGICAL LAW OF FEELING. 501
pleasure or, at most, with very little pain, wliile a small and quite
harmless degree of another kind of stimulation may result in great
discomfort. Attention, association, and control of the "will have
also much to do with determining the subjective state which is con-
nected with any given relation between the effect of the stimulus
and the conditions of vital activity.
§ 4. More recent attempts to give a general physiological law for
the phenomena of pleasurable and painful feeling can scarcely be
said to be any more satisfactory. It is true, as Bain ' declares, that
"a very considerable number of the facts maybe brought under
the following principle, namely, that states of pleasure are connected
iviih an increase, and states of pain with an abatement, of some, or all,
of the vital functions." But other facts in no small number cannot
be brought under this principle. It is not a difficult task for the
physician to abate all the vital functions of the patient, even down
to or beyond the line of danger, with the immediate result of pro-
ducing pleasure rather than pain. After objecting to Bain's state-
ment as being "too vague," etc., Grant Allen ^ declares the true
principle of connection to be the following : " Pleasure is the con-
comitant of the healthy action of any or all of the organs or mem-
bers supplied with afferent cerebro-spinal nerves, to an extent not
exceeding the ordinary powers of repai-ation possessed by the sys-
tem." Esthetic pleasure he provisionally defines as "the subjec-
tive concomitant of the normal amount of activity, not directly
connected with life-serving function, in the peripheral end-organs
of the cerebro-spinal nervous system." ^ Now, that pleasure is the
reflex of healthy and unimj)eded activity is an old psychological
truism ; and that we are dependent upon impulses propagated in
the sensory nerves of the cerebro-spinal system for sensations,
pleasureable or painful, of muscular, organic, or more special sort,
scarcely needs statement as a newly discovered law of "physiolooi-
cal sesthetics." Nothing, however, could well be more "vague"
than the limit fixed by the words " to an extent not exceeding the
ordinary powers of reparation possessed by the system." Does the
man whose powers of nervous reparation are extraordinarily great
necessarily find his quinine any the pleasanter? The statement
that pain is a warning of danger from excessive or abnormal activ-
ity of the nervous system must, of course, be accepted as summing
up a large number of facts ; but there are other facts not easily
brought under such statement. Moreover, until we have some objec-
' The Senses and the Intellect, p. 281 f.
^ Physiological Esthetics, London, 1877, p. 31.
3 Ibid., p. 34.
502 KATURE AND KINDS OF FEELING.
tive means of determining what is the " normal amount" of function
in any tissue, the alleged law that pleasure is " the subjective con-
comitant " of such amount is of little or no value. The whole sub-
ject is left in that indefinite condition which invites us, on the one
hand, to consider pain as the proof that the function of the nervous
system which occasions it is destructive ; and then tells us, on the
other hand, that the essence of the pain is in its being the subjec-
tive concomitant of such function.
§ 5. But if purely physiological theories of feeling do not suc-
ceed in defining its nature, or in stating the relation between the
action of the nerves and the pleasureable or painful tone of the
feeling, the success of the second class of theories is no greater.
Of this class the views of Nahlowsky/ as set forth in his interest-
ing monogTaph, are perhaps the best example. This author begins
by drawing a sharp distinction between sensation and feeling. The
" tone " of sensations as pleasant or unpleasant he would not call
by the term "feelwg ; " such tone is rather that which gives us
" the how " (" Wis ") of the sensation, and depends for its pleasant,
or unpleasant character upon whether the effect of the stimulus
furthers or inhibits the functions of the vegetative life. Even those
states of consciousness which are constituted from various ele-
ments due to stimulations of the nerves at various quarters not defi-
nitely localized, and ordinarily called " common feeling," Nahlow-
sky would define as "common sensations." Pain also is a sensation
and not a feeling. But feeling, according to this author, is neither
tone nor quality of sensation ; though it may be an elevation or de-
pression of mind produced indirectly by the sensations. FeelingSj
properly characterized, comprise all the conditions resulting from
the simultaneous existence of ideas in the mind, which either sup-
poi't or interfere with each other. In the former case, they are
agreeable ; in the latter, disagreeable. They are, then, secondary
conditions of mind, dependent on ideas, recognized as not of bodily
origin, but as having a content of a mental rather than physical order.
Hunger, thirst, weariness, shivering, etc., are sensations ; sympathy
love, gratitude, reverence, admiration, etc., are feelings. According-
ly', feeling is defined as " the immediate consciousness of the momen-
tary rising or depression of one's own psychical activity " (that is, of
the movement of the ideas) . Even to the affections this theory would
deny a place among the kinds of feeling — for the former spring
from the latter under the mediating influence of organic effects.
The foregoing view of the nature of feeling is adhered to sub-
' Das Gefiililslebeii, in seiuer wesentlichsten Ersclieinungen u. Beziigen,
2d ed. Leipzig, 1884.
PSTCHOLOGICAL THEORY OF FEELHSTG. 508
stantially by many others, especially by the followers of Herbart.
Thus Drbal ' holds that feelings are not primitive states of mind,
but result from the reciprocal action of ideas — if this ideating ac-
tivity is one of reciprocal inhibition, the feeling which is the be-
coming conscious of the inhibition is unpleasant ; if the activity is
one of reciprocal combination, the conscious feeling of this fact is
pleasant. Feeling in general is therefore the immediate conscious-
ness of the rising or falling of one's power of ideating, as it were.
Beneke,'' also, considers that two mental images excited belong to
every feeling ; of these, one is that which is felt, and the other is
one " against " which the first is felt. Feeling and no-feeling, or
this or that feeling, can therefore attach itself to one and the same
image. Volkmann von Volkmar, in his great work,' considers feeling
as the consciousness of the process of ideation itself as distinguished
from consciousness of this or that idea, and it is conditioned upon
some resistance being offered to the process. Feeling is, then, nft
one proper idea, to be placed in conjunction or classed with others.
It is rather a becoming conscious of the degree of tension, as it were,
which characterizes the process of ideation at each particular mo-
ment. The condition of the origin of a feeling is, then, the existence
of two simultaneous opposed ideas. Their coexistence occasions
a state of tension (" Spannung "), as it were, and this state gives
way as one idea triumphs over the other. The type of simple feel-
ing may be illustrated by the condition in which the mind finds
itself when listening to harmonious or discordant musical sounds.
§ 6. The theory which makes feeling a derived consciousness de-
pendent upon the relations of the ideas as furthering or checking
each other is unsatisfactory. It cannot be admitted, to begin with,
that feeling is a secondary or derived form of consciousness. No
form of mental activity is more primitive and unanalyzable than
feeling ; none is earlier in the development of mental life.^ Be-
fore the infant has localized the different sensations, and combined
them into percepts of the different parts of its own organism,
the consciousness of being affected in a given way, either pleasur-
able or not, must predominate. Other forms of feeling — of desire,
uneasiness, comfort, etc. — are inseparably connected with its first
states of consciousness ; they belong to its inherited impulses and
' Lehrbuch d. empirisclien Psychologie, 2d ed., pp. 200 ff. Wien, 1875.
^ Lehrbuch d. Psychologie als Naturwissenschaft, pp. 170 ff. Berlin, 1877.
3 Lehrbuch d. Psychologie, II., pp. 298 fif.
* This view of the feelings is maintained by Horwicz, and developed at length,
polemically, by Lotze (Horwicz, Psychologische Analysen, i. , p. 168 f . ; Lotze,
Medicin. Psychologie, p. 235 f . ; and references already cited in note p. 500),
n04 JSTATUEE AND KINDS OF FEELING.
instinctis, and are only later definitely related to the appropriate
ideas. The primary formation of self-consciousness is quite as
truly connected with self-feeling, pleasurable or painful, as with
the process of ideation in constructing the concept of "me "and
"not-me."
Moreover, although we are to distinguish sensation from feeling,
we must regard the feeling which inseparably accompanies sensa'
tion as feeling, strictly speaking, and not as tone of sensation ; or,
in other words, the tone of every sensation, as either pleasurable
or painful, is given to it by the feeling which accompanies and
blends with it. The sensation, as having a certain quality, quan-
tity, and locality, is capable of being built into a "Thing" which
the mind perceives as not-itself. But the feeling, the pleasurable
or painful tone of the sensation, is always recognized as purely and
simply a way in which the mind is affected. To refuse to speak of
sensations and emotions, with all their complicated physical basis,
as belonging at all in the realm of " feeling," is to restrict the use
of the word unwarrantably. The Herbartian theory commits in
this matter the mistake which it is guilty of committing repeatedly ;
it regards the " ideas " as realities that have in some sort a sub-
stantial existence, and can do something by way of furthering or
hindering each other. But ideas are themselves nothing more than
mental products that exist only when and so long as the mind acts
with a definite degree and kind of energy. In determining the
kind and degree of this ideating energy, the previous action and
habit of the mind by way of feeling is quite as influential upon the
mode of feeling as is the manner of its ideating energy. Finally,
this theory wrecks itself upon the denial of all that which the phys-
iological theory maintains and establishes. The two theories, then,
supplement and correct each other ; but even when combined they
only tell us in pai-t what are the physical and mental conditions
under which feeling arises.
§ 7. The truth appears to be as follows : Feeling is an original
and under ived form of consciousness, or mode of the operation of con-
scious mind. It can neither be defined by, nor deduced from,
sensation or ideation. To know what it is to feel, the highest in-
telligence of itself would be incapable. Such knowledge comes only
from having felt. Feeling accompanies all mental experience, both
that of sensation and of the higher intellectual processes. It un-
doubtedly has a certain physical basis ; and certain laws may be
stated which discover some of the relations that hold good between
conditions of the nervous system and resulting conditions of feel-
ing. Certain other laws may be laid down which partially define
' CLASSIFICATION OF THE FEELINGS, 505
the relations existing between the purely intellectual and the feel-
ing activities, or reactions, of mind. These two sets of laws give
us the physical and the intellectual conditions of different tones
of feeling respectively. But no one law has yet been discovered
which covers all the facts of relation, either between feeling and
the bodily states or between feeling and the ideas. Nor is it likely
that any such law exists to be discovered. Manifold relations, a3
determined by heredity, individual peculiarities, association, atten-
tion, etc., always exist, and contribute to the complex result.
§ 8. The various attempts to establish fixed classes of the feelings
can scarcely be pronounced more satisfactory than the attempts
to define their nature. Very great difficulties stand in the way of
such a classification, of which the following are most important :
The phenomena are themselves very obscure, changeable, and multi-
form ; they are also inextricably associated with the phenomena of
sensation and ideation. Moreover, the theory held by any inquirer
as to the origin and nature of the feelings is pretty sure to deter-
mine his classification of them. For example, two before-men-
tioned authorities (Nahlowsky ' and Drbal ^), as a result of the
"ideational" theory', divide the feelings into (1) such as are de-
pendent on the forvi of the course of ideas, and (2) such as ai'O
conditioned by the content of the ideas. Besides these simple
classes of feelings, one of these writers speaks of certain " mixed
feelings," that are feelings of oscillation and change. Under the
" formal " feelings, or such as are dependent on the form of the
course of representation, the other writer finds four classes — namely,
(a) feelings of expectation and impatience, (b) of hope, anxiety, sur-
prise, and doubt, (c) of tedium, and (d) refreshment and work — all
according to the aspect of the ideas in time-form. Four kinds of
" qualitative " feelings are also distinguished — these are the intel-
lectual, the sesthetic, the moral, and the religious — according as
the ideas exciting the feelings refer to truth, beauty, morality, or
religion. But the foregoing attempts and all similar attempts at
classifying the feelings lay a false emphasis upon the dependence of
certain feelings on mental representation ; they thus overlook all
those considerations on which the physiological theories of feeling
rightfully insist.
But, on the other hand, the classifications made under the in-
fluence of the physiological theory are even more unsatisfactory.
In their desire to reduce all the phenomena of human feeling under
some one physical " law," so called, they bring the higher forms of
' Das Gefiihlsleben, p. 44 f.
^ Lehrbucli d. empir. Psychologie, p. 205 f.
506 NATURE AND KINDS OF FEELING.
feeling into a mucli closer and more complete connection with the
feelings of sensation than the facts will warrant. Thus, with Grant
Allen, the aesthetic feelings are " the cumulative effect of many
infinitesimal physiological factors," ' which differ from the pleasures
and pains of sensation chiefly in the fact that the activity of the
end -organs in them is " not directly connected with life-serving
function ; " ° all the different tastes of different individuals, their
varying "perceptions of beauty and ugliness," are then boldly
stated to be " depending on the structural variations of the nervous
system."
Horwicz's more profound theory as to the nature of feeling leads
him to a more satisfactory classification of its forms. The variety
of feeling, he holds, is dependent on the natural organic variety in
the activities of the soul.' Thus we derive (1) the senswoit.s feelings,
or such as depend on the different qualities of the sensations of the
special senses and of common feeling ; (2) the cesthetic feelings, or
those agreeable or disagreeable forms of consciousness which cor-
respond to the mental images of perception and imagination ; (3)
the intellectual feelings, which correspond to the theoretic interests
called out by the higher forms of thinking ; (4) the moral feelings,
or those which correspond to the relations of desire and will. The
development of these feelings in varying relations to each other
gives rise to various mixed or complex forms. Certain moods and
characteristic affections result from the combined tone, color, and
rhythm, of the simple feelings, and the strength with which the
physical organism reacts. Higher feelings, or "feelings of feel-
ings," unfold themselves ; these are dependent upon the complex
relations of society as organized in its several existing forms.
A recent writer in Mind,^ after criticising all previous attempts
at classification of the feelings, proposes an exceedingly elaborate
substitute for them all ; but this substitute is so burdened Avith
uncouth terminology, is founded on so many false or doubtful psy-
chological assumptions, and involves so many artificial distinctions
and cross divisions, that it is little likely to meet with general ac-
ceptance.
§ 9. Another and insuperable difficulty in the way of a strict
classification of the feelings is the fact that they are actually, and
as peculiar conditions of consciousness, unclassifiable. In other
words, no principle of classification can be suggested which will
undeniably apply to them all. For example, if we classify them
' Physiological Esthetics, p. 42. "^ Ibid. , p. 34.
^ Psychologisclie Analyseii, ii., p. 82 f.
* Mercier, July and October, 1884, and January, 1885-
t»RIMITIVE CHAEACTEE OF FEELING. 507
into pleasurable or painful, we indicate in this way only a quality
of tone which itself constantly varies in dependence on more per-
manent characteristics. Besides, it is not easy to demonstrate that
feelings are never indifferent (neither agreeable or disagreeable) in
tone. If we classify according to the anatomical part or phys-
iological function of the nervous system which chiefly gives con-,
ditions to the feelings, we can carry our classification only a little
way without resorting to imwarrantable assumptions. Indeed,
there are grounds for supposing that the feelings are of central
origin — that is, have their physiological basis in those regions of
the nervous system that have thus far almost wholly eluded sci-
entific research. If we classify according to the relation of each
feeling to other activities of the soul (as Horwicz does), we en-
counter the facts that sense, will, and intellect, doubtless all enter
into all the aqtivities connected with our developed feeHng ; but
that the measure of the degree in Avhich they are influential upon
feeling is so uncertain and changeable as to render it unfit to serve
as a basis for classification.
No hard and fixed line can be drawn about the different so-called
classes of feelings. Feeling, with its color-tone of pain or pleasure,
enters into all conscious life. The aesthetic feelings cannot be
separated from the sensuous ; for example, the feeling which
accompanies the sensation of a musical chord, or of the color pur-
ple, may be classed tmder either head. Nor can the intellectual
feelings be separated from the aesthetic ; the perception of harmony
of colors and sound is inseparably connected with sesthetic and
sensuous feeling, and the latter is intensified or otherwise modified
under the intellectual laws of contrast, change, habit, and higher
association. Even the feelings which we call " moral," on account
of their connection with will and desire, often have an indefinite
part of them so combined with feelings located in the bodily
organism, or so dependent on its functions for their quantity and
quality, that a strict separation becomes impossible. Love is
seldom or never so purely ideal as not plainly to involve in itself
feeling of sensuous and sesthetic sort ; hate not mixed with anger,
and so supported on some elements of that physical basis which
underlies the latter, is hard to discover in real life. All psycho-
logical analysis that would extend to the point of establishing fixed
classes of the psychical activities is difficult ; but in the special
case of the feelings, the character of experience is such as to make
strict classification impossible.
Accordingly, in treating of the feelings from the physiological
point of view we shall content ourselves with selecting certain ex-
508 NATURE AIS^D KHSTDS OF FEELIXG.
amples from the cuiTent classes which admit of being thus treated
most successfully. Such are, obviously, the so-called sensuous feel-
ings, the so-called common feeling, certain aesthetic feelings, certain
of the feelings known as emotions or affections, and certain feelings
connected with the functions of will — especially the feeling of effort.
§ 10. All feelings are characterized by tone, strength, rhythm,
and content.' Their content is determined by the ideating activity
with which they are directly connected, or to which they are relat-
ed ; and this content may be simple, as is the case with the feeling
connected with the presentation of a colored surface (for example,
purple or green), or complex, as is the case with the sentiments of
patriotism, loyalty, and religious devotion.
Feelings, like all other mental jDlienomena, occur under time-
form; they are, in general, rhythmic in character, and change in re-
spect to content, tone, and intensity, with a movement marked more
or less distinctly by the quality of periodicit}'. Their rhythm,
with respect to content, is, of course, determined by the recur-
rence of changes in the ideating activity as dependent especially
upon attention and the laws of association. Feelings of sadness or
joy, comfort or discomfort, may come around again in conscious-
ness, as it were, according to the rhythmic movement of the sensa-
tions which occasion them. Sometimes an alternation of tone takes
place, which carries the mind back and forth by the point of indif-
ference (or hypothetical zero-point of feeling) between agreeable
and disagreeable sensations, or ideas of the same kind. Thus we
are sometimes forced to say that we do not know whether a certain
combination of colors, or quality of taste or smell, is pleasing to us
or not ; in such a case feeling seems to move rhythmically back and
forth between a slightly pronounced tone of pleasure and a slightly
pronounced tone of pain.
The intensitij, too, of feelings rises and falls alternately in de-
pendence upon the rhythmic movement of the nervous processes
and of the train of ideas. No feeling is kept at a long continu-
ous level with respect to its vigor and pitch of strength. The
law of quickly alternating exhaustion and repair of the nervous
elements underlies, to a large extent, this rhythmic movement of
the intensity of the feelings. This is one of many proofs which go
to show that the conditions of the end-organs and of the central
organs (comp. p. 108 f.) are determinative of the tone and strength
of feeling. Even when we are strictly attending to our painful
feeling, the toothache is not a perfectly uniform and steady strain ;
even when we are doing our best to abstract attention from the
' Conap. Volkmann vou Volkmar, Lehrb. d. Psychologie, II., p. 311 f.
THE TONE OF ALL FEELING. 509
pain, we succeed only intermittently. But the course of the ideas
must also be taken into account as influencing the rhythm of feel-
ing. As our sensations or mental images become more clear and
vivid, the feelings attached to them gather strength ; as the former
become more obscure and feeble, the feehngs also die away in
consciousness.
§ 11. The tone of all feeling is either one of pleasure or of pain
(using these words in their widest possible meaning). The feeling of-
pleasure and pain is probably the most general, most simple, and
earliest psychical process. That almost all feelings are characterized
by some positive tone — or, in other words, are not absolutely in-
different to us — there can be no question. Is it agreeable or dis-
agreeable, at least in some slight degree and in some more or less
indefinite manner ? is an inquiry which we can pretty readily an-
swer with respect to nearly all our sensations and ideas. The
question has been debated, however, whether this is necessarily true
of all our feelings. Is there any such thing as completely "neutral"
feeling, or feeling that is in no respect or degree either agreeable
or disagreeable to us ? Neutral or indifferent feelings were recog-
nized by Reid, but disputed by Hamilton.' Bain asserts it as un-
doubted that " we may feel, and yet be neither pleased nor pained,"
and that "almost every pleasurable and j)ainful sensation and emo-
tion passes through a stage or moment of indifference."^ Wundt^
argues, on theoretical grounds, that pleasure and pain, as tones
of feeling belonging to sensation, are conditions which may be
regarded as on different sides of a zero-point, or point of indif-
ference l^'ing between them. It does not follow, however, that,
because the mind passes in time from feeling of one positive tone
(pleasure) to feeling of the opposite tone (pain), it must, therefore,
at some instant be in a state of feeling that has no tone and lies
between the two. The curve plotted to represent the rise and fall
of feeling is a material line ; it cannot be at one time below, and at
another above, the abscissa-line, Avithout at some single point (the
zero-point) coinciding with it. But it does not follow that, because
such a curve is a picture of the phenomena of feeling in one respect,
it is so in all other respects. The question whether there is any
zero-point to the tone of feeling can only be answered by an aj^peal
to consciousness ; and this answer, like all others given to similar
appeals, is likely to contain dubious and conflicting elements. It
is quite certain that one can pass from a high state of pleasure to
' Hamilton's Works of Thomas Reid, p. 311. Edinburgh, 1854.
' The Emotions and tlie Will, p. 13.
^ Phjsiolog. Psychologie, i. , p. 465 f.
510 NATURE AT^D KINDS OF FEELING.
one of intense pain -without any interpolated neutral feeling. For
example, if while one is viewing a beautiful landscape one is stung
by hornets, the condition of quiet massive pleasure may be converted
into one of great physical suffering without any intervening feel-
ing of indifference. We incline, then, to agree with Sully ' in af-
firming that every feeling is either pleasurable or painful in some
degree. " We apply the name 'feelings,' " says Lotze," " exclusively
to states of pleasure and pain, in contrast with sensations as indif-
ferent perceptions of a certain content."
§ 12. Various questions may be raised as to the physical appar-
atus, the nervous elements and processes, for pleasurable or pain-
ful feeling, which cannot be answered satisfactorily. Are there
special nervous elements — whether end-organs, or nerve-fibres, or
nerve-tracts and centres in the central organs — which must be ex-
cited in order to give rise to the feeling of pain ? If the apparatus
for feeling is the same as that for the sensations to Avhich the feel-
ing gives its color-tone, do the feeling and the sensations imply
different processes in these same elements as the physical basis on
which they rest? Is not pleasure, rather, the result of a normal
and moderate amount of process in these elements ; and pain the
result of a process in the same elements whose amount has been
increased so as to be destructive or injurious to the tissue involved ?
Lotze ^ raised these questions, and answered tliem with the opinion,
somewhat doubtfully expressed, that sensation and feeling are due
to two forms of processes in the same nervous elements, and that
there is no need of assuming special oi'gans of feeling, whether
peripheral or central Probably the prevalent view hitherto has
been, that the same apparatus of end-organs, conducting nerve-
tracts, and central areas, which on moderate excitement produces
the simple sensations of pressure or of temperature, or the more
complex sensations of tickling, shuddering, etc., produces the feel-
ing of pain when irritated with increased intensity. Such a view
would apparently have also to hold that muscular sensations have
the same physical apparatus as do feelings of muscular weariness
or exhaustion ; and, perhaps, that cardialgia and hunger are due to
modifications of the action of the same nerves of the stomach. But
from the losychological point of view it is as certain that sensations
of pressure or mere temperature are unlike the feeling of pleasure
produced by gentle rubbing or by comfortable warmth, or the pain
' Outlines of Psychology, p. 449, New York, 1884 ; and comp. Volkmann
von Volkmar, Lehrb. d. Psychologic, II., p. 311 f.
'■' Outlines of Psychology, p. 73. Boston, 1886.
^ See Mediciu. Psychologie, pp. 245 fE.
PHYSICAL APPAKATUS OF FEELING. 511
that comes from heavy pressure or burning, as it is that sensations
of light are unlike those of musical tone.
Besides the obvious difference which the results of exciting it
have in consciousness, there are other and physiological reasons
for doubting the complete identity of the nervous apparatus of
pleasurable and painful feeling with that of the sensations with
which the feeling is allied. The facts upon which Schiff and others
support the view that nervous impulses resulting in pain travel by
more or less distinct paths along the spinal cord have already been
stated (Part I., chap. HI., § 32). The most recent experiments seem
to show that the end-organs of temperature, j)ressure, and pain are
locally separable in the different minute areas of the skin (Part 11.,
chap. rV., § 21 f.). Pathological results indicating the same separa-
tion of the nervous elements of feeling also deserve a brief men-
tion. In certain cases the sensibility of the skin to pain is lost (a
condition called "analgesic " by Beau, and " analgie " by Lotze),
while its sensibility to touch is not weakened or is even increased.
The reverse condition also sometimes occurs. " Analgie," as occa-
sioned by pathological states of the spinal cord due to lead-poison-
ing, was noticed in many cases by Beau. This loss of seusibility to
pain can hardly be explained by any change in the activity of cer-
tain end-organs co?n?7io;i both to touch and to painful feeling. What
impairment of function could possibly result in destroying the sen-
sitiveness to strong mechanical and thermic excitations, such as
ordinarily occasion great pain, while the response by way of sensa-
tions of touch to much feebler excitations remains undiminished?
The same argument would appear decisive against identifying, lo-
cally, the central nervous processes which result in sensation with
those which result in feeling. In certain stages of narcosis, produced
by ether or chloroform, the patient is able to perceive the slightest
contact with the skin, but feels no pain even when the same area is
treated severely. Moreover, in some cases of tabes dorsahs, a con-
stant difference seems to exist in the time at which the sensations of
pressure and the feelings of pain, simultaneously excited at the end-
organ, arise in the mind. If the patient is pricked with a needle,
he will instantly feel the contact, and the pain only one to two
seconds later.' The case of the eye, which responds with sensations
of light and color when the optic nerve is moderately excited, and
with the painful feeling of being blinded when the stimulus is in-
creased, is not perfectly clear. For cases of amaurosis are on
1 See Funke, in Hermann's Handb. d. Physiol., III., ii., p. 297 f . ; such
phenomena have been especiallj' discussed by Osthoff, Die Verlangsamung d.
Schmerzempfinduug bei Tabes dorsalis, Eiiaugeu, 1874.
512 NATURE AJSTD KINDS OF FEELING.
record where the painful feeling persisted after the eye had lost all
power to distinguish light. It has been argued, therefore, that
while the specific sensations of light and color are due to the irri-
tation of the optic nerve, the excitement of feeling indicates a si-
multaneous irritation of part of the trigeminus.
We are compelled, then, to confess that the localizing of the
nervous apparatus, and the nature of the physiological processes
which form the physical basis of painful and pleasurable feeHng,
require fiu'ther investigation. The tendency of the evidence, how-
ever, is toward a theory which assigns to feeling a more or less
separate mechanism of end-organs, conducting nerve-tracts, and
central areas (or at least of nervous elements in the central areas).
But how such a theory will reconcile itself with the other familiar
facts which appear, obviously, to make the tone of feeling depend
upon the degree of intensity which the nervous processes attain, it
is impossible to predict.
§ 13. One kind of feeling, which has the tone of pleasure or pain
belonging to all feeling, is undoubtedly of central nervous origin ;
this is the so-called sensus communis, or "common feeling."' Such
feeling may have more or less of content of one kind or another,
according to the state of perception and ideation with which it is
combined. Nervous impulses of indefinite variety and the most
manifold peripheral origin are constantly pouring in, as it were,
upon the cerebral centres — each one contributing some element to
the characteristic tone of consciousness. The resulting feelings are
modes of our being affected which are not converted into definite
presentations of sense, or referred to a particular part of our own
bodies. The effect of changes in the minute blood-vessels and
other capillaries about the nerve-endings, the presence of impuri-
ties in the blood, the condition of the lower cerebral centres, the
action of the heart and lungs and other internal organs, and the
connection of the sympathetic with the cerebro-spinal nervous sys-
tem, are all felt in this way. Moreover, inasmuch as few (if any)
sensations are without some tone of feeling, while many sensations
are exceedingly heterogeneous in their elements, and not clearly
referred to the place of their origin, a melange, as it were, of ob-
scure bodily affections is readily formed.
Sensations in themselves heterogeneous may also be brought
into a temporary relation by the partial identity of their source of
excitation, and of the nervous connections in the central organs.
It is also always a very important question, how the more obscure
' Comp. Funke, Der Tastsiuii u. d. Gemeiiigefiihle, in Hermann's Handb. d.
Physiol., III., ii., pp. 2a9 ff.
COMPOSITION OF COMMON FEELING. 513
and mixed bodily feelings stand related to the mind's course of idea-
tion, to attention, association, etc. This relation often determines
whether such obscure impressions shall be definitely objectified or
not ; whether they shall not rather run together in the dark stream
of common feeling. Let anyone suspend for an instant a train of
interesting thought, which has up to the moment been interrupted
only by certain obscure feelings of uneasiness, and such one will be
able instantly to select and localize in the cramped chest, or op-
pressed limbs, or tired organs of special sense, most of the sensa-
tions whose painful tone has thus colored the stream of common
feeling. Separation from localized sensations is, then, the chief
negative characteristic of common feeling.' Undei" its different
principal forms we may distinguish different total results, according
to the general relation in which the being aware merely that we are
affected in an agreeable or disagreeable manner stands to the being
aware of lohat affects us in this manner. Thus we sometimes feel
well or ill, elevated or depressed, without ability to assign these
feelings at all definitely to the physical organism, either as perceived
or imaged, or to any reason in the train of ideas. At other times
the general impression of being in the body, for some greater or less
amount of either weal or woe, is emphatic ; we feel ill all over, or
seem to enjoy the coursing of the ,blood through every artery and
vein, as though mentally present in the extended tissues.
§ 14. According to Strickei'," information derived from the pe-
ripheral nerves consists of either sensations or feelings ; the latter
implies self-reference, which may be of two kinds. If this reference
extends to the whole sensorium, and so to the whole organism, the
feelings are called "common" or "collective;" under certain cir-
cumstances they appear as fixing the mood of our consciousness.
Some of the organs, in their sound condition, have no organic feel-
ings ; others of them undoubtedly largely determine the character
of our common feeling by their condition, tension, action, etc. If,
now, we extend the sensations of touch so as to include all the ob-
scurely localized organic and muscular sensations, we feel the neces-
sity of distinguishing such sensations from what we have called
the "common feehng."
One characteristic which the sensations have as sensations, strictly
speaking, concerns the method of their excitation. In general, the
stimulus must affect the nerves through the specific end-organs of
sense, in order to give rise to a proper sensation. E. H. Weber
sought to prove that, whenever nerves are irritated, not through the
' Comp. Lotze, Medicin. Psycliologie, p. 278 f.
^ Studien iiber d. Bewusstseiii, p. 17 f. Wien, 1879,
33
514 NATURE AND KINDS OF FEELING.
end-organs, btit along the trunk, the irritation gives rise to feelings
of pain instead of sensations. One experiment for this purpose
consisted in dipping the point of the elbow into ice-cold water ;
when the sensation of cold is at once located in the skin, and the
feeling of pain arises as soon as the stimulus has penetrated to the
trunk of the nerve lying beneath. But other experiences seem to
show that tones of common feeling may be indirectly excited, which
are characterized by the massing of a great number of minute and
obscurely localized sensations of touch. For example, the prick of
a needle is felt at a given j^oint as a circumscribed pain. The tick-
ling from a feather, confined to a small surface, may be regarded
as consisting of complex sensations of light pressiu'e, with no fixed
locality for each one, but localized in general at about such a spot.
But the tickling may be continued until a general tone of painful
feeling is developed, which quite overwhelms all localized sensa-
tions. These phenomena may be considered as agreeing with the
other phenomena to show that common feeling is due to widely
extended and complex conditions of the central areas, in which
the results of a large number of separate peripheral stimulations
may unite so as to lose all their individual character, although each
one contributes something to the common result.
§ 15. There are feelings so connected with the operation of the
organs of sense as to be called feelings of sensation. A certain tone
of feeling (a third element, as distinguished from its specific quality
and intensity) belongs to most sensations. We are scarcely war-
ranted, however, in asserting that every sensation, as such, possesses
some tone of feeling.' The question whether every sensation has
some feeling must be distinguished from the question whether every
feeling is of either painful or pleasurable tone. The tone of the
feeling of sensations is the agreeable or disagreeable afi'ection of
consciousness which they often carry, as inseparably connected with
them. The particular tone belonging to any sensation is, to a large
extent, dependent on its intensity. The laws of this dependence
have been ingeniously conjectured by Wundf Sensations of mod-
erate intensity — that is, of intensity below the point at which the
minimum of painful feeling begins — are usually pleasurable. The
feeling of pain rises in intensity, from the point where it begins, as
the intensity of the stimulus increases. The curves which represent
the increase of feeling and the increase of sensation by no means
correspond. It is assumed by Wundt that the maximum point of
pleasure lies about the so-called "cardinal value" of the sensation,
' As Wundt does, for example, Physiolog. Psychologie, i., p. 465.
* Physiolog. Psychologie, i. , p. 469 ; comp. p. 360.
TONE DEPENDENT ON INTENSITY. 515
or place where the sensation ceases to increase in simple proportion
to the strength of the stimulus. The amount of pleasurable feeling
is also dependent on the element of time. It is thought to reach a
maximum at about the point where the strength of sensation is the
most favorable for accurate discernment of the objective stimulus.
As to the dependence of the tone of feeling belonging to a sen-
sation upon the quality of the latter, it has been held ' that no sen-
sation is ahsolately pleasant or unpleasant irrespective of its in-
tensity. Even then, however, it would have to be admitted that
qualitatively different sensations differ greatly in the amount which
is consistent with an agreeable tone of feeling. It is, of course,
with regard to the organic sensations, and the special sensations of
touch, smell, and taste, that the relation between tone of feeling
and the quality of sensation is most apparent. Doubtless large al-
lowance must be made in all cases for individual peculiarities of
organism, association, etc. Probably, also, the disagreeable tone of
feeling which almost universally attaches itself to certain qualities
of sensation, however moderate or unobtrusive their intensity, is
largely explicable on the principle of heredity. But, taking matters
as they stand in present experience, it is impossible to maintain
that the tone of feeling is not directly dependent on the quality of
sensation. This is a question upon which only consciousness can
pronounce. All degrees of some tastes and smells are disagreeable
to most persons. Bitter is a distinctive species of the quality of
gustatory sensations ; but the pleasure which some persons have
in greater or less degrees of it is, as a rule, acquired. It is true
that some substances, whose odor in large quantity is disagreeable,
become tolerable, or even pleasant, when the smell from them is
faint. But this faint smell is not the same, but a distinctly differ-
ent quality ; oftentimes it could not be immediately recognized as
coming from the same substance as that which emitted the stronjj
odor. Discordant sounds are, in all degrees of intensity, naturally
unpleasant ; and so most witnesses would pronounce certain com-
plex sensations of the skin (as of creeping, prickling, etc.).
§ 16. Characteristic mixtures of feeling — some of them scarcely
describable — seem to be attached inseparably to different kinds of
sensations. This is obvious when we consider the marked difference
in the wa^'- we are affected by major and minor chords, by succes-
sive tones having different musical intervals (for example, the di-
minished third, etc.), and by the characteristic clangs of different
musical instruments. Writers upon this part of musical theory
may disagi'ee as to the precise significance of the violin, clarinet,
' So Wundt, Physiolog. Psychologic, i., p. 470.
516 HIGHER FORMS OF FEELIISTG.
cornet, or hautboy, with respect to the tone of feeling belonging to
each ; but they can scarcely deny the fact of a marked difference.
Goethe ' called attention to the change in spiritual tone, as it were,
which harmonizes with what the eye sees when looking upon the
world through different-colored glasses. Here, again, the precise
equivalent, or value, in terms of feeling, which the different color-
tones possess, may be a matter of dispute ; but the fact that the
tones of feeling change with the color-tones is beyond dispute.
That feelings of soberness or gloom go with black, of excitement
with red, of cheerfulness with light green, of cool quiet with dark
blue, of intense sensuous pleasure with saturated j)urple, would
probably be admitted by most persons. Fewer would agree to de-
scribing the tone of feeling belonging to dark yellow or spectral
orange as one of " suppressed excitement," or to brown as one of
" perfectly neutral mood." °
§ 17. The character of the disagreeable or painful feeling belong-
ing to different classes of sensations also differs with respect to the
nature of its attachment to a recognized physical basis. Unhar-
monious colors produce in us a feeling of mild dissatisfaction,
which appears as almost wholly of a spiritual kind. Discordant
tones cause more of physical suffering ; and disagreeable smells
or tastes create a widespread sense of organic discomfort. Pains
in the skin and interior organs, however, may take a character of
intense bodily anguish, which is distinctive of no other qualities of
sensation, and which is capable of submerging all sensation, as such,
in a flood of painful feeling.^
§ 18. The tone of sensuous feeling is also dependent upon the
total condition of consciousness as determined by attention, mental
habit, association of the feelings among themselves and with the
ideas, control of the will, etc. Such feeling is, therefore, largely a
secondary element of experience, which arises through certain ac-
quired effects of the sensations as connected with previous activities
of the mind. But concerning the physical basis of the feehngs, in
this aspect of them, we know nothing whatever ; and the subject
is not as yet one with which physiological psychology can success-
fully deal.
§ 19. The consideration of the affections and the emotions, or
passions, involves at least three important particulars : (1) The
characteristic feeling which distinguishes each ; (2) its relations to
the train of ideas, and the changes induced by it in the ideas ; (3)
1 Farbenlelire, § 763.
' Comp. Wuiidt, Physiolog. Psycliologie, i., p. 477.
* Comp. Lotze, Outlines of Psychology, p. 75 f.
BODILY BASIS OF THE EMOTIONS. 517
the relations to the different bodily organs, and the reflex effect of
the changes in these organs upon both the feelings and the ideas.
Each of the various affections or passions is characterized by a
peculiar feeling, whose tone is either agreeable or painful, whose
intensity admits of various degrees, and whose content is determined
by the mental representations to which it has become attached.
Each may be considered as having its rise, psychologically, in some
form of blind, instinctive impulse that needs to be connected with
a mental image of the object which experience has related to it as
corresponding to the impulse. The germ of the impulse is the
natural susceptibility of having desire awakened by an appropri-
ate stimulus, and the capacity of forming by experience the idea
which corresponds to, or gratifies, the impulse.' Impulses may be
described as of two kinds — craving, or attraction, and repulsion.
When the feeling, which as mere impulse is blind with respect to
the object of gratification, becomes connected in experience with
appropriate presentations of sense or mental pictures, the basis for
an affection or passion has been laid. Thus the germ of anger and
hate is found in that instinctive impulse of repulsion which is pro-
duced by all unpleasant resistance of effort, or painful excitement
of the nervous system. Sudden and intense irritations — as the
striking of one's hand against the table, the slamming of a door in
one's ea]' — tend to arouse the feeliug of resentment. The affection
of the child for the mother ultimately becomes far more than the
feeling of comfort it has in her arms or at her breast ; but the
former is cradled and nursed in the latter. By varied associations,
impulses of attraction or of repulsion become developed into a
great variety of affections, emotions, and passions, characteristic of
the different manifold relations in which the sentient soul finds it-
self standing toward things and persons.
§ 20. All emotional forms of feeling are accompanied by abrupt
and marked changes in the character and time-course of the mental
train. Such changes may be regarded as standing in the relation
both of cause and of effect to these feelings. Some impression
with which strong feeling has become associated is made upon the
mind ; the result is a transitory interruption of the mental equi-
poise. This constitutes in part the justification for the saying that
from mere feeling to affection is a "leap." " As a rule, the effect of
any sudden and surprising impression — perception of some object
of sense, or remembered image — is to start the flow of emotion.
Thus anger, fear, desire, avarice, take men "off their guard;" the
' Comp. Wnndt, Pliysiolog. Psycliologie, ii. , p. 33 f .
^ Comp. NaLlowsky, Das Gefiililslebeu, etc., Eiuleitung.
518 HIGHER FGKMS OF FEELING.
feelings of sucli kind that are started by a given mental impression
themselves produce a confusion of the mental train. But, on the
other hand, this very disturbance of the mental train is itself pro-
ductive of a new phase of feehng, such as is associated with the
particular ideas that in confused and hurried throngs rush into
consciousness, as well as with the general state of consciousness
considered as one of haste and confusion. The physical basis of
this state is laid in the extraordinary condition of excitation that
exists within the central organs — the ideo- and sensory-motor cen-
tres of the cerebral hemispheres.
§ 21. But the wonderful, characteristic effect which these forms
of feeling produce upon certain of the vital oi'gans is the most
noteworthy peculiarity of all affections, emotions, and passions.
Upon this point science has far less than we could wish of informa-
tion reaching beyond the observations of ordinary experience. Of
such information, perhaps the most important concerns the influ-
ence exerted through many groups of muscles, from the central
organs, upon the vaso-motor system. The effect of shame, fear, or
anger, for example, upon the circulation of the blood is matter of
common remark. But some grow pale and others red, when angry.
In 1854, K. Wagner investigated the effect of fear upon the heart
of a rabbit. A blow on the table near the animal was found to
cause its heart to stand still a short time, and then resume beating
with accelerated frequency of stroke. Subsequent investigations
have made obvious the general effect of emotion upon the curve in-
dicating the blood-pressure. The effect produced ujDon the pulse
of a dog by hearing the sudden cry of another dog depends for its
character upon whether the vagus nerves are cut or not ; but even
after their severance a marked effect of this kind is still manifest.^
The great influence of these forms of feeling upon all the action of
the capillary vessels, upon the secretions, etc., and upon the respira-
tion to retard, or accelerate, or make it irregular, is of the same
order. That care and anxiety disturb nutrition, that pain and sor-
row cause the tears to flow, that fear and love and anger act upon
the abdominal organs, is generally recognized. The effect is some-
times seen in suddenly innervating, and sometimes in depressing,
one or more of the bodily organs ; or in both innervating and then
depressing them, in certain well-recognized cases. On the basis of
such facts, Kant suggested a division of the affections into " sthenic "
and '• asthenic." But many forms of feeling, as they run their
' This subject has been investigated by Conty and Charpentier, by Cyon,
Heidenhaiu, and others; comp. Exner, in Hermann's Handb. d. Physiol., II.,
ii., p. 289f.
BODILY BASIS OF THE EMOTIOl^S. 519
course, become by turns sthenic and asthenic. Strong emotions or
passions of all kinds tend to destroy the nervous mechanism ; " the
sthenic kill by apoplexy, the asthenic by laming the heart." ' Un-
usual tension or relaxation of certain groups of muscles characterizes
all these forms of feeling.
The marked effect which certain feelings have upon particular
organs of the body is complemented by the fact that such organic
effect has in turn a marked effect upon the feelings. The organic dis-
turbances advance step by step to form the physical basis of a rising
tide of emotion, and then fall off with equal pace as the tide of emo-
tion subsides. The organic changes are not merely an expression
of the mental ; they are its material cause and support. Professor
James has emphasized these facts with great skill and in an inter-
esting way.^ The effect upon the emotions and passions of putting
the muscles or other organs of the body into certain conditions,
which is so remarkable in all cases of hypnotism, is also undoubted
in what we ordinarily consider normal states of body and mind.
"What kind of an emotion of fear would be left, if the feelings nei-
ther of quickened heart-beats nor of shallow breathing, neither of
trembling lips nor of weakened limbs, neither of goose-flesh nor
of visceral stirrings, were present, it is quite impossible to think.
Can one fancy the state of rage and picture no ebullition of it in
the chest, no flushing of the face, no dilatation of the nostrils, no
clinching of the teeth, no impulse to vigorous action, but in their
stead limp muscles, calm breathing, and a placid face ? " In view
of the foregoing facts. Professor James propounds the thesis, that
the " bodily changes follow directly the perception of the exciting
fact, and that our feeling of the same changes as they occur i'8 the
emotion." '
To neglect, however, that element of feeling in ever}'' emotion
which is immediately attached to certain perceptions and ideas
would be quite as faulty as to neglect the elements which are only
reflexly blended with the coniplex of feeling on account of the condi-
tion into which the bodily organs are thrown. The relation between
perception and feeling as a psychological fact is as certain and im-
mediate as any relation can be. What the physiological basis for
this connection is we do not know ; but there is every reason to
suppose that it is, at the same time, direct and of the nature of re-
ciprocal influence between the nervous elements and areas of the
' Wundt, Physiolog. Psycliologie, ii., p. 330.
^Mind, 1884, IX., p. 188 1
^ But since its author seems scarcely to have taken this thesis seriously, it
may be thought superfluous even to object in brief to it (see p. 205).
520 HIGHER FORMS OF FEELING.
cerebral centres ; as well as indirect, through disturbances pro-
duced by perceptions and ideas within the remote bodily organs.
The influence of perception upon the feelings in the form of strong
emotion is partly, but not wholly, through the skin, muscles, blood-
vessels, organs of respiration, and viscera. At the same time the
characteristic tone which strong emotions have is largely colored by
the sensuous and common feelings occasioned by the disturbance
of the organs. When even the feelings called aesthetic, or intellect-
ual, or ethical and rehgious, are vehemently aroused, an "emo-
tional " equality is imparted to them from the same source.
§ 22. By mental " moods " is ordinarily understood those collec-
tive conditions of the mind which are characterized by some funda-
mental tone, but without any special feelings accompanied by clear
consciousness of their inducing causes. The principal elements that
enter into such moods consist of ill-locahzed sensations arising from
the internal organs — especially due, perhaps, to disturbed or de-
pressed cerebral function ' — and a throng of half-reproduced feel-
ings and ideas, or of vague single feelings, such as undefined fore-
boding, anxiety, fear, etc. Since these elements belong to the some-
what permanent equipment of the mind (at least until a marked
and lasting change in cerebral condition and the train of ideas is
brought about), their prevalent tone is characteristic of different
persons ; whereas the emotions and j^assions run their course
quickly, and give a color to the personality rather by the sudden-
ness and frequency with which this kind or that, respectively, is
present in consciousness. But mental moods also may be charac-
terized by emotions or affections of a low and lingering tone — pale
and faded specimens of the type, as it were.
§ 23. Of all the so-called "higher feelings" (aesthetic, intellectual,
ethical, religious), it is only certain elementary forms of aesthetic
feelijig concerning whose peculiar physical basis we have any as-
sured information. All these feelings, however, when they reach
a certain degree of intensity, tend to assume an emotional character.
They then come in part under the considerations which have ah'eady
been urged as applying to the emotions in general. A large portion
of the strong feelings of admiration for scientific objects, discoveries,
laws, and personalities, or of religious fervor, aspiration, and devotion,
or depression, is reflex ; it rests upon the jDhysical basis of effects that
are produced in the muscles and vital organs — especially the organs
of secretion, respiration, and circulation. But these facts do not
explain or annul the other class of facts, which leads the judicious
investigator also to emphasize tlie spiritual oiigiii of such feelings
' Comp. Strieker, Studien i'.ber d. Bewusstseiu, p. 63.
'FEELING OF HAEMONY AND EHYTHM. 521
considered as complex reactions of the mind in view of the presence
in consciousness of certain classes of ideas. So far as such spiritual
reactions by way of feeling have any even conjectural physical basis
peculiar to them, this basis must be sought for in the central
organs of the nervous sj'stem. How far such a basis really exists,
and in what it consists, we have as yet scarcely a right to imagine —
so complete is our ignorance.
§ 24, The cesthetic feelings arise and develop chiefly in connec-
tion with presentations of sense, or with the remembered or created
mental images that represent objects of sense. In their elementary
form, therefore, they plainly have a physiological side which admits
of scientific treatment — although they have received such treatment
far less than could be wished. Many interesting facts and certain
partial generalizations called law^s — having most application to the
lower classes of pleasurable feelings through the organs of smell,
taste, and the skin, when viewed in the light of the hypothesis of
evolution — are given in the work of Grant Allen on " Physiological
Esthetics." ' But even the most elementary aesthetic feelings can-
not be considered as on a par with the sensuous feelings, or as mere
aggregates of such feelings.^ The tone of feeling which characterizes
the sensations furnishes a material, as it were, for genuinely aesthetic
feeling ; but the latter always implies also the working of certain in-
tellectual laws, and a union of the simple feelings of sensation under
time-form and space-form. Esthetic feelings, then, may be said to
spring from the manner of the combination of sensuous feelings ;
time and space furnish the framework in which they are arranged.
Hearing is the principal sense for combining sensuous feehngs so
as to produce aesthetic feelings under time-form, and sight under
space-form. The development of even the elementary but genuine
cesthetic feelings by other senses than the eye and ear is extreme-
ly limited. The agi'eeable and disagreeable feelings which come
through sensations of smell, taste, and touch are for the most part
sensuous, rather than strictly aesthetic.
Hearing, as pre-eminently the time-sense, has two forms of aes-
thetic feeling — harmony and rhythm. The nature of the complex
sensations which produce the feeling of consonance and dissonance
has already been discussed. Harmony is determined by the co-
incidence of certain partial tones belonging to different clangs si-
multaneously sounded. The feeling of harmony is colored by the
peculiar Avay in which the combination of the clangs occurs. The
princiijal difference of this sort is that which obtains be ween major
' See pp. 30 ff.
^ Ou this point, see Wundt, Pliysiolog. Psychologie, ii., p. 179 f-
522 HIGHER EORMS OF FEELING.
chords and minor chords ; in the former the different clangs are
perceived as firmly held together by the fundamental clang, while
in the latter the coincident overtone performs the same office less
obviously. The one is jDroductive of agreeable aesthetic feeling
satisfied ; the other of such feeling left unsatisfied — a feeling of
longing. When, then, the one form of feeling becomes very intense,
it may involve the pain of over-excitement ; the other, when inten-
sified, stirs a kind of agreeable pain of nnrest. In musical time it is
the periodic nature of the excitation, with a change in the individ-
ual presentations of sense, which produces the pleasurable sesthetic
feeling.
Two or three regularly recurring impressions, having the same
or a different content of musical sound, are combined into a
series ; certain members among the whole number are then ac-
centuated, in order to form the different series that constitute the
various kinds of musical time. All musical time, fundamentally
considered as respects its rhythm, is either two-time or three-time.
The difference in the feelings which respond to these two classes of
musical rhythm is obvious in a pronounced form, in the funeral
march, on the one hand, and the waltz, on the other. In general, it
is the harmony of music which gives du'ection to its feeling, and
the rhythm which determines the rise and fall of feeling. Thus
waves of different kinds of feeling are made by music to pass over
the soul.'
The elementary aesthetic feelings which come through sight lead
to the consideration of the aesthetic effect of visual form. Such ef-
fect can be considered only very imperfectly from the physiological
point of view. In one important particular, however, pleasurable
sesthetic feeling is directly dependent upon the combination of the
sensations, with their accompanying tone of feeling, under the laws
of the mechanism of vision with both eyes in motion. Beautiful
form is detei-mined by the course of the limiting lines ; and limit-
ing lines, in order to have the effect of arousing agreeable aesthetic
feeling, must accommodate themselves to the physiological and psy-
cho-physical necessities of the eye when in motion. These neces-
sities thus determine both the direction and the extent of the limit-
ing lines. Lines of slight curvature, not too far continued in one
direction, best compl}' with such necessities. Lines of very sharp
cui-vature, or lines continued too long in one direction, do not pro-
duce a pleasing sesthetic effect. So also must the main lines of a
building lie in horizontal or vertical directions, preferably in the
' For a treatment of sestlietic feeling in music, comp. Wundt, Phjsiolog.
Psychologie, ii., pp. 180 ff.
THE GOLDEN DIAMETEE. 523
former direction. But long oblique lines — for example, from a
lower rigiit-hand to an upper left-hand corner of a building — are
scarcely tolerable. The ease with which the eye sweeps the lines,
in order to make that synthesis of successive similar presentations
of sense in which every perception of a line consists, is plainly a
determioing factor in all these cases.
The aesthetic effect of visual form is also determined by the way
in which the form is constructed, through repeating similar or un-
like simple shajDes and combining them into a totality. By this
means a feeling of pleasure akin to the feeling of musical rhythm
is excited by the successive impressions which occui" periodically as
the eye, with a nearly uniform movement, sweeps the entire field.
In horizontal directions, the law for the arrangement of the parts is
that of symmetry of the simple parts ; in vertical, rather the law
of asymmetry. Certain proportions between the connected parts,
and between the whole and the parts, are favorable to the develop-
ment of aesthetic feeling. The rule, that the whole of a presentation
of sight shall be to the larger part as the larger part is to the small-
er part, has been called " the golden diameter " (x + 1 : x : : x : 1) ;
since the proportion thus determined has been supposed to be par-
ticularly favorable to pleasurable gesthetic feeling. Ease of the
mental apprehension with which the relations in proportion of the
different parts are presented is favorable to agreeable aesthetic feel-
§ 25. But all the foregoing rules, and all others similar, are appli-
cable to the aesthetic feelings of form rather as coming under the
general class of intellectual feelwgs. That change in degree or kind
of activity, recognition of similarity or contrast, and mental appre-
hension of a law or principle as expressed in the presentations of
sense, determine the agreeable character of our intellectual feel-
ings, is recognized by psychologists ' generally ; but as to the
physical basis of mental facts of this order we are almost completely
ignorant. It is not unlikely, however, that the effects of monotony
and change upon the feelings of an intellectual order are connected
with the same law of the exhaustion of the nervous elements as ap-
plied to the cerebral areas which we know to hold good in other
parts of the nervous system.
§ 26. The only other class of feelings which admit of considera-
tion from the physiological point of view is the so-called "feelings
of effort, or of innervation." These feelings are especially con-
nected with all the motions of the body considered as furnishing
' See the judicious remarks of Sully, Outlines of Psjchologj', pp. 457 S.
New Yo:k, 1884.
524 HIGHEE FORMS OF FEELING.
information concerning its position and the condition of tension oi
strain to which its parts are subject ; as well as furnishing, through
revived mental images of such feelings, the means for reproducing
voluntarily the required definite modes of motion. Such feelings
also have a great psychological interest on account of their obvious
connection with the development and consciousness of acts of will.
The dispute as to whether they are of central or peripheral origin,
and as to that in which their precise nature consists, has already
been alluded to (pp. 344 and 415).
That we have a ' ' feeling of effort " is a fact, as says Professor
James,' " consecrated by the institution of the word effort, and its
synonyms exertion, striving, straining." The nervous process which
occasions this feeling the great physiologist Miiller ^ considered
to be purely central, and to consist in the discharge from a motor
centre into the motor nerves. This view has since been widely
adopted by physiologists ; it has also been used — especially by Bain
and AVundt — as an essential factor in a theory of sense-perception,
as of chief importance in accounting for our experience of solid re-
sisting objects of sense and of whatever belongs to the inertia of
matter in general. On the contrary, it has been maintained that
the feeling of effort, over and above what is purely " moral" (as in
the effort to remember to make a decision, etc.), is a comjDlex of
afferent sensations " coming from the tense muscles, the strained
ligaments, squeezed joints, fixed chest, closed glottis, contracted
brow, clinched jaws,^ etc."
Of the two views above mentioned, the latter has by far the most
in its favor. The argument from the consciousness of effort which
we may have when we intensely make believe use any limb, but
do not actually move it (as, for example, the pulling of a trigger
with the forefinger of an extended hand), has been answered by
Terrier. ■* This observer calls attention to the fact that the feeling
of effort in such cases is due to keeping the glottis tightly closed,
and actively contracting the resjoiratory muscles. If we tr}', how-
ever, to make believe exert ourselves without actually contract-
ing the muscles of the limbs, and at the same time keep breathing
regularly, we shall not experience the slightest trace of the feeling
of effort, no matter how hard we try. This feeling, then, when the
glottis is closed and the respiratory muscles are tense, is due to
centripetal impressions coming from the parts thus innervated.
The argument from the feelings of effort which determine our
' The Feeling of Effort, Anniversary Memoirs of the Boston Soc. of Nat.
Hist., 1880, last monograph. '^ Physiologie A. Menschen, II., p. 500.
^ See James, Feeling of Effort, p. 4. ^ The Functions of the Brain, p. 222 f
THE FEELITSTG OF EFFORT. 525
localization of objects lias been presented in the most convincing
way possible by Helmlioltz and Wundt, as applied to the case of
partial paralysis of the external rectus of one eye. Inasmuch as
the patient feels (so von Graefe ^ showed) that he has moved his
lame eye much farther than he really has, the inference is drawn
that this exaggerated feeling of effort must originate in central
motor impulses Avhich have followed ujDon the fiat of the will. This
argument, however, neglects to notice what goes on in the other
and sound eye. Since this eye, unlike the lame one, continues its
motion until the limit of motion and its corresponding condition
of peripheral strain is reached ; and since, as Hering " has shown
(comp. what has already been said, p. 439 f .), both eyes are innervated
by one common act, and their motor apparatus is to be regarded as
functioning as one organ — the feeling of effort is probably due to
afferent sensory impulses occasioned by the condition of the sound
eye as well as of the other eye.^ Moreover, the more critically we
examine those cases which occasionally occur, where, on account
of paralysis causing anaesthesia, the sense of position of the limbs
is impaired or lost, the more conclusive does the evidence appear
against the theory that the feeling of effort is of purely central ori-
gin. For, in general, it seems that, while the power of voluntary
motion remains unimpaired, if the sensations which have a pe-
ripheral origin are impaired or lost, the various feelings of effort
connected with the accomplishment of a given amount of motion,
or with the act of holding any member of the body against the pull
of gravity, are disturbed or disappear.'' As far as the evidence re-
garding this obscure subject reaches at present, the feeling of effort
' Handb. d. gesammten Augenlieilkunde, VI., p. 18 f.
' See Hermann's Handb. d. Physiol., III., i., pp. 512 f. and 520 f.
2 See James, Feeling of Effort, p. 10 f .
■* See a recent paper on " Le Sens mnscnlaire et les Sensations musculaires,''
by E. Gley, in the Revue Philosophique, 1885, pp. 601 ff. In this paper the
results of the investigations of M. Maguin, conducted upon paralytics in the
Hopital de la Pitie (Comptes rendus, Mars 1884, i. ), are appealed to as con-
firmatory of the view that the stretching and rubbing of skin, ligaments, joints,
etc., enter into our so-called feelings of effort. M. Demeaux has reported the
case of a woman who could move her limbs, but could not tell whether they
were moved, or in what direction, or how far. Xo fewer than three similar
cases were reported by French physicians in the year 1885. The same view
of the complex peripheral origin of the feeling of effort seems also to be fa-
vored by the experiments of M. Bloch, who tried placing his hands symmet-
rically on a screen with two leaves covered with paper, divided into small
squares, under the guidance of the so-called muscular sense. The testimony
of persons who have lost their limbs, as to whether they can produce any feel-
ing of effort by the fiat of will to move the lost member, is conflicting. In all
526 IN'ATURE OF THE BODILY MOTIONS.
must be held to be complex, and so is akin to other forms of com'
mon feeling ; its constituent elements are the various obscurely lo-
calized sensations, with their characteristic tones of feeling, which
arise in the condition of skin, muscles, ligaments, joints, etc.
§ 27. The feeling of effort is closely connected in experience
with the changing positions of the members of the body, and its
consideration therefore fitly introduces that of the bodily motions.
As concerns their relation to the phenomena of mind, these motions
may be divided into two great classes' — namely, such as are not
demonstrably connected with antecedent changes in the states of
consciousness, and such as, in addition to their physical condi-
tions and causes, require that their explanation should take account
also of preceding states of consciousness. The former are to be
regarded purely as activities of the physical mechanism,^ and are
either automatic or reflex. Automatic motions are such as, with-
out any corresponding idea or fiat of will, originate from inner
excitations of the central nervous system ; the rejiex are those in
which the central excitations resulting in motion are traceable to
the action of sensory nerves which have been peripherally excited.
It is extremely difficult to distinguish between automatic and reflex
motions, and scarcely less so to distinguish between the automatic
and the impulsive. Indeed, while it is true, on the one hand, that
reflex and centrally co-ordinated movements form the basis upon
which all our developed life of voluntary motion takes place, it is
also true, on the other hand, that the more complex co-ordinated
movements are themselves originally voluntary motions which have,
as it were, become habitual and so dropped out of consciousness
into a statical and mechanical way of taking place. The sensations
and ideas of motions may then be said to tend constantly in two
directions — either toward consciousness or out of it. It is by
means of these processes in two directions that all our learning of
complicated movements of the body, of feats of dexterity and skill
— learning to handle tools, to play on musical instruments, etc. —
takes place. The interest which psychology has in the automatic
such cases, however, it is probable that the alleged feeling of effort is 'to be
looked for in the actual condition of strain into which some existing part
of the body is thrown — especially the apparatus of respiration (see Bastian,
British Med. Journal, 1869, p. 461).
' Comp. Wundt, Physiolog. Psychologie, ii , p. 400 f . ; and Lotze, Medicin.
Fsychologie, p. 286 f.
■■' The mechanism of the bodily motions has already been treated at length :
for the nerve-muscle machine, see pp. lU4ff. ; for reflex motion, see pp. 182ff ',
for automatic motion, see pp 147 fE. ; for the sensory-motor areas of the cere*
brum, see p. 267 fE.
BASIS OF VOLUNTAKY MOVEMEN"T. 527
and reflex motions is chiefly on account of their relations to motions
which ai^e actually preceded by conscious ideation and voHtion.
§ 28. Such motions of the body as require us to take account of
antecedent or accompanying states of consciousness, in addition to
the connections of the physical mechanism, are either impulsive or
voluntarj'. But this distinction is one which admits of such a great
variety of degrees shading into each other, that, although it is
valid and necessary in principle, it cannot be carried through in
practice with any considerable precision. By an impulsive motion
we understand a motion which, without a conscious fiat of will, fol-
lows upon certain ideas and excited states of feeling. The motif
of the impulsive movement lies, then, in some form of feeling that
determines will one way without any proper choice. If we speak
of such motions as volitional or voluntary, it must be understood
tliat we are refei-ring to activities of will of a lower order, psycho-
logically considered, than those which come into play in all cases of
conscious choice. Impulsive motions are, in general, more quickly
accomplished than are voluntary motions; because the reaction-
time is shortened through will-time proper having been dropped
out (comp. chap. VIII.; § 19 f.).
§ 29. All voluntary movement has its basis laid, so to speak, in
impulsive movement, and in the reactionary effect which the latter
has upon the conditions of reflex and automatic bodily activities.
As laid in this basis, voluntary motions imply a development of in-
telligence and will. The infant finds itself equipped with a bod-
ily mechanism which, under the influence of external and internal
stimuli, is kept excited to unceasing activity of the peripheral mem-
bers. This activity results in certain sensations and feelings of
effort, in the manner previously described. The tone of these states
of consciousness is one of either pleasure or discomfort, under
those laws of relation between the nervous mechanism and conscious
feeling which can be only imperfectly stated ; and which, when
most perfectly stated, can only be accepted as ultimate matters of
fact. By nature the nervous mechanism is so arranged that certain
other bodil}' motions of peripheral origin are started on occasion of
the pleasant or painful feeling, and these motions are adapted to
enhance the feeling if pleasant and to relieve it if painful. The
feelings thus become further connected with the ideas of the mo-
tions that modify them ; yet the mechanism of the motions is not
to be regarded as originally dependent upon the ideas, but rather
as originated in connection with the feelings of pleasure or discom-
fort and naturally adapted to secure an increase of the one or a
diminution of the other.
528 NATURE OF THE BODILY MOTIOISS.
The voluntary naovemeBts of the body, accordingly, presuppose
the impulsive, and yet they reach far back into the obscurity of the
earlier development of consciousness. Strictly speaking, they imply
the presence in consciousness of two or more different or conflict-
ing ideas of motion, one of which rather than the others is realized
as a sequence of an act of conscious choice. They imply, then —
as has already been said — a considerable development of the men-
tal activities of ideation and volition. Moreover, those movements
which are ordinarily called voluntary ai'e really so only with respect to
certain of their elements ; they all also contain elements which must
be classed as reflex, centrally co-ordinated, and impulsive. The term
"voluntary " fitly lays the emphasis upon the conscious act of choice ;
and this, in turn, implies ideas of various possible forms of bodily
motion gained by previous experience with the correlated states of
conscious feeling and conditions of the body as giving rise to or
modifying these states.
The voluntary motions, therefore, constitute the highest class of
motions, both because their conditions include all those which be-
long to the other classes, and other conditions besides, and also
because of their more direct connection with the development of
certain mental phenomena of supreme psychological interest and im-
portance. To move any part of the body voluntarily requires the fol-
lowing particulars : (1) The possession of an educated reflex-motor
mechanism, under the control of those higher cerebi'al centres which
are :nost immediately connected with the phenomena of conscious-
ness ; (2) certain motifs in the form of conscious feelings that have
a tone of pleasure or pain, and so impel the mind to secure such
bodily conditions as will continue or increase the one and discon-
tinue or diminish tlie other ; (3) ideas of motions and positions of
the bodily members, which previoiis experience has taught us an-
swer more or less j^erfectly to the motifs of conscious feeling ; (4) a
conscious _/ia^ of will, settling the question, as it were, which of these
ideas shall be realized in the motions achieved and positions attained
by these members ; (5) a central nervous mechanism, which serves
as the organ of relation between this act of will and the discharge of
the requisite motor impulses along their nerve-tracts to the groups
of muscles peripherally situated.
As to the first and second of the foregoing particulars, nothing
further need be said ; and as to the definite nature of the physical
basis which underlies the connection of ideas of motion, fiat of will
adopting one idea, and the starting oiitward of the right motor im-
pulses, our ignorance is almost complete. It is more than probable
that we cannot will the movement of muscles, of the results of whose
WILL AS A PSYCHICAL ACTIVITY. 529
actual movement in the induced motion of the limbs we have ac-
quired no idea from previous experience. The mental images of the
various feelings of motion and position which have been acquired
in the past are our guides in realizing again the same motions and
positions of the limbs. To say I will, refers to the future. But we
can never " will" motion in general — motion, that is, of no partic-
ular members of the body, and without specific quality, direction,
and velocity of the motion. That certain nervous processes in the
central organs form a ph3'sical basis for the mental phenomena of
ideation and fiat of will there is sufficient ground for believing.
The phenomena of reaction-time show that interrelated cerebral
activities of more and more complicated sort are implied in the in-
creased time required for completing the mental actions of repre-
sentation and choice between two members of an alternative. It
would be a great mistake, however, to regard the mind as having
before it the cerebral machinery, all nicely laid out, together with
the acquired art of selecting and touching the right nervous ele-
ments in order to produce the desired motion, as a skilful player of
the piano handles his key-board. The mind has no native or ac-
quired knowledge of the different ideo-motor areas of the cerebrum.
Even less can we regard the mind, acting under the form of energy
of will, as bringing some stress to bear upon the right centi'es of
the brain, and thus setting them in motion by laying its own hand
to them, as it were. The activity of which we are directly con-
scious under the term "to will " is a purely psychical activity ; it
is marked by no transition of force from the spiritual realm to the
material molecules of the nervous structure. The feeling of effort,
which seems to us to accompanj' the active putting-forth of will, is
itself a resultant of mixed sensations that have a peripheral origin.
The whole description of such transactions of voluntary motion as
are constantly occurring — for example, when we rise to close the win-
dow, take the pen in hand to write, etc. — is as follows : We desire
to have something done ; mental images of the bodily motions and
positions involved in this doing arise in the mind ; the fiat of will
goes forth adopting one of them, and u-illing it, as we say ; an or-
der of nature which has correlated this fiat with certain cerebral
changes, but of which we know nothing whatever directly, and little
through the most searching investigations of science, runs its coiu'se,
and the transaction which we have ideated and willed tnkes place.'
The mind can represent the ideas in consciousness, and issue the fiat
of will ; it can do nothing more. Science can oul}^ conjecture at
' This view of the subject has been repeatedly enforced by Lotze ; see, espe-
cially, the Microcosmus, i. , pp. 283 fE. Edinburgh, 1885.
34
530 NATURE OF BODILY MOTIONS.
present what then takes place. It is to its advancing theory of
nerve-physiology,' and of the localization of cerebral function,'^ that
we must look for more light on the question — What happens in the
brain ivhen the fiat of will issues in consciousness ?
§ 30. Reflection on the foregoing principles makes it obvious
that the different concrete motions of ordinary experience cannot
be assigned with confidence to this or that class exclusively. In
the life of the infant we can trace a general progress from an
almost exclusive predominance of reflex and automatic motions,
through the impulsive, to more and more of the voluntary. But
even in the infant's case no hard and fixed lines can be drawn be-
tween the various classes of motions. It is impossible to say how
much of the constant movement of its legs and arms is reflex, how
much automatic. It is also doubtful how far and how long the
winking of the eyes, the grimaces of face accompanying the stimu-
lating of the tongue, the starting at sound, etc., are reflex rather
than impulsive. The same thing is true of its earlier cryings, mi-
metic and imitative movements, and various ways of thrusting out
and drawing in its limbs in a purposeful way. Nor can the earlier
voluntary motions be confidently distinguished from the impulsive.
This line of inquiry is especially interesting with respect to the
beginnings of articulate speech. A tolerably regular transition
from the sounds in which the earliest emotions express themselves
to the deliberate formation of words and sentences makes it impos-
sible to tell precisely when the child assumes control of its organs
of speech. But our difficulties with the unclassifiable phenomena
of infantile life do not seem so strange when we reflect upon the
fact that the complicated bodily motions of adult life partake at
one and the same time of all the four above-mentioned classes ;
and that precisely the same motions may pass rapidly out of one
class into another. The person, for example, who is balancing with
a pole on a tight-rope, or dancing to music, is involved at once in
motions which correspond to all four of these principal classes ;
and a quick change in circumstances may make any one of the
four more prominent than another. So perfectly may the nervous
mechanism be trained to its work that it may continue to play the
violin in an orchestra after the player has lost consciousness. Yet
the rise and fall of feeling usually serves as a guide to the artist, so
that impulsively his bowing draws nearer the bridge in the cres-
cendo, and nearer the key-board in the diminuendo, passages. If he
plays false or out of time, the sight of the leader's baton, or his own
' Comp. Part I., chaps. III. and VII.
Comp. Part II., chaps. I. and II.
' MOTION AS EXPRESSIVE OF FEELTNG. 531
sensations, may decide him to the fiat of will which changes the
spacing with the left hand oi' the bowing with the right arm.
§ 31. The origin and nature of those motions of the body that
are specifically expressive of certain ideas and feelings constitutes
one of the most interesting fields of inquiry. It is a field, however,
in which comparative psychology, by dealing with the facts of ani-
mal life under the theory of evolution, is particularly successful ;
whereas Physiological Psychology, strictly speaking, has little to
communicate. This little has been summarized by Wundt ' under
three general statements or principles — namely, the princi^Dle of
the direct alteration of innervation, the principle of the association
of analogous sensations, and the principle of the relation of motion
to the presentations of sense. Under the principle of the direct
alteration of innervation are placed those facts which show that
strong emotions exercise an immediate reaction on the central parts
of motor innervation in such a way that many groups of muscles are
lamed at once, and others are excited to tense action followed by ex-
haustion. Hence the tremblings of limbs and organs of speech, the
changes in the blood-vessels and capillaries connected with secre-
tion, the paling of fear, the reddening of anger and shame, the
erect hairs under the influence of terror, etc. The princi]ple of tbe
association of analogous sensations emphasizes such facts as imply
that sensations having a common tone of feeling are most easily
combined, and then operate mutually to strengthen each other.
Under this principle come the mimetic movements of mouth and
nose expressive of disgust or pleasant taste, the postui'ings of the
tongue in connection with ideas of sweet or bitter, the expressive
condition of the muscles due to certain sensations of the skin, etc.
The consideration of the third principle — that of the relation of
motion to the presentations of sense — brings before us the question
of the origin of all the gestures and pantomimic action not account-
ed for under the two foregoing principles. Gestures with eyes and
head and limbs, indicative of extension and relations in space ; the
arrangement of the muscles and skin of the countenance, and the
motions of the eyes under the influence of care, expectation, and
reflection ; the angles of the lines about the mouth and the open-
ings of mouth and nostrils when weeping or laughing, etc., all be-
long under this principle. But the physiology and psychology of
the comic, the science of physiognomy, and of articulation in expres-
sive speech, although properly coming in this connection, lead into
descriptive anatomy and the theory of aesthetics much beyond the
limits necessarily set to our investigation.
' Physiolog. Psycliologie, ii. , chap. 20.
CHAPTER X.
PHYSICAL BASIS OF THE HIGHER FACULTIES.
§ 1. An ardent advocate of " Psychology without a soul " affirms '
that "the study of abstract concepts (time, number, etc.) falls out-
side the province of physiological psychology, and has been made
incidentally only." To be sure, this author has previously ' antici-
pated the time when the science of mind will succeed " in deter-
mining the (physical) conditions of all mental action, of whatever
sort, as Avell of pure thought as of perception and movement," will
— in brief — be " entirely physiological." It is not necessary to in-
quire how these two sentences can be reconciled. But, undoubt-
edly, at present the statement of fact is far better founded than
the anticipation. It is not easy to predict how far psycho-physical
science will be able to push its discoveries in the future ; or just
where it will meet those insuperable barriers which surround all
fields of human inquiry. It is perfectly safe, however, to affirm
of all the phenomena of the so-called " higher faculties " of mind
what M. Ribot says of the study of abstract concepts — they still
" fall outside the province of physiological psychology." Certain
difficulties are so obviously intrinsic and essential to the very nat-
ure of the facts with which this science attempts to deal when ap-
proaching these faculties that we cannot see how they will ever be
successfully met.
§ 2. The foregoing conclusions apply most obviously to the for-
mation of abstract concepts, the conducting of trains of reason-
ing, the exercise of choice, and the activities of the creative imagi-
nation in artistic production, scientific discovery, or mechanical
invention. They apply only less obviously to the higher sesthetic,
ethical, and religious feelings ; although we have already pointed
out certain facts and laws which connect such feelings with a phys-
ical basis. We are also almost as much at a loss how to be " sci-
entific " (strictly speaking) in our treatment of the phenomena
which suggest some kind of physical basis for the action of will
' See M. Ribot, German Psychology of To-day, p. 306. New York, 1886.
''Ibid., p. 15.
THE METHOD OF IT7QCIRY. 633
— especiall}' in the direction of attention for the apperception of
objects of sense, and for the control of the train of ideas or the
movement of the bodily organism. The same thing is true of the
phenomena of memory, whether considered as involving retention
merely or reproduction as vs^ell. All the attempts hitherto made to
explain or deduce consciousness, either in general or in the par-
ticular phase called self-consciousness, from cerebral functions and
activities, have been quibbling and wholly unsatisfactory. Yet
there are indubitable proofs of the dependence of consciousness for
its existence and modes upon the cerebral centres.
The inquiry after the physical basis of the mental phenomena
usually classed as " higher " is, therefore, although peculiarly in-
teresting, peculiarly unjDroductive of assured results. We may sus-
pect that there exist in the nervous elements of the gray matter
of the cerebral hemispheres inherited and acquired peculiarities of
molecular constitution and of dynamical combination, which, if we
could only get at them, would throw a flood of light upon such
mental phenomena. But after all, to speak soberly, we are obliged
to admit that the very existence of such peculiarities is still almost
wholly a matter of conjecture ; while the request for precise and
verifiable information as to their nature, and as to the laws which
connect them with undoubted facts of consciousness, can only be
met by evasion, confession of ignorance, or poetizing and declama-
tion under the garb of science.' Physiological Psychology has a
right to its own hypotheses ; it has, however, no right to introduce
mj^ths about the genesis and marriage and "erethism" of nerve-
cells, and speculation as to nerve-fibres dynamically inclined, into
the domain of either physiological or psychological laws.
§ 3. The only safe method of arriving at the few probable con-
clusions attainable concerning the subject of this chapter is, accord-
ingly, the following : The points of starting and the guides as to
the way must, in nearly every case, be taken from introspective psy-
chology. In studying the higher mental phenomena, j)hysiological
psychology is obliged almost wholly to adopt, as the only direct
path open, the ?!0?i-pliysiological method. Here, at any rate, we
start from that which appears to us as terra firma. We know what
it is to attend, to choose, to remember, and to reason — in short, to
be conscious in some of the many modes or phases of conscious-
ness. Moreover, whatever may be said in disparagement of the
' It is only by such terms as " poetizing" that we can truthfiilly characterize
the greater part of what is said, for example, by M. Luys, in his work on The
Brain and its Functions ; this, while admitting the skill and brilliancy with
which the author treats his own interesting conjectures.
534 PHYSICAL BASIS OF TOLITIOlSr.
" old psychology," it cannot fitly be denied that it has most thor-
oughly and subtly analyzed the phenomena of judgment, memory,
and choice, as these phenomena appear connected with each other
in the flowing current of our conscious life. The result of such
analysis has been secured in the laws of logic, of the association of
ideas, etc., and in the various doctrines of the will and its relations
to motive and conduct. In fact, all study of these mental phenom-
ena from the physiological point of view is compelled to accept in
some form the conclusions of a study of the same phenomena from
the introspective point of view. For example, the reproduction of
ideas under the so-called laws of association is a general fact of
consciousness ; in the attempt to explain this fact according to
j)sycho-physical causes we are obliged to rely upon the results
reached by the introspective psj'^chology. The application to men-
tal phenomena of uncouth terms derived from the physical sciences
— such as " asfGflutination," " ac'^iomeration," "cohesion," "organic
phosphorescence," "histological catalepsy," etc. — has simply the
effect of repeating certain psychical facts and laws in a less appro-
priate way, without adding an item of information regarding the
real nature of their physiological basis. Ideas, or states and prod-
ucts of consciousness, cannot — speaking litei'ally — cohere, or be-
come agglutinated or agglomerated ; and we need some better
proof than mere declamation to show that these states and prod-
ucts depend upon any physical processes resembling agglutina-
tion, phosphorescence, or catalepsy of the nerve-cell. Physiological
psychology is obliged, then, to accept certain conclusions of the
psj'chology of self-consciousness ; otherwise it has no motif ox guide
in its investigation of the higher mental faculties.
But while our conscious psychical experience of the higher men-
tal activities is so far obvious as to make that side of the subject
capable of scientific statement, our knowledge of the physiological
processes connected Avith those activities is in jDrecisely the oppo-
site condition. Over and over again the confession has been forced
from us that — strictly speaking — a scientific physiology of the
cerebral hemispheres does not yet exist. We can only dimly con-
jecture what takes place in the nerve-elements of the cortex of the
cerebrum as the physical basis of conscious sensation and percep-
tion. The molecular physics, or general nerve-physiology of the
nerve-muscle machine — the simple peripheral nerve with muscle
attached — is in a very unsatisfactory state. A science for the vast
complex of nerve-cells and nerve-fibres which exists in the gi'ay
matter of the brain proper is at present scarcel}' a matter for even
hopeful anticipation. Faint and doubtful guesses, more or less
AUTOMATISM OF CENTRAL OKGANS. 535
intimately connected with general principles of molecular physics
and physiology of the nervous system, are all that can appear in
the name of such a science. But the very business of physiological
psychology is to connect together under general laws the mental
phenomena, on the one side, and the ascertained facts of physiol-
ogy, on the other side. In this case, we are tolerably equipped
with information as to the former ; we have little but unverifiable
assumption to take the place of the latter. In attempting the in-
quiry into the physical basis of the higher faculties (the physio-
logical psychology of volition, memory, conception, etc.), no other
course is open but to accept the facts of consciousness, and then
speculate as to how they may, perhaps in part, be accounted for by
a conjectural extension of certain physical and physiological facts
to the cerebral hemispheres. This procedure certainly cannot be
called "science ;" it is, however, the only one open instead of a
confession of complete ignorance.
§ 4. The mental phenomena of the higher order, concerning whose
physical basis conjecture is most plausibly supported by a number
of related facts, may be divided into two great classes. One of
these covers the phenomena of Will, in the forms of attentive per-
ception and the effort determining the extent and character of the
field of consciousness ; the other covers the phenomena of Memory,
whether considered as the retention or the reproduction of ideas.
Certain conjectures as to the physical basis of both these kinds of
mental activities are in good degree warranted by the principles
discussed in the foregoing chapters.
The physiological basis (so far as such basis can be said to exist)
for those mental phenomena which appear in consciousness as "acts
of will " is laid, in general, in that power of automatism which is
concentrated, so to speak, in the nerve-cells of the central organs.
Automatism, or the power of originating motions which cannot be
explained as due to external stimuli, is indeed in some sort a
property of all living protoplasm ; but in that elaborate differentia-
tion of structure and function which the human body exhibits, the
nei've-cells of the central organs have absorbed this power and be-
come distinctively automatic. To them chiefly does it belong to
initiate within themselves the molecular changes which are neces-
sary to keep the body, both as a whole and in its several parts,
adjusted to the changes of its environment. It is sometimes said
that " an amoeba has a will of its own." Our only right to speak
in this manner is derived from the fact that many of its formal
changes seem to arise from within, and are quite inexplicable under
any known laws of merely reflex motion. If we raise the inquiry
533 PHYSICAL BASIS OF VOLITION.
whether such automatic changes of its molecular structure are ac-
companied by anything which corresponds to what we call conscious
volition, it must be admitted that we are quite unable to answer
such an inquir3^ We can easily imagine the amoeba, however, to
have a consciousness of an " act of will " as an accompaniment of
each automatic change in the arrangement of its molecules. A
large part of man's activit}' in the control of his bodily organism,
we know, is unaccompanied by any conscious volition. Such un-
conscious but purposeful activity belongs to the spinal cord and
to the lower cerebi'al centres, which act both reflexly and automat-
ically under the laws of acquired skill and of habit. In this way
many even of our so-called voluntary movements really take place.
But some sudden emergency — as, for example, the sight of a
threatening object, a change in the character of the soil on which
the pedestrian treads, the parting of a rein in the rider's hand —
may call for a succession of distinct and intense acts of will. And,
ordinarily, mild and rather obscure volitions connected with the
movement of the body intermingle with the succession of sensa-
tions and ideas which compose the principal material of con-
sciousness.
In all such cases as the foregoing we have reason to suppose
that, either through external or internal stimuli (either through
sensory impulses coming in along the centrijpetal nerve-tracts or as
started by changed conditions of blood-supply), the nerve-cells of
the cerebral hemispheres are called upon to exercise their peculiar
functions. Such functions we may well believe are always both
reflex and automatic ; that is to say, the nerve-commotions which
issue from the cells are dependent for their intensity and charac-
ter both upon the excitations coming to them from without and
also upon their own internal molecular structure and condition —
especially as respects the blood-supply. Accordingly, it must be
held that volitions, or acts of will in consciousness, do not have
their physical basis in any special organ or area of the brain.
Tkere in no special organ of loill. All the central organs have pre-
eminently the projDerty of automatism. But since, in the case of
man at least, it is only on occasion of a certain kind and degree of
activity of the cerebral hemispheres that what takes place in the
nervous system has any corresponding expression in conscious-
ness, the physical basis for acts of will in general is the automa-
tism of these hemispheres in general.
§ 5. All act of will, however, is always an act of some special kind.
There can be no volition to motion in general, but only a volition
defined and limited to the movement of certain limbs, or of the
SIGNIFICAlSrCE OF SPECIAL AEEAS. 537
trunk including the limbs, with a certain direction and degree of
motion. Thus also every act of will for the control of the mental
train, or for the apperception of an object of sense, through con-
centrated attention, is defined by some particular mental state or
modification upon which it is directed. We have seen good reason
to believe that certain areas of the cerebral cortex are especially
connected with certain corresponding sensory-motor activities
(comp. Chap. II. throughout). In the same areas, then, the physical
basis is laid for those acts of will that are concerned with the
corresponding activities. The acts of will which have to do with
the movement of the upper and lower limbs, for example, im-
ply the special activity of the cerebral areas on either side the
Fissure of Rolando ; those acts of will that have to do with the
movement of the organs used in articulate speech are especially re-
lated to the areas lyiug about the lower part of the Fissure of Syl-
vius— the posterior third of the lower frontal convolution, etc. We
have no sufficient ground for locating in one circumscribed spot
the physical basis of such acts of voluntary attention as concern
the different presentations of sense and the images of memory de-
rived from them. The case is not as though the mind made a
transit, as it were, from some special seat of intelligence and will,
to contemplate with attention and pronounce upon the complicated
sensory impressions which have arrived and been elaborated in the
particular sensory areas ; or as though it travelled from adjacent
parts to lay its grip upon the right motor areas when sensation or
desire indicated to will that certain groups of muscles should be
innervated. Whenever an act of will takes place, then at the cerebral
area lohich corresponds to the particular nature of the act (namely,
the will to attend to this object of sense, or to start in motion that
limb) the particrdar molecular changes arise in the nerve-cells which
are correlated toith such mode of consciousness.
§ 6. As to the relation in time which is maintained between the
conscious act of will and the particular form of automatic cerebral
excitation which we have called its physical basis, it is not possi-
ble to pronounce with confidence. But there is no good reason
to suppose that the conscious mental act is interpolated as an
independent element of time, so to speak, among the physiological
processes. The flow of consciousness from obscure sensation to
perception and clear attentive discernment, then to the act of de-
cision between two or more possible forms of appropriate movement,
and, finally, to the issue of the right fiat of will, all keep pace with
the corresponding physiological processes in the cerebral areas.
As to the exact nature of these processes, and as to how they fur-
538 PHYSICAL BASIS OF VOLITION.
nish necessary conditions to the mental movement, there is no in-
formation to be imparted.
§ 7. The problem is complicated when our consciousness becomes
one of deciding to which of several presentations of sense or im-
ages of memory we will to direct the attention. " Concerning the
physiological processes," saysExner,' " from which we abstract the
conception of attention we know absolutely nothing." This is true
even when attention seems determined or forced upon us by causes
over which the mind has no control ; it is, of course, more obviously
true when the mind is conscious of deliberation and choice. The
attention which directs to the single object and heightens the clear-
ness of our perception, converting it into an "apperception," may
properly be spoken of as an act of loill ; but starting from the point
of view of consciousness, it must be admitted that, in the majority
of such activities of apjjerception, there is no consciousness of choice
^— the will is determined in one way. This is equally true of the
attachment of attention to certain particular images of the mental
train, as that train is conducted along under the laws of association.
Most things which we clearly perceive, or feel with any decided
jDain or jDleasure, or which are vividly brought before the mind as
images of memory and imagination, we cannot help attending to.
The sudden flashing of a light, the passing of a bright object across
the field of vision, the occurrence of a loud noise, or of a fainter
one with a character that interests us, the smells in the atmosphere
and the taste of om- food, the sensations of the internal organs and
of the skin, when sufficiently intense — all these compulsorily draw
after them the attention. They get themselves perceived by an im-
pulsive and involuntary act of will. So, too, do the revived images
of memory, in ordinary circumstances where the perception of ex-
ternal objects is relatively suppressed, appear to force themselves
upon the attention.
In view of the foregoing familiar facts of consciousness, we may
conjecture that when the cerebral centres are not preoccupied, as
it were, with contradictory forms and phases of nerve-commotion,
certain processes set up within them, whether due to external stim-
uli or to changes in the blood-supply, are necessarily followed by
the phenomena of conscious attention. Even when these centres
are largely thus jjreoccupied, similar changes may be rapidly forced
within them, by the action of some very strong excitation from the
end-organs of sense, or from some connected cerebral centre. Hence
the shock of surprise which sudden and vehement impressions cre-
ate. In all such cases oi forced attention the resulting tone of feel-
' In Hermann's Handb. d. Physiol., II., ii., p. 283.
THE DIKECTIOlSr OF ATTENTIOTT. 539
mg in consciousness is different from that which prevails when the
choice to attend is being dehberately maintained or persistently
revived. The motifs of much of our activity of will in attention,
therefore, plainly lie in that state of the cerebral centres which is
compelled by the intensity of the stimulation they receive (either
from external or internal stimuli).' If there were no other phe-
nomena of will than those of forced attention, it would be necessary
to admit the probability that all the mental activities are purely
mechanical and absolutely dependent upon the action of the ner-
vous system under the exciting influence of stimuli.
§ 8. Certain phenomena of will in the form of attention suggest
conclusions of a different order from the foregoing. Taking our point
of starting again from consciousness, we know by a manifold expe-
rience that the different degrees of clearness with which we perceive
objects or apprehend the images of memory implies a graded appli-
cation of attention. The grading of this application of attention is
by no means always determined solely by the intensity of the stim-
ulus, so far as we can measure such stimulus. It is a principle of
wide reach, that — to quote the words of Wundt — "the degree of
apperception is not to be measured according to the strength of the
external impression, but according to the subjective activity by
which the consciousness is applied to a definite sense-stimulus."
The subjective activity which applies the consciousness, as it were,
to this or that ^presentation of sense or image of memory, rather than
to some other, is an activity of will ; and the effect of the activity is
seen both in heightening the attention as directed to the object, and
also in adapting the attention to the particular object upon which it
is directed. Accompanying this twofold control of attention, and
indeed forming the veiy basis upon which it rests, when deliberately
exercised, is the consciousness of " choice " — the activity of will in
deciding the direction and amount of attention bestowed upon one ob-
ject among several in the f eld of consciousness. Percepts and ideas
do not move from the various obscurer parts of the field of con-
sciousness into the focal point by virtue solely of a momentum be-
longing to them as such ; they are placed and kept there by an act
of will. This must be admitted as an indubitable fact of conscious-
ness, whether or not the physiological correlate or so-called explana-
i tion of this fact can be discovered or even conjectured.
Many indisputably valid phenomena, both those accessible to
ordinary observation and those discovered by special experiment,
' Comp. Wxindt, Physiolog. Psychologie, ii. , pp. 387 ff.; and Stande, Der Be-
griff d. Apperception in d. neueren Psycliologie, Pliilosoph. Studieu, I., Heft
ii., p. 194 f.
540 PHYSICAL BASIS OF VOLITIOX.
illustrate the foregoing principle. By an act of will attention may
be heightened and accommodated to the object, with a marked in-
fluence ujDon apperception and the association of ideas. Upon this
point we have to recall facts already mentioned. The effect of a
voluntary increase of attention upon the reaction-time is to diminish
it, of distracted attention to increase it or destroy its value alto-
gether.' If, simultaneously, the ear is stimulated by the periodic
strokes of a bell, and the retina by regularly recurring electrical
sparks, the attention will naturally be directed to the former ; the
image of the latter will then be located only very obscurely in the
flow of consciousness, and the time of its occurrence may scarcely
be noticed at all. We incline to attend to the stronger of two ex-
citations of sense ; to yield to the inclination depresses the weaker
still further — perhaps below the plane of conscious perception.
But within certain limits we attend where ive ivill. We also incline
to attend to objects lying in the point of regard of the field of
vision, but we can will to attend to objects lying in the outward
portions of this field.'* The voluntary direction of attention in this
case determines the apperception of these objects to the neglect of
those lying in the more favorable parts of the field. We can at-
tend to the field of vision of one eye, neglecting the other, as skil-
ful microscopists do. We can see by voluntary attention the other-
wise invisible double images. It is claimed by some experimenters
with the " conflict of colors " in binocular vision, that, by the direc-
tion of .attention, when a green image is formed on one eye and a
red upon the other, they can see either at will, or at will can com-
bine the two.
Experiments with instantaneous illumination by the electrical
spark also demonstrate in a marked way the effect of attention.
Objects which under ordinary circumstances are without great effort
seen, either as stereoscopic or as double images, can also be seen
in both ways by the electric spark, according to the direction of
attention. The first impression is ordinarily stereoscopic ; but if a
pause of 10 sec. be allowed for the after-images to die away, the
experimenter can at will see the double images, although the point
of fixation and the influence of the light remain absolutely the
same.^ The effect of attention in analyzing composite musical
' See the table of Obersteiner, Brain, I., p. 439, to show the fluctuations of
the reaction-time of a person reacting while an organ was playing in the same
room. The normal reaction time of the person being 0.100 sec, it rose to
0.148, and even 0.215, while the instrument was heard, and fell to 0.095 and
0.087 during pauses in the playing.
-' See Helmholtz, Physiolog. Optik, p. 740 f. '■^ Ibid., p. 741.
EFFECT OF ATTENTIOIST OJST MEMOEY. 541
clangs into their elements is equally marked.' In addition to a
previous acquaintance with the character of such over-tones as are
to be expected and analyzed out of the clang, the analysis can take
place in no case w^ithout a " certain undisturbed concentration of
the attention." That changes in the clearness of perceptions take
place in dependence on the changes in the degree of attention is a
matter of the most ordinary experience. On waking gradually
from sleep our surroundings become less and less obscure to the
senses of eye, ear, and skin, as the grade of voluntary attention in
apperception progressively rises. On casting the glance casually
upon a landscape seen through a window, its objects are, at first,
scarcely perceived at all ; by gradual increase in the intensity of
attention (changing the casual glance into a steady look) these
objects become apperceived more and more clearly. The voluntary
concentration of attention (comp. p. 446 f.) often dissolves an error
of sense or changes the entire appearance of the visual object On
the other hand, a great strain of attention may lead one to anticipate
an expected impression of sense, and perceive its occurrence before
it has actually taken place. It may also cause other illusions, as
when, on expecting eagerly the stroke of the clock, some weaker
sound may be mistaken for it."
§ 9. Voluntary attention directed toward the images of memory
has also a marked effect upon their character and duration in con-
sciousness. In certain cases it may impart to them the vividness
of presentations of sense, although the power to bring this about
differs greatly for the different senses and in different individuals.
By an effoi't of will the player of a musical instrument can cause
himself to feel again the revived images of the muscular and tactual
sensations which accompanied a particular exercise of his skill.
The hearer of some impressive musical air may voluntaril}' set it
running, with its variation of tone and rhythm, through his mind's
ear, as it were. Not to speak of hallucinations and visions, most
men see sights in dreams, and even in reverie, that closely approach
the intensity of the presentations of sense in the waking state and
in broad daylight. Artists in forms of art involving a special sus-
ceptibility and activity of some one or more of the senses, are, of
course, gifted with a specialized creative energy of imagination.
Particular images of memory may be seized upon at will, as it were,
and the attention so concentrated upon them as to impart to them
much of the strength which their originals enjoyed.
Moreover, the effect of attention upon certain images of memory
' Helmholtz, Die Lehre von den Tonempfindungen. etc., p. 84 f.
* See Fecliuer, Eiemente d. Psycho-pliysik, ii., p. 491 f.
542 PHYSICAL BASIS OF VOLITION".
is such as apparently to localize them anew in the organs by which
these originals were formed. To try to revive a melody as distinctly
as possible produces a sense of strain (a feeling of being innervated)
in the region of the ear. We recall sounds, especially if we recall
them vividly, with the organs of hearing. The prolonged effort to
recall or image colors or visual forms tires the visual organs ; the
impression is as though the recollection or imagination were accom-
plished in and through these organs. The violin-player remembers
and goes over the solo he is to play, not only in his ear, but in his
arms and fingers. Upon such power of reproduction the power of
new jDroduction depends. Indeed, we may say that " the activity
of voluntary sensuous attention largely consists in a voluntary re-
production of earlier conditions of sensations." ' It has even been
claimed that vivid representative images of color-sensations may be
followed by the corresponding negative after-images.^
§ 10. Concerning the physiological basis of the phenomena of
voluntary attention, little is known. Apparently, j^art of the effect
must be due to the changed condition which is brought about in
the end-organs of sense when especially innervated and so j^repared
for receiving the stimulation approjDriate to them. To this fact is
due the peculiar feeling of strain in the oi'gan of attentive apper-
ception, or of vivid reproduction of the image of memory. But
the chief effect of attention is realized in the altered condition of
the cerebral centres. It is only obvious, according to Exner,' that
we have to do with changes in the central. mechanism set up by act
of will, and that these changes vary quantitatively and concern the
circles of our psychical activity. Moreover, the point of attach-
ment, as it were, for the attention is found only after the impres-
sion of sense has been elaborated to a certain degree. We cannot
voluntarily attend without perceiving, at least obscurely, that to
which (presentation of sense or image of memory) attention is to
be directed. Still further, fluctuations of the cerebral activity
are constantly occurring ; for, as every one knows who has expe-
rimented with himself (for example in determining reaction-time),
it is impossible to keep attention on a perfectly steady stretch with
respect to its object. Waves of consciousness in connection with
these fluctuations of attention rise and fall.'' In the most suc-
cessful reactions the attention is effectual in producing and main-
' Comp. G. E. Miiller, Zur Theorie d. siiinliclien Aufmerksamkeit, Leipzig,
p. 89.
^ Wundt, Vorlesungen iiber Mensch u. Thier, I., p. 387.
' In Hermann'.s Handb. d. Physiol., II., ii., p. 283.
* Comp. Fecliner, Elemeiite d. Psycho-pliysik, ii , p. 452 f.
INFLUEISrCE OF THE FRONTAL EEGIONS. 543
taining a state of strained expectation, in which the occurrence of
the expected stimulation sets the motor mechanism off without, and
even in spite of, a separate act of wiU. In such cases the cei'ebral
centres have apparently been thrown into an exalted and explosive
state of irritability. We all know that very little suffices to set the
muscles agoing when the mind is on the stretch. It is not unlikely
that the effect of attention is felt in depressing certain cerebral
areas not intimately connected with the production of the particular
image of memory or presentation of sense, as well as in heightening
the activity of others that are thus connected.' The phenomena, at
any rate, imply an increased difference of excitability and conductivity
for their specific forms of nerve-commotion in the different cerebral
areas. Under the influence of attention the cerebrum has become
more susceptible for certain impressions, less so for certain others.^
Stored energy of the nerve-cells is being rapidly called forth. Con-
centrated voluntary attention implies a large amount of ivork being
done in the cerebral hemispheres. We recognize this fact in the ac-
companying feelings of strain and in the subsequent feelings of
brain -exhaustion. The subject of experiment to determine the
reaction-time under concentrated attention often, though sitting
quiet, sweats profusely.
§11. What happens when two different excitations, arising either
from conflicting presentations of sense, or conflicting ideas, meet in
any single region of the brain ? We can only answer this question
with vague conjecture. The phenomena of the conflict of colors in
binocular vision seem to imply that either the more intense of the
two may prevail over the other, or the two may both persist and
interpenetrate as it were. In certain cases voluntary attention
may determine which event shall ensue. The sugar sweetens the
acid of the lemonade, not in the vessel which contains it or on the
tongue which tastes it, but in the brain. According to the con-
jecture of Wundt,^ the frontal regions of the cerebrum are the
"bearers (Trdger) of the physiological processes which accompany
the apperception of the presentations of sense." In order, then,
that the process set up in any cerebral region by an excitation of
the organs of sense connected with it may result in clear discern-
ment of an object, certain physiological processes must be con-
ducted from the frontal regions to that region. Wundt's con-
jecture is plausible, at least it gives the frontal region something
to do, and answers in part the inquiry why so much of the cere-
' See G. E. Miiller, Zur Theorie d. sinnliclieu Aufmerksamkeit, p. 52 f.
- See Exner, in Pfliiger's Arcliiv, xi., p. 428.
^ Physiolog. Psycliologie, i. , p. 218.
644 PHYSICAL BASIS OF VOLITION.
bral substance should seem merely negative as respects the phe-
nomena of sensation and motion.
§ 12. Nothing thus far said, and nothing of scientific value which
physiological psychology has to offer, throws any clear light on the
problem of the "freedom of the will." When M. Luys,'" for exam-
ple, maintains that to imagine " we think of an object by a spon-
taneous effort of mind is an illusion," and that, in fact, the object is
only forced on us by the cunning conjurer, the brain, "because the
cell-territory where that object resides has been j)reviously set vi-
brating in the brain," he is controverting a plain and universal
dictum of consciousness by his private and unverifiable hypothesis
on a question of cerebral physiology where exj^erts and novices are
alike ignorant. Physiology neither disproves nor verifies the post-
ulate of free will ; accordingly, this postulate must be raised and
discussed upon other grounds. Metaphysics and ethics cannot
properly dictate their facts and conclusions to the science of physi-
ological psychology ; but, in turn, this science cannot properly
dictate to metaphysics and ethics the conclusions which they shall
draw from facts of consciousness, by giving out its myths and fa-
bles in the garb of well-ascertained history of the cerebral pro-
cesses.
§ 13. Consciousness, or the having any form of sentient life, in
distinction fi'om being in a condition of dreamless sleep or swoon-
ing, and Self-cousciousness, or the recognition of the states of con-
sciousness as states of the ego or subject of them all, are inti-
mately connected with the johenomena of will. By the amount
and speed of the energy expended in attention we measure in large
degree the extent and intensity of consciousness. The stir of feel-
ing through the presentation of some object of sense, or through
some idea, causes us, either voluntarily or involuntarily, to rouse
ourselves to what is then recognized as a wider and higher energy
of consciousness. But inasmuch as consciousness is the condition
of all internal experience whatsoever, we cannot deduce or explain
the essential nature of consciousness from other forms of such ex-
perience.^ For the same reason we cannot define consciousness.
Concerning the physical basis of consciousness little can be added
to Avhat has already been said concerning the physical basis of
the various foi-ms of consciousness. Consciousness is never con-
sciousness in general — never an activity or state that ma}- be sep-
arated from the individual states and processes of consciousness.
In the case of man, the cerebrum is apparently the sole, as it cer-
' The Brain and its Functions, p. 254.
' Comp. Wundt, Physiolog. Psytfliologie, ii. , p. 195 f.
CONDITIONS OF CONSCIOUSNESS. C45
tainly is the chief, organ of consciousness (comp. pp. 249 ff.). By
calling the cerebrum the " organ " of consciousness, however, little
more is meant than that the constitution and processes of the ner-
vous matter of this organ are related in the most immediate and
special way to all mental phenomena, and that what takes place in
material elements outside of the cerebrum (including the elements
of the other portions of the nervous system) has an effect iipon con-
sciousness only in case it gets itself represented, as it were, in the
corresponding cerebral processes. As to a special organ of con-
sciousness in the brain — that is, a cerebi'al area where the mind
comes to consciousness — it is not proper to speak.
Accordingl}^, the physical basis of the diiferent forms of con-
sciousness is laid in those cerebral areas which have been found
to be — or, though still undiscovered, actually are — especially con-
nected with these forms. But if the question is further pressed as
to the physical basis for the activities of self-consciousness, no answer
can be given or even suggested. From its very nature that mar-
vellous verifying actus of mind in which it i-ecognizes itself as the
subject of its own states, and also recognizes the states as its own,
can have no analogous or corresponding material substratum. It
is impossible to specify any physiological process representing this
unifying actus ; it is even impossible to imagine how the descrip-
tion of any such process (in case we knew what to attempt to de-
scribe) could be brought into intelligible relation with this unique
mental power.
In general, concerning the physical conditions of consciousness, it
is known that they are dependent upon the character and amount
of the blood-supply. To stop this supply is to put an end for the
time to consciousness ; to impede or corrupt it is to depress and to
disturb consciousness ; to alter its character is to affect, more or
less promptly and profoundly, the character of consciousness. The
character of the circulation in the cerebrum largely determines the
nature of the phenomena of consciousness. Quickened circulation
here accelerates or agitates the circuit and time-rate of conscious-
ness ; slower circulation diminishes and inhibits them. It has
been alleged by Mosso that certain changes in the relative circula-
tion of the human body occur when the attention is occuj^ied in-
tensely either with external imj)ressions or with psjThical work.
Such observations are not as yet extended and accordant enough
to command unhesitating assent to the details of their results.
§ 14. The other group of so-called higher mental phenomena
which admits of the most of probable conjecture regarding the nat-
ure of its physical basis comprises Memory, as retentive and re-
35
546 PHYSICAL BASIS OF MEMORY.
productive, and the laws of the Association of Ideas. The experience
of consciousness is one of a constantly changing succession of states.
The rise and fall in voluntary or involuntary attention, and the
change of its direction, are accompanied by a continual alteration
of the phases and of the circuit of consciousness. Of these shifting
mental states certain ones bear the peculiar mark of a claim to rep-
resent previous states of consciousness, in some regard and to some
extent similar to themselves. The image of memory is itself a prod-
uct, a phase, of present consciousness ; it is not itself of the past,
and yet it claims, by virtue of its essential character, to stand for
the past. This claim can, of course, in no instance be verified by
carrying the consciousness back to that past ; we are never able by
attentive apperception to compare the image of memory with its
alleged original and thus make sure of the validity of the claim.
Experience also teaches us that the mental images do not come
and go wholly at random and irrespective of the characteristic con-
tent of such as are most closely connected in time. That these
images are associated in time is a part of the fundamental fact of
memory ; mental states are not states of memory without some
more or less definite localization of the ideas thus presented to the
mind with reference to its past.
Further examination of the particular character of the ideas
which most frequently occur simultaneously, or in closest succes-
sion, has given rise to the assumption that the images of memory
are associated in a regular way. Hence those general facts of psy-
chology called the "laws of the association of ideas." From the
phenomena of memory and reminiscence, as experienced in the
consciousness of the individual, arises the belief that the objects of
past experience are retained in the mind, and that they suggest each
other (at least ordinarily) in some orderly way. But properly
speaking, the " retention " of states of consciousness, whether of
ideas or of presentations of sense, is not a faculty or power of
mind. To ask, Where is the idea I once had, or the object I once
saw, between the time of the original experience and the time of
recall, is to ask a question that can have only one answer. Such
idea or presentation of sense is nowhere, for it does not exist in
any sense of the word whatever. Both presentation of sense and
image of memory are transitory phases of consciousness, each per-
ishes with that phase of consciousness in which, and as which, it
has its existence. It is the power of recall solely which induces us
to speak as though the mental object were retained or kept in the
Mind. It is only m the facts and laws of conscious reproduction that
any trace of the activity of mind, as memory, is to he found. Much
PRIMAEY IMAGE OF MEMOKT. 547
" cerebration " may be unconscious ; there may be considerable
periods of complete unconsciousness in tlie daily life of every indi-
vidual, as there certainly are such periods occasionally^ in the lives
of some individuals. But of unconscious retention or reproduction
of ideas as an activity of mind, there is none.
§ 15. Both ordinary observation and experiment in reaction-time
indicate that the speed with which the images of memory vanish
depends upon a variety of circumstances — such as individual pe-
culiarities, intensity and frequency of the repetition of the original
impression, condition of the cerebral centres and of the conscious-
ness at the time of this impression, etc. The thousands of faint
impressions which enter into every-day life seem quickly to A^anish,
without leaving a trace behind in either body or mind. But that
these impressions do linger for a time in memory, as we say, or
are reproducible in consciousness under the form of images of
memory, there can be no doubt. For example, if, while one per-
son is intently counting the lines of a page or adding a column of
figures, another near by makes some slight motion, the image of
the motion in the mind of the former may be recalled within a few
seconds of the occurrence ; a little later, however, such an image
may have so completely vanished that the observer will declare the
motion was not noticed at all.' The vividness of fresh images of
memory may be so great as even to make it difficult to distinguish
them from true presentations of sense. But even in the case of
impressions made clear and strong by the strenuous concentration
of attention, the vividness of the image of memory diminishes at
first very quickly. Even in such a case the so-called " primary ''
image of memory may not last beyond a few minutes ; while in
cases where there is little attentive apperception this image van-
ishes in a few seconds.^ Let a hne of given length be regarded for
a brief time, then removed, and after a varying interval the eflbrt
made to recall its image so as to compare it accurately with another
line of nearly the same length. It will be found that the clearness
of the image of memory, which quickly falls off at first^ falls off
afterward more slowly, and finally approximates more nearly to a
stationary condition. Lotze ^ has insisted upon the caution that
we should not confuse the clearness of ideas with their intensity ;
the idea of the most intense brightness is not intensely bright. Yet
we cannot agree with Lotze in the opinion that the ideating activity,
when applied to the recall of sensations, does not diflfer in intensity
' See Exner, in Hermann's Handb. d. Physiol., II., ii., p. 281 f.
'^ Comp Fecliner, Elemente d. Psycho physik, ii., p. 491.
^ Outlines of Psychology, p. 28 f.
548 PHYSICAL BASIS OF MEMOllY.
as well as in clearness. Besides the difference in the clearness with
which two persons, for example, remember a mosaic of colors, as re-
spects all the details of what particular colors were arranged in what
particular order, there is also a difference in the strength which the
various revived images of the colors have in the two consciousnesses.
§ 16. That the mental phenomena which lead us to speak of the
retentive power of memory have a physical basis there can be no
doubt. This conclusion is warranted by the nature of the phenom-
ena themselves, by the impossibility (already alluded to) of con-
ceiving of a permanent modification of unconscious mind, and by
all that we know of the principles of biology in general and of hu-
man physiology in pai'ticular. Every sensory impulse, and every
combination of such impulses, must produce changes both in the
end-organs and in the central organs ; and although these changes
vanish, so far as their effect in the corresponding phenomena of
conscious mind is concerned, they nevertheless cannot fail to leave
the organs in different condition from that in winch they found
them. As a matter of course, the effect of stimulus upon every
end-organ of sense consists in the production of molecular changes,
which, on account of the principle of inertia as applied to such or-
gan, continue for a time after the stimulus has been removed. Of
this fact the existence of the after-images on the retina is the most
notable example. The successive stages passed through by the af-
ter-images, both jDositive and subsequently negative, are themselves
indicative of a sei-ies of molecular changes set up by the action of
the stimulus. But the effects of stimulus must also be felt in the
production of molecular changes in the central organs, in the nerve-
elements (especially the nerve-cells) of the cei'ebral hemispheres,
if the sensory impulses are to result in conscious sensation and per-
ceiDtion. Experience would then lead us to infer, farther, that each
combination of sensations produces changes in the cerebral hemi-
spheres which outlast the action of the stimulus upon the end-organ
of sense. A study of consciousness, simply as consisting of chang-
ing sensations and perceptions, might appear to indicate that the
after-forms of molecular changes themselves die out and leave the
end-organs and cerebral centres in precisely the same condition
as before. But the formation of habits of perception and motion,
the phenomena of conscious mental reproduction, and the general
principles of molecular science as applied to the nervous mechan-
ism, suggest and enforce another view.
Certain experiences in the use of the senses show that molecular
activities induced in the end-organs by stimulation may, under cer-
tain circumstances, persist much longer than we are at first inclined
rOEMIiSTG OF MOLECULAR TENDEISTCIES. 549
to suppose. For example, a study of the after-images left by
strong impressions on the retina shows that traces of them recur
again and again, even several minutes after the eyes have been
closed. Prolonged work with the microscope will cause the images
seen in its focus to " live in the fundus of the eye " so that, after
several hours, shutting the eyes will cause these images to reappear
with great distinctness. Of a similar kind is our experience with
sounds — the rattle of the railroad-car after a long journey, the im-
pressive cries or words to which we have listened, the successive
notes and chords of the musical composition heard at a concert,
seem to be repeated in the ear for hours after the primary sensa-
tions have subsided. According to Dr. Moos,' after long musical
seances the sounds persisted for fifteen days in one patient ; and a
professor of music was accustomed to hear over again the notes
sounded, for several hours after each lesson. After startling and
impressive experiences with different kinds of sense-percepts —
sounds, sights, etc. — it is not an uncommon thing for the same
bodily affections to recur with such vividness as to make it almost
impossible at the instant to distinguish them from fresh experi-
ences of the same kind.
Moreover, all those inherited and acquired unconscious habits of
motion, with which the study of the nervous mechanism has already
made us familiar, imply that the effects of repeated stimulations
persist in the molecular constitution and tendencies to molecular
change of the nervous substance of the central organs. The puppy
which has inherited a brain and spinal cord embodying the habits
of his race, and the trained gymnast or skilled player on a musical
instrument, alike illustrate this principle of stored and organic ex-
perience as pertaining to the elements of the nervous system. The
general principle of molecular science, which finds numerous ex-
amples both in inorganic chemistry and in biology, compels a
similar conclusion as to the physical basis of memory. The estab-
lished practice of jDhotography depends ujDon the fact that a plate
of dry collodion, after being briefly exposed to the sun's rays, re-
tains for weeks, in the darkness, the effects of the indescribably deli-
cate changes which have been brought about in it. The " latent
image " contained in it may be revived by proper treatment. The
phenomena of phosphorescence, also, show that the impressions of
the luminous undulations persist in certain bodies for a consider-
able time after these undulations themselves have ceased acting.
Niepce de Saint- Victor "^ has shown that such undulations may be
' So Lays, The Brain and its Functions, p. 136.
- Comptes-reudus de 1 Academic des Sciences, xlv. , p. 811 ; and xlvi., p. 448.
550 PHYSICAL BASIS OF MEMORY.
" to some extent garnered up in a sheet of paper," ready to be re-
vealed at the call of special reagents. Inasmuch as the nervous
system consists of an inconceivably complicated and delicate molec-
ular mechanism, every element of which may be regarded as a
highly complex molecular structure, it may well be expected to ac-
complish much more wonderful results than the plate of dry col-
lodion or sheet of paper, in the way of storing up for future de-
maud the results of the impressions made upon it. We may even
go so far as to say that the retentive power of this molecular mech-
anism is perfect ; that it never loses entirely the effect of any im-
pression once made upon it.
§ 17. In view of such considerations as the foregoing it has been
proposed by some writers to regard memory simj^ly as one phase
of the general biological fact, as a particular form of synthesis " of
one of the primordial properties of the nervous elements." Con-
scious memory- is then considered as "a phosphorescence of the
nervous elements " pZws consciousness ; and this power of these
elements itself is to be called a power of " unconscious reminis-
cences " (M. Luys) or an " oi-ganic memory " (Hering and M. Ribot).
But, while admitting the general fact of molecular science, and the
application of it to the phenomena of habit in the nervous mechan-
ism as contributing something to the description of the physical
basis of conscious memory, it is wise to refuse to use such terms as
the foregoing. For tJiese terms are not needed to state the facts ;
of themselves they lend nothing to the desired explanation, and
they are liable to lead to serious confusion. " Organic" memory,
or the habitual mode of the behavior of the nervous system, to-
gether with that tendency to reproduce the mode which belongs
to all habits, when minus consciousness, is not memory at all ; it
bears, indeed, no resemblance to memory. " Unconscious " reminis-
cence, regarded as a function of material elements, is not reminis-
cence at all.
Moreover, when we inquire as to precisely what constitutes this
wonderful jjower of conserving the results of molecular changes
induced by the action of stinmli, which the nervous system pos-
sesses, we find it impossible to give a wholly satisfactory answer.
The most plausible answer consists in inferences touching the
highly probable apj^lication of certain biological laws to the special
case of the nervous system, regarded as furnishing a physical basis
for the phenomena of memory. The general fact from which these
inferences take their point of starting is undoubted ; the entire
nervous mechanism must be regarded as a vast system of interrelated
elements (nerve-iibres and nerve-cells), each of which must also be
EFFECT OF ALTEKEP ISTUTEITION. 551
regarded as a system of interrelated molecules. The excitation and
propagation of nerve-commotion consists in producing and continu-
ing changes in the atomic structure and mutual relations of these
molecules. In order to account for that " bent," direction, or ten-
dency to act in a certain way, which all habit of the nervous system
presupposes, the internal molecular alteration of the nervous ele-
ments, especially of the individual nerve-cells, has to be assumed.
But the power of propagating their kind belongs to these individ-
ual nerve-cells ; and it is likely that all the essential principles of
heredity and evolution apply to the exercise of this power in the
case of these cells.
The biological laws which control the nutrition of living organ-
isms also have an application to the nervous elements. The exer-
cise of any of the nerve-cells or groups of nerve-cells of which the
end-organ or the central organ is composed tends to enlarge them
by appropriation of the nutriment brought to them in the blood-
supply. Such nutrition, however, will necessarily be dependent,
for the special type which must characterize its manner of building,
upon the acquired molecular character of the cells that build the
new material into themselves. And when the cells, thus enlarged
and molecularly altered according to the character and amount of
their exercise, multiply themselves, their offspring of new cells will
necessarily come under the general principle of heredity in its ap-
plication to all living cells. Accordingly, three things must be
taken into the account when considering what has been called
(ineptly, as we believe) " organic memory," namely : (1) The en-
largement of the single cells or fibres of which the organ is com-
posed ; (2) the multiplication of these elements so that new cells
and fibres originate under the laws of heredity ; (3) the internal
molecular alteration of the nerve-cells and nerve-fibres.'
§ 18. Furthermore, it is certain that the unity and continuity of
the nervous system is such, even with respect to its individual cells,
that alterations in one group of elements involve alterations in
other groups. Indeed, it is much more difficult to predict where
such sympathetic alteration will end than to affirm that it certainly
must begin and proceed to considerable lengths. The phenomena
of aphasia, for example (see chap. 11., §§ 25 £f ), indicate how many
and intricate are the ways in which those elements of the central
organs must be internally connected and related that constitute the
physical basis of the memory as retentive and reproductive of the
ideas and symbols of articulate speech. The phenomena occurring
' See the Vortrag of E. Hering, Ueber d. Gedjiclitniss als eine allgemeine
Function d. organisirten Materie. Wien, 1876.
552 PHYSICAL BASIS OF MEMORY.
in other diseases than aphasia, and in so-called " freaks " of mem-
ory, clearly indicate the same truth. But no attempt to bring
these phenomena under any strictly scientific formulas has hitherto
been rewarded with any considerable success. By continual cor-
related action on the part of groups and areas of nervous elements
more or less remotely situated, such elements become in some sort
associated together ; being thus associated together, they tend to
act together for mutual helpfulness and modification (that is, to
intensify, inhibit, or characteristically alter each other), whenever
either one is in any manner roused to yield up the energy it has in
store.
The physical basis of memory as retentive is therefore laid in
the habit, or acquired tendency, of the elements of the nervous sys-
tem— both as respects the molecular constitution of the individual
elements, and also as respects the association of groups of these
elements more or less distant from each other. Each element of
this system, especially in the more significant of its central organs,
may be considered as a minute area intersected by an indefinite
number of curves of different directions and orders ; thus a molec-
ular commotion in any such area may, according to its character
and point of greatest intensity, run out into the system along any
one of these many curves. In every such small fragment " the
whole curve slumbers," although the microscope of the histologist
cannot detect the full significance of the fragment or distinguish
it from similar fragments of other curves intersecting each other in
the same area.'
§ 19. The nature of the physical basis of memory considered as
reproductive, under the so-called laws of association, is even more
purely conjectural than that of memory considered as retentive.
To speak of an excitation as imprinting itself upon the cerebral
cells, and "perpetuating itself in them in the form of persistent
vibrations," or to imply that mental reproduction is only the weaker
" echo " of these vibratory conditions, to persist in which is the
mysterious property of all the nervous elements — as does M. Luys ^
— is neither good physics nor good psychology. The nature of
nerve-commotion, so far as we know anything about it, is not such as
fitly to be described by the word " vibrations ;" and that the forms
of nerve-commotion, even if properly described by this word, do not
" persist " within the cells, there is every reason to believe. Much
more unobjectionable is the language used by M. Kibot ' to describe
' A figure of speech adapted from Hering, Ueber d. Gedachtniss, etc., p.
1.5 f. "•' See The Brain and its Functions, p. 147 f.
^ Diseases of Memory, p. 26 f.
SO-CALLED DYl^AMICAL ASSOCIATIONS. 553
the conjectural physical basis of the same psychical phenomena.
According to the hypothesis of this authority, " determinate associa-
tions," or "dynamic affinities," are formed among the nervous
elements by their acting together ; by repetition these affinities
may become as stable as are the primitive anatomical connections.
Such "dynamical associations have a much more important part to
play in conscious memory than in organic memory." A rich and
extensive memory is not a collection of impressions (for all such
terms as "impression," "imprint," "registration," etc., are inap-
plicable to the case), but an accumulation of those dynamical asso-
ciations that are "very stable and very responsive to proper stim-
uli." The recurrence of some ideas rather than others, as started
by this or that sensuous impression or other phase of conscious-
ness, would then depend upon the character, number, and strength,
respectively, of the different " dynamical associations."
§ 20. According to the physiological theory of memory, forget-
fulness, or loss of memory, is to be accounted for as the result of
the process of dissolution. As says M. Kibot: ' "To live is to ac-
quire and lose ; life consists of dissolution as well as assimilation.
Forgetfulness is dissolution," A large amount of such " forgetful-
ness " must then be considered as indispensable to the exercise of
memory ; for if all the alterations of the intermolecular constitution
of the nerve-cells were alike conserved and propagated, and if all
the dynamical associations among the different more or less remote
groups of these cells were equally stable, there could be no basis
laid for specific mid characteristic reproduction of the images of
memory. The survival of any of these associations involves the
dissolution of many others. Under this general fact of the condi-
tions of forgetfulness the phenomena of those sudden losses and
disturbances which lesion of the cerebral substance often produces
must be brought. Temporary forgetfulness or disturbance of
memory may be assumed to be connected simply with such func-
tional derangement of the cerebral centres as interfei'es with the
working of the customary " dynamical associations " among the
nervous elements of which these centres are composed, or with
which they are regularly connected.
§ 21. No good ground exists for speaking of any special organ or
seat of memory. Every organ — indeed, every area and every ele-
ment— of the nervous system has its own memory. This view be-
longs to the very essence of every theory which considers conscious
mental reproduction as only one form or phase of the biological
fact of " organic memory." We might properly speak, then, of the
■ Diseases of Memory, p. 61.
554 PHYSICAL BASIS OF MEMOEY.
memory of the end-organ of vision or of hearing, of the memory
of the spinal cord and of the different so-called " centres " of reflex
action belonging to the cord, of the memory of the medulla ob-
longata, the cerebellum, etc. But if only the cerebral hemispheres
are specially and directly related to the phenomena of conscious-
ness, then it is only the organic memory of these hemispheres
which can be spoken of as the physical basis of our memory. For
only the molecular constitution and dynamical associations of the
nervous elements of this organ can immediately determine the
character of conscious mental reproduction.
Much of the foregoing language arouses a protest against such a
misuse of psychological terms. The fact that repeated action un-
der stimulation of the nerve-cells of the cerebral cortex results in
a modification of their molecular constitution, and in the establish-
ment of certain tendencies to associated action among them, is
doubtless a biological fact. It is, perhaps, most important in lay-
ing the physical basis, in determining the physical antecedents and
concomitants of memory ; but it is not in any sense a fact of mem-
ory. It is no more fitly called " organic memory " than are the
molecular alterations produced by generations of use in the wood
of an old Cremona. The changes in nerve-cells are indeed far dif-
ferently related to memory from the changes that take place in the
molecules of the violin ; but it is only the addition of consciousness
to the whole transaction that gives us any right to characterize it by
the word " memory."
§ 22. Just as there is no such experience as that of willing in
general, so there is no such experience as that of remembering in
general. The image of memory always possesses certain character-
istic features ; and if it be an image representing the percept of
some one of the special senses, its features are determined by the
nature of the percept which it represents. There is sound reason
for the customary form of speech which recognizes a good or bad
" memory of the ear," of the eye, etc. Such phrases might fitly be
extended to all the forms of sensation and perception ; and, indeed,
to all the mental experiences capable of being represented by the
images of memory. It would be equally fitting to speak of a good
memory of the fingers, of the tongue, of the larynx and other or-
gans of speech, etc. Inasmuch as the sensations which arise in,
and the movements which are imparted to, all these periphei-al por-
tions of the body have their representatives in certain cei'ebral
areas, the physical conditions of the images of memory (the physical
basis of the different kinds of memory) are undoubtedly laid in these
same areas. There is no one place where memory, par excellence,
PECULIAKITIES OF MEMORY. 555
is at home in the brain ; or from which it rules the different organs
of expression by making involuntary or voluntai-y sallies forth, as it
were. Yet the memory of any one thing or event involves so many
complex and closely related activities of mind — and doubtless also
of the brain — that it is impossible to tell how far weakness or dis-
turbance set up at any single point may succeed in spreading itself.
As to the physical basis for characteristic weaknesses or excel-
lences of memory (such as the inability or marked ability to remem-
ber names, or dates, etc.), and for those apparent freaks of mem-
ory which some emotion or bodily disturbance may produce, little
can be affirmed with confidence. Where the mental peculiarity ex-
tends to rather a large range of subjects, such as come under one spe-
cial sense, or under one of the more general forms of the operation
of one sense, the natural constitution or acquired condition of the
particular organs involved may be assumed to be peculiar. The
phrases, " a good ear " for music, " a good eye " for form, color,
proportion, or whatever is visible, have doubtless both a psycho-
logical and a physiological significance. But what reason should
exist in the brain why some particular date or name should re-
peatedly slip away beyond the power of attention to recall it (Forbes
Winslow tells of a man who, after a fever, lost all knowledge of the
letter F), while other dates or names in which we have had little in-
terest cling so as to make it difficult to be rid of them, even conject-
ure fails to make evident. That there is such physical reason, how-
ever, the phenomena of aphasia, and of other diseases of memory', as
well as the results of experimentation upon animals for the locali-
zation of cerebral function, all seem strongly to indicate. The physi-
cal reason for those times of general depression or exaltation of con-
scious memory, with which almost all jDersons are familiar, is less
difficult to assign. Such reason is to be found chiefly in the
changes of character and quantity suffered by the blood-supply of
the cerebral areas — especially in their effect upon the extremely
sensitive nerve-cells Avhich abound there.
All calculations as to the possibility of representing all the in-
dividual ideas and images of memory by one or more nerve-cells
and nerve-fibres each, we regard as wholly useless — whether the
number of nerve-cells in the cei'ebrum be, as Meynert calculates,
600,000,000, or even many more, as Lionel Beale supposes. Every-
thing which psychology teaches as to the character of the mental
phenomena, and everything which physiology teaches as to the
nature of the cerebral functions, discourages the puerile attempt to
connect separate mental images or ideas with isolated nerve-cells
as their product.
556 PIIYSTCAL BASIS OF MEMORY.
§ 23. It will doubtless occur to thoughtful readers that nothing
which has thus far been said concerning the physical basis of will
and memory is, in any true sense of the word, an explanation of
these mental activities. In what sense physiological psychology
can be said to explain any mental phenomena we shall consider
elsewhere. But in the particular case of memory, for example,
none of the relations conjectured as probably existing between the
molecular constitution and dynamical associations of the cerebrum,
on the one hand, and the facts of conscious experience, on the
other hand, even on the supposition that these conjectured rela-
tions were all demonstrated facts of psycho-physical science, would
amount to anything approaching the character of an explanation.
For none of these physical conditions immediately concerns the
very mental activity which constitutes the essence of conscious mem-
ory. What is explained, if anything, is simply why I remember
one thing rather than another — granted the mind's j^ower to remember
at all. This power is a spiritual activity wholly sui generis, and in-
capable of being conceived of as flowing out of any physical condi-
tion or mode of energy whatevei'.
The truth of the position just taken may be enforced (among
other considerations) by certain conclusions which resulted from
our psyclio-physical study of perception. In the study of percep-
tion psycho-physics can do much toward a scientific explanation.
It can tell what qualities of stimuli produce certain qualities of
sensations ; it can suggest a principle relating the quantity of the
stimuli to the intensity of the sensation ; it can investigate the laws
under which, by combined action of various excitations, the sensa-
tions are combined into presentations of sense ; it can show how
the time-relations of the sensations and percepts in consciousness
correspond to the objective relations in time of the stimulations.
But for that spiritual activity which actually puts together in con-
sciousness the sensations, it cannot even suggest the beginning of
a physical explana+ion. Moreover, no cerebral process can be con-
ceived of which — in case it were known to exist — could possibly
be regarded as a fitting physical basis for this unifying actus of
mind. Thus also, and even more emphatically, must we insist
upon the complete inability of physiology to suggest an explana-
tion for conscious memory, in so far as it is memonj — that is, in so
far as it most imperatively calls for explanation.
Any example of an act of memory will serve to illustrate the fore-
going truth. Let it be supposed that one has looked for a few
seconds steadily at certain pickets of a fence standing in the open
sunlight. On closing the eyes, the strong positive after-image of
THE MYSTEKY OF MEMORY. 557
the object remains for some seconds presented to the mind ; this
positive after-image is then succeeded by a succession of negative
after-images. When these latter have subsided, one can still recall
the image of the section of the fence seen some minutes since ; one
can recall the same image the next day, or the next week, or after an
indefinite length of time. But a very marked difference exists be-
tween that which is before consciousness in these cases of so-called
I'ecollection and that which was before consciousness while the im-
pression of sense was going though its various phases of dying
away. Physiological explanations, having reference chiefly to the
action of the nervous elements in the retina, may be given as to
why the after-images are produced, and as to why they have the
order of succession which actually belongs to them. Other physio-
logical explanations, having to do chiefly with assumed activities of
the cerebral nervous elements, may attempt the problem, why the
image of memory is fainter than the original impression of sense, and
why this image rather than some other is represented at a particular
time. But all such psycho-physical explanation does not touch,
does not even approach, the real mystery of memory. The positive
after-image of the pickets of the fence is not the same as the per-
cept which preceded it ; nor is it the same as the negative after-
image, or the images of memory, which follow it. Yet all these
images are regarded by the mind as similar to the original object ;
indeed, as standing for it. How can they be regarded as similar
to one another, and to their common original, when no two of them
are at the same instant before consciousness in order to be com-
pared together there ? The very essence of the act of memory con-
sists in the ability to say : This after-image is the image of a per-
cept I had a moment since ; or this image of memory is the image
of the percept I had at a certain time — I do not remember precisely
how long since.
It would, then, be quite contrary to the facts to hold that, when
the image of memory appears in consciousness, it is recognized as
belonging to a particular original percept on account of its per-
ceived resemblance to this percept. The original percept does not
exist, and will never be reproduced. Even more palpably false and
absurd would it be to hold that any similarity of the impressions
or processes in end-organs or central organs explains the act of
conscious memory. Consciousness, of course, knows notliing of
such similarity in impressions and processes ; knows nothing even
of the existence of nervous impressions and processes. Moreover,
we could never know two impressions or processes that are sepa-
rated in time to be similar, without implying this same inexplicable
558 PHYSICAL BASIS OF JUDGMENT.
act of memory. It is a fact of consciousness, on which all possi-
bility of connected experience and of recorded and cumulative hu-
man knowledge is dependent, that certain phases or products of
consciousness appear with a claim to stand for (to represent) past
experiences to which they are regarded as in some respect similar.
It is this peculiar claim in consciousness which constitutes the es-
sence of an act of memory ; it is this which makes memory wholly
inexplicable as a mere persistence or recurrence of similar impres-
sions. It is this which makes conscious memory a spiritual phe-
nomenon, the explanation of which, as arising out of nervous pro-
cesses and conditions, is not simply undiscovered in fact, but
utterly incapable of approach by the imagination. When, then, we
speak of a physical basis of memory, recognition must be made of
the complete inability of science to suggest any physical process
which can be conceived of as correlated with that peculiar and
mysterious actus of the mind, connecting its present and its past,
which constitutes the essence of memory.
§ 24. We decline to enter upon the discussion of a special physi-
cal basis for the mind's power to form generalized concepts, to
combine the elements of past experience into the creations of in-
vention and art, to discover laws, and to reason about a world of
reality assumed to exist ea^/ra-mentally, or about the nature and
order of the phenomena of its own consciousness. There is abso-
lutely no scientific ground on which to place such a discussion.
A physical basis of the logical faculty, so far as it is a subject of
either knowledge or conjecture, is laid in those general processes
of the nervous system that are correlated with the elementary forms
of mental activity upon which the higher forms are built, as it
were, or which they presuppose. Particularly important is the
function of articulate language in serving as a support for the logi-
cal processes. But that which is peculiar to all these forms of
psychical activities, and which causes them to be spoken of as
higher and more distinctively spiritual faculties, does not, as such,
admit of being made the subject of psycho-physical researches.
The attempt to deal with this subject psycho-physically only leads
to a tedious and meaningless repetition of the phrases and state-
ments which the psychology of consciousness correctly employs ;
but nothing is made the clearer by repeating words that are only
applicable to psychical phenomena in connection with conjectures
concerning related physical phenomena. " For all the higher
spiritual faculties," says Lotze,' " which consist in judgment of the
relations of given conceptions, we neither know how empirically to
' Outlines of Psychology, p. 141 f.
HIGHER SPIRITUAL FACULTIES. 559
demonstrate a definite bodily organ, nor should we know how to
conceive precisely what, that is of any use, such an organ could
contribute toward the solution of the most essential part of the
problem — that is, the pronouncing of the judgment itself. It is
conceivable, on the other hand, that these higher activities might
presuppose the complete and clear representation of the content
about which the judgment is to be passed, and, consequently, also
the undisturbed function of those organs which contribute, first, to
perception by the senses ; then to its reproduction and combina-
tion with other perceptions ; and, finally, to the appropriate attach-
ment of feelings of value to each of them."
CHAPTEE XI.
CERTAIN STATICAL RELATIONS OF THE BODY AND
MENTAL PHENOMENA.
§ 1. The intimate relation between the constitution and func«
tional changes of the bodily structure, on the one hand, and the
character and course of the phenomena of consciousness, on the
other hand, is most easily made obvious by such alterations of ex-
perience as are connected with the use of the organs of sensation
and motion. These alterations are usually sudden. Where, on the
contrary, the relation of body and mind is stationary, or subject to
only very slow changes, it is far less obvious ; it may be, indeed,
completely hidden from our observation. The relation is not for
this reason, however, any the less certain and profoundly influential.
Indeed, it is just those physical conditions which are part of the
unchanging equipment of our lives that most surely, though most
stealthih-, determine the development of conscious experience.
These are the influences of whose very existence we are for the
most part unaware, and over the effect of which we have compara-
tively little or no control. Within certain limits, one can deter-
mine the character and number of the excitations that fall upon
the end-organs of sense, and the resulting changes in the movable
parts of the body ; one can also regulate to some extent the suc-
cession of images of memory and fancy, and so the character and
intensity of the feelings and emotions that possess the field of con-
sciousness. But one cannot determine one's own age, or sex, or
race, including parentage and prenatal and infantile environment ;
nor can one choose one's temperament. Yet how pervasive, mighty,
and enduring are the unobserved influences that flow into the
conscious life of the individual from age, sex, race, and tempera-
ment!
The bearing of the foregoing remarks might be enforced by
m^ny illustrations. No one is in need of technical information to
assure him that the character of his consciousness is every instant
dependent upon whether his eyes are closed or open. That we
hear with the ear, feel both the roughness and smoothness and
NATUEE OF POPULAR IMPRESSIOlSr. 661
also the heat and coolness of objects with the skin, taste with the
mouth, and smell with the nose are matters of experience belonging
to each moment of our work-a-day life. The pleasures and pains
of sense irresistibly demonstrate the dependence of our mental
states upon the condition of the body. Other common experiences,
although not arresting attention in the same obtrusive fashion,
nevertheless tend to confirm the same impression. The disturb-
ances of consciousness which follow the altered bodily condition of
sleep are too much an affair of daily expeiience wholly to escape
attention. The question, Why are dreams so queer ? taken in con-
nection with our observation of the abnormal state of the sleeper's
body, is necessarily answered in a way further to emphasize the
general relation between bodily and mental states. Almost every-
one has also particular times of experience when he is forced into
the admission that the physical system is to be blamed for the
altered conditions of his mental life. The loss of a night's rest
renders attention to work impossible on the following day ; a
slight fever sets the train of memory's images and fancy's creations
into accelerated and altered movement, or throws it into wild con-
fusion ; a settled melancholy comes as the obvious result of
chronic dyspepsia. In these ways the popular impression that the
body dominates the mind, and that bodily conditions determine
our feelings and thoughts, is strongly corroborated.
But other phenomena constantly tend to confirm the other popu-
lar impression, that the mind dominates the body and makes it the
servant of its feelings and thoughts. In the ordinary estimate, all
performance of physical work by the body, when accompanied by
the feeling of effort, is an indisputable proof of the immediate in-
fluence of the mind over the body. It is even more than this ; it
is a proof that the conscious self, the ego, is a source of physical
energy, which pours forth, as it were, into the limbs and braces
them to the appointed task. The thought of the aged but vig-
orous French philosopher, who insisted upon remarking how well
he carried his legs, rather than upon how well they carried him,
accords accurately with the popular impression. All the cus-
tomary language about looking, listening, recalling, etc., as dis-
tinguished from mere seeing, hearing, and happening to remem-
ber, also enforces the same impression. The average man or
woman, whose life is one of constant toil, is led to say with about
equal frequency — " My limbs are tired, and / must stop trying,"
or " / am tired, but my limbs must be made to go on with their
work."
Other phenomena of an abnormal kind tend to confirm still fur-
36
562 GENERAL BODILY DIFFERENCEa.
ther the above-mentioned vague popular impression. Among them
may be mentioned the wonderful cases of so-called diseases of mem-
ory or of will, and of double personality or other alienations from
normal self-consciousness. In such cases strange alterations of the
modes of the mind's behavior — alterations which appear to involve
the suspension or reversal of some of those mental laws and activi-
ties which we are accustomed to consider among the most funda-
mental— seem to be connected with certain alterations of the bodily
organs. The effect of certain drugs, through the body, upon the
feelings and mental train gives other occasions for insisting upon
the dependence of the phenomena of consciousness upon the state
of the body. On the other hand, hallucination, hypnotism, and the
yet more obscure phenomena of so-called " mind-reading," as well
as all the phenomena to which modern Spiritualism appeals, pi-e-
sent the question to us afresh from a somewhat different point of
view.
§ 2. It requires more reflection upon wider experience to origi-
nate and confirm the impression that all the characteristic experi-
ences of the individual are built upon a solid and enduring basis of
common relations which universally maintain themselves between cer-
tain types of physical constitution and activity and certain correspond-
ing types of the character and action of the mind. The development
of the child is ordinarily regarded, whether from the physical or the
psychical point of view, in an isolated and disconnected way. It is
perhaps noted that he has grown so much taller or heavier, or that
certain external features of the body are becoming relatively more
pronounced ; it is also noted that he is learning to walh, to talk, to
take an interest in certain things before unnoticed, and to remem-
ber what he has been taught. But the close relations between the
bodily changes of advancing years and the mental development of
the child are not (at least until the age of puberty is reached) apt
to be made the subject of careful observation. In somewhat the
same way does ordinary reflection deal with the question as to any
relation between the physical and the mental peculiarities of the
sexes. It is common enough to note that boys and girls do not,
even in selecting and conducting their plays, act precisely alike.
That the former are, as a rule, taller, heavier, coarser, than the lat-
ter is patent to all observers. But that the absolute and relative
\levelopment of all the organs of the male and female is different,
and that certain sexual peculiarities of perception, feeling, thought,
and action are constantly related to this difference, is something
which few — if they even susjDCct it — take any pains accurately to
remark or describe. Moreover, while almost all agree that the psy-
NATUEE OF POPULAR IMPRESSIOlSr. 563
chical life of the adult male and female is distinguished by sexual
peculiarities, there is the widest diversity of opinion as to the pre-
cise nature and range of these peculiarities.
When the inquiry concerns characteristics of both mind and
body belonging to race and ancestry, the answers given by different
observers seem to lose all claim to strictly scientific quality. The
Frenchman does not describe himself as the Englishman describes
him ; and neither one of the two can be expected to agree with the
Russian as to what are the peculiarities that characterize this last
type of the human species. The history of the discussion regard-
ing the kinds and significance of so-called "temperaments," and
even regarding the very existence of temperament, shows clearly
how uncertain is this entire field of research.
Perhaps the most remarkable instance of firm conviction con-
cerning the general fact that intimate relations exist between mind
and body, accompanied by the utmost vagueness concerning the
precise nature of the basis of such relations, may be derived from
the ordinary views as to heredity. It is constantly being remarked
of children that they resemble some one of their ancestors in one
or more physical characteristics. But this remark is scarcely more
frequent than the corresponding one with respect to mental con-
stitution or mental idiosyncrasies. Of course the obvious implication
is, that we are to look to the laws of heredity for an account of the
origin of both classes of qualities ; in other words, both physical and
mental qualities are regarded as inherited. Further than this ad-
mission ordinary reflection upon experience with facts of this order
does not lead most men. It is obvious, however, that even the
loose popular impression must be explained, if at all, by insisting
upon much more numerous and intimate relations between body
and mind than the impression would seem at first to imply. For
how can ancestral characteristics be transmitted, unless they are
potentially carried over in those living cells from the two parents
which actually fuse together in the production of the new life ; or
else are also due to the prenatal conditions that control the nutri-
tion of the infant's body before it separates from the body of its
maternal ancestor ? But to admit this is to insist upon the pro-
foundest connection between the molecular structure and dynam-
ical associations of the elements of the physical organism and the
development of conscious life. It is even to insist upon the
mysterious fact that the character of the conscious life is deter-
mined in no small degree by the statical peculiarities of the or-
ganism.
§ 3. In general, it may be said, then, that while no doubt exists
564 GENERAL BODILY DIFFERENCES.
in the popular impression as to tlie dependence of the mental life
upon the age, sexual differences, and inherited ancestral qualities of
the bodil}' organism, the greatest uncertainty and vagueness exist
as to the nature and extent of such dependence. When this kind
of inquiries is brought to the tests of science, it is found that all
the evidence confirms the positive part of the ordinary impression ;
but it cannot be said that any substitute for the uncertainty and
indefiniteness of the popular estimate has yet been found. The
reasons for this failure lie in the very nature of the subject. No
guidance by the immediate evidence of consciousness is possible
in determining the nature of this class of psychical phenomena.
What it is to will, to remember, or to reason, each one trusts him-
self to know as a matter of his own inner experience. But the in-
quiries, How are the mental peculiarities of the different ages, or
of the two sexes, to be distinguished from each other ? or. How
does a person of this or that I'ace or temperament think, feel, and
act differently from a person of another race or temperament ? are
plainly not subjects for an appeal to consciousness. Few questions
can be raised, for example, about which a wider diversity of view is
likely to be evoked, than the question as to how man and woman
differ mentally. Yet this question must be answered, if we are to
have an answer to the further inquiry concerning the correlations
between sexual differences of organism and sexual mental differ-
ences.
The difficulty of simply getting at the anatomical and physio-
logical facts necessary for an induction is scarcely less unmanage-
able. A great amount of careful measurement and a vast array
of statistics are necessary even to tell how human beings differ
in the most external features, at different ages and as between
the two sexes. Certain data with respect to the height, weight,
relative size of the different external members of the body, and of
the brain, are obtainable ; but other data equally desirable are as
yet unattainable. Concerning the nature of the physical basis of
temperament and of personal idiosyncrasies we are wholly in the
dark.
There are therefore many gaps and deficiencies in both the
physical and the psychical series. But where the members of both
of any two series to be compared are in this condition, the laws of
their relation cannot be pointed out. Nothing remains, then, but
to guide ourselves as best we may by general observation of the
psychical facts, and by use of such few statistical results as are
available. On few points will precise conclusions be found attain-
able. But the one conclusion of greatest value concerns the main
THE PHASES OF LIFE. 565
point called in Question — and tbis is the general fact of the corre-
lated action of the bodily organism and the mind as the subject of
the phenomena of consciousness.
§ 4. Certain facts of general import, concerning the height,
weight, comparative growth of the members, size of the brain and
organs of sense, etc, which characterize the different Phases of
Life may be relied on with considerable confidence. The struct-
ural and physiological development of the prenatal human being
has been investigated with more or less success by embryology
(comp. Part I., chap. VI. ) ; but scarcely any trustworthy data exist
for a comparative psychology of the foetus. It cannot be held that
its sentient life keeps even pace with the formation and growth of
its bodily organs — not even of those which, like the brain and the
end-oi-gans of sense, are most intimately connected with the phe-
nomena of consciousness.' Large or elaborate structures, such as
the lungs, the eyes, the ears, etc., are formed under morphological
conditions and influences with which we are only very imperfectly
acquainted, without any corresponding psychical development.
The brain at birth is apparently little different from the same
organ a few weeks later ; but at this later period an important
psychical advance has been made through the activity of the end-
organs of sense. This psychical advance must be represented in
the cerebral areas by the formation of such molecular changes and
dynamical associations of the nervous elements as constitute the
physical basis of memory considered as a retentive and reproduc-
tive power.
It is a reasonable conjecture that the psychical life of the un-
born child consists wholly of sensations of pressure and temperature,
for the most part exceedingly transient and disconnected, occa-
sioned by the stimulus of its changing conditions and positions in
the womb of the mother. Such a low grade of mental experience
— if, indeed, we are to speak of prenatal "consciousness" — can as
little be accurately represented by any conscious state of the hu-
man adult as can the experience of the animals to which the struct-
ure and functions of the body of the foetus, in succession, bear more
or less of resemblance. About such a matter it is safest to refuse to
speculate. About one principle, however, there can be little doubt
— many of those structural and physiological factors which form the
most important and intimate foundation for the spiritual functions
are secured only indirectly in the central organs through the culti-
vation given to these organs by the use of the end-organs of sense.
' Comp. the article of A. W. Volkmanii, in Wagners Handworterb. , I. , p
563 ; and the strictures of Lotze upon it, Medicin. Psychologie, p. 546 f.
566 GENERAL BODILY DIFFERENCES.
According to Soltmann' and others, stimulation of the cerebral
areas, considered as "motor" by Hitzig, in new-born animals,
does not produce the usual localized movements (comp. chap. 11.,
§ 5 f.). The use of his hand by the child, the use of his orgaus
of speech, etc., educates his brain. So that the dependence of
mind on brain is not— whether with respect to the life before or
after birth — merely direct and simple, but also indirect and com-
plex.
§ 5. Chaussier considered that the growth of the foetus in length
for the six months preceding birth is regular, and that it averages
about 54 mm. a month. The mean height at birth of 100 infants
of both sexes, measured in Brussels, was found to be O.oOl m. for
the boys, 0.491 for the girls,* or about 19| and 19^ inches respec-
tively. The most rapid growth of the child takes place in the first
year after birth ; this amounts to an average of about 2 dcm.
(7.87 in.). The growth of the second year is about half of that of
the first year ; that of the third year about one-fourth. From the
fourth or fifth year until the age of puberty the annual increase
of height is nearly regular, and amounts to some 5G mm. During
or shortly before this period a sudden rise in the curve of growth
occurs ; but after this period the rate continues to diminish until
the age of about twenty-five, when the full height may be regarded
as attained. In most cases, however, a slight increase takes place
between this age and fifty, after which a decrease goes on — esjDe-
cially in extreme old age. The average height attained by the
human being is an effect of race, of climate, of conditions of liv-
ing and work, etc. For nine hundred persons, measured in Brus-
sels, ranging from nineteen to thirty years of age, the mean was
1.6648-1.6841 m.^ The average height of eighty students, at Cam-
bridge, was 1.768 m. To express the facts by the fraction of the
whole height previously attained which the growth of each year
amounts to — for the first year it is about -| ; for the second, i ;
for the third, -^^ ; for the fourth, ^V '■> ^'^^ t^^® fifth, Jj- ; for the
sixth, yig ; etc.
§ 6. The weight of the newly born infant is said by Quetelet,^ as
a rule, to remain about stationary, or even to diminish a little, for
some seven days after birth ; it then, like the height, grows with
its maximum rapidity during the first year of life. Like the height,
also, the weight at birth varies according to parentage, prenatal
> Centrblt. Med. Wiss., 1875, p. 209.
' See Quetelet, Physique Sociale de rHomme, II., p. 13 f. Paris. 1869.
3 See Quetelet, Ibid., II., p. 19.
^Ibid., IL,p. 81 £.
PROPORTIONATE SIZE OF ORGANS. 567
conditions as respects nutrition, etc. The average weiglit of 119
infants weighed at birth, in Brussels, was found to be 3,055 kilo.,
or 6,735+ lbs. avoirdupois. With this the number 3.059 kilo.,
given in the " Dictiounaire des Sciences medicales," agrees very
closely. A year after bu*th infants of both sexes have, on the aver-
age, tripled their weight. Sis years more are necessary to double
the weight attained at the end of the first year ; and thirteen more
to quadruple it. At about the age of nineteen the meau weight of
both sex:es is nearly that of old age. The maximum weight of the
male is attained, as a rule, about forty ; that of the female, somewhat
later. At this time the weight is about twenty times that of the
infant at birth. At sixty the weight, like the height, begins to di-
minish, Quetelet ' has attempted to establish the empirical law
that, during the period of development, the square of the weight
at different ages is, on the average, as the fifth power of the height ;
while for fully developed individuals of both sexes the weight is as
the square of the height.
§ 7. The proportions which exist among the different organs
and members of the human body are of interest in this connection.
These proportions vary greatly for the different ages of life, but
remain nearly the same for all individuals (not obviously deformed)
of the same age. The parts least subject to any departure from
the normal tyjDe are the most essential parts. The height of the
head at birth is about one-half that attained on complete devel-
opment— or an average of about 111 mm. (4.37 in.). It attains
about 154 mm. by the end of the first year, and 173 by the end of
the second ; its growth of the first two years (62 mm.) is, there-
fore, more than all the subsequent growth up to complete develop-
ment (when it is, on the average, 228 mm.). The developed head
is about ^to^ oi the height of the entire body. The back of the in-
fant, however, has at birth only about i its subsequent length ; the
arm, ^ ; the leg, up to the place of bifurcation, only about 4. " The
foot of the infant (which Avill probably never afterward appear in
its natural form and proportions) is about -\ of the length of the
body. This member has naturall}', for all ages and both sexes,
about the same length as the head. The hand is about J of the
length of the entire body. Unlike the head, the limbs gTow rapidly
after the second year ; especially are they lengthened at the ex-
pense of their transverse dimensions at the age of puberty, when
the bony framework is outstripping the muscles, as it were. The
' Physique Sociale, 11., p. 92 f.
- See Quetelet, Anthropometrie, ou Mesure des Differentes Facultes de
THomme, pp. 45 1, 194 f.
568
GENERAL BODILY DIFFEREISrCES.
followiug table ' shows the relative weight of several internal or-
gans in the infant at birth and in the adult :
Organ.
Skeleton. . .
Muscles, etc
Lungs
Heart
Skin
Eye
Brain
Percentage of body-weight.
Infant at birth.
16.70
23.40
2.16
.89
11.30
.28
14.34
15.35
43.10
2.01
.52
6.30
.028
2.37
Ratio of the two,
the infant taken
as 1.
26
28
20
15
12
1.7
3.7
§ 8. A survey of the physical changes which take place in de-
pendence upon the age of the human being shows that most of
them are only indirectly connected with the development of the
mind. The connection is, however, scarcely less strongly marked
and important on that account. The changing size and weight of
different members of the body, both absolutely and relatively, gives
conditions to the life of sensation and motion ; and it is by act-
ual use of these members in sensation and motion that the de-
velopment of the mental powers of discernment, memory, and will
takes place, and all the knowledge of the spatial qualities and re-
lations of things is acquired. The metabolic activities of the infant
are much more pronounced than are those of the adult ; and much
of this metabolism is directed toward the ends of construction. To
make the rapid growths of the first years, a great amount of food,
representing a great amount of potential energy, must be converted
into living tissue. More rapid metabolism is also demanded by the
necessity of keeping up the normal temperature of the infant's
bod}', which is slightly warmer (3°) than the body of the adult,
and which loses heat much faster on account of its extremely
vascular skin. The heart of the infant is, relatively to its body-
weight (see table above), considerably larger than that of the adult,
and the whole circuit of the circulatory system is traversed much
quicker (in about 12 seconds, instead of 22). Accordingly, the heart-
beat is more frequent — namely, about 130-140 per minute, falling
off to about 110 in the second year and to about 90 in the tenth
year. The respiration is also more frequent — it being about 35 per
minute at first, 28 in the second year, and 26 in the fifth. The
brain and organs of sense are relatively very much larger in the
^ See Vierordt, Grundriss d. Physiologie (5tli ed.), p. 605.
SENSES OF THE IISTFAI^T. 569
infant than in the adult, and accordingly .grow less rapidly in early
life.
Everything in the infant indicates, therefore, a mobile, flexible,
changeable condition of the bodily organs, with a relatively large
development of the most important parts of the nervous mechanism.
Such a condition is significant of a paucity of bodily and mental
habits ; the lines of the habitual action of the mechanism, the
character and number of the dynamical associations among its
elements, have not yet been rigidly marked out and firmly fixed as
they subsequently are. But the advanced development of the brain
and end-organs of sense is significant of the potentialities, as it
were, rather than of the actual experience of the babe. There is
difficulty in tracing accurately the course of the earliest mental de-
velopment, if by "mental " we intend to designate the jDhenomena
of consciousness. The eyes of the child during the first days of its
life are seldom open for any length of time. Preyer ' asserts that
some newly born children move the eyes with associated and co-
ordinated movements, others not ; but there is no fixation of eyes
such as indicates an act of will in attentive regard until much later,
and then in such way as to show a gradual unfolding of the power
of attention.
All newly born children are deaf ; the temporary deafness is
caused by lack of air in the tympanum previous to respiration.
Great individual difierences exist as respects the age at which
children give unmistakable tokens of having sensations of sound.
It was not until the first half of the fourth day that one investigator
was satisfied his child could hear. From the conditions under which
the foetus grows we might suppose that the sense of touch, as re-
gards both pressure and temperature, would be well developed in
the infant. The reflex excitability of the diffei-ent regions of its
skin is, however, inferior to that of the adult, and only gradually
approaches it under the influence of constant cultivation. Accord-
ing to Preyer," it is highly probable that the sensations of sweet,
salt, sour, and bitter are distinguishable from birth. Taste may
then be said to be "instinctive" with it as with other young ani-
mals. There is more doubt about sensations of smell ; according
to some these are not experienced earlier than from four to eight
weeks, but according to others they belong to the first days of the
child's life. It is, of course, largely in connection with the unfolding
of the activity of these organs of sensation and motion that its en-
tire mental development takes place.
§ 9. After full maturity has been attained, and the period of
^ Die Seele d. Kindes, p. 25 f. Leipzig, 1883. ■ Ibid,, p. 76.
570 GENERAL BODILY DIFFERENCES.
decline for the bodily powers has begun, the mental jDowers also
are, as a rule, less aggressive and acquisitive, or even begin to de-
cline. But the period of the more immediate dependence of the
latter upon the sensory and motor activities of the bodily organs
has passed ; the lines of spiritual as well as of corporal habit have
become firmly drawn, and both mechanism and mind may be said
to contain a great amount of stored experience ; judgment is
trained, and less liable to sudden action under the assaults of vari-
ous forms of impulse. If, then, no sudden accident or slow decay
impairs the cerebral centres, the fullest and most impressive ma-
turity of the mental powers may arrive and continue years after the
activities of sense and motion are past their prime.
§ 10. That the two sexes differ in many ways, as respects both
physical and mental characteristics, is an almost universal im-
pression. As to what are the mental characteristics of either sex
a wide difference of opinion undoubtedly prevails. But the sta-
tistics of certain physical characteristics of the sexes are tolerably
complete. Besides the more obvious bodily differences of man and
woman, the two sexes differ from birth in average height, weight,
physical energy, proportion of parts, relative development of or-
gans, frequency of pulse, respiration, etc. They also differ in many
other subtler and less obvious characteristics. As we have already
seen (p. 566), the height of the male infant at birth slightly (about
0.01 m.) exceeds that of the female. The excess increases, but not
with perfect regularity, until full maturity is reached. At this time
the height of the man may be given as 1.467-1.890 m. (about 4 ft.
11 in. to 6 ft. 4 in.) ; that of the woman, 1.444-1.740 m. (about 4 ft.
10 in. to 5 ft. 10 in.). The curve of the growth of the two sexes from
birth onward runs somewhat differently ; although up to the age of
four or five the difference is scarcely perceptible. All the sexual
differences are, of course, least pronounced in the earliest years of
life. For these years the proportions of height remain about as 1
to 0.988 ; at complete development they are as 1 to 0.937, or about
as 16 to 15. But at sixteen or seventeen years of age the growth
of girls is relatively as far advanced as is that of boys at eighteen
or nineteen. Between five and fifteen years the foi-mer make an
annual growth of about 56 mm., the latter of about 52 mm.'
§ 11. The relative weight of the two sexes varies in somewhat the
same manner, but not precisely, as their height. Of 119 infants
weighed at birth, in Brussels (63 males and 56 females), the average
weight of the males was 3.20 kilo. (7.05 lbs. avoirdupois) ; of the
latter, 2.91 kilo. (6.42 lbs.). At the same age the male is, as a rule,
' See Quetelet, Physique Sociale, II. , p. 15 f. ; and Anthropomctrie, p. 176 f.
GROWTH OF SEXUAL DIFFERENCES. 571
heavier than the female ; but although the boy is born heaviex',
and in his earliest years makes a larger gain of weight, at about
twelve the two sexes have nearly the same average weight. The
limits of weight for persons normally formed are about 49.1-
98.5 kilo. (108-217 lbs.) for man, 39.8-93.8 kilo. (98-207 lbs.) for
woman. Woman attains her maximum weight several years later
than man.
The relative proportion of the bodily parts is different for the two
sexes. At about the age of four or five the sexual differences iu
this regard become more obsei'vable. The bony framework of the
boy is relatively prominent, and the outlines of the limbs become
more clearly traced in a Avay to conform to agile and strong move-
ment. Eounduess of limbs and amplitude of flesh concealing the
framework are more characteristic of the girl. At the age of puberty
these and other similar differences suddenly become more strongly
marked. Careful measurement of many individuals who have at-
tained the development of the adult shows certain noteworthy' stati-
cal differences of sex. The head, Avhich is contained about 7.4
times in the entire height of the man,, is contained only 7.2 times in
the height of the woman ; it is, then, relatively a little longer in the
latter. The chest of the adult male is more developed. The length
of the arms stretched out is about 1.045 of his height ; of the female,
only 1.015. The relative length of the legs is greater in the man.
The circumferences of the different parts of the body are also rela-
tively different in the two sexes. The relative step is as 1,000 to
1,157; and the weight of the brain as about 1,272 to 1,424 (see
chap. I., § 4).
There are also marked differences between the sexes in the forma-
tion of the pelvis, and in the part of the body on which the centre
of the line of length of the entire body falls. The costal mechan-
ism of respiration differs. The girl of five breathes with her ribs
as does the adult woman. The pulse of woman is quicker in about
the same proportion as her height is less. The physical energy of
which the male is capable, whether as measured by liftiug weights,
by pressure with the hands, or other ways of j^roducing a meas-
urable mechanical effect, is much greater than that of the female.
This follows, of course, from his larger brain and skeleton, and
from his superior equipment of muscles. Before jiubert}^ the dif-
ference has been estimated as expressed by the ratio 3:2; after
that age it is greater, and is measui-ed by the figures 9 : 5, or is
perhaps double. The average boy of nine or ten can support his
own weight for some time with his hands ; the girl cannot. The
average man can, by using his disjposable energy, lift some 154
572 GENEEAL BODILY DTFFEEElSrCES.
kilo. ; the woman scarcely half as much.' The metabolism of the
female, whether measured by respiratory or other excreta, is not
only absolutely, but relatively less ; her blood is not only less in
quantity, but also of lighter specific gravity, and contains fewer red
corpuscles." The woman is more inclined than the man to be "hy-
persesthetic " (in the physiological meaning of the word) ; this in-
volves a tendency to many forms of cramping of the muscles, to sud-
den secretions, to the wide spreading of stimulation so as to involve
a considerable number of the bodily jDarts.' Many of the woman's
sensations are less sharply discerned as to their qualitative content,
but stir up accompanying forms of feeling with more energy.
§ 12. In the description of those mental characteristics of sex
which undoubtedly exist, and which are dependent upon or con-
nected with the foregoing physical characteristics, a great diversity
of view prevails. We cannot enter into the details of the discus-
sion. It is plain, however, that the gTeater bulk of those nervous
and muscular masses which are involved in the conscious life of
sensation and motion both implies and necessitates great differ-
ences in the development of this life. But judgment and decision
are also involved in the conscious life of sensation and motion ;
they are dependent upon that life for the amount, direction, and
lower or higher order of their development. The superior strength
of the chest, shoulders, and hips of the male, in lifting and moving
heavy burdens, and the fitness of body and legs for walking firmly
and running swiftly, cannot fail to produce a marked consciousness
of ease, elasticity, and security, both of posture and of movement.
Other important sexual differences, consisting of variations in
the kind and amount of feeling — sensuous, sesthetic, intellectual,
moral — and especially of the so-called emotions, are undoubtedly
connected with the existence and development of those organs
specifically characteristic of sex. The differences in circulation,
resj^iration, metabolism, etc., are also the cause of characteristic
differences in sentiment and feeling. Especially important, and
even determinative, is the man's larger mass of nervous matter in
the cerebral centres. In active energy, whether as given out on
sudden call or in the form of sustained endurance of the strain of
labor, and in all pursuits and achievements requiring such energy,
the woman (however much she may seem to be superior in the
passive endurance of pain, etc.) can never compete successfully with
the man.
^ Quetelet, Antliropometrie, p. 359 f.
* Foster, Textbook of Physiology, p. 713.
^ Lotze, Mediciu. PsycLologie, p. 559 f.
SEXUAL MENTAL CHAEACTEEISTICS. 573
Other mental differences closely related to the more obvious
ones, and largely dependent upon them, are less obvious and easy
to demonstrate. Our purpose will be served sufficiently by citing,
concerning such differences, a few points from Lotze,' who has
treated the whole subject briefly, but with much insight and caution.
In Lotze's opinion, woman naturally adapts herself more easily to
new conditions of life ; while acquired habits have a stronger hold
on man. Her characteristics involve a mixture of the sanguine
temperament and the sentimental stage ; while varieties of educa-
tion conceal more of native qualities. This would seem to imply
a greater molecular immobility and stronger dynamical associations
among the elements of man's organism. The intellectual capacity
of the sexes, Lotze thinks, differs chiefly or solely in so far as
special emotional interests prescribe the course of the intellectual
life. It is characteristic of masculine philosophy to analyze strik-
ing phenomena ; it is characteristic of woman rather to hate analy-
sis. Masculine thought depends upon the conviction that whatever
is most great and beautiful in the world has its mechanical con-
ditions ; mascuhne effort upon a profound reverence for general
principles. The faith of woman is that no general principle or form
has an independent value, but that this value belongs to the living
reality founded upon such principle ; the sentiment of the feminine
mind is devout toward completeness. The notions of the two as to
spatial and mathematical relations, and their perceptions as to the
nature of the concrete realizations of the ideas of space and time,
are markedly different. In seeking for some physical basis for
these and similar differences — in case their existence be once as-
sumed— we are forced to admit that any such known basis can be
at best only indirectly related to the differences themselves. The
general truth holds, however, that certain intellectual differences
are intimately, and even necessarily, connected with certain emo-
tional differences ; and that the latter plainly have, in many cases,
their ground in the organic differences of the two sexes.
§ 13. The different intellectual and emotional characteristics of
the different races, and the relations of such characteristics to defi-
nite variations of the bodily type of each race from that of our com-
mon humanity cannot be discussed without raising even more
obscure and doubtful inquiries. If external influences of soil, cli-
mate, food-supply, character of the prevalent civilization, etc., have
any observable influence upon the type of the bodily form — and of
this there can scai'cely be a doubt — and if the laws of heredity are
to be allowed the scope and influence which belongs to them, the
' Microcosmus, ii., p. 39 f. Edinburgh, 1885.
574 DOCTRITSTE OF TEMPERAMENTS.
existence of both physical and mental characteristics of race must
be admitted. The popular impression confirms the assumption of
anthropological science. But there are few subjects concerning
which statistics and impressions are both more incomplete and
more unsatisfactory.
According to Quetelet's conclusions, the proportions of the aver-
age human body are such as to render it the type of manly beauty ;
and the limits of these proportions are the more fixed and un-
changeable the nearer we approach to perfection. In the special
features of height, weight, and relative form, rather than size of
the organs, certain differences appear which belong to different
peoples and races. Each people may be said to have its peculiar
type ; and among each people such type exists, not only in fact and
determinable by scientific means, but as vaguely established in the
general appreciation. According to Quetelet,' the principal pro-
portions of the human figure vary very little among different races
of men. " The real differences which the races present appertain
to characteristics which the eye seizes better than the compasses ;
in order to establish them firmly, an appreciation of minute differ-
ences is required, and a tact that presupposes a long experience in
such researches. One can see the difficulties with which phrenolo-
gists meet in making numerical estimates of the characteristics of
the skull ; nothing precise can be formulated in this regard " (comp.
chap, n., § 4). This conclusion of Quetelet is formulated in view of
careful measurement, not only of many individuals from the modern
European jjeoples, and of certain selected cases among the North
American Indians, the Chinese, and the Kaffirs, but also of Egyp-
tian mummies, of Greek statues, and of other means for ascertain-
ing the proportions of ancient man.
§ 14:. Few impressions are more firmly fixed than this, that dif-
ferent individuals (at least among all the more highly civilized
peoples) possess, each one, a characteristic "natural disposition."
Such disposition constitutes a predominating tendency to feel,
think, and act in certain forms rather than others among the many
that are conceivable. The conviction that the disposition of the
individual is innate and inherited, rather than the result of training
or environment, is doubtless due to the fact that it appears with
considerable strength in childhood, and generally maintains itself
under great alterations of circumstances, and against effort, to the
close of the individual's life. The so-called " disposition " can, in-
deed, be greatly modified, and even seem wholly changed ; but such
modification is invariably made at the expense of greater energy
' Anthropometrie, p. 323.
THE THEORY OF DR. GEORGE. 575
than is required to form and break those habits which are acquired
differently in different individuals after birth. Moreover, the
modification is often one of expression and povyer of control rather
than of dinposition.
Patent facts like the foregoing have given rise to the theory of
Temperaments. Curiously enough, the number four has usually
been chosen as suflScient to designate the kinds or types of native
disposition, the varieties of temperament. The attempt has also
often been made to connect the different temperaments with a
bodily basis. As in several of the foregoing inquiries, so in this,
our reliance is mainly placed upon the correctness of certain wide-
spread but vague impressions. It is impossible to classify the tem-
peraments with the use of methods required by strict scientific in-
duction. The individual can judge of his own temperament only
by remembering his actions and the states of consciousness con-
nected with them. But upon such a point memory, and even the
immediate recognition of consciousness, are but little trustworthy.
Few things are more common than for the individual quite to mis-
conceive and misinterpret his own mental states and tendencies.
On the other hand, we have no means of judging the temperament
of others except by their action — using the word action in its
broadest signification. A large part of such judgment is unavoid-
ably misjudgment. But notwithstanding all the doubts and un-
certainties which attach themselves to the subject of temperaments,
those who are carefully observant of their fellows will continue to
believe that important and determining natural diffei'ences exist
among them.
§ 15. Some of the older treatises on psychology contained elab-
orate discussions of the doctrine of temperament, in which many
well observed facts and shrewd conjectures were united with no
little fanciful speculation. This is to some extent true of the treat-
ment (on the whole admirable) given to the subject, for example,
by Dr. Leopold George. ' According to Dr. George, the four tem-
peraments are defined by the nature of the interior relation which
exists between perception and the affections of the mind. Thus
the greater the mind's wakefulness to impressions, the greater is
also its susceptibility to the feelings of pleasure or pain which are
attached to the impressions. The " sanguine " temperament is
distinguished by strength in this interior relation. But the greater
the attention given to the objects before the mind, the greater are
the emotions of hope or fearful expectation which the objects excite ;
and from the emphasis being laid, as it were, on this relation the
' Lelirbucli d. Psychologic, pp. 125-151. Berlin, 1854.
576 DOCTRINE OF TEMPERAMENTS.
" melancholic " temperament results. A large degree of suscepti-
bility to sensation is naturally accompanied by feelings of attrac-
tion or dread toward the object of sensation. This fact forms a
basis for the " choleric " temperament. And, finally, the so-called
"phlegmatic" temperament depends upon the degree of mental
apprehension with which different objects are seized, and the con-
sequent emotions of satisfaction or disgust. The theory is then
developed that different races and peoples are distinguished by
some one of these four temperaments — for example, the French
are sanguine, the English melancholic, the Spanish and Italians
choleric, the Germans phlegmatic. More generally still, the Cau-
casian race is sanguine, the Mongolian melanchohc, the Negro
phlegmatic, the Malayan choleric. The four periods of life cor-
respond to the four temperaments, according to Dr. George ; and
this opinion has undoubtedly a certain basis in fact, as well as a
suggestion concerning the nature of the physical conditions which
may possibly underlie the existence of temperaments. Even dif-
ferent species of animals are, in the opinion of this writer, charac-
terized by predominance of one of these four great tj'pes.
§ 16. Modern psychology, approaching the subject of temperament
from the physiological and biological points of view, is more likely
to be self-restrained and cautious in its conclusions. Accoi'ding to
Wundt,' the fourfold division of the temperaments is correct, be-
cause, in the case of every individual, there must be a certain com-
bination of the two factors of strength and speed in all change
which goes on in the mental movements. The various affections of
the mind are therefore classifiable as either strong and quick or
strong and slow, or else as weak and quick or weak and slow.
Choleric and melancholic persons are inclined to sti'ong affections,
sanguine and phlegmatic to those that are weak. By crossing
these two principles of division the following scheme is derived :
strong. Weak.
Quick Choleric Sanguine.
Slow Melancholic Phlegmatic.
The quick temperaments are directed rather toward the present,
the slow toward the future. The quick require additional strength,
and the weak additional time, in order to achieve the largest
amount of work possible for them. The choleric and phlegmatic
are temperaments of action rather ; while the sanguine and melan-
cholic are temperaments of feeling.
Wundt agrees with the observations of Dr. George respecting
' Physiologische Ps^'chologie, ii. , p. 345 f .
THE THEOKT OF LOTZE. 577
the applicability of the conception of temperament to orders, fam-
ilies, and species of other animals as well as to man. He ' also
makes the penetx'ating observations that Pessimism generally rests
upon an individual peculiarity of temperament ; and that the true
art of life consists in not having one temperament, but in combining
them all. " One should be sanguine amid the petty sufferings
and joys of daily life, melancholy in the more serious hours of
life's more important events, choleric toward impressions that fetter
one's profounder interests, phlegmatic in the execution of the re-
solves that have been reached."
Lotze's ' treatment of the doctrine of temperaments is more ex-
tended than Wundt's, but no less cautious and suggestive. Va-
rieties of temperament, as of all other innate natural capacities,
appear to be most marked under the conditions of an advanced
civilization. By the term "temperaments," according to Lotze, we
understand : " (1) The differences, in kind and degree, of excitability
for external impressions ; (2) the greater or less extent to which
the ideas excited reproduce others ; (3) the rapidity with which the
ideas vary ; (4) the strength with which feelings of pleasure and
pain are associated with them ; (5) finally, the ease with which ex-
ternal actions associate with these inner states themselves." The
ancient fourfold division of temperaments is approved by Lotze
— as, indeed, it must be by all who advocate intelligently any the-
ory upon the subject. The sanguine temperament is distinguished
by great rapidity of change and lively excitability. This indi-
cates a permanent excess of the general capacity for i-eciprocal ex-
citement among all the different psychical states, and an exces-
sive sensitiveness of the soul to all external stimuli. It is natural
in children and uncivilized tribes ; it is, on the whole, advantageous
to the beginnings of culture, and prevents the establishment of
narrow notions and attachment to ideas acquired accidentally. But
adults who are strongly marked by this temperament make the
impression of immaturity, of being " grown-up children." For the
temperament usually called "melancholic " Lotze prefers the term
sentimental. This temperament is distinguished " by special recep-
tivity for the feeling of the value of all possible relations," but is
indifferent toward bare matter of fact. Here a Hvely appreciation
of the harmonies and discords of surrounding objects may be com-
bined with little inclination for hard work ; a great variety of
aesthetic feeling, of imaginative activity, may go with theoretical
vagueness and the disturbance of an established sense of duty by
' Microcosmus, ii. , pp. 24 fE. , Edinburgh, 1885 ; Medicin. Psycliologie,
560 f. ; Outlines of Psychology, p. 137.
37
578 DOCTRiisrE of tempekaments.
this sesthetic feeling. The sentimental temperament shows itself in
science among those who "spend their ingenuity in constantly de-
vising some new dress for the knowledge they have acquired ; " and
in art by dealing with " isolated lyric movements of emotion," with-
out being capable of grasping them and bringing them together
into a coherent whole. It is distinctive of youth and, in its most
pleasant form, of those who retain a youthful disposition on into
the later and the latest years of life. "
The marks of the choleric temperament are " one-sided recep-
tivity and great energy in single directions." It is therefore dis-
tinguished by diminished susceptibility to excitement, but great
force and endurance in reaction when feeling has once been
aroused. Its fine effect is an apparent moral steadiness of char-
acter ; its uncomely effect is obstinate and narrow perseverance in
a path once entered upon, even when reasons exist for deviating
from or abandoning it. Its time of most natural development is in
adult manhood ; but its occurrence in a notable way even among
children shows it to be one of the native dispositions of the mind.
Finally, the phlegmatic temperament, which is the natural temper
of advanced age, is distinguished by slightly varied and slow, but
not necessarily weak, reactions. Sluggishness in youth and equa-
nimity in old age may both result from the action of this adjust-
ment of the feelings and impressions to external stimuli and the
train of ideas.
§ 17. The permanent common features of the foregoing views as
to the nature of temperament illustrate sufficiently the real truth
of the case. The doctrine as a whole is one which in its main
principles is undoubtedly required by the most wide and varied
observation. On the other hand, the differences in the details with
which the different descriptions are filled out show the uncertainties
which belong to every attempt to elaborate it. Common impres-
sions, producing a common play of feeling and regulating the train
of associated ideas, belong to all individuals. But in each individual
there is something characteristic as to the mode, the intensity, the
speed with which these impressions arise when the stimulus acts,
then combine with one another, and so provoke feeling or regulate
the ideas. In a more or less definite way, all men generalize the
various individual examples and form them into classes which
have necessarily lost that variety and minuteness of peculiarities that
characterizes the individual and have been conformed to some idea
of a type. No real individual perfectly expresses such a typical
idea. But especially in those conditions of civilization where the
expression of individuality in a varied and impressive way is pos-
PHYSICAL BASIS OF TEMPERAMENT. 579
sible most individuals are recognized as conforming more nearly
to some one rather than another of these types.
§ 18. As to the exact nature of the physical basis of temperament
nothing is known. The influence of abnormal bodily conditions,
and of certain diseases, to produce or alter the disposition of the
mind in a manner resembling temperament would seem to indicate
that the original constitution of the brain is not the principal
determining factor. The nature of the excitation which external
stimuli produce upon the end-organs of sense, the strength of the
resulting reactions in the form of common feeling, the habitual con-
dition of the internal and visceral organs and the coloring they
impart to common feeling, seem to be of prime importance in de-
termining the temperament. Further than this it is difficult to be
more specific, even in conjecture. The fact that the different periods
of life are apt to be characterized by a predominance of one of the
four temperaments is not an argument against the physical nature
of the basis of tempei'ament in general. Certain changes in the
nature, speed, and strength of the reactions derived from the end-
organs and the internal organs of the trunk necessarily accom-
pany the early development, riper maturing, and decay of the bod-
ily powers. These cannot fail to have a great, though indirect,
influence upon the activities of the cerebral centres. But where so
much already said is so uncertain, we refrain from adding further
conjectures.
§ 19. What has hitherto been developed in detail respecting the
relations which maintain themselves between the structure and
activity of the nervous mechanism and the phenomena of conscious-
ness may now be summarized in somewhat the following way. We
seem warranted in insisting that the following five great groups of
correlations between body and mind are always maintained during
the mind's conscious existence :
1. The quality and intensity of the sense-element in our expe-
rience is correlated with the condition of the nervous system as
acted on by its appropriate stimuli. That the precise character
and amount of our sensations are dependent upon what and how
much of various forms of physical energy acts upon the organs of
sense there is scarcely need to say. But the phenomena which
demonstrate the effect of attention upon the sense-element itself
prevent us from regarding the relation as only one-sided and sim-
ple. The true state of the case is never represented by considering
the sensations as mere passive impressions depending solely upon
580 COERELATIONS OF MIND AlSTD BODY.
tbe kind and degree of the action wliicli the stimuli exert, These
sensations depend also on the condition of the mind at the time
the stimulating effect of the excited sensorium is realized in con-
sciousness, and in terms of consciousness. To represent the men-
tal condition of attention as itself simply and absolutely dependent
upon the condition of the centres of the brain is to cover up much
of our ignorance concerning the relation of body and mind with a
scanty stock of conjecture in cerebral physiology. There are many
facts to countenance the reverse statement — the condition of the
centres of the brain depends upon the state of the mind with re-
spect to attention. For the present we content ourselves with this
expression : The sense-element in our experience is constantly
correlated with the condition of the nervous system as under excite-
ment from its appropriate stimuli.
2. The combination, whether simultaneous or successive, of our
conscioics experiences is coJTelated with the combination of the im-
pressions made, from whatever source, upon the nervous organism-
That the number and form of the different sensations composing
any presentation of sense is dependent upon the number and qual-
ity of the different excitations of the nervous system which com-
bine in such presentation there can be no doubt. So, too, does
the order and time-rate of the phenomena of consciousness depend
upon the order and time-rate of the separate excitations of the
nervous system. But no object of sense can be considered merely
as a compound of the elements of sensation entering into it ; nor is
the nature of the mental product to be derived from the physical
laws according to which the different stimulations modify, support,
supplement, or inhibit each other. A mental synthesis, an activity
that combines under different laws from those which govern the
putting together of stimuli of various wave-forms and degxees of
intensity, must take place in order that one object of sense may be
constructed out of several sense-elements. Again, the order in
succession and time-rate of the conscious states is not a mere copy
of the order and time-rate of the impressions made upon the ner-
vous system. It is simple matter of fact that mental education in
the making of those syntheses which take place in all acts of per-
ception is necessary in order to see or touch extended " Things,''
as distinguished from merely having visual and tactile sensations.
Whatever special form of activity in the cerebral centres is assumed
as the physical basis of this mental act of synthesis, it is by no
means certain that such cerebral activity does not as truly depend
upon the mental act as the mental act depends uj)on it. Here
again, at any rate, the word " correlation " seems best adapted to
CORRELATIONS OF MIND AND BODY. 581
express the connection between tbe physical basis and the mental
phenomena.
3. Those phenomena of consciousness which loe designate as
''memory" and "recollection," as weU as the play of the repro-
duced images of representation in general, are correlated with the
molecular constitution and tendencies, and with the so-called " dy-
namical associations," of the elements of the nervous system. It is
not necessary to repeat in this connection what has already been
said in proof of the fact that these elements furnish, in part, the
necessary conditions of conscious acts of memory ; and, on the
other hand, that the enumeration of certain physical conditions
throws no light upon what is peculiarly mental in the phenomena.
To say that memory depends on the condition of the cerebral
centres emphasizes the relations involved in one class of facts ; to
say that memory depends upon the conscious act of attention, both
to the original object and to its reproduced image, presents the
relations involved in another class of facts.
4. The course of thought, and all the higher forms of self-con-
scious experience, are correlated tcith the condition of the cerebral
centres. The dependence of these conscious mental activities upon
the quantity and character of the blood-supply in the brain, and
upon the integrity and unimpeded activity of its tissues, cannot be
called in question. Of the exact nature of this dependence we can
form only a very inadequate picture ; and Ave have no means what-
ever of subjecting this dependence to a rational explanation. But,
on the other hand, many of our experiences would just as certainly
lead to the conclusion that the condition of the cerebral centres
depends upon the higher forms of self-conscious experience. This
is true of the results of all our voluntary acts accompanied by
conscious discernment and choice of one among several possible
courses of action. The facts of which we are sure in such cases
are these : An idea of something to be done, an idea of the means
(the parts of the body to be moved, and the sensations and feelings
of effort which are associated in experience with such movement),
a fiat of will, and a result in sensations and perceptions showing
that the movement has been accomplished. The actual movement
we trace back, under the guidance of physiological facts and laws,
to the starting of some form of nerve-commotion in the requisite
motor areas of the cerebrum. But unless we stoutly, and from
mere prejudice, refuse to acknowledge a possibility of the mind
exercising any influence upon the body, we are warranted in
saymg that this nerve-commotion in the cerebral motor areas de-
pends upon the preceding ideas ending in the fiat of will to exe-
582 COERELATIONS OF MIND AND BODY.
cute a certain form of external motion. At this stage of the discus-
sion, however, we prefer to use the vague term " correlation " to in-
dicate the mutual connections between physical condition and this
class of so-called higher mental phenomena. It has already been
made clear that such connections are here much less patent, direct,
and suscej) bible of being stated in the form of general laws than
are those of the first two classes.
5. The statical condition of the body (by which we mean all
those inherited peculiarities of the organism, the sexual and tribal
bodily characteristics, the corporal constitution as dependent upon
age, which change only slowly and within narrow limits, or do not
change perceptibly at all) and the general tone or coloring of con-
scious experience are correlated. Upon this obscure subject we
may (at least at present) wisely decline to take either one of two
extreme and indefensible positions. It cannot be said to be re-
quu'ed by the facts that all the phenomena of consciousness should
be regarded as strictly predetermined by the constitution, environ-
ment, and independent action of the corporal elements. The really
convincing argument for all such thorough-going organicism is the
wish to have it so. At another extreme stands the fanciful philos-
ophy which considers the mind as the builder of the body — as in
some way fashioning to its own inherent constitution and uses the
organs of the physical mechanism. This conclusion, also, we must
decline to accept without further testing. All the facts, however,
do obviously impress upon us the conclusion, how pervasive, inti-
mate, varied, and profound are the mutual relations — the correla-
tions— of the physical mechanism and the phenomena of con-
sciousness. Any further speculation as to the real nature of this
connection, and as to the nature of the subject of the mental phe-
nomena— of the Mind — must be reserved, for the succeeding part of
our inquiry.
PART THIRD.
THE NATURE OF THE MIND.
CHAPTER I.
THE FACULTIES OF THE MIND, AXD ITS UNITY.
§ 1. Up to this point in our psycho-physical investigations we
have been content to speak of the mind simply as the "subject " of
the phenomena of consciousness. In other words, the phenomena
of consciousness may with equal propriety be spoken of as mental
phenomena ; for they are phenomena of, or appertaining to, what
all men indicate by the subject "I" (the ego) when describing their
different conscious experiences (comp. p. 3 f.). This indefinite and
provisional recognition of the mind as an existence to which differ-
ent states, or conditions, or modes of activity, may belong with-
out destroying its unity, suffices for a simple description of the
constitution and activities of the nervous mechanism, and of the
relations between it and the phenomena of consciousness. But
psychology, even when pursued from the physiological point of
view, can scarcely be satisfied to push its inquiries no farther into
the natui-e of mind. Psychology, from whatever point of view it is
pursued, aims to perfect a science of mind. Like every other
science, it strives to discover the essential nature of that which it
investigates.
Pains must indeed be taken to avoid substituting words for
things, abstractions for realities. By the " essential nature " of
mind we mean just that nature which is duly inferred from the
phenomena as essential to their rational explanation. But there
are especial and unique reasons why psychology should not will-
ingly desist from renewed attempts at such rational explanation.
Is the subject of the phenomena of consciousness — the so-called
Mind — entitled to be considered as having unity and reality in any
defensible meaning of the words ? Is it not peculiarly entitled to
be considered as a real being, with a permanent and essential nature
of its own ? It is impossible for human reason not to attach the
greatest interest and importance to these ultimate psychological
inquiries. A sentient and rational life, without any self interest in
the examination of its own permanent characteristics, and of the
grounds upon which it rests, would be an absurdity.
583 RELATIONS OF MIND AND BKAIN.
§ 2. Yarious objections maybe raised against allowing considera-
tions like the foregoing to apply to the researches of that branch of
psycholog}^ which is called "physiological. " It may be claimed that
the rational explanation of the mental phenomena belongs to Meta-
physics rather than to Physiological Psychology. To a certain ex-
tent the force of such objections must be admitted. They are
not of a nature, however, to debar us from the inquiries that are to
be raised in the following chapters. On the contrary, the result of
the discoveries made by starting from the point of view held by
experimental science is such as irresistibly to urge upon us some
of these very inquiries. For example, it has been shown beyond
doubt that the construction of presentations of sense requires the
activitj^ of both bod}^ and mind, considered as standing in peculiar
relations to each other with respect to the conditions which they
furnish for the spatial relations and spatial properties of these pres-
entations. But do body and mind themselves exist in spatial re-
lations ; and may the latter be spoken of as having spatial prop-
erties ? In other words : In what sense can we localize mind in
the body, or speak of the body as the seat or organ of mind?
Moreover, as we observe the two classes of phenomena (the organic
and the mental) the impression is inevitable that in some sort they
keep pace with each other in the order of development. This fact
unavoidably raises an inquiry as to the relation of the mind to the
body with respect to its origin and destiny.
As a matter of fact, moreover, it is found that those who are
most inclined to complain at the introduction of any " metaphysi-
cal " inquiries into the discussions of physiological psychology are
quite as apt as others to give grounds for the same complaint
against themselves. They themselves rarely escape the charge of
having a so-called metaphysical theory of the soul to maintain.
"With such complainants, moreover, it is often fi'om the very begin-
ning a foregone conclusion what the general natui'e of that theory
must be. They decry metaphysics and advocate a " psychology
without a soul." Yet they hold, as an unalterable but unverifiable
assumption, that psychological phenomena must not be so discerned
and interpreted as to seem to require for their explanation an ex-
istence called "a soul."
§ 3. In order to arrive at any satisfactory conclusions regarding
the essential nature of the Mind, it is plainly necessary that we
should take our point of starting from a consideration of mental
phenomena. For these are the very phenomena for which an ac-
count is to be given ; and there is no safe way of concluding what
is the nature of any reahty, or even of determining whether any
j^'AULTS OF THE OLD PSYCHOLOGY. 587
assumed reality actually exists, except by considering the phenom-
ena which are attributed to it. The questions, how far mental
states and mental changes ai'e explicable by referring them to ante-
cedent or concomitant states and changes of states in the nervous
system ; and how far such mental states and changes require us to
assume the existence of some other real being than the molecules
of the brain and spinal cord — cannot even be properh' approached
without a clear knowledge of what these states and changes in
themselves are. But the only way to know what mental phenom-
ena, as phenomena, in fact are, is through observation of such phe-
nomena by the method of introspection. We must then begin this
particular j^art of our general discussion by changing for the time
our point of view.
Much fault has been found of late with the failures of the so-
called " old " psychology. It has often been explained at length
that these failures were largely due to its wrong method ; and, as
is well known, its method was almost exclusively the method of in-
trospection or self-consciousness. The exclusive use of this method
resulted in confining the efforts of psychology very largely to the
rather barren task of classifying the different kinds of mental activ-
ities, and of discussing what so-called "faculties " must be assumed
to belong to the mind in order to account for so many kinds of
activities. Now, classification of phenomena is certainly one im-
portant part of the work of every science ; nor should it be forgot-
ten that much of the more recent progress in psychology is due to
previous painstaking observations of mental phenomena — resulting
in their classification — from the purely introspective point of view.
Classification, however, is not explanation ; and the " faculties "
into which the " old psychology " divided the mind were too often
mere names that repeated the bare fact of the observer having suc-
ceeded, to his own satisfaction, in classifying the phenomena. It
is demanded, however, in order to make real progress in psychology
as a science, that the correlations, under precise and definite laws, of
the mental phenomena with one another and with the events which
happen in external nature shall be ascertained. Nevertheless, even
after adopting this view of the problem we cannot dispense with
the method of introspection ; for we have no other way of ascer-
taining what ar'e the phenomena that require exiDlanation. If the
further question be raised, What is the real nature of that subject
of the mental phenomena popularly spoken of as the mind? we
surely cannot approach the answer to this question without calling
attention to the nature of the phenomena themselves.
So far as the necessities of the present discussion are concerned,
588 RELATIONS OF MIND AND BRAIN.
it may be said that there are two rival and contrary ways of reply-
ing to the general inquiry into the nature of the Mind. One of
these denies that, in order to account for naental phenomena, we
need assume — much less are able to prove — the existence of any
reality other than the material substance of the living and active
nervous system (especially, or wholly, of the brain). The other,
on the contrary, claims that no explanation of mental phenomena
is possible without referring them to a non-material or spiritual
entity as the real subject or gTound of them all. Both of these
ways of explanation admit of various modifications. The former,
as held by its different advocates, has used different terms to set
forth the relation in which it believes that the phenomena of con-
sciousness stand to the states and activities of the brain. The lat-
ter, also, has by no means always been self-consistent in its advo-
cacy of the unique and independent character of the subject of
mental phenomena. Even the power of immediately penetrating
in consciousness the secret of its own interior nature has sometimes
been claimed for the mind. The former of the foregoing views, in
whatever particular shape it may occur, has customarily been re-
garded as essentially the "materialistic," and the latter as the
" spiritualistic," theory of the human mind. A third view, which
regards both the so-called "brain" and the so-called "mind" as
merely phenomenal aspects of some one reality that is like neither,
but manifests itself in both, requires for its discussion so much of
subtle metaphysics, and is so foi-eign to all the scientific material
with which we have thus far been dealing, that it is for the present
passed by with a bare allusion.
§ 4. In the remaining part of our discussion we shall be chief-
ly occupied with considering which one of the two theories just
stated best accords with all the facts. These facts, which are to
test the theory, are facts of the nervous mechanism, and of the
correlations between this mechanism and the phenomena of con-
sciousness. The question before us may then be stated in the
following provisional form : Do the phenomena of consciousness
require for their explanation nothing more than a statement of
those changes in the material mechanism with which they are obvi-
ously correlated ; or do they also require the assumption of one
real and non-material being as the subject and ground of them all?
To repeat a remark already made, the approach to this question
must be through the introspective study of mind ; for only such
study can tell us what the phenomena of consciousness actually are.
§ 5. It is so obvious as scarcely to need or admit of debate, that
mental phenomena are not identical with the changing conditions
CONSCIOUSNESS AND NERYE-COMMOTION. 589
and activities of the nervous system. However our states of con-
sciousness may be related to the states of the brain — even if the
former are absolutely and without exception dependent upon the
latter — the two are certainly not the same. What the exact states
of the brain are with which any of the mental states are correlated
we know only very imperfectly and by remote conjecture. But so far
as we do know anything about the particular molecular activities
of the central nervous system which are most directly connected with
the phenomena of consciousness, they do not differ essentially from
other molecular activities of this system not thus connected with
consciousness. The chemical constitution and structural form of
the nerve-fibres and nerve-cells of the brain do not differ from
those of the spinal cord in any such respect as, of itself, to account
for the difference in the relations in which the two stand to con-
scious mental states. They do not so differ even from the mole-
cules which enter into the living plant or animal of much lower
species, mentally, than man. It is a surprise, from which scientific
investigation can never recover, to find that the connection between
our sensations, mental images, and vohtions and the peculiar ma-
terial constitution and functions of the cerebral mass of nervous
matter should be so intimate as it undoubtedly is. The foregoing
fact shows that it is quite impossible to regard the two classes of
events — the molecular changes of the central nervous mass and the
happenings of our conscious expeiience — as one and the same.
All physical events are modes of motion — alterations in the re-
lations of the material atoms or masses to each other in space.
This is as true of the human brain as it is of the clod of the valley.
Its atoms cannot be conceived of as doing anything, so long as they
remain material atoms, that does not essentially consist merely in
changing their relations in space to other mateiial atoms. This
is the activity which chemistry supposes to be continually taking
place as the work of nutrition and depletion in the nervous cen-
tres accompanies the process of thought ; this is what, as general
"nerve-physiology " rightfully conjectures, occurs when any form
of stimulus acts upon the afferent nerve through the end-organs
of sense, and corresponding states of sensation arise in the mind.
But the conscious process of thinking is not the change in the
chemical constitution of the nervous mass ; the conscious sensa-
tions are not the wave-like movements of nerve-fibres and nerve-
cells. It is not simply true that to identify these two kinds of
phenomena — phenomena of the motion of material atoms and
j)henomena of change in mental states — is difficult for the average
mind, but attainable by the scientific observer ; it is rather true
590 EELATIONS OF MIND AND BRAIN.
that no mind can frame any intelligible idea of what could be
meant by identifying the two.
Moreover, the history of investigation shows that a man may be
highly trained, both in the observation of the phenomena of the
animal body and of his own self-conscious mind (for example,
Ai'istotle), without even suspecting the important relation which
exists between the latter and the cerebral mass. Indeed, there is
no distinction which all men are compelled to make more clearly
than that between their own conscious states and the changing con-
ditions, by way of motion, of the masses and molecules of matter.
All theory which assumes the possibility of idenlifyhig molecular
motions of brain-atoms with the shifting forms of mental experi-
ence, or attempts to set forth the peculiar nature of the latter by
simply stating the conjectured laws which control the former, in-
creases the general confusion which tends to surround the whole
subject.
§ 6. Furthermore, it is not easy to see what could possibly be
meant, that is worth serious consideration, by speaking of the phe-
nomena of consciousness as the jjrodud of the brain. By the word
"product" we ordinarily understand the new form into which a
material substance has been thrown by the action upon it of some
machine or mechanism. Thus we call certain secretions of the body
the "pi'oduct" of the tissues where they are secreted in somewhat
the same way as that in which we speak of the products of the
field or of the loom. The function of the living molecular mech-
anism of which certain tissues consist is exercised in producing
from the pabulum brought to them by the blood the secretions of
gastric juice and bile. To speak of mental states and processes as
the " jDroduct " of the nervous mass of the brain, in any sense of
the words corresponding to that which we rightly apply to the
various secretions of the body, involves us at once in the grossest
absurdities. The secretory product of the brain is the fluid found
in certain of its cavities ; its nutritive product, so to speak, is the
new nervous tissue which is constantly being formed from the
blood by that activity of reproducing its own kind which this tis-
sue has in common with other living tissues. But this fluid and
these newly produced molecules or nerve-corpuscles in the brain
are in themselves no more like mental processes, and no more to be
identified with such processes, than are the tears that flow from the
tear-ducts or the pus that exudes from a wound. In so crass a
way of speaking it is diflficult to distinguish what can properly be
meant by comparing — under the term "product" — the relation of
conscious sensation and thought to the brain with the relation of
CO'lSrSCIOUSNESS AND NEEVE- COMMOTION-. 591
the gastric juice to the stomach or of the pancreatic juice to the
pancreas.
There is another and more plausible use of the word "product''
to describe the connection between the nervous matter of the brain
and the phenomena of consciousness. When a system of material
molecules is acting under relations to each other which are deter-
mined by their constitution, arrangement, and environment, we may
speak of the constantly new relations which they assume as the
'product of their previous constitution and arrangement, and of
whatever influences act upon them from material molecules outside
of the system (the environment). Thus the functional activity of
the nervous centres, the complex and interacting nerve-commotions
of the brain, might be regarded as the product of the matter
constituting these centres. This manner of speaking has certain
marked advantages. It emphasizes the merely mechanical point of
view. It insists upon the valid assumption that the account of
every change that arises in the material particles out of which the
brain is composed must be sought for in the previous constitution
and arrangement of those same particles as acted upon by stimuli
either external or internal to the whole brain-mass.
Let us suppose, for the sake of illustration, an incredible increase
in our powers of observation. Let us suppose that it were possible
with the microscope to discern the exact chemical constitution of
every molecule of the nervous substance of the brain, to Avatch the
motion of all the atoms composing these molecules as chemical
changes take place or as waves of nerve-commotion in infinite va-
riety move hither and thither among its countless nerve-fibres and
nerve-cells. All this would be in itself absolutely nothing more than
an expansion under the eye of the observer of what he sometimes
sees in somewhat grosser form — for example, in the amceba — and
of what he infers is constantly taking place in every kind of nervous
tissue. The status of the system of moving molecules at each in-
stant is to be explained — so far as explanation is possible — from its
status at the preceding instant, in connection with any influences
bi'ought to bear upon it from the outside. Moreover, all such out-
side influences, so far as they are of a physical sort, are nothing but
modes of the molecular activity of other material particles. Looked
at in this way, the product of the brain is the molecular activity of
the brain. That is to say, the function of this unique system of
molecules is to be constantly in motion, in the form of activity
which we have already examined as "nerve-commotion."
But if the foregoing statement be admitted, how does it help us
in the least to understand the phenomena of consciousness regarded
592 EELATIONS OF MIND AND BRAIN.
as the product of the brain ? In order to hold that mental phe»
nomena are related to the substance of the brain, in the same way
as that in which the nerve-commotions or molecular changes are
related to the same substance, we must identify mental phenom-
ena with molecular changes. But we have already seen that it is
impossible to identify the two classes of phenomena, as phenomena.
The phenomena of nerve-commotion may be regarded as the prod-
uct of the nervous mass in which they occur ; that is, they may
be attributed to the constitution and arrangement of the molecules
which compose this mass, as showing what the mass can do. But
the phenomena of consciousness cannot be regarded as the product
of the same nervous mass in any similar meaning of the word
"product."
§ 7. Yet another unsatisfactory way of regarding the relation
between the brain and conscious mental phenomena requires a
more detailed and careful consideration. Everything in our pre-
vious examination has tended to show that the molecular changes
which go on in the brain, whether they are occasioned by afferent
impulses that oi'iginate in the application of stimuli to the end-
organs of sense, or by the modified amount and quality of the blood-
suppl}^ are not only regular antecedents, but true causes of what
takes place in the mind. All the second part of this treatise was
occujDied in pointing out the different classes of such relations
between physical antecedents and consequent mental phenomena.
[The objections Avhich are ordinarily urged against speaking of
physical changes as the cause of the phenomena of consciousness
will be raised and answered later on.]
It is plain to every unprejudiced mind that, in some valid sense,
changes in the condition and activity of the substance of the brain
are sjDecially related to certain of the shifting phenomena of con-
scious mental life. From this admission, which is enforced by the
entire study of Physiological Psychology, the temptation is strong
to proceed at once to the completion of an apparently simple and
comprehensive theory. This theory claims thata/^ mental phenom-
ena, whatever their varied characteristic shading, have exact equiva-
lents, as it were, in specific forms of the nerve-commotion of the
living brain. Every such phenomenon, therefore, is only the man-
ifestation of what has previously taken place, or is simultaneously
taking place, in the physical molecular structure of the nervous
centres. To employ a figure of speech — for every state and action
of the so-called mind in consciousness, that collection of nerve-
fibres and nerve-cells which we call the brain exacts a payment
in some special kind of coin. For example, with the molecular
CEEEBRAL AND MENTAL COMBINATIONS. 593
chaiages in the substance of the brain which may be designated A,
B, C, D, etc., the mental states called a, ^, y, 8, etc., are uniformly
and necessarily joined ; and with the combination of molecular
changes which may be described by A 4- B + C + D, etc., the
mental states a + /3 + y + S, etc., are as uniformly and necessarily
joined. When the molecular changes recur in a fainter or modi-
fied form, as A', B', C, D', then there must be a recurrence of the
corresponding mental states, only in fainter form, as a', (i\ y', 8'.
Finally, it is without exception true — so this theory holds — that
nothing happens in the mind by way of conscious sensation, pres-
entation of objects of sense, ideation, reproduction of mental im-
ages, and higher aesthetic feeling or intellectual processes or choice,
w^hich does not find its only real explanation in the equivalent
changing states of the nervous system.
§ 8. Our first impression on considering the foregoing way of ac-
counting for mental phenomena is that of a certain surprising audaci-
ty. The theory, standing on a slender basis of real fact, makes a
leap into the dark which carries it centuries in advance of where
the light of modern research is now clearly shining. Physiological
Psychology, as we have been compelled to regard it, has been seen
to be encompassed with difficulties at every step ; and some of
these difficulties appear absolutely insurmountable. It has achieved
its greatest triumphs in giving a physical and physiological expla-
nation of the variations in the quantity and quality of sensation,
and of the time-rate of the simpler mental processes. But even in
these domains of greatest achievement it is found that almost every-
thing needed for an exact science of the relations of the molecular
changes in the substance of the brain and the changes in states of
consciousness is lamentably deficient. In the first place, little prog-
ress has been made in framing a theory of the nature of the phys-
ical changes themselves. Physical science is not as yet able to deal
with the phenomena of nervous action, as shown even by a single
living nerve with a muscle attached when acted upon by any one
form of external stimuli ; how much less, then, with that vast com-
plex of nerve-fibres and nerve-cells which constitutes the human
brain ! As to purely physical explanations of the variations in the
quantity of sensations we are also in great doubt. No adequate
means exist for measuring accurately the changes in the amount of
all the stimuli which act on the end-organs of sense. We have less
knowledge of the laws which regulate the amount of excitation set
up in these organs by changes in the amount of stimuli; and
scarcely any real knowledge at all of what molecular changes take
place within the central organs when the afferent nerves have stirred
38
594 MIJSD AS CONSCIOUS BEING.
them to their cliaracteristic action. Hence Fechner's laws, con-
sidered as merely empirical statements of relations between the
amounts of certain external stimuli and our judgments under ex-
traordinary conditions as to how much we are affected thereby, are
readily disputed. But considered as setting forth the essential re-
lations which exist between the physical changes in the brain and
the intensities of the resulting mental changes they are quite inde-
fensible. Moreover, the amount of our being affected, the quan-
tity of the sensation which results from the application of physical
stimulus, can be determined only by the judgment of the same
consciousness which is affected with the sensation. But judgment
itself is a form of mental phenomena for the essential part of
which no physical equivalent can be discovered or even conceived
of.
What has just been said concerning our inability to give a com-
plete physical explanation of variations in the quantity of sensa-
tions applies with equal force to their qualities and time-relations.
But even if the whole field of sensation, as respects the amounts,
kinds, and order in time of its phenomena, were already covered by
such purely physical explanation as refers them wholly to changes
in the molecular condition of the brain, the above-mentioned theory
would by no means be established. For in investigating the corre-
lations which undoubtedly exist between the nervous mechanism
and the phenomena of consciousness, it is found that some of these
phenomena imply activities of the mind which do not admit, in any
sense of the word, of being thus correlated. For an example upon
this point, we may refer to what was said (Part 11. , chapters VI. and
Vn.) as to a mental synthesis being implied in the formation of all
presentations of sense. " Things " are not mere loose aggregates
of sensations. They are the results of mental synthetic acts, the
laws of which cannot be attributed solely to the various ways in
which the physical molecules of the brain are made to move by the
action of stimuli reaching them. Let it be admitted that, with in-
creased information, we should find the scale of varieties in the
kinds of mental phenomena called sensations corresponding, point
for point, to the scale of varieties in the manner of the motion of the
waves of nervous excitation. Let it also be admitted that the scalp
of the changes in the intensities of mental phenomena, that are of
the same kind, corresponds with equal exactness to the scale of the
changes in the vibratory swing of these waves. Let it be still
further admitted that, whenever any presentation of sense occurs,
there exists a kind and amount of various excitations simultane-
ously effected in the brain which corresponds exactly to this par-
NATUKE OF ALL "THINGS." 595
ticular presentation of sense. The mere congeries or common
occurrence of such sensations, as the necessary result of the exci-
tations of the brain, does not constitute a real " Thing," Each
"thing" implies, not simply a vast number of moving physical
molecules, on the kind and amount of whose motion the phenomena
of conscious sensation are dependent, but a uniting energy and a
unity in mind. Fifty million molecules, even when they are highly
complex and unstable phosporized compounds, gyrating in the most
wonderful fashion with inconceivable rapidity, certainly do not
constitute 07ie thing. They do not, then, by molecular constitution
and activities, even constitute a physical basis which is conceivable
as a representative or correlate of one thing. Each molecule among
them all, even in order to be conceived of as being itself one such
thing among the other millions of more or less similar but not
identical molecules, is dependent upon this same synthetic activity
of the mind.
§ 9. Still further, the study of metaphysics shows us that certain
assumptions, which are not of a sensuous character, or verifiable
at all by an appeal to the sensations, enter into every presentation
of sense. No such presentation of sense consists of a mere put-
ting together of individual sensations. Whatever account one may
choose to give of the nature and origin of this belief, there can be
no doubt that all men do believe that the " things " they perceive
are neither bare groupings of mental phenomena nor forms of the
molecular motion of a nervous mass ; men believe that things are
real existences set in space outside of their OAvn bodies. Things
are known as real ; they are supposed to Jtave attributes ; they act
on each other and on us who observe them ; they exercise force ;
they are extended and movable in space, and continue uninterrupt-
edly through more or less of time. To be all this is necessary in
order to be a "Thing." Now, the assumptions which enter into
the popular belief may be regarded as all true or all false, or as
partly false and partly true, in the form in which men ordinarily
hold them. But not one of them is capable of being justified, or
in any way accounted for, by an enumeration of the sensory states
into which consciousness is thrown by the action of the stimuli
on the nervous system. Much less is it accounted for by refer-
ence to certain hypothetical wave-like motions in the substance of
the brain. That such wave-like motions occur we have no doubt.
That the changes in the quantity and quality of the sensations are
related to, and dependent upon, the intensity and the kind of these
motions is a most reasonable conjecture. That the motions which
are correlated with the presentations of sense differ in kind or de-
£96 MIND AS CONSCIOUS BEING.
gree from those whicli are correlated with mere images of imagi-
nation may also be true. It is true, furthermore, that our percep-
tions and ideas of the extension and motion of things are dependent
for their characteristics in great measure upon the structure of
the physical organism. But it is impossible to conceive of any
form of molecular motion which could serve as the physical basis
or physical representative of any of those metaphysical assumptions
which enter into all knowledge of things. What kind of nervous
action can be the equivalent of an unchanging conviction or belief
in the reality and true causal energy of all things both visible and
invisible ? What sjjlitting up of the chemical constitution of the
molecules of nervous substance, or difference in the character of
their agitations, can be conceived of as analogous to, or serving as
true cause of, the distinction which is involved in our speaking of
each Thing as though it were a substance with attributes ?
Reference to Avhat has already been said (Part II., chapter X.)
concerning the impossibility of assigning a physical basis to the
mental operations of voluntary recollection, with its recognition of
similarity, to attentive choice, and to all the discrimination which
underlies the work of the intellect proper, will furnish further oc-
casion for distinsting the above-mentioned theory. For example,
the new process of physical excitation, which serves as the " basis "
— so to speak — of any image of memory, may be similar to the
process which served as the basis of the original presentation of
sense. But the mental act of recognizing the similarity of the ob-
ject before the mind to one no longer before it, and yet of distin-
guishing the former from the latter as characterized by the time in
which it occurs, does not admit of being conceived of under any
analogy to such physical processes. The same thing may be said
of consciousness in itself considered, and so of every mental j)he-
nomenon considered as being what it actually is — a phase of con-
sciousness. But to make clear this aspect of the case requires that
we should resume the consideration of the so-called "material-
istic" theory of the relations between mental j^henomena and ner-
vous substance from a slightly different point of view.
§ 10. There can be no doubt that the popular and wellnigh imi-
versal belief regards the subject of the mental phenomena as a real,
non-material, and permanent being. This belief also undoubtedly
regards this subject as on« indivisible being, a "unit-being." In
other words, the prevalent conception of the Mind is that of an
existence which is spiritual and is a unity in some unique sense.
The many objections which have been raised against the belief
may be divided into two classes — one of which may be called
IKFLUENCE OF THE BLOOD-SUPPLY. 597
metaphysical, and the other physiological or physical. The meta-
physical objections arise, in part, from the difficulty which is felt
in defining what is meant by " reality," " spirituaUty " (or non-
materiality), and " unity " in that strict sense in which these terms
are thought to apply to the mind. The consideration, both of
these objections and of that way of considering the facts which es-
capes them as far as possible, will be for the present postponed.
But the other class of objections arises from the very facts with
which it is the special business of the science of Physiological
Psychology to deal. It may be summarily stated in the form of
questions like the following : What kind of permanent reality can
belong to a being whose essential characteristic of having various
states of consciousness can be temporarily laid aside when the brain
sleeps or is deprived of its blood-supply ; or can be wholly lost
when certain nervous centres are subjected to permanent pressure
or destroyed by disease or the surgeon's knife ? How can non-
materiality be affirmed of phenomena which — so far as we can
trace them at all — exist only in immediate dependence upon a cer-
tain chemical constitution, structural form and arrangement, and
functional activity of material atoms ? How can the claim of be-
ing the highest unity be made for that which exists at all only as it
is in a constant flux ; which, indeed, is possessed of its one charac-
teristic activity of being conscious, only on condition that it divides
itself into subject and object and experiences a constant change of
the f oi'ms in which it is conscious ?
In spite of such objections from the physiological point of view
as are the foregoing, the popular assumption, when freed from its
crudities and interpreted intelligently, may be shown to be the only
one compatible with all the facts of obsei'vation. It may be shown
that it is demanded by these facts. On the contrary, the attrib-
uting of mental phenomena to the substance of the brain (with or
without including the rest of the nervous substance) does not satisfy
the facts of observation. The relation between brain and mind is
not such that the former can be considered as a real being, of which
the phenomena of the latter may be regarded as activities. Another
real being must be assumed to exist as the subject of the mental
phenomena — a being with a nature quite unlike that of material
molecules.
§ 11. The phenomena whose relation to the molecules of the ner-
vous system is in dispute are phenomena of consciousness. Noth-
ing in regard to these phenomena is more impressive, upon first
subjecting them, as such, to introspective observation, than their
surprising complexity in unity. Or we may rather say, the way in
598 MIISTD AS CO]SrSCIOUS BEING.
A,\-lnch all states of consciousness, however different they may be
with respect to characteristic quality or origin, are attributed by
the conscious subject to one subject as his own states is the most
surprising of all facts. This fact underlies all the truths and law?
into which psychology inquires, whether starting from the physio-
logical or from some other point of view.
It has been customary for psychologists to classify all the mental
phenomena under a few so-called " faculties " of the mind. The
objection has often been made to such classification that it tends
to confuse or destroy a just appreciation of the unity of mind. A
more obvious objection to the ordinary psychological classification
is perhaps this, that it fails to take due account of the vast com-
plexity of mental phenomena. For — it should never be forgotten —
mental phenomena are always, primaribj considered, nothing more
than events. This is true of sensations and perceptions, with all
their objective reference, as well as of acts of imagination and of
so-called pure thought. The yellow of the watch, the red of the
rose, which I see, are modes of the affection of my consciousness.
Excluding for the present all reference to any metaphysical assump-
tions, these colors are simply events in consciousness. The real
jDrocesses outside of consciousness — the objective existences and
events — to which the events in consciousness are referred by science
are in no sense similar to the events of consciousness themselves.
What the real process outside of consciousness is — whether it
consist of I'apidly vibrating waves of ether, or of photo-chemical
changes in the tissues of the retina, or of nerve-commotions prop-
agated along the optic nei've and in the upper occipital lobe of
the brain — we know only by doubtful inference from certain con-
scious affections of our own to certain material existences assumed
to exist out of consciousness. Whether the right to make these
inferences be disputed or allowed, there can be no dispute over the
statement that the phenomena of conscious vision are not copies of
any of these external events. What is tnie of colors is also plainly
true of smells, and tastes, and sounds. These sensations are all
events in consciousness. Recent researches into the nature of the
sensations which come through the excitation of the skin show that
these also are, primarily considered, mental events of various kinds ;
such as having the feeling of cold, or of heat, or of pain, or of
pressure, or of motion, etc.
Moreover, the modern experimental view of the way in which the
sensations are localized and synthetically combined to form the
presentations of sense shows that the latter also must be consid-
ered as being, primarily, mental events. Of course there is a sense
COMPLEXITY OF MENTAL PHElSTOMElSrA. 599
in which it is absurd to say, not simply, "Perceptions of things are
always merely mental events ; " but also, " Things themselves are
merely mental events." It has already been shown that certain as-
sumptions enter into all our perceptions and conceptions of so-
called " things ; " but that even the attempt to account for these
assumptions, by assigning them to any conceivable form of a physi-
cal basis in the brain, leads to absurdity. Still there is also a sense
in which " things," that can certainly never be any different with
respect to their known qualities from the way in which they appear
to us when perceived, are mental events. Sensations are mental
events ; the discriminating, combining, and localizing of sensations
are mental events. Things to us are never more than discrimi-
nated, combined, and localized sensations, p?i<s the metaphysical
assumptions to which reference has been made.
§ 12. Eeflection upon facts like those just stated leads us to won-
der at the enormous complexity of mental phenomena. For the
purposes of the jji'^ctical life we are warranted in regarding the
surrounding world as composed of a limited number of material
existences that undergo little or no change from day to day. But
this way of regarding the objects of experience does not at all
satisfy the demands of psychological inquiry. Such inquiry con-
siders the knowledge of external nature, as well as of what is recog-
nized as pertaining most strictly to the world within, to involve an
unceasing change in the activities of consciousness. Indeed, with
the limitations already referred to, we may say that the entire
world, so far as it is our world, consists only of these changing
states. It follows, then, that the first truth of which we have to
take account is the following : Our entire conscious existence —
whether regarded simply as being ourselves affected in a certain
way or as having a purely objective experience of the existence and
qualities of so-called Things — is a continually shifting succession
of individual mental activities, no one of which is exactly like any
other or is to be considered as a mere repetition of any other.
It would be acknowledged by all that a mental state of pain on
account of toothache is different from a state of pleasure in smell-
ing a rose ; that the sensation of yellow is vinlike the sensation of
i-ed, and that these sensations, in common with all sensations of
color, are unUke those of touching a cold piece of iron or of hear-
ing a musical tone. All the practical activities of men are based
upon the conviction that the individual things with which they
deal differ from each other — not simply in respect to the qualities
they have, and the degree in which they severally possess these
qualities, but also as separate real beings differ. But the tinith
600 MIND AS CONSCIOUS BEING.
now undei' consideration reaches further than this common ac»
knowledgment. Strictl}' speaking, from the point of view taken by
an analysis of consciousness, the same so-called " thing " is never
in experience twice the same. Every time that it exists before the
mind, as a presentation of sense, it is constituted anew by an ac-
tivity of the mind. Unless various localized sensations and re-
membered images of sensations are "synthesized "under the laws
which govern such kinds of mental phenomena, there can be no
presentation of sense ; and the only " thing " which has immedi-
ate existence for us is the presentation of sense. Accordingly, the
variety of the mental phenomena, when we begin the attempt to
classify them, appears as great as that of all the individual acts
and states of consciousness, whether those acts and states have
reference to comparatively unchanging beings outside of conscious-
ness or not.
Even a description of the different kinds of mental phenomena
which psychological science proposes to explain would be impos-
sible, if the foregoing truth were not merely one side of the whole
truth. For what is infinite in variety and always changing its kind
cannot be described. There could then be no science of the mental
phenomena, no classification of the states of consciousness, or ex-
planation of them by relating them to each other and to the physical
basis on which they are supposed to rest.
§ 13. Observation of the jjhenomeua of consciousness, liowever,
shows us that they are plainly classifiable, and that the authority on
which this classifying reposes is immediate and indisputable. For
the phenomena of consciousness ai'e directly recognized in con-
sciousness as like or unlike with varying degrees of similarity and
dissimilarity. They are assigned by everyone possessed of a de-
veloped experience to this or that class, without any question that
the act of classification is legitimate and correct. The number of
distinguishable colors, or kinds of visual sensations, is indeed in-
definitely large ; and so is the number of sensations of musical
tone. The power to raake all the necessary discriminations in these
sensations varies greatly with different persons. It is perfectly
proper to say that the number of kinds of the states of conscious-
ness arising through the senses of sight and sound varies greatly
in different individuals. There are many more colors and tones
for some men than for others. The qualities belonging to the sen-
sations wbich follow excitation of the skin are also diverse ; and,
in the case of sensations of smell, the means of classification for
each individual are limited chiefly by the number of the different
smellable things with which he has happened to come in contact.
DIFFEEENCES IN PHET^OMENA. 601
It must also be confessed that the j)opular classifications of the
states of consciousness, as based on conscious experience itself, is
not infrequently erroneous. So far as the sensations are concerned,
this is partly due to the fact that they are ordinarily referred to some
thing or to some part of the body, which is only approximately cor-
rect, and yet correct enough for practical purposes. The taste of
the onion is no less clearly distinguished from other states of sensa-
tion arising through the mouth because the subject of the taste does
not know that his sensations are in fact largely sensations of smell.
Because one believes that one tastes the pepper instead oi feels it
with the tongue, one has lost none of one's power to make clear dis-
criminations in the domain of consciousness. Nor is this power
taken from the color-blind, although the length of their color-spec-
trum is shortened so that they have a less extended domain of sen-
sations of this order within which to discriminate.
It appears, then, that likenesses and unlikenesses in the phe-
nomena of consciousness, and an immediate "awareness" — so to
speak — of these likenesses and unlikenesses, or direct discrimina-
tion by consciousness of the quality of the states of consciousness, as
such, are involved in that classification of the mental phenomena
which all men make. If the classification becomes more refined
and elaborate, it at no time ceases to repose on the same founda-
tion. All classifications of mental phenomena which have any other
foundation, or which introduce any other consideration than the
simple one of how I, the conscious subject, am affected, are not
really classifications of mental phenomena as such. Such alleged
classifications may indeed tell us much that scientific inquiry de-
sires to know about the origin or correlations of the mental phe-
nomena. They may assume to say what special part of the external
organ of sense, or what special area of the brain, is more direct-
ly concerned in producing the physical state which precedes or
causes the mental phenomena. They may demonstrate what kind
of physical stimuli result, respectively, in exciting such and such
states of consciousness. But they tell nothing whatever as to what
the phenomena really are, whether like or unlike, or as to how they
may be ranged and rated together. They are classifications of the
causes, or occasions, or physical excitements of the mental phe-
nomena ; they are not classifications of mental phenomena, as such.
§ l-i. Moreover, the principles which regulate the formation of
classes among the conscious states of the mind are very different
from those which regulate the proposal to classify the elements of
the physical basis of these states, or the molecular activities of
these elements. To be sure, the Youug-Helmholtz theoiy of vis-
602 MI]S"D AS CONSCIOUS BEING.
ual sensations proposes to distinguisli red, green, and yellow as
the three kinds of retinal elements ; and the opto-ehemical theory
of vision speculates as to the classes of pigments connected with
the seeing of various colors. It has bee^ held by some physiolo-
gists that the two main parts of the inner ear (vestibule and coch-
lea) correspond to the two principal classes of sensations of sound
(to noises and musical tones) ; or even that the vibration of an in-
dividual nervous element in the organ of Corti represents, in some
sort, each definite one among the many states of consciousness that
constitute our hearing of a melody. Sensations of feeling may be
classified as of peripheral or central origin, in reference to the
place from which the nervous impulses occasioning them are sup-
posed to take their rise. But one need not be deceived by all this.
The " red " retinal elements are not themselves red ; and if they
did appear of this color to external observation, it would not in the
least degree help us the better to understand what is the quality
of that state of consciousness which we call the sensation of red.
The different nervous elements of the organ of Corti may be capa-
ble of being aiTanged in a scale ; if so, they are classified as longer
or shorter, and as arranged in space one above the other. But this
classification is in no real respect like that which we make when we
arrange the states of consciousness called musical tones in a scale
of their pitch.
In general, the physical elements of the nervous system are di-
visible into classes according to their chemical constitution — as,
for example, the phosphorized and the non-phosphorized proximate
principles of the brain ; or, according to their structural form, into
nerve-fibres and nerve-cells of a great variety of shapes, sizes, etc. ;
or, according to their physiological function, into afferent and effer-
ent, reflex or inhibitory or automatic. But no such principles of
division can be carried over to the mental phenomena. They have
absolutely no applicability to these phenomena, as such. We cannot
introduce distinctions of chemical constitution, structural form, and
physiological function into sensations and ideas, into feelings and
thoughts and acts of will. A phosphorized thought, or a stellate
feeling, or an afferent thought, are phrases that have no meaning.
Nor should we be any better able to apply the jDrinciples by which
we classify the different factors of the physical basis of conscious-
ness to the phenomena of consciousness itself, in case we had a
much more minute acquaintance with those factors. Let it be sup-
posed that psycho-physical science should so far advance as to be
able to tell precisely what kinds of molecular activities of what
nervous elements are correlated with all the various classes of
PRINCIPLES OF CLASSIFICATION. 603
mental plienomena. The latter woiild still remain precisely such
as they are in kind ; they would still have to be classified, if at all,
on the ground of their hkenesses and unlikenesses as directly
known in consciousness. If it should be discovered that the mo-
lecular agitation of a particular group of fibres and cells in the or-
gan of Corti is necessary in order to produce the sensation of the
musical note a , and that this agitation resembles that which some-
what similar fibres and cells in the retina undergo preceding the
sensation of a particular shade of green, the two sensations would
then be no easier to classify together than they are now. Both
stand near the middle of their respective scales. In that respect
it might be said that the sensation of the musical tone a is like the
sensation of green. This point of likeness is really, however, one
that appertains solely to a physical quality or function in certain
bits of nervous matter more or less directly connected with the
physical antecedents of the sensations ; it cannot be conceived of
as appertaining to the sensations themselves.
§ 15. Considerations derived from the theory of the quantity of
stimuli and their resulting intensities in the states of conscious-
ness might be urged in the same direction. The variations in the
amount of the molecular processes within the nervous system are
all measurable and classifiable, if at all, on principles with which
physics is familiar. The excitation in the nervous system always
consists simply of so many molecules, having such a chemical con-
stitution, moving so much in such a direction with relation to each
other. But the most nearly related mental phenomena are feelings,
and judgments comparing feelings, such as can be expressed only
somewhat as follows : " Now that shade of red seems to me a little
more intense ;" or, "now I think something has been added to the
sensation of pressure ; " or, " I should call this note the major
third of the other." In general, we may say that, quantitatively
considered, the changes in the nervous mechanism are all precisely
alike as to kind — that is, are all that mode of motion called "nerve-
commotion " — and admit of being measured off by a common phys-
ical standard or unit of measure. But the mental phenomena are
classifiable only as a succession of states, that are continually chang-
ing their qualit}' and have no quantitative measure which we can
separate from these changes of quality. Nerve-commotions can be
conceived of as added and subtracted, switched to the right or to
the left, concentrated, distributed, dissipated. But, strictly speak-
ing, the resulting mental phenomena admit of no treatment of this
sort. Every sensation exists, if at all, as an indivisible qualitative
state of consciousness ; it cannot even, as, such state, be retained to
604 MIND AS CONSCIOUS BEING.
be compared with some other succeeding state, in order to decide
whether it is more or is less in respect to quantity. Without
memory and comparison, which are complex activities of mind dif-
ferent from the mere having of sensation, we could not affirm of
any mental state that it is more or less than another.
Still further, other forms of mental activity which have an un-
doubted reality do not admit of even the loose application to them
of terms of quantity which is proper when speaking of sensations
and feelings. A " weighty" judgment and a " high " ideal ai'e not
to be measured by standards that admit' of correlation with the in-
creasing or diminishing swing of nervous molecules. Yet if those
classes of the phenomena of consciousness which these words imply
have, as such, any physical basis whatever, this basis must consist
in some form of nerve-commotion as to the quantity of which an
exact measurement is conceivable. If, however, a wide swing of
the molecules were found to go with a good, sound, clear judg-
ment, and a contracted swing to be the physical cause of narrow-
ness of mental apprehension, such a fact would not help us in any
regard the better to revise the Aristotelian classification of the syl-
logism. Reasoning, as a mental activity, would be deductive or
inductive, analytic or synthetic, as before, after making the discov-
ery that the one process is connected with a continual diminution
of the cortical areas over which the nerve-commotions spread them-
selves, and the other with a noble diffusion of such commotions
over an ever-widening expanse of the brain.
§ 16. It is an undoubted fact, however, that mental phenomena
admit of a fairly satisfactory arrangement into classes. The ar-
rangement can be made only upon the basis of their likenesses and
unlikenesses as known in consciousness and by consciousness. No
other arrangement of these phenomena, as such, is possible — none
that is not founded upon the same ultimate facts thus distinguished.
All attempts at an arrangement of them by other principles, and
from other points of view, result in the classification of something
else (such as the physical antecedents, causes, or concomitants)
than the phenomena themselves. It is not strange, then, that the
"old psychology" won its principal triumphs, by the method of
introspection, within the field of classification. The crude begin-
nings of a physiological psychology in the phrenology of Gall and
Spurzheim were obliged at that time to accept from introspective
psychology its division of the mind's activities into so-called " fac-
ulties." In its more scientific and experimental form at the pres-
ent time physiological psychology is just as dependent as ever
upon introspective psychology for a classification of the mental
KINDS OF MENTAL PHENOMElSrA. 605
phenomena. The inti'ospective science of mind has already arrived
at very general agreement upon this point.
It is very generally agreed that all the mental phenomena are
classifiable under three great heads — into phenomena of knowing,
phenomena of feeling, and j^henomena called acts of will. The
distinction of the two latter classes of phenomena is, indeed, a mat-
ter established in comparatively recent times. A certain number
of investigators, who use the method of introspection, still venture
to affirm that acts of feeling in the form of desire are not to be dis ■
tinguished as differing in kind from acts of will. In their view,
so-called acts of will are resolvable into phenomena of feeling.
But the oiDinion of the great majority of students of psychology
is decidedly in favor of adhering to the threefold division of the
mental faculties. There is also a large amount of agreement as to
the sub-classes that fall under these three — at' any rate, with the
exception of the varied efforts made to deal with the very complex
phenomena of feeling in its many forms. The more recent at-
tempts (made especially by certain English writers on psychology)
to depart from the accepted classifications of the " old psychology"
have attained little or no valuable result. These attempts have in-
troduced into psychology a great number of uncouth terms, derived
largely from false analogies of physical science, which tend to rep-
resent the case as though sensations could be weighed or measured
or compounded like the nervous shocks which cause them, and as
though ideas could become " agglutinated " or "agglomerated"
like globules of mercury or minute particles of water. Such at-
tempts, however, have thrown no light on the nature of the mental
phenomena, or on the question of their correct classification ; they
have not really succeeded in supplanting or discrediting the classi-
fications of the " old psychology." Nor is it at all likely that the
principal classes into which all mental phenomena are now throvni
will ever be changed. The "faculties" of the mind — however the
term is to be understood — will remain the same. At all events, if a
change should be made in these divisions, such change could only
be accomplished by the method of introspection.
§ 17. The question may now be raised : How are we to account
for facts like the foregoing ? In attempting an answer to this
question, the great significance of the facts themselves should be
recalled. It has been shown that mental phenomena cannot be
conceived of as identical with the molecular motions of the nervous
mass ; and that the fundamental relations between the two cannot
be expressed by the statement, the phenomena of consciousness are
the pr-oduct, of the brain — in any meaning of the word "product"
606 MIND AS CONSCIOUS BEING.
wliicb can be clearly defined. Nor can tbe tlieory be accepted that
every mental state and process bas its exact equivalent, with respect
to all its factors, in some antecedent or concomitant state or pro-
cess of cerebral nerve-fibres and nerve-cells, and that therefore all
mental phenomena are to be directly and exclusively referred to
these physical structures as their sole subject or ground. More-
over, it has been found necessary to admit that mental phenomena,
as such, can be classified only by introspection ; and that the prin-
ciples on which the classification must be based differ from those
applicable to the nervous substance, while the actual classes discov-
ered by the only available method do not correspond to any of
those with which physics and physiology make us familiar. And
yet there is no insuperable difficulty in classifying the phenomena
of mind. Introspective psychology furnishes us with a classifica-
tion, on the whole, tolerably satisfactory
What, then, is the fair inference from all these facts with respect
to a decision between the two theories of mind which were previ-
ously proposed ? (See § 3. ) Plainly, such inference favors looking
toward some other subject or ground of the mental phenomena
than the nervous substance of the brain. Its result commends sub-
stantially the same view as that held by the great majority of man-
kind. We shall state and explain this view, however, in different
terms from those employed by this majority.
The phenomena of human consciousness miud he regarded as activi-
ties of some other form of Beat Being than the moving molecules of
the brain. They require a subject or ground which is in nature
unlike the phosjDhorized fats of the central masses, the aggregated
nerve-fibres and nerve-cells of the cerebral cortex. This real be-
ing, thus manifested immediately to itself in the phenomena of
consciousness, and indirectly to others through the bodily changes,
is the Mind. To it the mental phenomena are to be attributed as
showing what it is by what it does. The so-called mental " fac-
ulties " are only the modes of the behavior in consciousness of this
real being. We actually find, by the only method available, that
this real being called Mind behaves in certain perpetually recur-
ring modes ; therefore, we attribute to it certain faculties. The
mental faculties, then, are not entities that have an existence of
themselves ; nor are the individual behavings of the mind (the
so-called " ideas ") existences that can become " agglutinated "
or " associated " or " compounded " in any way. They are not
divisions of the mind ; nor are they powers of the mind, if by
this word be meant some permanent recognizable reality, stored
up in a s^Diritual subject, or attached to it or inherent in it, after
' THE UNITY OF CONSCIOUSNESS. 607 .
the analogy of tlie relation of physical forces to their subjects, the
atoms. The faculties of the mind are the modes of the behavior,
in consciousness, of the mind. And the very nature of the classi-
fying acts "which lead to their being distinguished is explicable
only upon the assumption that a real being called mind exists, and
is to be distinguished from the real beings known as the physical
molecules of the brain's nervous mass.
That the subject of the states of consciousness is a real being,
standing in certain relations to the material beings which com-
pose the substance of the brain, is a conclusion warranted by all
the facts. That the modes of its activity in consciousness are cor-
related under law with the activities of the brain-substance is a
statement which Physiological Psychology confirms ; one upon
which, indeed, it is largely based. It will be our task, in a subse-
quent chapter, to consider under what general terms such correla-
tion may best be expressed. All physical science, however, is based
upon the assumption that real beings may have an existence such
as is sometimes called " independent," and yet be constantly re-
lated to each other under known or discoverable laws. If this as-
sumption could not be made and verified, all the modern atomic
theory would stand for nothing but a vain show of abstractions.
Upon what grounds of reason or courtesy — we may inquire at this
point — does Materialism decline to admit the validity of similar as-
sumptions as demanded by mental phenomena ?
§ 18. The foregoing view of the mind and its faculties is greatly
confirmed by a,nother consideration. Consciousness has a certain
remarkable unity. If the complexity of mental phenomena is be-
wilderingly great, the unity of consciousness is striking and unique.
Many disputed questions may be raised touching the essential nat-
ure of this unity, the means we have for recognition of it, and the
inferences which may legitimately be drawn therefrom. Some of
these questions will be merely alluded to at this point, and their
further consideration postponed until later on.
All developed forms of consciousness involve an attribution of the
present particular state of consciousness to a subject of the state.
It is for this reason, as has already been remarked, that we express
each state of our consciousness by saying : "/am in such or such
a condition ; " "/feel thus and so ;" "/ see, or hear, or smell, or
taste, or think, or plan," etc. Such language — and all language de-
signed to describe our mental phenomena is such — plainly shows
that some kind of distinction is made by everyone between the
state and the "^gfo" which is the subject of the state. It is no
adequate explanation of this fact to say that by the subject, in all
608 MIND AS CONSCIOUS BEING.
these sentences (the "I" to which the states are attributed), we
mean to denote a mere concept of myself formed upon the basis
of past experience. Such a concept may indeed be formed. Its
completeness and correctness furnishes an excellent test of the
amount of development attained by each individual in self-knowl-
edge. Few individuals, however, would be found able to give a
statement, at all satisfactory to themselves or to others, of just what
characteristics are to be considered peculiar to their "self -hood."
"We do not, then, merely designate the "self" when we thus con-
stantly refer to the " I " which is the subject of each state. Our
knowledge that the state is our state, or that we are in this definite
individual state, is perfectly clear and immediately conclusive with
reference to all the experience we have or can remember.
The clearness and immediateness of the reference which we are
continually making of our states to the subject of them all is in
marked contrast with the obscurity and indirect nature of the con-
cept we are able to form as to what manner of persons we are.
Moreover, all the ability we have to frame a concept of the " self "
is dependent upon this constant, primary, and inexplicable fact of
a possible reference of each state to the subject of the state (the
" I "). To explain this reference, we have to assume that it has
already been made ; we have to assume it in each attempt at ex-
planation. "We may express the absurdity of the effort to think or
imagine ourselves out of the reach of this form of all consciousness
by asking ourselves such questions as follow : How can there be
a pain, a sensation, a thought, an act of will, that is not somebody's
pain, sensation, thought, or act of will ? What is a state of con-
sciousness considered as separable, or . actually separated, from a
subject of such state ? That is to say, no state of consciousness
can even be conceived of that does not involve this same reference.
There may, indeed, be great doubt whether some of the lower
animals ever make any such reference. It may be that the amoeba
or the oyster can have a sensation that is not, quoad sensation, the
conscious state of the amoeba or the oyster. As to this we cannot
say. But we can say that if such a so-called sensation is possible
for any animal, it is impossible for us to imagine it. "We cannot
imagine what we cannot bring under the unchanging forms of our
own consciousness.
The force of the foregoing remarks is not destroyed by calling
attention to the fact that the attribution of the state of conscious-
ness to the subject of the state, to the " I," is by no means con-
tinually being made. It is plain that some distinction must here
be drawn between being conscious and being self-conscious. The
EEFERElSrCE TO THE EOO. 609
crowd intently watching a tragedy in a theatre, or a conflagration,
is certainly not unconscious, but is rather in an exalted state of
consciousness ; on the contrary, he who is intently watching the
spectacle is not at all, or is only in a slight degree, se//"-conscious.
There are considerable periods of every day when, so far as we can
remember, we have been "conscious" (not being in profound slum-
ber or having fainted away), but with little or no reference in con-
sciousness of its activities to the subject of them all. Nevertheless
there can be no doubt that we are capable of this reference ; that
it is found to be involved in every mental state just so soon as we
seek to determine the factors of such state ; and that to recognize
its being there is essential to any explanation of the nature of
mind,
§ 19. All the different mental phenomena of an individual must
be regarded as states of one consciousness ; they are all said to occur
in the unity of consciousness. There can be no doubt that every
person (with the exception, at most, of certain rare cases of so-
called double consciousness) attributes all the forms of his con-
sciousness to one and the same subject. This is what is meant by
saying that he regards them all as his states. We cannot conceive
of ourselves as dubitating whether some particular pain or pleasure,
or act of memory or of imagination or of will, present in conscious-
ness, is to be ascribed to our ego or not. We cannot attribute any
such state to some other than our own ego. It is true that in cer-
tain cases of disease or lesion of the brain an abnormal condition
in this respect seems to occur. The one person sometimes seems
to pass back and forth between two mental lives, which are so
distinct from each other that they may well be said to belong to
two personalities. But reflection upon these abnormal cases only
makes the stronger and clearer our conviction as to the unity of
consciousness. Living two seemingly distinct mental lives is not
possible without its being assumed that each one of the two is lived
in the unity of its own consciousness. This would be as true of
twenty distinct lives, if they followed each other in the case of any
individual as the result of disease of the bx-ain, as it is of two such
lives.
It is not at all surprising that the fact of the primary vrnitj of
consciousness should be inexplicable ; for it is itself the fact im-
plied and assumed in all attempts at exj)lanation of other mental
facts. Were this the line of thought necessary to introduce at this
point, it might be shown that all the unity possessed by "Things "
is dependent upon the unity of consciousness. Without memory
and judgment there can be no perception of Things. But the bind-
39
610 MIND AS CONSCIOUS BEING,
ing force of memory is dependent upon this unity. We cannot
remember that which has not in some form or other been previously
present in consciousness, in our own consciousness, in one and the
same consciousness as that in which the remembered image is now
present. We cannot judge except by uniting two terms in one con-
sciousness.
Of course, all language as to the unity of consciousness, when
carefully examined, turns out to be figurative, and to have no mean-
ing except as interpreted over from entities and relations of a
material sort into terms of consciousness. By the " unity of con-
sciousness " it cannot be meant that consciousness is some kind of
an entity which remains one and unchangeable throughout, like
those atoms which physical science has supposed to constitute the
whole world of material reality. It will be found, however, that no
conception can be formed of the unity which is supposed to belong
to the atom without involving in it the unity of consciousness.
We can, indeed, picture to ourselves a very little bit of extended
matter, barely visible under the highest powers of the microscope,
Vv'hich never changes its shape or color, etc., and which always be-
haves itself in exactly the same way under precisely similar circum-
stances. But this mental picture would itself have any unity be-
longing to it only as it existed in the unity of consciousness. It is
this unity which makes each " Thing " to be one thing ; it is this
unity which imparts to all else that is one whatever unity it may
have.
When, then, we speak of the unity of consciousness we mean,
fii-st of all and chiefly, to call attention to the following primary
fact of experience : All states of consciousness involve a reference
of the state to an "I," as the subject of the state ; and, in spite of
the constant change of states which goes on, so that in reality the
same state never recurs, and even the same thing is never twice
known, all the states are understood to be states of one and the
same subject. This reference and this understanding enter into
all our experience ; they give conditions to experience and make it
possible. Whatever changes experience may be conceived of as
undergoing, they, as conditions of all possible experience, must be
conceived of as remaining. To ask us to try to imagine a mental
state or act not involving this reference and understanding, with
respect to the unit-subject of consciousness, is to ask us to try to
be conscious and unconscious at the same time. The " I " may
become unconscious ; that is, the phenomena of consciousness in
that connected development which characterizes the individual may
cease to exist. But phenomena of consciousness cannot be con-
KNOWLEDGE OF SELF INDIRECT. 611
ceivecT of as occurring without being referable to some one subject
as its modes or states.
§ 20. Metaphysics, presuming upon its intimate relations to the
" old psychology," has doubtless often made an unwarrantable use
of the facts above mentioned. It has often declared that we have
an immediate and indubitable knowledge of the mind as one and
the same real being in all acts of consciousness. The facts have
been interpreted, as though the case stood as follows : I have the
power to look within myself, and by thus looking I can discern
what I really am. I immediately know (that is, know by the intro-
spective act of self-consciousness) that "/"am always, however my
states may change, one and the same real being. I am a real, self-
identical entity ; and if asked how I know that I am all this, ray
appeal is to the indubitable evidence of the act of self-conscious-
ness.
The foregoing metaphysical statement of the case is by no means
obviously correct ; we believe it, on the contrary, to be exaggerated
and incorrect. In thus overstating the case, there is liability that
the case itself will be lost. Consciousness carries with it no immediate
knowledge of any real and self-identical being — not even of that real
being which we call Mind and, with good reason, assume to exist
as the ground or permanent subject of mental phenomena. Meta-
physics is the science which treats of those assumptions that under-
lie all of our experience with what we call "reality." But it treats
of assumptions or beliefs such as we find do actually and inevita-
bly enter into all our experience. The real existence of " Things,"
whether of the masses of matter we daily test by the senses, or of
those hypothetical beings called atoms which physical science re-
quires in order to account for the phenomena, depends upon such
assumptions. If it be admitted that we cannot be immediately
conscious of ourselves as real unit-beings, we are no worse off than
we are with respect to our belief in the existence of any of the so-
called real beings of which all men suppose the world to be com-
posed.
It can also be shown that the case of the mind or soul, with re-
spect to its unity as a real being, is made no better by admitting
that an immediate consciousness of ourselves as such unit-beings is
possible. For let it be supposed that by concentrating all my at-
tention upon the present state of consciousness I most clearly and
indisputably discern myself as one real being, forming the ground
of that state. Let it be supposed that every half-hour in the day I
repeat this mental act. It would still have to be assumed, as some-
what altogether out of consciousness, that the real being discerned
612 mijs^d as conscious being.
in any one of these acts of introspection is one and the same real
being as that discerned in all the rest. A real unit-being that
should last only while the difficult act of concentrated introspec-
tion was taking place would be of no value to serve as a self-con-
scious mind. In fact, such a unit-subject of the individual state
would have no claim to be considered as a real being at all.
§ 21. The grounds on which depends the assumption, that the
subject to Avhich all the phenomena of consciousness are actually
referable is one real being, will be considered more in detail at
another point. For the present we merely adopt the assumption,
provisionally, as much more probable than any which accounts for
our conscious reference to such subject, by enumerating certain
possible relations into which the masses and molecules of the brain
may be thrown as conditions of the empirical unity of conscious-
ness. That there is such empirical unity of consciousness there
can be no dispute. Dispute itself would assume it. It scarcely
admits of more doubt that all physical theories to account for this
unity are wholly unsatisfactory. We know, indeed, certain of the
physical conditions and concomitants of consciousness. If oxygen-
ated blood is shut off from the cerebral substance, consciousness
disappears. If the blood has floating in it certain drugs, or prod-
ucts of the combustion of tissue, consciousness is disturbed. If
certain cerebral areas are injured or eradicated, the psycho-physi-
cal basis of certain forms of consciousness is altered. Still, all
this does not seem to bring us a step nearer a satisfactory physical
account of the unity of consciousness. The molecules of the brain
are infinitely numerous ; they are made up into structural forms of
indefinite number and variety ; the kinds of the relations they as-
sume toward each other are indescribably many. Consciousness,
so far as we know, has no special centre or seat within the cere-
brum ; and if it had, the constituents and activities of that centre
would have to be exceedingly manifold and complex. Now, all
this is precisely the opposite of what we should expect of a phys-
ical structure which should be called upon to exhibit the phenom-
ena of many conscious states, all referable to one subject. No help
toward solving the problem is derived from calling attention to
the fact that the different portions and elements of the brain are
all interconnected. The connecting structures only add still fur-
ther to its multiplicity and complexity of elements. It would be
easier to conceive of an atom as becoming conscious than the cer-
ebral cortex,
§ 22. But surely the assumption that one real being is the sub-
ject of these states, which are certainly all referable in conscious-
MIND A EEAL UNIT-BEIISTG. 613
ness to one and the same subject, is not an impossible one. On
the contrary, it is the most natural assumption ; it is the assump-
tion instinctively made by men in general. Notwithstanding the
difficulties which encompass it as soon as we attempt to define it,
or to test the ground on which it rests, we shall find that it is de-
fensible and valid.
We conclude, then, from the previous considerations : The sub-
ject of all the states of consciousness is a real unit-heing, called Blind ;
ivhich is of non-material nature, and acts and develops according to
laws of its own, but is specialhj correlated loith certain material mole-
cular and masses forming the substance of the Brain.
CHAPTER II.
THE DEVELOPMENT OF THE MIND.
§ 1. A DISTINCTIVE feature of modern science is its endeavor to
satisfy inquiry into the nature of the objects of its investigation by
a detailed description of their development. In answer to the in-
quiry what a thing is, we are invited to listen to an account of how
it hecavie what it is. Indeed, the universal process of " Becoming "
has been almost personified and deified so as to make it the true
gi'ound of all finite and concrete existences. There can be no
doubt as to the great fruitfuluess and value of this historical and
genetic way of studying everything. Any complex existence is cer-
tainly far better understood after it has been not simply analyzed
into its jjresent component parts, but has also been traced back to
its most nearly primitive and undifferentiated stages. The history
of the egg explains the bird even more than the nature of the bird
'explains the egg.
Both of the two subjects, with whose correlations Physiological
Psychology deals, require for their most satisfactory understanding
to be studied by this genetic method. The structure of the nervous
system appears in a new light when regarded as the result of a pro-
cess of evolution. Beginning with the unimpregnated ovum, by
propagation of cells of living protoplasm, by segmentation of larger
sections of these cells, by prolifei'ation of cells and separation into
layers, the one portion of the gei'm from vv^hich the mechanism of
nerve-fibres and nerve-cells is to unfold itself becomes differentiated
from the other portions. By vital processes kept up through nutri-
tion and resulting in the growth of some areas beyond others, and
by mechanical influences at work to crowd forward here or push
back there, to fold and tuck and cause to dip or curve, etc., this
epiblastic portion develops the system of end-organs, central or-
gans, and connecting tracts of nerves.
Psychology, also, has felt strongly this modern impulse. It has
been forced to confess that its real task is but begun when it has,
by introspection, examined and classified the j^henomena of adult
conscious Ufe. All the mental phenomena undoubtedly have a
MENTAL FACULTIES PROGRESSIVE. 613
truly vital connection. Those of the present have their roots in
those of the past. The so-called faculties of the mind are neither
hard and fixed lines drawn to exclude from internal relation the
various modes of its behavior in consciousness, nor are they kinds
of activities that spring up, full-formed at once, at different in-
tervals in its entire history. Although we can never reproduce
in adult self-consciousness the forms of the earliest stages, we
can show that these forms differed greatly from those taken in
this adult self-consciousness. We can show that, the earlier forms
must have been much the simpler. For exam.ple, an analysis of
the presentations of sense shows that the "things" of developed
experience are resolvable into certain elements of sensation which
the mind has learned to localize. In other words, perception is a
result of development ; for "things" are not ready-made products
existing, as they appear, outside of the mind, but resultants of
mental activities that have to be performed anew so often as the
things appear. It is in the evolution of the mind that we find our
means for understanding its true nature. Moreover, the character-
istics which distinguish one mind from another are to be under-
stood as largely resulting from the order and relative prominence
of different activities in the development of each.
§ 2. So far as the connection of mental phenomena with the in-
creasing complexity of the nervous activities, and with the stored
energies and hardening habitus of the nervous elements, affords any
explanation of the development of the mind, we have already said
all that is necessar3^ The growth of the mind in the acquirement
and arrangement of sensations, in the recalling of ideas, in the
forming of judgments about objects of sense, etc., is plainly de-
pendent upon the evolution of the bodily members. But the nat-
ure of the relation which exists between the mental phenomena
and the nervous mechanism, so far as this can be learned by study-
ing the development of both, furnishes us with another question.
Upon this question, also, the same conflict of view as that to which
we have already drawn attention may arise. On the one hand, the
attempt is made to refer all the so-called development of the mind
to the evolution of the substance of the brain, under purely physi-
cal and mechanical causes. This attempt, then, denies that any
real unit-being called the Mind needs to be assumed as undergoing
a process of development according to laws of its own. It cannot
be disputed that many facts of experience tend to strengthen such
an attempt.
There is a general correspondence, with respect to the complex-
ity and quality of the work done, between the different stages in
616 MIND AS A DEVELOPMENT.
the development of both body and mind. Nervous system and
mental condition are both immature in infancy ; both develop with
great rapidity in early childhood, and then more slowly on into
adult life ; both — it is claimed — remain comparatively stationary
through the period of man's highest maturity ; and as old age ad-
vances, both keep pace in their decline. Moreover, cases of arrested
development of brain are cases of arrested development of mind.
Idiots are frequently microcephalic ; many of them have brains
weighing less than thirty ounces. Degeneracy of the tissues of the
cerebral hemispheres is commonly connected with increasing de-
generacy of the mind. As the tides of molecular nerve-commotion
rise and fall in the nervous mass, so rise and fall the tides of men-
tal vigor. A temporary increase of cerebral action, caused by a
glass or two of wine, is expressed in the form of mental phenomena
by a heightening of imagination, a quickened flow of ideas. What
need, then — it is asked — of assuming any permanent subject of
what we regard as mental development, other than the mechanism
of physical molecules with its evolution under the control of physi-
cal law ?
On the other hand, all attempts to account for the orderly in-
crease in complexity and comprehensiveness of the mental phe-
nomena by tracing the physical evolution of the brain are wholly
unsatisfactory to many minds. We have no hesitation in classing
ourselves among this number. Those facts of experience which
show a correspondence in the order of the development of the body
and the mind, and even a certain necessary dependence of the lat-
ter upon the former, are, of course, to be admitted ; but they are
equally compatible with another view of the mind's development.
This other view has the additional advantage that it makes room
for many other facts of experience which are very difficult of rec-
onciliation with any materialistic theory. On the whole, the his-
tory of each individual's experience is such as requires the assump-
tion that a real unit-being (a Mind) is undergoing a process of de-
velopment, in relation to the changing condition or evolution of
the brain, and yet in accordance with a nature and laws of its own.
^ 3. That the development of a real non-material being is im-
plied in the history of the mental phenomena of each person may
be argued on two principal grounds. In the first place, it may be
shown that the stages and laws of the development of mind do not
fully correspond to those which are observed on tracing the evolu-
tion of the nervous system. It may also be shown that certain ele-
ments necessarily enter into the development of mind, which have
nothing like them, or strictly correlated with them, in the evolu-
EEALITY OF MENTAL HISTORY. 617
tion of the material mechanism. One real being may be dependent
on other beings for its starting, as it were, and for certain factors
that enter into its growth or furnish the indispensable conditions
of its growth. It may thus receive the form and direction of its
development, in large measure, fi'om these other beings. And yet
this fact gives us no right whatever to refuse to such a being all
title to take rank among other real existences with a complex nat-
ure of its own. No existence loses or impairs its claim to reality
by being dependent for its development on other existences. The
mind, on the contrary, most indubitably establishes such a claim,
because the stages and laws of its unfolding, and some of the
factors which necessarily enter into this unfolding, are peculiar to
itself (sai generis).
§4. That the words, "development of the Mind," stand for a
real process, there can be no reasonable doubt. The sum-total of
the conscious experience of each individual is something far more
than a mere series of states of consciousness. No difference in de-
grees under the same kind can be conceived of which is greater
than the difference between the most mature and highly developed
mental performances and those inconceivably simple activities with
which the mental life begins. So far as the character of the phe-
nomena of consciousness is concerned, the mind of the adult New-
ton or Kant is much farther removed from the mind of the infant
Newton or Kant than the latter is fi'om the mind of one of the
lower animals. There is much more which is companionable and
mutually intelligible between the adult man and his dog than be-
tween the adult man and his newly born child. The latter is,
however, raised at once above the most intelligent animal when
we consider the possibilities of its mental development. What the
human being is cannot be at all adequately described without con-
sidering the nature and limits of that process of becoming which
belongs to it.
There is no doubt, also, that the incomparable improvement of
the mental processes which distinguishes the adult from the infantile
human being is a true development. Each stage of this improve-
ment is dependent upon preceding stages. The changes are aU in
some sort according to a plan. Thus the life of every individual's
mental experience is capable of being made into a history. A cer-
tain tolerably uniform order in the relative development of the dif-
ferent faculties is discernible. At first the senses are awakened to
a lively and varied activity ; then memory and imagination become
more prominent ; and, finally, judgment and the reasoning powers
assert their sway. Gradually, things become known and conduct
618 MIND AS A DEVELOPMENT.
shaped under principles which are assumed to have a universal
vahdity as so-called general laws. The history of the mental life
of every human being, from the cradle (or even from its embryonic
existence) to the grave, has all these characteristics of unfolding
itself in a regular order, in which all that comes at all comes in
due sequence and acknowledged dependence upon what has pre-
ceded. This is the very essence of a true development.
§ 5. Can the development of the mind be explained as merely
the I'esultant or expression of the physical evolution of the nervous
system — this system being regarded as situated in the rest of the
bodily environment, and surrounded by the more extended envi-
ronment of the world of active physical energies outside ? Against
an affirmative answer to this inquiry stand many facts and laws of
all such mental development. In spite of what must be said con-
cerning the striking correspondence between the evolution of the
bodily organism and the development of the mental powers, it
must be held that there are marked divergences as Avell. At cer-
tain epochs of life the evolution of the brain seems to stand far in
advance of the mind ; at others, the mind appears to have over-
taken and passed by the stage reached by its physical substratum.
During a long period of life the growth of mental powers is con-
stant and solid, while the growth of the physical basis has nearly
ceased, and such changes as are taking place in it appear quite
inadequate to serve as correlates for the mental growth. More-
over, the most distinctly typical features in the develojDment of the
mind remain the same when malformation or disease or accident
have largely changed the physical evolution of the brain.
§ 6. We have no sufficient means for deciding how far the mental
life of the human embryo keeps pace with its organic evolution.
We do not even know beyond doubt that the embryo has a mental
life, in the only tenable meaning of the words — that is, a life of
conscious states. But it is probable that its antenatal movements
are not all purely reflex, and neither accompanied nor directed by
conscious sensation, feeling, and volition. The mental life of the
embryo, if it exist at all, can hardly be more than an irregular and
fitful succession of the lowest and least complex mental phenomena.
Taste, smell, hearing, and sight are, of course, not to be thought
of as entering into such a mental life. Touch, as we understand
the word to express the localized sensations of pressxire which arise
through the practised organ of the skin, is scarcely more likely to
belong to the human embryo. Obscure feelings arising from
changes in its relation to the surrounding tissues and fluids of the
mother, or from disturbances in its own internal organs, and result^
THE AROUSING OF THE MIND. 619
ing equally obscure feelings of innervation, as its limbs are moved,
must constitute the great part of its experiences. As yet there is
no experience, properly so called ; no perception of things, no feel-
ing of self, no discrimination of ego and state. Yet long before
the child is born it possesses a wonderfully elaborate nervous
mechanism, far surpassing in its grade of evolution the nervous
system of the most intelligent adult animals. Previous to birth
this nervous mechanism must also be constantly in action in a
highly complicated way ; it is engaged in supervising the processes
of nutrition, and in the reflex and automatic activities which are
expressed by the changes of the child's position within the womb
of the mother. The mind, however, is as yet unawakened ; this is
not because the nervous mechanism is not complex and active
enough to serve as the physical basis of a rich mental development,
but because the kinds of sensation — visual, tactual, auditory, etc. —
which start and furnish and direct this development have not yet
been supplied. The mental life cannot then be said to have kept
pace before birth with the evolution of the brain, or with its dis-
tinctive activities. On the contrary, it is far behind the stage al-
ready reached by its physical support. It waits to he aroused and
set to its own work of combining and interpreting those sensations
which are to serve as its chief means of early culture.
For the first few weeks of infancy the same relation between the
relative development of the body and soul of the child is maintained.
Both are subjects of a rapid growth, but the former is still much in
advance of the latter. The newly born infant is, in respect to the
condition of its nervous system, much the most highly oi-ganized
and fully equipped of all young animals ; but as judged by the
number and quality of its volitions and perceptions, many other
young animals are less stupid and insensate. If we may represent
its mental condition by anything conceivable through the adult
imagination, the human infant is in a dreamless sleep occasionally
interrupted by instants of unlocalized and unmeaning sensations.
The cavity of the infant's tympanum is filled with a fluid, the
place of which is only gradually taken by the air. Sensations of
sound, if they arise at all, must be at first only occasional and
faint. Binocular movements of the eyes in the direction of bright
objects take place early ; and it is through sensations of light and
color that the first activities of the mind in perception are aroused
and controlled. But for some weeks there ai-e only sensations and
impressions, without tme perceptions ; there is as yet no knowl-
edge of any " Thing." This earliest relation of mind and brain,
with respect' to the degree and rate of their development, is not
620 MIND AS A DEVELOPMENT.
favorable to any form of the materialistic theory. It rather favors
the view that the mental phenomena belong to another principle
than any material substratum. The dependence of the mind on
the brain is indirect and through the sensations (chiefly of sight
and touch) which must be furnished to the mind as the primary
factors in its development. The halt in the development of mind
at first, and its distinct backwardness with respect to the relative
stage it has reached, are due to a lack of such sensations as have
the characteristics of spatial series (see Part II., chap. VI.), and so
are able to stimulate the mind, and afford it the requisite material
for the construction of true presentations of sense.
§ 7. Within a few months after birth the child has undergone
an enormous mental development ; it has become a mind, in some
inchoate way recognizing itself as the subject of states, and per-
ceiving a little surrounding world of objects of sense. It has also
begun to attend to the objects presented in consciousness, and to
direct its attention by voluntary choice. The mind's relating ac-
tivity has been aroused ; and acts of memory, discrimination, and
judgment, as the basis for those concepts which require articulate
language to express them, are repeatedly taking place. The as-
sumptions of reason, as involved in all human experience of things,
and of their action and reaction upon each other, are found to be
shaping the growth of the mental powers.
As accompanying and forming the ground for this sudden blos-
soming of the mind in the use of its conscious powers, there is a
continuous and yet diminishing monthly increase of the substance
of the brain. No new organs are formed within the cranial cavity ;
but those which have been formed previous to birth are further
developed under the changed conditions of nutrition. In respect to
the quantity and arrangement of its molecules, the nervous mech-
anism certainly undergoes no development during the first year of
the child's life which at all corresponds to, or accounts for. the
development of the child's mind.
It may be claimed, however, that the most important develop-
ment of the nervous mechanism has been overlooked in the fore-
going description. This development does not consist so much in
the increased quantity of the brain's substance, or in the more
intricate arrangement of its elements with relation to each other.
It consists rather in the forming of what has already been alluded
to (Part n., chap. X., §§ 18 f.) as " dynamical associations " among
the existing elements. The statement that such is the nature of
the developing activities of the nervous mechanism, and the as-
sumption that such activities are an indispensable physical condi-
FORM ATI ON OF ASSOCIATIONS. 621
tion for the growth of the mind, may both be taken for granted.
But even then the argument is far from complete upon which the
development of mind as a real being, with a nature of its own, and
with a history controlled by its own laws, is denied. The forma-
tion of the so-called "dynamical associations" among the mole-
cules of the nervous mass furnishes no adequate account of the
development of mind. This development is not in the direction
simply of associating together states of feeling, each one of which
has an exact physical correlate in a physical association among the
molecules of nervous substance. It is rather a development which
for its very existence requires something different from such asso-
ciations. The child might go on forever merely associating together
affections of its own mind in correspondence to dynamical associa-
tions among the nervous molecules, and yet have no growth of ex-
perience such as it actually attains. The fact is that within a
single year, or within two years, the child has learned to know
"Things," to attend to some in preference to others, to refer its
states in some crude way to itself, to form concepts and judgments
by the mind's relating activity, and to underlay the world of its
sensuous experience with another world of assumption respecting
certain non-sensuous realities. To account for this boundless ex-
pansion of the activities of consciousness, with its surprising new
factors and mysterious grounds of synthesis and assumption, by
proposing an hypothesis of "dynamical associations" among the
particles of nervous substance in the brain, is a deification of im-
potency. So far as we really know anything about the development
of both brain and mind, we are compelled to say that the latter,
when once started by the sensations furnished through excitation
of the former, proceeds to unfold its activities with a rapidity and
in an order for which no adequate physical causes can be assigned.
During the period of young manhood, or young w^omanhood, the
dependence of the development of the mind on that of the body
is most strikingly seen in the influence over the emotions and
imagination from the sudden unfolding of certain bodily organs
and powers. The indirect influence of these acts of feeling and
imagination upon the more purely intellectual progress of the mind
is, of course, correspondingly great. But the dependence of mind
on body is by no means such as to favor the view that there is no
ground in a real being, other than the brain, for the order and rate
of the mental development.
This same statement is emphatically true of the long period of
maturity which constitutes what we call the "middle life " of man.
During this time the nervous matter undergoes scarcely any dis-
622 MIND AS A DEVELOPMENT.
cernible development. Nothing that microscope or electrometer
can detect distinguishes the brain of the man of twenty-five from
that of the man of fift3\ A few grammes of weight have perhaps
been added to it during this long period of years. Anyone is at
liberty to speculate as to the immense development of so-called
"dynamical associations" which has taken place during the same
period. We are far from denjdng the possibility of such develop-
ment. But the fact that a large development of mind may have
taken place during the same period cannot be denied. If it be
true that large numbers of mankind remain mentally stationary for
most of their adult life, this truth in no way favors a materialistic
view of the development of mind. Most observing persons will
rightly find the chief account of the failure of mental growth in
precisely those kinds of mental activity which least admit of being
explained by physical analogies. It is from want of mental curiosity,
attention, careful and comprehensive judgment, sound moral pur-
pose, etc., that most men fail to develop during adult life in their
mental powers. And these ai*e mental activities for explaining
which no one as yet has been able to conjecture any analogous or
corresponding class of cerebral changes.
Many minds, however, not only make vast acquisitions, but also
experience a large unfolding of mental capacities during the period
of middle life. How mature and wide-reaching do the judgments
of some men then become ! How profound the insight into the
most abstract and difficult speculations comes to be ! What cere-
bral evolution shall be conceived of as being the only true cause,
and the exact physical correlate, of the mental development of Kant
during the years preceding the appearance of the "Critique of Pure
Reason," or of Newton while he was unfolding the calculations and
conjectures of the "PrinciiDia?" To hold that the changing mole-
cules of the brain-substance of these thinkers were the sole subjects,
really being and acting in the unrolling of these great dramas of
human speculations, involves an astonishing credulity. On the
contrary, we seem compelled to affirm that no important activity,
or law, or fact, in the order of such mental development, fails to
demand the assumption of a real and non-material unit-being, un-
folding its powers according to its own nature, although in de-
pendence upon certain elements and conditions furnished through
the brain.
§ 8. Advancing old age is doubtless, as a rule, characterized by
a simultaneous decline both of certain mental and of certain bodily
powers. In this period of life, howevei", the correspondence be-
tween the changes in the character of the phenomena of conscious-
' THE FIISTAL MEISTTAL STAGE. 623
ness and tlie altered vigor and quality of the nervous mechanism is
not such as to suggest that the two have an altogether common
basis. In healthy normal old age the course of the mental life is
distinguished chiefly by the dropping out or diminished action of
certain factors that are relatively prominent in youth. The circu-
lation is slower ; the vital energy is declining ; the muscles are less
promptly and completely under the control of the volitions ; the
end-organs of sense are less sensitive under impressions ; and
certain emotions and passions whose physical basis is of the most
obvious sort become greatly modified or disappear. As to the
marked effect of these bodily changes upon the mental development
there can be no doubt ; and if the previous mental development has
been chiefly along lines indicated by organic activities the apparent
decay of mental vigor when the physical basis begins to fail is, of
course, also most plainly marked.
On the other hand, there are many other cases, where no notable
difference can be detected, or even fairly assumed, in the course of
the psychical evolution down to the " feebleness "of old age ; where
the course of mental development continues substantially undis-
turbed in all its most important features. The mind of the culti-
vated old man, with calm and broad judgment, with refined kind-
liness and fixed moral principles, is not to be spoken of as suffering
a decline which keeps pace with the failing of his physical powers.
It maj justly be claimed that the final period of human life, on the
whole, favors that theory which regards the mind as by no means
wholly conditioned upon the brain for the character, order, and
laws of its development.
§ 9. The same general view of the development of mind, which
is most consistent with the facts of the different stages of life, is
also favoxxd by considering those sudden checks or changes in the
course of this development that are caused by disturbing or de-
stroying considerable portions of the nervous matter. The phe-
nomena which follow experimental extirpation of the substance of
the brain in the lower animals, and loss of it by serious lesions in
the case of man, do not favor a materialistic theory of mental de-
velopment (see Part 11., chaps. I. and II.). Extensive losses in
certain areas of the cerebral hemispheres are often followed by
no appreciable disturbance even of any sensory or motor activity.
When lesions are followed by such disturbance, their effects may
in time wholly or partially disappear. When such disturbance is
permanent, it is not necessarily connected with loss in the power
of judgment, in the higher intellectual, aesthetic, and ethical activi-
ties of feeling, intellect, or will. Even where aphasia is so severe
624 MIISTD AS A DEVELOPMENT.
as to include the loss of all power to utter or understand articulate
language, the patient may still show a good degree of mental acute-
ness by ability to make calculations or play games of skill.
On the other hand, the much more serious interruption or com-
plete loss of mental development may occur when no adequate ex-
planation can be detected in the distui'bance or arrest of cerebral
development. It is, of course, natural to conjecture that, in all
this latter class of cases, more accurate information would show us
some diseased condition of the brain as the physical antecedent of
the mental defects. We know that subtle changes in the character
of the blood-supply, such as we have no physical means whatever
for detecting, are often the causes of most profound changes —
either temporary or more permanent — in the train of ideas. None
the less, however, do both classes of cases above mentioned favor
the theory we are advocating, rather than the so-called materialistic
theory of mind.
§ 10. All the foregoing considerations suggest the conclusion
that the mind is primarily and chiefly dependent in its develop-
ment upon the nervous mechanism for furnishing and directing
the combination and order in recurrence of those sensations which
enter into all presentations of sense. Let any person of normal
and sane brain and mind consider how intimate and extensive is
the connection between his sensations and his whole mental devel-
opment. Fickle and confused experience of sensation involves
fickleness and confusion of judgment on all matters of sense. Loss
of any class of sensations, as a whole or in part, involves a distinct
impairment of mental powers. Such loss necessarily changes to a
considerable extent the character of the subsequent mental life.
Such loss, however, is regularly compensated for, to some extent,
by an increase of mental activity along the lines which remain open
to the mind. The man blind from birth can never have the same
course of mental unfolding, with respect to his perceptions of
things, his idea of space, his feelings before the beautiful, etc., as
that open to his more fortunate fellow. But he is not necessarily
inferior in mental capacity and activity ; because the development
of his mind, as conditioned upon the other senses, proceeds with
the ordinary pace, although along a different path.
The mind is absolutely dependent upon the nervous organism for
its awakening and furnishing in the life of conscious sensation.
The case of Laura Bridgman, and others similar, show how large
mental development is possible with even a greatly diminished out-
fit of the senses. But, of course, if touch and muscular sensation,
as well as smell, taste, hearing, and sight, were lacking, no con-
. EELATION OF THE FACULTIES. 625
scious mental life would be possible in any form known to human
experience. The form in which the sensations shall combine, and
the time-order of their recurrence, are also dependent upon the
character, number, and succession of the cerebral excitations
caused by external or internal stimuli. But when once the mind
is started upon its career of unfolding its powers, it maintains a
relative independence of its physical basis. Not that sensations and
resulting presentations of sense, together with the reproduced im-
ages of such mental products, do not always continue to furnish
indispensable factors and conditions of all mental development.
In the most abstract thought, and in the highest flights of the im-
agination, the mind never wholly gets away from the world of sen-
sation and perception, with its immediate dependence upon the
activities of the physical and nervous basis. On the other hand,
the course and extent of its unfolding are such as to show that its
stages and laws do not all correspond to those which characterize
the evolution of this basis. Its general dependence upon such
basis, in all its development, is through the sensations and their
reproduced images.
§ 11. Several references to the second argument (comp. § 3) for
our view of tlie development of mind have ah-eady been made. This
argument is based upon the fact that certain indispensable elements
enter into the development of mind which have nothing similar to
them, or strictly correlated with them, in the evolution of the ma-
terial mechanism. The mind can, indeed, undergo no development
except as conditioned upon these elements. But the elements
themselves cannot be regarded as the expression in consciousness
of merely physical causes, or as flowing necessarily from more
primitive activities of the mind which may possibly be regarded as
the expression of such causes.
All three of those fundamental forms of activity which are recog-
nized in the ordinary threefold division of the soul into faculties —
namely, acts of feeling, acts of knowledge, and acts of will — neces-
sarily enter into the development of the mind. Its development
consists in the unfolding of these three classes of acts, in their
mutual dependence and according to the laws which belong to each.
Among each of these three great classes of acts there are certain
subordinate kinds that defy all attempts whatever to correlate them
with the changes in the nervous mechanism, or to explain them as
necessarily or actually arising out of such physical changes. Such
are the feeling of moral obligation, the sentiment of justice, the
love of truth, and certain of the higher aesthetic feelings. Among
the acts of knowledge, such are the mind's relating activity, its use
40
626 PSYCHICAL FACTOKS SUPREME.
of the principle of reason and consequent in drawing deductions,
its confident assumption that similar phenomena are signs of like
realities, and that the world of sensuous individual experience is
but the manifestation of an invisible world of real beings, with per-
manent properties and forces, acting and reacting under law.
Such, also, are the acts of deliberate choice among courses of con-
duct, under the influence of moral considerations — the acts of "free
will " in the highest sense of the term.
Not one of the higher acts of feeling, knowing, or willing, so far
as its sui generis character is concerned, admits of being correlated
with, or represented under, any of the conceivable modes of the
motion and relation of molecules of nervous substance. Certain
sensations and perceptions connected with the rise and growth of
the higher forms of feeling have, undoubtedly, a physical basis ;
but such basis is not assignable to the feelings themselves. Sen-
sations and perceptions, which are resultants (in some meaning of
the word) of physical processes, are discriminated by judgment and
made the basis of deductions and inductions. But admitting this
does not one whit the better enable us to conceive of a physical
process which can account for the sui generis character of the re-"
lating activity itself. Acts of " free will," so called, always take
place under certain conditions of sensation and perceiDtion, as well
as of desire ; but the physical correlates of these conditions can in
no respect be conceived of as being also correlates of the conviction
that the choice is responsible and free.
Now, if such activities as the foregoing do actually constitute
indispensable elements of mental development — and it is obvious
that they do — this development cannot properly be accounted for
by assigning it to a mass of nervous matter undergoing a physical
process of evolution, after the manner of the growing human brain.
Such development rather implies a real being of another than the
physical order. This being must be thought of as stimulated by
the rise and recurrence of sensations and images of past sensations,
to unfold its own activities as conditioned by its own inherent
powers. Like every other real being, the history of its unfolding
is dependent upon the relations in which it is placed to other real
beings ; but it is nevertheless a history determined also by what
the being is.
§ 12. The trial will doubtless be made to escape from the con-
clusions hitherto reached, by means of help derived from a certain
psychological theory of the development of mind. It may be ad-
mitted that the attempt to find, directly, an adequate phj^sical basis
for all these so-called higher faculties, or modes of the behavior of
' MECHANICAL THEORY OF MIND. 627
the mind in its development, must be abandoned. But the higher
faculties themselves — it is said — are to be regarded as develop-
ments of the simplest activities. These highest faculties of all may
then be directly connected with the evolution of the body,, or of
the cranial mass, through the simplest mental activities. In this
way a kind of necessitated psychical mechanism is set up, which is
itself entirely explicable as a development from one kind of element
(the sensation) ; and then, by regarding this one kind of element
as connected with the motion of nervous molecules in a purely
mechanical way, the need is obviated of supposing any real being
called Mind as undergoing a process of mental development.
For example, it may be claimed that the one simple and undif-
ferentiated element of all psychical experience is the "neroous
shock." This nervous shock is merely the simplest expression or
result in consciousness of a nerve commotion set up by the action
on the nervous mechanism of external or internal stimulus. By
differentiation and combination of the nervous shocks, the so-called
simple sensations arise. By reproduction of similar combinations
of fainter shocks, the images of memory are produced. By " ag-
glutination " and " agglomeration " of the sensations and ideas,
judgments take place — only, since some new kind of idea does cer-
tainly seem to be involved in the essence of judgment, it must be
held that a " feeling of relation " is somehow slipped in between the
agglutinated and agglomerated sensations and ideas. By still more
elaborate groupings of the simple ideas, systems of thought and so-
called ideas of the highest order of abstraction — like the ideas of
space, time, etc. — come into mental being.
In the foregoing way, all the so-called mental processes that con-
stitute the development of the mind are strictly correlated, under
laws analogous to those which control the relations of physical ele-
ments, with the processes that go on in the nervous system ; thus
so-called " psychology " results in bringing the mind of man into
the same strict subjection to the energy of outside nature, under
the law of the conservation and correlation of energ}'^, that charac-
terizes all the phenomena with which modern physical science is
accustomed to deal.
The above-mentioned theory is doubtless admirably simple and
thorough-going. But its somewhat extreme simplicity and thor-
oughness constitute very important objections to it. In so crude a
form it scarcely deserves detailed consideration. It is enough in
this connection to call attention to the fact that the theory is built
throughout upon unverified assumptions ; and that, even granting
its assumptions, it affords no adequate description whatever of the
628 PSYCHICAL FACTORS SUPUEME.
real process of human mental development. No theory of nerve-
commotion has yet been devised to connect it with the externa]
stimuli under the law of the conservation of energy. If by " ner-
vous shock " be meant a psychical event, the break between such
shock and the nerve-commotion which is its antecedent is absolutely
impassable ; no physical energy, under the general law of its con-
servation and correlation, can pass this break.
Moreover, there is no actual or conceivable psychical event cor-
I'esponding to the undifferentiated nervous shock. Sensations are
always, as such, and from their very nature, of this or that definite
quality. An undifferentiated psychical element is a pure abstrac-
tion. Nor do sensations and their remembered images constitute
such existences that they can be spoken of as " agglutinated " or
" agglomerated." The so-called " feelings of relation," slipped in
between the single ideas and sensations, if by this be meant any-
thing less than relating activities of the mind, are absurdities in no
way fitted to explain or represent the act of judgment. And, finally,
this entire account of the course of mental evolution is an utterly
inadequate description of what actually takes place in the history
of even the poorest and weakest human minds.
§ 13. All theoi'ies of the mental development which account for
the different so-called faculties and stages of the growth of mind as
■ though they flowed necessarily from some one fundamental activity
are inadequate and misleading. The mind is indeed a unit-being,
but its unity is not of the kind alleged by these theories. Its dif-
ferent constitutional modes of behavior are not to be resolved into
each other, or into any one most primitive activity ; nor do they all
necessarily flow forth from such a primitive activity. They manifest
the rich variety of the mind's nature. They do, indeed, preserve a
certain order in time with regard to the relative amount of their
unfolding. The different periods of life are characterized by dif-
ferent stages of mental development ; these different stages of men-
tal development are characterized by a relative jDrominence of partic-
ular faculties, or modes of the behavior of the mind. But because
such a time-order is followed in the development of the mind, we
can by no means conclude that the faculties latest develojDed are
any the less native and essential to the character of the mind. Nor
is it true that these latest and highest faculties can be explained as
mere developments from, or modifications of, the earlier and sim-
pler.
Strictly speaking, none of the faculties, or constitutional modes
of the behavior of the mind, admit of being explained as mere de-
velopments of other faculties. This is true even of those minor
NO DEDUCTION OF FACULTIES. 629
forms of activity which it is customary to class under the same fac-
ulty. That I have the sensation " red " is no reason why I should
have the sensation " green ; " and that I have the sensations "red "
and "green" is no reason why I should also have the sensation
" blue." Neither does the existence of all these so-called funda-
mental color-tones, of itself, form any reason why the mind should
be affected with any of all the thousands of sensations supposed to
be compounded from them. None of these color-tones, psychologi-
cally considered, can be regarded as a development from the fun-
damental color-tones. That I am affected with a certain sensation
of color, lying at the bottom of the spectrum's scale, when several
billion vibrations of ether strike the retina, and with a qualitatively
different sensation when the number of vibrations is increased by
several billions more, cannot be explained as an evolution. The
same remark holds within the Hmits of each of the other senses.
Their scales of quality are not such that experiences at one place
of the scale can be evolved from those at other places of the scale.
Some of them, such as smell and taste, do not admit of being re-
ferred to any form of a scale or diagram representing relations of
quality. The feeling of heat is not another phase of the feeling of
cold ; neither of the feelings of temperature is to be explained as
arising out of feelings of pressure or motion.
When the sensations of the different senses are compared with
each other, the impossibility of considering any of the classes as
developing from any other becomes yet more apparent. That a
sentient being has an experience of hearing musical tones which rise
in pitch as the number of acoustic vibrations varies from thirty to
thirty thousand is no reason at all why the same being should have
an experience of seeing colors that change their " color-tone " as the
number of light-vibi'ations varies from about four hundred billions
to about seven hundred billions. In the development of the mind,
the senses may actually awaken in a certain order more or less defi-
nitely fixed. But this is very different from holding that the}^ develop
out of each other, or that they are all developments of some undif-
ferentiated sense-element, the psychical correlate of the nervous
shock. Moreover, our percepts, or knowledges of " Things," cannot
be regarded as mere developments of sensations. That a sentient
being should have sensations of sound and smell and taste, and even
of light, color, temperature, and pressure, is not of itself a sufficient
reason for its having perceptions such as belong to human experi-
ence. The only way in which such perceptions can be regarded as
the necessary resultants of the sensations which enter into them as
component pnrts is by taking the nature of the mind into the ac-
630 PSYCHICAL FACTOES SUPREME.
count. But this implies that perceptions are not developed forms
of sensations ; that they are rather advanced forms of the activity
of that real being which is developing under the experience of
sensation — elaborate products of the synthetic activity of mind.
§ 14. The knowledge of things by perception involves the activ-
ity of the mind as memory and judgment. But acts of memory
and judgment are not developments from perception ; they are
not merely modified forms of sensations as recurring or combined
under the action of physical antecedents. All talk about the " im-
age " of memory as though it were merely a faint or faded-out im-
pression of sense is quite unavailing ; it does not hit the real point
of inquiry, and consequently does nothing to explain the mystery
(comp. Part 11., chajD. X., §§ 18 ff.). The vital element in memory,
that which makes it to be memory, is neither a sensation, nor a
modified form of sensation, nor a development of sensation. The
same statement is true of judgment.
The relating activity of mind, the power to bring two objects
together in the \inity of consciousness, and, while keeping their
ideas distinctly separate, to bind them into one under the mental
affirmation of their likeness or unlikeness — this is a new and start-
ling mode of the activity of mind as contrasted with merely being
affected in sensation. Minimize it as we may, we cannot look upon
this activity as a mere " resultant " of two sensations or images of
sensations arising simultaneously in the mind. We cannot consider
judgment under the principle of the conservation and correlation of
energy. To treat it as such involves the grossest misapplication of
the laws which control the coincidence or conflict of physical forces.
Nor are the different forms of the relating activity of the mind —
concept, judgment, deduction, induction — to be legarded, strictly
speaking, as developments from each other or from any one mental
activity simpler than any of them. They may all, indeed, be consid-
ered as modes of the relating activity, because they involve discrim-
ination, the discernment of likenesses and unlikenesses. Bat each
one of them involves somewhat more than simjDle discrimination ;
each one involves other elements peculiar to itself. That a sentient
being should simply judge, or affirm this of that, is not of itself a
sufficient reason why it should also make inferences by syllogistic
processes or arrive at general laws by induction. Indeed, the
former may belong to many animals which are incapable of the
latter.
§ 15. We may proj)erly continue the foregoing line of remarks into
the consideration of the mind's most general activities. Modern
losychology, we have seen, is accustomed to distinguish faculties of
UNITED ACTION OF FACULTIES. 631
knowing, feeling, and willing as belonging to the mind. But it is
emphatically ti-ue that no one of these three faculties can be
i-egarded as developed from any other one, or from any two com-
bined. That a being feels — that is, is affected with a state of
consciousness more or less pleasurable or painful, and having a
characteristic quality — is in itself no ground for explanation of its
knowing '• Tuings" through sense-perception, and inference. Con-
versely, a being is conceivable with the knowledge of an archangel,
but without experience of desire, emotion, or sentiment of attrac-
tion or rej)ulsion. Sucli a being would indeed have to attain its
knowledge in other ways than those open to us, and we find it
difficult or impossible to imagine precisely what such knowledge
could be like. But growth in knowledge is a different thing from
the unfolding of mere feeling ; and the former cannot be explained
as arising out of the latter. Acts of will are, indeed, always actually
dependent upon knowledge and feeling, and cannot even be con-
ceived of as taking place without this dependence. But acts of
will are not mere developments of those acts of knowledge and
feeling on which they undoubtedly depend. The act of choice in-
volves a new element, an element not to be necessarily evolved from
the other activities of mind.
§ 16. We are so accustomed to the action in common, in the
unity of consciousness, of all the so-called faculties, that any
attempt to account for them as different modifications of one form
of energy meets with a favorable reception. Nothing thus far said
is, of course, to be construed to the prejudice of the unity of the
mind. But, on the other hand, the incomparable wealth in variety
of its natural achievements should not escape our notice. From
the beginning to the end of conscious life, the forth-puttings of the
mind continue. They are all actual concrete events, happenings in
consciousness which has-e no permanent existence and are never
twice precisely alike. That they are, however, ahke in certain
particulars and unlike in others, we can observe in consciousness
itself. Indeed, it is upon this fact that the possibility of any
orderly progress, any true development of mind, depends. But
the different classes of mental activities are not to be regarded as
though they could themselves be explained each from the other, as
the different stages of the embrj'o of an animal or of the germinat-
ing and growing seed of a plant are successively evolved.
The development of mind, therefore, cannot be explained after
the analogy of the accretion of molecules within a germ, and the
resulting division, multiplication, and advancing arrangement of
the living cells into sepai'ate organs of the entire system. No real
632 PSYCHICAL FACTOES SUPREME.
elements of the mind exist which can aggregate to themselves other
elements by absorbing them as pabulum, or can grow by arranging
the new material thus gained according to the energies inherent in
the material already organized. The life of consciousness is a never-
ceasing change of states. Yet the result of this change of states is
an orderly history, a true development. Such development is not
merely the expression of the evolution of the material basis of some
of these mental states. For it does not follow the same order or
the same laws as govern the material evolution ; and some of its
most important factors cannot be regarded as having any physical
correlate, or as evolved from other factors which have such a corre-
late. The development of Mind can only he regarded as the progres-
sive manifestation in consciousness of the life of a real being which,
although taking its start and direction from the action of the physi-
cal elements of the body, proceeds to unfold powers that are sui generis,
according to laws of its own.
CHAPTER III.
EEAL CONNECTION OF BEAIN AND MIND.
§ 1. That certain uniform relations exist between the mental
phenomena and the action of stimuli upon the nervous system, is a
most general conclusion of Physiological Psychology. These rela-
tions are chiefly concerned with variations which take place in the
quality, intensity, combination, and time-order of the states of con-
sciousness, as dependent upon the varying amounts and order of
different modes of physical energy as applied to the end-organs of
sense. But evidence enough exists to show that the more ultimate
psycho-physical relations are those which exist between states of the
brain and states of the mind. The dependence of mental states on
physical events outside of the body, or at its periphery, is gained by
means of the central organs of the nervous system. In the case of
man, at least, what happens be^'ond the cerebral hemispheres is
significant for the states of consciousness only as the hemisiDheres
themselves are affected by it. What happens heyond the cerebral
hemispheres becomes the cause or antecedent of what happens in
consciousness, through this portion of the brain. If our informa-
tion were sufficient, then, the empirical science of the connection
of body and mind would comprise a statement of all the relations
which exist between the mental phenomena and the changes with
respect to chemical constitution, structural form, and physiological
function, which take place in the molecules of the cerebral areas.
But even if the conditions were already fulfilled for a complete
science of Physiological Psychology, we should scarcely find our
speculative inquiries satisfied by this science. The desire would
doubtless still be strong to discover some more general statement
for the real connection between physical and psychical phenomena.
The question would still be raised : What, then, is the one inclusive
proposition, or word, or term, which gives the essence of all the re-
lations between the brain and the mind ? It would seem tedious and
disappointing to reply to this question by again enumerating all the
particulars which psycho-physical science has discovered. Let it be
taken for granted that, when lesions happen in certain areas of the
634 MIND AND ITS OEGAN.
cerebral cortex, such or such disturbances of the phenomena of
consciousness take place ; that when so many molecular vibrations of
a given wave-form and intensity occur within the cerebral elements,
sensations of a certain fixed quality and quantity arise in the mind ;
that when certain fainter vibrations of like wave-form return in the
same elements, reminiscences of the aforesaid sensations are ex-
perienced, etc., etc. We are still inclined to ask : What is the
meaning of all this ? or, How are brain and mind, actually and in
principle, related to each other ?
It is in deference to the raising of inquiries of the foregoing
rational sort^ — inquiries which are perpetually repeated all the way
along the path of psychological research — that we speak further of
a 7^eal connection between brain and mind. Of course every such
form of speech involves the assumption that the mind is a real be-
ing which can stand in relation to other real beings, and not
merely the formal or grammatical subject of mental phenomena.
This assumption has already been made and partially verified. In
continuing to make it for the purposes of the present chapter, we
shall find it still further verified.
§ 2. Various attempts have been made, from one or another
point of view, to sum up in some single Avord the relations that
maintain themselves between the body and the soul. Thus, the
body has frequently been spoken of as the " seat " or "organ " of
the soul. Looking at these relations fi'om the more materialistic
point of view, we have already seen how mental phenomena may
be regarded as the " products " or " resultants " or "manifesta-
tions " of the functional activity of the brain. More highly figura-
tive terms even have often enough been employed. The body has
been called the " prison '"' or " tenement " or " tabernacle " of the
soul. Not seldom, also, has the mind been represented as master-
ing and controlling, and even " moulding " the body — somewhat
as the rider subdues and guides his horse, or the worker in clay
and metal shapes the product of his toil. One form of the doctrine
of " Animism " has held that the mind is identical with the vital
principle, which is busy from the very impregnation of the ovum
in shaping its increasing molecules according to an unconscious or
dimly conscious plan. Much debate has also been held as to
whether the conception of " cause " is applicable to any of the rela-
tions in which body and soul stand to each other — whether, indeed,
it must not rather be held that what happens in one is only the
" occasion " on which some underlying cause, common to both,
operates to pi'oduce a change in the other.
§ 3. The inquiry in what sense, if at all, the brain can be said to
BRAIN AS THE SEAT OF MIND. 635
be the " seat " of the mind is more easily answered in a negative
than a positive way. Nothing but the cnidest notions, both of the
nervous mechanism and of the mind, would be consistent with any
of the more literal and direct interpretations of this word. Few
would seriously regard the mind as a special entity, whether con-
structed of ordinary material atoms or constituted in ethereal form,
that maintains a sitting or other posture amidst the cerebral masses.
Nor is it any more correctly conceived of as thinly diffused over
the entire mechanism of nerve- cells and nerve-fibres, or as wander-
ing about among the nerve -molecules to find its temporary " seat "
where occasion seems to require its presence. And, although some
of the phenomena of mind and brain perhaps admit very well of
being brought under the conception of the atom, acting and acted
upon in varying relations to other atoms of kinds different from
itself, no essential gain is made by the attempt to regard the mind
as in reality an atom. In brief, there is no literal meaning of the
words in which we can speak of the mind as seated in the brain.
The phrase, the brain is the " seat " of the mind, is, hoAvever, very
well adapted to raise the whole question of the spatial qualities of
the mind, and of its alleged spatial relations to the molecules of
the central nervous system. We shall, then, briefly consider the
question in this form.
§ 4. There can be no doubt that ordinary language justifies us in
speaking of the soul as in the body, in some sense in which this
term does not apply to any other collection of material atoms.
The human soul is in the human body as it is not in the bird, the
tree, the house, the star. Even that waj' of regarding the mind's
nature which does not hesitate to speak as though it were a thinly
diffused and half-spiritualized form of matter, assents to the neces-
sity of asserting a special relation in space between it and the body.
Hence some old-time philosophies represented the soul in percep-
tion as streaming out through the avenues of sense in order to get
the sensuous object into its embrace : or else pictured some ethe-
realized copy of this object as streaming into the soul by the same
avenues. But even such a view of the nature and activities of the
mind is based upon the claim that the body is, in some sort, the
peculiar dwelling-place, or "seat," of the mind. A correct account
of the process by which the world of things becomes known shows
that all our experience is connected with the establishing and jus-
tifying of this claim. There are no " things " known to experi-
ence except as our sensations, or modes of being affected, are both
localized and projected ej;^ra-mentally. Inducements and consid-
erations, such as have already been treated in great detail (Part II.,
636 MIND AND ITS ORGAN.
chaps. VI. and VII.) irresistibly urge the mind to arrange all its
phenomena into two great classes — phenomena which are quaUties
of outside things, and phenomena which are mere states of internal
experience. But the same inducements and considerations compel
us to look upon certain phenomena of the first class as related to
our mere states of consciousness in a peculiar way. The world of
things outside always (at least in ordinary experience) affects us —
is perceived by us or modifies our consciousness — through the body.
The mind is, therefore, said to be in the body.
The conclusion from the foregoing general experience is con-
firmed by certain experiences of a special order. The feeUngs of
pleasure and pain, which have so immediate and incontestable a
value for the life of the mind, are all connected with sensations
more or less definitely localized in the body. Hence men say, "My
nose is ofiended by this smell," "My tooth is aching," or "My
limb is suffering." So close is the connection between the localized
sensations and the painful or pleasurable states of the mind, that
the mind actually seems to be suffering in that part of the body
■where the sensations are localized. When the localizino; of sensa-
• . ...
tions connected with feelings of strong "tone" is very indefinite,
as it is in cases where the feelings arise from the condition of large
areas of the internal organs, the soul seems to be suffering in, and
throughout, almost the entire body.
Furthermore, both ordinary experience and scientific observation
require us to regard the mind as standing under certain special re-
lations to parts of the body. The ancients located the soul in the
heart or lower viscera, because of certain marked connections be-
tween the states of the soid and the condition of these organs.
But to speak of the soul as seated in the heart or other viscera
plainly applies most pertinently only to the soul as an emotional
being ; the obvious connection of the head with most of the more
obtrusive sensations tends to confirm us in the belief that the
mind, as perceptive, has its "seat" in that region of the body.
For reasons already given in detail (see Book II., chaps I. and IE.
and elsewhere), modern scientific researches justify us in narrowing
more precisely the local domain within which we can affirm the
mind to have its seat. The mind is certainly in the nervous sys-
tem, in a sense in which it is not in any otlier of the systems of the
animal bod}'. More precisely yet, it is pre-eminently in the brain ;
and, among all the complex groups of encephalic organs, the final
and special claim of the cerebral cortex to be the " seat " of the
mind is most easily maintained. Here, in this convoluted rind
which forms the interlaced " projection-systems " of sensory and
NO MATEEIAL SEAT OF MIND. 637
voluntary motor-impiilses, here — if anywhere — must it be held
that the subject of the states of consciousness has its dwelling-
place and home.
§ 5. At this point, however, the results of modern scientific in-
quiry become unfavorable to the effort yet more particularly to
designate a material " seat " for the mind. The eager imagination
having, as it were, hunted the soul down as it retreats inward and
upward to the higher regions of the supreme central organs, re-
quires some more precise information as to just where in these
regions its existence may be pointed out. Is there any one mathe-
matical point, or minute area in the cerebral cortex that is most
especially of all the dwelling-place of mind ? If so, might it not
be properly conceived of as ordinarily remaining at this point to
receive the messages despatched to it from the various parts of the
periphery ; and as executing its will over those peripheral jiarts
by sending back to them corresponding messages despatched from
the same central point ? The pineal gland has undoubtedly lost
the significance which Descartes gave to it as the special seat of the
soul. But can no substitute be found to take and hold so impor-
tant a place ? The answer of cerebral histology and physiology to
the foregoing questions is, on the whole, a decided negative (comp.
Book I., chap. II., and Book II., chaps. I. and II.).
Certain areas of the cerebral cortex do, indeed, appear to have a
particular connection with the execution of certain functions of the
mind ; the exact nature of this connection, howevei", cannot as yet
be clearly indicated. But the very phenomena on which reliance
is placed for establishing the foregoing connection, forbid us to
regai'd the mind, in its special relations to the brain, as hmited to
any point or small area of the cerebral cortex. Considerable parts
of all the cerebral areas can be destroyed without impairment of
any of the essential functions or faculties of mind. Moreover, both
gross and microscopic anatomy show us that the cortical part of
the brain, like all its other parts, is not constructed on the plan of
having its uses for the mind concentrated in any one minute cir-
cumscribed spot. In any sense in which the mind can be said to
have its " seat " in the brain at all, in that same sense, and with
equal propriety, may the entire cerebral cortex, Avith its vast com-
plexity of nerve-fibres and nerve-cells, be said to be the "seat" of
the mind.
§ 6. And now the puzzling question recurs : What that is intelli-
gible can be meant by designating the supreme central organs of
man's nervous mechanism as the " seat " of his conscious mind?
No one is directly conscious of these organs. The subject of con*
638 MIN^D AND ITS OEGA]^.
sciousness is not a beiDg which can be conceived of as " posturing *
within or amongst a certain larger or smaller group of materia]
molecules. And yet, plainly, in some sense the mind is to be
thought of as in the brain, as it is not in any object outside of the
body, or in any of the non-nervous organs of the body (bones, hair,
nails, fat, muscular tissue as such, etc.), or even in the remainder
of the nervous system.
The only solution for such a puzzle as the foregoing — if solution
''t can be called — must always consist in calling attention anew to
\he essential facts of the case. Certain particles of very highly
organized chemical constitution, when grouped into nerve-fibres
and nerve-cells, and when further associated into organs, may be
acted upon by appropriate stimuli. These material particles are
locally in the cranial cavity, and, more precisely, in this or that area
or organ of the cranial contents. Moreover, a large and important
part of the phenomena of consciousness consists in localized bodily
sensations of a painful or pleasurable character. To these facts in-
vestigation adds the inference as based upon experiment and ob-
servation in the case of others, that the localized sensations are
themselves ultimately dependent upon the behavior of the afore-
said material molecules in the brain. That is to say, we directly
localize many of our mental affections in this or that part of the
body ; by remote pi'ocesses of observation and argument we infer
that the last material antecedent of them all is the behavior of cei*-
tain invisible parts of the body within the brain. Therefore we say :
The mind is in the brain ; or the seat of the mind is the brain. By
this, nothing further can be meant of an assured or intelligible
character than the emphatic repetition of the same principal facts ;
the sensations which we localize at the periphery of the body, or
project from the body in space, all have a sui generis connection
with the condition and action of that portion of the same body
which is contained in the cranial cavity. Our modes of being af-
fected are directly localized in space outside of the body, or in the
various peripheral parts of the body. The part of the body on
which the activity of having these percepts is immediately depend-
ent is localized by science in the brain. Other activities of mind
are probably also thus dependent on the brain. In no other sense
can the brain be said to be the seat of the mind.
As to the possibility of such a sui generis relation between
material elements which exist in space, and the localizing and other
activities of a being not to be conceived of as, strictly speaking, in
space, only experience is entitled to pronounce. Such a relation ia
an accomplished fact. The fact is not to be disputed on any so-
• MYSTERY OF THE EELATION. 639
called a priori gi'ounds whatever. Both the dicta which have some-
times been made to bear on the case are alike inapplicable. On
the one hand, it has sometimes been claimed that a being cannot
act where it is ; on the other hand, that a being cannot act where
it is not. Nothing, however, can be known as to how and where
beings can or cannot act, except through experience of how they
actually do act. Building our conceptions iipon the basis of facts,
we should be inclined to say that beings act upon, and are acted
upon by each other, according to their differences in constitution
and relations in space. Gravitation keeps constantly before us the
example of all bodies acting unceasingly upon each other, in many
cases over distances that are immense. Tlie amount of this action
depends, indeed, upon the distance over which it takes place ; but
the action at all is an instance of beings acting where they are not.
When material molecules are approached nearer to each other
than a given small distance we at once discover new modes of be-
havior set up, which depend upon what the molecules are, and
what their condition, etc. New laws, such as those of cohesion and
chemical affinity, have now to be taken into the account. But
gravitation, cohesion, and chemical affinity are all alike to be under-
stood as expressive simjDly of the regular modes of the behavior of
material elements, with reference to each other, under varying con-
ditions. All these modes of behavior modern physical science re-
duces to motions of various kinds, directions, durations, and veloci-
ties. What is true of all material elements is true of those of the
brain ; they can do nothing but move.
If, then, we are to speak of the mind as having its " seat" in the
brain, in a literal way, we must regard it as one among the many
molecules or atoms of which the brain is composed — wandering
(that is, moving in a peculiar fashion) among the others, and so
variously acting on them, and being acted upon by them. But if
the mind were such a molecule or atom, the only affection it could
receive from the rest of the brain-molecules would be to change
the kind and direction of its own motion ; the only effect the
mind-atom could produce in the material atoms of the brain would
be to modify their motion with respect to kind and direction. But
it would still be just as difficult as before to understand how the
phenomena of consciousness should result from the movement of
one atom among other atoms — no matter how peculiar in constitu-
tion each of these two kinds of atoms (the mind-atom and the
brain-atoms) might be.
It does not follow, however, that the relation of the mind to the
brain is any more ultimately mysterious than that of the molecules
640 MIND AND ITS ORGAN.
of tlie brain to one another. Nor does it form an insuperable ob-
jection to the former relation that it is not, like the latter, a rela-
tion of changes of position in space. For who shall undertake to
affirm that beings which are not extended and movable in space,
because their very nature is of another order, cannot exist in rela-
tions of any kind to beings which are thus extended and movable ?
If the existence of the former kind of beings consists essentially in
states of consciousness, this fact does not prevent their dependence
upon the changing relations in space of extended and movable be-
ings. It is, in reality, in this way that the mind is related to the
brain. To speak of the mind as having its "seat" in the brain is
to reaffirm the reality of such relations.
§ 7. The term "organ " (or instrument) of the mind, as applied
to the body, is particularly calculated to emphasize the relation of
the ideas and volitions which arise in consciousness to the control
of the muscular apparatus. But the same term may also be used,
though with less of propriety, to describe the relation of the brain
to the mind in sensation and thought. Thus we may be said to
feel or think with the brain, in some manner supposed to be anal-
ogous to that in which the workman accomplishes his task by
availing himself of a particular tool or instrument. It is obvious,
however, that the figure of speech suggested by these terms also
will not admit of a literal interpretation. We cannot conceive of
the mind as a peculiar kind of material entity which, when it de-
sires or wills to move the bodily members in a certain way, lays
a clutch — as it were — upon the nervous substance of the central
organs, and so makes the body serve as an "organ" of the desire or
volition. Even less are we to conceive of the brain as a complex
tool or mechanism which the mind uses in thought and feeling,
somewhat as senses and fingers avail themselves of a calculating
machine or of a musical instrument.
In producing changes of shape and position in masses of matter
outside of our own bodies, we ordinarily find it convenient to use
some material medium between those masses and the various mov-
able parts of our own bodies. We throw up the ground with spade
or shovel, cut down the tree with an axe, feed ourselves with knife
and fork, etc. We can, by means of much more complicated
mechanisms, accomplish a great variety of changes which it would
be quite impossible to accomplish without such aid. On the other
hand, we sharpen, define, and multiply our sensations and percepts
of things in similar manner. The deaf man hears with a trumpet
or other acoustic contrivance ; and the scientific observer contrives
an instrument for observing the absolutely simple tones as analyzed
THE USES OF THE BEAHST. 641
out of the composite clang. With the lenses of his spectacles the
man of defective vision sees what would othei'wise be invisible ;
and with a prism the optician beholds the colors of the spectrum.
Remote objects are brought near with the use of the telescope, and
very minute objects near by are revealed by the microscope.
It is characteristic of all the most skilful use of tools and instru-
ments that they come to seem to the observer like a part of his
own bodily mechanism. By feelings of " double contact " (see
Part II., chap. VI., § 31) the workman comes to know, with the
chisel, the wood or metal which he is carving — just as the blind
man seems to extend his conscious life to the very end of the stick
he is accustomed to carry. In these cases the mental picture before
the practised mind is not that of the hand and the way it must be
moved, but of the graving tool and the motion to be imparted to
it — as though the instrument itself were immediately subject to
volition.
§ 8. The conception of an " organ " or instrument may with pro-
priety be extended so as to cover the relation which exists between
the nervous system and the muscular, and between the central and
the peripheral parts of the nervous system. Thus it may be said
that the spinal cord and brain move the limbs with the use of the
afferent nerves, or that the cerebral hemispheres employ the lower
ganglia of the brain in effecting certain co-ordinations of sensation
and motion ; it may even be said that the end-organs of sense
communicate with the supreme central organs by means of the
afferent nerve-tracts and the lower ganglia. All such language ex-
presses, correctly enough for popular usage, the undoubted fact
that, in the complicated relations of position and motion which are
maintained among the different members of the nervous system, a
certain order of action is constantly preserved. Changes originate
in one part, and are propagated to other contiguous or more distant
parts. In such propagation of the changes a regular tract of the
advancing motions is assumed always to exist ; and thus the parts
that lie between the extremes may be looked upon as means or
media — as instrumental to the completion of the process. For ex-
ample, in quick succession upon a certain idea of motion, and a vo-
lition to a definite motion, my arm is raised or my whole body
changes its position in space. How can this come about ? To the
inexperienced person the result seems to be an " immediate " ef-
fect of the will — that is, no apparent media or instruments stand
between the volition and the subsequent changes in the relations of
the masses of the body to other objects.
The vulgar persuasion undoubtedly is, that a man immediately
41
642 MIISTD AND ITS ORGAN.
knows himself to be the cause of the movement of his own arms oi
legs ; that he knows that he can move them if he will. Little in-
vestigation, however, is needed to discover that such is in no respect
the state of the case. A thousand hidden links, any one of which
might drop out without our being immediately aware of it, inter-
vene between the volition and the actual motion. No one directly
knows that one can move as one will ; one knows that one can will,
and infers that, if one will, the movement will follow. In tracing
the line of physical sequences backward from the motion of the
limb toward the arising of the volition in consciousness, we bring
it to a termination in a hypothetical nerve-commotion in some (so-
called "motor") area of the brain. At this point the line of
sequences, considered as a succession of modes of motion, draw-
ing constantly nearer to the instant of the volition, comes to an
end. The connection beyond and into that state of consciousness
which is called a " volition " cannot be conceived of as the pro-
gressive propagation of a peculiar molecular motion called nerve-
commotion.
§ 9. It is obvious from the foregoing remarks that one part of
the nervous mechanism can be said to be the " organ " or instru-
ment of another part, in a meaning of the word which cannot prop-
erly aj^ply to the relation of the brain and the mind. In a certain
justifiable meaning of the word, all the rest of the body may be
said to be the organ of the brain. That is to say, those changes in
the molecules of the brain's substance which arise there — whether
because of certain ideas and volitions of the mind, or because of
changes in the character of the blood-supply, or of sensory imjDulses
thrown in from the periphery or other lower nervous centres — get
themselves expi-essed through the other members of the body. All
this system of instrumentalities or interdependent organs is of one
nature. It consists of material particles having a definite chemical
constitution, structure, and arrangement in space ; its functions are
all modes of motion of such particles. One part serves as an instru-
ment or " organ " for another, because the changes in the former
effect changes elsewhere, not directly, but through contiguous and
connected parts. If the necessary contiguous parts are wanting
or their relations disarranged, if the connection is interrupted or
destroyed, then the work cannot be done; the "organ," "instru-
ment," or " means," is lacking.
What is true of the relations described by the word "organ,"
as these relations exist between any two parts of the nervous
mechanism, is only partially true of the relations which exist be-
tween any particular portion of this mechanism and the phenom-
THE USES OF THE BRAIX. 643
en a of consciousness. In other words, only a part of the real rela-
tions existing between mind and brain can properly be described
under such terms as "organ," "instrument," etc. The brain,
with its appropriate functions, is an indispensable medium between
certain changes in the peripheral parts of the body and correspond-
ing changes in the states of consciousness. If ideas of motion and
volitions to move are to be followed by actual motions correspond-
ing to the ideas and volitions, then the brain must act with its ap-
propriate functions. The motions can be executed, if at all, only
through the brain. As much as this is true of all the efferent tracts
which lead from the cerebral cortex through the lower portions of
the encephalon, along the spinal cord, and out to the particular
groups of muscles. Something more and special is, however, true
of the brain. It is the first of the indispensable physical links in
the whole chain ; it stands nearest, as it were, to the mind. All
the other steps in the execution of the ideas and volitions of the
mind depend upon what takes place in the brain. If nothing
takes place here, nothing at the periphery of the body will come
from the volitions ; if anything wrong takes place here, all that
goes on at the periphery will be wrong, and the mind will not get
its volitions executed. In this sense, at least, the brain is the par-
ticular organ of the mind ; it is the most intimate and indispen-
sable means for the execution of all its ideas or volitions of motion.
It does not appear that the foregoing statement by any means
exhausts the description of the experience, reflection upon which
induces us to regard the brain as the '• organ " of the mind. For
the brain seems to serve as the special physical basis of the ideas
and volitions of motion themselves. After experience in moving
a particular member of the body has once been gained, that mem-
ber may be lost ; and yet if the proper areas of the brain remain
unimpaired, the ideas, feelings, and volitions connected with the
movement of the lost member will still arise in the mind. The man
whose leg or arm has been amputated can still feel it, can form the
image of how it should be moved to be in this position or in that,
and even will to have it moved. The leg is not, then, the organ of
these ideas, feelings, and volitions.
Experiments with animals, by extirpating the cortical areas, and
observation of human pathological cases — especially, perhaps, in
certain forms of aphasia (comp. Part II., chaps. I. and 11.)— seem
clearly to show that a much more intimate relation exists between
the brain and the mind. With the destruction or derangement of
certain of its areas, the power even to form such ideas and volitions,
or to have such feelings, seems to be impaired or lost. We cannot
644 MIJSTD AND ITS OEGAN.
say, to be sure, that the mind has lost a part of its general faculty
to conceive, to feel, and to will. It has, however, suffered in respect
to its power to frame a certain set of definite ideas and volitions as
I'espects the motion of the peripheral members. This class of facts
is certainly calculated to emphasize strongly our conception of the
brain as being, in a special sense, the indispensable means through
which the states of consciousness are related to changes in the
position of molecules and masses of matter. Thus much, then, we
are also entitled to include in our declaration that the brain is the
" organ " of the mind.
There is another most important class of facts which may be par-
tially described under the same terms as the foregoing. The brain
is the indispensable means for furnishing the mind with its sensa-
tions, and so with its presentations of sense or perceptions of things.
This statement is not to be understood as though the brain could,
of itself, construct the sensations and perceptions and hand them
over ready-made, as it were, to the mind. Sensations are states of
consciousness, not modes of the brain ; and even when they are
synthetically united, localized, and projected to the periphery of
the body, or into surrounding space, they are brought under no
essentially new relations to the nervous mechanism. Sensations
are not nerve-commotions, " etherealized " by the optic thalami and
cerebral convolutions, and then handed over to consciousness.
Therefore the instrumental relation between brain and mind is
not that of transmitting a peculiar kind of motion from one phase
into another, or from one being to another. The brain is not the
" organ " of the mind in the sense in which a being that starts or
receives some mode of motion becomes instrumental for the pro-
duction of changes in another being. Nevertheless, no sensations
will arise in the mind unless the brain be affected in a certain way.
Looking at the chain of sequences as it runs from v^'ithout inward,
we might say : The brain is the organ, or instrument, through
which the stimuli of the outside world, acting on the end- organs of
sense, finally reach the mind.
What is properly meant by speaking of the brain as the mind's
organ of sensation is, strictly speaking, to be described as follows :
The brain is the last and most important physical antecedent to the
mind's being affected with the different sensations. The eye, ear,
nose, etc., are jDopularly called organs of sense. Nothing is more
obvious about the whole process of sensation than the part played
in it by the peripheral sensory organs. It is apparently through
these, by means of these, only on condition of the acting of these,
that sensations arise in the mind. Further examination shows,
MATERIAL COlSTISrECTIOlSr IMPOSSIBLE. 645
however, that the end-organs of sense are more remotely connected
with the origin of sensations than might at first be supposed.
Excitement of the afferent nerve-tracts between the end-organs
and the brain will also produce sensations. If these sensations are
not so refined and complex as those which are caused by stimu-
lating the end-organs tbemselves, the reason is to be found in the
fact that we cannot stimulate the afferent nerves in the way to pro-
duce such sensations except through the appropriate end-organs.
Still further examination shows that the value of the stimulus ap-
plied to the afferent nerves for the production of sensation is en-
tirely dependent upon what the conducting organs convey to the
brain, according to their specific nature and appropriate connections.
Sensations can be equally well produced by stimulating the cerebral
substance directly. When drugs, or gases, or diseases, or increased
action of the blood-vessels change the character of the blood-supply,
we see, and hear, and feel a world of things that has no existence
for the end-organs of sense. The brain is then the "organ" of
sensation for the mind, in the sense of being the indispensable and
most immediate means for the production of sensation.
Nothing that has just been said interferes in the least with the
valid claim for the mind, that it alone is the producer of every sen-
sation ; or, in other words, all sensations are modes of the behav-
ior of a being that is non-material and a unit-being, and is called
Mind. When the physical conditions are fulfilled in the brain, and
according to the way in which they are fulfilled, the mind itself
puts forth the phenomena of sensation. For the sensations are
not copies of outside material molecules, whether acting on the
end-organs of sense or acting as excited nervous substance in the
brain ; it can scarcely be repeated too often — they are modes of
the conscious activity of mind.
§ 10. Still another class of attempts to generalize, and embody
in a single term, the various essential relations of the brain to the
mind leads to the inquiry after some one special " connection " or
" bond " between the two. How are mm d and brain connected ?
What real tie binds them, so that they are obliged to have re-
gard to each other in the modes of their behavior ? Here, again,
any too literal answer to this inquiry leads at once to manifest
absurdity. A material bond designed to unite mind and brain
might perhaps be conceived of as connected with the latter, and
yet as remaining material ; but in order to make it connect with
the former (the mind) it would have to become non-material, un-
less we are ready to concede that the material and the non-material
can stand connected without some special bond. In case this con-
d46 CONNECTIOJS" OF BRAIN AND MIND.
cession is once made, however, we cease to feel the need of a
special bond between the mind and the brain.
If it be at once admitted that no connection is to be sought, or
can be found, between the mind and' the brain, beyond the fact that
their modes of behavior are mutually dependent, it will not be
necessary to appeal to any special mystery. What bond connects
together the jjlanets of the solar system so that each one moves in-
variably witli reference to the position of all the others, and yet
in a path peculiarly its own ? We can only respond by talking of
the force and laws of gravitation. These "laws," however, are
simply a mathematical statement of the uniform modes of the be-
havior of certain physical beings; this "force" is no entity or
bond connecting the individuals with each other, as the rods of
the orrery bind its parts to a common centre. Did such rods
exist to bind the planets to the sun, we should still have to inquire
for some bond between the particles of the rods ; and for another
bond to unite the atoms into these jDarticle§. Nor would it be an
answer to such inquiry to discourse of cohesion and of chemical
afl&nity, or of the laws which control the action of those forces.
For cohesion and chemical affinity are not special bonds ; they,
too, are but expressions for the facts that the elements of material
reality, under certain conditions and according to the kind to
which they belong, behave as though bound ; these elements be-
have, that is to say, according to what they are, and according to
the relations in which they stand to each other.
No more obscure and ud satisfactory is our knowledge concern-
ing the "bond" which unites body and soul, or, more especially,
the mind and the brain. The brain is a vast collection of material
molecules, connected together in a great variety of ways, which
always act, as it were, with their own chemical constitution, and
relations to other similarly constituted bodies, fully in mind.
Even the molecules are not bound to each other by any one dis-
coverable or conceivable bond. So far as we can speak of them as
" connected " at all, they are connected by a great variety of bonds.
Each of these bonds depends upon the nature of the molecules
which enter into it, and upon the manner in which each molecule
is related to other molecules. Essentially the same thing is true
— and perhaps with no more of ultimate mystery in its truthful-
ness— of the connection between mind and brain. The mind is a
conscious being, a being that perceives, feels, remembers, imagines,
thinks, and wills. In respect to certain classes of its activities, at
least, what it does depends upon what is done by the molecules of
the brain with which it is, as we say, specially connected. The con-
BODY AS TENEMENT OF SOUL. 647
nection is not, however, sucli as can be explained by assuming
one special form of a " bond " between the two. An infinite variety
of relations, some of which are in a measure reducible under law,
and others of which elude all attempts thus to subject them, exists
between the unit-being called mind, and the composite structure
and varied functions of the brain. The connection is no less real,
however, because invisible ; no less valuable and cei'tain, because
not one bond, but an infinite variety of relations.
§ 11. It will scarcely be supposed that information of scientific
value concerning the nature of the real connection between the
bod}' and the soul can be obtained from terms which are almost
purely figurative and poetic. The limited and defective nature of
our sense-perceptions, the misery of much of life, the unrealized
longings for knowledge and happiness, and the work of imagina-
tion in framing a picture of some state of existence in which the
limitations are removed and the longings realized, have led men in
all ages to regard the body as the " prison " of the soul. Because
the senses are not more in number than they really are, or more
far-reaching and accurate than their construction permits them to
be, they are regarded as restraining the soul, rather than as bringing
it information which has the character of satisfying reality. The
brevity and uncertainty of life, and the speed with which accident
and disease impair or dissolve the bodily functions, together with
the persuasion that the thinking principle will have a continued
existence, suggest the reflection : the body is the "tenement" or
" tabernacle " of the soul.
However true and comforting the foregoing hopes and reflec-
tions may be, it cannot be claimed that they throw any clear light
on the subject of our investigation. Physiological Psychology
rests upon such facts as show a most intimate and unceasing cor-
relation between the body and the soul. It can never, therefore,
consider the ultimate connection of the two as though it were as
unimportant and superficial as that between the prisoner and the
prison which holds him, or between the tenant and the tenement or
tent which for the time being is his abode. We are not at present
engaged in considering the evidence that the mind is immortal,
and can exist apart from this body and in another body, if not
apart from all bodies ; nor even the proof that its nature is vastly
superior to that of all the material structures to which it might be-
come related. We are rather testing the assumption that the mind,
as connected with the brain, is a real being which, although depend-
ent upon what occurs in the brain for its character and the order
of its activities, has nevertheless that existence which belongs to
648 coNNECTioisr of brain and mind.
all real beings — a nature and a development of its own. This as«
sumption, indeed, is applied and confirmed in every attempt to
characterize the real connection which exists between the mind
and the brain — whether the words "seat," " organ," "instrument,"
or other corresponding words be used.
§ 12. Thus far little has been exphcitly said as to the propriety
of applying the terms of " causation " (such as " energy," " action,"
"force," "impulse," "effective agency," etc.) to the case of mind
and brain. Yet everything which has been said has implied that
these terms are really applicable. There would be no advantage to
the mind in being " seated " in the brain — that is, in being under
any special relations to a given extent of nervous matter — unless it
were somehow influenced or acted upon by this nervous matter, and
could in turn influence and act upon it. No "organ "or instru-
ment is of any use whatever — that is, no thing can become an organ
or instrument — unless it can be acted upon by that which employs
it as an organ, and can in its turn act upon other things. Action
of mind on brain is implied in calling the latter the organ of the
mind's volitions ; action of brain on mind is implied in calling it
the organ of the mind's sensations. To act and to be acted upon
is equivalent to standing in the relation of cause and effect.
It is not at present necessary to point out in detail how much of
obscurity and contradiction are involved in all the more popular
ways of mentally representing the foregoing relation. The trans-
mission of energy (or force) is popularly spoken of as though such
energy streamed off from one body and attached itself to another ;
and as though the quantity of energy thus given off were dependent
upon the strength of the blow given by one body to another. Let it
be supposed, however, that the application of the law of causation to
the case of brain and mind is made in the most approved manner.
It is simple matter of fact, as tested by thousands of observations
and experiments, that changes in the condition and functional ac-
tivity of the nervous centres are followed by changes in states of
consciousness, in a regular way ; and that, conversely, changes of
the latter sort are followed by changes in the relations of the
masses of the body, and of the functional activity of nervous cen-
tres and end-organs of sense. Now, unless we are ready to be
satisfied with simply stating the facts, without making the at-
tempt to find any rational account for them, we are obliged to con-
sider these correlated changes under the terms of cause and effect.
That is to say, we regard the mind as a real being with activities
called states of consciousness, and the brain as a collection of real
beings called moving molecules of nervous matter, and we aS'
INFLUENCE OF THE CEREBEAL CIRCULATION. 649
sume that the latter acts upon the former and is acted upon by it
in turn. In other words, brain and mind are conceived of as really?
connected under the law of causation.
Were it not for the influence of prejudice derived from specula-
tion upon certain philosophical, ethical, and religious questions, no
one would think of hesitating to apply the terms of causation to
the case of mind and brain. The stoppage of the arteries leading
to the cerebrum, by outside pressure or by embolism, is speedily
and regularly followed by a disturbance or cessation of conscious-
ness. Who doubts that a man loses his senses as truly as he loses
a portion of his brain-mass, because he has been struck a blow upon
the head ? The falling of waves of light or sound upon the eye or
ear, the contact of the hand with the hard substance of the metal
or wood, the breathing of the air into the nostrils, are universally
regarded as the causes of the sensations and perceptions which
follow. The general impression undoubtedly is, that the act of
will is the cause of the motion of the different limbs or of the en-
tire body. In each of these cases more careful observation I'esults
in supplying many links in the chain of causation which the popu-
lar account has overlooked. The result is a more minute and
careful picture of those molecular changes which take place in the
cerebral substance, as induced by the severe shock of the blow or
by the gentle stir of the stimulus acting through the end-organs of
sense. Science explains the way in which the visible changes in
the position of the ponderous masses of the body are due to ante-
cedent invisible changes in the molecules of the muscles, of the
efferent nerves, and of the lower and the supreme nervous centres.
But all this explanation implies the application of terms of causation
to the entire chain of physical events ; and if these events are to be
considered as in any measure explaining the psychical events with
which they are connected in time, the relation of the two classes of
events is also assumed to be one capable of statement in the same
terms.
How impossible it is to avoid speaking of the connection of mind
and brain, in terms of causation, may be illustrated by the relations
between the condition of the intercranial blood- supply' and the
states of consciousness. The character of the cerebi'al circulation
is said to have a great " influence " upon the condition of the mind.
A slight increase of this circulation, resulting from a small quantity
of alcohol or other drugs, or from the hearing of interesting news,
produces an increased speed in the mental train. Keaction-time is
found to vary with changes in the circulation. In the delirium of
fever the wild and quickly moving condition of the thoughts, fan-
650 CONISrECTION OF BRAIlSr AND MIND.
cies, and sensations is a direct expression of the kind of work which
is going on, because of the accelerated heart-beat and the disor-
dered character of the blood, within the cerebral arteries. Schroe-
der van der Kolk tells of a patient who, when his pulse was reduced
by digitalis to 50 or GO beats per minute, was mentally quiet and
depressed ; when it was allowed to rise again to 90 beats, his
mind was in maniacal confusion. Cox narrates the case of a sick
man who, at 40 pulsations in the minute, was " half-dead ; " at 50,
melancholic; at 70, quite "beside himself;" at 90, raving mad.
The character of dreams is determined, to a considerable extent,
by the position of the head and the way in which this position
affects the cranial circulation. Hallucinations not infrequently are
immediately made to cease, when the person having them assumes
the standing posture, or has leeches applied to the head.
§ 13. Objections have arisen from various sources, and have been
urged with various degrees of skill and intensity, against applying
the concej)tion of causation to the relations of mind and brain. So
far as these objections are more purely ethical or religious, it is not
consistent with the purpose of the present investigation to consider
them. But certain objections are more jDurely scientific, or per-
haps philosophical, upon a basis of observed physical and psycho-
logical facts. A brief examination of such objections is not only
consistent with the present investigation, but even required by it.
Among the followers of the Cartesian philosophy it was held
that body and soul cannot really act upon each other, because of
the obvious difference in the essential characteristics of the two.
The body is extended and material ; the soul, being non-material,
does not possess the characteristic most distinctive of all that
comes under the conception of matter. Matter and mind, as being
in their very essence opposed, are sepai-ated from each other by the
whole diameter of being. They cannot be regarded as united directly
through any real tie, but stand at the mutually exclusive poles of
being. That a certain marked corresjDondence exists between the
phenomena of the extended and material body and the phenomena
of the conscious non-material soul plainly cannot be denied ; and
some account for this correspondence must be given. No one can
doubt that his sensations, in their quality and order of succession,
are related to certain events in the physical organs of his own
body ; neither is it easy to persuade one's self that one's move-
ments are not, at least in some indirect way, " ordered " by one's
desires and volitions respecting them.
To account for the obvious regular relation between bodily
changes and mental phenomena, two or three somewhat different
THEORY OF OCCASIOlSrALISM:. " 651
theories may be proposed. One of these is the so-called doctrine
of " Occasionalism." According to this doctrine body and mind
do not stand in the relation of cause and effect toward each other ;
neither one ever really acts upon the other. But on occasion of
some event of a definite kind happening iu the bodily realm, a
corresponding event of its own definite kind happens in the domain
of consciousness ; and vice versa. To say this, however, is plainly
in itself nothing more than to repeat the facts of experience over
again, but without offering any explanation of them. Since some
real " ground " or reason that shall have causal efficiency seems
needed in order to explain why body and mind should take "occa-
sion " to act at all, in view of each other's action, theology readily
finds such ground in the Divine Being. God, it is said, on occasion
of an event occurring in either of the two diametrically opposed
spheres, causes the right corresponding event to occur in the other
sphere. Matter and mind are not causally connected immediately
with each other ; they are causally connected only through a com-*-
mon ground in God. Pure Occasionalism, however, seems to
make too large demands upon a pious credulity. To be always
observing mere " occasions," in order to cause body and mind to
keep the right pace with each other, may well be regarded as un-
worthy of Divine Being. To meet this difficulty the theory of
" Pre-established Harmony " is devised. According to this theory
God has eternally predestined the entire succession of events in
the world, down to every minutest detail. Body and mind, there-
fore, may be regarded as like two clocks which have been so con-
structed that, without either having any effect upon the other, they
go on exactly as though one were actually moved by the other.
It would scarcely be worth while , to consider seriously these
older forms of the denial that any real causal relation exists be-
tween body and mind, were it not for the fact of their essential
agreement with more modern forms of the same denial. Two re-
marks upon the foregoing theories, in special, are necessary. The
assumption that matter and mind are sepai-ated from each other
'' by the whole diameter of being," if it be held to mean that
the two forms of being are so disparate in nature as to be unable
to act on each other, is an unverifiable assumption. It even goes
squarely in the face of many of the most important psycho-physical
facts. We know nothing about what kind of beings can or can-
not act on each other, except through our experience of what
beings do actually act upon each other. The mystery involved in
any one being acting on any other is equally deep and unfathom-
able, in whatever direction we attempt to explore it. Before ex-
652 CONNECTION OF BRAIN AND MIND.
perience with the facts, we should be quite at a loss to tell whethei
atoms of oxygen could act on atoms of hydrogen, under the laws
of chemical affinity, or not ; whether molecules of iron could act
on other molecules of iron, under the laws of cohesion, or not,
etc. How it is that material masses or molecules can "influence"
each other, or what is the real nature of the force which binds
them together, physical science is quite unable to say. So that,
even if we were entitled to regard matter as somewhat, the very
essence of which it is to be spread out, and mind as somewhat,
the very essence of which it is to be conscious and not to be spread
out, we should still be quite without justification in asserting (a
priori, as it were) that one cannot act upon the other. But — just
the contrary — if we are to accept, unbiased, the obvious witness of
the facts, we are compelled to affirm : The phenomena of mind
and the conditions of the brain are related so constantly and im-
mediately under law, that we are warranted in beheving in the
action of each upon the other.
Moreover, the theory of Occasionalism, Pre-established Har-
mony, and all similar theories, do not in the least assist us to es-
cape the difficulties which attach themselves to every conception
of causation. "We cannot regard the Divine Being as bringing
about a change in either mind or body, on " occasion " of some
other change, without assuming that mind (the Infinite Mind)
stands in the causal relation to matter. Furthermore, we cannot
conceive of a " reason " why this Being should eifect one change
rather than another, without I'egarding Him as subjecting himself
to the same relation.
' § 14. It is interesting to notice certain relations, both of similar-
ity and of difference, between a prominent modern theory as to the
mutual action of mind and brain and the now-abandoned views
of Occasionalism and Pre-established Harmony. Modern science
raises most of its objections, against regarding the conditions of the
central nervous system and the states of consciousness as connected
by a real causal tie, out of a profound regard for matter and the
laws of physics. The great value and significance of physical phe-
nomena, and the regular modes of their recurrence, if not the in-
dependent and eternal existence of material beings, are taken for
granted by this theory, whatever difficulties, feai's, or hopes to the
contrary may arise from the sphere of mind. Elements of ma-
terial reality (called " atoms ") are assumed to exist ; the univer-
sal form of their relation is held to be the law of the conservation
and correlation of energy. By " energy " we are to vmderstand
that which moves or tends to move the elementary atoms, or their
NO TRANSMISSION OF ENEEGY. 653
aggreg-ations, into molecules and masses. The energy wliich is re-
garded as causing actual motion is kinetic ; that which is to be
regarded as tending to produce motion is stored or potential. But
inasmuch as we have no test or suggestion of the presence of en-
ergy except motion, we seem compelled to consider the so-called
" tendency " to move (potential energy) as motion that is beyond
the sphere of the senses, because distributed over so vast a number
of minute portions of matter whose amount of motion is too small
to be discoverable. All physical elements and masses are, accord-
ingly, always in motion, and the total quantum of this motion is
invariable throughout the entire universe. All forms of energy
must be classified, as respects quality, by the kind of their motion ;
and as respects degree, by the amount of their motion.
On attempting to account for the whole world of phenomena in
terms of motion, kinetic or potential, under the law of the conser-
vation and correlation of energy, we are met with insuperable diffi-
culty as soon as we enter the domain of consciousness. States of
consciousness are not modes of motion. If they were, the general
theory of physics would compel us at once to attempt a strict
mathematical correlation between physical and mental phenomena.
Just as the momentum of masses can be expressed, with a tolerable
approximation to exactness, in terms of heat as a mode of motion,
so Avould some formula be conceivable for indicating what amount
of chemical changes, or nerve-commotion, in the matter of the
brain, is the mathematical equivalent of the conception of home, of
the sense of obligation, or of the idea of God. In other words, it
seems impossible to regard any amount of physical energy as ab-
stracted from the bi'ain, so to speak, and expended or stored up in
consciousness. Energy is stored by the process of nutrition in the
nervous elements of the brain ; it becomes kinetic in connection
Avith the phenomena of consciousness. But between the mind,
whether regarded as merely the formal subject of consciousness or
as a real unit-being whose faculty or power it is to be conscious,
and the physical basis of mind in the brain, no correlation, no pass-
ing back and forth of energy, can occur.
Representing the same truth in another way, we may declare :
The entire circuit of the transmission and distribution of energy is
complete within the brain itself. Not a single atom enters its sub>
stance that does not come forth unchanged, with all its forces in-
herent in it. No atom is transferred from brain to mind, as all the
atoms are transferred from the blood to the nervous substance of
the brain. Not the most infinitesimal amount of energy exists,
stored in the constitution of the molecules of this substance, which
654 CONNECTION OF BRAIN AND MIND.
is not eitlier used up there or returned to external nature in con-
nection with the constitution of the molecules separated from this
substance. The stricter we make our application of the law of the
correlation and conservation of energy within the physical realm,
the more impossible does it become to apply it at all to the rela-
tions of body and mind.
§ 15. It is not surprising that, in the estimate of one who is un-
accustomed to regard with favor any explanation of phenomena
which does not come under the most general law of all phj^sics, the
case of the mind and the brain should seem to demand the most
extraordinary treatment. In any event, the facts of consciousness,
as facts, cannot be denied. Whether we can explain them or not,
with or without use of the law of the conservation and correlation
of energy, they are equally plain and persistent. Men perceive,
and imagine, and remember, and reason, and believe in the invisi-
ble, and choose, etc. AU this they do, as possessed C'f a body —
and, particularly, of a nervous mechanism, the activities of whose
central portion are related in some special and unique w^ay with
the doing of all this. And yet sure, beyond doubt — it is argued —
is the existence of the atom, with its host of inherent energies ;
and supreme is the law of the conservation and correlation of these
energies regarded as modifications of one fundamental form.
In view of so grave difficulties it has been of late customary to
escape from them in one of several different ways. The general
claim may be set up that all hopeful inquiry as to the nature of real
beings, which act upon and are acted upon by each other under the
law of causation, must be abandoned. Knowledge, it is said, con-
sists simply in the relating of phenomena under certain constant
and regular forms of their recurrence, called "laws," This is sub-
stantially the position of Positivism.
It may also be held that all mental phenomena are to be re-
garded as merely transitory appearances — shadows cast, as it were,
by the changing activities of the material molecules ; and that the
latter are the only realities. In this case the constitution and ac-
tivities of the molecules are all to be regarded as determined by
the interaction of the ultimate atoms which compose them, accord-
ing to their inherent and inseparable forces, under the law of the
conservation and correlation of 2>hysical energy. Whenever a cer-
tain constitution and consequent modes of activity are brought
about in the molecules, under this general law, then it is of their
own incomprehensible nature to exhibit, in addition to the various
forms of motion known as nerve-commotion, another peculiar class
of coexisting phenomena, called mental phenomena. The latter
MATEEIALISM AND MONISM. 65o
phenomena do not require a new subject; their appearance is the
necessary result simply of the special and unique constitution and
relations of the physical molecules of the brain. The mental phe-
nomena are one form of expressing the fact of the real existence
of these molecules, with such a constitution and in such relations.
And just as we do not require a new subject for the mysterious
and unique phenomena of magnetism, or of crystallization, but be-
lieve them to be only the expression of the new relations into which
the same subjects of all phenomena — the imperishable atoms —
have been brought under the one law of the conservation and cor-
relation of energy ; just so do we find no particular need of a
new kind of subject, other than the aggregated atoms, for the mys-
terious and unique phenomena of consciousness. This position is
Materialism.
Still further, the impossibility of binding together by a causal
tie, under the law of the conservation and correlation of energy,
phenomena so utterly incomparable as are those of mind and brain,
and the difficulty of assigning the mental phenomena to the same
subject as that which, otherwise, manifests itself only as modes of
motion rather than modes of thought, have led to more recondite
speculation. Hence a return to- the "mediaeval" view has been
made. The real connection of mind and brain has been found in
a third somewhat, which is neither mind nor brain, as we know
them, but is the ground of both. There is, then — it is claimed —
only one substance as the real subject for the two sets of proper-
ties. " The one substance, with two sets of properties, two sides,
the physical and the mental — a double-faced unity — would appear
to comply with all the exigencies of the case." This position may,
in general, be designated as that of Monism.
But immediately the inquiry arises and presses for an answer,
whether we may not know something as to the real nature of this
" double-faced unity," besides the mere fact that, phenomenally
considered, it has two faces, or sides — the physical and the mental.
Why does it manifest itself both as physical motion and as mental
states — one Being, in two utterly incomparable modes of manifes-
tation? Is it itself extended and movable, a material reality? or
is it unextended and conscious, a psychical reality? To refuse to
attempt the answer to this question is to take refuge in Agnosti-
cism— and that at a critical point, to which we have brought our-
selves unnecessarily through having been already overwise. For
no one who claims already to know enough about the nature of so^
called matter and of so-called mind to affirm confidently that they
cannot be two forms of real being, acting on each other and being
656 CONNECTION OF BEAIN AND MIND.
acted npon by eacli other, is entitled, just beyond this advanced
line of knowledge, to make a run sideways into the refuge of con-
fessed ignorance. Furthermore, if the " double-faced unity " is held
to be, in reality, either matter or mind, we raise again all the diffi-
culties as to a real connection between two sets of phenomena so
incomparable. Both Materialistic Monism and Idealistic Monism
have, then, to undertake the task of showing how the one reality
can appear under these two phenomenal forms of being — matter
and mind — with its two sides causally connected.
§ 16. So far as the theories, which are proposed in order to escape
the difficulty of admitting a direct causal connection between mind
and brain, involve the assumption that the phenomena of conscious-
ness can be regarded as modes of motion, or can be attributed to
the molecules of the brain as their sole subject, they have already
been refuted. So far as these theories resolve themselves into the
speculations joroposed by different schools of philosophy concerning
the supreme philosophical inquiry. What is the nature of the Ulti-
mate Reality (the Absolute)? psycho-physical researches have no
direct answer to offer to them. But our present inquiry is a more
modest one, namely : What is the nature of the real connection
between human mind and human brain, so far as psycho-physical
science throws any light on such connection ? Our general reply
is : This connection is, in reality, such as we find between all so-
called real beings, to whichever of the two supreme classes (material
or spiritual) such beings may belong. The molecules of the brain
(so far, at least, as psj'cho-physical science knows anything of them)
are composed of elements of material reality, called "atoms ; " these
atoms act by way of motion, according to their constitution and re-
lations to each other and to their environment. The mind, on the
other hand, is a real unit-being of another order than that of the
atoms. Its acts are the various modes or states of consciousness.
This being called mind is causally related to the beings called
atoms ; the relation is mutual. The mind behaves as it does be-
have because of the constitution and behavior of the molecules of
the brain. The molecules of the brain behave as they do behave
because of the nature and activities of the mind. Each acts in view
of the other. The action of each accounts for the action of the
other. But the action of neither is to be explained as solety due to
the action of the other ; neither mind nor brain can be regarded as
the subject for the phenomena ordinarily ascribed to the other.
The position just taken is, of course, the most unmistakable
Dualism. It assumes two kinds of real beings for the two incom-
parable classes of phenomena. Whether this position is the ulti-
THE VIEW OF DUALISM. 657
mate one attainable by bunian reason or not, tlie facts of Plij'siolog-
ical Psychology afford no basis for speculation. It is possible that
some higher point of view might enable us to resolve the Dualism,
and to discover a common ground for the body and soul of man, and
even for all physical and spiritual phenomena. But psycho phj'sical
science, simply observing the facts and building upon them, and
upon such assumptions as it, in common with all the sciences^ is
compelled to make, establishes this Dualism of brain and mind, and
then hands the case over to philosophy for further consideration.
Moreover, there is nothing in any science, physical or psychological,
which offers a single valid reason why both mind and brain should
not be regarded as real beings, material and spiritual, mutually in-
teracting. This last statement we shall now justify by considering,
briefly, the objections to it, which have induced the resort to the
before-mentioned other theories.
§ 17. The law of the conservation and correlation of energy — as
far as it has been observed, or can reasonably be assumed to hold
good — offers no valid objection to the existence of a real causal
connection between the mind and the brain. The present position
of this law is that of an empirical generalization, found to hold ap-
proximatel}' true for a large number of classes of phenomena, and
presumably true for yet other classes. To exalt it to the place of a
universal and necessary relation among all phenomena of every class
— mental as well as physical — would be unwarrantably to extend
its application. Even in the sphere of physical events the law is as
yet demonstrably true only to a limited extent. The various forms
of physical energy in the inorganic world are as yet by no means
all reducible to the terms of this law. Gravitation, on the one
hand, and magnetism, or chemical affinity, or cohesion, or the forces
that act when every crj-stal is formed, on the other hand, cannot be
as yet related together so as to be expressed in these terms. No
mathematical formula, or picture framed by the imagination, has
thus far bridged over the gap between the molecular energy of
inorganic and that of organic structures. In discussing the phe-
nomena of general nerve-j^bysiology, it was made obvious at every
turn that even the behavior of the vital nerve-muscle machine
under the influence of electrical or other excitation cannot be ac-
counted for by any conceivable application of the known laws of
those forces that move unorganized particles of matter. Nerve-
force — what it is and what it will do ; what it is as judged by what
it will do — cannot, at present, be correlated Avith any of the forms
of energy which act as nervous stimuli. Yet who would for a
moment hesitate to say that the action of the electrical current, or
42
658 coNNECTioisr or BRAiisr and mind.
of the irritating acid, or of mechanical impulse when applied to
the nerve, is a "■came" of the contraction of the muscle?
The effort of certain scientific observers to bring aU causal rela-
tion, all action of one being on another, under the law of the con-
servation and correlation of physical energy is mistaken, and must
prove unsuccessful. The discovery that all the action of physical
beings is to be understood only in terms of motion, and that all re-
lations of such beings are to be expressed as comparable quantities
of motion, either obvious or potential, has, of course, greatly stim-
ulated this effort. The effort is to a certain extent laudable. It
has unified the physical universe ; it has showed to us this universe
all alive, as it were, with unceasing, correlated, wondrous motions,
which it is indeed conceivable should be all commensurable one
with another. But it should never be forgotten that this picture
of an objective world composed of beings called atoms, eternally
moving with reference to each other and according to the law of
the conservation and correlation of energy, is itself a picture con-
structed by the imaging and reasoning mind. As such a mental
picture, it is, and must always remain, dependent on the imagina-
tion. Mind, as reasoning and imagining, follows the moving
beings into minutiae of forms and into places where observation
can never reach them. Hence the talk of atoms having "forces
inherent" in them, of energy "potential" as well as kinetic, of the
"influence" or "action" of molecule on molecule, and mass on
mass, under this one great law discovered by modern physics.
For the principle of causation is of far wider application, and of
far more secure foundation, than the law of the conservation and
correlation of energy. The one is a law which, in the form of the
principle of reason and consequent, is Avorked into the very struct-
ure of the mind, and is of universal and necessary application to all
phenomena ; the other is an empirical generalization, of doubtful
import and uncertain extent of application. Indeed, we should not
accept the phj'sical law at all, or seek to establish its further appli-
cation, were it not that the mental principle is already taken for
granted. It is in our search for causes, and as a result of our per-
suasion that real beings exist, which act on and are acted on by each
other, that we hit upon tlie hypothesis of the sum-total of their ener-
gies as shown by motion remaining unchanged, and of its different
kinds being all measurable one against the other. But no objection
exists, either in the nature of the mind or in the nature of things, so
far as we know, to the reverse of this being true. For example, a
world might be constructed in which a certain number of physical
beings, of a certain kind (molecules and masses), remained abso«
NATURE OF THE CAUSAL ISTEXUS. 659
lutely motionless and unchanged, while all other beings were in
perpetual motion. Or a world might be constructed in which the
activities of different physical beings, as expressed by motion, should
be related in a totally different way from that formulated by the
present law of the conservation and correlation of energy. In this
imaginary world, some kinds of beings might put forth an amount
of energy which was proportional to that of all the energy of the
beings acting on them, as the square to the square-root, or as the
cube to the cube-root ; and other kinds of beings might act and be
acted upou under very different laws of relation with resj)ect to the
quantity of energy. In fine, the fact that the law of the conserva-
tion and correlation of energy caunot hold true as to the connection
between physical and psychical phenomena furnishes no sort of
proof against the reality of the mind or of the causal connection
between it and the brain.
§ 18. Nor is there anything in the nature of the so-called "cau-
sal nexus " itself which forms a reason why it should not be as-
sumed to exist between brain and mind. For what do we mean
when we speak of one thing or event as the cause of another?
"What do we mean when we speak of "influence exerted," "force
transmitted " or " passing over " from one being to another, etc. ?
Nothing that can be explained or illustrated after the analogy of
any series or collocation of phenomena, of any relation of one ob-
ject to another as discernible by sense or picturable by imagination.
Nothing passes from the match to the gunpowder which explains
why the latter explodes ; or from the bat to the ball which explains
why the latter, when struck by the former, changes the direction of
its motion. The proximity of the earth and the unsupported con-
dition of the apple, shaken by the wind from its stem, are indeed
spoken of as the cause of the apple's fall ; but no invisible hands
are reached up from the ground to draw the apple down. Were
such feelers put out to clasp the smaller body and draw it to the
larger, the energy of the clasp and its effect would still as truly
need an explanation as does the action of the so-called force of
gravitation. None of the senses is capable of discovering or ap-
preciating the energy that is assumed to act ; the causes of an event
cannot be seen, handled, heard, smelled, or tasted. The w^orld of
experience given to us by the activity of the senses is a world in
which a ceaseless change of objects takes place, but any evidence
of a tie connecting the physical phenomena with real beings as
their attributes, or connecting our minds with these physical real
beings, so that they may be said to affect us, is quite beyond the
range of the senses.
660 cojS^jS'ECTION' of braij^ and mind.
In general, it may be said that the world of appearances is found
by an anaij^sis of our adult experience to be assumed to rest, as it
were, upon an invisible Avorld of reality. The popular and uncriti-
cal mode of the assumption is, that the world is made up of a great
number of real " Things ; " that these things exist ex-^j'a-mentally,
just as they appear to us as objects of experience ; that our knowl-
edge of them is a more or less true copy, obtained through the
senses, of what they extra-mentally are ; and that these things are
constantly doing somewhat to each other — acting on each other and
being acted on by each other. Scientific researches greatly modify
the character of the j^opular assumption. They show that it is de-
monstrably false in almost every particular ; and yet they re-estab-
hsh it in other forms. Physics, by a series of careful observations
and subtle and remote inferences, constructs an extra-mental world
of moving atoms ; it shows us how these atoms always have regard
to each other when they move, and are ceaselessly moving with
reference to each other ; it strives to image the direction and veloc-
ity of the most infinitesimal of these motions, and to formulate
their laws or constant modes of relation. Psychology shows how
the world of mental objects, the only world of immediate experi-
ences, is built up by the synthetic activity of mind ; it calls upon
the physicist to remember that he has no other way of reaching
these atoms, and of discovering the laws of their relations, except
by the path of mental activity ; and it reminds him that this activity
cannot escape the control of mental law. But both the popular
view and the scientific attainment are in substantial agreement as
to their fundamental view of the world. Both believe that our ex-
jjerience is exj)licable only on the general hypothesis of the exist-
ence of a vast number of real beings Avhich perpetually act on each
other and are acted upon by each other.
§ 19. The effort to restrict the working of the above-mentioned
assumption, in which common-sense and scientific analysis both
agree, just at the point w'here the relation of mind and brain is
subjected to scientific treatment, is as needless as it is unavailing.
Because it is both needless and unavailing it is often absuril. If it
be granted that the law of the conservation and correlation of ph^-s-
ical energy cannot possibly be applicable to the connection of mind
and brain, and yet that all which we know of the nature and extent
of this law forms no valid objection to regarding both mind and
material atoms as real beings standing in certain relations to each
othei' — What good reason can be urged for refusing to affirm a causal
connection between the two? The fear that either of the two parties
will suffer in dignity or integrity by such connection Avith the othei
CAUSAL INFLUElSrCE OF THE BIlAIlvr. 661
may easily be laid to rest ; and if it could not be, it would have no
right to interfere with the only reasonable interpretation of psycho-
physical facts. Beings do not lose their reality, or characteristic
natiu'e, or value in the universe of Being, because they are causally
connected with other beings. On the contraiy, none but real be-
ings can be thus connected with each other ; none but real beings
can act and be acted upon. The so-called causal connection is no
bondage of such nature as to destroy the nature of the beings which
act under it. Only beings that have natures of their own can be
causally connected. In, other words, all that apjDcars to us as a
causal relation between the objects of our experience is, ultimately
considered, due to no material spur or whip which urges, or band
that represses, as though one kind of real being could thus domi-
nate and subdue another. No atom acts without being acted on ;
what it does depends both upon what it is and also upon how it
stands related to other atoms.
§ 20. We affirm, then, that we are entitled to say : The changes
of the brain are a cause of the states of consciousness ; and the
mind behaves as it does behave, because of the behavior of the
molecules of the brain. Modify the constitution and functional
activity of the material atoms, and you make the activities of the
mind, its acts and states of consciousness, to be differently j)ut
forth by the mind. The nature and extent of this " influence " of
the material basis upon the psychical subject can never be deter-
mined a priori, or brought under any general formula applicable
only to a restricted sphere of physical action, like the law of the
conservation and correlation of physical energy. The nature and
extent of such influence must be learned by investigation. It has
been the special task of this treatise on Physiological Psychology
to investigate and, as far as possible, to formulate the causal action
of brain on mind. Such action has been seen to consist chiefly
(if not whoU}-) in determining the intensity, quality, mode of com-
bination, and of recurrence in time, of the sensational elements of
the mind's activity, and of its other activities so far as dependent
upon the sensational elements.
The affirmation of a causal influence of the brain on the mind,
however, does not really work any prejudice to the claims of the
mind to be considered a real being, or to be spiritual and free. For
the sole account or cause of the mind's activities can, in no instance,
be found in the molecular condition and changes of the brain.
The simplest sensation must be referred also to the nature of the
mind as its cause. It must be considered, not simply as caused by
a certain form of nerve-commotion in the cerebral cortex, but also
662 coNNECTioisr or beaijst and mind.
as a psychical activity put forth by the being called mind. There
is no incompatibility in these two ways of regarding each state of
sensation. Even in the case of some physical event, the nature of
each of the factors combining to form the event must be taken
into the account. For example, atoms of oxygen will, under cer-
tain circumstances, unite with atoms of hydrogen to form water ;
under other circumstances they will unite with atoms of iron to
form iron-rust ; they may also be mechanically mixed with nitro-
gen-atoms to form air, etc. In each case the cause of the result is
to be found in the presence with the oxygen, under certain definite
circumstances, of atoms of hydrogen, iron, nitrogen, etc. But in
each case the cause is also equally to be found in the nature of
the atom of oxygen. So every sensation, however closely it may
be correlated with the condition and functional activity of the
molecules of the brain, must be explained by referring it to the
nature of the mind which has the sensation. Nothing which Physi-
ological Psychology has ever discovered, or can hope to discover,
in the least mitigates the necessity of saying, when the question
is asked — AVhy does the mind behave in this particular way under
such circumstances ?^It is the nature of the mind so to behave
when its circumstances are such. In other words, our explanations
of the causes of mental phenomena, as lying in the physical basis
of such phenomena, does not at all satisfy the need of a real and
spiritual subject of the phenomena.
Moreover, we have seen that there are large and most important
classes of mental activities which can scarcely be conceived of as
standing in any direct relation to the nerve-commotions of the
cerebral cortex. These classics are indeed always allied with phe-
nomena of sensation and feeling for which we can trace a bodily
basis. But this fact only makes their connection with the brain
presumably more indirect. For the explanation of such classes of
mental phenomena we are driven much more imperatively and ex-
clusively to an appeal to the existence of a spiritual subject, with a
nature and laws of action very different from those ascribed to its
physical basis, the brain.
§ 21. We affirm, also, that we are equally entitled to say : The
states of consciousness are a cause of the molecular condition and
changes of the nervous mass of the brain, and through it of the
other tissues and organs of the body. And just as no fear for the
reality, integrity, and dignity of the mind prevents us from accept-
ing its dependence for the mode of its activity upon the condition
of the brain, so no fear for the reality of physical substance, and
for the value and extension of physical law, pi*events us from aa
• CAUSAL USTFLUENCE OF MIND. 6Qo
serting the dependence of the brain, for the mode of its activit}-,
upon the states of the mind. Of course — it need scarcely be said
again — no relation exists between these two kinds of beings which
can be represented as an interchange of physical energy, under
the law of the conservation and correlation of such energy. This
fact, however, affords no objection to our recognizing a true causal
counectiou between the two, unless we are ready to insist upon
the monstrous claim that modern physical science is entitled to
affirm the impossibility of any interaction (or conditional action)
taking place in the universe otherwise than between material atoms
under the aforesaid law.
The phenomena which indicate that mind operates as true cause
within the structure of the body are innumerable. They are quite
as numerous, though perhaps not so obvious and impressive, as
those which indicate the reverse relation. The chief reason why
these phenomena are relatively little regarded in psycho-physical
researches is, that the real causes are in this case not readily made
the objects of observation and measurement. External stimuli con-
stitute the causes of mental changes which we can most easily ob-
serve and estimate. Ideas, feeling, and acts of will arising in the
consciousness, and considered as causes of the resulting bodily
changes, cannot be treated by the same methods of experimental
science as apply to the physical stimuli. But that the mind acts
on the body is one of the most familiar of experiences. Such ac-
tion penetrates and modifies all the Hfe of the body. Hence the
material mechanism of the animal structure can never be consid-
ered, with a view to explain what is going on within it, as though
it were disconnected from the consciousness of the animal. The
most purely vegetative of the processes of the human body are de-
pendent for their character upon the states of the human mind.
The nutrition of the tissues, the circulation of the blood, the secre-
tion of different kinds of fluids, the healthy or diseased nature of
the vital processes, are dependent upon the states of the mind. If
abnormal digestion produces melancholy, it is equally true that
melancholy causes bad digestion. In the case of the rise of strong
emotions, like anger or grief, the increasing affection of the mind
builds itself up upon a physical basis of increasing disturbance of
the organs ; but it is equally obvious that the starting of the emo-
tion in consciousness, and the letting of it slip from control, are
necessarily followed by gathering momentum to the organic dis-
turbance. Irregular action of the heart, caused by organic defect
or weakness, occasions a feeling of indescribable alarm in the soul ;
fear is followed, through the action of the mind upon the nervous
064 coisrisrECTioN' of brain and mind.
centres, by functional incapacity of the heart. The impure condi-
tion of the arterial blood which is characteristic of certain diseases
brings about a chronic state of mental lassitude or anxiety ; care,
chagrin, and ennui poison the arterial blood. The lesion of the
cortical substance produced by a growing abscess or broken blood-
vessel impairs the mind's powers of sensation and thought ; ex-
cessive thought and over-excited feeling wear away the brain.
The entire class of phenomena which we are entitled to call
" voluntary," in the widest sense of the word, might be appealed
to in jDroof of the same principle. Whether they show that the
mind is " free," in the highest ethical meaning of the word, or not
(and upon this question psycho-physical science cannot pronounce),
they certainly do show that the condition of the bodily organs is
made dependent, through the nervous elements of the brain, upon
the states of the mind. And here are, in point, the phenomena of
the voluntary innervation of the organ by fixing the attention, of the
dependence of reaction-time upon the exercise of the will through
attention of the person reacting, of the abstraction of regard from
the images of sense when occupied in reflective thought, as well
as all the more marvellous instances of self-control in determining
the results of disease, etc.
The elevation of the bodily activities to the most astonishing
precision, under the influence of high and strong artistic feeling,
or sense of duty, is also a noteworthy fact of the same order. The
mind has not the poAver to constitute, in opposition to fixed chem-
ical affinities, a single molecule, or to execute the slightest move-
ment of a single muscle, without involving the nervous system in
the expenditure of the requisite energy. Moreover, this energy
must be started in the appropriate cortical area and descend along
the allotted motor tracts. We cannot explain how it is that mole-
cules of nervous matter can be acted upon in view of 'states of
consciousness. But neither can we explain how one kind of atoms
comes to act as it does in view of the presence and action of atoms
of another kind. Nevertheless, we can just as little assume to ex-
plain away the fact of such obvious causal connection, because we
cannot bring the measure of the connection under the same law as
that which maintains itself among certain modes of physical mo-
tion.
§ 22. No valid objection, therefore, can be urged against con-
ceiving of the connection between mind and brain in the following
way, at once most natural and most philosophical : The brain is a
vast collection of material molecules, whose constitution and ar-
rangement are such as to connect them, in a unique way, with cer-
' CAUSAL INFLUENCE OF MIND. 665
tain forms of physical energy outside of the body. Whenever these
appropriate forms of energy act upon the parts of the nervous sys-
tem lying below, and the impulses are transmitted to the brain,
or whenever the chemical character of its blood-supply is altered,
then the molecules of the brain are capable of undergoing very re-
markable and intricate changes of constitution and arrangement.
That is, the brain can be stimulated to certain of its peculiar com-
binations of nerve-commotion by external stimuli. Moreover, it is
constantly initiating other combinations of nei've-commotion that
are apparently not due to such stimuli. Some of its actions, that
is, are of a kind constantly arising within the system itself ; they are
called automatic. We have as yet no adequate means whatever
for making a quantitative statement of the relations which exist
between the energy of atoms thus constituted and arranged and
the energy of the masses or molecules that serve as stimuli of the
system composed of these atoms. Nervous energy is not an entity
to be dealt with by a sum in addition and subtraction of momenta.
For aught we know, it is of the nature of atoms, when they are
brought into relations so extraordinary as those which prevail in
the nervous system, to behave with reference to each other in a
way that is wholly irreducible to any simple formula like that of
the conservation and correlation of energy. If this should final-
ly appear to be indubitably true, the fact would not be specially
mysterious. All action and reaction of the atoms is mysterious ;
the methods of it are to be learned from experience as ultimate
and inexplicable facts.
Still further, the molecules of the brain are so constituted and
arranged as to be capable of standing in yet more surprising and
unique relations to a being of a different nature from their own —
that is, to the mind. These relations involve a causal connection as
truly as any relations of real physical beings in which such beings,
as we are compelled to believe, act on each other and are acted on
by each other. That molecules thus constituted and arranged are
causally connected with the subject of consciousness is an ultimate
fact ; it involves the nature of both classes of beings thus connected
— of the brain and of the mind ; it involves also the action of each
upon the other. In speaking, however, of mind and brain as act-
ing on each other, we accomplish nothing whatever for the comple-
tion of the picture by trying to introduce the conception of ener-
gy " transmitted " or "passed over" from one to the other. The
simple, ultimate fact remains, that how each behaves depends upon
the behavior of the other. It is the business of psycho-physical
science to discover, if possible, the general modes of this depend-
666 CONNECTION OF BRAIN AND MIND.
eBce — that is, the laws of the relation between the mind and the
brain.
§ 23. In more particular description of the connection between
the mind and the brain, it may be said that all intercourse between
material objects and the spiritual subject involves three processes
— a physical, a physiological, and a psychical. In these processes
the perceived object and the perceiving subject mutually condition
each other. This fact, however, does not destroy the necessitj^
under which all scientific investigation finds itself, of assuming that
both object and subject exist as real beings. The physical pro-
cess consists in the action of the appropriate modes of physical
energy upon the nervous end-apparatus of sense. The bringing of
such modes of energy to bear upon the apparatus is accomplished
through mechanical contrivances — such as the means for forming
an image on the retina in the eye, and for conveying the modified
acoustic impulses to the organ of Corti in the ear.
The second process consists in transmuting the physical ener-
gies, in part at least, into a physiological process, a nerve-com-
motion within the nervous system ; and in propagating such nerve-
commotion along the proper tracts and diffusing it over the various
areas of this system. Inasmuch as the physiological process is
also a physical process — that is, a mode of the motion of mate-
rial molecules, accompanied by chemical and electrical and other
changes — it must be conceived of as standing in certain relations
of quality and quantity to the first, or more distinctively j)hysical,
process. But that the law of the conservation and correlation of
energy, as formulated for much simpler cases of the relations of
forces between inorganic bodies, applies to the relations of the
nervous system and its stimuli, or within the different parts of the
nervous system itself, we are not yet able to affirm with confi-
dence.
The third process is psychical ; it is a process which is a psychi-
cal event, a forth-putting of the energy of mind. It is directly
correlated with the physiological process only when the latter has
been realized in certain cerebral areas. It is not to be explained
as a resultant of the cerebral physiological process, but as an ac-
tion of the mind which is conditioned upon that process. So, also,
are we entitled to say that, when certain psychical processes, by
way of feeling, ideation, and volition, take place, then, and as con-
ditioned upon these processes, certain corresponding physiological
processes occur in the brain ; the physiological processes, being
propagated from the central nervous system, end in physical pro-
cesses returning energy to the world outside of the body.
MIND A REAL BEING. 667
When the mental process is a perception of some object, called
an " external "' object, it is no less truly a psychical process. The
mind creates its own objects ; presents itself with its own presen-
tations of sense ; acts to bring forth that which it knows as not
itself. But it does all this as dependent upon the processes which
take place outside of itself, and with the assumption of extra-men-
tid realities as existing, to which it stands in the relation of cause
and effect.
§ 24. Finally, then, the assumption that the mind is a real being,
which can be acted upon by the brain, and which can act on the body
through the brain, is the only one compatible with all the facts of ex-
perience. There is nothing which we know about the nature of
material beings and the laws of their relation to each other, or
about the nature of spiritual beings and their possible relation to
material beings, or about the nature of causal eflficiency whether
in the form of so-called physical energy or in that of activity in
consciousness, Avhich forbids the aforesaid assumption. On the
contrar}', everything which we actually know, as distinguished
from what we conjecture to be true, or would like to have true, for
the satisfaction of certain of our quasi-scientific or ethical impulses
favors this assumption. And no other assumption, substantially
different from this, is compatible with the facts of experience.
CHAPTEE lY.
THE MIND AS EEAL BEING.
§ 1. No attempt need be made to conceal the fact that the last
three chapters have given to the phenomena aad laws of Physi-
ological Psychology a " metaphysical " treatment. In the intro-
duction (see § 5) to the scientific discussion of the subject, the in-
tention finally to raise and answer certain metaphysical questions as
to the nature of Mind was frankly avowed. Indeed, since all dis-
cussion of those assumptions which underlie our experience of what
we call " reality " is metaphysical, it is not easy to see how the
science of mind — from whatever point of view approached — can be
thorough and conclusive without involving metaphysics. In this,
the concluding chapter, certain still more distinctively metaphysi-
cal inquiries must be briefly pursued. The mind has been spoken
pf as "real," "spiritual " (or non-material), a "unit-being," etc.
These are terms which require further explication. What is meant
by speaking of the mind as a real being? What is it to be, in
reality, f^piritual rather than material ? W^hat is the real nature of
that unity which belongs to mind ; and on what grounds do we
affirm that the mind is a " unit-being ?"
Thus far the effort has constantly been made to maintain a close
connection between the answer given to semi-metaphysical inquiries
and the facts of physiological psychology. In rendering such an-
swer the appeal has constantly been taken to the facts. Should
the facts, in any case of appeal, not betir out — or, at least, should
they contradict — the conclusions alleged to be based upon them,
then the conclusions must be modified, or change the basis on
which they assume to rest, or utterly fall. But in answering the
more distinctively metaphysical questions now raised as to the nat-
ure of mind, the jDsycho-physical facts are of little direct assist-
ance. Such questions are fitly raised at the conclusion of psycho-
physical researches only because these researches have led us to a
certain view as to the nature of the subject of the researches —
namely, as to the nature of the mind.
§ 2. The mind is a " real " being in the highest sense in which
THE POPULAR IMPRESSION. 669
any finite being can be real. Indeed, its claim to be considered
real is more indisputable than the same claim as put forth for any
material thing ; it is unique. The reality of mind underlies and
makes possible all our knowledge of other real beings, and all our
assumptions as tp the existence of such beings. It is only on con-
dition of granting its reality, in the highest sense of the word, that
we can affirm the reality of other beings.
There can be no doubt that the popular impression attributes a
reality to material things which it does not consider to be pos-
sessed by the mind. This impression makes the clearly visible
and hard, tangible substances, experience of which constitutes so
injj5ortant a part of ordinary working-day life, the test and stand-
ard of the most indubitable reality. Substantial as a rock (that
is, a presentation of sense which consists of certain qualities made
known especially to the tactual and muscular senses) ; and unsub-
stantial as a day-dream (that is, a series of representative images
largely free from all admixture of presentations of sense) — thus
does the popular estimate express itself with respect to the reality
of the phenomena referable to things as compared with the pure
states of mind. Materialistic objections to the reality of mind,
when made to rest upon scientific data, repeat and confirm the
popular impression. These objections ordinarily assume that no
doubt can be raised as to the reality of material "Things." Such
things as are real in the highest sense of the word, however, are
not now understood in the same way as the things indicated in the
popular impression. Only the atoms, or elemental and permanent
factors which enter into the comjDosition of all the objects of sense,
are held from the scientific point of view to be real in the highest
sense of the word.
The things of experience by the senses are admitted to be con-
stantly changing, and at no time, extra-mentally, to resemble the
unchanging material realities with which science deals. Things,
as they appear to the eye and to touch, are spread-out, continuous,
without empty space between them, and for the most part motion-
less, except as they are moved in masses by application of external
energy. Things as they really are, however, are neither spread-
out, nor continuous, nor motionless. On the contrary', they consist
of a countless number of invisible and intangible real beings, called
atoms, that are ceaselessly moving, with incredible velocity and in-
tricateness of changing directions, in empty space, and according
to forces inherent in them. These atoms are real, and have always
been — the sole element of all which appears as real ; so this form
of quasi-scientific metaphysics goes on to declare.
670 THE KEALITY OF MIl^D.
On the other hand, it is argued by certain advocates of the fore-
going \ie\v that the so-called mind is wanting in every characteristic
which could justly entitle it to be called a reality. Certainly it is
not adapted to win the popular respect as a hard and sohd sub-
stance, which it is difficult to move, and imjoossible to remove from
the sphere of possible sensations. "What is the mind, in reality ?
It cannot be seen or touched, or apprehended by any of the senses.
It cannot be imaged as spread out in space, or as space-filling, by
virtue of some physical energy streaming uninterruptedly forth
from the mathematical point at which it is situated. It can do
nothing except through the body ; that is to say, all that is done,
which could possibly be referred to the mind, is really done by the
body. And the body is a material mechanism, which is nothing
except as it is constructed out of the same atoms, with their inherent
forces, which have composed the star, the crystal, the flower ; and
which can do nothing except as the ceaseless play of the energies
of great Nature (of which it is a point, a part) are kept j)laying
through it. Without the physical mechanism, as a real existence,
there is no manifestation of so-called mind, no manifestation actual,
possible, or conceivable. And when this mechanism is dissolved,
the mental phenomena, so far as appears, wholly cease, W^hat,
then, is Mind ? WTiat claim to reality can it jDOSsibly make valid ?
More particularly, certain jjuzzling questions regarding the nature
of the mind's behavior may be raised by the advocates of the same
foregoing view. Where is the real mind, it may be asked, when
consciousness is gone, as in swooning or deep sleejD ? W^hat becomes
of the mental Being when the mental faculties one by one drop
away, as in cases of general paralysis ? WTiat worthy kind of real-
ity can belong to the subject of j^henomena so evanescent and tem-
porary, so incapable of being measured, and weighed, and related
to the permanent forces and beings of the material world ? More-
over, if mind is a real being, what shall be said in answer to the
inquiry, why certain of the lower animals can apparently divide up
their souls by fission of their physical structure ? And cannot even
man's proud unity of real being become disturbed by the accident
or disease which results in a double consciousness, or in the loss
of all previously acquired knowledge — of the mind as previously
existing and developed ?
§ 3. That many puzzling, and even unanswerable, questions can
be asked concerning the nature of the mind, we have no interest to
deny. Doubtless, if difficulties growing out of our inability wholly
to clear up our ideas of "real being," "self-identical and perma-
nent existence," etc., are objections to believing that any real beings
' THE POPULAR IMPRESSION. 671
exist, they are also objections to our believing in the reality of mind.
But certainly it is one thing to ask unanswerable questions regard-
ing the ultimate nature of any particular real beings, so called, and
another thing to prove that our belief in the existence of such real
beings is unfounded. Moreover, the fact that we cannot conceive
of or define the real being of the soul, in terms which apply to
material things, is cheerfully conceded. Indeed, it is this general
fact ujDon which chief reliance is placed to prove that the being of
the soul is unlike that of "Things" — is non-material, or spiritual.
But how can this fact prejudice the claim of the soul to be real, un-
less it has previously been established that to be hard, and round,
etc., or to be a minute material bit (an atom) ceaselessly in move-
ment, is necessary in order really to be at all ? The truth is, how-
ever, that both the popular impression and the more scientific
theory, just so far as they can cogently be urged against the reality
of spiritual being, themselves rest on the most unverifiable and ab-
surd assumptions.
The popular conviction of the indubitable, and, as it were, supe-
rior reality of certain classes of things is easily explained as the
necessary result of the development of experience. All things
which are pre-eminently real, in this meaning of the Avord, are cog-
nizable by means of tactual and muscular sensations marked by a
strong color-tone of feeling. Things merely smellable have no
"reality," in this sense of the word, because they are not apprecia-
ble by touch and offer no muscular resistance. We cannot put our
hands on the effluvia which excite the olfactory nerve ; the air when
laden with sweet and sickening odors is not tangible or impenetra-
ble. Real things — that is, things which can be seen and handled —
are, however, regarded as the sources of our sensations of smell.
What is true of sensations of smell is also true, in less degree, of
sensations of sound. But in the case of sound we are generally
able at once to refer the origin of the acoustic sensation to some
so-called real "Thing." Objects tasted are popularly regarded as
real, because they are objects which are handled before tasted, and
constantly touched as they are being tasted in the mouth. A "bad
taste in the mouth " is not regarded as giving evidence of the pres-
ence of any real thing ; it may simply be regarded as a sensation
located in that region. Accordingly, one does not consider one's
self to be tasting one's own mouth as a real thing, although one
may say that the mouth has a bad taste.
Even when the presentation of sense is a clearly visible object,
it does not necessarily seem to have the characteristics of a real
thing. For the object of vision readily and quickly changes its
672 THE REALITY OF MIND.
color, apparent magnitude, characteristics of superficies, and visible
outlines as a solid. Moreover, everybody knows that his eyes have
often deceived him ; even when they have been closed visual im-
ages have appeared before the mind, such as could not possibly
represent any so-called reality. But the nature of tactual and mus-
cular sensations is different from the visual in several important
particulars. Such sensations, on bestowing the requisite attention,
may ordinarily be brought strongly into consciousness. They do
not so readily change their quality regarded as coming to us from
an apprehension of the properties of things. The feeling of effort
colors them highly ; and the pain from being struck, pressed,
pinched, or impeded, is a frequent accompaniment. Therefore,
children are educated in their knowledge of, and belief in, a world
of reality by being constantly resisted by material things ; and adults
naturally suppose that when they can lay hands on an object they
know that it really is, and what it really is, with a certainty impos-
sible in any other way.
It wholly escapes the ordinary observation that the same assump-
tions— whether they be deemed verifiable or unveritiable — underlie
the conviction of the reality of things tangible which belong to
the operation of all the senses. It is true, as experience shows,
that tactual and muscular sensations are, from their very nature,
and from the manner and frequency of their recurrence, pecul-
iarly adapted to serve the mind well in those acts of synthesis
by which it constructs the real things of its experience. But this
fact does not in the least diminish the force of the other fact —
namely, a certain assumption or postulate as to an exti'a-mental
reality (an X, which is not any one of the attributes — a, b, c, etc. —
of the "Thing," but which is the subject or ground of them all)
underlies and conditions all the apiDrehensions of sense. Without
granting and using this assumption we cannot affirm that even by
tactual and muscular sensations we know any reality whatever,
beyond the real fact that so our own minds stand affected with the
presentation of an object of sense. If the popular impression con-
cerning the reality of "things " does not extend beyond this simple
act of self-knowledge, as it were, it certainly forms no ground for
affirming the superior and undoubted nature of such reality.
§ 4. The cause of the scientific objector to the reality of mind, as
standing on an equality, with respect to the cogency of its evidence,
with those material atoms about whose reality he tolerates no doubt,
is not a whit better off than is that of the popular impression. In-
deed, it is by no means so good. That ready-made " things " really
exist in independence of mind (meaning by such "things" the ob-
THE SCIENTIFIC OBJECTION. 673
jects of everyone's immediate experience) is a proposition which it
involves fewer doubtful elements to maintain than the proposition
that so-called " atoms " have such existence. It is time to raise the
question : How can one know, so confidently, that those cerebral
molecules exist extra-mentallj, with all their incalculable and almost
inconceivable motions, on whose real being the phenomena of mind
are sometimes made to depend? The brain — it is claimed by Ma-
terialism— may be made responsible for mental phenomena, for the
latter are mere manifestations in consciousness of the changes which
are going on in the material constituents of which this organ is
really composed ; there is no need of a real non-material being as
the subject of the mental phenomena ; the physical phenomena,
however, must have some real being as their subjects ; such reality
is to be found in the molecules of the brain. But what are the
grounds and the nature of our knowledge of this wonderful con-
jurer styled the brain ?
The so-called scientific argument against the reality of mind, as
often applied, may be stated in terms somewhat like the foregoing.
Little examination is needed, however, to show that its conclusive-
ness involves certain assumptions which cannot themselves be vali-
dated without weakening or destroying the very ground on which
the argument is itself based. Let the case be tried by making a
beginning with that sort of testimony with which everyone is most
familiar. I know that I think, feel, will ; that is to say, phenomena
take place in consciousness which there is no conceivable way of
describing except by attributing them to the subject of all con-
sciousness— to the self-conscious " me " called mind. But because I
cannot perceive this subject of all consciousness as an extended and
external somewhat — a " Thing " so large, and shaped and colored
in just such a manner, with a definitely hard or soft feel — that is to
say, because I do not appear to myself in consciousness to be just
such a kind of being as are some of the objects of my perception,
I begin to raise the question whether this subject (the "I" that
thinks, etc.) has any real being at all. May it not in fact be, I ask
myself, that some "thing," or collection of things, like those which
I have often seen and felt, is the subject to which the thoughts
and feelings and acts of will that I haVe called " mine " should be
attributed? Of course, if this question is to be answered in the
light of modern physiology with even a provisional affirmative, the
particular "thing," to which such activities as those I am conscious
of are to be attributed, is my hrain. Nothing, surely, but my brain
can think, and feel, and will — so to speak — for me. For if physical
science has established anything whatever with regard to a particu-
43
C74 THE EEALITY OF MIND.
lar organ or substratum of the mental phenomena, it is that such
organ or substratum is the brain.
But the inquiry must next be raised : How does one know that
one has a brain, which may serve as the real substratum of the
phenomena of one's consciousness ? It scarcely need be said that
no one has ever had any evidence presented directly to the senses
that such organ exists within his own cranial cavity. To be con-
scious, and at the same time to observe the substratum of one's
consciousness, is an unattainable opportunity. It may even be
that the ego (the "I" of consciousness) which is engaged in the
search for its own real being in a material substratum has never
seen so much as a single human brain. It is certain that no ego
has directly observed the molecular changes of any central nervous
mass, whether belonging to another or to itself, when such mass
was engaged in the activities whose resultant the phenomena of
consciousness are claimed to be. Since there is such scarcity of
direct ocular and tangible demonstration of a special relation be-
tween the brain and mental phenomena, it is plain that the testi-
mony of experts must be summoned. Resort must be had to the
great anatomists and experimental physiologists who have had most
experience as to the structure and functions of the brain-mass.
It must, of course, be confessed that no expert has any more
direct evidence than every self-conscious ego has of the existence
of a real material structure called brain, which may account, by its
presence and activities, for his own mental phenomena. Nor can
he offer an}' evidence peculiar to himself for his belief that the par-
ticular ego which each one calls " myself" is connected with a brain.
How many soever other brains he may have seen, he only knows
by a series of very indirect and complicated inferences that any
individual whose brain lie has not seen really possesses one. But
whence these inferences ? and, "What are the grounds on which the
confidence attached to them is based? To these questions only
one answer is possible. The inferences themselves are acts of
knowledge, modes of consciousness, phenomena of mind. The
only possible grounds of confidence in them, as valid inferences,
must be referred back to our inherent faith in the power of the
mind rightly to infer, from its own phenomena, the real existence
of beings the phenomena of which it has never perceived. More-
over, if the mind had perceived the phenomena of its own brain,
there could be nothing in the phenomena themselves to account for
the power to make inferences which belong to it as mind. On the
ground, then, of' an inferred reality called the brain, I am asked
to dispense with my confidence in the reality of the being whicli
THE ATOMS AS AGENTS. 675
makes the inference, and which, at the same time, makes a much
more irresistible inference as to its own reality as an active infer-
ring force.
§ 5. The case is, however, by no means so favorable, as the state-
ment just made would imply, for that phase of scientific material-
ism which refers the phenomena of consciousness to the brain as
their sole cause. For it is not in the brain, as a mere mass of mat-
ter whose structure and mechanical functions can be made obvious
to any intelligent observer, that the real substratum of mental phe-
nomena must be sought. Considered as such a mass, this organ
is no better than any other similar soft and pulp-like bulk. It is
the wonderful molecular constitution, atomic play, and changing
dynamic relations of the invisible particles of this mass, which are
responsible for its unique functions. In all the first Part of our
investigation we saw how necessary physiology finds it to regard
the nervous centres as molecular mechanisms. Nothing that is in
itself of first importance appears to the eye of the observer who
looks upon the freshly extracted mass of the human brain. And
when this mass has been skilfully prepared for investigation under
the microscope, the investigation itself does not reveal directly, to
the highest magnifying powers of the glass, the ultimate agents
in the wonderful drama it has been playing. These agents are the
atoms, to whose real being and so-called " inherent " forces all that
is done by the complicated mechanism must be referi'ed. But the
existence of the atoms as real beings, capable of acting on each
other and of being acted on — how shall this remote and obscure
fact be ascertained ? And how shall we learn what is the nature of
these beings, so as to determine whether or not they are capable
of performing the stupendous task of bringing forth the various
mental phenomena?
In attempting to answer the last two questions we are in great
danger of losing completely all that we have taken most pains to
gain. It is to the all-powerful " atoms," with their potent forces,
that -we are now looking as the real subjects at once of the molec-
ular changes in the brain-mass and of the phenomena of conscious-
ness. From these real beings and their relations there must be
derived, not only the activities which all ascribe to nervous matter,
but also those which some are constrained to ascribe to conscious
mind. And yet, how do we know that any real beings whatever
called atoms exist ? Certainly not by direct evidence of any of the
senses. Not even the most pronounced materialist would venture
to affirm that he has seen or touched an atom, or can demonstrate
its existence and nature to ordinary observation through the human
G7G THE KEALITY OF MIND. *
senses. Atoms are supersensible beings. Moreover, tliey are hj]pO'
thetical existences, or beings whose existence is inferred in an ex-
tremely roundabout way in order tbat we may be able to give to
ourselves a rational account of the grounds on which certain classes
of phenomena rest.
The phenomena whose rational explanation seems most peremp-
torily to demand some hypothesis of atoms are the phenomena of
chemistry. When, however, the further inquiry is raised as to the
real nature of the atoms, it is found that modern physical science
is by no means satisfied with its own answer. Dynamical theories,
tending to resolve the atoms into mathematical points acting as
mere centres of force, contend with other more realistic theories
which regard the atoms as simply the smallest bits of matter into
which we can by any known means break ujd the larger collections.
What is meant by the forces being " inherent " in the atoms is a
still more difficult question to answer. Indeed, to this question no
answer can be given which gets much beyond the simjole declara-
tion of the facts of experience ; that is to say, these hj'pothetical
and yet sole real material beings are always supposed to behave,
with respect to their motions, in the same way under the same re-
lations, and something can be done by science toward measuring
their various motions in terms one of the other.
Moreover, the best efforts of modern investigation to describe
the nature of the atoms appear, not only incomplete, but also, in
certain particulars, self-contradictory. It is certain that the atom
cannot be regarded as an independent reality. What it is can only
be described by telling what it does ; but in telling what it does
we always find ourselves implj'ing certain relations to o/Ae/' atoms.
That is to say, we know nothing about the nature of any of the
atoms which does not involve also comjDlicated hypotheses concern-
ing its mode of behavior as caused by the presence and mode of
behavior of other hypothetical beings. In this way the realitj^ of
the atoms is made ultimately to depend on the reality of some form
of being that binds them together, as it were, and makes them
work to a unity of plan. But here, again, we are reminded that we
can form no conception of a "plan " which is not a phenomenon of
mind, and no conception of a "unity " that does not depend ujDon
the unifying actus of the mind. Moreover, all ideas of "relation"
are dependent upon mental activities that are quite without phys-
ical analogy. All "Things" are made into the units which they
appear to be by the unifying action of the mind. Such action is
implied in perceiving the things ; for the study of perception, from
the physiological point of view even, has enabled us to show that
ATOMS AS DUE TO MIND. 677
no so-called " thing " is a ready-made material product, appre-
hended by mind in a form which is a copy of some extra-mental
being. In trying, therefore, to comprehend what is the nature of
those real beings (the atoms), on whose existence, activity, and rela-
tions all mental phenomena are assumed by Materialism to depend,
we find that the picture we frame of them is the work of the mind.
§ 6. Accordingly, the whole course of argument and the whole
weight of conviction appear to be the reverse of what is assumed
by the objector to the reality of mind. The material molecules of
the brain are not beings about the reality and exact nature of which
we have the most indubitable evidence — evidence so indubitable
that we may venture to press it into the contradiction of the more
immediate data of consciousness. If these elements of all physical
being are real, they come to us as inferences and hj^potheses ; they
involve a vast amount of conjecture, indirect inference, and unsolved
difficulties, or even contradictions. And if we ask, On what au-
thority are these inferences made ? Whence comes the demand for
any rational explanation whatever? Where do the conjecture, hy-
pothesis, and sense of difficulty and seeming contradiction exist?
then the only answer to be given to all these questions refers them
to the Mind. What atoms and forces and laws can be, or mean,
without the being and activity of self-conscious mind, is even harder
to conjecture than what a color can be which is not seen, a sound
which is not heard, an odor that is not smelled.
And now let the attempt of materialistic theory be made anew ;
let it be assumed that the phenomena of consciousness have no
I'eal subject in the mind. Such phenomena must, accordingly, be
attributed to the peculiarly constituted and mutually interacting
molecules of the brain. But these supreme physical beings are
themselves, as far as they are the object of knowledge, pre-emi-
nently mental creations ; and the sole warrant for carrying them
over into the realm of extra-mental reality consists in certain irre-
sistible convictions or assumptions of mind. To make their real
being the account of the mental phenomena, and thus to deny the
real being of the subject of mental phenomena, is not only to ex-
plain what is most direct and certain by what is most indirect and
uncertain ; it even involves the wonderful paradox, that the one be-
ing inwhose active energizing all conceptions of all real being arise,
feels justified in denying its own reality in the supposed favor of cer-
tain of its most remote and donbtfid conceptions.
§ 7. What is meant by affirming the reality of mind may be
made obvious by pursuing the following train of reflections : In
the development of the mental life its phenomena come inevitably
678 THE EEALITY OF MIND.
to divide themselves into two great classes. As it appears to adult
experience, not only tlie unfolding, but even the very existence of
self-consciousness seems to involve the distinction between the ego
and the non-ego — between the "I" with its states, and the "Things"
which it knows with their manifold jDroperties or attributes. Each
of these two classes of phenomena — the so-called subjective and the
so-called objective — is inevitably attributed in consciousness to a
different subject ; the one to the " I " as its own states, the other to
somewhat left undefined, except that it is not the " I," and is called
"matter," "material substance," etc. (the unknown X which is not
I). It is only as involving all this mental jorocess that any real
being is known or believed to exist ; but the mind in the develop-
ment of experience inevitably completes the process, which involves
the assumption that real beings do exist, and that all these real
beings are either " things," such as I know, or myself and other
conscious beings, such as I am. What any real being is can only
be told by an enumeration of its so-called attributes ; and this is as
true of myself as of the things which I know. It is also as true of
them as it is of myself. If the foregoing statements covered the
entire case, it would simply be true that I have no better reason
for attributing a real Being to any material thing than to the
subject of consciousness. But we have already seen that the pro-
cess by which we reach the real being of the molecules of the
brain is much more indirect and doubtful than that by which we
reach the affirmation of a real being for the things of daily experi-
ence and for the subject of all that experience.
§ 8. Peculiar and cogent reasons may be given, however, which
further enforce and verify the assumption of a real existence for
the Mind. We have seen (comp. Part IT., chap. X., and the pre-
ceding chaps, of Part III.) that there is a class of so-called mental
faculties, most important and distinctive, for the distinguishing-
characteristic of which no physical analogies or correspondences
whatever can be discovered or imagined. This is true of memory
as active reminiscence, of the unity of consciousness, of voluntary
attention, and of the relating activity. The existence of these
modes of mental behavior requires the assumption of a charac-
teristic real being, other than the molecules of the brain, to which
they may be referred. Some of these modes of behavior are con-
spicuously unintelligible and meaningless without granting such
an assumption. For example, an act of recollection involves the
presence in consciousness of a state the very essence of which is
that it claims to represent (or stand for) an absent past state of
consciousness. No way of verifying this claim which does not
TO EE AND BE CONSCIOUS. 679
involve its acceptance can possibly be devised. But tlie present
state of memory is a state of my consciousness, and the state which
it claims to represent was also a state of my consciousness. To
recollect the past state of another consciousness than my own in-
volves an absurdity ; to recollect a past state otherwise than as
represented in a present state of my own consciousness also involves
an absurdity. Of course, such reflection upon the nature of the
act of memory affords no demonstration of the claim that the sub-
ject of the present state is one and the same real being with the
subject of the past state. On the contrary, all demonstration itself
rests on this assumption ; for without accepting it as valid we could
not reach the conclusion of any demonstration. The premises of
every syllogism are connected with one another and with their
conclusion in a living unity of thought, only on the assumption
that one real being is the subject of each of the thoughts Avhich
constitute the syllogism.
To "he really," and to be the one permanent subject of changing
states, are, in our conception, but different ways of expressing the
same truth. That really is which is such a subject of its own
states. It is for this reason that modern physical science regards'
the atoms as having a permanent reality which does not belong
to the composite structures — the things of our experience — into
which the atoms enter. Every " Thing " may perish — that is to
say, as such thing, it may cease to be the object of observation,
the subject of states. But the atoms are supposed to remain with
unchanged natures through all the changes of relation which they
may undergo toward other beings with somewhat similar natiires.
Even if we were obliged to adopt the hypothesis of a constant
change of states in the interior of the atoms, since every atom
shows a variety of possible activities according to the relations in
which it stands for the time to other atoms, it is not considered
to have lost its real being or distinctive nature by changing its
states. For it — the atom — can be brought into the same relations
again, and then it will again display the same modes of behavior.
Its reality does not depend upon its interior rigidity, the unchang-
ing nature of its being ; it rather depends upon its capacity for
being the subject of so-called states, and for following a law or an
idea which recalls it, as it were, to the same states when the same
circumstances recur.
How can it be denied that all our conceptions of the atoms as
enduring subjects of various states are derived from our experience
with ourselves? The " I " which is the subject of all consciousness
is accustomed to attribute to itself every state of that great variety
680 THE REALITY OF MIND.
into which consciousness may be shaped. The states are changing,
they have a transitory and phenomenal being. But they are all
states attributable to one subject. On what ground, then, shall one
undertake to deny the confidence which the soul comes to have in
itself as the real and permanent subject of its own states ? For we
can form no conception of real being at all which is not modelled
after this pattern. To have a variety of changing states attributed
to it as the subject of them all — this is to demonstrate in conscious-
ness a claim to real Being. Unchanging rigidity, the permanence
of the mathematical point or of the material atom, on the supposi-
tion that the latter undergoes no interior changes whatever, if such
rigidity and permanence any where exist, constitutes no claim to the
title of real being.
The soul exists in reality, above all other kinds of being, because
it alone, so far as we know on good evidence, knows itself as the
subject of its own states ; or, indeed, knows the states of which it
is the subject as states belonging to itself. But its law is that of
development; and, unlike all " things " which are subjects of va-
rious kinds of evolution, so called, the soul can recognize the law
of its own being. When, therefore, we are asked what the Mind
really is, we can respond by telling what it comes to be as the re-
sult of its unfolding under the fixed conditions of its native powers.
But these " powers " cannot be called native, as though they were
actual achievements of the mind's inborn faculties, or separate forms
of energy inherent in it, after the analogy of the forces said (some-
what unintelligibly, it must be admitted) to be " inherent " in the
atom.
But we do not define the nature of any real being simply by
stating how it appears and behaves in its most germinal and unde-
veloped form. The tree explains the seed ; the adult bird, the
egg ; the character of the highly differentiated product must be
studied in order to know the full description of the energies that
are potential in the simpler stages. It is an undoubted fact that
the mind has a historj' in each individual case ; and in each case
such history is a development. The great service which Physiolog-
ical Psychology has rendered to the general science of mind con-
sists in its description of the nature and stages of this develoi^ment,
so far as concerns the jDhenomena of sensation and perception by
the senses. This self-recognizing unity of development which be-
longs to the mind is a striking proof of the validity of its claim to
be considered a real being. As the being which acts and kuovvs
itself as acting, which is acted upon and knows itself as affected,
which is the subject of states and itself attributes these states to
• KOA' -MATERIALITY OF MIND. 681
itself, which develops according to a plan and so remembers and
comprehends the significance of its past states that it can recognize
the fact of its own development — as such a being the Mind is more
entitled to consider itself " real " than to consider real any of the
various objects that, immediately or indirectly, appear before it in
the course of its history.
§ 9. The question whether the mind is to be spoken of as non-
material or " spiritual " scarcely merits the gi-ave and lengthy dis-
cussion to which it has often been carried. Materiality, as predi-
cated of any real being, is only a complex term including a num-
ber of so-called attributes, which are all the subjects of experience
only as belonging to individual things. All real things are to be
called material which have these attributes, so called. Primarily, as
has been frequently shown already, the attributes are simply modes
of the affection of the mind which we have learned to localize and
objectify as belonging to extra-niental reality. But if we raise the
question whether the Mind, too, is known to itself as having those
attributes which make up our complex, general notion of "materi-
ality," no one would find it easy to think of giving this question an
affirmative answer. The mind attributes to "things" the qualities
of extension, impenetrability, and all the various subordinate mod-
ifications of these qualities. It perceives these things as colored,
cold, hot, rough, smooth, etc. But it does not attribute such quali-
ties to itself ; it can find nothing in the modes in which it mani-
fests itself to itself which would warrant the application of similar
terms to these modes of its own behavior.
Indeed, all the terms which do apply to the recognized qualities
of mind have to be understood as figurative when, having been
borrowed from physical relations, they are made to apj)ly to psychi-
cal states. Even in those cases where the analogy seems almost
to amount to an identity, closer inspection shows that this seem-
ing does not correspond to the actual fact. For example, we do
attribute quantity to sensations and feeling. But when the suffer-
ing from pressure becomes more intense, we do not regard the
mind as actually passing, like some material thing, under a heav-
ier load (sub-fero), against which it must either bear up or break,
through the physical strain. Just so, movements of the mind are
not to be defined as changes of its position with relation to other
things in space. We are, then, surely warranted in affirming that,
so far as the mind has any immediate information as to what quali-
ties should be assigned to itself and what to " things " — which it
always looks upon as not-itself — it is compelled to regard itself as
>*on-material.
6S2 SPIRITUALITY OF MIND.
"We have no way, however, of telling what is the nature of any
so-called real being except by enumerating its qualities, or those
modes of behavior which we attribute to it on account of its affect-
ing our consciousness in certain definite ways. To attempt to re-
gard the mind as material, when it manifests itself to itself as
non-material, compels us either to use the word " material " in an
unwonted and unauthorized way, or else to attribute to matter in
general certain occult powers which it never manifests itself to the
mind as possessing, and which make it really to be quite different
from what its manifestation of itself would indicate.
The only way of maintaining the materiality of mind would then
appear to be that of denying its real existence at all, and of attrib-
uting its phenomena to the material molecules of the brain as their
real and material substratum or basis. But the untenable nature
of this view has already been sufficiently indicated. Or perhaps a
strong temptation may be again felt, at this point, to recur to the
hypothesis of a third somewhat, a " two-faced unity," which is the
ground of the phenomena of both body and mind. But such hypoth-
esis can throw no light whatever on the inquiry whether the mind
is material or non-material. The phenomena we call " mental,"
and attribute to the subject of consciousness, would remain just as
radically uulike those which we call " physical," and attribute to
matter, after making the hypothesis as before. And to the hypoth-
esis itself the same objections would lemain opposed.
The negative conclusion that mind is won-material is quite in-
evitable for everyone who admits that mind is a real being with
any nature whatever.
§ 10. It is not difl&cult, also, to show that we must make the cor-
x'esponding positive statement, and affirm the spirituality of mind.
This we can do with confidence, however, only so long as we mean
by the term "spirituality " simply to sum up and express in one word
the list of attributes which describes the kiK)wn activities of mind.
To perceive, feel, think, will — in brief, to be conscious in some one
of the various forms of conscious life — this is to be positively spirit-
ual, in the only sense in which we are entitled to affirm spirituality
of mind as such. As soon as we conceive of spirituality as some
ethereal extension of thinking substance, we enter upon the vain
effort to conceive of mind under terms of matter, and at the same
time escape the consequences of so conceiving of it. Nor can we
hope to vindicate for the mind such spirituality as would be implied
in its being freed from all relations to material things, or from de-
pendence for the modes of its being upon the material substratum
of the brain. How spirit, in the sense of disembodied or unem-
•MENTAL ACTIVITIES SPIRITUAL. 683
bodied mind, would perceive, and feel, and think, and will, is a ques-
tion toward the answer to which we can make no beginning. To
attempt its answer at all involves us in the vain effort to use the
very relations which are most inseparately connected with the con-
scious activity of the mind in such way as to escape from the con-
trol of the relations themselves.
It is true, nevertheless, that a marked difference exists in the
directness and intimacy which belong to different classes of mental
states, as regards their comparability to the classes of physical
stimuli which rouse the mind to its fundamental activities. Those
which appear to be most indirectly, and, as it were, loosely related
to these fundamental activities are fitly most relied upon to show
the spiritual nature of mind. To control the mental train as dis-
tinguished from being a passive member of a mental mechanism,
to reason so as to deduce conclusions and make inductions to gen-
eral laws, to recognize the call of duty, and to call up and classify
in the consciousness the lofty and complex ideas which answer to
words like " beauty," " truth," and " God " — these and other simi-
lar operations of the mind pre-eminently emphasize its spirituality.
§ 11. In somewhat the same way must it be admitted that the
question of the unity of mind has given rise to much fruitless and
by no means altogether pertinent debate. The attempt to conceive
of the mind as a unit-being, constituted after the analogy of those
physical structures which we are accustomed to regard as unities,
inevitably leads to confusion and error. The important psycho-
logical fact is, that there is no one of these physical unities which
does not derive its unity from the unifying actus of the mind. This
statement is true of each such so-called unity, whether it is per-
ceived as one or is conceived of as one. The unity which belongs
to the percept finds its source in the synthetic activity of the per-
ceiving mind ; the unity of the conception, in the unifying activity
of the mind's relating faculty. It is sometimes supposed, however,
that an atom which should have no parts, be perfectly homogeneous
throughout, and so incapable of changes of its interior states, would
be the highest possible type of a unity of real being. Nothing-
could ever happen to disturb or destroy such a unity. Wherever
in all space it might be moved, or whatever in all time might hap-
pen to it, it could ex hijpothesi never be made two. If, now, such a
unit-atom were to be endowed with consciousness and spiritual be-
ing, how secure would its unity continue to be ! Unlike the mind
of man, it could not fear that some rude concurrence of other
atoms, not of the right affinities, or setting themselves in untoward
relations, would dissolve its complex material substratum and so
684 THE UNITY OF MIND.
destroy its spiritual oneness. The molecules of tlie human brain
ai'e in number beyond computation ; they are highly complex and
unstable compounds ; they are not so protected by their inclosure
in the cranial cavity as to make them invulnerable against all man-
ner of assaults. In how dangerous a position, then, is this so highly
valued unity of our present spiritual organization !
Now, it must be admitted that such a thinking atom would be in
far less danger of suffering from the death of the physical basis of
its tliought than is the thinking man. But two considerations of
great importance are likely to be overlooked in the mere making
of the hypothesis of such an atom. Surely such an atom could hard-
ly have any experience corresponding to what we call the unity of
our consciousness ; and if it had any unity of consciousness what-
ever, such unity could no more be explained as arising out of, or
conditioned upon, the simplicity of the physical being of the atom
than the unity of our consciousness can be explained as arising out
of, or conditioned upon, the complexity of our physical being.
It is impossible to see how a unity of consciousness at all resem-
bling what we understand by the term could find an adequate ma-
terial substratum in a single rigid atom. In other words, if a spirit-
ual being having a unity of consciousness were brought into si^ecial
psycho-physical relations with a material being incapable of any
interior changes, because possessed of no parts to undergo change,
these relations would have to be totally different from any which
we can conceive of as holding between the body and mind of man.
For the very nature of the mind's unity is dependent upon that
variety of exj^eriences which is occasioned in the miud through the
changing states of the brain. The physical basis of the human
mind is undoubtedly an extremely complex system of interacting
molecules. Certain relations can be traced between the character
of these physical interactions and the character of the states arising
in the mind. These states depend for their character, and even for
their very existence, upon the occurrence of the corresponding
material changes. A brain that is not in a ceaseless change of ac-
tivities of the peculiar sort called " neural " is a dead brain, so far
as its influence on the mind is concerned ; such a brain could not
serve as the substratum or physical cause of mental phenomena.
Comparative anatomy shows us that the greater the number of
molecules, and the larger the variety and the size of the organs
specially related to the mental processes, the richer in variety and
nobler in quality the mental processes themselves become. More-
over, so far as we can ascertain, the highest unity of consciousness
belongs in connection with the greatest complexity of the material
THE UNITY OF THE ATOM. 685
substratum. The animals whicli have the largest cerebral develop-
ment appear to have, too, not only the most manifold and extensive
mental life, but also, in the highest degree, the capacity for attrib-
uting the phenomena of that life to one subject. Those psychical
activities which are connected with the physical interaction of the
greatest number of material elements are the most numerous and
significant ; and they are, also, actually most perfectly harmonized
into a higher unity of spiritual self-conscious being.
§ 12. No information derived from the study of Physiological
Psychology warrants us in affirming that a highly developed self-
conscious existence must, from the universal necessities of the case,
be united with a vastly complex material structure like the human
brain. Such study does, however, compel us to affii'm that such
a unity in variety as is the human mind cannot be conceived of
in dependence upon the movements in space of a single jjerfectly
rigid and unchanging atom. The development of human experi-
ence is conditioned upon the arising in consciousness of many
sensations of varied quantities, qualities, and orders in time ; upon
the synthesis of these sensations into presentations of sense ; and
upon the recall of the presentations in the form of I'epresenta-
tive ideas. What experience would be, if its basis were not laid
in such rise and combination and i-ecurrence of sensations, we can-
not even conjecture. In the highest flights of imagination, i:i the
profoundest explorations of reflection, we never escape out of the
influences arising from this basis. The nature of this psychical
basis of sensation and perception depends upon the nature of the
physical basis of the living and acting brain. In other words, what
sensations and perceptions constitute, at least in part, the " stuff"
of all consciousness depends upon what the molecules of the cen-
tral nervous system are doing. We cannot even conceive of any
other relations as possible between the mind, on the one hand,
and the brain, on the other, than relations between a system of
moving molecules and a corresponding change of conscious states.
§ 13. Furthermore, the unity of a single indestructible and eter-
nally unchanging atom would afford no explanation of a mental
unity. In the case of man's mind and brain, the vai'iety of the
nervous changes in part explains the variety of the mental states ;
but nothing in the changing relations of the innumerable moving
molecules throws any clear light on the origin of the unity of mind
in consciousness. A material being absolutely without distinction
of parts would be, for that fact, no better fitted to become conscious
of itself as one. A series of states of consciousness can indeed be
attributed by our imagination to such a being. From the purely
686 THE UNITY OF MIISTD.
psychological point of view we can conceive of the unit-atom as
having an experience resembling our own. We, in our conscious-
ness, can imagine such a being as the subject of states, and as
attributing each of these states to one and the same subject —
namely, the " I " of the unit-atom — after the fashion of our cus-
tomary mental behavior. But this is quite a different thing from, ex-
j)laining the consciousness of such an atom as arising, with respect
to its unity, out of the material nature of the atom. By the very
hypothesis, the material nature of this particular kind of atom can
have no states ; it never changes ; it is always the same. But con-
sciousness is always some particular definite state ; and self-con-
sciousness is always the being aware of some particular definite
state. There is no consciousness in general ; there is no conscious-
ness which does not involve change of state. Indeed, change is a
reality in human consciousness, if nowhei-e else in the universe of
being. No particular state of consciousness, whether considered as
involving an attribution of that state to a subject or not, could be
exjDlained by reference to the material nature or condition of such
a unit-atom.
§ 14. The foregoing remarks have their value chiefly as a warn-
ing against supposing that the unity of the soul's real being suffers
any prejudice because it is not to be regarded or explained from a
point of view furnished by physical analogies. To be one, as a rigid
material atom may possibly be regarded as one, would be no ad-
vantage to the soul. Or if it be admitted that, in case it had such
unity, it could never lose its real being, it must also be admitted that
we are unable to see how it could ever gain any real being as a soul.
Si the unit-atom could never die, it could also never live — as a con-
scious psychical existence. And it is the unity which the mind
plainly has in self-consciousness that is alone worth contending for.
If the mind were really — that is, regarded as out of its own con-
sciousness— one, and yet two or more in consciousness, it would
be no better, but rather the worse off. If it were really one, but
were obliged not to know itself as one, and could never be aware
of its own states, or attribute them to the one "I" which is the
subject of them all, it would surely be the worse off. To be one, in
the only meaning of the word that is of real value, is to have and
to keep the unity of consciousness. If this unity were reaU}'- a mere
seeming — a trick of nature to cheat the mind — the seeming would
forever seem real, would, indeed, be the ground of all reality ; the
trick would be the kindest of all illusions, and one from which we
should crave never to be set free. When, then, we have recognized
the fact that aU ordering and development of human consciousness
, SEL>APPEAEANCE OF MIND. 687
implies this kind of unit-being as belonging to the mind, we have
gone as far in vindication of the mind's rights as we have any psy-
chological interest in going.
§ 15. That the mind attributes its own conscious states to a sub-
ject of such states (the " I " in all sentences such as " I think," " I
feel," etc.), we have seen it necessary to admit from the very be-
ginning of our psycho-physical researches. As one result of the
study of perception by the senses, it was also found necessary to
recognize a certain unifying or synthetic activity in order to ac-
count for the way in which sensations combine to form the " pres-
entations of sense ; " such unifying activity seems plainly to imply
the existence of a unit-being, the so-called Mind. Further argu-
ments in the same direction came to light as the phenomena of the
mind in memory, voluntary attention, and judgment were brought
under examination. More recently still, an examination of the
factors of self-consciousness, from the more purely introspective
point of view, has confirmed the same opinion. In this connection
we may add, finally, the argument for the existence of the mind as
a real unit-being, which has been so forcefully urged by one of the
greatest of modern psychologists (Lotze). The mind is a real unit-
being, not simply because it appears to itself to be such, but chiefly
because it ai^pears to itself at all. Granted that all that which
only appears to another maybe mere seeming, it still remains indis-
putable that somewhat appears. The somewhat which merely ap-
pears may be really many when it appears as one ; this happens,
in some sort, in the case of all " Things " which appear many or
one according to the way we consider them. But how can that to
which all else appears, whether as one or as many, and that which
also appears to itself — whether it appear to itself as one or as many
— really be other than one, in the highest sense of the word unity ?
No twisting of imagination, or subtlety of argument, can show how
a mind not really one could appear to itself at all ; or break the
strength of the conviction inwrought into the very structure of
human self-consciousness, that the real and spiritual being, which
we call Mind, is not a fortunate confluence or phenomenal centre
of changing modes, but a unit-being, and a reason of all unity in
whatever becomes the object of its thought.
§ 16. As to the first and last things of the Mind — its origin and
destiny, its mortality or corruptibHity — Physiological Psychology
finds itself unable to pronounce. It cannot, indeed, explain the en-
tire being of the mind as arising out of the development of the
physical germ fi'om which the bodily members unfold themselves.
It knows no decisive reason against the behef that such a non-
688 THE UNITY OF MIND.
material and real unit-being, as the mind is, should exist in other
relations than those which it sustains at present to the structure of
the brain. On the contrary, it discloses certain phenomena which
at least suggest, and pei-haps confirm, the possibility of such exist-
ence for the Mind. But, in general, if it remain faithful to its own
mission, within its own limits, it entrusts the full consideration of
these questions, after it has cleared the way from barriers of igno-
rance and prejudice, to Eational Psychology, to Ethics, to Meta-
physics, and to Theology.
INDEX.
Agraphia, nature of, 294
Allen, Grant, on nature of feeling, 501 f.,
521
Aphasia, phenomena of, 292 f . ; kinds of,
394 f.
Aqueduct of Sylvius, 88 ; gray matter of,
91
Aqueous Humor, the, 173
Arachnoid, the, structure of, 63 f .
Attention, effect of, on reaction-time,
480 f., 495 f.; physical basis of, 538 f.,
542 f.; effect of, on perception and
memory, 539 f .
Aubert, on measurement of light, 374 f.
Automatic Action, nature of, 49 f., 130 f.;
in spinal cord, 138 f. ; and brain, 144 f . ;
physical basis of volition, 535 f.
Bain, on local signs, 397 (note) ; theory
of feeling, 501 ; feeling of effort, 524
Baxt, on reaction-time, 481
Bechterew, on the olivary bodies, 150,
161 f . ; and central gray matter, 161 f.
Bell, Sir Charles, discovery of, 123 f .
Ben eke, on nature of feeling, 503
Berger, on reaction-time, 478
Bernstein, on exhaustion of nerves, 109.
Betz, " giant- cells " of, 97, 283
Birge, E. A., on number of nervous ele-
ments, 46, 70 ; excitability of cord, 143
Blastoderm, the, 300 £; layers of, 203 £;
areas of, 202 f.
Blind-spot {papilla optica), 183
Body, general relations of, to mental
phenomena, 560 f.; early development
of, 563 f. , 567 ; phases of, 565 f. ; sexual
differences of, 570 ; relative proportions
in, 571 f . ; race-characteristics of, 573 f .
Brain, chemistry of, 25 f., 27 f.; mem-
branes of, 61 f.; structure of , 73 f., 85
44
f.; ventricles of, 85, 149 f.; ganglia of,
85 f.; hemispheres of, 91 f.; lobes of,
92 f. ; cortex of, 95 f.; inhibitory in-
fluence of, 143 f. ; as central organ,
143 f . ; development of, 204 f . ; general
functions of, 239 f.; temperature of,
243; comparative weight of, 243 f.;
weight of human, 244 f.; relation of, to
mind, 247 f., 605 f., 633 f., 640 f.
Broca, convolution of, 292 f,
Briicke, on neutralization of taste, 403 ;
perception of depth, 442
Byasson, on brain-waste, 243
Cameker, on measurement of taste,
376 f.
Capsule, the internal, 90, 91
Carville and Duret, on stimulation of
motor areas, 257
Cattell, on reaction-time, 485, 493 f.
Cells, the olfactory, 164f.; the gustatory,
]67f.; the auditory, 193
Central Canal, 66 f .
Cerebellar tract, 71 f., 75, 77
Cerebellum, 74, structure of, 78 f.; pe-
duncles of, 79 ; arbor vitce of, 79 ; func-
tions of, 153 f.; lesions of, 153 f.
Cerebrin, 24, 35
Cerebro-spinal system, axis of, 62, 204 f . ;
development of, 204 f., 213
Cerebrum, 74, 82 ; shape of, 83 ; gyri of,
84, 91 f.,95 ; sulci of, 84, 91 f.; nervous
elements in, 91, 95 f . ; layers in its cortex,
95 f. ; fibres of, 97 f . ; nervous paths in,
127 f., 269 f.; functions of, 150 f., 156
f., 239 f.; development of, 204 f.; local-
ization in, 239 f., 250 f., 255 f., 269 f.;
significance of, 249 f . ; effects of injury
to, 258 f., 269 f.
Charcot, scheme of decussation, 290
690
INDEX.
Charcot and Pitres, on localization of
cerebral function, 383
Chaussier, on growth of foetus, 566
Chemistry, of nervous system, 21 f., 217
f . ; of cells and fibres, 28 ; of physio-
logical function, 28 £, 111 1, 222; of
vision, 184 f.
Chodin, measuring power of the eye, 451
Cholesterin, 23 f.
Choroid, the, 171 f.
Clarke, columns of, 70
Cochlea, the, 191
Color, stimulus of, 328 f., 338 f.; saturated,
328 ; tones of, 329 ; brightness of, 330,
376 ; shades of, 331 f . ; complementary,
333 f ., 343 ; dependence of, on time,
334 f.; and place of the retina, 335,
388 ; blindness to, 335 f . ; contrast of,
337, 460 ; Young-Helmholtz theory of,
338 f . ; symbolism of, 342 f . ; sensitive-
ness to, 375 f.
Consciousness, the circuit of, 494 f.;
physical basis of, 544 f . ; possibility of
a prenatal, 565 f. ; psycho-physical ex-
planations of, 596 ; phenomena of, 597
f.; unity of, 607 f., 631 f.
Cornea, structure of, 171, 173, 175 f.;
index of refraction of, 176 ; function
of, 176 f.
Corona Radiata, 91
Corpus albicans, 83, 87
Corpus callosum, 82, 85 ; function of,
98
Corpus dentatum, of the medulla, 78 ; of
the cerebellum, 79
Corpus geniculatum, 87, 89
Corpus quadrigeminum, position of, 87-
structure of, 90 f . ; functions of, 156 f . ;
development of, 208 f.
Corpus striatum, 86 ; nuclei of, 86 f . ;
paths in, 129; functions of, '58f., 160
f.; development of, 208 f.
Corpus subthalamicon, 89
Cortex of Cerebrum, structure of, 95 f .
Crura Cerebri, 83, 87; crusta and teg-
mentum of, 87 f.; fibres in, 87 f.; func-
tions of, 156
Crusta, see Crura Cerebri
Crystalline Lens, the structure of, 173
Deitebs, processes of, 43, 70; conical
hair-cells of, 195, 197
Dietze, on the circuit of consciousness,
4941
Dobrowolsky, on measurement of color-
sensations, 375 f .
Donders, on localization of depth, 465;
time of mental processes, 468 f ., 479 f.
Dove, the experiment of, 442
Drbal, on nature of feeling, 503 ; kinds
of feeling, 505.
Du Bois-Reymond, discoveries of, 104,
112, 115, 117 ; theory of nervous ac-
tion, 227 f .
Dura Mater, structure of, 61 f . ; processes
of, 63.
Eak, 185 f . ; the external, 185 ; the middle,
186 f . ; bones of, 187 f . ; tympanum of,
188 ; vibrations in, 188 ; the internal,
189 f . ; vestibule of, 189; canals of,
189 f. ; cochlea of, 191 ; nerve of, 191 f. ;
terminal apparatus of, 192 f., 324;
problem of, 195; development of , 211 f.;
sensitiveness of, 317, 319
Ecker, view of cerebral cortex, 263 ;
charts of, 276 f .
Eckhard, law of central mechanisms, 161
Electricity, " current of rest " in nerves,
104, 106 f., 117, 227 f. ; as stimulus of
nerves. 111, 112, 114 f., 228 f. ; "nega-
tive variation " in nerves, 118, 227 f.
Electrotonus, Pfliiger's law of, 113, 115 f.;
theory of, 233 f., 336 f.
Embryo, knowledge of, 198 f., 212 f. ; of
the fowl, 199 f. ; development of , 200 f.,
2041, 212 1, 618
Encephalon, see Brain
End-organs of Motion, place in nervous
system, 60, 164 ; structure of, 197
End-organs of Sense, place in nervous
system, 60, 164 ; significance of, 1631;
end-organs of smell, 164 f. ; of taste,
166 f. ; of touch, 168 1 ; of sight,
171 f. ; of hearing, 185 f.
Engelmann, on continuity of axis-cylin-
ders, 40 f .
Estel, on reaction-time, 490
Eustachian Tube, 186 1, 189
Exner, on speed of reflex action, 135 ;
regio olfactoria, 165 ; nature of nerve-
commotion, 234 f. ; general function of
the brain, 340 ; cerebral physiology,
254, 367 ; views of, on localization, 267,
279 f ., 384 1, 389 f. ; methods of, 276 £ ;
on aphasia, 294; reaction-time, 4701,
480, 496 f . ; attention. 538
Eye, structure of, 171 1; tunics of, 171 f. ;
INDEX.
691
refracting media of, 173 f., 175 f. ; ap-
pendages of, 173 £, 177 ; muscles of,
174 f., 428 f. ; problem of, 174 f. ; ad-
justment of, 177 f., 433 ; pigments of,
184; development of, 210 f.; motion of,
428 f., 439 f. ; meridians of, 431 f. ;
torsions of, 432 f. ; innervation of,
439 f . ; stereoscopy of, 440 f.
Fasciculus Gracilis, 68, 73
Fechner, conception of psycho-physics,
12 ; on measurement of sensation, 361 f.,
369 f. ; lavi^ of, 365 f., 374 f., 594
Feeling, mixture of, in local signs, 398 f , ;
of innervation or effort, 415f. ,5'73 f. ;
of " double contact," 417 f. ; nature of,
499 f., 504 ; classes of, 505 f. ; intensity
of, 508 f . ; tone of, 509 f . ; physical ap-
paratus of, 510 f . ; common, 512; of
sensation, 514 f. ; the emotions, 516 f.,
519 f.; sthenic and asthenic, 518 f. ; the
higher aesthetic and intellectual, 520 f.,
523
Ferrier, on corpora quadrigemina, 157 ;
and striate bodies, 159 ; experiments of,
254, 264; centres of, 268 f., 285 f., 291 ;
on feeling of effort, 524
Fick, on muscle-contractions, 119 ; mi-
nute color-sensations, 334 f.; curve of
intensity, 475
Filum terminale, 64
Fissures, of Sylvius, 92, 94, 210, 267 f.; of
Kolando, 92, 94, 267
Flechsig, on tracts in spinal cord, 71 f.
Flourens, on respiratory centre, 147 f . ; op-
tic lobes, 156 ; localization of cerebral
functions, 253
Foramen magnum, 64
Formatio reticularis, in the medulla, 77
f . ; in the tegmentum, 88
Foster, on the respiratory centre, 148
Fovea centralis, 183
Franck and Pitres, on stimulation of
brain, 257
Friedrich, on reaction-time, 483 f.
Fritsch, expeiiments of, 253 f., 264
Frohlich, classification of sensations of
smell, 310
Funke, on Weber's "sensation-circles,"
407
Gall, on cerebellum, 156 ; phrenological
theory of, 252
Gamgee, on chemistry of brain, 35 f .
Ganglia, the "basal," 88 f.
Ganglion-cell, see nerve-cells
George, theory of temperament, 575 f.
Gerlach, on intimate structure of the
cord, 70 ; and cerebral cortex, 96
Gliky, on nerve-tracts, 261
Goldscheider, on " pressure spots," 346
f., 369, 410; temperature-spots, 348 f.,
370, 413
Goll, column of (see fasciculus gracilis)
Goltz, experiments of, on spinal cord, 140;
on optic lobes, 157 ; view of localiza-
tion, 264 £, 273 f.; experiments of,
297 f.
Griitzner, on nature of nerve-commotion,
225 f.
Gyri (or convolutions) of the cerebrum,
84, 92, 93 f.; development of, 210
Hall, G. Sta?«ley, on perception of mo-
tion, 411 f., 416 ; studies of rhythm,
490
Hamilton, on the circuit of consciousness,
494 ; tone of feeling, 509
Hearing, end-organ of, 185 f.; sensations
of, 195, 315 f.; perceptions of, 403 f.
Helmholtz, on speed of nervous processes,
120 f.; index of refraction of cornea,
176; accommodation of eye, 177 f.,
433 ; size of blind-spot, 183 f . ; analysis
of sound, 196; nature of noises, 316;
consonances of tone, 323 f.; theory of
color-sensations, 338 f . ; and of percep-
tion, 389 f. , 452 ; on Listing's law, 431 ;
movements of the head, 454 ; localiza-
tion of depth, 465
Hensen, on function of labyrinth, 194 f.,
196; nature of noises, 316
Hering, theory of color-sensations, 340 f. ;
of tem'perature-sensations, 350 f.; in-
nervation of the eye, 439 f., 451, 525;
movements of the head, 454
Hermann, on electrical phenomena, in
nerves, 118 f., 120; theory of nervous
action, 226 f.
Herschel, on brightness of stars, 373 f.
Herzen, on sensations of temperature,
352 f.
Hill, A., view of " basal ganglia," 89
Hirsch, on reaction-time, 470
Hitzig, experiments of, 253 f., 264; on
localization of cerebral function, 253 f.,
267 ; centres of, 367 f .
692
INDEX.
Horopter, calculation of, 437
Horwicz, theory of feeling
Inhibition, nature of, 51, 144; from
brain on cord, 143 f.
Iris, the, 172
Island of Reil, 93 ; layers in, 97 ; function
of, 295 f .
James, Professor, theory of the emo-
tions, 519 f.; on the feeling of effort,
524 f.
Jastrow, on comparative judgments of eye
and hand, 466 ; studies of rhythm, 490
Kant, on sthenic and asthenic feeling,
518 f.
Keppler, on measurement of taste, 377
Klug, on localization by temperature, 414
KoUiker, on end-organs of touch, 170
KoUert, on reaction-time, 489 f .
Kraepelin, on measurement of visual sen-
sations, 375
Krause, end-bulbs of, 169 f.; on index of
refraction, 176
Kuhne, on chemistry of retina, 28, 184 f . ;
function of nerve-fibres, 54 ; structure
of end-plates, 197
Kunkel, on inertia of the retina, 474
Kussmaul, on aphasia, 393
Lamanskt, on measurement of color-
sensations, 375
Lecithin, 36 f .
Le Conte, on Listing's law, 431, 439;
torsions of the eye, 431 ; nature of the
horopter, 437 f. ; theory of double
images, 443
Listing, the law of, 430 f., 439
Lobes, of the cerebrum, 92 f.
Local Signs, theory of, 387 f., 396 f., 398
f., 409
Lob, on visual areas, 388 f.
Lohmeyer, on cases of aphasia, 296
Lombard, on temperature of brain, 242
Longet, on columns of the cord, 125 f. ;
localization of cerebral function, 253 f.
Lotze, theory of local signs, 387, 396 f.,
451 ; on distinctions by the skin, 409 ;
perception of magnitude by the eye,
451 ; errors of sense, 455 ; theory of
feeling, 499 f., 510; image of memory,
547 f.; differences of the sexes, 573;
kinds of temperament, 577 f.
Luchsinger, on reflexes of the cord, 138,
141
Luciani, on localization of cerebral func-
tion, 369 f., 385, 288, 301
Luys, on basal ganglia, 129 ; attention
and will, 544 ; memory, 553.
Mach, on fusion of nervous shocks, 473
Magendie, discovery of, 123 f.
Materialism, views of, 607 f .
Matteucci, on electrotonus, 338
Mechanism, nervous system as, 4 f., 19f.,
198, 314 f.; the nerve as, 104; develop-
ment of, 198 ; theory of the nervous,
214 f., 223 f., 226 f.
Medulla Oblongata, structure of, 74 f.;
tracts of white matter in, 76 f. ; gray
matter in, 77 f.; nuclei of, 78; reflex-
motor functions of, 146 f. ; as auto-
matic, 147 f.; centres of, 147 f., 150;
vaso-motor function of, 148
Meissner, calculation of the horopter,
437 f.
Membranes, of the brain, 63 f.; the bas-
ilar, of Reissner, 191 ; Kolliker, 194
Memory, reproduction of images of, 491
f., 54t) f. ; physiological study of, 535 f.;
physical basis of, 545 f., 550 f. ; as re-
tentive, 548 f.; the organic, 550 f.; as
reproductive, 553 f . ; psychological nat-
ure of, 554 f .
Merkel, on reaction-time, 483 f., 486,
495 f .
Mesencephalon, development of, 307 f .
Meynert, description of brain, 73, 98 f.,
246; on layers of cerebral cortex, 95;
relation of brain to intelligence, 348 ;
nerve-tracts in cerebrum, 283
Mind, subject of phenomena, 3 f., 585 f.,
596 f . ; relation to nervous mechanism,
235 f., 560 f., 579 f.; and to the brain,
247 f., 588 f., 593 f., 605 f., 633 f.; syn-
thetic act of, in perception, 388 f., 416
f., 463 f., 467, 594 f.; faculties of, 5S7
f., 600 f.; physical explanations of, 593
f., 603 f., 635 f.; as a unit-being, 596 f.,
668 f., 683 f.; phenomena of, 597 f.; as
a real being, 606 f., 611, 633 f., 656,
668 f.; development of, 614 f., 633 i;
seat of, 634 f . ; physical organs of, 640
f.; as a cause, 648 f. ; spirituality of,
681 f.
Moldenhauer, on reaction-time of tast^
479
INDEX'.
693
Moos, on duration of the image of mem-
ory, 549
Motions, the Bodily, classes of, 526 f.; the
impulsive, 5'37 ; the voluntary, 527 f.,
530 ; the expressive, 531
Mtiller, G. E., on measurement of sensa-
tions, 368
Muller, J., on brain as measure of intelli-
gence, 248
Munk, experiments of, 370 f.; on localiza-
tion of cerebral function, 272 ; motor
areas of, 272 f. ; visual areas of, 286 f.;
auditory area of, 291
Nahlowsky, on nature of feeling, 503 ;
kinds of feeling, 505 f.
Nerve-ceUs, chemistry of, 28 ; elements of
nervous system, 30 f. ; kinds of, 31 f. ;
intimate structure of, 42 f . ; shapes of,
44 f. ; processes of, 44, 70 ; size of, 45 ;
as a typical element, 45 f . ; number of,
46; functions of, 49 f., 134, 234 f.; of
the embryo, 300 f., 213
Nerve-commotion, causes of, 48 ; condi-
tions of, 106 f., 132; phenomena of,
111 f., 230; nature of, 116 f., 122,
222; laws of, 118 f., 122, 230; speed of ,
130 f., 123 f. ; paths of, 123 f., 127 f.,
261, 283 ; summation of, 223 f., 233 f. ;
facilitation of, 224 £
Nerve-fibres, chemistry of, 28 ; ele-
ments of nervous system, 30 f. ; kinds
of, 34 f . ; size of, 34, 41 f. ; structure of
the medullated, 35 f. ; fibrillated axis-
cylinder of, 38 £. ; origin of, 45 f. ;
number of, 46 ; in the cord, 68 f., 123 f.,
134 ; of the embryo, 212
Nerve-muscle machine, 104 f. ; behavior
under electricity, 111 f . ; as a mechan-
ism, 215 f.
Nerves, structure of, 33 f . ; general func-
tion of, 47 f., 54, 59 f., 106 f. ; excita-
bility of, 47, 106 f., 353 f.; conductivity
of, 47, 60, 102-122, 118 1, 120; kinds
of, 51 f., 60, 353 f.; aflferent, 52 f., 120 ;
efferent, 53 f., 120; the cranial, 100 f.;
the encephalic, 100 f. ; exhaustion of,
108 f.; mechanical properties of, 109;
thermic influences upon, 110 f.; chemi-
cal influences on. 111 ; processes in,
117 f.; specific energy of, 300 f., 307 f,,
353 f.
Nervous Matter, kinds of, 23 f . ; specific
gravity of, 23 f.
Nervous System, a mechanism, 4 f. , 19£,
198 f., 314 f., 233 f . , 236 i ; general func-
tion of, 181, .57, 2191; elements ol 31
1,301, 2161; chemistry of, 211,3171;
cells and fibres in, 30 f . ; structure of,
56-101 ; plan of, 57 1, 219 1 ; sets of
organs in, 59 1; the sympathetic, 60 f.;
the cerebro-spinal, 60 f . ; development
of the, 198 1; inertia of, 473 f.
Neuclein, 24 f .
Neuroglia, nature of, 31 f.
Neurokeratin, 24
Nothnagel, on striate bodies, 159 ; fine-
ness of temperature-sense, 369 f .
Nuclei of nerve-cells, 43 ; of the medulla,
78 ; of the corpus striatum, 86, 88, 90,
159 ; of the tegmentum (red nucleus),
88, 89
Nystagmus, 153 1
Olives, the, 75, 78 ; functions of, 150
Optic Thalami, position of, 86 f . ; struct-
ure of, 89 1; connections of, 90, 1271;
cells and fibres of, 90 ; paths in, 129 ;
functions of, 158 f. ; development of,
2081
Organ of Corti, 193 1
Organs, kinds in nervous system, 59 f. ;
the central, 60, 73 f. ; functions of,
130 f ., 224 f .
Ott, on centre of temperature, 161
Pacini, corpuscles of, 169
Paneth, on excitation of cerebral cortex,
2691
Papillse, circumvallatae, 166 f. ; fungi-
formes, 166 f .
Peduncles, of the cerebellum, 79 ; of the
cerebrum, 82, 87 1 , 97 1
Perception, nature of, 383 f., 4621, 467,
538 1; nativistic and empiristic the-
ories of, 389 1; by smell, 403 1; taste,
403; hearing, 403 f.; touch, 405 1; of
motion, 411 1, 453 1; by temperature,
413 1; of sight, 421 1, 440 1, 448 1;
of depth, 441 1, 459, 464; of spatial
relations, 448 1, 464 1; development
of, 462 1 ; physical basis of, 538 f .
Pfluger, table from, 113; law of, 113 1,
115 ; on reflexes of the cord, 137 f.
Physiological Psychology, definition of,
1 1, 4 1; combines two sciences, 6 1;
divisions of, 8 1; method of, 9 1, 12,
532 ; claims of, 13 ; successes of, 304 f .,
694
INDEX.
532 f., 592 f. ; theory of perception of,
382 f.; limits of, 532 f.
Physiology, relation to psychology, 1 f.;
of nerves in general, 103 f.
Pia Mater, structure of, 64
Pons Varolii, 74 ; structure of, 81 f.
Presentations of Sense, elements of, 304
f., 383 f., 468 f.; process of construc-
tion of, 382 f., 387 f., 416 f., 448 f.;
space-form belonging to, 385 f . , 391 f . ,
448 f; synthesis of, 386 f., 416 f., 467;
analysis of, 388 f., 595 ; nativistic the-
ory of, 389 f. ; empiristic theory of, 389
f.; stages of, 400 1; by smell, 402 f.;
taste, 403 ; hearing, 403 f . ; by touch,
405 f.; by sight, 421 f., 433 f., 443 f.;
time-relations of, 468 f.; assumptions
entering into, 594
Pressure, sensations of, 345 f., 367 f.;
spots of, 346
Preyer, on sensitiveness to pitch, 319 f.;
fusion of nervous shocks, 472; sensa-
tions of new-born child, 569
Protagon, 25 f.
Psychology, conception of, 2 f.; method
of, 9 f., 587 f., 605 f. ; classifications of,
5871, 605 f.
Psychometry, method of, 469 f.; elements
of time in, 470 f . ; results of, 497
Psycho-physics, Fechner's conception of,
12, 380 f.; method of, 359, 361 f.. 365
f.; the laws of, 359 f.; 365 f.; 379 1;
of sensations of touch, 367 f . ; • of sound,
370 ; of light, 373 f.; of smell and taste,
376 f.
Purkinje, cells of, 80
Pyramidal tract, 71 f., 77, 97
QuETELET, proportions of human body,
566 f., 574
Ranvier, nodes of, 36 f., 40 f. ; on struct-
ure of ganglion-cell, 43
Reaction -time, nature of, 475 f.; influ-
ences upon, 476 f., 495 f. ; methods of
determining, 479 f.; complex processes
of, 491
Reflex action, 50 1, 130 f.; kinds of, 131 ;
in spinal cord, 131 1, 136 f.; conditions
of, 134 f., 1361; speed of, 135 f.; in the
brain, 143 f., 224 f.
Regio olfactoria, 164 f., 308 f.
Reissner, membrane of, 191
ilemak, fibres of, 34, 41
Retina, the, 172 f.; problem solved by
174 f., 178 f., 183 f.; layers of, 179 f.,
183 f.; nervous elements of, 180 f. , 32ti
f. ; rods and cones in, 181 f., 327 ; own
light of, 326 ; relation of, to sight, 335,
423 f.; field of, 423 f.; identical and
corresponding points of, 434 f .
Ribot, on physiological study of con-
cepts, 532 ; and of memory, 552 f .
Ritter, on sensations of smell, 309
Rolando, funiculus of, 77 ; tubercle of,
77 ; fissure of, 92, 267, 282
Romieu, on stimulus of smell, 311
Rosenthal, on speed of reflex action, 135
f.; electrical taste, 313
SCHAFHADTL, on limits of sound, 372 f.
SchifF, on posterior columns of cord, 125
f. ; on excitability of cord, 141 f. ; on
cerebellum, 153, 155 f.; temperature of
brain, 242 ; localization of cerebral
function, 273 f., 283 f.
Schultze, Hans, on structure of axis-
cylinder, 39 f.
Schultze, Max, on varieties of nerve-
fibres, 34 f.; and structure of nerve-
ceU, 42 f.; on olfactory cells, 164 f.;
auditory cells, 192
Schwann, sheath of, 36 ; substance of, 36
Sclerotic, the, 171
Seguin, on cases of aphasia, 295
Semicircular canals, the, 189 f.
Sensations, end-organs of, 164 f.; analysis
of auditory, 195, 324 ; quality of, 303 f.,
325 f.; simple, 305 f. ; conditions of,
307 f.; of smell. 308 f., 376 f.; of taste,
311 f., 376 f.; of sound, 315 f., 370 f.; of
sight, 325 £, 373 f.; theory of the vis-
ual, 338 f . ; of temperature, 344, 369 f. ;
of pressure, 314, 345 f., 367 f.; the mus-
cular, 344 f . ; quantity of, 356 f . ; meas-
urement of, 359 f., 364 f., 369 f.; least
observable difference in, 361 f., 364 f.;
range of, 362 f . ; spatial series of, 386 f .,
393 f.; localization of, 387 f., 405 f.
Senses, organs of the, 164 f.; classifica-
tion of the, 303 f . ; the geometrical, 386
f. ; errors of the, 455 f .
Setschenow, on inhibitory centres, 144.
Sight, end-organs of, 171 f., 174 f., 338 f.
photo-chemistry of, 178 f., 184 f., 326
sensations of, 335 f.; stimulus of, 325 f.
after-images of, 336 f . ; elements m per-
ception of, 420 f., 447 f.; motion of eye
INDEX.
695
in, 428, 431 f . ; single and double images
in, 434 f . , 438 f . ; stereoscopic and per-
spective, 440 f. ; secondary helps of, 443
f., 455 t
Smell, organs of, 164 f . , 308 f . ; nerve of,
165,310; stimulus of, 165 f., 308 f.,
310 ; sensations of, 308 f . ; kinds of,
310 ; measurement of, 378 f . ; percep-
tions of, 403 f .
Soul, see Mind
Sound, analysis of, 195 f., 324; sensa-
tions of, 315 f., 370 f.; kinds of, 316;
nature of the musical, 316 f . ; limits of,
317, 371 f; "entotic,"403f.; direction
of, 404
Spinal cord, membranes of, 61 f . ; struct-
ure of, 64 f ., 143, 207 ; fissures of, 64 f.;
columns of, 66, 67, 135 f.; commissures
of, 66 ; horns of, 67 ; white substance
of, 68; nerve-fibres in, 68 f., 133 f.;
gray substance of, 69 f . ; nervous tracts
in, 71 f., 133 f.; as mechanism, 73, 123,
133 f., 144; nerves from, 100 f. ; nervous
processes in, 122, 134 f.; roots of, 123 f.,
207; as a central organ, 133 f., 138 f. ;
automatism, 138 f. ; "centres" of, 140
f. ; excitability as a whole, 141 f.; '' £es-
thesodic" and " kinesodic," 142; in-
fluence of brain on, 143 £ ; develop-
ment of, 207
Stimulus, kinds of, 48; heat as, 110 f.;
electricity as, 111 f., 312 f. ; of smell,
165 f., 308 £, 376 f.; of taste, 311 f.,
376 f.; of hearing, 315, 370 f.; of sight,
335 f . , 338 £ , 373 f . ; measurement of,
359 £, 367 £; limits of, 363 £, 367 £
Strabismus, 153 f .
Strieker, on common feeling, 513
Stumpf, on judgment of tone, 330
Substantia gelatinosa, 69
Substantia nigra, 87
Sulci, of the cerebrum, 84, 91, 93 £; de-
velopment of, 210
Sully, on tone of feeling, 511
Suspensory ligament, 173; function of,
177 £
Sympathetic System, structure of, 60 f.
Talbot, the principle of, 473
Taste, end- organs of, 166 f., 313; nerve
of, 168, 314; sensations of, 311 f.,
376 f. ; stimulus of, 313 f. ; kinds of,
314; measurement of, 376 £ ; percep-
tions of, 403 £
Tegmentum, see Crura Cerebri
Temperament, theory of, 575 £, 579;
kinds of, 575 £ ; physical basis of,
579
Temperature, sensations of, 344, 348 £ ,
369 £ ; after-images of, 351 £ ; measure-
ment of, 369 £ ; sense of locality by,
413 £
Thalamen-cephalon, 208
Things, distinguished from sensations,
359 f . , 382, 594 ; results of mental syn-
thesis, 594 f., 609 ; unity of, 609 £
Thudichum, on chemistry of brain, 27
Tischer, on Weber's law, 373
Tones, the musical, 316; pitch of, 317 f.;
table of, 318 ; sensitiveness to, 319,
370 £; purity of, 319 £ ; judgments of,
320 ; relations of, 322 f .
Touch, kinds of, 168, 345 £ ; end-organs
of, 168 f. ; sensations of, 345 £, 367 £;
perceptions of, 405 £ ; the field of, 406
£, 416 £
Trautscholdt, reaction-time of complex
processes, 491 f.; on effect of practice,
496
Turck, method of, 71 ; on columns of
cord, 126
Tympanum, the, 186 f. ; membranes of,
186, 188 f . ; windows of, 186 ; muscles
o£ 187 ; office o£ 187 £
Tyndall, on stimulus of smell, 311 f.
Valentin, on nervous excitation, 233 £ ;
sensations of smell, 308 f. ; of taste,
314, 377 £ , 403 ; on sense of locality,
406 £ ; fusion of nervous shocks, 473
Valli, principle of, 107
Vestibule, of the ear, 189
Vierordt, on measurement of sensation,
371 f . ; localization by touch, 409 f. ;
subjective estimate of time, 488 £
Vitreous Humor, the, 173
Volkmann, A. W., on measurement of
sound, 371 ; of light, 374 ; of length of
lines, 376; on sense of locality, 407
Volkmann von Volkmar, on motifs of
monocular vision, 430; nature of feel-
ing, 503
Volta, on electrical taste, 313 £
Von Gudden, on optic chiasm, 390
Von Kries, on the number of colors, 333 ;
on theories of color-sensations, 341 £;
sense of locality, 397
Von Kries and Auerbach, on sense of
696
INDEX.
locality, 397; reaction- time, 476, 481 f.,
487, 496
Von Vintschgau, on conduction in nerves,
121 ; reaction-time for multiplying, 493
Von Wittich, on fusion of nervous shocks,
472 ; reaction-time of taste, 478
Vulpian, on nervous function, 54 ; on ex-
citability of cord, 142 ; centres of the
medulla, 149 ; and cerebellum, 154 f.
Wagner (H. and R.), corpuscles of, 170;
on measurement of brain-mass, 247 ;
effect of fear, 518
Waller, method of, 107 f.
Weber, E. H., on temperature-sensations,
110, 347, 351 ; smell, 308 ; law of, 365
f., 368 f., 374 f., 378 f.; on direction of
sound, 404 ; perceptions of touch, 405
f.; "sensation-circles" of, 406 f.;
measuring power of the eye, 452
Wertheim, on ductility of nerves, 109
Will, effect of, on bodily motions, 528 f.;
physiological study of, 535 f . ; physical
basis of, 536 f . ; in attention, 539 f .
Wundt, on columns of the cord, 126 ; on
cerebellum, 152 ; optic thalami, 158 f . ;
and striate bodies, 160 ; mechanical
theory of, 231 f.; kinds of taste, 314;
theory of color-sensations, 341 ; on com-
plementary colors, 343 ; theory of apper-
ception, 380, 539 f.; on Weber's law,
381 ; on theories of perception, 389 f.;
''sensation-circles," 408 ; visual percep-
tion, 422, 425 f., 451 ; judgment of
distance, 433 ; feelings of innervation,
439, 451, 524 ; psycho-physical time,
471, 477, 483 f., 488, 496 ; curve of feel,
ing, 514 ; theory of temperament, 576 f,
Zonule of Zinn, 173
THE
Philosophical Works
OF
GEORGE TRUMBULL LADD
Professor of Philosophy in Yale University
GENERAL
DESCRIPTIVE
PSYCHOLOGY
Psychology : Descriptive and Explanatory
8vo. $4.50
Primer of Psychology
i2mo. $1.00 nei
PHYSIOLOGICAL
PSYCHOLOGY
Elements of Physiological Psychology
With Numerous Illustrations. 8vo. $4.50
Outlines of Physiological Psychology
Illustrated. 8vo. $2.00
METAPHYSICAL
PSYCHOLOGY
Philosophy of Mind
5VO. $3.00
Philosophy of Knowledge
8vo. $4.00
NOTE.— The philosophic writings of Dr. Ladd have now become so numerous and
are so widely known in a general way, that the publishers take pleasure in giving them
some special notice, with the object that the adaptation and purpose of each volume may
be better understood. It is believed that this author's "Primer of Psychology,"
" Psychology : Descriptive and Explanatory," " Elements of Physiological Psychology,"
and " Philosophy of Mind " form a continuous course in the subject which surpasses any
similar course that has appeared. Naturally, where several books by one author treat of
the same subject, some confusion in ordering results, and it is to prevent this, as well as
in the hope of leading to a wider interest in the books, that the following description has
been prepared.
J GENERAL DESCRIPTIVE PSYCHOLOGY
PSYCHOLOGY: DESCRIPTIVE AND EXPLANATORY
A Treatise of the Phenomena, Laws and Development of Human Mental Life
8vo. 676 pages. $4.50
As indicated in the sub-title, this work has for its object the study of
human mental life, and is perhaps better defined by the term introspective
psychology than by any other in common use. It is a general treatise
for those who wish to gain a thorough knowledge of the subject, not de-
signed merely for use as a text-book, while at the same time the product
of one who has taught a large number of pupils, and embodying much
experience gained through the work of the class-room. The size and
scope, the amount and kind of material, and the style of its presentation
unite in making it a suitable book for mature students, as those usually
are who begin the subject in colleges. It is therefore a college text-book,
and is recommended without qualification for such use.
" Professor Ladd has presented in this work a great body of facts on all the important
points in psychology, and has subjected them to a keen and illuminating criticism. I know
of no other work that gives so good a critical survey of the whole field as this."
— Prof. B. P. BowNE, Boston University.
" It is rich in material, admirably clear and well arranged, and a thoroughly satisfac-
tory introductory book for the student in this rapidly developing field of study. I shall
at once recommend its use by my classes."
— Prof. J. W. Stearns, University of Wisconsin.
" My impression of it is that it is Professor Ladd's best work, that it contains the
maturest and most independent expression of his views on all the principal topics in
psychology. It is a distinct honor to American scholarship to have produced it."
—Prof. H. N. Gardner, Smith College.
PRIMER OF PSYCHOLOGY
i2mo. 226 pages. $1.00 net
As its title indicates, this is a text-book for elementary students, and
was written by this eminent author because no book in America had been
found satisfactory for academies and high schools, and for a large class
of general readers who might find some pleasure and perhaps more
profit in reading a very brief and very simple treatise on psychology.
The author's success in his undertaking may be measured by the fact
that within eighteen months of its publication six editions were ex-
hausted. The book will be used the coming year in more than sixty
high schools and academies, as well as in many colleges and normal
schools,
CONTENTS:
I. The Mind and Its Activities. VII. Hearing and Sight.
II. Consciousness and Attention. VIII. Memory and Imagination.
III. Sensations. IX. Thought and Language.
IV. Feeling. X. Reasoning and Knowledge.
V. Mental Images AnD Ideas. XI. Emotions, Sentiments and Desires.
VI. Smell, Taste and Touch. XII. Will and Character.
XIII. Temperament and Development.
'PHYSIOLOGICAL PSYCHOLOGY
ELEriENTS OF PHYSIOLOGICAL PSYCHOLOGY
A Treatise of the Activities and Nature of Mind from the Physical and Experimental
Point of View. With numerous illustrations. 8vo, $4.50
In distinction from the introspective psychology and as a companion
to it this book is devoted to physiological and experimental psychology.
By its proportions and subject matter it is adapted, like the other book,
to mature students, and is of equal interest to general readers as well as
to specialists in this field. It was the first book in English to discuss the
whole subject, and is the only one which may be regarded as an adequate
treatise. It includes the latest discoveries, and by numerous excellent
illustrations and tables, and by gathering material from an immense
number of sources inaccessible to most persons, it brings before the stu-
dent in the most lucid form the entire subject. The most competent
critics pronounce it a credit to America's scholarship and an unrivalled
authority. Without reserve it is recommended as a text-book for
advanced study.
" His erudition and his broad-mindedness are on a par with each other ; and his vol-
ume will probably, for many years to come, be the standard work of reference on the
subject."— Prof. William James in The Nation.
" He writes at once as a scientist bent on gaining the fullest and clearest insight into
the phenomena of mind, and as a metaphysician deeply concerned with the sublime
question of the nature of the spiritual substance." — James Sully in The Academy.
" Professor Ladd's noble book is in the interest of true science, of sound theology, of
real religion. We commend it in the highest terms, both to physiologists and to psychol-
ogists ; to the former for its fresh studies in their own field, and to the latter for its fresh
proof that they have still a field to cultivate. The book, so far as we know, is the most
elaborate and comprehensive attempt yet made in the English language to give all the
data which are claimed to connect the nervous system with the phenomena of conscious-
ness, in a way to lay the foundation for an explanation of mind in terms of matter. The
book is fully illustrated, and well indexed."— W. K Evangelist.
OUTLINES OF PHYSIOLOGICAL PSYCHOLOGY
A Text-book of Mental Science for Academies and Colleges
Crown 8vo. 505 pages. $2.00
The volume is not an abridgment or revision of the larger book,
Elements of Physiological Psychology, which is still to be preferred for
mature students, but, like it, surveys the entire field, though with less de-
tails and references that might embarrass beginners. Briefer discussions
of the nervous mechanism, and of the nature of the mind as related to
the body, will be found in the " Outlines " ; while the treatment of rela-
tions existing between excited organs and mental phenomena offers much
new material, especially on "Consciousness," "Memory," and " Will."
The author aims to furnish a complete yet correct text-book for the brief
study of mental phenomena, from the experimental and physiological
point of view. Both pupil and teacher have been considered, that the
book may be readily learned and successfully taught.
" We regard it as even better than the larger work, as it is more judicious and mature,
having the advantages of longer reflection upon the subject and larger experience in teach-
ing it. For its purpose there is not a better text-book in the language." — The Nation.
"He has discharged his task with great thoroughness, with a lightness of touch, and a
clearness and precision of style that come only from perfect mastery of the matter in hand.
The book fills, and fills solidly, a great gap in our psychological literature. "—J. G.
ScHURMAN, Cornell University.
METAPHYSICAL PSYCHOLOGY
PHILOSOPHY OF MIND
Aa Essay In the Metaphysics of Psychology. 8vo. 412 pagac. %i.*»
This is a speculative treatment of certain problems suggested, but
not discussed, in the study of psychology, and therefore appropriately '
follows the author's earlier works on that subject. The subjects treated
are : Psychology and the Philosophy of Mind, The Concept of Mind,
The Reality of Mind, The Consciousness of Identity and the so-called
Double Consciousness, The Unity of Mind, Mind and Body, Materialism
and Spiritualism, Monism and Dualism, Origin and Permanence of Mind,
Place of Man's Mind in Nature.
JOURNAL OF MENTAL SCIENCE, London.— "We may say of this book that it
is written in the author's best style. The destructive criticism is in places markedly
effective, and the book ought to be widely read as one of the most able and suggestive
contributions of recent years to the literature of the philosophy of mind."
THE DIAL.—" Its raking attack upon over-hasty monism is particularly well timed.
Although the border-land which divides Psychology from Metaphysics is partially sur-
veyed in manv philosophical and psychological works. Professor Ladd has for the first
time brought the more important questions within the limits of a single volume."
PHILOSOPHY OF KNOWLEDGE
8vo. 614 pages. $4.00
This is the first adequate discussion of the subject by any American
author, and naturally will attract special attention aside from the fact that
it is the work of Dr. Ladd, whose name is so familiar to students of
philosophy both in this country and abroad. The book appeals to the
general reader by reason of the relation this subject bears to questions
now so prominently before the philosophical and religious world, as well
as through the broad sympathy of the author with different phases of
thought. It will also find a place waiting for it as a text-book for
advanced and postgraduate students in the study of logic and the laws
of thought. Ministers, too, will get from it much material for which
they find a constant use.
THE PHILOSOPHICAL REVIEW.— "It would ill become one to take leave of a work
which must lay many under obligation without noting its broad basis in a knowledge
carefully garnered from many sources during long years, its candor, its striking variety of
content, and its suggestiveness."
Copies of these books will be supplied to teachers for examination or intro-
duction at Special Net Rates, regarding which correspondence is solicited.
CHARLES 5CRIBNER'S SONS
PUBLISHERS - - NEW YORK CITY
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