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ANIMAL MECHANISM:

A TREATISE ON

TERRESTRIAL AND AERIAL LOCOMOTION.

BY

E. J. MAREY,

PROFESSOR AT THE COLLEGE OF FRANCE, AND MEMBER OF THE
ACADEMY OF MEDICINE,

WITH ONE HUNDRED AND SEVENTEEN ILLUSTRATIONS, DRAWN AND ENGRAVED UNDER
THE DIRECTION OF THE AUTHOR,

NEW YORI :

Dowie een rON AND COMPANY,
549 AND 551 BROADWAY.

1879.

45403 Ge Coo

oat haa

wt tita, "

TABLE OF CONTENTS.

PAGE
INTRODUCTION . . ° : . : ooh is : 1

BOOK, THE. EURST:

FORCES AND ORGANS.

CHAPTER I.

OF FORCES IN THE INORGANIC KINGDOM AND AMONG
ORGANISED BEINGS.

Matter reveals itself by its properties—When matter acts, we con-
clude that forces exist — Multiplicity of the forces formerly
admitted ; tendency to their reduction to one force in the inor-
ganic kingdom—Indestructibility of force ; its transformations
—Vital forces, their multiplicity according to the ancient
physiologists—Several vital forces are reduced to physical
forees—Of laws in physics and in physiology—General theory
of physical forces. . ° ° . ° * ° . 5

CHAPTER II.
TRANSFORMATION OF PHYSICAL FORCES.

To prove the indestructibility of forces, we must know how to
measure them—Units of heat and of mechanical work—Ther-
mo-dynamics—Measure of forces in living beings—Successive
phases of the transformation of bodies ; successive development
of force under this influence—Thermo-dynamics applied to
living beings . . ° . . : : ° e a lg}

CHAPTER III.
ON ANIMAL HEAT.

Origin of animal heat—Lavoisier’s theory—The perfecting of this
theory—Estimates of the forces contained in aliment, and in
the secreted products—Difficulty of these estimates—The force

v1 CONTENTS.

PAGE
yielded by alimentary substances is transformed partly into heat
and partly into work—Seat of combustion in the organism—
Heating of the glands and muscles during their functions —Seat
of calorification—Intervention of the causes of cooling—Animal
temperature—Automatic regulator of animal temperature . ee

CHAPTER IV.
ANIMAL MOTION.

Motion is the most apparent characteristic of life; it acts on
solids, liquids, and gases—Distinction between the motions of
organic and animal life—We shall treat of animal motion only
—Structure of the muscles—Undulating appearance of the still
living fibre—Muscular wave—Shock and myography—Multi-
plicity of acts of contraction—Intensity of contraction in its
relations to the frequency of muscular shocks—Characteristies
of fibre at different points of the body =. . . ° -

CHAPTER V.
CONTRACTION AND WORK OF THE MUSCLES,
The function of the nerve—Speed of the nervous agent—Measures
of time in physiology—Tetanus and muscular contraction—
Theory of contraction— Action of the muscles . ° . ae: |

CHAPTER VI.
OF ‘ELECTRICITY IN’ ANIMALS.

Electricity is produced in almost all organised tissues—Electrie eur-
rents of the muscles and the nerves—Discharge of electric
fishes; old theories ; demonstration of the electric nature of
this phenomenon—Analogies between the discharge of electrical
apparatus and the shock of a muscle—Electric tetanus—Rapidity
of the nervous agent in the electrical nerves of the torpedo ;
duration of its discharge . : 2 ° : ° ° on, 49

CHAPTER VII.
ANIMAL MECHANISM.

Of the forms under which mechanical work presents itself—Every
machine must be constructed with a view to the kind of work
which it has to perform—Correspondence of the form of muscle
with the work which it accomplishes—Theory of Borelli—
Specific force of muscles—Of machines; they only change the

CONTENTS.

form of work, but do not increase its quality— Necessity of
alternate movements in living motive powers—Dynamical energy
of animated motors .

CHAPTER, VIII.

Vil
PAGE

59

HARMONY BETWEEN THE ORGAN AND THE FUNCTION.—

DEVELOPMENT HYPOTHESIS.

Each muscle of the body presents, in its form, a perfect harmony
with the nature of the acts which it has to perform—A similar
muscle, in different species of animals, presents differences of
form, if the function which it has to fulfil in these different
species is not the same—Variety of pectoral muscles in birds,
according to their manner of flight— Variety of muscles of the
thigh in mammals, according to their mode of locomotion—
Was this harmony pre-established ?—- Development hypothesis —
Lamarck and Darwin. : : : ° . °

CHAPTER IX.
VARIABILITY OF THE SKELETON.

Reasons which have caused the skeleton to be considered the least
variable part of the organism—Proofs of the yielding nature of
the skeleton during life, under the influence of the slightest pres-
sure, when long continued—Origin of the depressions and pro-
jections which are observed in the skeleton—Origin of the
articular surfaces—Function rules the organ—Variability of the
muscular system c - 3 : . : . 0

BOOK THE SECOND.
FUNCTIONS: TERRESTRIAL LOCOMOTION.

CHAPTER. I.
OF LOCOMOTION IN GENERAL.

Conditions common to all kinds of locomotion—Borelli’s comparison
— Hypothesis of the reaction of the ground—Classification of the
modes of locomotion, according to the nature of the point of
resistance, in terrestrial, aquatic, and aerial locomotion—Of the

69

85

vill CONTENTS.

PAGE
partition of muscular force between the point of resistance and
the mass of the body—Production of useless work when the point
of resistance is movable . ° . ° s . “ - 102

CHAPTER II.
TERRESTRIAL LOCOMOTION (BIPEDS).

Choice of certain types in order to study terrestrial locomotion—
Human locomotion—Walking—Pressure exerted on the ground,
its duration and intensity—Re-actions on the body during
walking—Graphic method of studying them—Vertical oscilla-
tions of the body—Horizontal oscillations—Attempt to repre-
sent the trajectory of the pubis—Forward translation of the
body—Inequalities of its velocity during the instants of a
pace. : : s - : . . ° ° . 7 Pa’

CHAPTER III.
THE DIFFERENT MODES OF PROGRESSION USED BY MAN.

Description of the apparatus for the purpose of studying the various
modes of progression used by man—Portable registering appara-
tus—Experimental apparatus for vertical reactions—Walking—
Running —Gallop-—Leaping on two feet and hopping on one—
Notation of these various methods—Definition of a pace in any
of these kinds of locomotion—Synthetice reproduction of the
various modes of progression. . . ° . ° ° . 124

CHAPTER IV.
QUADRUPEDAL LOCOMOTION STUDIED IN THE HORSE.

Insufficiency of the senses for the analysis of the paces of the horse

—Comparison of Duges—Rhythms of the paces studied by means

of the ear—Insufficiency of language to express these rhythms

—Musical notation— Notation of the amb/e, of the walking pace,

of the trot—Synoptical table of paces noted according to the

definition of each of them by different authors—Instruments

intended to determine by the graphic method the rhythms of the

various paces, and the re-actions which accompany them . - 138

CHAPTER V.
EXPERIMENTS ON THE PACES OF THE HORSE.

Double aim of these experiments ; determination of the movements
under the physiological point of view, and of the attitudes with

CONTENTS. 1x

PAGE ~

reference to art—Experiments on the trot—Tracings of the
pressures of the feet and of the re-actions— Notation of the trot
— Piste of the trot—Representation of the trotting horse—Ix-
periments on the walking pace—Notation of this kind of motion ;
its varieties—Piste of the walking pace—Representation of a
pacing horse. . a aes : { . . . oe dbl!

CHAPTER: VI.
EXPERIMENTS ON THE PACES OF THE HORSE.
(Continued. )

Experiments on the gallop—Notation of the gallop—Re-actions—
Bases of support—Piste of the gallop—Representation of a
galloping horse in the various times of this pace—Transition, or
passage, from one step to the other—Analysis of the paces by
means of the notation rule—Synthetic reproduction of the
different paces of the horse—Modes of walking of various
quadrupeds . . . ee ve . . Bg GA eee AMR iE

BOO THE THIRD:
AERIAL LOCOMOTION.

CHAPTER I.
OF THE FLIGHT OF INSECTS.

Frequency of the strokes of the wing of insects during flight ; acoustic
determination ; graphic determination—Influences which modify
the frequency of the movements of the wing—Synchronism of
the action of the two wings— Optical determination of the move-
ments of the wing; its trajectory ; changes in the plane of
the wing; direction of the movement of the wing . . - 180

CHAPTER II.
MECHANISM OF THE FLIGHT OF INSECTS.

Causes of the movements of the wings of insects—The muscles only
give a motion to and fro, the resistance of the air modifies the
course of the wing—Artificial representation of the movements
of the insect’s wing—Of the propulsive effect of the wings of

x CONTENTS.

PAGE
insects—Construction of an artificial insect which moves hori-
zontally—Change of plane in flight . : . . . - 196

CHAPTER III.
OF THE FLIGHT OF BIRDS.

Conformation of the bird with reference to flight—Structure of the
wing, its curves, its muscular apparatus—Muscular force of the
bird, rapidity of contraction of its muscles—Form of the bird ;
stable equilibrium, conditions favourable to change of plane—
Proportion of the surface of the wings to the weight of the body
in birds of different size . . ; - . : . - 209

CHAPTER IV.

OF THE MOVEMENTS OF THE WING OF THE BIRD
DURING FLIGHT.

_ Frequency of the movements of the wing—Relative durations of its

rise and fall—Electrical determination—Myographical determi-

nation—Trajectory of the bird’s wing during flight—Construe-

tion of the instruments which register this movement—Experi-

ment— Elliptical figure of the peers of the point of the

wing 226

CHAPTER V.

OF THE CHANGES IN THE PLANE OF THE BIRD'S WING
AT DIFFERENT POINTS IN ITS COURSE.

New determination of the trajectory of the wing—Description of
apparatus—Transmission of a movement by the traction of a
thread—Instrument and apparatus to suspend the bird —Experi-
ment on the flight of a pigeon—Analysis of the curves—
Description of the apparatus intended to give indications of the
changes in the plane of the wing during flight—Relation of
these changes of plane to the other movements of the wing . 244

CHAPTER VI.

RE-ACTIONS OF THE MOVEMENTS OF THE WING ON
THE BODY OF THE BIRD.

Re-actions of the movements of the wing—Vertical re-actions in
different species; horizontal re-actions or changes in the
rapidity of flight; simultaneous study of the two orders of
re-actions—Theory of the flight of the bird—Passive and active
parts of the wing —Reproduction of the mechanism of the flight
of the bird : 4 ‘ : : : : , ‘ . 264

FIs.

Fic.
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LIST OF ILLUSTRATIONS.

er

APPARATUS FOR EXPERIMENTING ON MOVEMENT.

PAGE
2.—Theoretical representation of myograph : 56 Gl
3.—Marey’s myograph . : . - 382
7.—Arrangement of a ee ‘araille Berea two myo-

graphical clips. . eon

19. —Experimental shoe, a eeiedl to om the pressure of the
foot on the ground, with its duration and its phases
42.—Experimental apparatus to show the pressure of the

tS

horse’s hoof on the ground : : : 4 . 148
43,—Apparatus to give the signals of the pressure and rise ai

the horse's hoof . : ° ° ° . 149
26.—Apparatus to determine the speed of polar at very

instant . : . 122
27.—Runner provided oie the apparatus intended i eee

his different paces © 26
28.—Instrument to register the sepals re- cote dine the

various paces . - . : E c oe) LOY,

44,—Figure to represent a trotting horse, eoned with
the different experimental instruments ; the horseman
carrying the register of the pace. On the withers aud

the croup are instruments to show the re-actions . 150
93.—Apparatus for the purpose of experimenting on the con-
traction of the thoracic muscles of the bird. 229
99.—Buzzard flying, with the apparatus for giving signals of
the movements of the extremity of its wing 241
103.—General arrangement of the recording instr cient a pigeon
attached to it, and conveying signals . : on ee!
104.—Suspension of the bird in the apparatus . . . 25
109.—Apparatus to examine the movements of the aie and
the changes in its plane . : ae 200
21.—Transmission of an oscillatory ane to the regis- ;
« LG

tering apparatus . ° . ° ° ° :

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LIST OF ILLUSTRATIONS.

PAGE

24.—Showing two successive positions of the arm of the instru-
ment, and the corresponding Beets ons of the ie

points of the levers . 4 120
98.—Elastic point, tracing on a piece of noked eae . 239

. 102.—Transmission of a to-and-fro movement by means of a
simple traction thread . ° . . . 245

ILLUSTRATIVE APPARATUS.

1.—Showing the transformation of the electricity of a coil
into mechanical work, heat, light, and chemical action. 10
6.—Appearance presented by the waves in a muscular fibre 36

9.—Transformation of heat into work by a strip of india-
rubber . - 5 . ° . ° ° 2 ae woo

OF THE FLIGHT OF INSECTS.

84,—Artificial representation of the movements of the insect’s
wing . ° ° . . . . . . 199
85.—Changes in the plane of the inseet’s wing ‘ : - « 200
87.—Artificial insect, to illustrate its flight 202

88.—Arrangement of the artificial insect, so as to @hiain the
hovering motion or the ascending flight 205

Or THE HoveRING OF THE B:rp.
90.— Instrument to illustrate the hovering of the bird . . 217
91.—The same, explaining the upward turn ° . . « 218
92.— » ey downward ditto = : . 219
ANATOMY.

13.—Skeleton of a flamingo (after Alph. Milue-Edwards; the

wing is very large, the sternum very short and deep,

which indicates the size and the shortness of the pectoral
muscles . . . : : ; ee heey

14.—Skeleton of a penguin sternum a, long, wing very
short . 73

15.—Skeleton of the wing and sternum of ‘he's sea sw raliow

(Hirundo marina); “showing the extreme shortness of
the sternum, and the great length of the wing. 74

89.—Different curves in the wing of the bird at various parts of
its length . . : ° ° 210
117.—Active and passive parts of the bird’ 8 wing . 276
83. —Structure of the inseet’s wing . 196

Fia.

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LIST OF ILLUSTRATIONS. Xlil

PAGE
16.—Muscles of the thigh in man : . ° ° 5 3 we
17.—Muscles of the thigh ofthe magot . ° ° ° a Wt
18.—Muscles of the thigh of the coaita . 6 c Be aS

DETERMINATIONS,
8.—Two determinations of the speed of the muscular wave . 38
10.—Determination of the speed of the nervous agent in man. 43
12.—Measure of the time which elapses between the excitation
of the electric nerve, and the discharge of the torpedo . 58
82.—Determination of the direction of the moyernents in an
insect’s wing “ ° - 195
94.—Experiment to determine by the ieee iad eee
methods at the same time, the frequency of the move-
ments of the bird’s wing, and the relative duration of
its elevation and depression. 2 . 5g wa
26.—Determination of the rapidity of walking He various
instants, by means of a chronographic tuning fork . 122
NOTATIONS.
34.—Notation of a tracing of man’s mode of walking Pewecee (80
35.—Synoptical notation of the four kinds of progression used
by man . . - : : : 5 @ IBY!
36.—Notations of the aie qoanie : . : . 134
37.—(Upper line) notation of a series of jumps on two feet.
(Lower line) notation of hops on right foot ae loo
NoTATIONS OF THE PAcES OF THE HorsE,
38.—Notation of a horse’samble . C , . - 142
39.—Notation of the horse’s walking pace . - 6 26 9 lee
51.—Notation of the walking Bach with BecoeeuuEce of the
lateral pressures . : . 160
45.—Graphic curves and notation ee the horse’ s tr ot - - 153
4¢,—Notation of a horse’s trot - E . ° ° . 144
46.—Notation of the irregular trot. - . 156

41.—Synoptical notations of the paces of the gay Become
to various writers.

No. 1. Amble, according to all writers.
No. 2 {eon amble, nein to Merche.

High steps, according to Bouley.
Ordinary step of a pacing horse, according to Magure.

No. 3. Broken amble, according to Bouley.

Traquenade, according to Lecoq.

xiv LIST OF ILLUSTRATIONS.

PAGE
No. 4. Normal walking pace, according to Lecoq.

No. 5. Normal walking pace (Bouley, Vincent and Goiffon .
Solleysel, Colin).

No. 6. Normal walking pace, according to Raabe.
No. 7. Disconnected trot (trot de coursier).

No. 8. Ordinary trot. (In the figure, it is supposed that the
animal trots without leaving the ground, which oceurs but
rarely. The notation only “takes into account the rhythm
of the impacts of the feet).

No. 9. Norman pace, from Lecoq.

No. 10. Traquenade, from Merche : S woe. ne - « 146
Fic. 56.—Gallop in three-time : : . . . . . 166
Fic, 62.—Notation of the gallopinfour-time . ode baad
Fic. 63.—Notation of full gallop ; re-actions of this pace ° rae f
Fic. 64.—Transition from the walk tothe trot . ° . o « 174
Fic. 65.—Transition from the trot to the walk : . . ~ 174
Fic. 66.—Transition from the trot to the gallop. . . Rielly!
Fic. 67.—Transition from the gallopto the trot . . ° - 174
Fic. 68.—Notation rule, to represent the different paces. - 175

Fic. 69.—Notation rule forming the representation of the gallop i in
three-time . : : Rf 5 ° . - = L7G

PISTES OR FOOT TRACES OF THE HORSE'S FEET.

Fic. 52.—Piste of the walking pace, after Vincent and Goiffon . . 162
Fic. 53.—Piste of the amble, after Vincent and Goiffon . : - 162
Fia. 47.—Piste of the trot according to Vincent and Goiffon coeelod
Fic. 57.—Piste of the short gallop in three-time. : . - 167

Fic. 58.—Piste of Eeclipse’s gallop, from Cornieu. The prints of the
hind-feet are very fur before those of the fore-feet . . 167

REPRESENTATION OF THE HORSE IN ITS VARIOUS PACES.

Fic. 54.—Representation of the horse at a walking pace. ‘ - 163
Fic. 48.—Horse trotting with a low kind of pace . ° spe LOd,
Fic. 49.—Horse at full trot. The dot placed in the notation corre-

sponds with the attitude represented . : ; . 158
Fic. 59.—Horse galloping in the first time (right foot advancing),

the left foot only on the ground, . . 2) oo
_ Fic. 60.—Horse galloping in the second time (right foot forward) . 169
lic. 61.—Horse galloping in the third time (right foot forward) . 169

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LIST OF ILLUSTRATIONS. XV
PAGE
TRACINGS.
TRACINGS OF THE MUSCLES.
4,.—Character of the shock according to the degree of fatigue
of the muscle . : . 34
’ 5.—Successive transformations of ie none ae a meee be-
coming gradually poisoned by veratrine. Underneath
and on the left of the figure are shown the first effects
of the poison . : : 35
11.—Gradual coalescence of the plas produced ee Sucre
excitations of increasing frequency . : : see) 46
Tracincs oF Human Locomotion.
20.—Tracings of the impact and the Pane of the two fect in
our ordinary wall . 114
22.—Tracings of the oscillations of the hae fee alae 5 iil?
25. itches of the impact and rise of the right fot fur Breed
by a “lever subjected at the same time to 10 vibrations
per second, 2 : 5 1
29.—Tracing produced by Follies oe : . c - 128
30.—Tracing produced by running (in man) 6 og URE
31.—Man galloping (right foot foremost). Step-curves and re-
actions. There is an encroachment of one curve over the
other, and then a suspension of the body 5 US
33.—Series of hops on the right foot. The duration of the
time of suspension remains evidently constant, even
when that of the pressure of the foot varies. . 132
32.—Leap on two feet at once . 5 : ° : ° - Isl
TRACINGS OF THE LocoMorion oF THE HORSE.
50.—Tracing and notation of the walking pace, with equal
pressures of the feet, both diagonally aud laterally . . 160
45.—Tracing and notation of the trot. . - a 153
55.—Tracing and notation of the gallop in three- fie “ 6 on Hae
TRACINGS OF THE FLIGHT OF INSECTS.
70.—Showing the frequency of the strokes of the wing of a
drone. flyandabee , 5 . 183
72.—Graphic tracing of the middle sit tion i the course ath a
bee’s wing. . - : : ; ‘ = +» 189

XV1

LIST OF ILLUSTRATIONS.

PAGE
Fic. 73.—Tracing of the middle zone of a humming-bird moth . 190
Fic. 74. —Tracing of the course of a ha wing showing the upper
part ‘of the curve. 5 - ss
Fic. 75.—Tracing of the course of a SS s wing : lower loops . 191
Fic. 77. —Tracing obtained from a bee’s wing in a plane tangential
to the cylinder - . : ° * sire te
Fic. 78 and 79.—Tracing of a wasp’s wing compared with a Wheat-
stone’s rod . : : M - 192, 193
Fic. 80.—Tracing of the wing of a humming. bind moth (lower
border) 7
Fic. 81.—Tracing of the wing of a a omining: bird moth . . 194
TRACINGS OF THE FLIGHT OF Birps.
Fic. 95.—Myographical tracing to determine the frequency of the
strokes of the wing in different species . : - . 232
Fic. 96.—Differences of frequency and of merits in the strokes
of a pigeon’s wing ° . . 234
Fic. 105.— Tracing of different movements of the pigeon’ s wing - » 258

. 106-107. Si pastries of the trajectory of a pigeon’s wing, 254, 255
. 110.—Simultaneous tracing of be different movements of a

buzzard’s wing E = 262

. 111.—Inclination of the plane of he wing, matt ices to ‘the

axis of the body during flight ; : : : - 263

. 113.—Vertical oscillations of the bird during flight . - » 266
. 114.—Relation of oscillations with muscular acts. : . 268
. 115.—Simultaneous tracing of two kinds of oscillation in the

buzzard . : > a i : wise Dal
TRAJECTORIES.

23.—Attempt to illustrate, by means of a metallic wire, the
sinuous trajectory passed through by the pubis : - 119

71.—Appearance of a er the tips of whose wings have been
gilded. . . ‘ 5 . . > ae kag
. 86.—Trajectory of an teat s wing . - , 5 "201
. 100.—Elliptical course of the point ofa bird’s wing. «kn eae
76.—Tracing of a vibrating Wheatstone’s rod . ; . - 191
79.—Do. tipped with a wasp’s wing . «eye 198

. 101.—Ellipse traced by a Wheatstone’s red on a revolving

cylinder . ° os ot . ° . ° « 243

ANIMAL MECHANISM:

TERRESTRIAL AND AERIAL LOCOMOTION.

INTRODUCTION.

Livine beings have been frequently and in every age
compared to machines, but it is only in the present day
that the bearing and the justice of this comparison are fully
comprehensible.

No doubt, the physiologists of old discerned levers, pulleys,
cordage, pumps, and valves in the animal organism, as in the
machine. The working of all this machinery is called Animal
Mechanics in a great number of standard treatises. But these
passive organs have need of a motor; it is life, it was said,
which set all these mechanisms going, and it was believed
that thus there was authoritatively established an inviolable
barrier between inanimate and animate machines.

In our time it is at least necessary to seek another basis
for such distinctions, because modern engineers have created
machines which are much more legitimately to be compared
to animated motors; which, in fact, by means of a little com-
bustible matter which they consume, supply the force requisite
to animate a series of organs, and to make them execute the
most various operations.

The comparison of animals with machines is not only legiti-
mate, it is also extremely useful from different points of view.
It furnishes a valuable means of making the mechanical
phenomena which occur in living beings understood, by
placing them beside the similar but less generally known
phenomena, which are evident in the action of ordinary

2 ANIMAL MECHANISM.

machines. In the course of this book, we shall frequently
borrow from pure mechanics the synthetical demonstrations
of the phenomena of animal life. The mechanician, in his
turn, may derive useful notions from the study of nature,
which will often show him how the most complicated problems
may be solved with admirable simplicity.

- Animel mechanics is a wide field for exploration. To
every function, so to speak, a special machinery is attached.
The circulation of the blood, the respiration, &c., may and
ought to be treated separately, so that we shall limit this work
to the study of one single, essentially mechanical, function,
locomotion in the various animals.

It is easy to demonstrate the importance of such a subject as
locomotion, which, under its different forms, terrestrial, aquatic,
and aerial, has constantly excited interest. Whether man has
endeavoured to utilize to the utmost his own motive power,
and that of the animals; whether he has sought to extend
his domain, to open a way for himself in the seas, or to rise
into the air, it is always from nature that he has drawn his
inspirations. | We may hope that a deeper knowledge of the
different modes of animal locomotion will be a point of
departure for fresh investigations, whence fuither progress
will result.

Every scientific research has a powerful attraction in itself;
the hope of reaching the truth suffices to sustain those who
pursue it, through all their efforts; the contemplation of the
laws of nature has been a great and noble source of enjoy-
ment to those who have discovered them. But to humanity,
science is only the means, progress is the aim. If we can
show that a study may lead to some useful application, we
may induce many to pursue it, who would otherwise merely
follow it from afar, with the interest of curiosity only.
Without pretending to recapitulate here all that has been
gained by the study of nature, we shall endeavour to set
forth what may be gained by studying it still further, and
with more care.

Terrestrial locomotion, that of man, and of the great mam-
mals, for instance, is very imperfectly understood as yet. If
we knew under what conditions the maximum of speed, force,

INTRODUCTION. 3

or labour which the living being can furnish, may be ubtained,
it would put an end to much discussion, and a great deal of
conjecture, which is to be regretted. A generation of men
would not be condemned to certain military exercises which
will be hereafter rejected as useless and ridiculous. One
_ country would not crush its soldiers under an enormous
load, while another considers that the best plan is to give
them nothing to carry. We should know exactly at what
pace an animal does the best service, whether he be required
for speed, or for drawing loads; and we should know what
are the conditions of draught best adapted to the utilization
of the strength of animals.

It is in this sense that progress is being made; but if we
complain with reason of its slow advance, we must only
blame our imperfect notion of the mechanism of locomotion.
Let this study be perfected, and then useful applications of it
will soon ensue.

Man has been manifestly inspired by nature in the con-
struction of the machinery of navigation. If the hull of
the ship is, as it has been justly described, formed on the
model of the aquatic fowl, if the sail has been copied from the
wing of the swan inflated by the wind, and the oar from its
webbed foot as it strikes the water, these are but a small part
of nature’s loans to art. More than two hundred years ago,
Borelli, studying the stability and displacement of fish, traced
the plan of a diving-ship constructed upon the same principle
as the formidable Monitors which made their appearance in
the recent American war.

In modern navigation the dynamic question still leaves
‘several points in obscurity. What form should be given to a
ship so as to secure its meeting with the least possible resist-
ance in the water? What propeller should be chosen in
order to utilize the force of the machine to the best advan-
tage? The most competent men in such matters avow that
these problems are too complex to admit of the conditions
most favourable to the construction of ships being determined
by calculation. Must we wait until empiricism, by dint of
ruinous guesses, shall have taught us how a problem of
which nature offers us such diverse solutions, should be

+ ANIMAL MECHANISM.

solved? Ingenious constructors have already attempted to
imitate the natural propellers; they have fitted up small boats
with machinery which works like the tail of a fish, oscillating
with an alternate motion. And it has been found that this
apparatus, although still imperfect, already constitutes a
powerful propeller, which will perhaps be preferred hereafter
to all those which have hitherto been used.

Aerial locomotion has always excited the strongest curiosity
among mankind. How frequently has the question been
raised, whether man must always continue to envy the bird
and the insect their wings; whether he, too, may not one day
travel through the air, as he now sails across the ocean.
Authorities in science have declared at different periods, as
the result of lengthy calculations, that this is a chimerical
dream, but how many inventions have we seen realised which
have also been pronounced impossible. The truth is, that all
intervention by mathematics is premature, so long as the
study of nature and experiment have not furnished the precise
data which alone can serve as a sound starting point for
calculations of this kind.

We shall then attempt to analyse the rapid acts which are
produced in the flight of insects and of birds; afterwards we
shall endeavour to imitate nature, and we shall see, once
more, that by seeking inspiration from her we have the
best chance of solving the problems which she has solved.

We may even now affirm, that in the mechanical actions of
terrestrial, aquatic, and aerial locomotion, there is nothing
which can escape the methods of analysis at our disposal.
Would it be impossible for us to reproduce a phenomenon
which we understand? We will not carry our scepticism
so far.

It was considered for a long time that chemistry, all-
powerful when it was a question of decomposing organic
substances, would always remain incapable of reproducing
them. What has become of this disheartening prediction ?

We hope that the reader who follows the experimental
researches detailed in this book will draw from them this
conviction, that many of the impossibilities of the present,
need only a little time and much effort to become realities.

BOOK THE FIRST.

CHAPTER I.
FORCES AND ORGANS.

Of forces in the inorganic kingdom and among organised beings—Matter
reveals itself by its properties— When matter acts, we conclude that
forces exist —Multiplicity of forces formerly admitted ; tendency to
their reduction to one force in the inorganic kingdom—Indestruc-
tibility of force ; its transformations—Vital forces, their multiplicity
according to the ancient physiologists—Several vital forces are
reduced to physical forees—Of laws in physics and in physiology—
General theory of physical forces.

We know matter only by its properties, which we could not
conceive of apart from matter. ‘The word property does not
answer to anything real : it is an artifice of language ; thus, the
expressions, weight, heat, hardness, colour, c., attributed to
various bodies in nature, mean that these bodies manifest
themselves to our senses by certain effects which have been
made known to us by daily experience.

When matter acts, that is to say, when it changes its state,
there occurs what we call a phenomenon, and by a new appli-
cation of language we call the unknown cause which has
produced this phenomenon, [orce. A body which falls, a
river which flows, a fire which warms us, the lightning which
flashes, two bodies which combine, &c., all these correspond to
manifestations of forces which we call gravity, mechanical
force, heat, electricity, light, chemical affinities, &c.

In the first ages of science the number of forces was almost
infinitely multiplied. Each particular phenomenon was re-
garded as the manifestation of a special force. But by degrees
it was recognised that divers manifestations might result from

6 ANIMAL MECHANISM.

a single cause; and thenceforth the number of forces which
were admitted diminished considerably.

Weight and attraction were reduced to one and the same
force by Newton, who recognised, in the falling of the apple
to the ground, and the retention of the star in its orbit, the
effects of an identical cause—universal gravitation. Ampcre
reduced magnetism to a manifestation of electricity. Light
and heat have long since been regarded as manifestations of an
identical force, an extremely rapid vibratory motion imparted
to the ether.

In our own time a grand conception has arisen, once more
to change the face of science. All the forces of nature are
reduced to one only, Force may assume any appearance ; it
becomes, by turns, heat, mechanical work, electricity, light ;
it gives rise to chemical combinations or decompositions.
Occasionally, force seems to disappear, but it has only hidden
itself; we can find it again in its entirety, and make it pass
anew through the cycle of its transformations.

Force, which is inseparable from matter, is, like it, inde-
structible, and to both the absolute principle, that in nature
nothing is created and nothing is destroyed, is applicable.

Before we enter upon a detailed exposition of this great
conception of the conservation of force and its transformations
in the inorganic world, let us see whether any analogous
generalisation has been arrived at in the science of organised
bodies.

The living being, in its manifestations of sensibility, intelli-
gence, and spontaneity, shows itself to be so different from
the inert and passive bodies of inorganic nature; the genera-
tion and the evolution of animals are so peculiar to them-
selves; that the earliest observers traced an absolute boundary
between the two kingdoms of nature.

Particular forces were imagined, to which each of the
normal phenomena of life was attributed, while others, like
malignant genii, presided over the production of the maladies
by which everything that has life may be attacked.

The complexity of the phenomena of life hindered observers
for a long time fiom discerning the link which united them,
and prevented their referring to one and the same cause these

FORCES AND ORGANS. 7

manifold effects, and thus reducing the number of forces
which had at first been admitted. Man ended by taking
the fictions of his imagination for realities. Little by little,
the charm of the unintelligible exercising fascination over
him, he at last denied that physical laws had any in-
fluence upon living beings. ‘This extravagant mysticism
represented certain animals as capable of withdrawing them-
selves from the influences of weight; according to it, animal
heat was of another essence than that of our hearths; subtle
and impalpable spirits circulated in the vessels and the nerves.

Time has not even yet disposed of all these absurdities ;
but we can prove that the science of life tends at present
to undergo a transformation as complete as that of the phy-
sical sciences, whose development we have just sketched.
Physiology, guided by experience, seeks and finds the physical
forces in a great number of vital phenomena; every day sees
an increase in the number of cases to which we can apply
the ordinary laws of nature. That which escapes them
remains for us the unknown, but no longer the unknowable.
Among the phenomena of life, those which are intelligible
to us are precisely of the physical or mechanical order.

In the living organism we shall find those manifestations
of force which are called heat, mechanical action, electricity,
light, chemical action; we shall see these forces transforming
themselves one into the other, but we must not hope to arrive
immediately at the numerical determination of the laws which
regulate the transformations of these forces. The animal
organism does not lend itself to exact measurements, its com-
plexity is too great for valuations, to which physicists attain
with great difficulty by making use of the simplest machines.

Each science, according to its degree of complexity, is
approaching more or less surely to the mathematical precision
at which it must arrive sooner or later. A law is only the
determination of numerical relations between different phe-
nomena; there is then no perfect physiological law. In the
phenomena of life it is scarcely possible to determine and to
foresee anything except the manner in which the variation will
be produced. Hitherto, the physiologist has reached only that
degree of knowledge which the astronomer would possess, who

8 ANIMAL MECHANISM.

knew, for instance, that the attraction between two heavenly
bodies diminishes when their distance increases, but who had
not yet determined the law of inverse proportionality to the
square of distances. Or, he is like the physicist who has proved
that compressed gases diminish in volume, but who has not
found the numerical relation between their volume and the
pressure.

Without doubt, however, there are numerical relations
between the phenomena of life; and we shall arrive at the
discovery of them more or less speedily, according to the
exactitude of the methods of investigation to which we have
recourse. ;

If physicists had limited themselves to establishing that
bodies dilate as they become heated, and if they had not
sought to measure the temperature of those bodies and the
volume which they assume with each variation of the temper-
ature, they would have had only an imperfect idea of the
phenomena of the dilatation of bodies by heat. For a long
time physiologists confined themselves to pointing out that
such or such an influence augments or diminishes the force of
the muscles, causes the rapidity of their motions to vary,
increases or diminishes sensibility and motive power. Science,
in our time, has become more exacting, and already the
rigorous determination of the intensity and duration of certain
acts, of the form of different movements, of the relations of
succession between two or several phenomena, the precise
estimation of the rapidity of the blood, or of the transference
of the sensitive or motive nervous agent; all these exact
measures introduced into physiology, lead us to hope that
from more scrupulous measurement better formulated laws
will soon result.

In the comparison which we are about to make between
the physical forces and those which animate the animal
organism, we shall take it for granted that the fundamental
notions recently introduced into science, and by which all those
forces tend to reduce themselves to one only, that which
engenders motion, are known; and shall, therefore, confine
ourselves to a rapid sketch of the new theory.

The value of a theory depends on the number of the facts

FORCES AND ORGANS. 9

which it embraces; that of the unity of the physical forces
tends to absorb them all. From the invisible atom to the celes-
tial body lost in space, everything is subject to motion. Every-
thing gravitates in an immense or in an infinitely little orbit.
Kept at a definite distance one from the other, in proportion
to the motion which animates them, the molecules present
constant relations, which they lose only by the addition or the
subtraction of a certain quantity of motion. In general,
increase of motion enlarges the orbit of the molecules, and
widening their distance from each other, increases the volume
of the bodies. By this rule, heat is proved to be a
source of motion. Underits influence the molecules, becom-
ing more and more separated, cause bodies to pass from
solid to liquid, and then to a gaseous state. These
gases become indefinitely dilated by the addition of fresh
quantities of heat. But that force which lends extreme
rapidity to the motion of the molecules, that force which is
admitted in theory is rendered tangible by experiment; its
intensity is measured by opposing to the dilatation of a body
an obstacle which it will have to surmount. Thus it is that
the molecules of gases or vapours imprisoned in the cylinder
of machines, communicate to the partitions and to the piston
the pressure which is employed in producing action by
machinery. ‘This mechanical action is, in its turn, trans-
formed into heat if the conditions of the experiment be re-
versed ; if, for example, an external force, thrusting back
the piston of an air-pump, restrains the molecular motions by
violent compression.

The new theory has thrown light upon certain hypotheses,
those, among others, which claimed admission for the latent
heat of fusion, or cf vaporisation of bodies, the latent heat of
dilatation of gases. It has suppressed others; for instance,
the discovery of atmospheric pressure has banished the
hypothesis which has now become ridiculous, that nature
abhors a vacuum.

Although the theory accommodates itself with less ease to
the interpretations of luminous and electric phenomena, it
admits, according to the great analogy between these phe-
nomena and heat, of supposing that they themselves are only

2

10 ANIMAL MECHANISM.

manifestations of motion. Besides, the transformation of
motion into heat, into electricity, into light, may be proved
experimentally.

Fig. 1 represents the details of the experiment.

Fic. 1.—Showing the transformation of the electricity of a battery into mecha-
nical action, into heat, light, and chemical action.

Various instruments are so arranged upon a table that an
electric current, engendered by a battery P, may be made to
pass through them.* The current is conducted in an elliptic
circuit, on a small square board, represented in the centre of
the figure. This circuit is formed of a thick copper wire;
at certain points this wire is interrupted and dipped into
cups of mercury, from which other wires communicate with
the various apparatus through which the current is to be con-
ducted. In Fig. 1, the metallic bridges 1, 2, 3, 4, 5, connect
the cups of mercury, and form a complete circuit, which the
current may traverse without passing through the various
apparatus placed around it.

If we take away loop No. 1, the current which passed
through that loop is forced to traverse the elliptical circuit
without passing through the surrounding apparatus. But if we

* Jnstead of the single element represented in the Figure, it 1s necessary
to employ a series of Bunsen’s cells, to realise the experiments perfectly.

FORCES AND OPGANS. ll

afterwards remove loop No. 2, the current must traverse the
apparatus M, which is an electro-magnetic motor. This appa-
ratus will begin to move and will produce mechanical action.

Let us at the same time remove loop No. 3, the current
must also traverse a registering thermometer. [That
instrument is constructed as follows. It is a sort of Reiss’
thermometer, formed of a spiral of platinum, which the current
traverses, and which is conducted into a flask full of air.
Under the influence of thé heating of the spiral by the current
which traverses it, the air in the bottle dilates, and passes,
through a long tube, into the registering apparatus. The
latter is composed of a drum of metal, closed on the upper
side by a membrane of india-rubber. When the air pene-
trates into the drum, the membrane swells, and lifts up a
registering lever, which traces on a turning cylinder E, a curve
whose elevations and depressions correspond with the rise and
fall of the temperature. |

By removing loop No. 4, we force the current to traverse
an apparatus L, with carbon points, in which electricity
gives birth to the bright light with which every one is
acquainted. When it passes through the voltameter V, the
current produces decomposition of the water. ‘The intensity
of the current is measured by the quantity of water decom-
posed, z.e., by the volumes of hydrogen and oxygen which
are disengaged.

We see, in the first place, by means of this apparatus,
that electricity can become successively mechanical work in the
motor M, heat in the spiral of the thermometer T, light
between the carbon points L, and chemical action in the
voltameter V.

But we also recognise that the electricity which undergoes
one of those metamorphoses is taken away from the current
whose energy is thus diminished. If, for example, we make
the motor M work, we shall see that the register marks a
diminution of heat in the thermometer. If we stop the
electro-magnetic motor with the hand, an increase in the
temperature becomes immediately apparent; the registered
curve rises.

When the electro-magnetic motor is working, we see the

12 ANIMAL MECHANISM.

intensity of the light diminish, and the decomposition of
the water in the voltameter grow less. All these phenomena
resume their pristine energy as soon as we suppress thie
production of mechanical action.

During this time, all the force expended in these various
forms of apparatus is disengaged from the battery under the
influence of a chemical action: the transformation of a certain
quantity of zinc into sulphate of ziuc. Thus, in the furnace
of a steam engine, the combustion of the coal, that is to say,
the oxidation which transforms carbon into carbonic acid
disengages heat, which is afterwards converted into work.

But this force, disengaged from bodies, was contained in
them when the zine was iu the condition of metal, and the
carbon in the state of coal; these bodies had employed in
their formation the same quantity of force which they
have yielded up in passing into another condition. Thus it
would be necessary to restore to the sulphate of zine and to
the carbonic acid as much electricity or heat as they have
thrown out, in order to reproduce the metallic zine or the
carbon in a pure state.

According to the modern theory, force which manifests
itself at a given moment is not created, but only rendered
sensible, from being latent.

Here in tension is that potential force, which, stored up in
a body, waits the opportunity to manifest itself. Thus a
stretched spring will at the end of an indefinite time give back
the force which has been used to stretch it; and a weight,
lifted to a certain height, will restore, the instant it falls,
the work that has been employed upon raising it.

TRANSFORMATION OF PHYSICAL FORCES, 13

CHAPTER II.
TRANSFORMATION OF PHYSICAL FORCES.

To prove the indestructibility of forces, we must know how to measure!
them—Units of heat and of mechanical work—Thermo-dynamies—
Measure of forces in living beings—Successive phases of the trans
formation of bodies ; successive throwing off of force under this influ-
ence—Thermo-dynamics applied to living beings,

We have just seen that force, in the different states which.
it presents, may be now latent, or potential, or again in action,
in the form of heat, electricity, or mechanical activity.

To follow this force through all its different transformations,
to establish that no portion of it is lost, a means of measuring
it under all its forms is necessary. The chemist can prove
the indestructibility of matter, by showing, with a balance,
that a gramme of matter will preserve its weight through all
the changes of condition that can be imposed upon it. Let
that matter be weighed in the liquid state, in the solid state,
or in the gaseous state, the, weight of a gramme will always
be found under the most various volumes and aspects.

A measure is then necessary for the different manifestations
of force. Every quantity of heat, of electricity, or of mechani-
cal work ought to be compared with a particular unit, as every
weight ought to be compared with the unit of weight.

Unit of heat. The sensations of heat and cold which we
experience at the contact of different bodies do not correspond
with the quantity of heat which those bodies contain. Ther-
mometrical apparatus are not in a condition to give us the
measure of the quantities of heat, since different bodies,
presenting to our senses and by the thermometer the same
temperature, may yield very unequal quantities of heat. But,
to warm the same weight of a body to the same number of
degrees, the same quantity of heat will always be necessary.

Now, according to the agreement which has been come to
in France and in many other countries, the unit of heat or

14 ANIMAL MECHANISM,

calorie is the quantity of heat necessary to raise a kilogramme
of water from zero to one degree centigrade.

Unit of work. Mechanical force has been accurately de-
fined only since the notion of work has been introduced into
science. The unit of mechanical work admitted in France
is the kilogrammetre; that is to say, the force necessary to
raise the unit of weight—the kilogramme—to the unit of
height, the metre.

Kilectric force is measured by one of its effects, the decom-
position of water, for it is demonstrated that to decompose
the same. volume of water the same quantity of electricity will
always be requisite.

These measures of forces in action furnish, in their turn,
the means of estimating the quantity of potential force con-
tained ina body. Thus, it will be demonstrated that ina
kilogramme of coal, and in the quantity of oxygen necessary
to transform that coal into carbonic acid, there were in tension
7000 units of heat, since by combining all the heat disen-
gaged by combustion, a mass of water of 7000 kilogrammes
shall have been heated.

But a substance which burns is not always completely
oxidized; hence, it does not put in action the totality of the
force which it contained in tension. A kilogramme of carbon,
for example, may undergo only a first degree of oxidation, and
thus becoming oxide of carbon it yields only 5000 units of
heat. This oxide of carbon burning in its turn, and becoming
carbonic acid, will then yield only the remaining 2000 units
of heat.

Transformation of physical forces takes place, as we have
said, without any loss of the transformed force. To demon-
strate this, it must be proved that a certain number of units
of heat transformed into work, will furnish a constant number
of kilogrammétres, and inversely, that this work in becoming
heat again, will restore the primitive number of units of heat.

The science which explains the relations between heat and
mechanical work, and fixes the value of the mechanical equivalent
of heat is called thermo-dynamics. 'This conception, which is
the complement of the theory of the transformation of forces,
and which proves that in their transformation they lose

TRANSFORMATION OF PHYSICAL FORCES, 15

nothing of their value, is justly considered the most remarkable
of modern times.

Partly seen by Sadi-Carnot, clearly formulated by R. Mayer,
demonstrated brilliantly by the experiments of Joule, the
notion of the equivalence of forces is now admitted by all
physicists. Each day furnishes a fresh confirmation of this
doctrine, and leads to greater precision in the determination of
the mechanical equivalent of heat. The value now generally
admitted for that equivalent is 425, that is to say, that work
equal to 425 kilogrammetres must be transformed into heat
to obtain a unit, and inversely, that the heat capable of heat-
ing to one degree one kilogramme of water at zero, if it be
transformed into work, can, in its turn, lift a weight of 425
kilogrammes one metre.*

But one restriction must be placed upon the estimation
of thermo-dynamic transformations. Carnot suspected, and
Clausius had clearly established that in the case of heat being
employed to produce work, the heat cannot transform itself
altogether, and that the greater part remains still in the state
of heat; while in the inverse operation the whole of the work
applied to that effect may be transformed into heat. This
does not exclude the law of equivalence, of which we have
just spoken; for if it be true that, in a steam engine for
instance, there is only to be found under the form of work a
small quantity, about 12° of the heat produced by the fur-
nace, it is no less true that the quantity of heat which has
disappeared furnishes in work the exact number of kilo-
grammétres which corresponds to its mechanical equivalent.

These notions had no sooner been introduced into science
than the physiologists endeavoured to use them for the
clearing up of the obscure question of heat and work pro-
duced by animals. The assimilation of living beings to
thermal machines was already in the state of vague con-
ception. We shall see what light has been thrown upon it
by the new theory.

* Some experiments made by Regnault on the rapidity of sound, and
on the expansion of gases, give as the true value of the equivalent the
number 439,

16 ANIMAL MECHANISM.

We have said that forces are produced within the organism.
All living beings give out heat and produce work. ‘The-
disengagement of these forces is caused by the chemical
transformation of food,

In the living being it is possible to measure approximately
the quantities of heat and work produced, and even to estimate
the quantity of force contained in feod; in order to do this
it is sufficient to apply the methods which physicists have
-employed in the estimation of inorganic forces.

Thus, aman placed for some time in a bath will yield to
the water a certain number of units of heat, which may be
easily measured. Applied to the moving of a machine, the
force of a man or an animal will produce a number of kilo-
grammétres no less easily to be measured. If the aliment be
subjected to the experiments which determine the heating
power of different combustibles, it will be found that each of
them contaius a certain quantity of potential force. Favre and
Silbermann have supplied most valuable information, attained
by great labour, on this point; and Frankland has continued
their investigations. We now know the calorific power of
almost all the alimentary substances, it is, therefore, possible
to caleulate what free force their complete oxidation will yield
either under the form of heat or under the form of work.

But, as we have seen with respect to eombustibles employed
for industrial purposes, the oxidation is not always complete.
Coal partially consumed, gives solid or gaseous residues,
such as coke and oxide of carbon, which, being oxidized in
a more complete manner, furnish a certain quantity of heat.
In the same way, the residues of digestion still contain non-
disengaged force. All these forces ought to be estimated if
we want to know how much of their force in tension has been
lost by the alimentary matters in passing through the organism,
and how much ought consequently to be found again under
the form of force in action. ‘The urinary secretion also elimi-
nates incompletely transformed products; the urea and the
uric acid contain force in tension, which ought to be taken
into account in calculations.

The watery vapour which saturates the air as it comes out
of the lungs removes from the organism and carries away with

TRANSFORMATION OF PHYSICAL FORCES, 17

it a certain quantity of heat; the same thing takes place in the
boiler of a steam-engine, as well as in cutaneous evaporation.

This complication in the measure of force among organized
beings shows what difficulties await those who are en-
deavouring to verify the principles of thermo-dynamics in
animals; yet, nevertheless, it would be illogical to admit with-
out proof that, in living beings, the physical forces do not
obey uatural laws, Several savants, firmly convinced of the
generality of the laws of thermo-dynamics, have attempted to
demonstrate them upon the animal organism.

J. Béclard was the first who endeavoured to prove that in
the muscles of man heat may be substituted for mechanical
work, and vice versé. For this purpose he examined the
thermometrical temperature of two muscles, both of which
contracted, but one worked, that is to say, raised weights, while
the other did not work. It might have been expected that less
heat would have been found in the first muscle, because a
portion of the heat produced during its contraction ought to
have been transformed into work.

The idea which governed LBeéclard’s experiments was
assuredly correct, but the means at his disposal for ascer-
taining the heating of the muscles were altogether insufficient.
A thermometer was applied to the skin at the level of
the. muscle, in order to give the measure of the heat pro-
duced; thus the variations of temperature obtained by Beclard
according as the muscle worked or not, were so slight that no
real value could be attached to them.

Herdenheim obtained clearer results by operating upon
frogs’ muscles, which he made to contract with or without the
production of work, ascertaining their temperature by means
of thermo-electric apparatus.

Hirn was bolder in his experiments, for he sought to deter-
mine the equivalent of mechanical work in animated motors.

In order to make Hirn’s experiment comprehensible, let us
consider the simpler case of a mechanician desiring to establish
the thermal equivalent of the work of a steam engine, knowing
how much fuel it has burned, what heat has been given out,
and what quantity of work has been produced.

First, he will estimate the heat which should correspond

18 ANIMAL MECHANISM.

with the combustion of the coal which he has burned; he will
prove that the heat which he has obtained is less than this,
which is made evident by the disappearance of a certain
number of units; this disappearance he will attribute to the
transformation of heat into work. Now as he knows the
number of kilogrammetres produced by the machine, he will
only have to divide this number by that of the units of heat
which have disappeared, in order to find the number of
kilogrammetres equivalent to each of them.

Hirn believed that the combustion effected, the heat given
out, and the mechanical work produced by a man could be
estimated at the same time. He enclosed the subject in a
hermetically closed chamber, and made him turn a wheel
which could, at choice, revolve with or without doing work.

The air of the chamber being analysed, showed what
quantity of carbonic acid had been given out; from thence
were deduced the combustion produced and the number of
units of heat to which that combustion ought to have corre-
sponded.

The heat given out in the chamber was ascertained by the
ordinary calorimetric processes ; it was, in proportion to the
work produced, sensibly inferior to that which ought to
have been found according to the quantity of carbonic acid
exhaled.

This disappearance of a certain number of units of heat
was explained by their transformation into mechanical work.

From these experiments Hirn deduced a valuation of the
mechanical equivalent of heat for animated motors; but the
number which he obtained differed considerably from that
which has been established by physicists. This difference is in
no wise surprising when we think of all the causes of error
which are united in such an experiment. There may have been
an error concerning the quantity of carbonic acid exhaled; an
error concerning the nature of the chemical actions which
disengaged this carbonic acid, and therefore respecting the
quantity of heat which ought to have accompanied the disen-
gagement; an error in the ‘estimation of the heat diffused
through the calorimetric chamber; finally, an error as to the
quantity of mechanical work produced by the subject. In

ANIMAL HEAT. 19

fact, while it is relatively easy to estimate the work of our
muscles when employed in lifting a burden, there are other
muscular actions which constitute an important sum of work
and which we do not yet know how to value with precision ;
we allude to the movements of the circulation, and especially
to those produced by the breathing apparatus.

The remarks which we have made upon the greater number
of the physiological experiments from which it has been sought
to establish numerical data, apply to that of Hirn. But
though it cannot furnish an exact determination, this ex-
periment at least enables us to perceive the manner in which
the phenomena vary; it shows that a certain quantity of heat
always disappears from the organism when external work
is produced. No greater precision could be obtained in the
measure of thermo-dynamic transformation in the greater
number of steam-engines, and yet nobody disputes that in
these motors heat and work are substituted for one another in
equivalent relations.

CHAPTER III.
ON ANIMAL HEAT.

Origin of animal heat—Lavoisier’s theory—The perfecting of this theory
—Estimates of the forces contained in aliments, and in the secreted
products—Difficulty of these estimates—The force yielded by ali-
mentary substances is transformed partly into heat and partly into
work—Seat of combustion in the organism—Heating of the glands
and muscles during their functions —Seat of calorification— Interven-
tion of the causes of cooling—Animal temperature—Automatic regu-
lator of animal temperature.

Durtnc a long period, animal heat was considered to be of
a peculiar kind, distinct from that which is manifested in the
inorganic kingdom; this arose from certain conditions under
which the living tissues become hot or cold, without its
being easy to discover how this heat appears, or how it
disappears. _ It was almost natural to admit that heat is

20 ANIMAL MECHANISM.

connected with influences of nervous origin, when it was
seen that certain violent emotions produce icy coldness in
human beings, whereas others bring into the countenance
sudden heat. Now all these facts have found an explanation
in which there is nothing to infringe the ordinary laws of
physics. In order to comprehend them thoroughly we must
pess under our review the production of heat and its dis-
tribution throughout the various parts of the organism.

It has long since been established that aliment is indis-
pensable in the living being for the production of heat, as well
as of muscular power. Inanition, at the same time that it
reduces the strength of the animal, produces profound cold
in it. We owe to the genius of Lavoisier the comparison
of the living organism to a grate which burns or incessantly
oxidizes substances taken from without, by borrowing from
the atmosphere the oxygen requisite for these transforma-
tions. ‘This theory has triumphed over all the attacks which
have been made upon it, and their only result has been the
perfecting of its details.

Let us reduce to its true proportions the comparison of the
living organism with a burning grate. In both, an oxidable
matter finds itself placed in relation with oxygen; but while,
in a grate, the natural gas comes in contact with the com-
bustible previously raised to an elevated temperature, in the
organism the gas dissolved in the blood comes in contact with
materials which are themselves dissolved in that liquid, or
which have deeply entered into the tissue of the organs.
Thus, the circulation transports into every part of the
organism the elements which are necessary to the disengage-
ment of force. These bodies remain in contact, without acting
one upon the other, until the moment arrives when a specific
action brings about their combination. This office, analogous
to that of the spark which kindles the flame, or to that of
the cap which discharges gunpowder, belongs to the nervous
system.

When the oxidation is at an end, and the forces necessary
to the functions have been set at liberty, there remain in the
tissues certain products which have become useless, and which
may be compared to the ashes in the grate and to the gases

ANIMAL HEAT. 21

which go up the chimney. These products must be elimi-.
nated. Again, the circulation undertakes this office; the
blood dissolves the carbonic acid and the -salts which are the
ultimate products of organic oxidation, and then carries
them, in its perpetual course, to the eliminating organs, the
lungs and the glands.

So long as it remained unsuspected that heat and mechanical
work could be substituted for each other, an attempt was
made to account for all the combustions which take place
in the living organism, by estimating the quantity of heat
discharged by an animal in a given time. Physicists and
physiologists made great efforts to determine this illusory
equality between the theoretical heat, which corresponded
with the combustions which take place in the organism, and
the quantity of heat furnished by the animal under experi-
ment.

Just as a machine, when it is working, furnishes less heat
to the calorimeter than would be given out by a simple grate
consuming the same quantity of combustible matter, so the
living being gives out less heat in proportion as it executes
more mechanical work. We have seen, by Hirn’s experiments,
that it is solely according to the difference which exists
between the heat experimentally obtained and that theo-
retically estimated, that we now endeavour to find the value
of the equivalent of mechanical work in living beings.

Whatever may be the varied manifestations of force in the
organism, a certain portion of that force always appears
under the form of heat, and this it is which gives to animals
a higher temperature than that of the medium in which they
live.

May we not, by ascertaining the temperature of the different
parts of the body of the animal, discover the points at which
heat is formed, and define the actual seat of those com-
bustions of which we establish only the distant results ?

It is now demonstrated that the lungs, by which the oxygen
of the air penetrates into the organism, are not the seat of
combustion, because the blood which comes out of that organ
is, in general, colder than that which has gone into it. If
two thermometers or thermometrical needles be introduced

22 ANIMAL MECHANISM.

into the heart of an animal, in order to ascertain the tempe-
rature of the blood which is returning through all the veins
of the body into the right cavities, and that of the blood which
is coming into the left cavities from the lungs, we find that
the blood of the right-hand side of the heart is the warmer ;
so that it follows that heat is principally produced along the
course of the great circulation.

If we would more particularly localize the origin of heat,
we must take a special organ and investigate, in a com-
parative manner, the temperature of the blood which comes
to it through the arteries, and goes out of it through the
veins. Thus it has been recognized that the muscles, in
action, and the glands while they are secreting, are orgavs
for the production of heat; and in them the most energetic
chemical action takes place.

But we must not expect, when examining all the muscles or
all the glands at the moment of their action, to find an un-
varying elevation in the temperature of their venous blood.
A third element enters into the problem; it is the loss of
heat which tales place while the blood is passing through the
organ. Now, all portions of the body are not equally sub-
jected to loss of heat; the most superficial are the most
exposed to them, while the deeper organs are sheltered
against the causes of cold.* Under these conditions every dis-
engagement of heat in the glands ought to be represented by
an elevation of temperature in the venous blood. _ If, on the
contrary, we lay the sublingual gland bare, in cold weather,
and investigate the temperature of the blood in the veins of
that gland, we shall find the blood colder than that which
has entered through the arteries. Must we conclude from
thence that there has been no disengagement of heat in that
gland? In no wise. We must simply admit that the loss
of heat has exceeded its production.

In short, heat appears to be produced in all the organs,
but in various degrees, according to the intensity of the

* When we wish to ascertain the increase of temperature of the blood
in the glands, we must choose, for this investigation, the blood of the
veins of the liver or the kidneys, organs sheltered from cooling influences.

ANIMAL HEAT. 23

chemical action which takes place in them. Tho temperature
of an organ necessarily results from the heat supplied to it
by the blood, from that which has been produced in its
interior, and from that which it has lost. Thus it is that
certain veins, those of the limbs, for example, bring back
blood colder than that of the corresponding arteries; whilst
others, like the sub-hepatic veins which leave the liver, bring
back blood warmer than that which has entered the hepatic
gland. In fact, after all compensations are made, the heated
venous blood predominates in the living organism over the
cooled blood; so that it re-enters the heart 14° warmer than
when it came out of it.

This leads us to study the question of the temperature of
animals,

Among the different animal species, some, while producing
heat, are subject to the variations of the surrounding tem-
perature, so that they have been called cold blooded. They are
now called animals of variable temperature, which is more
exact. As for the animals called warm blooded, they possess
the singular property of having the blood in the deeper
portions of their bodies almost always at the same tempera-
ture, notwithstanding the variations of the external heat.
Thus, a man, sailing from the polar regions to the equator,
may be subject, in a few weeks, to changes of 30° in the
surrounding temperature, but his blood remains at about
38°.

It is easy to understand that in the midst of incessant
variations in the production of heat inside the organism,
and of the no less great variations in the causes of its
waste, such uniformity can only be obtained by means of a
regulator of the temperature. We shall now proceed to certain
developments of the wonderful functions of the regulator of
the animal temperature.

Human industry has often found it difficult to provide fixed
temperatures, or at least to counterbalance the causes of ex-
cessive heat and cold. A hot-house must neither fall below,
nor rise above a certain temperature. But this problem is
relatively a simple one; the hot-house is always warmer
than the external air; it can only be subjected to more or less

24 ANIMAL MECHANISM.

intense causes of cooling, which may be compensated by a
suitable variation of heat. Bunsen’s regulator solves this
problem satisfactorily, by regulating the supply of gas which
serves as a combustible, augmenting it if the inclosed air
tends to grow cold, diminishing it in the opposite case.

In the animal economy, two orders of influences tend in-
cessantly to cause variation of temperature in its production
and in its expenditure. Causes of loss of temperature exist,
as in the instance just mentioned. The temperature of the
surrounding air, against which our clothing protects us more
or less efficiently, on the one hand, and the more or less
easy evaporation by means of cutaneous perspiration, accord-
ing to the hygrometrical state of the atmosphere on the
other; the action of the wind, or of air-currents; the tem-
perature of the baths which we take, all these different
causes tend to increase or diminish the waste of heat to
which the body is subject. To these influences must be added
those of the hot or cold food which we eat; of the hot or
cold air introduced into our lungs by respiration, &c. All
these constitute in general the causes of loss of heat.

Another variable element in the establishment of the
animal temperature is the production of heat which takes
place in the interior of the organism, and which, as well as
its loss, varies under numerous influences. ‘The aliments of
which we partake, act, through their nature and quantity, on
this production of internal heat; the activity of the glands
causes a discharge of caloric; and the case is the same with
respect to muscular action, which cannot be produced without
the heating of the muscle.

It is true that within certain limits our senses warn us to
restrict the production of heat, or to promote it, according as
external influences diminish or augment its waste. Thus,
the amount of food taken varies with climate, so that the en-
forced sobriety of the dweller in hot countries has no razson
d@étre in cold ones. Obligatory idleness during the heat
of the day under a burning sky is one manner of diminishing
the production of heat; the Northmen, on the contrary, en-
deavour to compensate, by muscular activity, for the cold to
which they are subjected.

ANIMAL HEAT. 25

But these are not the true regulators of the animal
temperature. Our will commands all those actions whose
influence may be favourable to the regulation of our tempe-
rature; but, in general, Nature, in order to secure the indis-
pensable functions of life, removes them from the control of
our will. It is in an automatic apparatus that we shall find
the real regulator of temperature.

This apparatus must obey external and internal influences
at the same time, it must retain heat when it tends to be
dissipated too rapidly, and, on the other hand, it must facili-
tate its decrease when it is produced too abundantly within
the organism.

This double end is achieved by a property of the circu-
latory system: the blood vessels, animated by nerves whose
action has been revealed by M. Cl. Bernard, close under the
influence of cold, and open under the effect of heat. This
property regulates the course of the blood in each of the
organs, and at the same time the temperature throughout the
entire economy.

Let us take an animal which has just been killed; the
circulation of the blood is stopped, and with it all the
functions. This animal, if placed in a low temperature,
becomes cold. According to physical laws, the extremities of
the limbs and the surface of the body will lose heat in the
first instance, while the central portions will still remain very
hot, being sheltered by the more superficial layers against the
causes of loss of heat. This corpse will resemble an inert
body which has been heated, and is growing cold. The cir-
culation of the blood opposes itself, during life, to the
unequal partition of heat over the various points of the
organism; bringing the arterial blood, at a temperature
of nearly 38° (centigrade), to the superficial portions, it warms
tl:em when the external temperature tends to chill them. On
the other hand, if, in the living animal, the production of
heat has been augmented, the circulation opposes the inde-
finite heating of the central regions of the body; it brings
that heat to the surface, where it is lost in contact with the
external colder medium.

The effect of the circulation of the blood is therefore to

26 ANIMAL MECHANISM.

render the temperature of the organism uniform. But this
uniformity is never complete; in fact, except in the case of the
animal’s being in a vapour bath at 38°, and losing none of
its heat, the surface of the body is always colder than the
interior, but no ill effect is produced by the chill, which does
not act upon the essential organs.

If the circulation of the blood were of equal swiftness in every
part, such a uniformity would not result in the preservation of
the uniform temperature necessary for the internal regions of
the body; we should then merely see it exposed to more general
elevations and depressions of temperature, according to the re-
spective predominance of causes of heat or the loss of it. To
produce uniformity of central heat it is indispensable that some
influence should augment the rapidity of the circulation
each time that the organism produces more heat, or that the
elevation of the surrounding temperature diminishes the causes
of cooling. Circulation in the superficial portions of the body
is extremely variable, as we may ascertain by observing the
varying aspects of those portions, which are sometimes red,
hot, and swollen, sometimes pale, cold, and shrunken, accord-
ing to the more or less abundance of the blood which circu-
lates in them. This variability depends upon the contraction
or the relaxation of the little arteries, whose muscular sheaths
obey special nerves. When, under the influence of these nerves,
named vaso-motors, the vessels contract, circulation slackens,
while by a contrary action, the relaxation of the vessels ac-
celerates the course of the blood. Now, it is the tempera-
ture itself which most generally acts in regulating this state
of contraction or relaxation of the vessels, so that the animal
temperature possesses in reality an automatic regulator.

Every one has observed the influence of heat and cold on
the circulation in the skin. If we dip one hand in hot, and
the other in cold water, the first will grow red and the second
pale; heat has, therefore, the effect of relaxing, and cold of
contracting the vessels. In other words, according to what we
have already seen, heat, by its action upon the circulation,
fayours the loss of heat; while cold acts in an inverse sense,
and tends to diminish the intensity of the chilling process,
And it is not only under the influence of the variations of the

ANIMAL MOTION, Q7

external temperature that these effects are produced; they are
equally observed when the animal heat varies in its produc-
tion. The heating of the organism which accompanies
muscular activity, or which results from taking very hot
drinks, produces the acceleration in the superficial circulation,
which throws out this excess of heat to the surface. Inanition,
muscular repose, the drinking of. iced waters, &c., slacken the
circulation near the surface and check its cooling action.

Such are, as far as we can explain them in a short chapter,
the origin and the distribution of heat in the animal organism.
The part played by the circulation of the blood in the distri-
bution of heat, perhaps demands more ample details; and,
indeed, we have treated it more fully elsewhere.* In the
present chapter we have studied heat only as manifestation of
force, and have merely designed to show that, notwithstanding
all appearances, heat is of the same nature in the inorganic
world and in organised beings.

CHAPTER IV.
ANIMAL MOTION.

Motion is the most apparent characteristic of life; it acts on solids,
liquids, and gases—Distinetion between the motions of organic and
animal life—We shall treat of animal motion only—Structure of the
muscles—Undulating appearance of the still living fibre —-Muscular
wave —Concussion and myography—Multiplicity of acts of contrac-
tion—Intensity of contraction in its relations to the frequency of
muscular shocks—Characteristics of fibre at different points cf the
body,

Morton is the most apparent of the characteristics of life ;
it manifests itself in all the functions; it is even the essence of
several of them. It would occupy much space to explain the

* Physiologie médicale de la Circulation du Sang. Paris, 1863 ; and
Théorie physiologique du Choléra, Gazette Hebdomadaire de Medecine.
1867.

238 ANIMAL MECHANISM.

mechanism by which the blood circulates in the vessels, how
air penetrates into the lungs, and escapes from them alter-
nately, how the intestines and the glands are perpetually
affected by slow and prolonged contractions. All these move-
ments take place within the organs without the exercise of the
will; frequently even the individual in whom they occur is
unconscious of them; these are the acts of organic life.

Other movements are subjected to our will, which regulates
their speed, energy, and duration; these are the muscular
actions of locomotion, and the different acts of the life of rela-
tion. We shall treat specially of this order of phenomena,
which are more easy to observe, and to analyse. Suffice it
here to say that the absolute division between the acts of
organic life and those of the life of relation ought not to be
accepted unreservedly. Bichat, who established it, based it
upon anatomical and functional differences which are of less
importance now than they were in his time. The mus-
cular element of organic life is unstriped fibre obedient to the
nerves of a particular system called the great sympathetic,
on which the will has no action; motions produced by this
kind of fibre are manifested some time after the excitement of
the nerve or of the muscle, and continue for a considerable
time. In fact, the object of those acts which are intended to
maintain the life of the individual imprints upon them a
special character. The muscular element of the life of rela-
tion consists of a fibre of striated appearance, whose action,
under the control of the will, is dependent upon nerves
emanating directly from the brain or from the spinal marrow.
These movements become evident rapidly as soon as they are
provoked by excitement; they are of brief duration, and are,
generally, not indispensable to the maintenance of the life of
the animal.

Although this distinction is, in a general way exact, it is
plain that it is too arbitrary, and that numerous exceptions
to the anatomical and physiological laws which it tends to
establish may be quoted. ‘Thus, the heart, an organ directly
indispensable to organic life, and not under the governance of
the will, is a structure which much resembles the voluntary
muscles. Certain fishes of the genus tinca have striated muscles

ANIMAL MOTION. 29

in the large intestine, as Ed. Weber has pointed out. Very
often, on the other hand, the will has no power over certain
muscles which, by their structure, and by the nature of the
nerves which animate them, belong to the system of the life
of relation. Habit, besides, by repeated exercise, appears to
extend the action of the will over the muscles, almost
indefinitely. The young animal. shows, by the awkwardness
of his movements, that he is not in full possession of his
muscular functions; he seems to have to study the simplest
acts, and performs them badly; while the gymnast, or the
skilled piano forte-player executes prodigies of agility, strength,
or precision, without any apparent, effort of the will propor-
tionate to the result obtained. Many physiologists think, and
we are of the same opinion, that there exist in the brain,
and in the spinal marrow, centres of nervous action which
acquire certain powers, by force of habit. They attain to the
command and co-ordination of certain groups of movements
without the complete participation of that portion of the brain
which presides over reasoning and the consciousness of our
actions.

Let us lay aside these questions, which are still under inves-
tigation, and examine into the production of motion in a
voluntary muscle. The organ which generates motion is
composed of several elements. Simple as it is supposed to
be, it requires the intervention of muscular fibre, of the blood
vessels, which unceasingly convey to it the chemical elements
at whose expense the motion is to be produced, and finally, of
the nerve which excites motion in the fibre.

When the physiologist desires to analyse the actions
which take place in the muscles, he does not deal, in the first
place, with voluntary motions, whose complexity is too great.
‘The operator isolates a muscle, and induces motion in it, by
bringing to act upon its nerve artificial excitements which he
has under his control.

To give an idea of the part played by each of the elements
of the motive apparatus in the production of movemeis, it is
sufficient to operate upon the leg of a frog. By laying bare
and severing the sciatic nerve, the influence of will upon the
muscle may be suppressed, so that the latter will only execute

30 ANIMAL MECHANISM.

such motions as are produced by excitation, electric or
otherwise, applied to the portion of the nerve which remains
in communication with it. On the sides of the sciatic nerve
are an artery and a vein. Compression of the artery will
prevent the blood from reaching the muscle; compression of
the vein will produce stagnation of the blood. The influences
which different states of circulation produce upon the muscular
function may then be observed; and, finally, by making an
incision in the skin of the foot, the muscle will be laid bare,
and cold, heat, or the various poisonous substances by which
its action is modified, may be brought to bear directly upon it.

When the nerve of a frog thus prepared is excited by an
electric discharge, a very brief convulsive movement in the
muscle is produced; this motion is called Zuckung by the
German physiologists, and we propose to call it shock, in
order to distinguish it from true contraction. It is so rapid
that its phases cannot be distinguished by the eye, so that, to
appreciate its characteristics aright, recourse must be had to
special instruments. Registering apparatus only can supply
this need, for they faithfully render all the phases of motion
communicated to them. The general disposition of these forms
of apparatus, which for a long time were used almost exclusively
in the service of meteorology, is generally known. . The
indications of the barometer, of the thermometer, of the force
or the direction of the wind, of the quantity of rainfall, &c.,
register themselves under the form of a curve which, accord-
ing as it is elevated or depressed, expresses the increase or
diminution of intensity of the phenomenon to be registered.
The time during which these variations are accomplished may
be estimated by the length occupied by the curve upon the
paper, which travels in front of the marking pen with an
ascertained and perfectly regular speed.

The use of instruments of the same kind has been introduced
into physiology by Volkmann, Ludwig, and Helmholtz. We
have endeavoured to extend the employment of them to a great
number of phenomena, and we have constructed many instru-
ments whose description would be out of place here. The
apparatus which registers muscular motions bears the name
of myograph; it shows the disturbance of the muscle by

ANIMAL MOTION. 31

means of a curve which readily allows us to study its phases.
We have fully explained elsewhere the nature of this in-
strument, the experiments for which it is suitable, and
the results which it gives.* At present we shall limit our-
selves to a summary description of the chief results of
myography.

—

| i

Fic, 2.—The Myograph.

In order to explain thoroughly the function of the appa-
ratus, let us reduce it in the first place to its essential
elements. Fig. 2 shows a muscle of the calf of a frog’s leg, m,
suspended by a clip by means of the bone to which the upper
part of the muscle is attached. The tendon, t, of the muscle
has been cut and then tied by a thread to the lever, L, one end
of which can be raised or lowered while the other is fixed ; the
nerve, n, is susceptible of electric excitement, which produces
certain contractions followed by relaxations in the muscle, that
is to say shocks. Each of these movements of the muscle is
communicated to the lever, which is raised or lowered, ampli-

* Du Mouvement dans les Fonctions de la Vie. Paris, 1867: G. Bailliere.

32 ANIMAL MECHANISM.

fying at its extremity the motions which it has received.
This lever, which ends in a point, traces on a turning cylinder
certain curves, which, when they are raised, indicate the con-
traction of the muscle, and when they are lowered, show
its return to its primitive length.

With the arrangement which we have made in the myograph
a muscle may be operated upon without being detached from
the animal, which allows of the organ being left in the normal
conditions of its function.

In Fig. 3 the frog is represented in the experiment, fixed,
by means of pins, on a piece of cork.

Fic. 3.—Marey’s Myograph.

The brain and spinal marrow have been previously destroyed,
so as to extinguish all voluntary movement and sensibility.
Although, to all appearance, the animal is dead, it will never-

OF MOVEMENT IN ANIMALS. 33

theless retain for several hours the circulation of the blood,
and the power of motion under the influence of electric
discharges. An electric excitator conveys the current from an
induction coil to the nerve of the frog.

In order to register these movements and to depict them
by curves which express their different phases, they are trans-
mitted to the myograph in the manner already described.
The tendon of the muscle is cut, and connected by a wire
which is fastened at the other end to the lever of the
registering apparatus ; the latter moves in a horizontal plane,
when the contractile force of the muscle is exerted upon it.
As soon as the muscle ceases to act, the lever returns, under
the pressure of a spring, to its original position. At the free
extremity of the lever is a point which traces, on a turning
cylinder covered with smoked paper, the motions produced by
the alternate contraction and relaxation of the muscle.

When the cylinder is motionless, the lever traces, for each
muscular shock, a straight line which expresses (by amplifying
it in a known proportion) the extent of the coutraction of the
muscle. Several authors limit themselves to this kind of
myography, by which they ascertain the variations produced by
different influences in the intensity of muscular action. By
giving the cylinder a rapid rotatory motion, a curve is obtained
which expresses by its height the extent of the contraction,
and indicates by its inclination, which constantly varies, the
speed with which the muscle passes through the different
phases of the shock. Finally, in order to obtain, without
confounding them, a great number of successive tracings,
the foot of the myograph is placed upon a little railroad
which works parallel to the axis of the cylinder. Tho
writing point then traces an indefinite spiral all round the
cylinder, and on this spiral a number of regularly graduated
curves (Fig. 5) are traced, answering to a series of electric
excitations produced at equal intervals; each of these curves
corresponds with one of the electric shocks.

If the speed with which the cylinder turns be augmented
or diminished, a change ensues in the appearance of the
curves, which necessarily occupy a greater or less space on
the paper, but if a uniform speed in the rotation of the

34 ANIMAL MECHANISM.

cylinder be maintained, the curves retain the same form so
long as the muscle gives the same movements.

Not only are shocks produced in the muscle by acting
upon its nerve by electricity, but also by applying electric
excitement to the muscle itself. Pinching, percussion, and
cauterization of the nerve are also excitants which provoke
shocks of the muscle.

The character of these movements changes under certain in-
fluences. Fatigue of the muscle, the cooling of that organ, the
stoppage of circulation in its interior, modify the form of the
shock, diminish its force, and augment its duration. Under
these influences the myographic curve passes through different
forms, such as 1, 2, 3, Fig. 4.

Fic, 4.—Character of the shock, according to the degree of fatigue of the
muscle: 1, muscle fresh ; 2, muscle a little fatigued ; 3, muscle still niore
fatigued,

Among the different species of animals, the durations of the
shock vary considerably ; in the bird they are very brief (two
to three hundredths of a second). In man they are longer ;
in.the tortoise and hybernating animals longer still. Certain
poisons modify the characteristics of this movement in so
special a manner, that the slightest traces of those poisons
introduced into the circulation of the animal may be disco-
vered in the form of the tracings.

sy Fig. 5, we may judge of the successive forms which
will be assumed by the shocks of the muscle of a frog, under
the influence of a gradual absorption of veratrine.

These experiments still reveal only one fact: it is that
the muscle is shortened or lengthened by a movement whose

OF MOVEMENT IN ANIMALS. 35

phases vary under the different influences which we have just
described.

If we endeavour to pursue the study of this phenomenon of
the contraction of the muscle, we see that it is only a change
in the form of that organ, and that the diminution of length
is accompanied by a corresponding dilatation which might
be expected in a sensibly incompressible tissue. But the
manner in which this dilatation is produced is curious.

Fic. 5.—Successive transformations of the shock of a muscle becoming
gradually poisoned by veratrine. Underneath to the left of the figure
are shown the first effects of the poison.

It has been long since observed that there are formed upon
living muscles at the points where they are excited, lamps or
nodosities which run along the whole length of the muscle,
with more or less rapidity, like a wave on the surface of the
water. Aeby* has shown that this is a normal phenomenon,
and, under the name of muscular wave, he has described this
movement, which, from the excited point, passes to the two
extremities of the muscle at the rate of about a metre in a
second. By means of an apparatus, which we have called

* Untersuchungen uber die Fortpflanzungsgeschwindiskeit der Reizungs in
der querzgestreijten Muskelfasern. Braunschweig : 1862.

36 ANIMAL MECHANISM.

myographical clips, the reality of this movement of the wave
may be verified in the living animal.

When the wave appears in the muscle, it produces con-
traction. During the whole of its passage the contraction
continues, and when, having reached the end of the muscular
fibre, the wave vanishes, the contraction disappears with it.

These facts resemble those which the microscope reveals in
living muscular fibre. Let a bundle of muscular fibres be
taken from an insect, and placed under the objective of the
microscope (the feet of coleoptera are well suited for this
purpose) ; we first observe the beautiful transverse striation
of these fibres, and then we perceive on their surface an undu-
latory movement often alternating, which resembles the motion
of waves on the surface of water. Oa examining this
phenomenon more closely, we see that the transverse stric
of the fibre are, at certain points, very close together, which
is shown in the figure by a dilatation of the fibre. This
is the wave shown by the microscope; the longitudinal con-
densation of the muscle at this point gives it greater opacity
than in the other portions (Fig. 6.) This opaque wave travels

Fic, 6.—Appearance presented by a wave in muscular fibre.

through the length of the fibre. In other words, the points
at which the strize approach each other are not always the
same, the longitudinal condensation disuppears in one place
whilst it is produced in the contiguous parts.

Since the contraction of the muscle is accompanied by its
transverse dilatation, we may study the characteristics of
the motion produced in a muscle, according to this expansion.
We have succeeded in registering these changes in the
volume of the muscle, as we have registered the changes
in its length. Under these conditions we might study
muscular action in man himself, because there is no need
of mutilation.

Let us suppose a muscle held between the flattened ends of

'OF MOVEMENT IN ANIMALS. 37

a clip; at each of its dilatations the muscle will force open
the clip, and this movement may be registered. ‘This method
enables us to study the phenomenon of the muscular wave,
and the speed with which it travels throughout the whole
length of the muscle.

Fig. 7 exhibits a bundle of muscle held at two points
of its length between the myographical clips, 1 and 2.
Those instruments are so constructed that when their ends
are pushed apart by the dilatation of the muscle, the move-

all |||
mS LL

G. 7.—Disposition of a bundle of muscle between two pairs of myo-
graphical clips. Clip No. 1 holds the electric excitators of the muscle. A
wave is represented at the moment when it has just crossed each of the
clips.

ment compresses a sort of little drum which sends a portion
of the air which it contained through an india-rubber tube
into a similar little drum. Fig. 7 shows two of these instru-
ments fixed upon a foot. The expansion of the membrane
lifts a registering lever, and thus gives notice of the dilatation
of the muscle at the point where it is compressed by clip
No. 1. The movement is shown upon the tracing by a curve
analogous to those which we have already seen.

38 ANIMAL MECHANISM.

Let us suppose that the muscle is electrically excited
the level of the first clip; notice is given of the formation of
the wave at that part of the muscle, but clip No. 2 does
not yet give its signal. In order that it may act, the wave,
as it passes along the muscle, must reach it. As this occurs,
clip No. 2 gives the signal in its turn, and it is shown by
the tracing, that this second movement is later than the first
by a certain space whose duration may be estimated according
to the speed of the rotation of the cylinder.

The influences which modify the intensity and the duration
of the muscular shock have appeared to us to modify the
intensity and the speed of the propagation of the wave. Thus
the two lower curves represented in Fig. 8 show that the
transference of the wave is retarded by cold.

Fic. 8.—Two determinations of the speed of the muscular wave.

The experiment has been made upon the muscles of the
thigh of a rabbit. The clips were placed as far as pos-
sible apart, about seven centimetres. Electricity was applied
to the lower extremity of the muscle, and the two upper curves
of Fig. 8 were obtained. The interval which divides those
curves marks the duration of the transference of the muscular
wave. After the muscle had been chilled with ice the curves
at the bottom of the figure were obtained. We see that the
transference of the wave is slackened, for there is a longer
interval between these curves than between the first.

Production of mechanical force in the muscle. —We have seen
that chemical action is the source of muscular force ; through

OF MOVEMENT

IN ANIMALS. 39

what media does this foree pass before it becomes mechanical

work ?

In steam engines, heat is the necessary medium between
the oxidation of the fuel and the developed mechanical work.

It is very probable that the same
thing takes place in the muscles.
The chemical action produced by
the nerve within the fibre of the
muscle disengages heat from it :
this heat in its turn is itself
partially transformed into work.
We say partially, since accord-
ing to the second principle of
thermo-dynamics, heat cannot be
entirely transformed into me-
chanical work.

Certain facts seem to justify
these views: thus, by warming
a muscle, we change the form of
it, and may see it contract in
length as it expands in breadth.
These effects disappear when the
muscle is cooled.

Muscular fibre is not singular
in its power of transforming heat
into work. India-rubber, for in-
stance, has an analogous property,
and this sabstance may be made
to imitate the muscular phe-
nomena to a certain degree. If
we take a strip of india-rubber
(not vulcanised), and, drawing it
between the fingers, stretch it out
to ten or fifteen times its original
length, we see that it becomes
white, and of a pearly lustre.

Fic. 9.—Transformation of heat into
work by a strip of ind.a-rubber.

At the same time the strip

will become sensibly warm, and it will tend energetically to
return to its original condition, so that if we let go either of
its ends, it will instantly resume its furmer length, aud fall to

40 ANIMAL MECILANISM.

its original temperature. According to our view, tlie sensible
heat has disappeared and become mechanical work. If we
plunge the strip when extended into water, so as to deprive it
of its heat, if remains, as it were, congealed in its extended
state, and does not develop any mechanical work. But if we
restore to the elongated strip the heat which it had lost, it
will recover its elasticity with considerable force. Tig. 9
represents a strip of india-rubber thus pulled out and cov led.
It has been laden with a weight that it may have no tendency
to recover itself. But, if we take the strip between our fingers,
we feel it swell and shorten at the same time that it lifts the
weight ; there is again production of mechanical work.

If we thus heat the strip at various points we create a
series of lateral expansions, each of which raises a certain
quantity of the weight. Lastly, if we heat it throughout all
its extent, the strip returns to its original dimensions, with
the exception of the slight elongation produced by the sus-
pended weight.

Strong analogies exist between these phenomena, and
those which take place in muscular tissue. The identity would
be perfect if the wave which heat produces on the strip of
india-rubber were transmitted to each end. ‘This transference
implies, in the muscular fibre, the successive propagation
of the chemical action which disengages the heat. It is thus
that if we light a train of powder at one point, the in-
candescence spreads throughout its entire length.

These analogies have struck us as being remarkable: they
seem to us to open uew views of the origin of muscular
action.

CONTRACTION AND WORK OF TUE MUSCLES, 41

CHAPTER YV.

CONTRACTION AND WORK OF THE MUSCLES.

The function of the nerve— Rapidity of the nervous agent— Measures of time
in physiology—Tetanus and muscular contraction—Theory of con-
traction — Work of the muscles.

Tue experiments described in the preceding chapter show
us the muscle under artificial conditions, which may, perhaps,
induce us to suspect the results which they furnish. Can
this electrical agent, which has been employed to excite
motion, be assimilated to the unknown agent which the will
sends through the nerves to command the muscles to act?
And these artificially-produced movements, those brief shocks,
always similar if the conditions of the muscle be not changed,
in what do they resemble the motions commanded by the
will, which are so varied in their form and their duration ?
These objections deserve at least a brief discussion.

The function of the nerve. When a nerve is excited by an
electric discharge, the electricity employed does not always
pass to the muscle in which the reaction takes place. The
shock is produced equally well when all propagation of the
electric current along the nerve is prevented, and it exhibits
itself equally when excitants of a quite different nature are
employed, for instance, pinching or percussion. Thus, the
excitant employed only excites in the nerve the transference
of the agent which is proper to that organ. Is not this
nervous agent itself electricity? Notwithstanding the able
labours of the German physiologists, and especially of
M. Du Bois Reymond, science has not yet decided on that
subject. We know that electric phenomena are produced in
the nerve when it has been excited in a certain way, and
that their propagation throughout the nervous cord seems
to have precisely the same speed as that of the transference
of the nervous energy itself. How has this speed been
measured ?

42 ANIMAL MECITANISM.

Helmholtz had the boldness to undertake this incasurement,
and, by determining the speed of the nervous agent, he has
furnished physiologists with a method which enables them to
measure the duration of other phenomena connected with tlie
nervous or muscular functions. Thus the experiment described
above, in which we have measured tlie speed of the trans-
ference of the wave in a muscle, is only an application of the
method of Ilelmholtz.

In order to make thg conditions of this experiment
thoroughly comprehensible, let us make use of a comparison.
Let us suppose that a letter is despatched from Paris to go to
Marseilles, and that, being resident in the latter town, we
should be informed of the precise instant at which the postal
train leaves Paris, while we have nothing to warn us of its
arrival at Marseilles except the knowledge of the moment at
which the letter is delivered there. How ean we, according to
these data, estimate the speed of the mail train? It is clear
that the instant at which we receive the letter does not indi-
cate that of the arrival of the train; for between that arrival
and the distribution, many preliminaries take place, the sorting
of letters, delivery, &c., which require a certain time not
within our knowledge. In order tu have an exact idea of thie
speed of the train which carries the mail, we must receive
a signal of the passage of that train through an intermediate
station between Paris and Marseilles, Dijon, for instance ;
then we shall see that the distribution of letters takes place
six hours sooner ufter the departure from D jon than after the
departure from Paris. Knowing the distance which separates
these two stations, we may ascertain from the time employed
in traversing it, the speed of the train. By supposing this
speed to be uniform, we shall know the hour at which the
train will have arrived at Marseilles, which will give us know-
ledge of the time consumed in the sorting and distribution of
the letters.

Helmholtz, in experimenting upon the nervous motive
agent, first excited the nerve at a point very distant from the
muscle, and noted the time which elapsed between the excite-
ment which despatched the message carried by the nerve, and
the appearance of motion in the muscle. Then acting on a

CONTRACTION AND WORK OF THE MUSCLES. 43

point of the nerve very near to the muscle, he ascertained
that under these new conditions the motion followed the ex-
citement more closely. The difference of time which he
observed in these two consecutive experiments measured the
duration of the transference of the nervous agent along the
known length of the nerve, and consequently expressed its
speed, which varied from 15 to 30 metres per second. It
is feebler in the frog than in warm-blooded animals.

Fic. 10.—Determination of the speed of the nervous agentin man. 1. Shock
produced when the nerve has been excited very close to the muscle.
2. Shock produced by the excitement of the nerve at a farther dista: ce
of 30 centimetres. D, Vib ation of a chronographie tuning-fork vibrating
250 times in a second, serving to measure the time which corresponds with
the iuterval of the shucks.

Now, it results from the experiments of Helmholtz, that all
the time which elapses between the excitement and the motion
is not occupied by the transference of the nervous agent; but
that the muscle, when it has received the order carried by the
nerve, remains an instant before acting. This is what Helm-
holtz calls lost time. This time would: correspond, in the
comparison which we have employed above, with the duration
of the preparatory labour between the arrival of the letters
and their distribution.

Physiologists have repeated the experiment of Helmholtz
with some improvements. In fig. 10 tracings may be seen
which we have ourselves obtained while measuring the speed
of the nervous agent.

Two muscular shocks are successively registered upon the
same cylinder, care being taken that the nerve shall be excited
in the two experiments, at different points, but at the same
instant with regard to the rotation of the cylinder; for
example, at the precise moment at which the point of the

44 ANIMAL MECHANISM.

myograph passes over the vertical which corresponds with the
origin of the lines 1 and 2.

In the experiment which regulated the shock of line 1, the
nerve was excited very near the muscle. In that which was
traced by the shock of line 2, the nerve was excited 30 centi-
metres farther off. As the cylinder turns with a uniform
motion we can estimate the time corresponding with the
distance which separates the two shocks. ‘To facilitate the
measurement of this interval, the vertical lines indicate the
starting points of these shocks; in fig. 10 the interval which
separates them corresponds with a “hundredth of a second,
during which the nervous agent has passed over 30 centi-
metres of nerve, which corresponds with a speed of 30 metres
per second. In order to measure this time with very great
exactitude, we use a method invented by Duhamel. It con-
sists in making the cylinder trace the vibrations of a chrono-
graphic tuning-fork provided for this purpose with a very
fine style, which scratches on the sensitive paper. We have
recourse to this method in all our experiments.

Let us return to fig. 10. If the interval which divides the
starting points of the two shocks corresponds with the time
which the nervous agent has taken to pass along 30 centi-
metres of nerves, tliere is a much more considerable time,
which, for each of the lines 1 and 2, is measured between the
signal of the excitement marked by the first of the three
vertical lines and the first shock. ‘This is the lost time of
Helmholtz; it represents more than a hundredth of a second
in this experiment.

The greater number of authors think that the speed of the
nervous agent varies under certain influences; that heat
augments it, while cold and fatigue diminish it.

It seems to us, on the contrary, that this variability of
duration belongs almost exclusively to those still unknown
phenomena which are produced in the muscle during the
lost time of Helmholtz.

Just as the employcs of the post, fatigued or chilled by cold,
cause delay in the distribution of despatches, without there
having been any change in the speed of the train which has
brought them, so the muscle, according to whether it is rested

CONTRACTION AND WORK -OF TIIE MUSCLES. 45

or fatigued, heated or chilled, executes more or less rapidly
the movement dictated by the nerve.

Besides this, all the influences which cause variation in the
moment at which the shock of the muscle appears, cause
variation of speed in the propagation of the wave in its
interior; which proves that the conditions which accelerate
or retard chemical actions, the first causes of all these phe-
nomena, are solely concerned.

Of the contraction of the muscle. Ilitherto, we have applied
to the nerve only one single excitation, to which one single
motion responded, the muscular shock. Notwithstanding its
brevity, this shock has an appreciable duration; in man it takes
8 or 10 hundredths of a second for the muscle to accomplish
its contraction ; then a longer time for it to resume its normal
length; after which, if it receives a new order from a nerve,
it gives a fresh shock. But if the excitations of the nerve
succeed each other at such short intervals that the muscle has
not time to accomplish the first shock before it receives a
second, a special phenomenon is produced; these movements
are confounded and absorbed into a state of permanent con-
traction, which lasts as long as the excitations go on suc-
ceeding each other at short intervals.

Thus the shock is only the elementary act in the function of
the muscle; it plays therein, after a fashion, the same part as
a sonorous vibration plays in the complex phenomenon which
constitutes sound. When the will ordains a muscular con-
traction, the nerve excites in the muscle a series of shocks
which follow one another so closely that the first las not time
to end before a second begins, so that these elementary
movements combine together and coalesce to produce tlie
contraction.

Volta pointed out, in a letter to Aldini, this singular fact,
that a frog which receives a series of excitations, by the reite-
rated contacts of two heterogeneous metals applied to his
nerve, does not react at each of these contacts, but undergoes
a sort of permanent contraction. Ed. Weber shows that the
action of successive induced currents is of the same kind,
and he has given the name of tetanus to the state of the
muscle thus excited. Helmholtz perceived that the muscle

46 ANIMAL MECHANISM.

vibrates in the depths of its tissue under these conditions of
contraction, because the ear applied to this muscle hears a
sound whose acuteness is exictly determined by the number
of the electric excitations sent to the muscle in a second.

By means of a very sensitive myograph, we have been able
to render visible the vibrations of the muscles under tlie in-
fluence of tetanus-producing shocks.

Fig. 11 shows how this fusion of shocks is manifested
by a contraction of the muscle, permanent in appearance, but
in which the tracing reveals vestiges of vibrations. Vibrations
may be found in the tetanus which strychnine produces in the
muscles of an animal, as well as in that which is caused by
the irritation of a nerve by heat and chemical agents.

Fic 11.—Gradual coalescence of the shocks produced by cle: tric excitations of
increasing frequency.

In short, these voluntary contractions seem to be only a
series of shocks, combining together by the rapidity of their
succession.

It has long been known that by applying the ear to a
muscle in a state of voluntary contraction, we can hear a
grave sound, whose tone several authors have sought to
determine. Wollaston, Houghton, and Dr. Collongue are
almost agreed upon this tone, which would correspond to a
frequency of 32 or 35 vibrations per second. Helmholtz
thinks that this tone of 32 vibrations per second is the normal
sound given out by the muscle in contraction, and according
to his experiments in electric tetanization, he regards this

CONTRACTION AND WORK OF TIIE MUSCLES, 47

number as the minimum necessary to produce the state of
apparent immobility of the electrically tetanized muscle.

If voluntary contraction, studied with the aid of the myo-
graph, furnishes no trace of vibrations, we must not be sur-
prised, since the essential character of that act consists in the
coalescence of shocks. But the existence of the sound which
accompanies the contraction of the muscle sufficiently proves
the complexity of this phenomenon. Let us add another proof
in favour of this theory. When a muscle receives excitations
of equal intensity, the contraction which results from thei is
all the stronger in proportion to their frequency. Now, in
contracting the muscles of the jaws with more or less force,
we have been able to convince ourselves that the acuteness of
the muscular sound increased with the energy of the effort.
We may thus obtain variations of a /ifth in the tone of the
muscular sound,

We shall also see hereafter how the electric state of the
muscles in contraction proves still more the complexity of this
phenomenon.

The conclusion at which we have arrived is, that during
voluntary contraction, the motor nerves are the seat of suc-
cessive acts, each of which produces an excitation of the
muscle. The latter, in its turn, causes a series of acts, each
of which gives birth to a muscular wave producing a shock.
It is in the elasticity of the muscie that we must seek for the
cause of the coalescence of these multiplied shocks; they are
extinguished just as the jerks of the piston of a fire engine
disappear in the elasticity of its reservoir of air.

Of work done by the muscles. After having seen how
mechanical force is produced, let us try to measure it—that
is to say, to compare it with the kilogrammetre, the unit of
measure of work. If we suspend a weight to the tendon
of a muscle which we cause to contract, we easily obtain the
measure of work by multiplying this weight by the height to
which the muscle raises it.

In animated motors, the measure of work is less easy to
obtain. Sometimes, indeed, the strength cf an animal is
utilized in the lifting of a weight, but the greater part of the
acts in which the strength of animals is employed can only

48 ANIMAL MECIIANISM.

be estimated by enlarging the definition of mechanical work.
Thus, a horse which tows a boat, a man who planes a koard,
a bird which strikes the air with its wing, does mechanical
work, and yet they do not lift weights. In order to reduce
cases of this kind to a general definition, we must admit as
the expression of work, the effort multiplied by the space traversed.
This effort, besides, may always be compared with the weight,
the lifting of which would necessitate an equal effort, so that
we say of a traction or an impulse, that it corresponds with
10 or 20 kilogrammes. When a workman planes or turns a
piece of metal, if the tool which he drives into it penetrates
only on condition of receiving an impulse of one kilogramme,
the workman, in order to have effected a kilogrammetre of
work, ought to have detached from the mass a shaving of a
metre in length. A horse which tows a boat with 20 kilo-
gramme force, will have employed a force of 20,000 kilo-
grammetres when he has gone 1,000 metres.

But still that is not yet sufficient to be applied to all the
forms of mechanical labour. If, for example, force be em-
ployed to displace a mass, the effort necessary for the move-
ment will vary with the speed which is given to that mass.
Let us imagine a block of stone suspended freely at the end
of a very long rope; the lightest pressure applied to this
block for a few instants will produce movement in it, while
the strongest blow of the fist will scarcely cause any sensible
displacement, because the force requisite to displace masses
increases according to tle square of the speed which is com-
municated to them.*

A force of very short duration applied to a mass, produces
only a shock incapable of displacing it. But this same shock,
if it be exerted by means of an elastic medium, is transformed
into an act of longer duration, and without having added
anything to the quantity of motion, becomes capable of pro-
ducing work.

This elasticity intervenes in the auimal economy to permit
the utilization of the very brief act which constitutes the
formation of the muscular wave. ‘The formation of the wave,

m v2,

* This action is expressed by

OF ELECTRICITY IN ANIMALS, 49

which lasts only for some hundredths of a second, represents
the time of application of each element of the force of the
muscle. At each new wave, there would be produced a true
shock if the elasticity of the fibre did not extinguish this
abruptness, and transform these jerky little contractions into a
gradual increase of teusion which constitutes the prolonged
effort of the muscle.

A motor only works on the double condition of developing
an effort, and accomplishing a motion. Thus a muscle which
contracts, performs no external work, except while it is con-
tracting; as soon as it has reached the limit of its contraction,
it ceases to work, whatever may be the effort which it
develops. When we sustain a weight after having lifted it,
the act of sustainment does not constitute work.

But, in tliese conditions, to maintain the elastic force of the
muscle, the same acts are produced in its interior as during
the work; the muscular waves succeed each other at short
igtervals, and heat is disengaged by chemical action. Now,
this heat, which cannvot transform itself into action, ought
to remain in the muscle, and heat it strongly, ‘This is pre-
cisely what we observe, so that in the malady called tetanus,
which consists of a permanent tension of the muscles, it
is ascertained that heat is produced with an exaggerated
intensity, the temperature of the entire body rising several
degrees.

CHAPTER VI.

OF ELECTRICITY IN ANIMALS.

Electricity is produced ih almost all organised tissues—Electric currents
of. the muscles and the nerves—Discharges of electric fishes ;_ old
theories ; demonstration of the electric nature of this phenomenon —
Analogies between the discharge of electrical apparatus and the shock
of a muscle—Electric tetanus—Rapidity of the nervous agent in the
electrical nerves of the torpedo ; duration of its discharge.

Mosr of the animal or vegetable tissues are the seat of
chemical actions, whence result an incessant disengagement
of electricity. In this way, the nerves and muscles of an

50 ANIMAL MECIIANISM.

animal furnish manifestations of dynamic electricity. Mat-
teucci has discovered the manner in which the muscular
current is usually produced. Du Bois Reymond has added
much to our knowledge of this current, of its intensity, and
of its direction in every part of a muscle. Treatises on phy-
siology give copious details of experiments relative to nervous
and muscular electric currents. This study has been the
more eagerly pursued becaus3 the proximate cause of the
function of the nerves and muscles was expected to be found
in these electric phenomena.

The most interesting fact connected with muscular elec-
tricity, with respect to the transformation of force, appears to
be the disappearance of the electrical state of a muscle at the
moment when it contracts, or when it is tetanized. It appears
then that the chemical actions of which the muscles are the
seat, are entirely employed in the production of heat and
motion.

To observe these phenomena, we must make use of a ver
sensitive galvanometer. Suppose a muscle connected with one
of these instruments; it gives its currents, and deflects the
magnetic needle a certain number of degrees. When this de-
viation has been effected, and the needle lias become stationary
in its new position, it is only necessary to produce tetanus in
the muscle, and immediately the needle retrogrades towards
zero. Thisis what Du Bois Reymond calls the negative varia-
tion of the muscular current. ‘The same phenomenon is
ubserved in the voluntary contraction of the muscles.

The interpretation of the negative variation is very im-
portant. Du Bois Reymond having remarked, that for a
single muscular shock no deflection of the needle from zero is
obtained, coucluded that this is on account of the short dura-
tion of the electrical disturbance accompanying a shock. In
tetanus, on the contrary, a series of modifications in the
electrical coudition of the muscle correspond to the series of
shocks produced—their accumulated influence deflects the
magnetic needle,

This phenomenon is familiar to physicists: It is known
that the needle of a gulyanometer suljected to a frequently-
interrupted current, takes a fixed position intermediate be-

OF ELECTRICITY IN ANIMALS, 51

tween zero and the extreme point which it would have occupied
if the current had been continuous.

In the muscles in which the shock is protracted, as in
the tortoise, a very prolonged change in the electrical state is
produced; and therefore these muscles can by each of their
shocks cause a deflection of the magnetic neelle. It is the
suiné with the movements of the heart; each of these appears
to be only a shock of the cardiac muscle, and yet it deflects the
magnetic needle in the same manner as tetanus of an ordinary
muscle. This fact, that a negative variation is equally seen
in a muscle which is contracted voluntarily, is of the greatest
importance. It confirms the theory which assimilates con-
traction with tetanus, that is to say, with a discontinuous or
vibratory action.

One point which has been long under discussion relative
to the manifestations of muscular electricity, is whether the
negative variation is caused by a change of direction in the
musculw eurrent, or by a transitory suppression of this
eurrent. ‘The latter hypothesis has been rendered extremely
probable by the numerous experiments in which the needle
of the galvanometer has never been seen to retrograde beyond
the zero point. Thus the phenomenon of negative variation
seems to prove the principle which we laid down at the com-
mencement of this article, that force is manifested in the
muscles in a different manner during activity and repose, and
that the manifestation under the form of mechanical work is
substituted for that under the form of electricity.

Electrie fishes. —Anuimal electricity appears in a much more
striking form in the discharges produced by certain fishes.
In this case the special organs have for their object the pro-
duction of electricity; nevertheless, by their structure, their
cheniical composition, and their dependence on the nervous
system, these organs remind us of the conditions of the mus-
cular apparatus.

The number of species provided with electrical organs
which was formerly restricted to five,* has been remarkably

* The five species formerly known were the Raya torpedo, the Gym-
notus electricus, the Silurus electricus, the Tetraodon elcctricus, and the
Trichiurus electricus.

52 ANIMAL MECHANISM.

increased since Ch. Robin has shown that ail the species of
the genus ray have electrical apparatus and functions in a
more or less rudimentary condition. Besides, the analysis
of this singular act, which is called the electric discharge, las
been better studied, as physicists have then selves learned the
different properties of the electric agent.

In the 18th century, they said, when speaking of the torpedo,
that “this fish when it is touched throws out a kind of
venom which paralyses and benumbs the hand of the fisher-
man.’ Muschenbroeck, in the last century, ascertained the
electrical nature of the torpedo's discharge. Walsh, in 1778,
saw plainly that the numbness produced by this animal differs
in no respect from that which is caused by the discharge ofan
electrical machine. He proved by a great number of experi-
ments, that the effect produced by this fish is manifestly
electrical. He subjected the discharge to a series of trials,
in which it had the same effect as the electricity deve-
loped by machine. For instance, he showed that the animal
might be touched with impunity, by taking as a medium of
communication non-conductors of eleciricity. Besides, he made
the discharge pass through a chain of individuals holding each
other by the hand, and ull felt the same singular effect which
is produced by the Leyden jar.

At a later period Davy obtained with the current of the
torpedo the deflection of the galvanometer, the magnetization
of steel needles placed within a spiral of brass wire traversed
by the discharge, and the decomposition of saline solutions.

Becquerel and Breschet verified the same facts in the wire
of the galvanometer, the current circulating from the back to
the belly of the animal.

The demonstration of the spark came still later. Father
Linari and Matteucci obtained this spark by breaking in
various ways a metallic circuit through which the current of
the torpedo was passing. The inost ingenious process is that
of Matteucci, who made use of a file in the following manner :
A metallic plate attached to a brass wire is fixed under the
belly of the torpedo; on its back is placed a file on which the
end of a metallic wire rubs. The animal is then irritated,
and one or even several sparks are scen in the dark to pass

OF ELECTRICITY IN ANIMALS. 53

between the wire and the file. The production of the spark
is probably effected when the circuit is broken at the precise
moment of the passage of the torpedo’s current,

The use of the file is clearly seen, since the friction
causing the circuit to be closed and broken at very short
intervals, some of them will necessarily coincide with the dis-
charge, as it has but a short duration. Let us observe, in
passing, that the production of two sparks during the discharge
of the torpedo, shows very clearly that it hasan appreciable
duration, measured at least by the time which has elapsed
during the passage of tle wire across two successive teeth of
the file.

A. Moreau succeeded in collecting this electricity on a con-
denser which allowed him to measure the variation of the
intensity of the discharge by the indications of a gold leaf
electroscope. We have seen how our acquaintance with the
electrical phenomena of the torpedo has passed through many
successive stages, and how the progress of physical inquiry
has, on this subject, invaded the domains of physiology.

Nevertheless, the discharge of the torpedo, as the above-
mentioned experiments have shown, seeins like a kind of
hybrid phenomenon, in which the effects of tension machines
appear to be confounded with those of a galvanic battery.
We must, by new researches, endeavour to assign the place
in the series of well-known manifestations of electricity, which
the discharge of electric fishes ought to eceupy.

Considered in a physiological point of view, this pheno-
menon possesses another kind of interest. The most receut
discoveries tend to assimilate the function of this electrical
apparatus with that of a muscle. If, for example, we com-
pare the action of the nervous system on the electrical organs
of certain fishes, with that which the nerve exercises over the
muscle, we are struck with the following analogies :—

The electrical discharges, like muscular shocks, can be
produced under the influence of the will of the animal; they
may also be considered as reflex phenomena; excitation of
the electric uerve produces the discharge, as that of the motor
nerve produces, the shock of a muscle; an entire paralysis of
the electrical apparatus takes place when the nerve is cut, as

54 ANIMAL MECIIANISM.

in a muscle v. hen its nerve is divided. This paralysis takes
place also under the influence of curare, although this poison
appears to act more slowly on the electric nerves than on the
greater part of the nerves of motion. Indeed, the electric
tetanus, to employ the happy expression of A. Moreau, is
manifested, not only when the nerve of the torpedo is sub-
jected to excitations very rapidly succeeding each otker, but
ulso when the animal is poisoned with strychnine or any
other tetanizing substance.

It was natural enough to compare the different cells or
laminae of the electrical apparatus in fishes, with the elements
of the voltaic pile, and following up this idea, to inquire what
was the electro-motive power of each of these little elements,
and what were the effects of tension resulting from the
association of these pairs. The following is the result of the
experiments of Matteucci.

A portion of the electrical apparatus of the torpedo, placed
en rapport with the extremities of a gulvanometer, gives
birth to a current of the same order as that in the apparatus
of which it formed a part. The longer the prism thus
detached, the more numerous must be the elements of this
kind of animal pile, and the greater the deflection of the gal-
vanometer at the moment of its discharge; this is produced
by exciting the nervous fibre which corresponds with the
small portion of the electrical apparatus of the torpedo placed
on the pads of the galvanometer. ‘Thus far, the analogy of
the electric apparatus with the pile is perfect, since the effects
of tension increase with the number of elements which are
employed. This analogy holds good with all the electrical
fishes, when we endeavour to compare the intensity of the
currents obtained in diflerent parts of the apparatus.

In the torpedo it is found that the discharges are at their
maximum when we touch the two surfaces of its apparatus on
the inner side, that is to say, at the thickest part, which con-
tains the greatest number of discs superposed on each other.
In the gymnotus, whose electrical prisms have so great a
length, it is found that the discharge is stronger still, on
account of the greater volume and number of the elements.
It is proportional to the extent of space contained Letween the

OF ELECTRICITY IN ANIMALS, 59

two points which receive this impulse. In the silurus it is
tle same; a much greater impression is made on us when
we touch different points of the animal at a greater distance
from each other.

In fact, we may receive a discharge from a single surface
of the electric apparatus of the torpedo, by touching unsym-
metrical parts, that is to say, points where the number of
the elements of the pile is not so great, because of the
different length of the prisms which compose it. Thus,
although the polarity may be identical on the same surface of
the apparatus, the fact of the inequality of electric tension
on the different points of this surface suffices to create the
possibility of a current, and to determine its direction.

As to the origin of the electric force, we think that no one
can now see anything in it but the result of chemical actions
produced in the interior of the apparatus

But before they arrived at this opinion, physiologists ad-
vanced many hypotheses as the source of animal electricity.
Thus, when Du Bois Reymond had shown that the nervous
tissue possesses an electro-motive force sufficiently powerful,
and that there exists in living nerves a current in a constant
direction, it was thought that the voluminous nerves which
belong to the electrical apparatus of fishes carry electricity
to it, as the blood-vessels supply blood to the organs. Mat-
teucci has demonstrated that a large lobe of the brain of the
torpedo is the origin of the nerves belonging to its electrical
apparatus. Ile has observed that it is possible to remove all
the rest of the brain, without depriving the animal of the
power of giving voluntary or reflex discharges; but that it
can no longer do so when this lobe is destroyed. Ho has for
this reason named this the electric lobe of the torpedo,

When a dying animal no Jonger gave spontaneous dis-
charges, it was sufficient, said Matteucci, to touch the electric
lobe in order to obtain discharges more violent than those
which the animal gave voluntarily during the state of perfect
activity.

Nevertheless, the notion of Matteucci has been exaggerated,
when this thought was attributed to him, that electricity is
formed in the brain of the torpedo, and is conveyed by its

56 ANIMAL MECHANISM.

nerves. It is as much as to say that the motive force is created
in the brain and conveyed to the muscles by the nerves of
motion. ‘The electricity of the torpedo has its origin in the
special organ of this fish—as mechanical work is originated
in a muscle. When we see the phenomena of electricity
or of motion produced, the motive or electric nerves fulfil
only the duty of transmitting the order received from the
brain; but the electricity which circulates in the nerves is
not that which is manifested so energetically in the discharge
of the apparatus. It is, says Matteucci himself, as if we
were to confound the effect of the gunpowder with that of
the priming which has been used in order to fire the charge.

Thus, the most probable theory is that which assimilates
the electric nerves to those of motion, the discharge to a
muscular shock, the series of discharges to tetanus.

In order to verify this theory, we have endeavoured to
ascertain* whether the nerves of the torpedo carry out the
commands of the will with the same rapidity as the nerves of
motion; if, when the electric apparatus -has received the order
transmitted by the nerve, it hesitates, like the muscle, an
instant before it re-acts (ost time); in fact, whether the dis-
charge of the torpedo, contrary to those given by tension
machines, possesses a certain duration which may be compared
to that of the shock of a muscle.

It lias been seen, that heat, cold, the ligature of the arteries,
and the action cf certain poisons modify considerably the form
and duration of the muscular shock. If experiment showed
that as to its retardation, its duration, and its other phases,
the torpedo’s discharge corresponds with the shock of a muscle ;
if it is proved, that in both cases, the same agents produce thie
same effects, we should be right in assimilating still more
completely the electrical phenomena with those of motion; the
physiology of the furmer would illustrate, in many points,
that of the latter.

During a stay of a few weeks at Naples we have been
able to sketch out this mode of inquiry, which has furnished

* Sce, for the details of these experiments, ‘‘ Journal de Vunatoimie et
de la physiologic.” 1872.

OF ELECTRICITY IN ANIMALS, 57

results as yet incomplete, but which tend to assimilate the
electrical with the muscular action. These results are as
tollow :—

1. The rapidity of the nervous agent in the electrical nerves
of the torpedo seems evidently to be the same as that of the
nervous agent producing motion in the frog.

2. The phenomenon called by Helmholtz lost time exists
also in the electric apparatus of the torpedo, and lasts about
the same time as in the muscle.

3. The discharge of the torpedo is not instantaneous, like
that of certain kind of tension electrical apparatus, but it
is prolonged about fourteen hundredths of a second ; which is,
in a remarkable degree equal to the duration of a shock in a
frog’s muscle.

We cannot enter here into the details of the experiments
which have furnished these results, but we will endeavour, in
a few lines, to explain the method which we employed.

Registering apparatus measure the slightest intervals of
time; this we have seen in speaking of the estimated rapidity
of the nervous agent. But, in order to employ the graphic
method, we must have motion to give the required signal.

Thus, in the experiment of Helmholtz, the muscular shock
itself announced that the order of movement which the nerve
had to convey had arrived at its destination.

In order to obtain the signal of the electric discharge, we
have employed it to excite the muscle of a frog, the shock of
which was inscribed on the registering cylinder.

The trace furnished by the frog-signal is somewhat delayed,
it is true, after the excitation has been produced; but this
delay is a known quantity, and it can easily be taken into
account. é

The following is the method adopted to measure with the
ordinary myograph the duration of the different acts which
precede the discharge of the torpedo.

In a preliminary experiment (fig. 12) the nerve of the frog
was directly excited, and a note was taken of the time (e g)
which elapsed between the instant (e) of the excitation, and
the signal (y) given by the frog.

In a second experiment the torpedo was excited, still at the

4

5S ANIMAL MECHANISM.

instant (e), and the electricity of its discharges was collected
by means of conducting wires which sent it to the nerve of
the frog signal. ‘This would give its shock at the point (¢).

EE Pere

Fic. 12.—Measur of the time which elapses between the excitation of
the electric nerye, and the discharge of the torpedo.

The difference (g t) would express the time consumed by
the torpedo between the excitetion of its nerve and the’ dis-
charge. By varying the experiment, as we have done for the
motive nerves (page 43), we obtain the measure of the
rapidity of the electric nervous agent, and that of the lost time
in the torpedo apparatus.*

Finally, in order to measure the duration of the electrical
action, we had recourse to a method which consists in col-
lecting this discharge during a very short time (1-100th of a
second) to send it to the frog signal, and varying gradually the
instant at which the electricity of the torpedo was collected.
It was thus ascertained that starting from the point (t) one
might, during 14-100ths of a second, obtain a series. of signals
from the frog—t’, t’, ¢’”, t’’’, but that beyond that time the
frog gave no signals, thus proving that the discharge had
terminated.

We have not been able to follow out farther the compari-
son of the electric with the muscular action; but, according
to the results already furnished by experiment, we can foresee

* Deprived of appropriate apparatus, we have been obliged to construct

for ourselves a kind of registering instrnment which should measure short
intervals of time with sufficient precision. We refer the reader, for the
real arrangement of the experiments, to the ‘‘ Journal de l’anatomie et de
la physiologie,” loc. cit. Fig. 12 represents tracings which one would
obtain with the registering instruments already known.

ANIMAL MECHANISM. 59

that new analogies will still show themselves between these
two manifestations of force in living beings, mechanical work
and electricity.

CHAPTER VII.

ANIMAL MECHANISM.

Of the forms under which mechanical work presents itself— Every
machine must be constructed with a view tothe kind of work which
it has to perform—Correspondence of the form of muscle with the work
which it accomplishes—Theory of Borelli—Specific force of muscles
—Of machines; they only change the form of work, but do not
increase its quality— Necessity of alternate movements in living
motive powers—Dynamical energy of animated motors.

If we have lingered long over the origin of heat, of
mechanical work, and of electricity in the animal kingdom,
it was in order to establish clearly that these forces are the
same as those which are seen inthe inorganic world. Certain
evident differences must have struck the earlier observers, but
the progress of science has shown, more and more clearly,
this identity, which is now disbelieved only by those whose
minds are still under the influence of obsolete theories.

Mechanical force, to which our attention must now be
exclusively directed, has hitherto been studied only in its
origin; we must follow it through all its applications to
work of different kinds which it executes in animal me-
chanism.

In all the machines employed in the arts we must have
organs which serve as media between the forces which we
employ and the resistance which are required to be overcome.
This word organ is precisely that which anatomists use to
designate the portions which compose the animal machine.
The laws of mechanics are applicable as well to animated
motors as to other machines; this truth, however, has to be
demonstrated, but, like many cthers, it was for a long time
unrecognized.

60 ANIMAL MECHANISM,

Of the forms of mechanical work. —When we have at our
disposal a certain quantity of force, it is necessary, in order to
utilize it, to collect it under conditions which vary according
to the nature of the effects which we desire to produce.

We have seen that the measure of work actually employed
is the product of the resistance multiplied by the space
through which it has to pass. Sucha measure, being the
product of two factors, may remain constant if the two factors
vary inversely. So that a considerable weight, raised to a .
slight height, will give the same result of work as a light
weight raised to a greater height.

These will be two different forms of the same quantity of
work ; but, in this case, the form is of extreme importance.
In order that the work applied should be available, it is ne-
cessary that its form should be the same as that of the
resisting foree—that is, of the work required to be done.

If we have as a moving power a piston of a steam engine
of large diameter and short length, capable of lifting 100
kilogrammes to the height of a centimetre, and that it is
necessary with this generator of force to lift one kilogramme
to the height of a metre, which equally represents a kilo-
grammetre of work, the motive force in this machine cannot
be utilized directly ; for at the end of the stroke of the piston
the weight of a kilogramme will only have been lifted
one centimetre, and 5%°, of the force at our disposal will re-
main unemployed. Every machine, therefore, must be con-
structed with a view to the special form under which the
resistance to be overcome presents itself.

It is true that by means of certain contrivances, levers or
wheel-work properly combined, it is possible to cause a cer-
tain quantity of work to pass from one form to another, and
to apply it to the resistance to be overcome. But this will
be the object of ulterior study. We have only to consider at
this moment the case in which the force is directly applied
to the obstacle which it has to surmount, which is a very
frequent condition in animated motive powers.

Let us return, then, to the hypothesis in which the moving
force of the piston of an engine must be applied directly to
overcome resistance. Under these conditions the constructor

ANIMAL MECHANISM. 61

will be careful to give to the surface of the piston such an
area, that the pressure on this surface may be precisely equal
to the resistance which it has to overcome; then he will give
to the cylinder such a length that it will allow the piston to
travel just as far as the resistance ought to move. It is only
under these conditions that the machine will do the desired
_ work, and utilize all its moving power. On the contrary,
in the case in which work answering to a kilogrammetre
must be done by lifting 100 kilogrammes to the height of a
centimetre, the cylinder must be made so large that the pres-
sure of steam on the surface of the piston will develop an
effort of 100 kilogrammes, and such a length only must be
given to the cylinder, that the movement of the piston may
be merely a centimetre,

One cannot substitute one of these forms of cylinder for
the other, for in one case the force would be insufficient, and
in the other, the range would be too restricted.

The only thing which is equal in both is the amount of
work that the two machines can do, that is to say, the pro-
duct of the force employed multiplied by the space passed
through; this is again the product of the surface of a section
of the cylinder multiplied by its length, or, in other terms,
it is the volume of steam contained in each machine, this
vapour being supposed to be at an equal tension.

This proportion of the volume of the matter which works
to the work performed, is found in every case in which a
moving force is employed.

Two masses of lead falling from the same height will do
work proportionate to their volume, or, which is the same
thing, to their weight. Two threads of india-rubber of the
same length, both of which have been stretched to the same
degree, will do work proportionate to their transverse sec-
tions, and, consequently, to their respective weights. Lastly,
two threads of the same diameter, but of unequal lengths,
after having been subjected to the same elongation in pro-
portion to their original lengths, will, as they contract, do
work proportionate to their respective lengths, that is to say,
to their weight.

This leads to the consideration of muscle, which conforms

62 ANIMAL MECHANISM.

rigorously to the general laws which we have just enunciated.
The larger a muscle is, that is to say, the more extensive is
its surface, the more susceptible it is of considerable effort.
But, on the other hand, a muscle contracts only in proportion
to itsown length. We may estimate that the mean shortening
of a muscle while contracting, when it is not detached from
the animal, is about a third of its length when in repose. It
follows that the work done by a muscle will be in proportion
to its length and its transverse section; that is to say, to its
volume or to its weight.

Thus, it is possible to ascertain, according to the anatomi-
cal characters of a muscle, what is the force which it pos-
sesses, relatively to that of other muscles of the same animal,
and what is the form under which its work is done.

The substance of the muscles, that is to say, of red flesh,
presents the same density in the different parts of the animal
frame; in consequence of which the weight is the most exact
and the most expeditious method of estimating the relative
importance of two masses of muscle, and of predicting the
quantity of work which they are able to execute.

As to the form under which muscular work must be pro-
duced, it is deduced not less easily from the form of the
muscle. If it be thick and short, it should produce a strong
effect multiplied by a short range; if it be long and slender
it will have a more extended range, but will only develop
feeble energy.

There are many examples in proof of tliis law which
regulates muscular action—the sterno-mastoidal, the sarto-
rius, and the rectus abdominis, are muscles of a long range,
or, as it may be otherwise expressed, having a great ex-
tent of movement; they have a fleshy portion of greater
length. The large pectoral muscle, the gluteus maximus,
or the temporal muscle are large and short muscles, that
is to say, capable of a considerable effort, but of slight
contraction.

Borelli already understood the laws of muscular force ;
without the intervention of the notion of work, which was not
introduced into mechanics at the time when he lived; he
made a very clear distinction between these two opposite

ANIMAL MECHANISM. . 63

characteristics of the action of a muscle according to the
impulse of its volume or its length. And as a theory is
always required to satisfy the mind, this author sought to
interpret these different effects by a theory of the structure of
the muscles.

Let us imagine, said he, a minute chain of metal formed
of circular elastic rings, and that an extensile force should be
exerted on this chain. Each ring will change its shape and
assume an oval form, and the whole chain will be lengthened
in proportion to the number of its rings. When it recovers
itself, under the influence of elasticity, the chain will grow
shorter again in proportion to its length. The minute chain
of Borelli is the primitive fibre revealed to us in the animal
economy by the microscope. But, said Borelli, if we form a
bundle of a great number of these chains, each one of them
will resist the extensile force in proportion to the elasticity of
its rings, that is to say, the thickness of the bundles, and the
force with which the extended bundle will recover itself will
be in the same ratio.

We do not reason otherwise now that histology has shown
us, in a muscle, a bundle of fibres whose actions are com-
bined like the chains suggested by the Naples professor.

Passing to other considerations, this author studied the
influence exerted by the direction of the fibres on the force
which they develop. He remarked that the muscles whose
fibres converge obliquely on the same tendon, like the barbs
of a feather on the central shaft, afford neither a range nor
an effort proportionate to their length and their sections. We
have no modification to make of this estimate of the composi-
tion of forces in the muscular organ.

Of the specific force of muscles.— In the machines constructed
by man, it is not enough to measure the longitudinal and
transverse dimensions of the cylinder, in order to know what
quantity of work each stroke of the piston will develop; we
must also know under what pressure the steam acts. ‘That
is estimated by the number of atmospheres it can lift as it
escapes. At other times the force of the steam is measured
by the number of kilogrammes of pressure which it exerts on
every square centimetre of the surface of the cylinder. In

64 ANIMAL MECHANISM,

every case it is an estimate of the specific force of a certain
volume of steam which is to be determined.

In the same manner, in hydraulic machines, we must know
the charge of water or its pressure, in order to ascertain the
work which the machine can perform.

Physiologists have also sought to determine the specific
force of muscular tissue in different animals, and to compare
with the unit of transverse section of muscle the effort which
it can make. In this manner they have estimated that the
muscle of the frog would develop an effort of 692 grammes
(E. Weber) for each square centimetre of section ; that human
muscle would develop 1087 (Koster). In the bird the force
would be about 1200 (Marey); in the insect it would be still
greater (Plateau).

According to Straus Durkheim, a muscle of the stag-beetle
weighing 20 centigrammes would carry, if we measure the
moment of power and that of resistance a weight of seven
kilogrammes.

By such estimates as these, we might compare animated
moving powers with machines working under variable pres-
sures. The frog, we might say, works with a pressure less
than one atmosphere, man with a pressure greater than one
atmosphere. ‘There would be a greater pressure in the bird,
and still greater in the insect.

Of machines.— When mechanical force cannot be directly
utilized, because it is not in harmony with the form of work
which it ought to effect, various means are employed in the
arts to transform it. Machinery known under the names of
wheels and levers are continually used for this purpose. In
the animal organism contrivances are also found which change
the form of the work of the muscles. The lever is almost
exclusively used by nature for this purpose. The arrange-
ment of the bony levers which form the skeleton is so generally
known that it needs no explanation here; but there is a very
common error on this point, even among physiologists, which
it is necessary to point out.

Almost all the levers which are found in the organism belong
to the third order, that is to say, where the muscular force is
applied between the fulcrum and the resistance. Under these

ANIMAL MECHANISM. 65

conditions, the effort that can be developed at the extremity of
the lever is less than that of the muscle; but the space passed
through by this extremity of the lever is proportionately
increased, so that the product of the force multiplied by the
distance remains the same.

Thus, we find in a great number of standard treatises, a
sort of accusation brought against nature, for having entirely
wasted a great part of the force of our muscles by causing
them to act under a disadvantageous leverage. It is true,
that to extenuate this fault, they are willing to grant that
this arrangement, unfavourable in an economical point of
view, gives to our muscles an elegance which they would not
have possessed, if for example, a long muscular band had
extended from the sternum to the wrist. These mechanical
and esthetic notions ought to give place to more correct ideas.
We must, above all, remember that a muscle produces work
corresponding to its volume or its weight, whatever may be
the proportions of the lever to which it is attached. The
effect of the latter is only to regulate the form under which it
produces the work, without adding to it or subtracting from
it. An error of the same kind is often committed in con-
sidering the part played by levers made use of by man in his
work. It often happens that human force is unable to raise
certain weights; we have recourse in these cases to levers of
the first or second order, in which we increase the power of
the arm in the ratio of the longer to the shorter arm of the
lever.

In this manner we utilize a motive force which could not
produce external work if we endeavoured to bring it to bear
directly on the resistance to be overcome. But a lever which
amplifies the force exerted, diminishes as much the extent of
the work produced; it adds nothing to the work executed by
the motive power.

Before the notion of work had been introduced into
mechanics, and when it was not clearly understood that it was
impossible to increase by mechanism the amount of force at
our disposal, many false ideas were entertained with regard
to the part played by machinery. When we consider those
gigantic masses of stone the pyramids of Egypt, or those

al

635 ANIMAL MECHANISM.

enormous blocks, called dolmens, which our forefathers
erected in prehistoric times, it was admitted that these
Titanie works pre-supposed a very advanced knowledge of
mechanism. Even now it would require an immense time,
or an army of workmen, to execute similar works by employ-
ing only the force of man and that of animals.

We must not imagine that the old Gauls or ancient
Egyptians-were able to escape from the inevitable necessity of
employing many men or an enormous lapse of time in these
labours at the period when the only source of mechanical
work was that derived from living beings.

But we live under new and better conditions, thanks to
the invention of machinery whith develops mechanical work.
In addition to the utilization of natural motive powers, such
as water courses and wind, man is now able to employ steam
engines, by means of which a small quantity of fuel does the
work of a great many animals. It is by these means that
Egypt has succeeded in a few years in cutting through the
Isthmus of Suez, an enterprise which, four thousand years ago,
would have absorbed the efforts of many generaticns.

Necessity of alternate motion in living motive powers.—When
the piston of a machine has reached, the end of its stroke, the
steam which impelled it must escape, and the piston must
return in the opposite direction to accomplish fresh work.
In the same manner, the muscle, after having contracted,
must be relaxed in order to act afresh. But mechanicians
have found that in the alternate movements there is a loss of
work. When a heavy object impelled forward with rapidity
has to be brought back in the opposite direction, it is neces-
sary first to destroy the work which it contains, so to speak,
under the form of active force. Precisely in the same manner,
when a limb suddenly extended is required to be rapidly bent,
the momentum acquired must first be destroyed; to do which
requires an expenditure of work.

To guard against this loss of motive power, mechanicians
have recourse, as much as possible, to the employment of
circular movements instead of motion to and fro, © ‘Thus, man
who is so often inspired in his inventions by the arrange-
ments of which nature offers him examples, deviates in this

ANIMAL MECHANISM. 67

ease from his model; he endeavours to surpass it, and he is
right. To make this understood we cannot do better than
quote a passage in which L. Foucault compares the screw-
propeller of ships to the organs of swimming in fishes :—

“Tn our machines,” said he,* ‘‘ we have usually a great
number of parts entirely distinct one from the other, which
only touch each other at certain points; in an animal, on the
contrary, all the parts adhere together; there is a connection
of tissue between any two given parts of the body. This is
rendered necessary by the function of nutrition which is
continually going on, a function to which every living being
is subject during the whole of its existence. We can, besides,
understand the absolute impossibility of obtaining a con-
tinued movement of rotation of one part on another, while
still preserving the continuity of these two parts.”

Thus,:a profound difference separates mechanisms employed
by nature from those invented by man; the former are sub-
ject to special requirement from which the latter can be freed.
The muscle can only act under the condition of being attached
by its vessels and nerves to the rest of the organism. No
portion of the body, not even the bones themselves, which
have the least vitality, can be free from this necessity.

One might find, in the animal organism, many other
mechanical appliances, the arrangement of which resembles
that of machines invented by man, but with differences ever
of the same kind as those which we have just described.

For instance, the circulation of the blood is effected in living
beings by a veritable hydraulic machine, with its pump, valves,
and pipes. But the fundamental difference between this
complicated mechanism and machines constructed by man,
arises from the absence of independent portions, and especially
of the piston. ‘The heart is a pump without a piston, and its
variations of capacity are obtained by the contractility of
the coats of the vessels themselves. With the exception of
this difference, we find perfect analogies between the circula-
tory apparatus of animals and hydraulic motive powers. The
function of the valves is identical in both in spite of apparent
differences,

* « Journal des Débats,” Oct. 22, 1845.

68 ANIMAL MECHANISM.

We have formerly noticed in the cirenlation of the blood an
influence which regulates and increases the effective work of the
cardiac pump; it depends on the elasticity of the arteries.*
In like manner, in hydraulic machines, man has recourse to the
employment of elastic reservoirs, to utilize more fully the work
of pumps, and to render uniform the movement of the liquid,
notwithstanding the intermittent character of the motive
power. This effect may be compared to that which we have
before remarked in the elasticity of muscles.

Dynamic energy of animated motors.—Animated motive
powers and machines are subject to the same estimation of
work; it is the dynamic energy of the former as compared
with the latter.

The production of external work corresponding to 75 kilo-
grammetres per second, has been called the horse-power, or,
in more general terms, the motive power of one horse, it being
supposed that one horse could develop the same amount of
work.

But animal motors cannot work incessantly, so that the
horse-power would represent at the end of the day a much
greater amount of work than the animal could have produced,
had it been employed as a motive force.

Man is estimated much lower as to his dynamic energy,
(+'7 of a horse-power), and yet, if we only require from the
muscular force of a man an effort of short duration, it will
furnish dynamic energy exceeding that of a horse-power. In
fact, the weight of a man is often more than 75 kilogrammes ;
each time that the body is raised to the height of a metre
per second, in mounting a staircase, the man has effected
during this second the work adequate to one horse-power.
And if, during several instants, he can give to his ascent the
speed of two metres per second, this man will have developed
the work of two horse-power.

Thus, in our estimate of the work done by the greatest or
the smallest animals, we must consider it as a multiple or a
fraction of the ordinary measure of horse-power.

* < Physiologie médicale de la circulation du sang.”

ORGAN AND FUNCTION. 69

CHAPTER VIII.

HARMONY BETWEEN THE ORGAN AND THE FUNCTION.—
DEVELOPMENT HYPOTHESIS.

Kach muscle of the body presents, in its form, a perfect harmony with the
nature of the acts which it has to perform—A similar muscle, in
different species of animals, presents differences of form, if the
function which it has to fulfil in these different species is not the
same—Variety of pectoral muscles in birds, according to their manner
of flight— Variety of muscles of the thigh in mammals, according to
their mode of locomotion—Was this harmony ‘pre-established }—
Development hypothesis —Lamarck and Darwin.

Tue comparison between ordinary machines and animated
motive powers will not have been made in vain, if it has
shown that strict relations exist between the form of the
organs and the characters of their functions; that this cor-
respondence is regulated by the ordinary laws of mechanics,
so that when we see the muscular and bony structure of an
animal, we may deduce from their form all the characters of
the functions which they possess.

It is known that the transverse volume of a muscle corres-
ponds with the energy of its action; that the athlete, for
instance, is recognized by the remarkable relief in which each
of his muscles stands out under the skin. But less is known
concerning the physiological signification of the length of
the muscles, that is to say, the less or greater length of
their contractile fibres. And yet Borelli has already given
the true explanation. In his opinion, as we have seen, this
length of red fibre is proportioned to the extent of movement
which the muscle is fitted to produce.

This distinction between the contractile or red fibre and
the inert fibre of the tendon is of the utmost importance.
Experiment has shown that the muscles when they contract
are shortened to an extent which represents a constant frac-
tion of their length. We may, without erring from the truth,
estimate at 1 of their length, the extent to which a muscle

70 ANIMAL MECHANISM.

can contract. But, whatever may be the absolute value of
this contraction, it is always in proportion to the length of
red fibre ; that is the result of the nature of the phenomena
which produce work in the muscle.

Thus, every muscle whose two points of attachment are
susceptible of being much displaced by the effect of contrac-
tion, must necessarily be a long muscle. On the contrary,
every muscle which has to produce a movement of short
extent must of necessity be a short muscle, whatever may be
the distance which separates the two points of attachment.
Thus, the flexors of the fingers and toes are short muscles ;
but they are furnished with long tendons, which convey even
to the phalanges of the fingers or toes the slight movement
originated at a considerable distance at the fore-arm or the leg.

It is easy to estimate, in the dead hody, the extent of the
displacement which a muscle can exercise on its two points of
attachment. By producing the movements of flexion or
extension in a limb, we can ascertain with sufficient exact-
ness the extent by which they separate or draw together the
osseous attachments of its muscles. Ina recent skeleton we
can also judge with sufficient accuracy of the amount of these
movements by the extent to which the articulated surfaces
can glide over each other.

In examining the muscular frame of man we are struck
with the extreme length of the sartorius muscle; it is easy
to be seen that no other can displace to such an extent its
points of bony attachment. The sterno-mastoidal and the
magnus rectus abdominis are, after this, the longest muscles ;
these also are muscles which have very extensive movements,
We might thus cause all the muscles of the organism to pass
under review, and in them all we should see that the length
of the red fibres corresponds with the extent of the movement
which this muscle has to execute. But, in the study, we
must be on our guard against a cause of error which would
tend to arrange certain short muscles among those which are
longer.

Borelli himself has noticed this cause of error; he has
shown how penniform muscles, that is to say, those whose
fibres are inserted obliquely into the tendon, like the barbs of

ORGAN AND FUNCTION, 71

a feather into the common shaft, are short muscles. which
appear like long ones. These considerations are indis-
pensable when we wish to understand the action of the
various muscles of the organism; it is only by this means
that we can estimate the real length of their contractile parts.

Though the harmony between ‘the form and the function of
different muscles is revealed everywhere in the anatomy of the
human frame, this harmony becomes much more striking if
we compare with each other different species of animals.
Comparative anatomy shows us, in species closely allied to
each other, a singular difference in the form of certain
muscles whenever the function of these muscles varies. Thus,
in the kangaroo, essentially a leaping animal, we find an
enormous development of the muscles of leaping, the ylutei,
the triceps extensor cruris, and the gastrocnemial muscles.

In birds the function of flight is exercised under very dif-
ferent conditions in different species; so, also, the anatomical
arrangement of the muscles which move the wing, the pectoral
muscles, varies in a very decided manner in different species.
To show the perfect harmony which exists between the func-
tion and the organ, it would be necessary to enter into long
details of the mechanism of flight. ‘The reader will find,
farther on, explanations on this head. We will content our-
selves with giving in a few words the differences which have
been observed in the movements of the wing, and in the form
of the muscles which produce them.

Every one has remarked that birds which have a large
surface of wing, as the eagle, the sea-swallow, &c., give strokes
of only a slight extent; that depends on the great resistance
which a wing of so Jarge a surface meets with in the air.

Birds, on the contrary, which have but very little wings,
move them to a great extent, and thus compensate for the
slight resistance which they meet with from the air; the
guillemot and the pigeon belong to the second group. If it
be admitted that the first-mentioned birds must make
energetic but restricted movements, and that the second must
move with less energy, but with greater amplitude of stroke,
the conclusion arrived at must necessarily be that the first
ought to have large and short pectoral muscles, while in the

72 ANIMAL MECHANISM.

second, these muscles should be long and slender. This is
precisely what takes place ; we can be assured of this, by the

Fia. 18.—Skeleton of a flamingo (after Alph. Milne-Edwards) ; the wing
is very large, the sternum very short and deep, which indicates the size
and the shortness of the pectoral muscles,

ORGAN AND FUNCTION. 73

simple inspection of the sternum in different species; for
this bone measures, in some degree, the length of the pectoral
muscles which are lodged in its lateral cavities. Thus, birds
with long wings, havo a wide and short sternum ; the others
have one which is long and slender.

Fig, 14. Skeleton of a penguin; sternum very long, wing very short.

The comparison of homologous muscles in mammals of
different kinds is not less instructive under the aspect in
which we are now considering them. But one is often em-
barrassed in this comparison by the difficulty of recognizing
the homology. The discrepancies are sometimes so striking

14 ANIMAL MECHANISM.

that anatomists have described under various names the same
muscle in different species.

Still, in the greater number of cases, the homology is not
doubtful; it is implicitly admitted by the fact of an identical
designation being applied to certain muscles in different
species. These are precisely the muscles which we shall take
for an example, to show the harmony which exists between
the function and the organ.

Fic. 15.—Skeleton of the wing and sternum of the sea-swallew (Hirundo
marina)—showing the extreme shortness of the sternum, and the great
length of the wing.

Thus the femoral biceps is easily recognized in all mam-
mals ; and it varies considerably, especially in its lower attach-
ment. In certain quadrupeds it is inserted all along the leg,
almost to the heel; in these animals the leg is never ex-
tended upon the thigh; in animals which have the power of
leaping, the lower attachments of the biceps is more elevated ;
it is still more so in the simis, which can almost extend
the leg upon the thigh and stand upright. In man the biceps

ORGAN AND FUNCTION. 5
is inserted high in the perinwum. If one can rely on the
anatomical plates of Cuvier and of Laurillart, the negro has
the perineal insertion of the biceps not so high as in the
white man, thus approximating to its position in the ape.

Neglecting at present the question why there should be
this variety in the attachment which regulates the motion of
the biceps, let us content ourselves with considering the con-
sequences which this arrangement may have upon its function.
It is clear that during the movement of the flexion and ex-
tension of the knee, each portion of the bone describes around
this articulation an arc of a circle which is larger as it recedes
from the centre of motion. It is equally evident that each of
these points will move to a greater or less distance from the
femur or the ischium, according to the extent of the circular
movement which it-executes. And as great movemeuts should
correspond with long contractile fibres, we ought to find
inequalities in the length of the biceps in different mammals.

This is precisely what is observed. In man, whose biceps
has its lower insertion very near the knee, the extent of the
movements of the moveable attachments is not very consider-
able, so the contractile fibre will have relatively little length,
while the tendon will occupy a certain part of the extent of
the biceps. In the ape, the inferior attachment of the muscle
taking place lower down will consequently have greater mo-
bility ; whence the necessity of a greater length of active
muscle, which is effected by the tendinous part beirg shorter.
In quadrupeds the tendon of the biceps almost entirely dis-
appears, and the muscle is formed of red fibre throughout
almost all its extent.

The rectus internus muscle of the thigh presents the same
variability in its attachments and its structure. If we observe
its arrangement in man (fig. 16), we see at once that the
attachment of this muscle to the leg is very near the knee,
and that its tendon is very long. Let us examine the same
muscle in an ape (figs. 17 and 18), we find that its tibial
attachment is much farther from the knee, and as a conse-
quence of the more extended movements which this attachment
executes, we find that the muscular fibre gains length at the
expense of that of the tendon, which is extremely short.

76 ANIMAL MECHANISM.

This variability in the point of attachment is still very
noticeable in the semi-tendinosus muscle, which derives its
name from the fact that in man, about half of the length

Fie. 16.—Muscles of the thigh in man. The sarterivs muscle (above) and
the rectus internus (below), are darkly shaded, that they may be more
easily recognized. The rectus internus is, at its lower extremity, pro-
vided with a long tendon; its fleshy part is short, which is in harmony
with the slight extent of movement in this muszle, the attachment of
which is very close to the knee. The sartorius muscle is provided with
a short tendon at its inferior attachment.

of the muscle is occupied by the tendon. In fact, the inferior
attachments of the semi-tendinosus in man is very close to the
articulation of the knee, but in apes, where it is attached
lower down, the muscle has almost entirely lost its tendon ;
it is altogether lost in the greater part of other mammals, in
the Couita, for example.

ORGAN AND FUNCTION. 77

We might multiply indefinitely examples which prove the
perfect harmony between the form of the muscles and the
characters of their functions. Everywhere the transverse
development of these organs is associated with strength, as
in the triceps of the kangaroo, or the masseters of the lion:

Fic. 17.—Muscle of the thigh in the Magot ; rectus internus muscle almost
entirely formed of red fibres ; the attachments of this muscle being at
a considerable distance from the knee, give ita great extent of move-

ment in bending the leg upon the thigh, Sartorius muscle, having a very
short tendon.

everywhere also, the length of muscle is connected with the
extent of movement, as in the examples which we have just
cited.

Is this harmony pre-established, or rather is it formed under
the influence of function in different creatures? In the same
manner as we see the muscles increase in volume by the
habit of employing energetic efforts; we also observe them,

78 ANIMAL MECHANISM.

under the influence of more extended movements, acquire a
greater length ? Can we see a displacement of the tendinous
attachments of the muscles to the skeleton, under the influence
of changes in the force of muscular traction ? Such is the second
problem which we propose to ourselves, and which experiment
should be called on to determine.

Fic. 18.—Muscles of the thigh of the Coaita Rectus internus, inserted
at a distance from the knee, almost entirely without tendon. The
sartorius having its superior attachment very far from the coxo-femoral
articulation, has very extended movements ; it possesses in consequence
a great length of red fibre, und not of tendon.

THE DEVELOPMENT THEORY.

The natural sciences have derived at the present day a
great impulse from the influence of the ideas of Darwin.

THE DEVELOPMENT THEORY. 79

Not that the opinions of the illustrious Englishman are yet
universally accepted; it has been recently seen with what
vehemence the defenders of the prevalent theory reject the
development hypothesis. But the appearance of the Darwinian
theory has excited long discussions; to the arguments which
Lamarck formerly brought forward in favour of the vari-
ability of living beings, many others have been added by the
partizans of development. On the other side, the old doctrine
has been maintained with a passion which was little antici-
pated, so that at the present day, naturalists are divided into
two camps; almost all who have devoted themselves to the
study of zoology or of botany have taken one side or the other.

In one of these camps we find that the old school, those
who consider the organized world almost unchangeable, have
retrenched themselves. According to them, the very numerous
series of animals and plants is limited to a certain number of
species, unalterable types which have the power of transmit-
ting themselves through successive generations, from their
origin to the end of time. It is scarcely admitted that the
species has the power of departing even slightly, and in a
temporary manner, from the primitive type. Those slight
changes, which are brought about by variations of climate or
of food, by domestication, or some other disturbing force of the
same order pass away when the species is again placed under
the normal conditions of its existence. The primitive type
then re-appears in its original purity.

In the other camp the belief is entirely different ; the living
being is incessantly modified by the medium which it inhabits,
the temperature which it finds there, and the nourishment
which it procures. The habits which it is forced to assume
in order to live under new conditions cause it to acquire
special aptitudes which modify its organism, and change the
form of its body. And because hereditary descent transmits
to descendants, within certain limits, the modifications acquired
by their ancestors, the species is modified by degrees. Lamarck
was the author of this theory of development, to which Darwin
anc his followers have recalled the attention of naturalists.
Darwin adds to these external influences, which can modify the
species of animals, another cause which maintains and increases

80 ANIMAL MECHANISM.

these modifications continually, when they are advantageous
to the species. This cause is natural selection.

If the chances of birth have given to certain individuals a
slight modification which renders them stronger or more
active, as the case may be, but altogether more fitted to main-
tain the struggle for existence, these individuals are destined by
that very circumstance to reproduce their kind. Not only does
their physical superiority increase their chance of longevity, and
give them by that means more time to multiply, but, according
to Darwin, the very existence of a physical superiority in an
animal causes it to be preferred above others, for the purpose
of reproduction. Thus the entire species would be improved
by successive acquisitions of new qualities every time that an
individual happened to be born with better endowments than
the other representatives of this species.

The struggle between the old school and that of development
threatens to endure yet a long time, without either side finding
a victorious argument to overcome the other. Every one
knows the reasons which have been alleged on both sides, and
for which, in their turn, geology, archeology, zoology, and
agriculture have been laid under contribution. When and
how will the strife end? No one can as yet answer this ques-
tion. Yet, if one might venture a prediction as to the issue
of the combat, founded on the actual attitude of the adverse
parties, one might predict the defeat of the old school. Their
ranks are, in fact, thinned every day; they evidently grow
discouraged, and seem to avow their inability to furnish proofs
of a scientific character, by sheltering themselves under an
orthodoxy that has nothing in common with the dispute.

One objection might perhaps be brought against both
systems—that of keeping too much to generalities in their
discussions, and not bringing sufficiently into relief the promi-
nent points of the debate.

Thus, we must allow that Lamarck is much too vague in
his explanations, when he attributes to outward circumstances
the changes in the living organism. Between a need which
is manifested and the appearance of a form of organ which
corresponds to that need, there is a hiatus which his theory
has not filled. He tells us that the animal species which we

DEVELOPMENT THEORY. Sl

now sce, so admirably adapted, each to the kind of life which
it leads—provided, according to their necessities, with claws
or hoofs, wings or fins, sharp teeth or horny beaks—have
not always lived under this form; that they have gradually
acquired these diverse conformations, which are at present in
perfect harmony with the conditions under which they live.
But, when we ask him to show us a modification of this kind
in process of accomplishment under an external influence, the
author of the “Philosophie Zoologique” has little wherewith
to furnish us, except modifications of slight importance; he
objects that scientific observation does not go far enough back
into the ages of the world. If we open the tombs of Mem-
phis and show Lamarck the skeletons of animals identical
with those which live in Egypt at the present day, he replies
without being disconcerted: ‘‘It is because these animals
lived under the same conditions as those which exist at the
present time.” The answer is as good as the attack, but
‘proves nothing. We might carry on the discussion for ever
ou such grounds as these.

Darwin is more precise when he pleads in favour of natural
selection, ‘There is no one at the present time who does not
admit the enormous power of selection in modifying the type
of organized beings. Breeders have produced the most
curious transformations in the animal kingdom, by choosing
continually for the purpose of reproduction, individuals pos-
sessing in a high degree the physical characteristics which
they desire to impress on the race. Selection produces in the
vegetable kingdom transformations of a similar kind; so that
Darwin has, without giving way too much to hypothesis,
attributed the principal part in transformation to a selection
which is made naturally, for the reasons that have just been
given. But Darwin, as well as Lamarck, only considers under
a restricted point of view the causes of the transformation of
organized beings. Each of the two chiefs of this doctrine
gives the greatest prominence to the cause of variation which
he first has pointed out.

The new school which, by a judicious eclecticism, endea-
vours to make a due partition between these two kinds of
influences, in order to explain by successive transformations

5

82 ANIMAL MECHANISM.

the surprising variety of living beings, has already furnished
important arguments in favour of development. But many
savants look with suspicion on these studies; they consider
that the immutability and variability of animal species belong
to the domain of insoluble questions.

It is true, that if we ask the partizans of development to
prove experimentally the reality of their doctrine; if we
require of them, for example, to transform the ass species into
the horse or anything analogous to it, they are forced to avow
their inability, and they reply that it is necessary, in order
to effect this, to exercise modifying influences during millions
on millions of years. It must indeed have been by very slow
transitions that the variation of species has been effected, if it
indeed has taken place. Consequently, in the absence of an
experimental solution, the development hypothesis can neither
be proved nor refuted.

Learned men, whose minds are habituated to rigorous de-
monstration, are not interested in such questions; they have
no scientific value in their estimation. And yet science meets
with-such every day. When an astronomer studies the in-
fluences which may cause the heavenly bodies to move more
slowly; when he predicts a modification of the orbit of the
earth after the lapse.of some millions of years, or a lengthen-
ing of the period of rotation of our planet—changes which
would affect all the inhabitants of the earth with a mortal
chill—this philosopher is listened to. When he speaks of a
cause, however slight it may be, of the retardation of a
planetary movement, every one understands that if this cause
should continue during many ages, its effects will be exag-
gerated by the lapse of time. No one tells this astronomer
to wait till some millions of years have proved the accuracy of
his reasonings.

Why should we be more unjust to the theory of develop-
ment? It cannot, it is said, bring before our eyes the trans-
formation of one animal into another. ‘This is true, but it
may show us some tendency to this transformation. However
slight it may be, yet accumulating more and more during
many ages, it may become as complete a transformation as
we can imagine,

DEVELOPMENT THEORY. 83

But what we have a right to demand of the advocates of
development, even now, is that they should show us this
tendency ; that they should bring it before us under the form
of a slight variation iu the anatomical characters of individuals
when exposed to certain influences, which continued from
generation to generation, would in the end produce the most
important modifications in the species. No one denies that
the morphological characteristics of individuals are transmitted
in different degrees to their descendants. The point which
is to be demonstrated is the manner in which an external
cause acts in order to impress on the organism the primary
modification. Researches of this kind belong to experimental
physiology, and this science may even now furnish us with
some reliable arguments.

At the time when Lamarck lived, scientific logic was not
very exact in its requirements. In his opinion, a want which
was felt, originated the organic conformation suited to satisfy it.

A certain bird which was in the habit of seeking its food
at the bottom of the water, made constant efforts to lengthen
its neck, and its neck grew longer; another bird wished to
advance as far as possible into the waters of a pond without
wetting its plumage; the efforts which it made to extend its
legs gradually gave them the proportions observed in the
wading birds (Grallatores). The giraffe, attempting to feed
on the foliage of trees, gained by this exercise cervical vertebree
of a surprising length.

Lamarck, certainly, attributed to hereditary descent the
function of accumulating continually for the profit of the
species that which each individual had acquired for his own
benefit ; but he did not show what the slight acquisition
was which was made by the individual himself, under the
influence of external circumstances, and of the habits which
he was forced to acquire. J. Hunter reasoned in a similar
manner in sciences of a different order. When he wished to
explain the cicatrization of wounds and the consolidation
of fractured bones, he recognized the necessity that new tissue
should be supplied by the blood; but why did the blood
carry these elements to the parts which needed them? “It
was,” said he, “in virtue of the stimulus of necessity.”

S4 ANIMAL MECHANISM.

We seek at the present day to state with precision the rela-
tion between causes and effects, to ascertain the gradual transi-
tions which the animal or vegetable organism is able to pass
through when it finds itself placed under new conditions.
We have a glimpse of the influence which function exercises
over the organ itself which produces it. The short and pithy
formula of Mons. J. Guérin, ‘‘ Function makes the organ,” ex-
presses in a’ general manner the modifying action of function.
This formula will acquire additional force when supported by
individual examples.

It must be shown how the bones, the articulations, the
muscles are modified in various ways by the effect of func-
tions of different kinds; how the digestive apparatus, yielding
to very varying kinds of food, passes through transformations
which adapt it to new conditions; how a change effected in
the circulatory function produces in the vascular system, cer-
tain anatomical modifications which may be predicted before
they take place; how the senses acquire new qualities by
exercise, or lose by desuetude their former powers. These
changes of function under the influence of the function itself
are accompanied by anatomical modifications in the apparatus,
physiologically modified.

The first demonstration to be furnished will be to ascertain
one of these transformations, and to show that it is always
produced in a certain manner under certain circumstances.
And if, in the second phase of the experiment, it can be
proved that hereditary descent transmits even the least part
of the modification thus acquired, the development theory will
be in possession of a solid starting-point.

This seems to be the true course, to follow, if we desire to
obtain a solution of this important question. During several
years serious efforts have been made in this direction. Having
been ourselves for a long time conversant with the problems
of animal mechanism, we have often been induced to reflect
on the reciprocal relations of the organs of locomotion and of
their functions. We will therefore attempt to show how the
skeleton and the ‘muscular apparatus harmonize with the
movements of each animal under the ordinary conditions of its
existence,

CLAP THR JX.
VARIABILITY OF THE SKELETON.

Reasons which have caused the skeleton to be considered the least variable
part of the organism—Proofs of the yielding nature of the skeleton
during life under the influence of the slightest pressure, when long con-
tinued—Origin of the depressions and projections which are observed
in the skeleton —Origin of the articular surfaces—Function rules the
organ.

Awy one who examines the skeleton of an animal, and holds
in his hands its osseous portions as hard as a stone; who knows
how these bones have survived the destruction of all the other
organs, and how they can remain, after the lapse of thousands
of ages, the only vestiges of extinct animals, may naturally look
upon the skeleton as the unchangeable part of the organism.
This skeleton, he argues, is the framework of the body, and
the soft parts are grouped around it as best they may, reposing
in its cavities, spreading over its surfaces, but always obey-
ing a law stronger than their own, and arranging themselves
in the spaces which have been allotted to them among the dif-
ferent portions of the bony structure.

The observer, however little he may be acquainted with
anatomy, soon perceives on the surface of the bone a thousand
curious details; he sees there numerous small hollows, little
abodes which seem to have been destined to receive or to shelter
some organ that has disappeared. These hollows correspond
with the origin of the muscles which adhered at these points to
the excavated bones. Elsewhere there are deep rounded grooves
which remind one of the channels found in the curbstones of
ancient wells. A cord has also passed in that direction ; it was
the tendon of a muscle which incessantly glided along that bone.
But at the two extremities of this humerus the bone is polished
as if by friction; in the upper part it is rounded like a
sphere, and it is lodged in a cavity of the shoulder-blade which
it exactly fits. One would say that the movement of these

86 ANIMAL MECHANISM.

bones had worn the surfaces smooth; the humerus continually
changing its position, and turning upon its axis, seems to
imitate the action we employ when we wish to obtain by
means of friction a body of a spherical form.

It is thus, for instance, that opticians produce the forms
and the polished surfaces of convex and concave lenses. At
its lower end the shoulder-bone shows the trace of the same
phenomenon, a small spherical projection articulating it with
the radius; it shows also that there existed movements of
two kinds, and close by, we meet with a surface cut like
the groove of a pulley; this, in fact, only contributed to the
flexion and extension of the fore-arm.

If we examine the skull we meet with fresh surprises; here
every want is foreseen. Deep cavities lodge in their interior
the brain and the organs of sense.

The nerves have conduits which allow them to pass through ;
each vessel creeps along a furrow which forms a canal for it,
and is ramified with the minute arteries whose rich foliation it
delicately traces out.

If the bone were not so hard, one would really suppose that
it had been subjected to external force, of which it bears, as it
were, the impression. But it is in vain to press a bony sur-
face ; it resists absolutely the force which is applied to it. It
is necessary to use a saw or a gouge if we wish to make a
channel in it. How could the pressure of soft parts hollow
out these cavities which are sometimes so deep ?

The foresight of nature has prepared everything in the
skeleton so that it may be disposed in the best possible manner
to receive the organs to which it offers its solid and invari-
able support. Such is the natural argument of all those
who have not seen, with their own eyes, these osseous changes
take place, and these channels hollowed out. ‘The anatomist
as well as the zoologist have necessarily reasoned in this
manner. They have considered the skeleton as the unalterable
element of the organisin, and therefore they have derived from
it the greater part of the specific characters in zoology.

It must be very difficult to oppose an opinion which has
been for a long time received. ‘Thus, when Mons. Charles
Martin, carrying out and rectifying the ideas of Vic. d’ Azir,

VARIABILITY OF THE SKELETON. 87

has shown that the humerus of a man or of an animal is the
homologue of the femur, but of a femur twisted on its axis, so
that the knee turned behind becomes an elbow, zoologists
have replied that this torsion was purely virtual. Instead of
being the effect of a muscular effort, whose slow and gradual
action has reversed the axis of the bone, this singular form
is, in their opinion, the result of a pre-established arrange-
ment of the organism; for the embryo shows a contorted
humerus, before muscular action has been sufficiently developed
to produce such a modification of its skeleton.

We might, with greater show of reason, argue in a directly
opposite manner.

No one denies at the present day that the bony system is
perfectly yielding in its character. These organs, which are
so compact and so hard in the dead skeleton, are, on the con-
trary, essentially capable of being modified while the organism
is living. If we exert upon a bone a pressure or a tension,
however slight it might be, yet if prolonged for a considerable
time, it can produce the strangest changes of form; the bone
is like soft wax which yields to all external forces; and we
may say of the skeleton, reversing the proposition to which we
have just alluded, that it is completely under the influence of
the other organs, and that its form is that which the soft parts
with which it is surrounded permit it to assume.

We are indebted to medicine and surgery for the knowledge
of important facts, of which many examples could easily be
given. Thus, when an aneurism of the aorta is developed,
and it happens to meet in its course the sternum or the clavicle,
it does not stop at this barrier of bone, but perforates it
in a few months. The substance of the bone is absorbed and
disappears under the pressure of the aneurism; it certainly
resists less the effort of the invading tumour than do the softer
parts—the skin, for example.

But this pressure of the aneurism differs in no respect
from that of the arterial blood; the force with which the
aneurismal sac compresses and perforates the bones, is present
in every part where an artery touches a bone. The same ab-
sorption of the bony material still goes on, so that the artery
hollows out for itself a furrow in which it lodges with its dif-

88 ANIMAL MECHANISM.

ferent branches, an example of which is seen in the internal
surface of the parietal bones of the humanskull. Even a vein
is able to form a considerable hollow in a bone. The ab-
normal dilatation of those veins which are called varicose, and
which is usually produced in the legs, is accompanied with a
change of form in the anterior surface of the tibia; the bone
wears the impress of the dilated veins. We cannot say that
these osseous furrows enter into the pre-established plan of
nature; that the skeleton had originally these furrows in
order to provide for the swollen state which should hereafter
be produced. Surgeons know that these hollows are formed
in the bone of an adult, which was in a perfectly normal state
before accident had caused the varicose dilatation of the veins.

It is a similar mechanism which forms along the bones the
furrows imprinted by the muscles, and which gives to the
perineum, for instance, the prismatic form by which it is
characterized.

The hollows in which the tendons are lodged are not formed
beforehand in the skeleton; it is the presence of the tendon
which has hollowed them out, and which still maintains them.
Should a luxation take place and change the position of the
bone with respect to the tendon, the former furrow which is
now empty is gradually effaced; at the same time a new
furrow is formed, and by degrees assumes the necessary depth
to allow the tendon to repose in its fresh place.

But, it may be said, that the articular surfaces, so perfect
in their structure, so well adapted to the movements which
they carry on, are certainly organs formed beforehand. Here
the bony surfaces are clothed with a polished cartilage
moistened with a synovial fluid which facilitates their move-
ment still more; all around them, fibrous ligaments prevent
the bones from passing the limits allotted to them, and the
surfaces from separating from each other. So perfect an ap-
paratus could not be formed by the function alone.

We have here at least a proof of the foresight of nature
and of the wisdom of her plans.

Let us turn once more to surgery, which will show us that
after dislocations, the old articular cavities will be obliterated
and disappear, while at the new point where the head of the

VARIABILITY, OF THE SKELETON. 89

bone is actually placed, afresh articulation is formed, to which
nothing will be wanting in the course of a few months, neither
articular cartilages, synovial fluid, nor the ligaments which
retain the bones in their place. Here again, according to the
expression which we used just now, function has produced
the organ.

So much for the furrows formed in the bone. But how
can we attribute to external influences those decided promi-
nences which we observe everywhere on the surface of the
skeleton, those apophyses, as they are called, to which each
muscle is attached.

The answer is not less easy; it is sufficient to account for
the formation of projections on the face of the bone, if we call
into play an influence contrary to that which we know to be
capable of hollowing out the indentations. We must admit
that traction has been exercised on the portion of the bone
where the projection is observed.

The existence of traction on all the points in the skeleton to
which muscles are attached is absolutely evident; it is clear
that the intensity of these tractions is proportional to the force
of the muscles which produce them. ‘Thus, it is precisely in
the tendinous attachments of the stronger muscles that we find
the more projecting apophyses; a proof that the prominences
in the bone are intimately connected with the intensity of the
effort acting upon them. ‘Theright arm, more frequently used
than the left, acquires more decided projections on its bony
structure. When paralysis of a limb suppresses the action of
the muscles, its skeleton is no longer under the influence of
muscular power, and the apophyses become less prominent ;
in fact, if paralysis dates from birth, the bone remains nearly
in its foetal form, which function has not supervened to
modify.

Comparative anatomy also confirms this general law that
the longer the apophysis is, the greater energy it reveals on
the part of the muscle which was inserted into it.

Mons. Durand de Gros has clearly shown the influences of
muscular function on the form of the torsion of the humerus
in different species of fossil and recent animals. Thus the
humerus in the mole, the ant-eater, and several other burrow-

90 ANIMAL MECHANISM.

ing animals is scarcely recognizable, so thickly is it studded with
ridges and projections, each of which gave insertion to a
powerful muscle.

The skull and the lower jaw in the carnivora bear the traces
of a powerful muscular action. In the skull a deep hollow
retains the impression of enormous temporal muscles ; all
around the temporal depression, decided ridges were the solid
points of attachment of the muscle; again, a strong and long
apophysis by the side of the lower jaw shows the violent
tractile force to which it has been subjected in the efforts of
mastication.

If the effects of muscular actions on the bones augment with
the intensity of the force of the muscles, they do not vary less
in proportion to the duration of their action. From infancy
to old age, the modification of the skeleton goes on more and
more, and even allows us, to a certain degree, to determine
the age of the subject.

Mons. J. Guérin has shown that in the old man the verte-
bree have longer apophyses, the ribs more angular curves, &c.
Compare the cranium of a young gorilla with that of an adult
animal; the form will appear to you so different that unless
you had been told that the two skulls belonged to animals of
the same species, you would scarcely have believed it. Of a
rounded form in the young gorilla, it changes its shape in
the adult; it assumes a kind of ridge like the crest of a
helmet ; this is the apophysis into which the temporal muscles
are inserted. We should never finish if we were to point
out all the modifications to which the skeleton is subjected
in different species of animals; modifications which from the
beginning to the end of life become more and more marked.

Medicine, in its turn, furnishes us with curious information
as to these questions, by showing us the sudden development
of accidental apophyses which are called ewostoses. In certain
maladies which attack the entire body, we see the skeleton
covered, in a great number of points, with accidental osseous
projections; and almost all these prominences are developed at
the points of attachment of the muscles, and as they increase,
they extend especially in the direction in which muscular
traction is applied.

VARIABILITY OF THE SKELETON. 9]

The curvature of the bones, or their contortion on their
axis, is a phenomenon which is frequently observed. I have
mentioned that Mons. Ch. Martin has demonstrated that in
all the mammalia, the humerus is a contorted femur, whose
axis has made half a turn upon itself; this contortion, accord-
ing tc Gegenbaiier, is less in the foetus than in the infant,
and becomes still more marked in process of age. It is
therefore partly effected by causes which are in action during
life; and if it be true that every foetus brings into the world
a contorted humerus, it is not less true that this form may
be ecnsidered as the effect of muscular action accumulated
from generation to generation in terrestrial mammals.

Articular surfaces are particularly interesting to study when
we wish to ascertain the influence of function over the organs.
If we admit that the friction of these surfaces has polished
them, and given them their curvature, it is easy, when we
consider the movement which takes place in each articulation,
to foresee the form which these surfaces ought to possess.

The surfaces whose curvature has the greater number of
degrees, will correspond with the more extensive movements.
Moderate movements, on the contrary, will only produce sur-
faces whose curvature will correspond with an are of but few
degrees. As a necessary consequence, the radius of curvature
in the articular surfaces will be very short, if the move-
ments are very extended ; it will be very long if the movement
is moderate.

Let us examine, from this point of view, the articulations
of the foot in man; we see in the tibio-tarsal articulation a
curvature of small radius, on account of the considerable move-
ment of the foot on the leg. In the tarsus the radius of the
curvature increases in proportion as the mobility of the bones
diminishes. The scaphoid shows articutar surfaces of a great
radius; the radius increases still more in the tarso-metatarsal
articulations, in which the movements are very limited; then
it diminishes again in the articulations of the metatarsals
with the phalanges, and of the phalanges with each otber, at
which point there is great mobility.

Kveryone knows that if the articular movement is only
effected in one direction, the surfaces will curve only in that

92 ANIMAL MECHANISM.

direction ; such are the trochlear surfaces, of which the articu-
lation of the elbow, the condyles of the jaw, &c., are examples.
But if the movement is executed in two directions at once,
the surfaces will present a double curvature, and in the case
of an inequality in the amplitude of the movements, the radii
of these curvatures will be unequal. Thus, in the wrist there
exist movements of flexion and extension which are consider-
ably extensive, but the lateral movements are restricted. The
result of this is that in the elliptical head formed by the
carpal bone, there is a curvature of small radius in the direc-
tion of the movements of flexion and extension, while, in the
lateral direction, the curvature belongs to a cirele of much
greater radius.

It is still more interesting to observe the articular surfaces
of a series of animals in different classes and species.
Similar articulations present movements of very different kinds,
which must bring about no less important differences in the
articular surfaces.

Let us take, for example, the head of the humerus, and
fullow the changes of its form, in man, in the ape, the earni-
vora, the herbivora, the birds. We shall see that the perfect
equality of movement in every direction which can be exe-
cuted by the human arm corresponds with a perfect sphericity
to the head of the humerus—that is to say, a curvature of the
same radius in every direction. Among apes, those which in
walking throw a part of their weight usually on their anterior
limbs, have the head of the humerus flattened at the upper
part, as if by the weight of the body. Besides this, the
movements which are required in walking being more ex-
tended, the curvature of the head of the humerus in these
animals presents its least radius in the antero-posterior direction.
This modification is more marked still in the carnivora, and
above all in the herbivora, the head of whose humerus, flat-
tened above, presents its short radius of curvature in the
direction of the movements which serve for walking, and
which predominate in this articulation.

Birds possess, in the articulation of the shoulder, two
movements of unequal extent. One, by which they spread
and fold their wings, and which carries the elbow sometimes

VARIABILITY OF THE SKELETON. 93

near to the body, and sometimes very forward; the other,
usually more restricted, is made in a direction perpendicular
to the former; it is that which constitutes the stroke of the
wing.

Curvatures of different radii correspond, therefore, to these
two movements of unequal amplitude; to the greater move-
ment of stretching and folding the wing a curvature of short
radius corresponds; to the less extensive movement which
raises and lowers the wing during flight, there is a corre-
sponding curved surface of very long radius. The result of
this is that the head of the humerus in birds assumes the
form of a very elongated ellipse, at the level of the articular
surface.

But the movements of flight present in different species
great variations of amplitude. Birds which have sail-like
wings give but very small strokes with them, while the
pigeon, at the moment when it takes flight, strikes its wings
one against the other above and below, producing a clapping
noise, which is familiar to every one.

To these variations in the extent of the movements corre-
spond varieties of surface in the head of the humerus, which
in birds with sail-like wings has a very elongated elliptical
surface; but in the pigeon it tends to the circular form, and
very nearly attains it in the spheniscus, an aquatic bird found
in southern seas, and closely resembling the penguin.

From all this we may gather, that in the form of the bony
structure, everything bears the trace of some external influ-
ence, and particularly of the function of the muscles. There
is not a single depression or projection in the skeleton,
the cause of which cannot be found in an external force,
which has acted on the bony matter, either to indent it, or
draw it forward. It was not, therefore, a metaphorical exag-
geration to say, that the bone is subject, like soft wax, to all
the changes of form which external forces tend to impress
upon it; and that, notwithstanding its extreme hardness, it
resists less than the most supple tissues the efforts which tend
to change its form.

And will this new form, acquired by means of function,
disappear with the individual? Will he not transmit even

D4 ANIMAL MECHANISM.

the slightest trace to his descendants? Will hereditary
descent make an unique exception with respect to these ac-
quired characters? ‘This appears very improbable, and yet
we must admit it, if we negative the development theory.
We «must bring forward a contrary hypothesis, which would
reverse the ordinary laws of hereditary descent, if we refuse
to certain anatomical characters the power of becoming trans-
missible.

VARIABILITY OF THE MUSCULAR SYSTEM.

We have stated that the bony system is subject to external
influences, and especially to those of the muscles, which im-
press on each bone the form which we observe in it. The
great variety of forms in the skeletons of different animal
species corresponds, therefore, with the diversity of their
muscular systems. Thus, whenever in animals of different
species we find resembiances in certain bones, we may affirm
that the muscles which were attached to these bones were
also similar. Whenever we observe in an animal, on the
contrary, a bone of a peculiar form, we may feel assured of
a peculiarity in the muscles which were attached to it.

But if the muscle and the bone vary simultaneously, what
can be the cause which influences them both? It is under-
stood that the skeleton, as it is modified, plays a passive part;
that it is subject to the form imposed upon it by the muscle.
But what gives to the muscle itself, an organ eminently active,
and the true generator of the mechanical force by which
the skeleton is in some degree modified, the particular form
which is revealed to us by anatomy ?

We hope to demonstrate that the power to which the mus-
cular system is subjected belongs to the nervous system. ‘The
nature of the acts which the will commands the muscles to
perform, modifies the muscles themselves, in their volume and
their form, so as to render them capable of performing these
acts in the best possible manner. And, as this necessity
which determines all the actions of animal life, governs the
will, it is this, which, according to the external conditions
under which every living being is placed, influences its form,

VARIABILITY OF THE MUSCULAR SYSTEM. 95

and regulates it according to the laws which we must now
endeavour to make known.

Nothing in the organic form is under the dominion of
chance. ‘The specific varieties of living beings have been too
often compared to the fancies of an architect, who, while
adhering to an uniform plan, invents a thousand varieties of
details, as a musician composes a series of variations on a
given theme.

In our present inquiry we may say that the great variety
which is found in the muscular apparatus, whether in the
different parts of the body of an animal, or in the homologous
parts of animals of different species; for instance, varieties
in the volume or the length of muscles; the very unequal
partition of the red contractile fibre, and the inert, white,
glistening fibre of the tendon ; that all this is entirely subject
to the dynamic laws of muscular function.

Adaptation of the form of muscles to the requirements of function.
Normal anatomy can only furnish us with examples of the
harmony which exists between the form of the organs and
their habitual function, Experiment alone can show us that,
by changing the function, we may bring into the form of the
organs modifications which may harmonize them with the
new conditions which may be imposed upon them. It will
be easy to make experiments for this purpose. From the
moment when we know in what direction the modification
ought to be produced, in order to adapt the organ to the
function, the changes effected in animals placed by us under
conditions of peculiar muscular function, will derive an im-
. portant significance. But while we wait for the realization of
this vast series of experiments, there are some which we can
employ even now. Experiments made ready to our hand are
furnished by pathological anatomy.

Medicine and surgery are full of information on this in-
teresting subject. ‘They show us, for example, that it is
movement itself which keeps up the existence of the muscle.
A long repose of this organ brings about first the diminution
of its volume, and soon a change in the elements which com-
pose it. Fatty corpuscles are substituted for the striated fibre
which form its normal element; at last, these corpuscles,

96 ANIMAL MECHANISM.

becoming more and more abundant, invade the entire sub-
stance of the muscle. This phase of alteration, or futty dege-
neration, is followed by an absorption of the substance of the
muscle, which disappears entirely at the end of a certain
time.

Thus, not only does the volume of the organ increase or
diminish according as the necessities of its habitual function
require a greater or less force, but it wholly disappears when
its function is entirely suppressed. This effect is observed in
paralysis, where all nervous action is destroyed; in certain
cases of dislocation, which bring closer together the two inser-
tions of a muscle, so as to render its action useless ; sometimes
even in fracture and anchyloses, which, by an abnormal con-
nection, render the two extremities of a muscle immovable,
and prevent any contraction of its fibres.

But what will happen, if the muscle, instead of losing all
its function, only experiences a change with respect to the
extent of the movements which it can execute? After certain
incomplete anchyloses, or certain dislocations, we see tlie
articulations lose more or less of their movements; as tlie
muscles which command flexion and extension only need, in
such cases, a part of the ordinary extent of their contraction.

If the theory just enunciated be correct, these muscles ought
to lose a portion of their length. In order to verify this fact,
we have only to make a short excursion into the domain of
pathological anatomy.

A warm discussion arose, some twenty years ago, as to the
transformation which the muscles underwent in those patients
who were afflicted with the deformity commonly known by the
name of club foot. Sometimes the foot is twisted upon the
leg, so that the surface which should be uppermost is next
the ground; sometimes the foot is so forcibly extended that
the patient walks continually on its extremity. In all these
cases the muscles of the leg have only a very limited play ;
they undergo, therefore, either fatty or fibrous transformation.
Among these muscles, those which have no longer any action
undergo fatty degeneration, and then disappear; while those
whose action is partly preserved, present only a change as to
the proportion of red fibre and tendon. In the latter case

VARIABILITY OF THE MUSCULAR SYSTEM. o7

the contractile substance diminishes in length, and is re-
placed by tendon, which often assumes a considerable develcp-
ment.

J. Guerin, when pointing out the fibrous degeneration of
the muscles, thought that he saw in it the proof of a primi-
tive muscular retraction, which would ultimately have pro-.
duced dislocation of the foot. This eminent surgeon also
thought that the alteration of the fibre was the only lesion of
the muscles in club-foot. Scarpa maintained, on the contrary,
that in the greater number of cases the luxation of the foot
was the original phenomenon.

As to the nature of muscular change, all surgeons at present
agree in admitting that it may have two different forms, and
that sometimes the muscle undergoes fatty degeneration, and
in other cases it is transformed into fibrous tissue. We are
especially indebted to the beautiful works of Cuvier, for our
knowledge of the conditions under which each of those
changes in the muscular substance is produced.

An example will illustrate how the muscles are affected
according as their function is suppressed, or simply limited
in extent.

The muscles of the calf of the leg, or gastrocnemians, are
two in number; their attachments and their functions are
very different. Both are inserted below in the caleaneum, by
the tendon of Achilles, and are, consequently, extensors of the
foot on the leg. But their superior insertions are different ;
the soleus, having its insertion exclusively in the bones of the
leg, has no other office than that of extending the foot, as we
have said before. The twin gastrocnemii, on the contrary,
being inserted in the femur, above the condyles of that bone,
have a second function, that of bending the leg upon the
thigh.

Let us suppose that anchylosis of the foot has been pro-
duced; it entirely suppresses the function of the soleus, which
passes through the fatty degeneration, and disappears. ‘The
two gastrocnemii are in a different condition; if their action
on the foot has ceased, there still remains their function of
bending the leg on the thigh; these muscles have, therefore,
only one of their movements reduced in amplitude. Con-

98 ANIMAL MECHANISM.

sequently, under such conditions, the twin muscles lose only
a part of the length of their fibres; they undergo what sur-
geons call partial fibrous transformation, a modification which
is only a change of proportion between the red fibre and the
tendon.

Those who are accustomed to regard pathology as a com-
plete infraction of physical laws, will perhaps be astonished
to see us search among these cases of dislocation and anchy-
losis for the proofs of a law which regulates the form of the
muscular system in its normal state. It would be easy to
show that these scruples have no foundation; but it will be
better still to bring forward other examples which may not lie
open to the objections so often urged against the applications
of medicine to physiology.

It is again from J. Guerin, that we must quote the facts
of which we are about to speak.

When we examine the muscular system at different periods
of life, we find that it varies greatly in its aspects. It seems
that the muscles have distinct ages, and that, formed at first of
contractile substance, they lose by degrees, as they grow
older, their red fibres, which are replaced by the white and
glistening fibres of the tendon.

Thus, the diaphragm of a child is principally muscular,
while in the old man the aponeurotic centre, the true tendon
of the diaphragm, is extended at the expense of the contrac-
tile fibre. The substitution of tendon for muscular fibre is
still more marked in the muscles of the leg in infancy; they
are relatively much more rich in contractile substance than
during adult age. In the old man, in fact, the tendon seems
to invade the muscle, so that the portion of the calf of the leg
which remains is placed very high, and is very reduced in
length. The muscks of the lumbar and dorsal regions present
the same character; in old age they are poorer in red fibre,
but richer in tendon.

What then, is the change which takes place in the muscular
function during the different periods of life? Every one knows
that, except in the very rare cases in which the man keeps up
the habit of gymnastic exercises, the muscular function be-
comes mcre and more restricted—at least, as far as the extent

VARIABILITY OF THE MUSCULAR SYSTEM. SIS,

of movement isconcerned. The articulations of the limbs, and
those of the vertebral column, undergo normally a sort of
incomplete anchylosis, whish continues to lessen more and
more the flexibility of the’ trunk.

Look at a young child tossing about at his ease: one of his
movements is to play with his foot; to take it in his hands
and carry it to his mouth appears to him very natural, and as
easy as possible. In the adult, the muscular force attains its
maximum; but the movements are not so extensive as in
infancy; man has no longer, as is well known, the same
flexibility in his limbs.

The old man can neither stoop readily nor completely
draw himself up; his vertebral column has iost its supple-
ness; he takes only short steps; to sit down on the ground,
with the knees raised, is to him extremely difficult; and if
we examine the extent of flexién and extension in his foot,
we find that it has become very limited.

The function of the muscles, therefore, changes with the
different periods of life, and becoming more and more restricted,
employs continually less contractile fibre. It is thus that the
muscular modification of which we have been speaking is
naturally explicable. This modification, which consists in the
increase of the tendinous element at the expense of red fibre,
may be prevented by keeping up the extent of muscular
movements, by means of suitable exercise.

Let us now return to comparative anatomy. Since it
shows us perfect harmony between the form of the muscles in
different species of animals and the characters of muscular
function in the same species, the most natural conclusion seems
to be that the organ has been subjected to the influence of
function.

If the race-horse is modified in its form by the special exer-
cise which is called training, is it not an evident proof of the
influence of function on the anatomical characters of the
organism? And if a species, thus modified artificially,
returns to the primitive type when replaced under the con-
ditions from which it had been taken, is it not the counter-
proof of the theory which assigns to function the office of
a modifier of the organ ?

100 ANIMAL MECHANISM.

These very fucts are, however, interpreted in an opposite
sense by the partisans of the invariability of species; they
seem to find an unanswerable argument in support of their
cause, in the return to the primitive type, when the modifying
influences have ceased.

To what conclusion can we come when we meet with these
contrary opinions? It must be that the partisans of develop-
ment have not completed their task, and that they ought to
add new proofs to those which they have already given. It
is to experiment that the principal part belongs, while theory
is not without its importance; by causing us to foresee in what
manner a certain kind of function ought to modify a muscle,
it will give its proper value to the modification which may
subsequently be obtained. Indeed, without theory, the ex-
perimenter can seldom recognize the modification which he
has observed. We seldom “find in anatomy anything but
that which we seek for, especially when we have to do with
slight variations like those which we might hope to produce
in the organism of an animal.

The experiments to be tried are tedious and troublesome ;
their plan, however, is easy to trace.

If man, adapting to his necessities the domestic animals,
has already succeeded in modifying their organization within
certain limits, he has produced these changes, as we may
say, fortuitously. Only intending, for example, to obtain
draught horses or racers, it was not necessary to place
the species under conditions entirely artificial. This must,
however, be done, if we aim at elucidating the problem of
which we speak, and of carrying to the farthest possible
limit, changes in the conditions of the mechanical work of
animals.

Man has utilized the aptitudes of different animals, rather
than sought to give them new ones. It would be necessary
to do violence to the habits of animals, and to constrain
them gradually to perform acts to which their organism is
but slightly adapted. If, in order to get its food, a species
with an organization unsuitable for leaping, should be com-
pelled to take leaps of gradually greater height, everything
leads us to suppose that it would acquire at length great

VARIABILITY OF THE MUSCULAR SYSTEM. 101

facilities for leaping. If the descendants of these animals
retained any of the power of their ancestors, they might per-
haps, in their turn, develop still more this faculty of leaping.
Graduating thus the effort imposed on this particular species,
no longer in a utilitarian point of view, which there would
be no inducement to surpass, but requiring indefinitely more
force or greater extent in the play of the muscles, we might
hope that the anatomical development would increase indefi-
nitely, and that we might obtain something analogous to that
which is now called the passage of one species into another.

What we have said of the muscular function applies to all
the rest. By modifying in a gradual manner the conditions
of the food of animals, as well as those of light and dark-
ness, temperature, and atmospheric pressure under which they
may be made to live, we may impress upon their organism
modifications analogous to those which zoologists have already
observed under the influence of climate, and of the various
atmospheric conditions and different altitudes in which animals
have been placed by nature. These changes, brought about
by well-managed transitions always tending to the same end,
would have a chance of producing considerable transformations
in animal organization, provided that, by persevering determi-
nation, these efforts were indefinitely accumulated; as in the
case of breeders of animals, who use similar means for the
production of selected kinds of stock.

We will proceed no farther in the field of hypothesis, but
we will, in conclusion, make an appeal to zealous experimen-
talists. Many who have been convinced of the great import-
ance of this enquiry seem already to be engaged in this
enterprise. What question, in fact, can more nearly concern
the human race than this: Can our species be modified ?
According to the tendency which may be given to it, can it be
directed either towards perfection, or degradation ?

BOOK THE SECOND.

FUNCTIONS: TERRESTRIAL LOCOMOTION.

CHAPTER I.
OF LOCOMOTION IN GENERAL.

Conditions common to all kinds of locomotion—Borelli’s ecomparison—
Hypothesis of the reaction of the ground—Classification of the modes
of locomotion, according to the nature of the point of resistance, in
terrestrial, aquatic, and aérial locomotion—Of the partition of muscular
force between the point of resistance and the mass of the body—Pyo-
duction of useless work when the point of resistance is movable.

Tue most striking manifestation of movement in the dif-
ferent species of animals is assuredly lccomotion: the act by
which each living creature, according to its adaptation to out-
ward circumstances, moves on the earth, in the water, or
through the air. Therefore it is more convenient to study
movement with regard to locomotion, for we can thus observe
it under the most varied types.

At the commencement of these studies we ought to consider
the general characteristics of the function which is’ to occupy
attention, and to point out the general laws which are to be
found in all the modes of animal locomotion. But what can
be more difficult than to ascertain the common features which
unite acts so different as those of flying and of creeping, as
the gallop of a horse and the swimming of a fish? Still this
has been frequently attempted. Borelli has endeavoured to
represent the various modes of terrestrial locomotion, by the
different methods which a boatman employs to direct his boat.

This comparison may, with some additional developments,
serve to explain the mechanism of the principal types of loco-
motion,

LOCOMOTION IN GENERAL, 103

Let us suppose a man seated in a boat in the midst of a
tranquil lake. Under these conditions, his skiff will remain
perfectly motionless. If he wishes to advance, he must find
what is called a point of resistance. Suppose him to be fur-
nished with a pole, he will plunge it towards the bottom of
the water till it reaches the ground; then, making an effort,
as if to drive from him this resisting body, he will cause his
boat to move in the opposite direction. This progression with
the point of resistance on the ground is similar to the ordinary
conditions of terrestrial locomotion.

If the boatman be provided with a boat-hook, he will
get his point of resistance under different conditions. Laying
hold of the branches of trees, or the projections of the shore,
he will drag his pole towards himself, as if to bring near to
him the bodies to which it is fastened; and if these bodies
resist his efforts, the boat alone will be displaced and drawn
towards them.

Here are then two opposite modes of progression with
bearings on solid bodies; in one the tendency is to repel, in the
other, to draw them nearer: the effect is the same in each case.

But if the lake be too deep, or if the shores be too distant
to furnish the boatman with the solid fulerum which he had
used before, the water itself will serve as a medium of
resistance. ‘The boatman, armed witha flattened oar, endea-
vours to drive the water towards the stern of his boat; the
water will yield to this impulse, but the boat, impelled in
an opposite direction, will go forward. The various kinds of
paddles for steam-boats, the screw, in fact, all nautical pro-
pellers, present this feature in common, of driving the water
backward, in order to produce in the boat an impulse in the
ccntrary direction, and to cause it to advance.

Instead of an oar acting on the water, we may suppose the
boatman provided with a much larger paddle with which he
might drive back the air at the stern; he will propel his
boat on the surface of the lake. He might make progress
also by turning a large screw like the sails of a wind-
mill, or by agitating at the stern some large fan which would
drive the air in the direction opposed to that in which he
desired to force his boat.

104 ANIMAL MECHANISM.

In all these modes of locomotion a force is expended which
impels in opposite directions two bodies more or less resisting ;
the one is the fulcrum, the other the weight to be displaced.

Old writers called the force acting on the boat re-action—
they considered it as an effort emanating from the soil, the
water, or any resistance whatever to which the effort of the
rowers was applied. We can now understand clearly that all
the motive force is derived from the boatman. This force can
lave as its result, either the repulsion of two points to which
it is applied, or their approach to each other. In these two
cases one of the points may be fixed, it is then the other which
will be displaced; or the two points may be movable, and
then, according to their unequal movability, one of them will
be displaced more than the other.

This gereral principle can be applied to all cases of loco-
motion; it will be sufficient for us to notice that which is
essential in all the types which we shall consider.

The most natural classification seems to be that which is
based on the nature of the point of resistance ; accordingly, we
may distinguish three principal forms of locomotion—terres-
trial, aquatic, or aérial. But in each of these forms, what a
variety of mechanism we shall meet with!

If it be true that walking and creeping are the two
principal types of terrestrial motion, that swimming corre-
sponds with the more habitual mode of aquatic locomotion,
and fl'ght with aérial locomotion, it is not less true that in
certain media many kinds of locomotion are employed. Thus,
walking and creeping are used both on the earth and in the
water; flight is habitually performed in the air, and yet
certain birds take a decided flight in the water.

In fact, if we were compelled to assign to every animal its
particular type of locomotion, our embarrassment would be
as great as if we were classifying these movements. Some,
indeed, move with an equal facility on the earth, the water,
and in the air. We will not therefore attempt a strictly
methodical classification of the different modes of locomotion
of which we are about to take a rapid survey.

Terrestrial locomotion furnishes two principal types: in one
the effort consists in pressing on the ground in the direction

LOCOMOTION IN GENERAL. 105

opposite to the intended movement; this is the more usual mode
of locomotion; walking, runuing, leaping, belong to this first
form. Vor this purpose the limbs serving for locomotion are
composed of a series of rigil levers, susceptible of change in
length; they can be shortened by the angular flexion of the
far auilatipus: and they grow lounger. by being drawn up. If
the leg when Lent touches the und at its extremity, and if
a muscular effort be made to produce the extension of the
limb, this can only be effected Ly removing to a greater dis-
tance from each other the ground on which the extremity of
the leg rests and the body of the animal which is united
to the base of this limb; the ground offers resistance, and the
body, yielding to the impulse, is displaced. Sometimes the
displacement in terrestrial locomotion is effected, not by a
change in length, but by a simple change of the angle formed
between the limb which causes the motion and the body of
the animal.

In the second type, namely erecping, a tractile effort is pro-
duced ; the animal lays hold by a part of its body on an ex-
ternal fixed point, and then drags the mass of its bulk towards
this point. Let us take a snail, and place it on a piece of
transparent glass; at the end of a few moments the animal
begins to crawl. If we turn the glass over, we shull see
throneh the plate the details of its movements. Throughout
all the length of its body appears a series of transverse bands,
alternately pale and deeply coloured, opaque and transparent.
These bands are transmitted by a continual motion, from the
tail to the head of the animal; they seem like the spirals of
a screw which turns incessantly in the same direction. It we
fix our attention on one of these bands in the neighbourhood
of the tail, we see it pass towards the head, which it
reaches in fifteen or twenty seconds, but it is followed by
a continued series of bands which seem to spring up behind
it as it advances. ‘These bands remind us of the muscu-
lar wave and its progress through a contracting fibre, only
with greater dimensions. IJich time that a wave arrives
at the cephalic region of the animal, it disappears, producing a
forward motion of the head, which slips a little on the surface
of the glass and advances slightly without any retrogression.

6

106 ANIMAL MECHANISM.

It appears that the cephalic region lays hold on the fixed
point towards which all the rest of the body is dragged for-
ward. In fact, in the posterior region an opposite phenome-
non takes place; each new band which takes its rise there, is
accompanied by a backward motion of that region, which moves
as if it were drawn by a longitudinal retraction of the con-
tractile tissue.

Other modes of creeping are not less curious; that, for
example, which takes place in the interior of a solid body ;
as a worm, when it advances in the tubular cavity which it
has hollowed out in the ground. ‘The hinder part of the body,
soft and extensible, is assuredly of much less size than the
cavity of the hole from which we endeavour to pull it, and
yet the worm resists the force of traction, and breaks rather
than be drawn out. ‘This is because, within the ground,
the anterior portion of the body, shortened but swollen, dilates
within the passage, and finds there a solid point of resistance.
If we let the worm go we shall see it rapidly shorten its
body, and withdraw the rest of it into the ground, being
dragged backward towards the anterior portion which has a
firm hold on the soil.

By the side of the action of creeping we may naturally
place that of climbing, in which the anterior limbs seek to liy
hold of some elevated projection, and as they bend raise the
rest of the body of the animal. ‘The hinder part then fixes
itself in its new position, and the anterior limbs, thus set free,
seek, higher up, a fresh resting place to make a new effort.
What different types in these two modes of terrestrial locomo-
tion! ‘The varieties are so great that we can scarcely give
an exact idea of them, except by describing the mode of pro-
gression adopted by each particular animal.

Locomotion in water presents a still greater diversity. In
one case, we see a fish which strikes the water with the flat
of its tail; in another, a cuttle fish or a medusa, which, com-
pressing forcibly its pouch full of liquid, drives out the water
in one direction and propels itself in a course directly opposite ;
the same phenomenon is produced when a mollusk closes rapidly
the valves of its shell, and projects itself in the direction opposed
to the current of water which it has produced. ‘The larvee of

LOCOMOTION IN GENERAL. 107

dragon-flies expel from their intestines avery strong jet of liquid,
aud acquire, by this means, a rapid and forcible impulse.

The oar is found in many insects which move on the sur-
face of the water. A contrivance is employed by other
animals, which resembles the action of an oar used at the
stern of a boat in the process called scewling. ‘To this
latter motive power may be referred all those movements
in which an inclined plane is displaced in the liquid,
and finds in the resistance of the water, which it presses
obliquely, two component forces, of which one furnishes a
movement of propulsion. ‘This mechanism will require some
explanation; it will be found in its proper place, with all
the developments which it affords.

Aérial locomotion. This mechanism is still the same; the
motion of an inclined plane, which causes motion through
the air. The wing, in fact, in the insect as well as in
the bird, strikes the air in an oblique manner, repels it in a
certain direction, and gives the body a motion directly oppo-
site. With the exception of certain birds which spread their
wings to the wind, and which, hovering thus without any
other cffort than simply stecring, have received the picturesque
name of hovering or sailing birds (oiseaux voiliers), all
animals move forward only by an cflurt exerted between two
masses unequally movable. It can be easily understood that
if one of these points where the force is applied is absolutely
fixed, the other alone will receive without diminution the
motive work developed ; such is the condition of terrestrial
locomotion on soil perfectly solid. But we can understand
also that the softuess of the ground constitutes a condition un-
favourable to the utilization of the force employed, and that
the extreme mobility both of the air and the water offer still
less favourable conditions for swimming or flight.

But this mobility of the point of resistance varies with the
rapidity of the movement; so that a certain stroke of the
wing or the oar, which would be without effect if produced
slowly, would become efficacious by its very rapidity.

In different kinds of locomotion, the resistance which it
is necessary to overcome in order to displace the body, does
uot vary less than that which serves as an cxternal point of

108 ANIMAL MECHANISM.

resistance. This variability depends on many causes. Thus,
different kinds of animals, when they move, have not to
struggle with the same effort against their weight. ‘The fish,
which is of nearly the same specific gravity as water, finds
itself suspended in it without having to exert any force;
aud if it wishes to move in any direction, it has only to
overcome the resistance of the fluid which it is necessary
to displace. The bird, on the contrary, if it desires to sus-
tain itself in the air, must make an effort capable of
neutralizing the action of its weight. If it moves forward
at the same time, it must perform, in addition, the work
which is consumed in overcoming the resistance of the air.

Partition of muscular force between the points of resistance and
the muss of the body. When, in physivlogy, we seek to es-
timate the work of a muscle, we fix it firmly by oue of its
attachinents, and we ascertain the extent passed through
by its movable extremity. If we know the weight which
this muscle can raise as it contracts, and the extent through
which that weight is raised, we have elements by which we
can estimate the work effected. But these are almost ideal
conditions, which are scarcely ever found in terrestrial loco-
motion; nor can we observe them in animals which move in
the water, and more especially in those which fly through the
air. Let us only compare the effort necessary to walk on a
movable soil, on sandy dunes, for instance, with that required
in walking on firm soil, We shall see that the mobility of
the resisting surface presented by the sand destroys a part of
the effort necessary for the contraction of our muscles; in
other words, that a greater effort is necessary to produce the
same useful work, when the point of resistance is not stable.

This amount of work is easy to be understood, and even to
be measured.

When a man, while walking, places one of his feet on the
ground, the corresponding leg, slightly bent, draws itself up,
and pressing on the ground below, gives at the same time an
upward impulse to the body. If the ground entirely resist
this pressure, all the movement produced will be in the
direction of the trunk of the body, which will be raised
to a certain height, three centimetres for example. But if

LOCOMOTION IN GENERAL. 109

the ground sink two centimetres under the pressure of the
foot, it is evident that the body will only be raised one
centimetre, and the useful work will be diminished by two-
thirds.

The compression of the soil under the foot certainly con-
stitutes work, according to the mechanical definition of this
word. In fact, the soil, as it yields, offers a certain resist-
ance. This resistance must be multiplied by the extent to
which the soil is indented, in order to ascertain the value of
the work accomplished in this direction. But this woik is
absolutely useless with respect to locomotion: it is an entire
loss of the motive force expended.

When a fish strikes the water with his tail, in order to
drive himself forward, he executes a double work; a part
tends to drive behind him a certain mass of fluid with a
certain velocity, and the other to drive the animal forward in
spite of the resistance of the surrounding water. ‘his last
work alone is utilized; it would be much more considerable
if the tail of the animal met with a solid point of resistance
instead of the water which flies from before it.

Is it possible to measure the diminution of useful work
in locomotion, according to the greater or less mobility of the
point of resistance ?

If the ground on which we walk resist perfectly, it must be
admitted that no part of the muscular work is lost; but in
every case in which a displacement of the resisting surface
exists at the same time as that of the body, it is necessary to
determine the law according to which this partition is made.
A principle established by Newton regulates the science of
mechanics; this is that ‘action and re-action are equal.”
Does this mean, in the case before us, that half of the work
is expended on the resisting surface, and the other half on
the displacement of the body of the animal? ‘This cannot be
true, if we may judge by the many cases in which a force acts
on two bodies at the same time.

Thus, in the science of projectiles, the motive force of the
powder—that is to say, the pressure of the gases which are
disengaged in the cannon, acts at the same time on the pro-
jectile and on the piece, giving these masses a velocity in

110 ANIMAL MECITANISM.

opposite directions. Thus, the momentum (M.V.) is equally
divided Letween the two projectiles, so that the mass of the
caunon and of its carriage, multipliel by the velocity of the
recoil which is communicated to it, is equal to the mass of
the projectile multiplied by the velocity of propulsion which
it recvives. As the cannon weighs much more than the ball,
the velocity of its recoil is much less than that communi-
cated to the projectile.

As to the work develope: by the powder against the cannon
and against the ball, it is Bustos very unequally between
these two masses.

In fact, the work produced by an active force being pro-
portional to the square of the velocity of the mass in motion
(its formula is %*), calculation shows that this work, when
the piece weighs 300 times more than the ball, would be 300
times greater for the ball than for the cannon.

We shall return to these questions, when in considering the
particular kinds of animal motion, we enter on the investiga-
tion of liuman locomotion.

CHAPTER II.
TERRESTRIAL LOCOMOTION (BIPEDS).

Choice of certain types in order to study terrestrial locomotion — Human
locomotion— Walking — Pressure exerted on the ground, its duration
and intensity—Re-actions on the body during walking—Graphic
method of studying them—Vertical oscillations of the body—
Horizoutal oscillatiuns—Attempt to represent the trajectory of the
pubis—Forward movement of the body —Ineqnalities of its velocity
during the time occupied by a pace.

ACT OF WALKING IN MAN,

Tue types of terrestrial locomotion are so various that we
must, for a time at least, confine ourselves to the study of the
most important among them. Tor locomotion among: bipeds
we will tuke as a type that of man. The horse will be chosen

TERRESTRIAL MOTION (MAN). TH

as the most important reprexentative of the method of walking
adopted by quadrupeds. As to other animals, they will be
studied in an accessory manner, and especially with reference
to the resemblances and differences which the modes of their
locomotion present when compared with the types which we
have chosen.

Many authors have already treated on this sulject; from
the time of Borelli to that of modern plisiologists, science
has slowly advanced: it seems to us that it can now resolve
all obscure questions, and determine them definitely, by the
employment of the graphic method.

While observation employed alone furnishes only incom-
plete and sometimes false data, the graphic method carries its
precision into the analysis of the very complex movements
concerned in locomotion. We shall sce, when we treat of the
paces of the horse, that the disagreement we find among
writers on this subject shows clearly the insufficiency of the
methods hitherto employed.

Ifuman locomotion, though much more simple in its mechan-
isin, is still very difficult to analyse; the works of the two
Webers, though considered as the deepest investigation of
human locomotion that have yet been made, show many
omissions an some errors.

The most simple and usual pace is walking, which, according
to the received definition, consists in that mode of locomotion
in which the body never quits the ground. In running and
leaping, on the contrary, we shall see that the body is en-
tirely raised above the ground, and remains suspended during
a certain time,

In walking, the weight of the body passes alternately from
one leg to the other, and as each of these limbs places itself
in turn before the other, the body is thus continually carried
forward. ‘This action appears very simple at first sight, but
its complexity is soon observed when we seek to ascertain
what are the movements which concur in producing this
motion.

We see, in fact, that each movement of the limbs brings
under consideration a phase of impact and one of support in
euch of these; the different articulations bend and extend

112 ANIMAL MECHANISM.

alternately, while the muscles of the leg and the thigh, which
produce these movements, pass through alternations of con-
traction and relaxation.

The intensity of the pressure of the feet on the ground
varies with the rapidity of walking and with the length of the
step. Besides this, the body passes through periodical oscil-
lations, the re-action of the impact of each foot on the ground;
and the different parts of the body are subject to this re-action
in various degrees. ‘These oscillations are produced in diffe-
rent directions; some are vertical, others horizontal, so that
the trajectory which follows any point of a body is a very
complex curve. In addition to this, the body is inclined and
drawn up again at each movement of one of tle legs; it
revolves as on a pivot round the coxo-femoral articulation, at the
same time that it is slightly bent following the axis of the
vertebral column; and, under the action of the lumbar muscles,
the pelvis moves and oscillates with a sort of rolling motion.
At the same time the anterior limbs, exerting an alternate
halancing power, Jessen the influences which, at each instant,
tend to cause the budy to deviate from the straight cvurse
which it strives to maintain.

All these acts have been analysed with much sagacity by
oue of our pupils, Mons..G. Carlet,* from wlum we quote some
of the results which he has obtained.

The motive force developed in walking, its pressure on the
ground in one direction, and its propelling effects on the mass
of the body on the other land, are the three elements which
will at first occupy our attention.

Motive force. ‘This is found in the action of the exterior
muscles of the thigh, the leg, and the foot. The lower limb
forms, as a whole, a broken column, whose angles are rounded
off, and whose return to the perpendicular is effected by pres-
sure on the ground below, and on the body above. This is all
that we can say on this head, which, if treated more at length,
would require considerable amplifications.

Pressure on the ground. ‘This pressure, equal, as we have
hefore scen, to that in the opposite direction, which tends to
impel the body forward, must be studied in its duration, its

* G. Carlet, Etude de la Marche. Annales des Sciences naturelles, 1872.

WALKING. L138

phases, und its intensity. The registering apparatus enables us
to do this perfectly ; an experimental instrument placed under
the sole of the foot is connected with a lever which gives the
signals of the impact and of the rising of the foot, as well as
tie expression of the force with which the foot is pressed upon
the ground. We call this first instrument the e perimental
shoe, which may be thus described :—
Under the sole of an ordinary shoe is fixed with heated
gutta percha a strong sole of india- rubber 1} centimetres in
Alene. Within this sole there is an air chamber, which

in fig. 19 is represented by dotted lines.

Fic. 19.—Experimental shoe, intended to show the pressure of the foot
on the ground, with its duration and its phases.

This chamber, having upon it a small piece of projecting
wood, is compressed at the moment that the foot exerts its
pressure on the ground. The air expelled from this cavity
escapes by a tube into a drum with a lever attached, which
registers the duration and the phases of the pressure of
the foot.

Let us suppose that the experimenter is provided on both
feet with similar shoes, and that he walks at a regular pace
round a table which supports the registering apparatus; we
shall then understand the arrangement of the experiment.

The registering instruments employed are already known to
the reader; they resemble in all poimts those which have

114 ANIMAL MECHANISM.

—

served for the investigation of the muscular wave (fig. 7,
page 37). Ifwe substitute in this figure an experimental
shoe for each of the myographical clips 1 and 2, we shall
have the arrangement of the apparatus necessary for the study
of fuotsteps or impacts of the foot on the ground.

Fig. 20 has been furnished by an experiment in walking.
Two tracings are given by the intermittent pressure of the
feet on the ground. The full line D corresponds with the
right foot; the dotted line with the left.

lic. 20.—Tracings of the impact and the rise of the two feet in our ordinary walk.

Knowing the arrangement of the apparatus, we can under-
stand that each impact of the foot on the ground will be
represented by the elevated part of the corresponding curve.
In fact, the pressure of the foot on the ground compresses the
india-rubber sole and diminishes the capacity of the included
air-chamber, A part of the contained air escapes by the con-
uecting tube, and passes into the registering drum,

We see in fig. 20 that the pressure of the right foot, for
instance, Commences at the moment when that of the left
begins to decrease; and that in all the tracings there is an
uliernation between the impacts of the two feet. The period
of support of each foot is shown by a horizontal line which
joins the minima of two successive curves.

The impacts of the right and left feet liave the same dura-
t-on, so that the weight of the body passes alternately from
one foot to the other. It would not be the same with respect
to a lame person; lameness corresponds essentially with the
inequality of the impacts of the two feet.

There is always a very short period during which the body
iS partially supported by one foot, but when it already be-
rea is to rest on the other; this time is scarcely equal to the

WALKING. 115

sixth pert cf the duration of a single tpact or pressure of
the foot.

Litensity of the pressure of the foot upon the ground.—The
curves traced by walking may also furnish the measure of the
effort exerted by the foot upon the ground. The eaperimental
shoes constitute a kind of dynameter of pressure; they com-
press the drum, less or more, according to the effort they
exert ; and consequently they transmit to the registering lever
more or less extensive movements. In order to estimate,
according to the elevation of the curve, the pressure exerted
by the foot, we must substitute for the weight of the body a
certain number of kilogrammes. We see thus that, if the
weight of the body (75 kilograimmes, for example) is sufficient
to raise the lever to the height which it attains at the com-
mencement of euch curve, an additional weight will be required
to raise it to the maximum elevation which it attains towards
the end of its period of pressure.

That proves that, in walking, the pressure of the foot on
the ground is not only equal to the weight of the body which
the foot has te sustain, but that a greater effort is produced at
a given moment in order to give tle body the movements of
elevation and progression which we have just been studying.

According to Mons. Carlet, this additional effort is not more
than 20 kilogrammes, even in rapid walking, but it is much
greater In running and leaping.

Teactions.—We shall designate by this name the movements
which the action of the leg produces on the mass of the body.
These movements are very complex; they are effected at tle
same time in every direction, and give to the trajectory
which a point of the body describes in space, some very com-
plicated sinuosities. ‘The graphic method alone can enable
us, at least as yet, to appreciate the real nature of these
movements.

In the first place, what point of the body shall we choose
in order to observe the displacement caused by the act of
walking? Almost all authors have taken for this purpose the
cenire of gravity, the point which Borelli places iter nates et
pubim. But if we reflect that the centre of gravity changes
as soon as the body nioves, that in the flexion of the legs this

116 ANIMAL MECHANISM.

centre rises, that it is altered if we raise our arms, that, in
fact, it describes within the interior of the body all sorts of
movements, as soon as we cease to be motionless, it is easy
to understand that it will be impossible to refer to this
ideal and movable point, the reactionary movements produced
by the pressure of the feet upon the ground. It will be
better to choose a determinate part of the truuk of the body,
the pubis, for example, in order to study its movements in the
act of walking.

Fic. 21.—Transmission of an oscillatory movement tothe registering apparatus.
g S Up

The instrament which we have already employed will be
applicable to the study of these displacements.

Let there he two lever drums, united by a long tube T TT.
Let a vertical oscillary movement be given to one of these
levers, so as, for example, to carry the lever L downwards
into the position indicated by the dotted line, the cther lever
will be displaced in the opposite direction, and wiil assume the
position also shown by the dotted line near it. Under these
conditions the lowering of one lever corresponds with the ele-
vation of the other, since the compression of the air in one of
the drums must lead to its expansion in the other. If we
wish to obtain from the two parts of the apparatus indications
in the same direction, it would be necessary to turn one of
the drums, so as to place its lever downwards.

Vertical oscillations of the body —Let us suppose that one of
these levers traces a curve on the registering apparatus, while
the other rests, by its point, on the pubis of a man who is

WALKING. by

walking; all the vertical oscillations of the pubis will be
registered.

But, in order that the experimental lever may receive and
transmit faithfully the vertical oscillations which the pubis
executes during the act of walking, the drum itself must be
protected from these oscillations. For this purpose an instru-
ment has been invented, composed of two horizontal arms,
which turn on a centre. These arms can move only in a hori-
zontal plane, situated at the height of the pubis of the person
under experiment; to one of these arms is fixed the experi-
mental lever drum.

Fic. 22.—The upper curves, one in full line. the other do'ted, represent
the phases of the impact and of the rise of the right and left foot. Reading
the figure from left to right, each rise of the curve denotes the commence-
ment of pressure: the upper horizontal part corresponds with the dura-
tion of the pressure, and the descent with the rise of the foot. The
lower horizontal part cf the curve indicates that the corresponding foot
is intheair. © Pv. Oscillations of the pubis from above downwards,
that is. vertically, O Ph. Oscillations in a lateral direction, or hori-
zontally. It is evident that two oscillations in the vertical direction
correspond with a single horizontal oscillation.

The person who walks, follows during this time a circular
path, pushing before him the arm of the instrument, to which
is fixed the apparatus which is to experiment on the vertical
vscillations of the pubis. We get thus the tracing repre-

118 ANIMAL MECIIANISM.

sented by the line O Po (fig. 22). It is seen that the pubis
rises at the middle of the pressure exerted by each foot, and
sinks at the instant when the weight of the body passes from
one foot to the other.

The real amplitude of these oscillations is about 14 milli-
metres, according to Mons. Carlet. This movement, however,
varies with the length of the step; it increases with it, but
this increase does not depend on the maxima of the curve
being more elevated, but on its minima being lower.

We may explain these phenomena very easily. When the
body is about to quit the support of one leg, this limb is in
an inclined position, and the result of its obliquity is that its
superior extremity which sustains the trunk is at a Jess height.
The other leg, which reaches the ground at this instant, is
slightly bent; it will soon draw itself up, and thus raise the
body which is supported by it; but in this movement, the
leg describes the are of a circle around the foot resting on the
ground; therefore, in the series of successive positions which
it occupies, the body rises more and more as the leg which
supports it approaches the vertical position; it sinks again as
the leg becomes oblique.

We can easily perceive that the length of the step lowers
the trunk, by increasing the obliquity of the legs. Indeed,
the constant character found in the maxima of the vertical
oscillations is explained by this fact, that the leg, when ex-
tended and vertical, constitutes necessarily a constant height
—that which answers to the maximum of the elevation of the
body.

Horizontal oscillations of the body.—The pubis, since that is
the point whose displacement we are now studying, is carried
alternately from left to right, and from right to left, at the
same time as it moves vertically. In order to register these
movements, we make use of a lever-drum arranged in such a
manner that the membrane is forced inwards and outwards
alternately by the lateral movements which are given to the
lever. During this time the registering lever, connected with
it by means of the tube, oscillates vertically, in which direc-
tion alone tracings can be made on the cylinder. If, in the
curve which is traced, the elevation corresponds with a trans-

WALKING. 119

ference of the pubis towards the right, the depression will
express a deviation of this point towards the left.

The experiment gives the curve O Ph (fig. 22) for the
tracing of the horizontal oscillations. It is first to be ob-
served that the number of these oscillations is only half that
of those which take place in the vertical direction ; so that
the body is carried towards the right side at the moment of
the maximum of elevation, which corresponds with the middle
of the pressure on the right foot, and towards the left at the
middle of the pressure on the left foot. This lateral sway-
ing of the trunk is the consequence of the alternate passage
of the body into a position sensibly vertical over each foot.

If we would give un idea of the true trajectory of the pubis
under the influence of these two orders of oscillations com-
bined with forward movement, we must coustruct a solid
figure. With an iron wire bent in different directions, we
inay illustrate very clearly this trajectory. Fig. 23 is intended
to reyresent the perspective view of this twisted iron wire ;
but we can scarcely expect the reader to comprehend clearly
this mode of representation.

Fic. 23.—Attempt to illustrate, by means of a metallic wire, the sinuous
trajectory passed through by the pubis. To understand the sketch of
this selid f gure, we must suppo e the wire to be close to the observer
atits left hand extremity, while it is removed from him at the right ex-
tremity. The amplitude of the oscillations has been greatly exaggerated
to render them more intelligible.

In short, according to the formula of Mons. Carlet, the
trajectory of the pubis may be inscribed in a hollow half-
cylinder, with its concave portion upwards, at the base of

120 ANIMAL MECHANISM.

which lie the minima, and on the sides of which, the maxima
terminate tangentially.

Forward progress of the body.—lIt is clear that during the
act of walking, the body never ceases to advance; but the
forward movement has not always the same velocity. To
appreciate these alternate phases of acceleration and retarda-
tion, it is necessary to employ a method which would give the
measurement of tle space passed through during each of the

Fic. 24.—Showing two snecessive positions of the arm of the instrument

and the ¢ rresponding positions of the tracing points of the levers rhe
arm of th lever being three metres in length, and the radius of the
cylinder being only six centimetres, a similar angular displacement of
the person walking, and of the style which writes, will correspond with
paces Which will be to each otter as 50 tol

movements in the act of walking, and which would also
express the time employed in passing through each of these
spaces. In order to obtain this double indication, we have
recourse to the following method :—

It is necessary, first, to ascertain how far the body advances
at the different instants of the act of walking. This measure
of the spaces passed through, is obtained by inseribing the
curves of locomotion, no longer on a cylinder turning with a

revular motion, but on an immovable one, on which the

WALKING. TOW

registering levers are displaced by a quantity proportionate to
the space passed through.

For this purpose the cylinder is placed on the axis round
which the instrument turns, and on the central end of one of
these revolving arms the registering instruments are fixed.
The ratio of the radius of the cylinder to that of the circle
described by the person walking, allows us to estimate in the
tracings the length of the space passed through at each instant.
This ratio was 50 to 1 in our experiments.

Thus, in the tracing obtained, if from one point to another
we reckon an interval of a centimetre, this corresponds with
50 centimetres passed over on the ground by the person
walking. ‘This first notion would be but slightly interesting
in itself, since it would teach us nothing more than what we
learn concerning the intervals between two positions of the
feet, as measured on the ground. The impressions left by
our steps on soft ground would furnish in a very simple’
manner this measurement. But if, in addition to this kuow-
ledge of the space traversed, the tracing gives us the intima-
tion of the time passed in traversing it, we are provided
with a method of estimating the rapidity of the advance of the
body at every instant.

Fie. 25.—D. Tracing of the impact and rise of the right foot, furnished hy
a lever subjected at the same time to 10 vibrations per second. It is
seen that the vibrations occuny more space at the end of the pressure
of the foot; this expresses the greatest rapidity of the advance of the
body at this moment. ‘he same accelerition is observed at the end of
the period of support of the right foot; this is explained by the action
of the left foot, which is, at th sm ment, at the end of its pressure.

Fig. 25 shows (line D) the tracings of the impact and rise
of a limb, and those of the vibrations of a chronograph
inscribed simultaneously. To obtain these tracings, we cause
to converge at the same time, on the same lever-drum, two
transmitting tubes, one of which conveys the variations of

12?

~~

ANIMAL MECHANISM.

gre

pressure to which the experimental shoe is sul,jected (fig. 19),
and the other, ten vibrations per second furnished by a chrouo-
phic tuning-fork of large size.

Fic. 26

A large tunine-fork whose vibrations are reduced by masses of
lead to 10 per second acts on the registering lever drum, by an experi
mental drum atta hed to on f its branches Chis also receives at the
same time, by a tube with two branche th
and rising of the foot of the

influence both of the impact
person who walks

Fig. 20 shows how these instruments are arranged.

It. 36
seen that the drum will be affected by the double influence

WALKING. 123

of the changes in the pressure of the foot on the ground, and
of the vibrations of the tuning-fork ; and this produces in a
single tracing the interference of two movements, giving at
the same time the notion of the spice traversed, and that of
the time employed in passing over it.

In order to analyse this tracing, let us consider only, in the
first place, tle sinuous curve which obeys at the same time
the tuning-fork, and tle experimental shoe on the right foot ;
and in this curve let us only examine the elevated part—that
which cvrresponds with the pressure of the foot wpon the
ground. We see that, during the duration of this pressure,
the style las passed through a space on the cylinder measuring
about 2 centimetres ; therefore, as the displacement of the style
is fifty times less than that of the persou walking, he will have
advanced about one metre during the pressure of one foot. But
while he traversed this metre, he did not advance with an
uniform velocity; in fact, during the first half of this distance,
the tuning fork made about four vibrations, whilst in the
second, it has scarcely made two andahalf. ‘Thus the foot
which presses the ground with a force increasing from the
commencement to the end of its impact, gives tle body an
impulse whose velocity equally increases.

During the rise of the foot, the line traced by the tuning-
fork indicates also that the body of the person walking
progresses with an accelerated motion. That is easily under-
stood if we remember that, in walking, the rise of one foot
corresponds exactly with the tread of the other. It is, there-
fore, the impact of the left foot on the ground which gives the
body of the walking person an accelerated motion, which is
observed during the rise of the right foot.

This method appears to us applicable to all cases in which
it is necessary to measure the relative durations of different
phases of movement.

The inequality in the speed of the man who walks brings
with it an important consequence. When a man drags a
load, the effort which he makes cannot be constant; at each
feot-fall a reduubled energy is produced in the traction that is
developed, and as this increase of effort has but a very short
duration, a series of shocks, as we may call them, occurs at

124 ANIMAL MECHANISM.

each instant. But we know that these shocks are very un-
fuvourable to the full utilization of mechanical force; we have
explained (page 49) the inconvenience which would arise
from them in the work of living motive agents, and the
manner in which these shocks are lessened by the elasticity
of muscular fibre.

Under the conditions in which a man dragging a load is
placed, if he is attached by a rigid strap to the mass which
he has to draw, the shocks of which we have spoken will be
produced, and he will feel their reaction on his shoulders. In
order to avoid these painful jerks, and to utilize more fully
the effort which he makes, we have placed between the car-
riage and the traction strap an intermediate elastic portion,
the effect of which has answered our expectations.

We are endeavouring to construct analogous contrivances,
which may be adapted to the traces of ordinary carriages, so
as to lessen the violence of the pressure on the collar, and to
utilize more fully the strength of the horse.

CHAPTER III.
TIE DIFFERENT MODES OF PROGRESSION USED BY MAN.

Description of the apparatus for the purpose of studying the various modes
of progression used by man—Portable registering apparatus —Experi-
mental apparatus for vertical reactions —Walking—Running —Gallop
—— Leaping on two feet and hopping on one—Notation of these various
methods— Definition of a pace in any of these kinds of locomotion
—Syuthetic reproduction of the various modes of progression.

Tue principal modes of progression employed by animals,
are walking, which we have already described at some length
us fur as it relates to man, running at different rates of speed,
the gallop, and leaping on one or two feet.

The act of walking varies according to the nature or the
slope of the ground; we sliuall have to treat of these different
influences.

In this new study it is no longer possible to employ the

MODES OF PROGRESSION USED BY MAN. 2

apparatus which we have used in our previous researches,
The cireular and horizontal track on which the experimenter
was obliged to walk must be exchanged for surfaces of every
kind and of every slope.

If the new instruments to which we must have recourse
leave the experimenter more liberty in his movements, they
are, on the other hand, relatively less complete as to the indi-
cations which they furnish; therefore, we can only require
from them two kinds of indications ; those of the pressures of
the feet on the ground, and those of the vertical re-actions
which are communicated to the body by these pressures.

Vig. 27 shows a runner furnished with apparatus of the
new construction. He wears the experimental shoes which
we have already described, and holds in his hand a portable
registering instrument, on which are traced the curves produced
by the pressure of his feet. As the cylinder of this instru-
ment turns uniformly, the curves will be registered in propor-
tion to the time, and not to the space traversed during each
of the acts by which this curve is traced.

In order to facilitate the experiment, and to allow the
apparatus to assume a uniform motion before it traces on the
paper, we have recourse to a special expedient. The points
of the tracing levers do not touch the cylinder; but in order
to bring them in contact with the paper, an india-rubber ball
must be compressed. As soon as this compression ceases, thie
points retreat from the cylinder, and the tracing is no longer
produced. In fig. 27 the runner holds this ball in his left
liand, and compresses it with his thumb.

In addition to this, the runner, in order to obtain the
tracings of the vertical re-actions, carries on his head an
instrument whose arrangement is represented in fig. 28.

It is an experimental lever-drum fixed on a piece of wood,
which is fastened with moulding wax on the head of the ex-
perimenter, as seen in fig. 27. The drum is provided with
a piece of lead placed at the extremity of its lever; this mass
acts by its tertia.

While the body oscillates vertically, the mass of lead resists
these movements, and causes the membrane of the drum to
sink when the body rises, and to rise when the body descends.

ANIMAL MECHANISM.

126

1

Hi]

i

‘=
:

Fic, 27.—Runner provided with the apparatus intended to register his
different paces,

MODES OF PROGRESSION USED BY MAN. 127

From these alternate actions a current of air results, which,
transmitted by a tube to a registering lever, shows by a curve
the oscillatory movements of the body.

Fic. 28.—Instrument to register the vertical re-actions during the various p:ces.

We will not enter into the details of the experiments which
have served to verify the exactitude of the tracings thus
obtained ; they consisted in adjusting the weight of the dise
of lead and the elasticity of the membrane of the drum,
until the movements given to the apparatus are faithfully
represented in the tracing.

We will eall step-curves each of the curves formed by the
pressure of a foot upon the ground, and we will designate by
the name of ascending or descending oscillations, the curve of
the vertical re-actions on the body.

1. Of walking. —We have already pointed out the distine-
{ive character of walking considered as one of the modes of
progression in man. We have said that the body, in walking,
never leaves the ground, and that the footsteps follow each
other without any interval, so that the weight of the body
passes alternately from one foot to the other.

But this definition cannot apply to walking on an inclined
surface, on yielding soil, or upstairs. Being obliged to pass
rapidly over these peculiar conditions of walking, we will only
give the tracing which corresponds with the act of mounting
a staircase (fig. 29).

It is to be remarked that the step-curves encroach on each
other, showing that each foot is still pressing on the ground,
when the other has already planted itself on the next step.
Besides this, it is at the time of this double pressure that
the lower foot exerts its maximum force; it is at this moment,
in fact, that the work is produced which raises the body to
the whole height of a step.

—
ras)
es

ANIMAL MECIIANISM.

Nothing like this is observed in the descent of a staircase ;
the step-curves cease to encroach on each other, and succeed
each other very nearly as in ordinary walking on level
ground.

Fie. 29 —Tracing produced by walking upstairs. TD. tracing of the pressure
und vise of the right foot (full line. G. tracing of the left foot (dotted
line) It is seen that the curves produced by the feet encroach one on the
o'ber, and that the maxima of the pressures of the feet correspond with
the end of the pressures.

2. Of running.—This mode of progression, more rapid
than walking, consists, like it, in alternate treads of the two
feet, whose step-curves follow each other at equal intervals ;

the body

but it presents this difference, that in running,
leaves the ground for an instant at each step.

Accordingly, as running is more or less rapid, different
names are given to it; those of the gymnastic march aud the
trot present no utility in a physiological point of view; they
correspond, with but slight variations, to running at various
degrees of speed. To ascertain the principal characters of
this mode of progression, it is only necessary to analyse
fir. 30.

Fic. 30.—Tracing produced by runn’n¢y (in man). D. (curve formed by a
full line), impact and rise of right foot. G. (dotted line) action of the left
foot. O. oscillations and vertical re actions of the b dy.

The pressures of the feet are more energetic than in
walking; in fact, they not only sustain the weight of the

MODES OF PROGRESSION USED BY MAN. 129

body, but impel it with a certain speed both upwards and
forwards. It is known that to give a mass a rising motion,
a greater effort must be exerted than would be sufficient
simply to sustain it.

The duration of the pressures on the ground is less than in
walking; this brevity is proportional to the energy with
which the feet tread on the ground. These two elements,
force and brevity of pressure, increase generally with the
speed at which a person runs. The frequency of the foot-
falls increases also with the speed of the runner; but among
the various kinds of runniye, there are some in which the
extent of space passed over in a given time depends rather
on the extent of each pace than on their number.

The essential character of running is, as we have said, the
time of suspension during which the body remains in the air
between two foot-falls. Fig. 30 clearly shows the suspension, by
the interval which separates the descent of the curves of the
right foot from the ascent of the curves of the left foot, and
vice versd. The duration of this time of suspension seems to
vary but little in an absolute manner; but if we compare it
with the speed of a runner, we see that the relative time
occupied by this suspension increases with the speed of the
course, for the duration of each tread diminishes in proportion
to this speed.

How is this suspension of the body at each impulse of the
feet produced? We might think, on first consideration, that
it is the effect of a kind of leap, in which the body is pro-
jected upwards in so violent a manner by the impulse of the
feet, that it would describe in the air a curve, in the midst of
which it would attain its maximum elevation from the ground.
In order to convince ourselves that such is not the case, let us
make use of the apparatus which registers the re-actions or
vertical oscillations of the body.

In fig. 30 is seen (upper line O) the tracing of oscillations
inrunning. This trace shows us that the body executes each
of its vertical elevations during the downward pressure of the
foot, so that it begins to rise as soon as the foot touches the
ground; it attains its maximum elevation at the middle of the
pressure of this foot, and begins to descend again, in order to

7

130 ANIMAL MECITANISM.

reach its minimum, at the moment when one foot has just
risen, and before the other has reached the ground.

This relation of the vertical oscillatious to the pressure
of the feet shows plainly that the time of suspension does not
depend on the fact that the body, projected into the air, has
left the ground, but that the legs huve withdrawn from the
ground by the effect of their flexion; and this takes place at
the very moment when the bedy was at its greatest elevation.

We shall have again to recur to these phenomena when we
come to speak of tlhe paces of the horse, in which a similar
suspension of the body exists, and which are called on that
account elevated paces.

The influence of the different inclinations of the ground
acts in nearly the same manner in ruuning as in walking,
_ with this difference, that in running, their effects are generally
greater.

3. Of the gallop.—In the modes of progression described
hitherto, the movement of the limbs is regularly alternate, so
that the succession of steps is made at equal intervals.
These are the normal J:inds of human locomotion; but man
can imitate, to a certain extent, by the movements of his feet,
those periodically irregular cadences which are produced by a
horse when he gallops Children, in their amusemeuts, often
imitate this mode of locomotion, when they play at horses.
This abnormal kind of motion is of no interest, except to
explain the mechanism of the gallop in-quadrnpeds.

By registering together the step-cnrves and the re-actions,
it is seen (fig. 31) that the foot placed behind is the first
which reaches the ground; that it exerts an energetic and
prolonged pressure, towards the end of which the foot in front
touches the ground in its turn, but during a shorter time ;
after which there is a considerable period of suspension.
Thus, there is a moment when the two feet are in the air.

In this mode of progression, the re-actions are similar in
character, in some respects, to the pressures. In fxef, a long
re-action (line O) is produced, in which we recognise the
interference of two vertical oscillations, the second of which
commences before the first has finished. After this re-action
there is observed a lowering of the curve, whose minimum

MODES OF PROGRESSION USED BY MAN. 131

corresponds with the moment when the two feet are in
the air.

Fic. 31.—Man galloping with the right foot first. Step-curves and re-
actions. There is an encroachment of one curve over the other, and then
asuspension of the body. The curve O, which corresponds with the
re-actions, snows the effect of the two successive impulses exerted on
the body by the feet.

4. Of leaping.—Although leaping is not a sustained mode
of progression in human locomotion, we will say a few words
about it, in order to complete the series of the movements
which man is able to execute.

The two feet being joined together, we can make a series
of leaps, and advance thus, by imitating the mode of locomo-

tion of some birds, or of certain quadrupeds, as the kangaroo.

Fic. 22.—Leap on two feet at once, D and G. The line R, the curve of re-
actions, shows that the maximum of elevations corresponds with the
middle ot the pressure of the feet.

The apparatus intended to illustrate the vertical oscillations
ot the body, being placed on the head of the experimenter,

132 ANIMAL MECHANISM.

we get three tracings at once ; those of the pressures of the two
feet, and that of the re-actions; these furnish fig. 32

We see here that the maxima of the curve of re-actions
(line R) coincide with the pressures. Thus, by their united
energy, the two legs raise the body, and then let it fall again at
the moment when they bend and prepare to act afresh.

Hopping on one foot gives the tracings (fig. 33) which
only consist in the pressure and rise of a single foot. The
elevations of the body coincide with the step-curves In fact,
when the speed of the leap is lessened, it is prolonged more
especially at the period of the pressure of the foot on the
ground, that of suspension remaining very nearly constant.

Fic. 33.—D, series of hops on the right foot. The duration of the time
of suspension remains evidently constant, even when that of the pressure
of the foot varies,

In certain species of animals, successive leaps constitute
the ordinary mode of locomotion; it will be interesting to
study by the graphic method the various paces of these
animals.

NOTATION OF RHYTHM IN DIFFERENT MODES OF
PROGRESSION.

Among the characters of various modes of progression, it
is the rhythm of the impact of the feet which is the most
striking. The strokes of the feet upon the ground give rise
to sounds, the order of whose succession is sufficient for a per-
son with an ear accustomed to them to recognise the kind of
pace which originates them. We will, therefore, endeavour
to establish the classification of the various paces by attending
to this order of succession.

In order to give the figure of each of these rhythms, we shall
employ the musical notation, modified so as to furnish at the

MODES OF PROGRESSION USED BY MAN. 133

same time the notion of the duration of each pressure, that of
the foot to which this pressure belongs, and also the length of
time during which the body is suspended. ‘This notation of
rhythms is constructed in a very simple manner from the
tracings furnished by the apparatus.

Fic. 34.

Let us return (fig. 34) to the curve which corresponds with
the act of running in man. Below this figure let us draw
two horizontal lines—1 and 2; these will form the staff on
which will be written this simple music, consisting only of
two notes, which we shall call right foot, left foot. From the
commencement of the ascending part of one step-curve be-
longing to the right foot, let us let fall upon the staff a per-
pendicular (a); this line will determine the commencement of
the pressure of the right foot. A perpendicular (4) let fall
from the end of the curve will determine where the pressure
of this foot ends. Between these two points, let us trace a
broad white line; it will express, by its length, the duration
of the pressure of the right foot.

A similar construction made on the step-curve (No. 1) will
give the notation of the pressure of the left foot. The nota-
tions of the left foot lave been shaded with oblique lines to
avoid all confusion.

Between the pressure of the two feet there is found to be silence
in the rhythm; that is to say, the expression of that instant
of the course when the body is suspended above the ground.

134 ANIMAL MECHANISM.

If we note in this manner the rhythms of all the paces used
by man, we shall obtain a synoptical table which will much
facilitate the comparison of these varied rhythms. Fig. 25
represents the synoptical notation of the four kinds of progres-
sion, or paces, which are regularly rhythinical, and in which
the two feet act alternately.

Line 1 represents the notation of the rhythm of the walking
pace, ‘This is the principle of the representation.

The pressure of the right foot on the ground is represented
by a thick white stroke, a sort of rectangle, the length of
which corresponds with the duration of that pressure. For
the left foot there is a greyish rectangle shaded with oblique
lines.

‘These alternations of grey and white express, by their suc-
cession, that in walking the pressure of ove foot succeeds the
other without allowing any interval between the two.

Fic. 35.—Synoptical notation of the four kinds of progression used by man.

Line 2 is the notation which corresponds with the ascent of

w staircase. It is seen, agreeably with what has been already
explained (fig. 29), that the step-curves encroach on each
other, and that, consequently, the body during an instant rests
on both feet at once.

Line 3 corresponds with the rhythm of running. After a
shorter step-curve of the right fuot than in the walking pace,
an interval is reen which corresponds with the suspension of
the body ; then a short impulse of the left fuot, followed by a
fresh suspension, and so on continually.

Line 4 answers to a more rapid rate of running. We find in
it a shorter duration of the pressures, a longer time of the

MODES OF PROGRESSION USED BY MAN, le

Ce
or

suspension of the body, and a more rapid succession of the
various movements

Fic. 36.—Notations of the gallop. 1. Left gallop. 2. Right gallop.

Fig. 36 is the notation of the gallop of children, a mode of
progression in which both the feet do not move in the same
manuer. In this figure, line 1 represents the left gallop—that
is, with the left foot alwavs forward. It is seen that the right
foot presses on the ground first; then the left falls and touches
the ground for a shorter time.

Then, there occurs a suspension of the body, after which
the right foot falls afresh, and so on. ‘The time of the simul-
taneous pressure of both feet is measured according to the
space by which the shaded rectangle rests on the white one.

Line 2 is the notation of the right yallop ; that is to say,
when the right foot is always in advance, reaching the ground
later than the left. Thus, in the gallop, the body is sometimes
in the air, sometimes on one foot, and sometimes supported
by two.

Finally, the notations represented in fig. 87 would be:
upper line, a series of jumps on two feet ; lower line, a series
of hops on the right foot only.

1a, 37.—(Upper line), notation of a series of jumps on two feet. (Lower
line), notaiion of hops on right foot. It is seen that there is constancy
in the durations of suspension, notwitustanding the variability of the
pressures,

This method of representaticn is less complete than the

136 ANIMAL MECIIANISM.

curves given before, for it does not indicate the phases of
variable pressure exerted by the foot upon the ground; but it
is much more simple, and allows the two modes of progression
to be compared much more easily than the other. It will be
seen farther on, when speaking of quadrupedal locomotion,
that the complication of the subject renders it indispensable.
to employ this very simple notation of the rhythm of move-
ment.

Definition of a pace in any kind of progression.—It is usually
considered that a pace is produced by the series of movements
which are executed between the action of one foot and that
of the other, whether we choose for the commencement of
the pace the instant that the feet reach the ground, or that
when they rise from it. Thus, in measuring a pace on the
ground, we usually take as its length the distance which
separates one portion of the print of the right foot from
a similar point of the impression made by the left.

We shall be obliged to depart from this usage. Although
we regret any innovation, yet we shall consider the standard
pace only as half a pace, and we shall thus define it: A pace
is the series of movements executed between two similar positions of
the same foot—between the two successive treads of the right
foot, for example, or two successive elevations of the left
foot, &c.

In the same manner the extent of a pace on the ground
will be the distance which separates two homologous points
taken in the two successive impressions of the same foot.
The pace is estimated in this manner in Mexico. ‘This is the
only method of counting which will prevent errors in the very
complicated moments of quadrupedal progression.

SYNTHETIC REPRODUCTION OF THE MODES OF PROGRESSION
EMPLOYED BY MAN.

Since we have completed the analysis of a phenomenon of
which we now seem to understand all the details, it is by
synthesis that we will endeavour to construct a counter-proof.
This method has proved very useful in verifying our theories
concerning certain physiological actions, as, for instance, the
circulation of the blood. It consisted in representing, by arti-

MODES OF PROGRESSION USED BY MAN. 137

ficial means, the movements and the sounds of the heart, the
arterial pulsations, &c., and we thus proved the correctness
of our theories as to the nature of these phenomena. The
same method will serve hereafter to verify our theories of the
flieht of insects and birds. In the present case it is necessary
to represent, according to the data afforded by analysis, the
movements of walking and of the other paces employed by
man.

Every one knows the ingenious optical instrument invented
by Plateau, and called by him ‘‘Pheénakistoscope.” This
instrument, which is also known by the name of Zootrope,
presents to the eye a series of successive images of persons or
animals represented in various attitudes. When these atti-
tudes are co-ordinated so as to bring before the eye all the
phases of a movement, the illusion is complete; we seem to
see living persons moving in different ways.

This instrument, usually constructed for the amusement of
children, generally represents grotesque or” fantastic figures
moving in a ridiculous manner. But it has occurred to us
that, by depicting on the apparatus figures constructed with
care, and representing faithfully the successive attitudes of the
body during walking, running, &., we might reproduce the
appearance of the different kinds of progression employed
by man.

Mons. Carlet, whose remarkable studies of walking we have
before quoted, aud Mons. Mathias Duval, professor of anatomy
at the Ecole des Beaux-arts, have carried out this plan, and,
after many attempts, have arrived at excellent results.

Mons. Duval is engaged in perfecting his diagram, which
furnishes to the eye sixteen successive positions for each kind
of locomotion employed by man. Each figure is carefully
drawn according to the results afforded by the graphic method.
When rotated with suitable speed, the instrument shows, with
perfect precision, the different movements of walking or run-
ning. But its principal advantage is that, by turning it less
quickly, we cause it to represent the movements much more
slowly, so that the eye can ascertain with the greatest facility
these actions, the succession of which cannot be apprehended in
ordinary walking.

138 ANIMAL MECHANISM.

CHAPTER IV.
QUADRUPEDAL LOCOMOTION STUDIED IN THE ITORSE.

Insufficiency of the senses for the analysis of the paces of the horse — ~
Comparison of Duges— Rhytlins of the paces studied by means of the
ear—Insufficiency of language to express these rhythms —Musical
notation —Notation of the amble, of the walkiny pace, of the trot—
Synoptical table of paces noted according to the definition of each of
them by different authors—Instramenuts intended to determine by the
graphic method the rhythms of the various paces, and the re-actions
which accompany thein.

Tere is scarcely any branch of animal mechanics which |
has given rise to more labour and greater controversy than the
question of the paces of the horse. ‘The subject is one of
great importance to a large number of persons engaged in
special pursuits, but its extreme complexity has caused in-
terminuable discussions. Any one who proposed at the present
time to write a treatise on the paces of the horse, would have
to discuss many different opinions put forward by a great
number of authors.

While reading these works, on which so much sagacity of
observation and such rigorous reasoning have been expended,
one is astonished to find that the greater number of these
writers are not agreed in their definitions of the paces. ‘This
disagreement in similar observers can only be accounted for
on the principle of the insufiiciency of the means at their
disposal to enable them to analyse the very complex and rapid
movements of the horse. ‘The difficulty of expressing in
words the rhythms and the durations of these various move-
ments adds still more to the confusion. When a horse is
running, and passing from one kind of motion to another;
when he moves his limbs with a rapidity which makes one
dizzy, and according to the most varied rhythms, how can we
appreciate and describe faithfully all these actions? It would
be as easy a task, after looking at the fingers of a pianist

PACES OF TIE IIORSE. 139

when running over the keys, to try and describe the move-
ments which have just been executed.

S4ill, in the midst of this confusion, it has been found
possible, by observation alone, to establish certain divisions
which singularly simplify the study. Thus, certain paces give
to the ear a rhythm in which the strokes of the hoots succeed
each other at sufficiently regular intervals; others, such as the
different kinds of gallop, offer au irregular rhythm, recurring
at periodical times, These latter paces are the most difficult
to analyse.

But if we observe a horse either at a walking pace, ambling,
or trotting, and if we concentrate our atteution on the anterior
limbs alone, or on the posterior ones, we perceive that the
rhythm of the impacts and elevations of the right and left
foot entirely resemble those of the feet of a man walking or
running more or less quickly. ‘The alternation of the strokes
of the feet is perfectly regular, if the horse be not lame of
one of the limbs under observation.

If we then pass to the comparison of the movements in the
two fore and hind legs on the same side, we see that the two
feet on the right side, for example, make the same number of
steps, and that if one of them strikes the ground at a greater
or less interval before the other, tlis is preserved as long as
the same pace is continued. Add to this that the length of
the step is the same for both the fore and tind limbs, of
which fact we may convince ourselves by seeing that these
two feet always leave on the ground prints situated at the
same distance from each other. In general, the hind-foot
covers the print left by the corresponding fure-foot; if the
prints be not covered, they preserve always the same distance
from each other. ‘Thus, the steps of the fore and hind legs
are of the same number and the same extent; these facts
liave not escaped former observers.

Dugés has compared the quadruped when walking to two
men placed one before the other, and following each other.
According as these two persons (who ought both to take the
same number of steps) move their limbs simultaneously, or
alternately; according as the man in front executes his move-
meuts more quickly or more slowly than the one behind, we

140 ANIMAL MECHANISM,

see all the rhythms of the movements which characterise
the different paces of the horse reproduced.

Every one has seen in the circus or tlhe masquerade those
figures of animals whose legs are formed by those of two mem
with their bodies concealed in that of the horse. This gro-
tesque imitation bears a striking resemblance to the animal,
when the movements of the two men are well co-ordinated, so
as to reproduce the rhythms of the paces of a real quadruped.

In the examination of tle tracings furnished by the graphic
method when applied to the paces of the horse, we may havo
recourse to the theory propounded by Dugés; we shall then
find the curves furnished by human locomotion twice repeated.
We shall see that the difference between one pace and another
consists in the manner in which the footfalls of the hind leg
of a horse succeed each other, with relation to those of the
fore leg on the same side. But this determination of the
order of the succession of footfalls presents siugular difli-
culties, even for the most skilful observers.

Many attempts have been made to bring to perfection the
means of observation, and to remedy the insufficiency of
language in the description of the observed phenomena.
Long since, the rhythm of the steps according to the sounds
which they produce hus been substituted for their examination
by means of the eye. ‘The ear, in fact, is better adapted than
the eye to distinguish the rhythms or relations of succession.
To ascertain the order in which each limb strikes the ground,
certain experimenters have attached to the legs of the hors»
bells of different tones, which can be easily distinguished from
each other.

A point which has been better ascertained with respect to
the locomotion of the horse, is the determination of the space
passed over on the ground during each of the various kinds
of paces. This space has been directly measured by means
of the distance between the prints of the feet left on the
ground. To render the distinction between the footprints
more easy, each of the animal’s feet has been shod in a
ifferent manner. Besides this, observers have studied the
proportion which exists between the height of the animal and
the length of its various paces. All those who have made

PACES OF THE HORSE. 14]

any progress in this interesting study have arrived at it by
the employment of rigorous methods of observation.

On the other hand, the manner of expressing the observed
phenomena has occupied the attention of different authors.
Almost all have had recourse, with great advantage, to the
use of drawings, but have agreed but little in their mode of
representing the successive actions which characterise the
different paces. The most perfect kind of representation
is that employed during the last century by Vincent and
Goiffon.* A sort of musical staff, eomposed of four lines,
served to note the instant of each impaet of the four feet, and
the duration of the succeeding pressures on the ground. This
notation resembles, to a certain degree, that which we have
employed to represent the different rhythms of human loco-
motion, and which will hereafter serve to explain the various
paces of the horse. But we must not forget that the method
of Vincent and Goiffon only expressed a suecession of move-
ments observed by the sight or the ear, and that it realised no
greater exactitude than that of the individual observer.

Our registering instruments resolve the double problem of
analysing with fidelity the acts whieh the senses could not
accurately appreciate, and expressing clearly the result of this
analysis.

Before we describe our experiments, we shall, in order that
the reader may understand their utility, try to present a
summary of the present state of the science, and to show what
disagreement exists on various points among different authors.
As the standard definitions are not always easy to be under-
stood, we shall add to them the notation of each of the paces,
trusting that this method of representation will render them
more intelligible, and especially more easy to be compared
with each other.

Notation of the carious paces of the horse.—Recurring to the
comparison used by Dugés, let us represent the horse as com-
posed of two bipeds walking one behind the other. We must
determine the manner in which the rise and full of the feet

* Mémoire artificielle des principes relatifs & la fidéle représentation des
animaux, tant er. peinture qu’en sculpture, Alford, 1769,

142 ANIMAL MECHANISM.

succeed each other, in each of the persons supposed to he
walking.

Of the amble.—Let us take the simplest case, in which the
two persons walking steadily go through the same movements
at the same time. If we represent, by the notation before
employed, the movements of these two men, placing at the top
the notation which belongs to the foremost, and below it that
of the hindmost, we shall have the following figure :—

LLL LL

Fie. 38.—Notation of a horse’s amble.

The footfalls of the right and left foot being produced at
the same time by the person walking in frout and by him who
follows, must be represeuted by cates signs placed exactly
over each other. Thus, in the paces of the horse, this
agreement between the movements of the fore and hind limbs
belongs to the amble. ‘The notation (fig. 38) will be that of
a horse’s amble; the upper line referring to the movements
of the fore quarters of the animal, and the lower line to the
hind limbs.

The standard definition is the following: ‘‘The amble is a
kind of pace characterised by the alternate and exclusive
action of two lateral bipeds.” Authors are entirely agreed on
this point. Let us add that in the amble the ear perceives
only two beats at each pace, the two limbs on the same side
striking the ground at the same instant. In the notation
these two sounds are marked by vertical lines joiuing the two
syuchronous impacts.

‘In the amble the pressure of the body on the ground is
said to be lateral, as the two limbs on one side only are in
contact with the ground at the same time.

Of the walking pace.—According to the definition of the
oreater number of authors, the walking pace consists in an
equal succession of impacts of the fvur feet, which strike the
ground in the following order: if the right foot be considered
as moving first, we shall have the following succession —right
fore foot, left hind foot, left fore-foot, and then right hind-foot.

PACES OF THE HORSE. 143

To express this succession of movements of the two persons
walking, it is only necessary to alter the place of the signals of
the hind feet with respect to those of the fore feet. We shall
obtain the rhythm indicated by authors by causing the signals
of the hind feet to slip towards the left, which will give the
following figure :—

Why Lille, GLLLLLLLLLLILLLA TILLED,
fe pelep.tsLoteD
| VILL LLL VDI. ULL

Fic. 39.—Notation of the horse’s walking pace

It is seen, therefore, that when compared with the amble,
the walking pace consists in an anticipation of the hinder
limbs, whose footfalls precede those of the corresponding fore
limbs by the half of the duration of one of their pressures
on the ground.

If the notations be read from left to right, like ordinary
writing, it is evident that each sign situated farther to the
left than another precedes it in order of succession. Thus,
in fig. 39, the impact of the right hind-foot precedes that of
the right fore-foot. But as it is of little consequence, in the
series of successive acts of the same kind of pace, whether we
choose one instant rather than another as the point of depar-
ture, we shall always take as the commencement the impact
of the right fore-foot.

The ear distinguishes four beats, separated by regular
intervals, each of which is indicated in the notation by a
vertical line. Finally, the body rests on the ground twice
laterally and twice diagonally during one entire pace. It is
easy to ascertain this by looking at fig. 39, in which, after
the first impact, the body rests on the right feet (lateral biped
L); after the second impact, on the right foot in front, and
the left foot behind (diagonal biped D), &e.

But this notation only expresses the theory of the most
extended pace. ‘The equality of intervals between the strokes
of the feet is not admitted by all writers. We shall see, in

144 ANIMAL MECHANISM.

the course of our experiments, that the walking puce, in fact,
may present different rhythms.

Of the trot.—The notation of the trot is obtained by a
more decided anticipation of the hinder limbs, each of which
will have entirely completed its pressure on the ground,
and begun to rise at the moment when the fore-leg on the
same side has completed its stroke. Fig. 40 expresses the
absolute alternation of the two persons supposed to be
walking.

Ce ae 777)

ee Wilds

Fia, 40.—Notation of a horse’s trot

Authors agree also on this point, that in the trot, the
limbs which act together are associated in diagonal pairs.

The ear perceives but two sounds of the hoofs, as in the
amble, but with this difference, that it is always a right and
left foot together, and not two feet on the same side, which
produce each sound.

The notation also shows that the pressure of the body on the
ground is always diagonal. What it does not express is, that
between successive pressures, the body of the animal is, for an
instant, suspended in the air. This suspension arises from
the fact that the trot is not a walking, but a running pace, and
that to represent it faithfully we must place together two
notations similar to that which is represented in fig. 34.

We have designedly omitted the time of suspension in the
former notation; it would have rendered a difficult subject
still more complicated. Besides, this suspension does not
always take place; certain horses have a low trot, which has
nothing to characterise it except its rhythm in double time
and the diagonal impacts of the feet.

We will not fatigue the reader by detailing the definition
of all the paces admitted by different authors. We shall
merely present in a synoptical table the series of notations
which correspond with them. In this table (fig. 41) it is
seen, that all the lower paces may be considered as derived

PACES OF THE HORSE. 145

from the amble, and that if we wished to make a methodical
classification, we should group them in a series of which the
amble would be the first term, and all the other terms would
be obtained by means of an increasing anticipation of th

movements of the hinder linbs, Fig. 41 represents this series.
In the notation of each kind of pace, we have left on the same
vertical the impact of the right fore-foot, which we shall choose
as the commencement of each pace, and which will serve as
a point of reference to characterise each kind of locomotion.

This table, prepared from different treatises on the horse,
represents as faithfully as we have been able to depict it,
that which each author admits as constituting each particular
kind of pace. The explanatory notes show the disagreement
which exists between the various theories relative to the suc-
cession of movements which characterise each of them. ‘Thus
we see, that with the exception of the amble, on which all
are agreed, all the other kinds of paces are defined in a
different manner by various authors. ‘Thus, the notation
No. 2, which, aceording to Merehe, would correspond with
the broken amble, would be, according to Bouley, the expres-
sion of the high step, or the pace of Norman ponies; while
this same Norman pace would be, according to Lecoq, that
which is represented in No. 9. We also see that the notation
of No. 3 would correspond, according to Merche, with the
ordinary step of a pacing horse, while Bouley would consider it
as a broken auble, and Lecoq the traquenade ; which traquenade,
according to Merche, would not differ from the pace repre-
sented by the notation No. 10. The ordinary walking pace
itself is not understood in the same manner by different
writers, and if the greater part of them, with Vincent and
Goiffon, Colin, Bouley, &c., admit in this pace a succession of
impacts at unequal intervals, it is to be observed that the
theory of Lecoq and Raabe, concerning the normal pace, is
different.

This disagreement can easily be explained: first, tle
observation of these movements is very difficult; then, each
pace must naturally present, according to the conditions
under which it is studied, the different forms which each
writer has arbitrarily taken as the type of the normal walking

ANIMAL MECHANISM.

WIITTITIVLLLLLLA

ALELULLLLTLLSS ED

VTE LAL be

QITTLLMMALA

VIIIIIISILELSLL LS

HILLLILLLLLLL LL,

IFITILITS SS te

SLLELELLLETEL LS WTTZLLLEEPETLEL A,

WLLL SLILILILLIELSL LE SLITTSTALEL SELL 2

VSLILILESL ES Shh SPTLLIPIULILILLLA

WITILILILILLL LLL:

IIEAITIILSTTES

LELEITLLEL LALLA.

VL OIPIDISISES OA, FP, WITT) VIVAL!

A Avoure av

Fic. 41.—Synoptical notations of the paces of the horse, according to
various writers.—See Description at the foot of page 147.

PACES OF THE JIORSE. 147

pace. Each one has suffered himself to be guided in this
respect by theoretical considerations. Those who admit equal
intervals between the four footfalls, have thought that they
found in this type more clearness and a more decided dis-
tinction between the amble and the trot. The other writers
have attempted the realisation of a certain ideal in the kind
of pace which served them as a type. For Raabe, it was the
maximum of stability, which, according to his theory, is
obtained when the weight of the body rests longer on the two
diagonal feet than on the two lateral feet; whence arises the
choice of the type represented by the notation Nu. 6. Lecoq,
thinking, on the contrary, that the most rapid pace is the best,
has chosen as his type the pace in which the body rests longer on
the two lateral feet than on the diagonal ones (notation No. 4).
Whatever may be the value of these considerations, of
which practical men alone can judge, it seems to us that the
physiologist must first of all endeavour to search for facts, and
must take simply such types as experiment may reveal to him.
It is for this purpose that the investigations have been made with
registering apparatus, the result of which will now be given.

APPARATUS INTENDED FOR TILE STUDY OF TILE MODES
OF LOCOMOTION OF THE HORSE.

For the eaperi.nental shoe employed in the experiments made
on man has been substituted, on the horse, a ball of india-
rubber filled with horsehair, and attached to the hurse’s hoof
by a contrivance which adapts it to the shoe.

DESCRIPTION OF Fia. 41,
No. 1. Amble, according to all writers.

No. 2 Broken amble, according to Merche.
Sues { High step, according tu Bouley.

Ordinary step of a pacing horse, accor.iing to Mazure,
No. 3. 4 Broken amble, according to Bouley.
Traquenade, accordins to Lecoq.

No. 4 Normal walking pace, according to Lecnq.

No. 5. Normal walking pace (Bouley, Vinceut and Goiffon, Soll ysel, Colin).
No. 6.. Normal w:lking pace, according to Raabe.

No. 7. Irregular trot (trot décousw).

No 8. Ordinary trot. (In the figure, it is supposed that the animal trots with-
out leaving the ground, which oceurs but rarely. The notation only takes into
account the rhythm of the impacts of the fect.)

No. 9. Norman pace, from Lecoq.
No. 10. Traquenade, from Merche.

148 ANIMAL MECHANISM.

By turning an adjusting screw we fix it to the horse-shoe
by three catches, which
keep the instrument se-
curely fastened. <A strong
band of india-rubLer passes
over the apparatus (fig. 42),
and keeps in its place the
ball filled with horse-hair,
so as to allow it to rise
slightly above the lower
surface of the hoof. When
the foot strikes the ground,
the india-rubber ball is
compressed, and drives a
part of the confined air
into the registering instru-
ments. When the foot is
raised, the ball recovers its
form, and draws again into
ee its interior the air which
Fic. 42.—Experimentul apparitus fo show the pressure had expelled.
Coa of the horse’s hoof on the These instruments soon
wear out on the road, but
will last during some time on the artificial soil of the riding-
school.
For experiments which we have made on ordinary roads,
we have had recourse to an instrument represented in fig. 43.
To the leg of the horse just above the fetlock joint is
attached a kind of leather bracelet fastened by straps. In front
of this bracelet, which furnishes a solid point of resistance,
are placed various pieces of apparatus. There is, first, a flat
box of india-rubber firmly fixed in front of the bracelet; this
box communicates, by a transmission tube, with the registering
apparatus. Every pressure exerted on the box moves the
corresponding registering lever. It is evident that all the
movements of the horse’s foot are shown by pressures on the
india-rubber box, and are immediately signalled by the regis-
tering levers.
For this purpose, a plate of copper, inclined about 45°, is

aX
AK

4\

i\
(|

DESCRIPTION OF APPARATUS. 149

connected at its upper extremity with a kind of hinge, whilst
its lower end is fastened by a solid wire to the upper face of
the india-rubber box, on
which it presses by means
of a flat disc. On a wire
parallel to the slip of
copper slides a ball of lead,
the position of which can
be varied in order to in-
crease or diminish the
pressure which this jointed
upparatus exerts on the
india-rubber box.

The function of this
apparatus is analogous with
that of the instrument re-
presented in fig. 28, in-
tended to show the re-
actions which are produced
in various kinds of loco-
motion ; only the inclina-
tion of the oscillating por-
tions allows them to act on
the membrane during the
movement of the elevation,
the descent, and the hori-
zontal progress of the foot.

When the hoof meets
the ground the ball has a
tendency to continue its
motion, aud compresses Fia. 43.—Appiratus to give the signals of
with foree the india-rubber the pressure and rise of the horsc s hoof.
box. When the foot rises,
the inertia of the ball produces in its turn a compression
by a kind of mechanism already described with reference to
fig. 28.

Through the kindness of Mons. Pellier, we have been able
to experiment on several horses, ridden by himself, while
holding in his hand the registering instruments.

150 ANIMAL MECHANISM.

When the horse had his feet furnished with the india-rubber
boxes which have just been described, thick transmitting
tubes not easily crushed were fitted to these receptacles.
These tubes are usually fastened by flannel bands to the legs
of the animal, and thence directed to a point of atticlment
at the level of the withers; they are then continued to the
registering apparatus, which has been already described
in the experiments ou biped locomotion. ‘he registrar now

Fic. 44.—This figure represents a trotting hors’, furnished with the divferent
experimental inst)uments ; the horseman carrying the register of the
pace. On the withers «nd the croup ure instruments to show the re-
actions.

carries a great number of levers; he must have four at
least—one for each of the legs, and usually two other levers
which receive their movements cf re-action from the withers
and the croup. Similar kinds of apparatus to those repre-
sented in fiz. 28 are employed for this purpose.

The rider carries by the handle a portable registering in-
strument, to which all the levers give their signals at once ;
the han. which holds the reins is also ready to compress a

PACES OF THE HORSE. 151

ball of india-rubber at the moment when tle horseman wishes
the tracings to commence. Fig. 44 represents the general
arrangement of the apparatus at the moment when the rider
is about to collect the graphic signals of any particular pace.

CHAPTER V.
EXPERIMENTS ON THE PACES OF TITE MORSE.

Doubie aim of these experiments : determination of the movements under
the physivlogical point of view, and of the attitudes with refereuce
to art.

Experiments on the trot—Tracings of the pressures of the feet and of the
re-actious— Notation of the trot— Piste of the trot—Representation
of the trotting horse.

Experiments on the walking pace—Notation of this kind of motion ; its
varieties—Jiste of the walking pace—Itepresentation of a pacing
horse.

Tne aim of these experiments is twofold; as far as
physiology is concerned, we derive from them the expression
of the duration, actions, and re-actions of each pace, the
energy and duration of each movement, and the rhythm of
their succession. But the artist is no less interested in
knowing exactly the attitude which corresponds with each
movement, in order to represent it faithfully with the varions
poses which characterise it. All these details are furnished
by the registering apparatus; the artist need fear no error if
he conform his sketches to the indications furnished by the
tracings made by the instrument.

The remarkable work of Vincent and Goiffon was expressly
intended to establish principles relative to the faithful repre-
sentation of the horse. We shull borrow some things from
this book, which scems to have been too much forgotten, and
not to have excrcised upon art the influence that might havo
been expected. ‘This is doubtless owing, in some degree, to a
certain obscurity in the mode of explanation, and still more
to the fact that the writers, having had recourse only to direct

152 ANIMAL MECIIANISM.

observation in order to analyse the paces of the horse, have
not been able to give all the details. We trust that we shall
be more fortunate in our treatment of the sul,ject; but we are
assured, at least, of the perfect exactitude of the data fur-
nished by the apparatus which we have used.

Cvlonel Duhousset has been kind enough to offer us his
assistance in representing the horse in its various paces; it is
to his skilful pencil that we owe the figures represented in this
chapter, which are the faithful trauslation of the notation
which accompanies them. We are also indebted to Mons.
Duhousset fur some documents relating to the representation
of the paces.

‘The knowledge of the pistes—that is to say, the impressions
which the feet of the horse leave on the ground—is of great
importance ; they euable an experienced eye to recognise the
pace of the animal which has marked them.

These pistes are of extreme value to the artist; they
alone can represent to him the limbs as they strike the ground,
with the true distances which they ought to preserve from
each other according to the size of the horse and the speed of
the pace. We refer the reader to the works of Vincent and
Goiffon, of Baron Curnieu, of Colin, &c., on this subject, con-
tenting ourselves with giving mercly, from these writers, the
piste which characterises each pace.

The first series of experiments, the results of which we are
about to analyse, were made in. the riding school of Mons.
Pellier, fils. The horses were furnished, on each foot, with
an instrument for determining pressures, similar to that which
is represented in fig. 42. We shall first discuss the experi-
ments on the trot; the tracings which they give are easy to
be understood ; the study of these will serve as a preparation
for the more complicated analysis of the other paces.

OF THE TROT.

Experiments on the trot —An old and very quiet horse fur-
nished the tracing represented in fig. 45, In this plate are
shown at the same time the tracings of the pressures of the
four feet. with their notations, and on the other side, the re-
actions produced on the horse by this kind of pace.

wD

THE TROT.

ON

Above are the

s for the fore part of the

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154 ANIMAL MECHANISM.

animal, which are given by the line RA (anterior re-actions),
and from the croup for the hinder part, which correspond
with the line R P (posterior re-actions).

Below are given the curves of pressure of the four feet ;
they are drawn at two different levels; above are the curves
of the anterior, below those of the posterior limbs. In each
of these series the curves of the left foot are drawn with
dotted lines, those of the right with full lines. Whether
dotted or full, these lines have been made thicker for the
fore-limbs than for the hinder ones; this difference, though
of little use in curves as simple as those of the trot, will
serve to render tlhe more complicated tracings much more
intelligible.

The moment when the curve begins its rise, represents the
commencement of the pressure of the foot on the ground.
The instant when the curve descends again gives the signal
of the rise of the foot.* It is seen from these tracings
that the feet A G and P D, left fore-foot and right hind-foot,
strike the ground at the same time. The simultaneous lower-
ing of the curves of the two feet shows that they also rise from
the ground simultaneously. Under these curves is the nota-
tion which represents the pressire of the left diagonal biped.t

The second impact is given by the feet AD and PG (right
diagonal biped), and so on through all the length of the
tracing.

This experiment confirms the correctness of the standard
theory of the trot, and at the same time affords additional
information on some points. Thus, all writers agree in
choosing, as the type of the free trot, the pace in which all the
four feet give but two strokes, and in which the ground is
struck in turn by the two diagonal bipeds. It is admitted

* The duration of the pressure ought to be marked by a horizontal line,
but we have made the tube somewhat narrow in order to lessen the force
of the shocks given to the registering lever; the narrowing of the tube
has slightly affected the curve, which, however, produces no inconvenience
in studying the rhythms.

+ Each diagonal biped is named after the anterior foot of which it forms
a part ; the left diagonal bijcd means, therefore, left fore foot, right lind
foot.

ON THE TROT. 155

also that the trot is a high pace, and that, in the interval
between two successive strukes, the animal is for an instant
raised above the ground.

But we find disagreement when we come to estimate the
duration of this suspension. ‘Thus, according to Bouley, it is
very short in proportion to the duration of the pressure ;
whilst Raabe thinks, on the contrary, that the pressure is
very short, so that the animal is a longer time in the air than
on the ground.

In the notation of the tracing (fig. 45), it is reen that the
pressures are twice as long as the periods during which the
body is suspended above the ground. ‘This experiment, there-
fore, would confirm the opinion of Bouley in opposition to
that of Raabe; but it appears to us that there is a great
variety in the relative duration of the pressures, and of the
periods of suspension above the ground during the trot.
Thus, certain horses running in harness have furnished
tracings in which the phase of suspension was_ scarcely
visible ; so that this form of trot resembled the low paces,
only preserving that characteristic of the free type which
arises from the perfect synchronism of the diagonal strokes of
the feet. We have not yet been able to study the movements
of rapid trotters; in these perhaps we should see, in an
inverse ratio, the time of suspension increase over that of the
duration of pressures.

If we seek to ascertain the correspondence between the
re actions (RR A and R P) and the movements of the limbs, we
see that the moment when the body of the animal is at the
lowest part of its vertical oscillation coincides precisely with
that at which its feet touch the ground. The time of suspen-
sion does not depend on the fact that the body of the horse is
projected into the air, but that all four legs are bent during
this short period. ‘The maximum height of the suspension of
the body corresponds, on the contrary, with the end of the
pressure of the limbs on the ground. It seems, according to
the tracings, that the elevation of the body does not com-
meunce till after each double impact, and that it continues
during the whole time of the pressure.

It is also scen, in tle same fizure, that the re-actions of the

156 ANIMAL MECHANISM.

fore-limbs are much more considerable than those of the
hinder ones. ‘This fact appears to us to be constant; and the
inequality of the re-actions is still more marked in the walk-
ing pace, because the apparatus placed on the withers almost
always gives appreciable re-actions, while that on the croup
gives scarcely any.

Of the irregular trot (trot décousw).—We call that a free
trot which gives two distinct sounds to the ear fur each pace,
and we name that irregular, each sound of whieh is in a cer-
tain degree divided by the want of synchronism in the strokes
of each diagonal biped. ‘The irregular trot has been met
with in many of our experiments. Occasionally this pace was
continued, and then the want of synchronisin existed som: -
times in the impacts of the two diagonal bipeds, and some-
times in‘ one pair only; at other times, on the contrary, the
trot was irregular only for an instant, at the moment of’ the
passage from one kind of pace to another. In all the experi-
ments which we have hitherto made, the want of synchronism
depended on the hinder limb being behind the anterior limb
which corresponded diagonally with it.

Fig. 46 represents the notation of an irregular trot, in
which the diagonal impacts leave between them an appre-
ciable interval of time. We can recognise this by the
obliquity of the dotted line which unites with each other the
impacts of the two diagonal bipeds.

AD

ALLL
> C

SILLS A

Fic. 46.—Notation of the irregular trot.

The piste of the trot is represented in fig. 47, according to
Vincent and Goiffon. All the prints are double, for the
hinder-foot always comes up to take the place of the fore-foot
on the same side.

In fig. 47 we have rendered this superposition imperfect

ON THE TROT. Lon

in order to avoid confusion; for the same purpose, we have
represented the prints of the fore-feet by dotted lines, those of
the lind-feet by full lines. In the trot, the prints of the left
f et alternate perfectly with those of the right feet.

Fie. 47.—Piste of the trot according to Vincent and Goiffon.

According to the speed of the trot, and the size of the
horse, the piste varies much with respect to the space which
separates the prints on the same side

VT ee UUM

& MUU MMMM : UUM

Fia. 48.—Horse trotting with low kind of pace. The instant corresponding
with the attitude represented in this figure, is marked with a white dot
on the notation.
In the representation of the trotting horse we must dis-
tinguish the different forms of this pace.
The low and short trot is represented in fig. 48. We usually

158 ANIMAL MECHANISM.

make our observations at the start of the animal, or at the
moment when he passes from the walking pace to the trot.
The diagonal impacts succeed each other without interval, as
is seen in the notation placed below the figure. ‘The animal
has been depicted from the notation.

The instant which the artist has chosen is that which is
marked in the notation by a white dot. At this moment, as
the superposition indicates, the left fore-foot is at the end of
its pressure ; the right fore-foot is about to reach the ground ;
the right hind-foot is finishing’ its pressure; the left hind-foot
is about to fall. ‘The inclination of the limbs is that which
corresponds with each of the phases of the pressures and the
rise of the feet. The distance separating the feet is that
which is indicated by the prints on the ground. ‘Thus, in
fig. 48, it is seen that the trot is shortened, for the hind-foot.

WMT Te

a
WONT Me Wi, Ubddddlle.
eT

Wiltttltilldls

Fic, 49.—Horse at full trot. The dot placed in the notation corresponds
with the attitude represented

ON TITE WALKING PACE. 159

on the point of striking the ground, will not reach the place
of the fore-foot on the same side.

The elevated and lenythened trot is represented in fig. 49,
which has already served to show the rider and his horse
furnishcd with the ivs'ruments for the purpose of forming
tracings of the various paces. The animal is depicted at the
instant which, in the notation, is represented by a dot; that
is to say, during the time of suspension, at the moment when
the left diagonal biped has just risen and the right diagonal
biped is about to descend.

OF TIIE WALKING PACE.

Experiments on the walking pace—The explanations into
which we have entered in order to analyse the tracings of a
trot, will facilitate the interpretation of that of the walking
pace, represented in fig. 50. These tracings have been obtained
from the same horse as the preceding ones.

If we let fall a perpendicular from the points at which the
curves commence, we shall have the position of the successive
impacts of the four legs, On account of the thickness of the
stvle employed to trace these curves, the foot corresponding
with each of them is easily recognised, therefore we can
mark on each of these perpendicular lines tlie initial letters
of the foot which at this moment reaches the ground, ‘The
order of succession of impacts is represented by the letters
AD, PG, AG, PD; that is to say, right fore-fuot, left hind-
foot, left forefoot, right hind foot, which is the succession
admitted by writers ou the subject.

‘There remains to be determined the greater or less regu-
larity in the succession of these impacts, and the relative
extent of the intervals which separate them. Four this purpose
it is sufficient to construct the notation of the rhythm of the
pressure of each foot according to the registered curves.
‘This notation for fig. 50 shows that the interval which sepa-
rates the impacts is always the same, and, consequently, that
the horse rests during the same time on the lateral as on the
diagonal bipeds. But this is not always the case.

That we may render the successive positions of the centre
of gravity easily understood, we will explain in few words the

SCHANISM.

ME

ANIMAL

160

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OF TUE WALKING PACE. 161

footfalls, beginning with that of the right fore-foot, which is
marked No. 1, we shall divide the figures into successive por-
tions, in which will be found the impacts, sometimes of two
legs on the same side (lateral biped), at others, of two placed
diagonally (diagonal biped). Thus, from 1 to 2, the horse
will rest on the right lateral biped; from 2 to 3, on the right
diagonal biped (that is to say, on that in which the right foot
comes jirst); from 3 to 4, on the left lateral biped; from 4
to 5, on the left diagonal biped ; again, from 5 to 6, the horse
pill find himself, as at the beginning, on the mene lateral
biped.

‘This experiment has reference entirely to the standard
theory of the pace (see No. 5 of the synoptical table), but
some horses walk in a manner somewhat different.

Fig. 51 is the notation of the walking pace of a horse
which rested longer on the lateral than on the diagonal
pressures.

Sometimes the contrary is observed ; in the transitions
from the walk to the trot, for instance, we have found the
duration of the diagonal pressures predominate.

This study, in order to be complete, ought to have been
earried on under more favourable conditions than those which
we havo hitherto been able to meet with. It would be
desirable to obtain many horses belonging to different breeds ;
to study their movements when led by the hand, mounted, or
harnessed ; to vary the load which they carry or draw; to
experiment on level or sloping ground, &c. All this can sail
be effected by men especially interested in these inquiries, and
placed in favourable circumstances to undertake them.

While making observations on draught horses, it has
seemed to us that when the animal strives to re-act against
the weight of the carriage pressing upon him, he may have
three feet on the ground at once. ‘This Borelli considered
to be the normal walking pace; we have just seen, on the
contrary, that in the natural walking pace there are never
more than two feet on the ground at a time.

As to the re-actions during the walking pace, they are not
represented in fiz. 50. We have ascertained generally that
the re-actions of the fore-limbs are the only ones of any im-

162 . ANIMAL MECHANISM.

portance ; we are led to suppose, by the extremely slight re-
actions of the hinder parts, that their action consists chiefly
in a forward propulsion, but with very slight impulsion of
the body in an upward direction. This agrees with the theory
somewhat generally adinitted, by which the fore legs would
have little to do in the normal pace except to support alter-
nately the fore part of the body, while to the hind limbs
would belong the propulsive action and the tractive force
developed by the animal.

The piste of the walking pace, according to Vincent and
Goiffon, is analogous with that of the trot, except that it pre-
sents a shorter interval between the successive footprints on
the same side.

Fic. 52.—Piste of the walking pace, after Vincent and Goiffon.

In the ordinary walk, this distance would be equal t» the
heiglit of the horse, measured at the withers. As in the trot,
the prints are covered at each pace; those of the right foot
alternate perfectly with those of the left. This character of
the piste of the walking pace is, however, observed ouly under

Fig. 53.—Piste of the amble, after Vincent and Goiffon : it differs from that
of the walking pace, only by the non-superposition of the footprints on
the same side. The hind foot is placed on the ground beyond the im-
pression of the fove foot.

certain conditions of speed, and on level ground. On rising
ground the prints of the hind-feet are usually behind those of
the fore-feet ; in a descent, on the contrary, they may possibly
pass beyond them, which would give the piste of the walk
some resemblance to that of the amble,

OF THE WALKING PACE. 163

Representation of a pacing horse. The representation of a
horse at the walking pace has been given by Mons. Duhousset
in fig. 54. The instant chosen is marked in the notation by
a dot. We shall not give an enumeration of the positions of
the limbs of the animal as shown in the notation, as we have
already done so in the representation of the trot.

cme OT gay MT tl ggg ltt
panes 7) SLL (TT

Fia. 54.—Representation of the horse at a walking pace.

LO+ ANIMAL MECHANISM.

CHAPTER VI.

EXPERIMENTS ON THE PACES OF TILE HORSE.
(Continued. )

Expcriments on the gallop— Notation of the gallop—Re-actions—Dases of
support—Pistes of the gallop—Itepresentation of a galloping horse in
the various times of this pace.

Transitions, or passage, from one step to the other—Aualysis of the paces
by means of the notation rule—Synthetic reproduction of the
different paces of the horse.

OF TIIE GALLOP.

SrverAt different paces, the common character of which is
tat irregular impacts return at regular intervals, are compre-
hended under this name. Most of the writers distinguish
three kinds of gallop by the rhythm of the impacts, aud
name them, according to this rhythm, gallop in two, three,
and four time. The most ordinary kind is the gallop in three-
time; this we shall study in the first place.

Experiments on the gallop. Fig. 55 has been obtained from
a horse. which galloped in three-time. At first sight, the
notation of this pace reminds us of that which we have
represented when speaking of human gallop (fig. 36, p. 184),
a pace used by children when “ playing at horses.” It
appears tliat the notation of the horse's gallop has been
obtained by placing one over another two of these notations
of the biped gallop; so that, in fact, the comparison used by
Dugés is perfectly just, even when it is applied to the gallop.

Analysis of the tracing. At the commencement of the figure,
the animal is suspended above the ground; then comes the
impact P G, which announces that the left hind-foot touches
the ground. This is the foot diagonally opposed to that which
the horse places forward in the gallop, and whose impact A D
will be produced the last. Between these two impacts, and
distinctly in the middle of the interval which separates them,
comes the simultancous impact of the two feet forming the

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166 ANIMAL MECHANISM.

In this series of movements tle ear has, therefore, dis-
tinguished three sounds, at nearly equal intervals. ‘The first
sound is produced by a hinder foot, the second by a diagonal
biped, the third by a fore-foot. Between the single impact of
the fore-foot, which constitutes the third sound, and the first
heat of the pace which follows, reigns a silence whose dura-
tion is exactly equal to that of the three impacts taken
together; then the series of movements recommences.

3y the inspection of the curves, we see that the pressure
of the feet on the ground must be more energetic in the
gallop than in the other paces already represented, for the
height of the curves is evidently greater than for the trot,
and especially so as compared with the walk. In fact, the
animal must not only support the weight of its body, but give
it violent forward impulses. ‘The greatest energy seems to
belong to the first impact. At this moment, the body, raised
for an instant frum the ground, falls again, and one leg
alone sustains this shock.

3 TEMPS

WM

Fia 56 —Gallop in three-time (A) indiextion of three-time. B. indication
of the number of feet which form the support of the body at each instant
of the gallop in three timy,

If we wish to take account of the successive pressures which
sustain the body during each of the steps in the gallop, we
have only to divide the duration of this pace into successive
instants in which the body is sometimes supported on one or
on several feet, arid sometimes suspended. ‘The notation (fig.
535) allows us to follow in (A) the succession of impacts, and
shows in (B) the succession of the limbs which cause these
presstires on the ground.

If we wish to ascertain what are the re-actions produced at
the withers, we see them represented in fig. 55 (upper line R).
We find an undulatory elevation, which lasts all the time

OF THE GALLOP. 167

that the animal touches the ground; in this elevation are
recognised the effects of the three impacts, which give it a
triple undulation. The minimum elevation of the curve cor-
responds, as in the trot, with the moment when the feet do
not touch the ground. Therefore, it is not a projection of the
hody into the air which constitutes the time of suspension in
the gallop. Lastly, by comparing the re-actions of the gallop
aie those of the trot (fig. 45), we see that in the gallop the
rise aud fall of the body are effected in a less sudden manner.
These re-actions are, therefore, less jarring to the rider.
though they may, in fact, present a greater amplitude.
Piste of the gallop w three-time.— According to Curnieu, this
piste is the following :—

Fic. 57.—Yiste of the short gallop in three-time. The hindcr feet, whose
prints have the frm of an U, reach the ground in front of the prints of
the fore feet. The latter have been represcnted by a form somewhat like
an O.

The piste of the gallop varies according to the speed. In
the short gallop of the riding school, the find: feet leave their
prints behind those of the fore- fens in the rapid gallop, on
the contrary, they come in front of the prints of the fore-feet.
A horse which, in the pace of the riding school, gallops
almost entirely within his own length, will, when started at
full gallop, cever an enormous space. According to Curnieu,
the famous Eclipse covered 22 English feet. ‘The following
is the piste which this very rapid pace leaves on the ground :-—

Fig. £8.—Piste of Evlipse’s gallop. from Curnieu. The prints of the hind-
fect are very far before those of the fore-feet,

Representation of a horse galloping—For this representation
we will give three attitudes, differing much from each other,

168 ANIMAL MECHANISM.

and corresponding nearly with the three kinds of time found
in this pace.

Fic. 59.—Hoerse galloping in the first time (right foot advancing), the hind left
foot only on the ground. The white dot, in the notation, corresponds
with the instant at which the horse is represented.

In the first time, fig. 59, the left hind-foot, on which the
horse has just descended, alone rests on the ground.

In the second time, fig. 60, the left diagonal biped has just
finished its impact, the right fore-foot is about to reach the
ground, the left hind-foot has just risen.

The third time of the gallop, fig. 61, has been drawn as
well as the others by Mons. Duhousset according to the nota-
tion; the moment chosen is that in which the right foot
alone rests on the ground, and is about to rise in its turn.

OF THE GALLOP 169

Fie. 61.—Horse giJloping in the third time (right fot forward).

170 ANIMAL MECHANISM.

The figure which represents it is rather strange ; the eye is
but little accustomed to see this time of the gallop, which is
doubtless very rare. When considering this ungraceful figure,
we are tempted to say with De Curnieu, ‘the province of
painting is what one sees, and not what really exists.”

The gallop in four-time differs from that which has just
been described only in this point, that the impacts of the
diagonal biped, which constitute the second time, are disunited
und give distinct sounds ; we see an example of this in fig. 62.

7 ULL
VIM Ly aed

2Psuls 211 [0

Fic. 62.—Notation of the gallop in four-time. (A) determination of each
of the successive times. (B) determination of the number of feet which
support the body at each instant.

According to this notation, the body, at first suspended, is
borne successively on one foot, on three, on two, on three, and
on one, after which a new suspension recommences.

Of the full gallop —tThis very rapid pace could not he
studied by means of the apparatus which we have employed
hitherto. It was necessary to coustruct a special registering
instrument, and new experimental apparatus.

To leave the two hands of the rider free, the registering
instrument was enclosed in a flat box, attached to the back of
the horseman by straps like the knapsack of the soldier. We
shall not attempt the detailed description of this instrument,
which carried five levers, tracing on smoked glass the curves
of the action of the four legs, and the reaction of the withers.
The violence of the impacts on the ground is such that they
would instantly have broken the apparatus before employed.
We have substituted for this a copper tube, in which moves a
leaden piston, suspended between two spiral springs. The
shocks given to this pisten at each footfall, produce an effect
like that of an air-pump acting on the registers. A ball of
india-rubber, which can be pressed between the teeth, sets the

OF THE GALLOP: Det

register going, and allows the tracing to be taken at a suitable
time.

Through the kindness of Mons. H. Delamarre, who placed
at our apace his stables at Chantilly, we have beet able to
procure tracings of the full gallop, of which the following is

the notation :—

WZ MU) meee

VII
= Baars

Fig. 63.—Notation of full gallop; re-actions of this pace.

It is seen that this pace is, in reality, a gallop in four-time.
The impacts of the hinder limbs, however, follow each other
at such short intervals, that the ear can only distinguish one
of them; but those of the fore-legs are noticeably more dis-
sociated, and can be heard separately. Another character cf
the full gallop is, that the longest period of silence takes
place during the pressure of the hinder limbs. ‘The time of
suspension appears to be extremely short.

To get the best possible results from these experiments, it
would be necessary to repeat them on a great number of
horses, and to ascertain whether there may not be some rela-
tion between the rhythm of the impacts and the other
characters of the pace. We must leave this task to those
who especially addict themselves to the study of the horse.

Lastly, let us add, that the ve-actions, in full gallop, repro-
duce with great exactness the rhythm of the impacts. Thus,
it is observed, that at the moment of the almost synchronous
impacts of the two hinder limbs, there 1s a sharp and_pro-
longed re-action, after which two less sudden re-actions take
place, each of which corresponds with the impact of one of
the fore-legs.

The line placed above fig. 63 is the tracing of the re-actions

172 ANIMAL MECITANISM.

of the withers. This curve, being placed above the notation,
enables us, by the superposition of its various elements, to
notice with which impact of the limbs each re-action cor-
responds.

OF THE TRANSITIONS BETWEEN TILE DIFFERENT KINDS
OF PACES.

An observer finds great difficulty in ascertaining how one
kind of pace passes into another. The graphic method fur-
nishes a very easy means of followins these transitions; this
will perhaps be not one of the least advantages of the employ-
ment of this method of studying the paces of the horse.

In order thoroughly to understand what takes place in these
transitions, we must refer again tu the comparison made by
Dugés, and represent to ourselves two persous walking, and
following each other's fvotsteps, both in the trot and the
gallop. In these continued paces, these two persons present
a constant rhythm in the relatiou of their movements ; while,
in the transitions, the foremost or hindermost person, as the

ase may Le, quickens or moderates his movements so as to
change the rhythm of the fovtfalls, Suvme examples will
render this more evident.

The principal transitions are represented in page 174.

Vig. 64 is the notation of the transition from the walking
pace to the trot. The dominant character of this change, inde-
pendently of the increase of rapidity, consists in the hinder
impacts gaining upon those of the fore-limbs; so that the
impact of the left hind-foot, P G, for instance, which, during
the walking pace, took place exactly in the middle of the
duration of the pressure of the right fore-foot, A D, gradually
advances till it coincides with the commencement of the
pressure A D, and with the impact also, at which time the
trot is established.

Fig. 65 indicates, on the contrary, the transition from the
trot to the walk. We see here, in an inverse manner, the
diagonal impacts, synchronous at first, become more and more
separated. A dotted line, which unites the left diagonal
impacts, is vertical at the commencement of the figure in the
part which corresponds with the pace of the trot; by degrees

TRANSITION OF PACES. 173

this line becomes oblique, showing that the synchronism is
disappearing. The direction of the obliquity of this line
proves that the hinder limbs grow slower in their movements
in passing from the trot to the walk.

In the passage from the trot to the gall p the transition is
very curious; it is represented by the notation, fig. 66. We
see, from the very commencement of the figure, that the trot
is somewhat irregular; the dotted line which unites the left
diagonal impacts A G, P D, is at first rather oblique, and in-
dicates a slight retardation of the hind-foot. This obliquity
constantly increases, but only for the left diagonal biped ; the
right diagonal biped A D, P G, remains united, even after
the gallop is established. The transition from the trot to the
gallop is made, not only by the retardation of the lind-foot,
but by the advance of the fore-foot, so that two of the diagonal
impacts, which were synchronous in the trot, leave the greater
interval between them; that which in the ordinary gallop con-
stitutes the great sileuce. An opposite change produces the
transition from the gallop to the trot, as is seen in fig. 67. The
transition from the gallop in four-time to that in three-time is
made by an increasing anticipation of the impacts of the

linder limbs.

SYNTIIETIC STUDY OF TIIE PACES OF THE TNORSE,

The analytical method to which we have hitherto had
recourse in describing the paces of the horse may have left
many things obscure in this delicate question. We hope to
clear them up by recurring to the synthetic method.

When tracing, at the commencement of this study, the
synoptical table of the different paces, we classed their nota-
tions in a natural series, the first term of which is the ainble,
and in which the difference between one step and the next
consists in an anticipation of the action of the hinder limbs.
This transition is just what is observed in animals. A drome-
dary, for instance, whose normal pace is the broken amble,*

* Through the kindness of Mons. Geoffrey St. Ililaire, director of the
“Jardin d’Acclimatation,” we have been permitted to study the paces of
different quadrupeds, and especially those of the large dromedary which
unat garden possesses.

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TRANSITION OF PACKS. 175

has given us the whole series of notations, which, in our
svnoptical table, separate No. 2 from No. 8. When urging
on the animal and forcing him to trot, he first broke his amble
in an exaggerated manner, then he began to walk, and after-
wards commenced an irregular trot, which soon became a free
trot. We have just seen that the paces of the horse are formed
in the same order when the animal passes from the walk to
the trot.

When a horse begins to move more slowly, the change of
pace is effected in an inverse manner ; the paces succeed each
other by running up the series represeuted in the plate.

‘The greater or less anticipation of the action of the hinder
limbs is represented in the plate by a sliding backward of the
notation towards the left of the figure. ‘This fictitious sliding
may become real by using a little instrument, which enables
us to understand and explain very simply the formation of the
different paces. It consists of a little rule, somewhat analo-
gous to the sliding rule used in calculation, and which carries
the notations of the four limbs on four little slips, which can
glide side by side, aud be arranged in various positions.

Fra. 68.—Notation rule, to represeut the different paces.

Figs. 68 and 69 show the arrangement of this little instru-
ment. Let us imagine a rule made of black wood, having
four narrow grooves, in which slip sliding portions, alternately
black and white, or grey and black, in order to represent the
notation of the amble, as in No. 1 of the plate. If we push
towards the left the two lowest slides simultaneously (fig. 68),
we shall form, according to the amount of displacement, one

176 ANIMAL MECHANISM.

or other of the notations in the table of regular paces. A
scale, marked 1, 2, 3, 4, &e., up to which we can bring the
mark representing the left hinder impact, allows us to form
without hesitation any notation whatever.

To form the notations of the gallop, it is necessary to shift
the slides corresponding with the fore-legs, so as to make
them encroach on each other as is seen in notation, fig. 69.

Fic. 69.—Notation rule forming the representation of the gallop in three-
time.

The notation rule is thus used. When we are sure that
the pace is regular, it is sufficient, for instance, to examine
the impacts of the two right feet, in order to construct the
whole notation. According as the hinder impact is synchro-
nous with that in front, or precedes it by a quarter, half,
three-quarters, or the whole of the duration of a pressure, we
place the two lower slides in the position which they ought to
occupy, and the notation is thus simply constructed ; it shows
the rhythms of the impacts, the duration of the lateral and
diagonal pressures, &e. The construction of the various
paces of the gallop is effected in the same manner.

The artist who wishes to represent a horse at any instant
of a particular pace, can thus easily determine the correspond-
ing attitude. He forms on his rule the notation of the pace
of the horse which is to be represented. Then, on the length
which corresponds with the extent of a single pace in this
notation, he erects a perpendicular line at any point. This
line corresponds with « certain instant of the pace. Thus, as
he can trace, on the length corresponding with a single pace,

PACES OF THE HORSE. 177

an indefinite number of perpendicular lines, it follows that the
artist may choose in the duration of any pace, in any kind of
locomotion, an indefinite number of different attitudes. Sup-
pose him to have made his choice, and that he wishes to
represent in the kind of pace (fig. 68), the instant which is
marked by the vertical line 7, the notation will show him that
the right fore-foot has just been placed upon the ground, that
the left fore-fvot is therefore beginning to rise, that the right
hind-foot is almost at the end of its pressure on the ground,
and that the left hind-foot is near the end of its rise. All
that is necessary, in order to represent the animal exactly, is
to know the attitude of each limb at the different instants of
its rise, fall, or pressure, which is a comparatively easy matter.
But the artist, guided by this method, will thus inevitably
avoid altogether those false attitudes which often cause repre-
sentations of horses to be so utterly unnatural.

FIGURES ARRANGED TO SHOW THE PACES OF TITE HORSE.

Mons. Mathias Duval has undertaken to make, in order to
illustrate the locomotion of the horse, a series of pictures,
which, seen by means of the zootrope, represent the animal
as if in motion in the various kinds of paces. This ingenious
physiologist formed the idea of reproducing in an animated
form, as it were, that which notation has done for the rhythm
of the movements. ‘The following is the arrangement which
he employed. Le first drew a series of figures of the horse
taken at different instants of an ambling pace. Sixteen suc-
cessive figures enabled him to represent the series of positions
which each limb successively assumes in a pace belonging to
this kind of locomotion. ‘his band of paper, when placed
in the instrument, gives to the eye the appearance of an
amnbling horse in actual motion.

We have said that all the walking paces may be considered
as derived from the amble, with a more or less anticipation of
the action of the hind limbs. Mons. Duval has realised this
in his pictures in the following manner. Each plate, on
which has been drawn the series of pictures of the ambling
horse, is formed of two sheets of paper placed the one on the
other. ‘The upper one has in it a number of slits or openings,

178 ANIMAL MECILANISM.

so that each horse is drawn half on this sheet, and the other
half on that which is placed beneath. The hind quarters,
for example, having been drawn on the upper sheet, the fore
quarters are drawn on the under sheet, and are visible through
the portion cut out of the upper sheet. Let us suppose that
we cause the upper paper to slide as far as the interval which
separates two figures of the horse, we shall have a series of
images in which the fore limbs will fall back a certain dis-
tance towards the hind limbs. We shall thus represent,
under the form of pictures, what is obtained under the form of
notation, by slipping the two lower slides of the notation rule
one degree. And as this displacement to the distance of one
degree for each of the movements of the hinder limbs gives
the notation of the broken amble, we shall obtain, in the
figures thus drawn, the series of the successive positions of
the paces of the broken amble. If the paper be made to slip
a greater number of degrees, we shall have the series of atti-
tudes of the horse at his walking pace. A still greater dis-
placement will give the attitudes of the trot.

In all these cases, these figures, when placed in the instru-
meut, make the illusion complete, and show us a horse which
ambles, walks, or trots, as the case may be. ‘Then, if we
regulate the swiftness of the rotation given to the instrument,
we render the movements which the animal seems to execute
more or less rapid, which will permit the inexperienced
observer to follow the series of positions of each kind of pace,
and soon enable him to distinguish with the eye a series of
movements in the living animal which appear at first sight to
be in absolute confusion.

We hope that these plates, though still somewhat defective,
will soon be sufficieutly perfect to be of real use to those who
are engaged in the artistic representation of the horse.

After these studies of terrestrial locomotion, we ought to
explain the mechanisin of aquatic locomotion. Some recent
experiments of Mons. Ciotti have thrown great light on the
propulsive action of the tails of fishes; not that they have
overthrown the theory held ever since the time of Borelli,
concerning the mechanism of swimming, but they have ap-
prouched the question in another manner, that of the synthetic

PACES OF TIE WORSE. 179

reproduction of this phenomenon. This method will certainly
permit us to determine, with a precision hitherto unknown,
both the motive work and resistant work in aquatic
locomotion. It will, therefore, be advisable to wait for the
results of experiments which are now being made, and
which will be of equal service both to mechanicians and to
physiologists.

BOOK THE THIRD.

AERIAL LOCOMOTION.

CHAPTER I.
OF THE FLIGHT OF INSECTS.

Frequency of the strokes of the wing of insects during flight; acoustic
determination ; graphic determination—Influences which modify the
frequency of the movements of the wing—Synchronism of the action
of the two wings—Optical determination of the movements of the
wing ; its trajectory ; changes in the plane of the wing; direction
of the movement of the wing.

In terrestrial locomotion we have been able to measure by
experiment the pressure of the feet on the ground, and hence
we have deduced the intensity of the re-actions on the body
of the animal. ‘These two forces were easily ascertained by
direct measurement. In the problem which is now to occupy
us, the conditions are very different. The air gives a certain
resistance to the wings which strike upon it, but it is a resis-
tunce every instant yielding, for it is only in proportion to the
rapidity with which it is displaced, that the air resists the
impulse of the wing. When we study the phenomena of flight,
it is therefore necessary to know tlie movement of the wing in
all the phases of its speed, in order to estimate the resistance
which the air presents to that organ. We will propound in
the following order the questions which must: be resolved.

1. What is the frequency of the movements of the wing of
insects ?

2. What are the successive positions which the wing occu-
pies during its complete revolution ?

FLIGHT OF INSECTS. Isl

3. Ilow is the motive force which sustains and transports
the body of the animal developed ?

1. Irequency of the movements of the wing of insects —The
frequency of the movements of the wing variés according to
species. ‘The ear perceives an acute sound during the flight
of mosquitos and certain flies; there is a graver sound during
the flight of the bee and the drone fly; still deeper in the
macroglosse and the sphingida. As to the other lepidoptera,
they have, in general, a silent flight on account of the few
strokes which they give with their wings.

Many naturalists have endeavoured to determine the fre-
quency of the strokes of the wing by the musical note pro-
duced by the animal as it flies. But in order that this deter-
mination should be thorouglily reliable, it must be clearly
established that the sound produced by the wing depends
exclusively on the frequency of its movements, in the same
manner as tle sound of a tuning-fork results from the fre-
quency of its vibrations. But opinions differ on this subject ;
certain writers have thought that during flight there is a
movement of the air through the spiracles of insects, and that the
sound which is heard depends on these alternate movements.

Without giving our adherence to this opinion, which
scems to be contradicted by many fucts, we think that the
acoustic method is insufficient to furnish an estimate of the
frequency with which the wing moves. The reason which
would induce us not to employ tl.is method, is that the
musical note produced by the flying insect is varied by other
influences besides the changes in the’strokes of the wing.

When we observe the buzzing of an insect flying with a
uniform rapidity, we perceive that the tone does not continue
constantly the same. As the insect approaches the ear, the
tone rises; it sinks as it goes further from us. Something of
an analogous kind happens when we cause a vibrating
tuning-fork to pass before the ear; the note at first becomes
more shrill and then more grave, and the difference may
attain to a quarter or even to half atone. We must, there-
fore, take care that the insect on which we experiment should
be always at the same distance from the observer. This dis-
turbing phenomenon, howevcr, presents no real difficulty of

182 ANIMAL MECITANISM.

interpretation; Pisko, the German writer on acoustics, has
perfectly explained it. There is no doubt that the vibrations
always follow each other after the same interval of time ; when
a vibrating plate remains at the same distance from the ear,
the vibrations require the same time to reach us, and the
phenomenon, uniform for the instrument, is uniform also for
our organ. On the contrary, if the instrument be brought
rapidly nearer, the vibration which is produced every instant
has less space to traverse before it reaches the tympanum ; it
thus approximates to that which preceded it, and the sound
grows sharper. If the instrument be removed to a greater
distance the vibrations are more extended, and the tone he-
comes more grave. Every one has remarked, when travelling
on a railroad, that if a locomotive passes us while the driver
is sounding the whistle, the sharpness of the tone increases as
the engine comes nearer, and becomes graver when it las
passed by us, and the whistle is rapidly carried to a greater
distance.

From these considerations we must be eenvinced that it is
very difficult to estimate from the musical tone produced by
a flying insect, the absolute frequency of the strokes of its
wings. This depends to some extent on the variation of the
tone thus produced, which passes at each instant from grave to
sharp, according to the rapidity and the direction of the flight.
Besides this, it is not easy to assign to each wing the part
which it plays in the production of the sound. We have also
to take into consideration that the wing of an insect may, by
brushing through the air as it flies, be subjected to sonorous
vibrations much more numerous than the complete revolutions
which it accomplishes.

The graphic method furnishes a simple and precise solution
of the question; it enables us to ascertain almost to a single
Leat the number of movements made per second by an insect’s
wing.

Experiment.—A sheet of paper blackened by the smoke
of a wax-candle, is stretched upon a cylinder. ‘This cylinder
turns uniformly on itself at the rate of a turn in a second
and a-half.

The insect, the frequency of the movement of whose wings

FLIGHT OF INSECTS. 183

is to be studied, is held by the lower part of the abdomen, in
a delicate pair of forceps; it is placed in such a manner that
one of its wings brushes against the blackened paper at every
movement. Each of these contacts removes a portion of
the black substance which covers the paper, and, as_ the
cylinder revolves, new points continually present themselves
to the wing of the insect. We thus obtain a perfectly regular
figure, if the insect be held in a steadily fixed position. ‘These
figures, of which we give some examples, differ according as
the contact of the wing with the paper has been more or
less extended. If the contact be very slight, we obtain a

series of points or short cross-lines, as in fig. 70,

SAK SERS FE
SARK Ap ASA DOD.ww

MARE DAA ALES SAA AR ee eS Ae as

PAPRR Ry a Ne SHED PRY PBRAAA A CASASBARSV AVERT EMER TARR AVE SE RNT ANS SAA A SARA ERE

Fic. 70.—Showing the frequency of the strokes of the wingof a drone-fly
(the three upper lines), and of a bee (the lower dotted line’. Th fou th
line is produced by the vibrations of a chronographic tunin’- ork, fur-
nished with a style which registers 250 double vibrations per second.

Knowing that the cylinder revolves once in a second and
a-half, it is easy to sce how many revolutions of the wing
are thus marked on the whole circumference of the cylinder.
But it is still more convenient and accurate to make use of a
chronographie tuning-fork, and to register, near the figure
traced by the insect, the vibrations of the style with which
the tuning-fork is furnished.

Fig. 70 shows, by the side of the tracing made by tlhe
wing of a drone-fly, that of the vibrations of a tuning fork,
which executes a double oscillation 250 times in a second.
This instrument, enabling us to give a definite value to any
portion of the tracing, shows that the wing of the drone per-
formed from 240 to 250 complete revolutions per second.

184 ANIMAL MECHANISM.

Tifluences which modify the frequency of the movements of the
wing. — Since we know the influence of resistance to the rapidity
of the movements of animals, we may suppose that the wing
which rubs on the cylinder has not its normal rate of motion,
and that its revolutions are less numerous in proportion as
the friction is greater. Experiment has confirmed this opinion.
An insect performing the movements of flight by rubbing its
wings rather strongly against the paper gave 240 movements
per second; by diminishing more and more the contacts of
the wing with the cylinder, we obtained still greater numbers
—282, 305, and 821. ‘This last number may perhaps ex-
press with sufficient accuracy the rapidity of the wing when
moving freely, for the tracing was reduced to a series of
scarcely-visible points. On the contrary, as the wing rubbed
more strongly, the frequency of its moyements was reduced
below 240.

Another modifying cause of the frequency of movement in
the wing is the amplitude of these movements. We must
compare this cause with the preceding, for it is natural to
admit that great movements meet with greater resistance in
the air than smaller ones.

When we hold a fly or a drone by the forceps, we see that
the animal executes sometimes strong movements of flight;
we then hear a grave sound; but occasionally, when its wing
is only slightly agitated, we perceive ouly a very shrill tone.
That which the ear reveals to us with regard to the difference
in the frequency of the strokes which the insect gives with its
wings, is entirely confirmed by the experiments which we
have made graphically.

Choosing the instants when the insect is at its strongest
flight, and also when it gently flutters its wing, we find that
the frequency varies witlin very extensive limits, nearly in
the proportion of one to three —the least frequency belonging
to the movements of greatest amplitude.

The diferent species of insects on which we have experi-
mented, presented also very great variations in the rapidity of
the movements of their wings. We have endeavoured as far
as possible to compare the different species under similar con-
ditions, during their swiftest flight, aud with slight friction

FLIGIIT OF INSECTS. 185

on the cylinder. The following are the results obtained as
the expressions of the number of movements of the wing per
second in each species :—

Common fly - ° : - . 330
Drone-fly . ° . : Se a)

Jee. > ° . . . epee S10)
Wasp . : : : ; Ae IND)
Ifumming-bird moth ee) St Epa
Dragon- fly : ‘ a es 28

Butterfly (Pontia Rape) : : : 9

Synchronism of the action of the two wiings.—By holding the
insect in a suitable position we can make both wings rub on
the cylinder at the same time. It is then seen, on thie
tracing, that the two wings act simultaneously, and that both
perform the same number of movemen’s. Independently of
this, we may easily convince ourselves that there must neces-
iy be a similar motion in both wings.

if we move one of the wings of an insect recently killed,
we shall find that a similar mouvement is given, in a certain
degree, to the other corresponding wing ; if we extend one
wing laterally, the other is also extended, if we raise one up,
the other rises. The wasp is well suited for this experiment.

Still, in captive flight, certain insects can perform great
movements with one bE their wings, while the other only exe-
cutes slight vibrations. The dung-fly, for instance, usually
affects this kind of alternate flight; when it is held with the
forceps, its two wings rarely move together. The sudden-
ness and the unforeseen condition of these alternations, and
the violent deviations which they give to the axis of tiie body,
lave prevented us from taking the simultaneous tracings of
the movement of its two wings, and from ascertaining whether
the synchronism continues under these conditions, in sj ite of
the unequal amplitude of the movements.

The preceding figures show the regular periodicity of the
movements of insect flight, but they also prove that the
graphic method cannot represent the whole course of the wing,
for this organ can only be tangential to a certain portion of
the surface of the cylinder. Whatever may be the movements

186 ANIMAL MECHANISM.

which the wing describes, its point evidently moves on the
surface of a sphere, the radius of which is the length of the
wing, and the centre at the point of attachment of this organ
with the mesothorax. But a sphere can only touch a plane or
convex surface at one point; thus, we only obtain a number
of points for a series of revolutions of the wing, if the turn-
ing cylinder be only tangential to the extremity of the wing.
More complicated tracings can only be obtained by more
extensive contacts, in which the wing bends, and thus rubs
a portion of its surfaces or its edges on the blackened paper.

We will explain the means by which the graphic method
can serve to determine the movements of the wing, but let
us first show the results obtained by another method, in
order to render the explanation more clear.

2. Optical method of the determination of the movements of
the wing.—llaving being convinced by the furmer experi-
ments, of the regular periodicity of these movemeits, we have
thouglt it possible to determine their nature by the eye. In
fact, if we can attach a brilliant spot to the extremity of thie
wing, this spot passing continually through the same space
would leave a luminous trace which would produce a figure
completely regular, and free from the deformity incident to
that effected by the friction on the cylinder. This optical
method has already been employed for a similar purpose by
Wheatstone, who placed brilliant metallic balls on rods pro-
ducing complex vibrations, and thus obtained luminous
figures varying according to the different combinations of the
vibrating movements.

By fixing a small piece of gold-leaf at the extremity of the
wing of a wasp, and throwing upon it a ray of the sun while
the insect was executing the movements of flight, we have
obtained a brilliant image of the successive positions of the
wing, which gave uearly the appearance represented in
fig. 71.

This figure shows that the point of the wing descriles a
very elongated figure 8; sometimes, indeed, the wing seems
to move entirely in one plane, and the instant afterwards the
terminal loops which form the 8 are seen to open more and
more. When the opening becomes very large, one of the

FLIGHT OF INSECTS. 187

loops usually predominates over the other; it is generally the
lower one which increases while the upper diminishes. Indeed,
by a still greater opening, the figure is occasionally trans-
formed into an irregular ellipse, at the extremity of which we

can recognise a vestige of the second loop.

Ny Danburtau

Fic. 71.—Appearance of a wasp, the extremity of each of whose larger
wings has been gilded. ‘Ihe insect is supposed to be placed in a sun-
bean.

We thought that we had been the first to point out the form
of the trajectory of the wing of the insect, but Dr. J. B. Petti-
grew, an English author, informs us that he had already
mentioned this figure of 8 appearance described by the wing,
and had represented it in the plates of his work.* It will
be seen presently that, notwithstanding this apparent agree-
ment, our theory and that of Dr. Pettigrew differ materially
from each other.

Changes of the plane of the wing.—The luminous appearance
given during flight by the gilded wing of an insect, shows

* On the Mechanical Applianees by which Flight is Maintained in the
Animal Kingdom. Transact. of Linnean Society, 1867, p. 233.

188 ANIMAL MECIIANISM,

besides, that during the alternate movements of flight, tl.c
plane of the wing changes its inclination with respect to the
axis of the insect’s body, and that the upper surface of the
wing turns a little backward during the period of ascent,
whilst it is inclined forward a little during its descent.

If we gild a large portion of the upper surface of a wasp’s
wing, taking precautions that the gold-leaf should be limited
to this surface only, we see that the animal, placed in the sun’s
rays, gives the figure of 8 with a very unequal intensity in
tle two halves of the image, as represented in fig. 71. The
figure printed thus $ gives an idea of the form which is then
produced, if we consider the thick stroke of this character as
corresponding with the more brilliant portion of the image,
and the thin stroke as representing the part which is less
bright.

it is evident that the ecxuse of the phenomenon is to be
found in a change in tle plane of the wing, and consequently
in the incidence of th:e solar rays; being favourable to their
reflection during the period of ascent, and unfavourable during
the descent. If we turn the animal round, so as to observe
the luminous figure in the opposite direction, the 8 will then
present the unequal splendour of its two halves, but in the
inverse direction; it Lecomes bright in the portion before
relatively obscure, and vice versd.

“We shall find in the employment of the graphic method,
new proofs of changes in the plane of the wing during flight.
This phenomenon is of great importance, for in it we seem to
find the proximate cause of the motive force which urges for-
ward the body of the insect.

In order to verify the preceding experiments, and to assure
ourselves still more of the reality of the displacement of the
wing, which the optical method has revealed to us, we have
introduced the extremity of a small pointer into the interior of
the figure 8 described by the wing, and we have proved that
in the middle of these loops there really exist free spaces of
the form of a funnel, into which the pointer penetrates with-
out meeting the wing, whilst, if we try to pass the intersection
where the lines cross each other, the wing immediately strikes
against the pointer, and the flight is interrupted.

FLIGHT OF INSECTS. 189

Graphic method employed for the determination of the move-
ments of the wing.—The preceding experiments throw great iight
on the traces which we obtain by the friction of the insect’s
wing against the blackened cylinder. Although the figures
thus produced are for the most part incomplete, we are able,
by means of their scattered elements, to reconstruct the figure
which has heen shown by the optical method.

It is to be remarked that without sensibly interfering with
the movements of the wing, we can obtain traces of seven or
eight millimetres when the wing is rather long. ‘The slight
flexure to which the wing is subjected allows it to remain in
contact with the cylinder to that extent; we thus obtain a
partial tracing of the movement; so that if we are careful to
produce the contact of the wing with the cylinder in different
parts of the course passed through by the limb, we obtain a
series of partial tracings which are complementary to each
other, and thus allow us to deduce from them the form of a
perfect curve of the revolution of a wing. Suppose, then,
that in fig. 71, the curve described by the gilded wing is
divided by horizontal lines into three zones: the upper one,
formed by the upper loop; that in the middle, comprehending
the two branches of the 8, crossing each other and forming a
sort of X; the lower one including the lower loop.

By registering the movement of the middle zone, we get

Fic. 72.--Tracing of the middle region of the course of the wing of a bee,
showing the crossing of the two branches of the 8. One of the branches
is prolonged rather far, but still the tracing of the lower loop bas not been

produced.

firures somewhat resembling each other, in which the lines,
placed obliquely with respect to each other, cut cach other.
‘This is the case in fig. 72, the middle region of the tracing
of a bee, and in fig. 73, the middle portion of that of a
humming-bird moth.

190 ANIMAL MECHANISM.

The upper zone of the revolution of the wing gives tracings
analogous with that of fig. 74, in which t’ e upper 'oops of the
8 are plainly visible. The tracings of the zone which ccrre-

Fia. 73.—Tracing of the middle zone in the course described by the wi: g of

a humming-bird moth. The numerous strokes ot which this tracing is
formed, arise from the extremity of the wing being fringed and present-
ing a rough su: face,

sponds with the lower course of the wing give also loops like
those of the upper arch (fig. 75 shows a specimen of them) ;
so that the figure 8 of the tracing can be reproduced by

Fie. 74.—This figure shows, in the tracing made by a wasp, the upper ‘oop,
and all the extent of one }ranch o° the 8 The middle part of tus
branch is merely dot:e | because of the feeble friction of the wing.

bringing together the three fragments of its course successively
obtained.

If we could only once procure the entire tracing formed by
the wing of an insect, we should then get a figure identical
with that which our learned writer on acoustics, Koenig, was
the first to obtain with a Wheatstone rod tuned to the octave,
that is to say, describing an 8 in space. This typical form is
represented in fig. 76. We shall see that the graphic method

FLIGHT OF INSECTS. 191

is adapted to other experiments intended to verify those which
we have already made by other means. By varying the inci-
dence of the wing on the revolving cylinder, we can foretell
what will be the figure traced, if it be true that the wing
rally d. scribes the form of aun 8. Thus, if we obtain a figure

he)

f f f iN , ‘4
bh bid
{

Fie. 75.—Tracings of the wing of a wasp; several of the lower lo ps are
dist.n-tly seen This tracing was obtained by holding the insect so as
to rub the cylinder by the hinder point uf the wing, which gives very cx-
tenled curves

cenformable to that which we have foreseen, it will be an
evident proof of the reality of these movements,

Fic. 76.—Tracing of a Whertstone’s kaleidophone rod, tuned to the octive,
that is tosay. vibriting twice transversely for each tonvitudinal vibration.

(This figure is ta'cen from R. Keenig.: The slacken'ny speed of the
eylinder produces an approxima ion of the cui ves towards the end of the
figure.

Let us suppose that the wing of the insect, instead of
touching the cylinder with its point, as we have seen just
now, brushes it with one of its edges; and let us admit for
an instant that the 8 described by the wing is so lengthened
that it departs but slightly from the plane passing through
the vertical axis of this figure. If we press the wing slightly
against the cylinder the contact will be continuous, and the
tracing uninterrupted; but the fizure obtained will no
longer be an 8; if the cylinder be immovable it will be an
are of a circle, whose concavity will be turned towards the
point of insertion of the wing, a point which will occupy pre-
cisely the centre of the curve described.

192 ANIMAL MECHANISM.

If the cylinder revolve, the figure will be spread out like
the oscillation of a tuning-fork registered under the same
conditions, and we shall obtain a tracing more or less ap-
proaching in form to that which is represented in fig. 77.

Fic. 77.--Traciny obtained with the wing of a bee oscillating in a plane
which is sensibly tangential to the generatrix of tue registering cylinders.

This form, which theory enables us to predict, is always
produced when the plane in which the wing moves is tan-
gential to the generatrix of the cylinder.

But in examining these tracings we easily recognise chanyes
in the thickness of the stroke—parts which appear to have been
made by a greater or less friction of the wing on the cylin-
der; we here find a new and certain proof of the existence of
a movement in the form of an 8, as we now propose to show
by a synthetic method.

Let us take a Wheatstone’s rod tuned to the octave ; let us fix
on it the wing of an insect as a style, and let us trace the vibra-
tions which it executes. We shall obtain, if the cylinder be
motionless, figures of 8 when the wing touc'es the paper by
its point applied perpendicularly to its surface; and if the
cylinder revolve, we shall have lengthened figures of 8.

We may obtain, with a rod tuned to the octave, tracings
identical with those given by the insect; of which a proof is
afforded by the comparison of the two followius figures :—

VDDD

I'ic. 78 Tracings of a wasp; the insect is h-ld so that its wing touches

‘

the cylinder by its point, and traces especially the upper loop of the »

FLIGHT OF INSECTS. 193

The graphic method also furnishes us with the proof of
changes in the plane of the wing of the insect during the
various instants of its revolutions.

Fic. 79.—Tracings of a Wheatstone rod tuned to the octave. furnished
with the wing of a wasp, and arranged so as to register especially the
upper loop of the 8.

Fig. 80 shows the tracing furnished by a wing of a hum-
ming-bird moth, arranged so as to touch the cy linder with its
posterior edge. By be inging the insect not too near, we can
succeed in producing only intermittent contacts; these take
place at the moment when the wing describes that part of the
loops of the 8 whose convexity is tangential to the cylinder.
The contacts which occupy the upper half of the figure alter-
nate with those occupying the lower half. It is seen, besides,
that it is not the same surface of the wing which produces
these two kinds of friction. In fact, it is evident that the

Fic. 80.—Tracings of the movements of the wing of a humming-bird
moth (macroglossa) rubbing on the cylinder by its lower edge.

marks of the upper half, each formed of a series of oblique
strokes, are produced by the contact of a fringed border, while
the contacts of the lower part are produced by another portion
of the wing which presents a region unprovided with fringes,
and leaves a whiter trace with boundaries better defined.

194 ANIMAL MECHANISM.

These changes of plane are only found in great movements
of the wing. ‘This is an important fact, for it will explain to
us the method of their production. Fig. 81 was furnished
like fig. 80 by the movements of the wing of a moth (macro-
glossa); but on account of its fatigue these movements had
lost nearly all their amplitude.

Fic. 81.—-Tracing of the wing of a fatigued macroglossy. The figure 8 is
no longer to be seen, but only a simple penduiar osciilation.

We see only in this figure a series of pendular oscillations,
showing that the wing merely rose and fell without changing
its plane. The bright line which borders the ascending and
upper parts of these curves is explained by the alternate
flexions of the wing as it rubs upon the paper, and shows
that the upper surface was rough, and left a distinct trace,
while the lower surface presented no similar roughness.

3. Direction of the movement of the wing.—Oue more very
important element is required to give us a complete knowledge
of the movements which the insect’s wing executes in its flight.
The optical method, while it shows us all the points in the
curve described by the gilded extremity of the wing, does not
indicate the direction in which this revolution is accomplished ;
whatever may be the direction in which the wing moves in its
orbit, the luminous image which it affords must be always
the same.

A very simple method has furnished a solution of this new
question. Let fig. 82 be the luminous image furnished by
the movements of the right wing of an insect. The direction
of these movements which the eye cannot follow is indicated
by arrows.

To determine the direction of these movements, we take a
small rod of polished glass and blacken it with the smoke of
a wax taper; when holding the rod at right angles to the
direction in which the wing moves, we present the blackened

FLIGHT OF INSECTS. 195

end to (a), that is to say, in front of the lower loop. We
endeavour to pass this point into the interior of the course
described by the wing; but as soon as it enters this region,
the rod receives a series of shocks from the wing, which rubs
on its surface, and wipes off the soot which covered it. When
we examine the surface of the glass, we see that the soot has
been removed only on the upper part, which shows that at
the point (a) of its course, the wing is descending. The
same experiment being repeated in (a’), that is to say, in the
hinder part of the orbit of the wing, it is found that the rod
has been rubbed Leneath ; so that the wing at a’ was ascending.
In the same manner it may be shown that the wing rises at
b and descends at LU’.

)
‘|

Fic. §2.—Determ‘nation of the direction of the movements of en insect’s
wing.

We now know all the movements executed by an insect’s wing
during its revolution, as well as the double change of plane which
accompanies them. The knowledge of this change of plane
was given to us by the unequal brightness of the two branches
of the luminous 8. Thus we may feel assured that in the
course of the descending wing, that is from b’ toa in fig. 82,
the upper surface of the wing turns slightly forward, while
from a’ to b, that is, in ascending, this surface turns a little
backwards.

196 ANIMAL MECHANISM.

CHAPTER II.
MECHANISM OF THE FLIGHT OF INSECTS.

Causes of the movements of the witigs of insects—The muscles only give
a motion to and fro, the resistance of the air modifies the course of
the wing—Artificial representation of the movements of the insect’s
wing —Of the propulsive effect of the wings of insects—Construe-
tion of an artificial insect which moves horizontally—Change in the
plane in flight.

1. Causes of the movements of the wing.—These exceedingly
complicated movements would induce us to suppose that there
exists in insects a very complex muscular apparatus, but
anatomy does not reveal to us muscles capable of giving rise
to all these movements. We scarcely find any but elevating
and depressing forces in the muscles which move the wing ;
besides this, when we examine more closely the mechanical
conditions of the flight of the insect, we see that an upward
and downward motion given by the muscles is sufficient to pro-
duce all these successive acts, so well co-ordinated with each
other; the resistance of the air effecting all the other move-
ments.

If we take off the wing of an insect (fig. 83), and holding
it by the small joint which connects it with the thorax, expose
it to a current of air, we see that the plane of the wing is

Fic. 83.— Structure of an insect’s wing.

inclined more and more as it is subjected to a more powerful
impulse of the wind. ‘The anterior nervure resists, but the
membranous portion which is prolonged behind bends on
account of its greater pliancy. If we blow upon the upper sur-

MECIIANISM OF INSECT FLIGIIT. 197

face of the wing, we see this surface carried backwards, while
by blowing on it from beneath, we turn the upper surface
forwards. In certain species of insects, according to Félix
Plateau, the wing resists the pressure of the air acting from
below upwards, more than that exerted in an opposite
direction.

Is it not evident, that in the movements which take place
during flight, the resistance of the air will produce upon the
plane of the wing the same effects as the currents of air which
we have just employed? The changes in the plane, caused
by the resistance of the air under these conditions, are pre-
cisely those which are observed in flight. We have seen that
the descending wing presents its anterior surface forwards,
which is explained by the resistance of the air acting from
below upwards; while the ascending wing turns its upper sur-
face backwards, because the resistance of the air ucts upon it.
from above downwards.

It is, therefore, not necessary to look for special muscular
actions to produce changes in the plane of the wing; these,
in their turn, will give us the key to the oblique curvilinear
movements which produce the figure of 8 course followed by
the insect’s wing.

Let us return to fig. 82: the wing which descends has at
the same time a forward motion; therefore, the inclination
taken by the plane of the wing, under the influence of the
resistance of the air, necessarily causes the oblique descent
from b’ toa. An inclined plane which strikes on the air has
a tendency to move in the direction of its own inclination.

Let us suppose, then, that the wing only rises and falls by
its muscular action; the resistance of the air, by pressing on
the plane of the wing, will force the organ to move forward
while it is being lowered. But this deviation cannot be
effected without the nervure being slightly bent. The force
which causes the wing to deviate in a forward direction neces -
sarily varies in intensity according to the rapidity with which
the organ is depressed. ‘Thus, when the wing towards the
end of its descending course moves more slowly, we shall
see the nervure, as it is bent with less furce, bring the wing
backwards in a curvilinear direction. Thus we explain

198 ANIMAL MECHANISM,

naturally the formation of the descending branch of the 8
passed through by the wing.

The same theory applies to the formation of the ascending
branch of this figure. In short, a kind of pendular oscilla-
tion executed by the uervure of the wing is sufficient, to-
gether with the resistance of the air, to give rise to all the
iovements revealed to us by our experiments.

2. Artificial representation of the movements of the insect’s wing.
—These theoretical deductions require experimental veritica-
tion, in order that they may be thoroughly borne out. We
have succeeded in obtaining the following results :—

Let fig. 84 be an instrument, which, by means of a multi-
plying wheel and a connecting rod, gives to a flexible shaft
rapid to and fro movements in a vertical plane. Let us take
a membrane similar to that in the wings of insects, and fix it
to this shaft, which will then. represent the main rib of the
wing; we shall see this contrivance execute all the move-
ments which the wing of the insect describes in space.

If we illuminate the extremity of this artificial wing, we
shall see that its point describes the figure 8, like a real wing;
we shall observe also that the plane of the wing changes
twice during each revolution in the same manner as in the
insect itself. But in the apparatus which we now employ,
the movement communicated to the wing is only upwards
aud dowuwards. Were it not for the 1esistance of the air,
the wing would only rise and full in a vertical plane; all
these complicated movements are due therefore only to the
resistance presented by the air. Consequently, it is this
which bends the main rib of the wing, turning it in a direc-
tion perpendicular to the plane in which its oscillation is
effected,

But if the wing be pushed aside from its main-rib at each
of its alternate movements, it is evident that the air, acted
upon by this wing, will receive an impulse in an opposite
direction ; that is to say, it will escape at the side of the
flexible portion of the wing, and cause in this direction a
current of air. It is seen, in figure 84, that a candle placed
by the side of the thin edge of the wing, is strongly blown
by the current of air which is produced. In front of the wing,

MECHANISM OF INSECT FLIGHT. 199

on the contrary, the air will be drawn forwards, so that the
flume of another candle placed in front of the nervire will be
strongly drawn towards it.

Fic. 84.—Artificial representation of the movements of an insect’s wing.

8. Ofthe propulsive action of the wings of insects.—In the
same manner as the squib moves in the opposite direction to
the jet of flame which it throws out, the insect propels itself
in the course opposed to the current of air produced by the
movement of its wings.

Each stroke of the wing acts on the air obliquely, and
neutralizes its resistance, so that a horizontal force results,

200 ANIMAL MECHANISM.

which impels the insect forwards. This resultant acts in the
descent of the wing, as well as in its upward movement, so
that each part of the oscillation of the wing has «n action
favourable to the propulsion of the animal.

An effect is produced analogous with that which takes place
when an oar is used in the stern of a boat in the action of
sculling. Each stroke of the oar, which presents an inclined
plane to the resisting water, divides this resistance into two
forces: one acts in a direction opposed to the motion of the
oar, the other, in a direction perpendicular to that movement,
and it is the latter which impels the boat.

Most of the propellers which act in water overcome the
resistance of the fluid by the action of an inclined plane.
The tail of the fish produces a propulsion of this kind; that
of the beaver does the same, with this difference, that it
oscillates in a vertical plane. Even the screw may be con-
sidered as an inclined plane, whose movement is continuous,
and always in the same direction.

Fic. 85.—Representation of the changes in the plane of the insect’s wing.

If we wish to represent the inclination of the plane of the
wing at the different parts of its course, we shall obtain
fiz. 85, in which the arrows indicate the direction of the
course of the wing, and the lines, whether dotted or full,
show the inclination of its plane.

After this, we need only show the figure traced by Dr. Pet-
tigrew in his work on flight, to prove how far the ideas of
this English writer differ from ours.

The trajectory of the wing is represented by Dr. Petti-
grew by means of fig. 86. Four arrows indicate, according
to this writer, the direction of movements in the different por-

MECHANISM OF INSECT FLIGHT 201

tions of this trajectory. These arrows are in the same
direction, and this first fact is opposed to the experiment
described in page 195, where we have investigated the direc-
tion of the movement of the wing, and have found it pass in
opposite directions in the two branches of the 8. In order to
explain the form which he assigns to this trajectory, Dr. Pet-
tigrew admits that in its passage from right to left, the wing
describes by its thicker edge the thick branch of the 8, and the

SS

<_—_—.

—— > ae

Fic. 86.—Trajectory of the wing.

thin branch by its narrow edge. The crossing of the 8 there-
fore would be formed by a complete reversal of the plane of
the wing during one of the phases of its revolution. In fact,
the author seems to perceive in this reversal of the plane, an
action similar to that of a screw, of which the air would form
the nut. We will not dwell any longer on this theory, but
we have deemed it necessary to bring it forward, in con-
sequence of the appeal which has been made to us.

4. Artificial representation of an insect’s flight.—In order to
render the action of the wing and the effects of the resistance
of the air more intelligible, we have made use of the following
apparatus :—

Let fig. 87 represent two artificial wings composed of a rigid
main-rib connected with a flexible membrane, composed of
gold-beater’s skin, strengthened by fine nervures of steel; the
plane of these wings is horizontal; a system of bent levers
raises or lowers them without giving them any lateral mo-
tion.

The movement of the wings is caused by a little copper
drum, in which the air is alternately condensed and rarefied
by the action of a pump. The circular surfaces of this drum

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‘ MECHANISM OF INSECT FLIGHT. 203

are formed of india-rubber membranes connected with the
two wings by bent levers; the air when compressed or rarefied
gives to these flexible membranes powerful and rapid move-
ments, which are transmitted to both wings at the same time.

A horizontal tube, balanced by a counterpoise, allows the
apparatus to turn upon a central axis, and serves at the same
time to conduct the air into the drum, which produces the
motion. This axis is formed of a kind of mercurial gaso-
meter, which hermetically seals the air conduits, while it allows
the instrument to turn freely in a horizontal plane.

Thus arranged, the apparatus shows the mechanism by
which the resistance of the air, combined with the movements
of the wing, produces the propulsion of the insect.

If we set in motion the wings of the artificial insect by
means of the air-pump, we see the apparatus soon begin to
revolve rapidly around its axis. The mechanism of the mo-
tion of the insect is clearly illustrated by this experiment,
entirely confirming the theories which we have deduced from
optical and graphic analysis of the movements of the wing
during flight.

It may be asked whether the figure of 8 movements de-
scribed by the wing of a captive insect are also produced when
the creature flies. We have just seen that the bending of the
main-rib is entirely due to the force which carries the insect
forward when it has become free. We might therefore sup-
pose that the main-rib of the wing does not yield to this force
when the insect flies freely, and that the resulting horizontal
force is shown only by the impulsion of the whole of the insect
forwards.

If, after having gilded the wing of the artificial insect, we
look at the luminous image produced during its flight, we still
. see the figure of 8 remaining, provided the flight be not too
rapid. In fact, this figure is modified by the movement of
the apparatus ; it becomes more extended, and resembles the
8 registered on a revolving cylinder, but it is not reduced toa
simple pendular curve, which would be the case if the main-
rib were always rigid. We can understand that this may be
caused by the inertia of the apparatus, which cannot be
affected by the variable movements which each stroke of the

204 ANIMAL MECHANISM.

wing tends to bring to bear upon it. The artificial insect,
when once set in motion, is sometimes before, and at others
behind the horizontal force developed by the wing: on this
account the rib of the wing is forced to bend, because the
mass to be moved does not obey instantaneously the resulting
horizontal force which the wing derives from the resistance of
the air. The same phenomenon must take place in the flight
of a real insect.

5. Plane of oscillation of an insect’s wing.—The apparatus
which has just been described does not yet give a perfect idea
of the mechanism of insect flight. We have been compelled,
for the sake of explaining the movements of the wing more
easily, to suppose that its oscillation is made from above
downwards; that is to say, from the back of the insect towards
its lower surface, when lying horizontally in the air.

But we need only observe the flight of certain insects, the
common fly, for instance, and most of the other diptera,
to see that the plane in which the wings move is not verti-
cal, but, on the contrary, very nearly horizontal. This plane
directs its upper surface somewhat forward, and therefore
the main-rib of the wing corresponds with this surface.
Consequently, it is from below upwards, and a little forward
that the propulsion of the insect is effected. The greater part
of the force exerted by the wing will be employed in sup-
porting the insect against the action of its weight; the rest of
this impulse will carry it forward.

By changing the inclination of the plane of oscillation of its
wings, which can be done by moving the abdomen so as to
displace the centre of gravity, the insect can, according to its
wishes, increase the rapidity of its forward flight, lessen the
speed acquired, retrograde, or dart toward the side.

It is easily to be seen that, when a hymenopterous insect
flying at full speed, stops upon a flower, this insect directs the
plane of the oscillation of its wings backwards with consider-
able force.

Nothing is more variable, in fact, than the inclination of
the plane in which the wings of different species of insects
oscillate.

The diptera appear to us to have this plane of oscillation

206 ANIMAL MECHANISM,

very nearly horizontal; in the hymenoptera, tle wing moves
in a plane of nearly 45°, but the lepidoptera flap their wings
almost vertically, after the manner of birds.

In order to render the influence of the plane of oscilla-
tion more evident, and to show that the force derived from the
resistance of the air has the double effect of raising the insect
and directing its course, we must arrange the flight instrument
in a peculiar manner. It will be necessary, in the first place,
to be able to change the plane of oscillation of the wings,
which is effected by placing the drum on a pivot at the ex-
tremity of the horizontal tube, at the end of which it turns.
To show the ascensional force which is developed in this new
arrangement, the instrument must no longer be confined to a
simple movement of rotation in the horizontal plane, but it
must be able to oscillate in a vertical plane like the scale beam
of a balance.

Fig. 88 shows the new arrangement which we have given
to the instrument in order to obtain this double result.

In this modification of the apparatus, the air-pump which
constitutes the moving force is retained ; as is also the turn-
ing column which moves in the mercurial gasometer. But
above the dise which terminates this column at the upper end,
is fixed a new joint, which allows the horizontally-balanced
tube at the end of which the artificial insect is placed, to
oscillate in the vertical plane like a scale-beam. In order to
establish a communication between the revolving column and
the tube carrying the insect, we make use of a little india-
rubber tube, sufficiently flexible not to interfere with the
oscillatory movements of the apparatus.

Other accessory modifications may be seen in fig. 88; one
consists in employing a glass tube to convey the air from the
pump which moves the insect; the other in a change of the
mechanism by which motion is imparted to the wings. ‘The
most important alteration is the introduction of a joint which
allows us to give every possible inclination to the plune in
which the wings oscillate.

The apparatus being arranged so that the counterpoise,
haviug been brought nearer to the point of suspension, does
not cxuctly bulance the weight of the insect, the latter is

MECHANISM OF INSECT FLIGIIT. 207

placed so that its wings may move in a horizontal plane, the
main-rib being uppermost. Thus all the motive force is
directed from below upwards, and as soon as the pump begins
to act, we see the insect rise vertically. We can easily esti-
mate the weight raised by the flapping of the wings, and as
we can vary the weight of the insect by altering the position
of the counterpoise, we can determine the effort which is
developed according to the frequency or the amplitude of the
strokes.

By turning the insect half way round, so that its wings,
still oscillating in a horizontal plane, should turn their main-
rib downwards, we develop a descending vertical force which
may be measured by removing the counterpoise to a greater
or less distance, and causing it to be raised by the descent of
the insect.

If we adjust the plane of oscillation of the wings vertically,
the insect turns horizontally round its point of support in
the same manner as has been previously described and
represented in fig. 87.

Lastly, if we give to the plane of oscillation of the wings,
the oblique. position which it presents in the greater number
of insects; that is to say, so that the main-rib turns at once
upwards and slightly forward, we see the insect rise against
its own weight, and turn at the same time round the vertical
axis; in a word, the apparatus represents the double effect
which is observed in a flying insect, which obtains from the
stroke of its wings, both the force which sustains it in the
air, and that which directs its course in space.

The first of these forces is by far the more considerable ;
thus, when an insect hovers over a flower, and we see it
illuminated obliquely by the setting sun, we may satisfy our-
selves that the plane of oscillation of its wings is nearly hori-
zontal. ‘This inclination must evidently be modified as soon
as the insect wishes to dart off rapidly in any direction, but
then the eye can scarcely follow it, and detect the change of
plane, the existence of which we are compelled to admit by
the theory and the experiments already detailed.

A curious point of study would be the movements prepara-

208 ANIMAL MECHANISM.

tory to fliglt. We speak not only of the spreading of the
wings, which in the coleoptera precedes flight, a movement
which is sometimes so slow as to be easily observed, nor of
the unfolding of the first pair of wings, as wasps do before
they fly. Other insects, the diptera, turn their wings as on
a pivot around its main-rib in a very remarkable manner,
at the moment when the wings which were previously ex-
tended on the back in the attitude of repose start outwards
and forwards before they begin to fly. Flies, tipule and
many other kinds, show this preparatory movement very clearly
when tlie insect, being exhausted, has no longer any energy
in its flight. We see the main-rib of the wing remain sen-
sibly immovable, and around it turns the membranous portion
whose free border is directed downwards. ‘This position
having been obtained, the insect has only to cause its wing
to oscillate in an almost horizontal direction from backwards
forwards, and from forwards backwards. If this motion as on
a pivot did not exist, the wing would cut the air with its edge,
and would be utterly incapable of producing flight. In other
species, as in the agrion, a small dragon-fly, for instance, the
four wings, during repose, are laid back to back one against
the other above the abdomen of the animal. ‘Their main-
ribs are upwards, and keep their position when the wings pass
downwards and forwards; here no preparation for flight is
necessary, In these insects, as in butterflies, the wing has
only to set itself in motion when the creature flies.

It is interesting to follow throughout the series of insects
the variations presented by the mechanism of flight.

The confirmation of the theory just propounded is found in
the experiments which certain naturalists have made by
means of vivisection. For the most interesting of these we
are indebted to Professor M. Giraud, All these experiments
prove that the insect needs for the due function of flight a
rigid main-rib and a flexible membrane. If we cover the
flexible part of the wing with a coating which hardens as it
dries, flight is prevented. We hinder it also by destroying
the rigidity of the anterior neryure.

If we only cut off, on the contrary, a portion of the flexible
membrane, parallel to its hinder edge, the power of flight

THE FLIGHT OF BIRDS. 209

is preserved, for the wing retains the conditions essential to
this function—namely, a rigid main-rib and a flexible sur-
face. Lastly, in some species the combination of two wings
is indispensable to flight; a kind of pseudo-elytron consti-
tutes the nervure, and behind this is extended a membranous
wing, which is locked in with the posterior border of the
anterior one. This second wing does not present sufficient
rigidity to enable it to strike the air with advantage, and in
these insects flight is rendered impossible, if we cut off the
false wing-case; it is as if we had destroyed the main-rib of
a perfect wing.

CHAPTER III.
OF THE FLIGHT OF BIRDS.

Conformation of the bird with reference to flight—Structure of the wing,
its curves, its muscular apparatus—Muscular force of the bird ;
rapidity of contraction of its muscles—Form of the bird; stable
equilibrium ; conditions favourable to change of plane—Proportion of
the surface of the wings to the weight of the body in birds of different
size. ;

Tue plan by which we have been guided in the study of
insect flight must also be followed in investigating that of
birds. It will be necessary to determine, by a delicate mode
of analysis, the movements produced by the wing during
flight; from these movements we may draw a conclusion as
to the resistance of the air which affords the bird a fulcrum
on which to exert its force. Then, having propounded cer-
tain theories respecting the mechanism of flight, the force
required for the work effected by the bird, &c., we will under-
take to represent these phenomena by means of artificial
instruments, as we have already done with respect to insects.

But, before we enter methodically on this study, it will be
useful to prepare ourselves for it by some general observa-
tions on the organization of the bird, the structure of its wings,
the force of its muscular system, its conditions of equilibrium

in the air, &e.

210 ANIMAL MECHANISM.

Conformation of the bird.—By the simple inspection of a
bird’s wing, it is easy to see that the mechanism of its flight
is altogether different from that of an insect. From the
manner in which the feathers of its wing lie upon each other,
it is evident that the resistance of the air can only act from
below upwards, for in the opposite direction the air would
force for itself an easy passage by bending the long barbs of
the feathers, which would no longer sustain each other. This
well-known arrangement, so carefully described by Prechlt,*
has caused persons to suppose that the wing only needed to
oscillate in a vertical plane in order to sustain the weight of
the bird, because the resistance of the air acting from be-
low upwards is greater than that which it exerts in thie
opposite direction.

This writer has been wrong in basing on the inspection of
the organ of flight all the theory of its function. We shall find
that experiment contradicts in the most decided manner these
premature inductions.

If we take a dead bird, and spread out its wings so as to
place them in the position represented in fig. 89, we see that at

Fic. 89.—Various curves of the wing of a bird at different points in its
length.

different points in its length, the wing presents very remark-
able changes of plane. At the inner part, towards the body,
the wing inclines considerably both downwards and_back-
wards, while near its extremity, it is horizontal and some-
times slightly turned up, so that its under surface is directed
somewhat backward.

Dr. Pettigrew thought that he could find in this curve a
surface resembling a left-handed screw propeller; struck with
the resemblance between the form of the wing and that of
the serew used in navigation, he considered the wing of a

* Untersuchungen iiber den Flug der Vogel. S8vo. Vienna: 1846.

THE FLIGHT OF BIRDS. PA ih

bird as a screw of which the air formed the nut. We do
not think that we need refute such a theory. It is too evi-
dent that the alternating type which belongs to every muscular
movement cannot tend to produce the propulsive action of a
screw; for while we admit that the wing revolves on an axis,
this rotation is confined to the fraction of a turn, and is fol-
lowed by rotation in the opposite direction, which in a screw
would entirely destroy the effect produced by the previous
movement. And yet the English writer to whose ideas we
refer has been so fully convinced of the truth of his theory
that he has wished to extend it to the whole animal kingdom.
He proposes to refer locomotion in all its forms, whether
terrestrial, aquatic, or aerial to the movements of a screw
propeller. Let us only seek in the anatomical structure of
the organs of flight the information which it can afford us ;
that is to say, that which refers to the forces which the bird
can develop in flight, and the direction in which these forces
are exerted.

Comparative anatomy shows us in the wing of birds an
analogue of the fore limb of mammals. The wing when
reduced to its skeleton, presents, as in the human arm, the
humerus, the two bones of the fore-arm, and a rudimentary
hand, in which we still find metacarpal bones and phalanges.
The muscles also present many analogies with those of the
anterior limb of man; some parts of these bear such a resem-
blance both in appearance and in function, that they have
been designated by the same name.

In the wing of the bird, the most strongly developed muscles
are those whose office it is to extend or bend the hand upon
the fore-arm, the fore-arm on the humerus, and also to move
the humerus, that is say, the whole arm, round the articula-
tion of the shoulder.

In the greater number of birds, especially of the larger °
kinds, the wing seems to remain always extended during flight:
Thus, the extensor muscles of the different portions “of this
organ would serve to give this organ the position necessary
oe rendering flight possible, and for maintaining it in this posi-
tion ; as to motive work, it would beexecuted by other muscles,
nuh stronger than the preceding —namely, the pectorals.

212 ANIMAL MECHANISM.

All the anterior surface of the thorax of birds is occupied
by powerful muscular masses, and especially by a large
muscle, which by its attachments to the sternum, to the ribs
and the humerus, is analogous with the large pectoral muscle
in man and the mammals; its office is evidently to lower the
wing with force and rapidity, and thus to gain from the air
the fulcrum necessary to sustain, as well as to move the muss
-of the body. Underneath the large pectoral is found thie
medium pectoral, whose action is to raise the wing. On the
exterior, the small pectoral, acting as accessory to the large
one, extends from the sternum to the humerus.

Since the force of a muscle is in proportion to the volume
of this organ, when we consider that these pectoral muscles
represent about one-sixth part of the whole weight of the
bird, we shall immediately understand that the principal
function of flight devolves on these powerful organs.

Borelli endeavoured to deduce from the volume of the pec-
toral muscles the energy of which they are capable; he con-
cluded that the force employed by the bird in flight was equal
to 10,000 times its weight. We will not here refute the
error of Borelli; many others have undertaken to combat his
notions, and have substituted for the calculations of the Italian
physiologist others whose correctness it would be difficult to
prove. Such great contradictions as are to be found in the
different estimates formed of the muscular force of birds have
arisen from the fact that these attempts at measurement were
premature.

Navier, depending on calculations which were not based on
experiment, considered himself authorized in admitting that
birds develop enormous mechanical work: seventeen swallows
would exert work equal to a horse-power. ‘‘ As easy would it
be,” said M. Bertrand, facetiously, ‘‘to prove by calculation
that birds could not fly—a conclusion which would rather com-
‘promise mathematics.”

Besides, we find that Cagniard Latour admitted, basing his
assertion on theory, that the wing is lowered eight times more
quickly than it rises. Experiment, however, proves that the
wing of the bird is raised more quickly than it descends.

Estinate of the inuseular force of ‘he bird.—We must at the

FORCE OF BIRDS. 213

present day measure mechanical force under the form of work.
It is necessary for this purpose to know what’ resistance is
met with by the wing at each instant of its movements,
and the direction in which it repels from it this resisting
medium.

Such an estimate requires a previous knowledge of the
resistance of air against surfaces of different curvature moving
with various degrees of velocity ; it supposes at the same time
that we know the movements of the wing as well as their
velocity and direction at every instant.

.This problem will perhaps be the last which we may hope
to solve, but we may even now study from other points of
view the force exerted by the muscles of the bird, and esti-
mate some of its characteristics.

Thus, we may obtain experimentally a measure of the maxi-
mum effort which these muscles can exert. This measure may
not really correspond with the real effort displayed in flight,
but it may keep us from forming exaggerated estimates.

If the calculations of Borelli, or even those of Navier were
correct, we ought to find in the muscles of the bird a very
considerable statical force. Experiments show, however, that
these muscles do not seem capable of more energetic efforts
than those of other animals.

Experiment.—Our first experiment was made upon a buz-
gard. The creature being hoodwinked was stretched upon its
back, with its wings held on the table by bags filled with
small shot. The application of the hood plunges these birds
into a sort of hypnotism, during which we can make any num-
ber of experiments upon them, without their evincing any pain.

We laid bare the great pectoral muscle and the humeral
region, we placed a ligature on the artery, disarticulated the
elbow-joint, and took away all the rest of the wing. A cord
was fixed to the extremity of the humerus, and at the end of
this cord was placed a scale-pan, into which small shot was
poured. The trunk of the bird being rendered perfectly im-
movable, we excited the muscle by means of interrupted in-
duced currents ; while the artificial contraction was produced,
an assistant poured into the pan the small shot, until the
force of contraction of the muscle was counteracted. At this

214 ANIMAL MECHANISM,

movement, the weight supported was 2 kilogrammes 880
grammes (about 6°38 lbs. troy).

If we take into account the unequal length of the arms of
the lever, on the side of the power and that of the resistance,
we find that the pectoral muscle had been able to produce a
total effort of 12 kilogrammes 600 grammes (about 33°78 lbs.
troy), which would correspond with a traction of 1298
grammes (3°66 lbs. troy) for each square centimetre of the
transverse section of the muscle.

A pigeon placed under the same conditions has given, as its
entire effort, a weight of 4860 grammes, which, according to
the transverse section of its muscle, raised to 1400 grammes
the effort which each muscular bundle could develop for every
square centimetre of section.

If we admit that the electrical action employed in these
experiments to make the muscles contract, develops an effort
less than that which is caused by the will, it is not less true
that these estimates, which are less than those which we
generally obtain in the muscles of mammals under the same
conditions, do not authorize us in recognizing in the bird any
special muscular power.

Lastly, if we were to take into account in this estimate
the laws of thermo-dynamics, we might affirm that the bird
would not develop in flight a very especial amount of work.

All work, in fact, can only be performed with a certain
waste of substance, and if the act of flying involved a great
expenditure of work, we ought to find a notable diminution
of weight in a bird when it returns from a long flight. Nothing
of this kind is observed. Persons who train carrier pigeons
have given us information on this point, from which we gather
that a bird which has traversed in a single flight a distance ot
fifty leagues (which it seems to do without taking any food),
weighs only a few grammes less than at its departure. It
would be interesting to make these experiments again with
greater exactitude.

Of the rapidity of the muscular actions of birds.—One of the
most striking peculiarities in the action of a bird’s muscles
is the extreme rapidity with which force is engendered in
them. Among the different species of animals whose muscular

RAPIDITY OF BIRDS. 215

acts we have determined, the bird is that which, after the
insect, has given the most rapid movements.

This rapidity is indispensable to flight. In fact, the wing
when lowered, can meet with a sufficient resistance in the
air only when it moves with great velocity. The resistance
of the air against a plane surface which strikes upon it
and repels it, evidently increases in the ratio of the square
of the velocity with which this plane is displaced. It
would be of no use for the bird to have energetic muscles,
capable of effecting considerable work, if they could only
give slow movements to the wing; their force could not
be exerted for want of resistance, and no work could be pro-
duced. It is otherwise with terrestrial animals which run or
creep on the ground, with a speed more or less rapid accord-
ing to the nature of their muscles, but which in every case
utilize their muscular force by means of the perfect resistance
of the ground. The necessity of velocity in the movements
of fishes has been already observed, since the water in which
they swim resists more or less, according to the rapidity
with which their tails or their fins act upon it. Thus the
muscular action of fishes is rapid, but much less so than
that of birds, which move in a medium far more yielding.

In order to understand the rapid production of movements
in the muscles of the bird, we must remember that these
movements are connected with chemical action, produced in
the very substance of the muscle, where they give rise, as in
machines, to heat and motion. We must therefore admit
that these actions are excited and propagated more readily
in the muscles of birds than in those of any other species of
animals. Inthe same manner the different kinds of powder
used in war differ much from each other in the rapidity of
their explosion, and consequently give very different velocities
to the projectiles which they impel.

Lastly, the form of movement presents in different species
of birds peculiarities which we have already noticed. We
have seen in Chapter VIII. how much the dimensions of the
pectoral muscles vary according as the strokes of the wing are
required to have much force or great extent; therefore we
shall not recur again to this subject.

216 ANIMAL MECHANISM.

Form of the bird.—All those who have studied the flight of
birds have very properly paid great attention to the form of
these creatures, as rendering them eminently adapted to flight.
They have recognised in them perfect stable equilibrium in
the aerial medium. They have thoroughly understood the
part played by the large surfaces formed by the wings, which
may sometimes act as a parachute, to produce a very slow
descent; while at other times these surfaces glide through the
air, and following the inclination of their plane, allow the
bird to descend very obliquely, and even to rise, or to hover
while keeping its wings immovable. Some observers have
gone so far as to admit that certain species of birds play
an entirely passive part in flight, and that giving up their
wings to the impulse of the wind, they derive from it a force
capable of carrying them in every direction, even against the
wind. It seems to us interesting to discuss, in a few words,
this important question in the theory of flight.

The stable equilibrium of the bird has been well explained ;
there is nothing for us to add to the remarks which have been
made on this subject. The wings are attached exactly at
the highest part of the thorax, and consequently when the
outstretched wings act upon the air as a fulcrum, all the
weight of the body is placed below this surface of suspension.
We know also that in the body itself, the lightest organs, the
lungs and the air vessels, are in the upper part; while
the mass of the intestines, which is heavier, is lower; also
that the thoracic muscles, which are so voluminous and heavy,
occupy the lower part of the system. ‘Thus the heaviest
part is placed as low as possible beneath the point of sus-
pension.

The bird, as it descends with its wings outspread, will thus
present its ventral region downwards, without its being neces-
sary to make an effort to keep its equilibrium; it will take
this position passively, like a parachute set free in space, or
like the shuttlecock when it falls upon the battledore.

But this vertical descent is an exceptional case; the bird
which allows itself to fall is almost always impelled by some
previous horizontal velocity; it therefore slides obliquely upon
the air, as every light body of large surface does when placed

FORM OF THE BIRD. 217

under the conditions of stable equilibrium which we have
just described. Mons. J. Pline has carefully studied the
different kinds of sliding movement which may take place; he
has even represented them by means of small pieces of appa-
ratus which imitate the insect or the ‘bird when they fly
without moving their wings.

If we take a piece of paper of a square form, and fold it in

]

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|

-}—_$_ '___—_&_--—
3
-g—_ —_——_o-

Fre. 90.—R: presenting, on the left, a contrivance intended to imitate the
hovering of birds; it is placed in equilibrium by two equal weights
attached to the extremities of a wire which is fixed in the lower part of
the angle formed by the folded paper. This piece of apparatus falls verti-
cally, as shown by the successive positions of the wire when attwched to
the two weights. On the right is seen the same contrivance connected
with one we.ght only. Its fall is parabolic, as shown by the dotted
trajectory.

the middle, so as to furm a very obtuse angle (fig. 90); then,
at the bottom of this angle, let us fix with a little wax a
piece of wire attached to two masses of the same weight; we
shall have a system which will maintain stable equilibrium
in the air. If the centre of gravity pass exactly through the
centre of the figure, we shall see it descend vertically when
we let it go, the convexity of its angle being directed down-
wards.

If we take away one of the weights, so as to alter the
position of the centre of gravity, the apparatus, instead of
descending vertically, will follow an oblique trajectory, and
will glide through the air with an accelerated motion (fig. 90,
to the right).

218 ANIMAL MECHANISM.

The trajectory passed through by this little instrument will
be situated in a vertical plane, if the two halves of the appa-
ratus are perfectly symmetrical; but if they are not, it will
turn towards the side in which while it cuts the air it finds
the greater resistance. These effects, which are easily un-
derstood, are identical with those which the resistance of the
rudder causes in the advancing motion of a ship. They can
also be produced in a vertical direction ; so that the trajectory
of the apparatus may be a curve with its concavity above or
below, as the case may be.

Every thin body which is curved tends to glide upon the
air according to the direction of its own curvature.

Fic 91.—We have turned back the rivht hand corner of the two planes
which form the angle. After a descent in a parabolic curve, the apparatus
rises again, as shown by the dotted trajectory.

If we turn back either the anterior or posterior edge of our
little apparatus, we shall see it at a given moment of its
descent rise in opposition to its own weight, but it will soon
lose its upward movement (fig. 91). Let us consider what
has taken place.

So long as the paper descended with but slight rapidity,
the effect of its curvature was not perceptible, because the
air resists surfaces only in the ratio of the velocity with which
they move. But when the rapidity was sufficiently great, an

FORM OF THE BIRD. 219

effect was produced similar to that of a rudder, which turned
up the anterior extremity of the little apparatus, and gave it
an ascending course. Immediately, the weight which was
the generating force of its gliding movement through the air
began to retard it; in proportion as it rose, it lost its velo-
city until it reached the poiut of rest. After that, a downward
movement commenced, then an ascent in the opposite direc-
tion, so that the paper descended to the ground by successive
oscillations.

If we give the apparatus a slight concavity downwards,
the opposite effect is produced; we see (fig. 92), at a certain

See
2 ees
| =
_—
bee

Fic. 92.—The right hand corner of the pline of the angle has been bent
downwards. After a parabolic desceut, the apparatus falls very rapidly
in a perpendicular direction.

moment, the trajectory turns abruptly downwards, and the
falling body strikes the ground with considerable violence. In
this second case, when the rudder-like effect is produced, the
new direction has in its favour the weight which hastens the
fall of the little instrument, as in the former experiment it
rendered the re-ascent more slow.

We have dwelt upon these effects, because they often occur
in the flight of birds. They are mentioned in the old treatises
on falconry, which describe the evolutions of birds used in

220 ANIMAL MECHANISM.

hawking. Without going further back, we find in Huber* the
description of these curvilinear movements of falcons, to which
they gave the name of passades, and which consisted of an
oblique descent of the bird, followed by a re-ascent, which
they called ressource (from the Latin, resurgere). ‘‘ The bird,”
says Huber, ‘‘ carried forward by its own velocity, would dash
itself against the ground, were it not that it exercises a cer-
tain power which it possesses of stopping when at its utmost
speed, and turning directly upwards to a sufficient height to
enable it to make a second descent. This movement is able
not only to arrest its descent, but also to carry it without any
further effort, as high as the level from which it started.”

Surely, there is some exaggeration in saying that the bird
can rise, without any active effort, to the height from which
it stooped; the resistance of the air must destroy a portion of
the force which it had acquired during its descent, and which
must be transformed into a rising impulse. We see, how-
ever, that the phenomenon of the ressource has been noticed
by many observers, and that it has been considered by them
as, to a certain extent, a passive motion in which the bird
has to employ no muscular force.

The act of hovering presents, in certain cases, a great ana-
logy with the phenomena just described. When a bird—a
pigeon, for example—has traversed a certain distance by flap-
ping its wings, we see it suspend all these movements for
some instants, and glide on either horizontally, ascending or
descending. ‘The latter kind of hovering motion is that which
is of longest duration; in fact, it is only an extremely slow
fall, but in which the weight assists the movement, while
it checks it in the horizontal or ascending course. In the last
two forms, the wing, directed more or less obliquely, derives
its point of resistance from the air, like the child’s plaything
called a kite, but with this difference, that the velocity is
given to the kite by the tractile force exerted on the string
when the air is calm, while the bird when it hovers utilizes
the speed which it has already acquired, either by its oblique
fall or by the previous flapping of its wings.

We have already said, that observers had admitted that

* 8vo. Geneva, 1784.

FORM OF THE BIRD. 221

certain birds which they called ‘sailing birds” could sustain
and direct themselves in the air solely by the action of the
wind. This theory has all the appearance of a paradox; we
cannot understand how the bird, when in the wind, and using
no exertion, should not be affected by its force.

If the passades, or the changes which it effects in the plane
of its wings, can sometimes carry it in a direction con-
trary to that of the wind, these can be only transient effects,
compensated afterwards by a greater force driving them
before the wind.

Nevertheless, this theory of sailing flight has been advo-
cated with great talent by certain observers, and especially by
Count d’Esterno, the author of a remarkable memoir on the
flight of birds.

“Every one,” says this author, ‘‘ must have seen certain
birds practise this kind of sailing flight; to deny it, is to
contradict evidence.”

We know s0 little yet of the resistance of the air, especially
with reference to the resolution of this force when it acts
against inclined planes under different angles, that it is im-
possible to decide on this question as to sailing flight. It
would be rash absolutely to condemn the opinion of observers,
by depending on a theory or on notions as vague as those
which we possess on this subject.

Fiatio of the surface of the wings to the weight of the body.—
One of the most interesting points in the conformation of birds
consists in the determination of the ratio borne by the surface
of the wings to the weight of the bird. Is there a constant
relation between these two quantities? This question has
been the cause of many controversies.

It has already been shown that, if we compare birds of
different species and of equal weight, we may find that some
have their wings two, three, or four times more extended
than the others. The birds with large wing surfaces are
those which usually give themselves up to a kind of hovering
flight, and have been called sailing birds; while those whose
wing is short or narrow are more usually accustomed to a
flight which resembles rowing. If we compare together
two “rowing” or two “sailing” birds; if, to be more

222 ANIMAL MECHANISM.

exact, we choose them from the same family, in order to have
no difference between them except that of size, we shall find
a tolerably constant ratio between the weight of these birds
and the surface of their wings. But the determination of this
ratio must be based upon certain considerations which have
_ been long disregarded by naturalists.

Mons. de Lucy has endeavoured to compare the surface of
the wings with the weight of the body in all flying animals.
Then, in order to establish a common unit between creatures

of such different species and size, he referred all these esti- »

mates to an ideal type, the weight of which was always one
kilogramme. ‘Thus, having ascertained that the gnat, which
weighs three milligrammes, possesses wings of thirty square
millimetres of surface, he concluded that in the gnat type
each kilogramme of the animal was supported by an alar sur-
face of ten square millimetres.

Having drawn up a comparative table of measurements
taken in animals of a great number of different species
and sizes, Mons. de Lucy has arrived at the following re-
sults :—

Surface per

|
Species. eight of omens ie? of Wings. Kilogramme.
nat . 4 4 3 milligr. 30 sq. millim. 10 sq. millim.
Butterfly. - 20 centigr. |1663 ,, e 398 abse
Pigeon .| 290 grammes. | 750 sq. centim. |2586 sq. centim.
Stork . +: | 2265 - 4, AGOB os asks LORS <a tetiy
Australian Crane.| 9500 ,, 8548 ,, . S99 eS ona.

From these measurements we obtain the-following im-
portant consideration, that animals of large size and great
weight sustain themselves in the air with a much less pro-
portionate surface of wing than those of smaller size.

Such a result plainly shows that the part played by the
wing in flight is not merely passive, for a sail or a parachute
ought always to have a surface in proportion to the weight
which it has to support; but, on the contrary, when con-
sidered in its proper point of view, as an organ which strikes
the air, the wing of the bird ought, as we shall see, to pre-

FORM OF THE BIRD. 223

sent a surface relatively less in birds of large size and of
great weight.

The surprise which we feel at the result obtained by Mons.
de Lucy disappears when we consider that there is a geome-
trical reason why the surface of the wing cannot increase in -
the ratio of the weight of the bird. In fact, if we take two
objects of the same form—two cubes, for example—one of
which has a diameter twice as large as the other, each of the
surfaces of the larger cube will be four times as large as that
of the smaller one, but the weight of the large cube will bs
eight times that of the small one.

Thus, for all similar geometrical solids, the linear aoe
sions being in a certain ratio, the surfaces will increase in
proportion to their squares, and the weights in that of their
cubes. Two birds similar in form, one of which has an
extent of wing twice as large as the other, will have wing
surfaces in the proportion of one to four, and weights in that
of one to eight.

Dr. Hureau de Villeneuve, basing his enquiries on these
considerations, has determined the surface of wing which
would enable a bat having the weight of a man to fly; and
he has found that each of the wings need uot be three metres
in length.

In a remarkable work on the relative extent of wing and
weight of pectoral muscles in different species of flying ver-:
tebrate animals,* Hartings shows that in a series of birds we
can establish a certain relation between the surface of the
wing and the weight of the body. But we must be careful
only to compare elements which admit of comparison; for
instance, the length of the wings, the square roots of their
surfaces, and the cube roots of the weights of different birds.

Let ¢ be the length of the wing; a, its area or surface ;
and p the weight of the body; we can compare together 1, ./a,
and ~/p.

Making observations on different types of birds, Hartings
ascertained their measurements and weights, from which he
obtained the following table :—

* Archives Néerlandaises, Vol. XIV., p. 1869.

224 ANIMAL MECHANISM.

| =F Ratio,

Name of Species. ° W wee Si Ja

VP

1. Larus argentatus . . : 565°0 541 2°82

2. Anas nyroca . ° Pore 5080 321 2°26

3. Fulica atra . ° ° : 495°0 262 2 05

4. Anas ecrecca . ° arc 275°5 144 1°84

5. Larus ridibundus . e + 197°0 331 3°13

6. Machetes pugnax ° *; Ke 190°0 164 2°23

7. Ralius aquaticus . . ; 1705 101 1°81

8. Turdus pilaris . . outs 103°4 101 2°14

9. Turdus merula - - Z 88 8 106 2°31

10. Sturnus vulgaris ° e- 86°4 85 2°09
11. Bombicilla garrula. ° ° 60°0 44 1°69
12. Alauda arvensis. ° e 32-2 75 2.69
13. Parus major . ° ° ° 14°5 31 2°29
14. Fringilla spinus . ae 101 25 2°33
15. Parus ceeruleus. ° 91 24 2°34

To this list of Hartings we will add another which we have
prepared by the same method (p. 225). All the experiments have
been made on birds killed by the gun, and a few instants after
death. We have taken the surface of the two wings instead
of only one, as Hartings had done; this modification, which
appeared necessary, is the principal cause of the difference
which the reader will find between our numbers and those of
the Dutch physiologist. To compare the two tables, it will
be necessary to multiply by 4/2 the number obtained by
Hartings as the expression of the ratio ue

The variations that we find in the ratio of the weight of
the body to the surface of the wings in different species of
birds, depends in a great degree on the form of the wings.
In fact, it is not immaterial whether the surface which strikes
the air has its maximum near the body or near the extremity ;
these two points have very different velocities. For an equal
extent of surface the resistance will be greater at the point of
the wing than at its base. It follows from this, that two birds
of unequal surface of wing may find in the air an equal resist-
ance, provided that these surfaces are differently arranged.

The weight of the pectoral muscles is, on the contrary, in
a simple ratio to the total weight of the bird, and notwith-

FORM OF THE BIRD. eat

standing variations which correspond with the different apti-
tudes for flight with which each species is endowed, we find
that it is about one-sixth of the whole weight in the greater
number of birds.

Surface of

< : Weight = p.| Wings = 2a. A 2
Name of Species. Crnmmes, (Square centi- Natio = V2 ‘
: ; metres.

Vultur 5 : ° " 1663 °94 3131 4°722
Vultur cinereus. el eloson00 8233 4:929
Falco tinnunculus’ =. 5 128°94 642 5-015
5 a minor. . 147°36 546 4-424
Falco Kobek 5 ; 28244 970 4-747
Faleo sublatio(?) . aes 50962 1684 5138
Falco palustris . ° : 208°76 1188 5°810
Falco milvus c 5-0 620°14 1904 5117
Strix passerina . : : 122°80 394 3°993
irc) he alt= ogr04 442 4°162
Saxicola cenanthe ‘ : 56°05 125 2°922
Alauda cristata. ont 36°80 202 4°273
Corvus cornix . , ‘ 374°54 1156 4-717
Upupa epops ‘ ae 49°12 329 4°952
Merops apiaster. 2 < 18°30 ialZ 4°105
Alcedo ispida 5 og 82°89 270 3-769
Aleedo afra (?). : - 85:96 288 3°845
Columba vinacea . Oran 112:00 292 3°545
Vanellus spinosus . 159 64 636 4-649
Glarecola ‘ fs et oe 95°17 343 4:056
3uteo vulgaris . 3 ; 735°00 1651 4°405
Perdix cinerea. ot ee 280-00 320 2°734
Sturnus vulgaris : - 78°00 202 3°326
Corvus pica . : ape 8 212°00 540 3°906
iis. : - : 275 00 690 4:039
Hirundo urbica are 18-00 . 120 4-180
Turdus merula . : 4 94-00 230 3°335

In conclusion, each animal which sustains itself in the air
must develop work proportionate to its weight; it ought, for
this purpose, to possess muscular mass in proportion to this
weight; for, as we have already seen, if the actions performed
by the muscles of birds are always of the same nature, these
actions and the work which they perform will be in proportion
to the mass of the muscles.

11

226 ANIMAL MECHANISM,

But how is it that wings whose surfaces vary as to the
square of their linear dimensions are sufficient to move the
weights of birds which vary in the ratio of the cubes of these
dimensions ?

It can be proved that, if the strokes of the wing were as
frequent in large as in small birds, each stroke would have a
velocity whose value would increase with the size of the bird;
and as the resistance of the air increases for each element of
the surface of the wing, according to the square of the velo-
city of that organ, a considerable advantage would result to
the bird of large size, as to the work produced upon the air.

Hence it follows, that it would not be necessary for large
birds to give such frequent strokes of the wing in order to
sustain themselves as would be required for those of smaller
size.

Observers have not, hitherto, been able to determine very
accurately the number of the strokes of the wing, in order to
ascertain whether their frequency is in an exact inverse ratio
to the size of birds; but it is easy to sce that the number of
strokes varies in birds of differeut size in a proportion of this
kind,

CHAPTER IV.

OF THE MOVEMENTS OF THE WING OF THE BIRD
DURING FLIGHT.

Frequency of the movements of the wing—Relative durations of its rise
and fall— Electrical determination—M yographical determination.
Trajectory of the bird’s wing during flight— Construction of the instru-
ments which register this movement—Experiment—Elliptical figure

of the trajectory of the point of the wing.

In the general remarks on the form of the bird, and on the
deductions to be drawn from it, the reader must have seen
that many hypotheses await experimental demonstration. For
this reason, we have been anxious to apply to the flights of

MOVEMENTS OF TIE WINGS OF BIRDS. 227

the bird the method which has enabled us to analyse the other
modes of locomotion.

Frequency of the strokes of the wing.—The graphic method
which enabled us so easily to determine the frequency of the
strokes of the insect’s wing cannot be employed under the same
conditions when we experiment on the bird. — It will be neces-
sary to transmit signals between the bird as it flies and tlie
registering apparatus. We have here to deal with a problem
similar to that which we solved with respect to terrestrial
locomotion, when we registered the number and the relative
duration of the pressures of the feet upon the ground.’ We
must now estimate the duration of the impacts of the wing
upon the air, and the time which it occupies in its rising
motion.

Electrical method.—We made use at first of the electric
telegraph. The experiments consist in placing on the ex-
tremity of the wing a kind of apparatus which breaks or closes
an electric circuit at each of the alternate movements which
it is induced to make. In ‘this circuit is placed an electro-
magnetic arrangement which writes upun a revolving cylinder.
Vigure 94 shows this mode of telegraphy applied to the study
of a pigeon’s flight, simultaneously with the transmission of
signals of another kind, to be hereafter described. In this
figure the two conducting wires are separated from each other.

The writing point will trace a wavy line, the elevations and
depressions of which will correspond with each change in the
direction of the movement of the wing. In order that the
bird may fly as freely as possible, a thin flexible cable, con-
taining two conducting wires, establishes a communication
between the bird and the telegraphic tracing point. The two
ends of the wires are fastened to a very small light instrument
which acts like a valve under thie influence of the resistance of
the air. When the wing rises, the valve opens, the current
is broken, and the line of the telegraphic tracing rises. When
the wing descends, the valve closes, the current closes at the
same time, and the tracing made by the telegraph is lowered.

This instrument, when applied to different kinds of birds,
enables us to ascertain the frequency peculiar to the move-
ments of each. The number of species which we have been

228 ANIMAL MECITANISM.

able to study is very small as yet; the following are the
results obtained :—

Revolutions of wing
per second,

Sparrow . . ° ° . . . 13
Wild duck . 7 . . 9
Pigeon . “ - ° . ° Abomapss:
Moor buzzard : a 5 gy ee bd
Sereech owl . - . . e 5
Buzzard < 3 - as 3

The frequency of the strokes of the wing varies also, according
as the bird is first starting, in full flight, or at the end of its
flight. Some birds, as we know, keep their wings perfectly
still for a time; they glide upon tlie air, making use of the
velocity already acquired.

Nelative duration of the depression and elevation of the wing —
Contrary to the opinion entertained by some writers, the
duration of the depression of the wing is usually longer than
that of its rise. The inequality of these two periods is more
distinctly seen in birds whose wings have a large surface, and
which beat slowly. Thus, while the durations are almost
equal in the duck, whose wings are very narrow, they are
unequal in the pigeon, and still more so in the buzzard.
The following are the results of our experiments :—

Total duration of a
revolution of the wing. Ascent. Descent.

It is more difficult than would have Leen expected, to determine
the precise instant when the direction of the line traced by the
telegraph changes. ‘The periods during which the soft iron
is first attracted and then set free, have an appreciable duration
when the blackened cylinder turns with sufficient rapidity to
enable us to measure the rapid movements which are the
subjects of this inquiry. The inflections of the line traced by
the telegraph then Lecome curves, the precise commencement

MOVEMENTS OF THE WINGS OF BIRDS. 229

of each of which it is difficult to discover. There is therefore
some limit to the precision of the measurements which we can
take by the electric method; we can still, however, estimate
by this means the duration of a movement with a tolerably
accurate approximation.

_ Myographic method.—We have seen that a dilatation accom-
panies the contraction of the muscles, and follows it through
all its phases. A shortening of the muscle, either rapid or
slow, feeble or exergetic, as the case may be, will therefore be
accompanied by a lateral dilatation which will have similar
characters of rapidity or intensity. At each depression of the
wing of a bird, the large pectoral muscles will be subject to a
dilatation which it will be necessary to transmit to the re-
gistering apparatus.

We shall have recourse, for this purpose, to the apparatus
which we have employed in determinations of the same kind,
when treating of human locomotion. Some slight modifica-
tions will enable them to give signals of the alternate phases
of dilatation and relaxation of the large pcctoral muscle.

PRA

Z ae
Wongegtes>= SSS

od
ae

Fic 93.—Apparatus to investigate the contraction of the thoracic muscles
of the bird. The upper convex surface is formed of a membrane of india-
rubber supported by a spiral spring; this part is applied to the muscles.
The lower surface, in contact with the corset, carries four small hooks
which are fastened in the stuff and keep the instrument in its place,

The bird flies in a space fifteen metres square and eight
metres high. ‘The registering apparatus being placed in the
centre of the room where the experiment is made, twelve
metres of india-rubber tubing are sufficient to establish a
constant communication between the bird and the apparatus,

A sort of corset is fixed on a pigeon (see figure 94). Under
this corset, between the stuff, which is tightly stretched, and

230 ANIMAL MECHANISM.

the pectoral muscles, a small instrument is slipped, which is
intended toshow the dilatation of the muscles, and is constructed
in the following manner :

A little metal pan (fig. 93), containing within it a spiral
spring, is closed by a membrane of india-rubber. This closed
pan communicates with a tube transmitting air.

Fic. 94.—Experiment to determine by the electrical and myographical
methods, at the same time, the frequency of the movements of the wing
and the relative durations of its elevation and depression.

Each pressure on the india-rubber membrane depresses
it, and the spring gives way ; the air is driven out of the pan,
and escapes by the tube. When the pressure ceases, the air
is returned to the instrument by the elasticity of the spring

MOVEMENTS OF THE WINGS OF BIRDS. 231

which raises the membrane. Alternate outward and inward
currents of air are thus established in the tube, and this
movement transmits to the registering apparatus the siguals
of the less or greater pressures exerted on the membrane of
the small pan.

The registering instrument is the lever drum, with which
the reader is already acquainted. It gives an ascending curve
while the muscle contracts, and a descending one when it is
relaxed.

Vig. 94 represents the general arrangement of the experi-
ment, in which the electric telegraph and the transmission of
air are used at the same time.

It shows a pigeon fitted with a corset, under which is
slipped the instrument which is to show the action of the
pectoral muscles. ‘The transmitting tube ends ina registering
apparatus, which writes on a révolving cylinder.

At the extremity of the pigeon’s wing is the instrument
which opens or closes an electric current, as the wing rises
or siuks. ‘The two wires of the circuit are represented as
separated from one another; within the circuit are seen two
elements of Bunsen’s pile, and the electro-magnet which,
being furnished with a lever, registers the telegraphic signals
of the movements of the wing,

Expceriment.—The bird is set free at one extremity of the
room, the dove-cot in which it is usually kept being placed
at the opposite end. The bird as it flies naturally seeks its
nest in which torest. During its flight we obtain the tracings
represented by fig. 95.

-It is seen that the tracings differ according to the kind of
bird on which the experiment is made. IJlowever, we ob-
serve in each of the tracings the periodical return of the two
movements a and 6, which are produced at each revolution of
the wing. :

On what do these two muscular acts depend? It is easy
to discover that the undulation a corresponds with the muscle
that elevates the wing, and 6 with that which depresses it.
This can be proved: first, by collecting, at the same-time as
the muscular tracing, those of the ascending and descending
movements of the wing transmitted by electricity. When

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MOVEMENTS OF TIIE WINGS OF BIRDS. 233

these two tracings are placed over each other, they show that
the time of the elevation of the wing agrees with the dura-
tion of the undulation a, and the time of its depression coin-
cides with the undulation b.

From this we may see how the undulations a and b are
produced in all the muscular tracings obtained from birds.
In fact, close by the portion of the bird’s breast on which the
experiment is made, and near the projecting edge of the
sternum, there are two distinct layers of muscle; the more
superficial one is formed by the large pectoral, the depressor
of the wing; the deeper one by the middle pectoral, or ele-
vator of the wing, whose tendon passes beliind the forked
part of the sternum to attach itself to the head of the
humerus.

These two muscles, being superposed, will act by their
dilatation on the apparatus applied to them; the elevator of
the wing, swelling as it contracts, gives its signal by the un-
dulation a; the great pectoral signals the depression of the
wing by the undulation 8.

We may verify the correctness of this explanation by means
of a very simple experiment. Anatomy shows us that the
muscle which elevates the wing is narrow, and only covers the
depressor in its most inward part, situated along the ridge
of the sternum; so that if we displace the little apparatus
which shows the movement of the muscles, and remove it a
little outwards, it will occupy a part where the depressor of
the wing is not covered by the elevator, and the tracing
will only present a simple undulation, corresponding with
b in the curves of fig. 95. Itis thus plainly shown that the
undulations a and b in the muscular tracings of the birds on
which we have experimented correspond exactly with the
actions of the principal muscles-which elevate and depress
the wing; but we cannot attach great importance to the form
of the tracings, in order to deduce from them the precise
nature of the movement performed by the muscle. These
movements seem, in fact, to encroach on each other; so that
the relaxation of the elevator of the wing is probably not
completed when the depressor begins to act.

We expcct nothing more from these tracings than that

231 ANIMAL MECHANISM.

which they more readily furnish ;
namely, the number of the revolu-
tions of the wing, the greater or less
regularity of these movements, and
the equality or inequity of each of
them.

Confining the question within
these limits, experiment shows that
the strokes of the bird’s wing differ
in amplitude and in frequency from
one moment to another as they fly.
When they first start, the strokes
ate rather fewer, but much more
energetic ; they reach, after two or
three strokes of the wing, a rhythm
almost regular, which they lose
again when they are about to settle

fir. 96).

‘oonds

.
<

a
®
=
=
=
<a

AOUL RAID BAS

as TRAJECTORY OF THE WING OF THE
PEs BIRD DURING FLIGHT.

ces We lave seen, when treating of
aa the mechanism of insect flight, that
Fo the fundamental experiment was
oe that which revealed to us the course
FSR of the point of the wing throughout
ee E each of its revolutions. Our know-
24 ledge of the mechanism of flight
ae naturally flowed, if we may so say,
eas from this first notion.

ge ‘The same determination is equally
r 2 necessary for the flight of birds ;
Sia but the optical method is unsuitable
Eg? for this purpose. In fact, the move-
een ment of the bird’s wing, although
Bog too rapid to be appreciable by the
Se eye, is not sufliciently so to furnish
BS = such a persistent impression on the

retina as to show its whole course.

‘MOVEMENTS OF TIE WINGS OF BIRDS. 235

The graphic method, with its transmission of signals, which
we have hitherto employed, only furnishes the expression of
movements which take place in a straiglit line, such as the
contraction or lengthening of a muscle, the vertical and hori-
zontal oscillations of the body during the act of walking, &c.
It is only by combining this rectilinear movement with the
uniform advance of the smoked surface that receives the
tracing, that we obtain the expression of the velocity with
which the movement at each instant is effected,

The action of the wing during flight does not consist
merely of alternate elevations and depressions. We have only
to look at a bird as it flies over our head to ascertain that the
wing is carried also forward and backward at each stroke.
From this double action must result a curve which it is neces-
sary to describe.

It can be geometrically shown that every plane figure,
that is to say, every figure susceptible of being dese1ilbed upon
a plane surface, cin be produced by the rectangular combina-
tion of two rectilinear movements. ‘The tracings obtained by
Koenig by arming with a style Wheatstone’s vibrating rods,
aud the luminous figures of musical chords which Lissijous
produced by the reflection of a pencil of light upon two
mirrors vibrating perpendicularly to each other, are well-
known examples of the formation of a plane figure by means
of two rectilinear movements at 1ight angles to each other.

Thus, if we can transmit at the same time the movements
of elevation and depression executed by the wing of the bird,
as well as those which the organ makes forwards and back-
wards; then, supposing that a tracing point can receive simul-
taneously the impulse of these two movements at right angles
to each other, this point will describe on the paper the exact
tracing of the movements of the bird’s wing.

We have endeavoured first to construct an instrument which
would thus transmit to a distance any movement whatever,
and register it on a plane surface, without attending to the
method by which this machine, which may be more or less
heavy, might be adapted to the body of the bird. Fig. 97
represents our first experimental instrument, the description
of which is indispensable in order to enable our readers to

236 ANIMAL MECIIANISM.

understand the construction of the machine which we finally
employed.

On two solid feet carrying vertical supports, we placed
two horizontal arms parallel to each other. ‘These were two
aluminium levers, which, by means of the apparatus we are
about to describe, will both execute the same movements.
Each of these levers is mounted on a Cardan joint, that is to
say, a universal joint which allows every kind of movement ;
so that each lever can be carried upwards, downwards, to
the right or the left; it can describe with its point the base
of a cone of which the Cardan forms the apex; in fact it will
execute any kind of movement which the experimenter may
please to give it.

It was requisite to effect the transmission of the move-
ments of one of tlicse levers to the other, and that at a dis-
tance of ten or fifteen metres. This is done by a method with
which the reader is already acquainted—the employment of
air-drums and tubes.

The lever, which in fig. 97 is seen to the left hand, is
fastened by a vertical metallic wire to the membrane of a
drum placed underneath it. In the vertical movements of
the lever, the membrane of the drum, alternately depressed
and raised, will produce a current of air, which will be trans-
mitted by a long air-tube to the membrane of a similar drum
belonging to the apparatus on the right band. ‘The second
drum, placed above the lever which corresponds with it, and
is fastened to it, will faithfully transmit all the vertical
movements which have been given to drum No. 1 (that on
the lefi). ‘The motion of the two levers will be in the same
direction, on account of the inversion of the position of the
drums.

Let us suppose that we lower the lever No. 1; we com-
press the membrane of the drum beneath it; a current of
air is produced which raises the membrane of the second
drum, and consequently lowers lever No. 2. On the contrary,
the elevation of lever No. 1 will produce an inward current of
air, which will raise the membrane and the lever of No. 2.

Proceeding in tlhe same manner for the transmission of
movements in the horizontal plane, we place to the right of

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238 ANIMAL MECHANISM.

one of the levers and to the left of the otl.ers, a drum whose
membrane, situated in the vertical plane, acts in a lateral
direction; the transmission of these movements is made by a
special tube, as in the case of the vertical movements.

The apparatus having been thus constructed, if we take in
our fingers the extremity of one of the levers, and give it any
motion whatever, we shall see the other lever repeat it with
perfect fidelity.

All the difference consists in a slight diminution of the am-
plitude of the movemeuts in the second lever, This is because
the air contained in each of the systems of tubes aud drums
is slightly compressed, and consequently does not transmit
completely the movement which it receives. It would be easy
to remedy this inconvenience, if it were found to be one, by
giving to the receiving apparatus a greater sensibility, which
might be effected by placing the Cardan joint a little nearer
the poiut where the movement is transmitted to the lever of
the second instrument. But it is better uot toseek to amplify
the moyemeuts too much when we wish to register them by
tracings, since we then augment the friction, and diminish the
force by which it must be overcome.

After having ascertained that the transmission of any move-
ment whatever is effected in a satisfuctory manner by this ap-
paratus, we sought for a means of tracing this movement on a
plane surface. The difficulty which occurred in the application
of the graphic method to the study of the movement of the
insect’s wing, again presents itself here ; but in this case there
are no meaus of avoiding it by taking only partial tracings.

The point of the lever No. 2 describes in space a spherical
fizure incapable of becoming tangential, except in a single
point, to the smoked surface which is to receive the tracing.
Consequently, it has been necessary to register the projection
of this figure on a plane surface, and to arrange the lever in
such a manner that it may lengthen or shorten itself as re-
quired, in order to keep always in contact with the smoked
glass. This result was obtained by means of a spring which
served as a writing point.

Fig. 98 shows the spring in question, at the extremity of a
lever. It is wide at the base, in order to resist any tendency

MOVEMENTS OF THE WINGS OF BIRDS. 239

to lateral deviations under the. influence of the friction ; this
base is fixed to a vertical piece of aluminium, which is
attached by its lower part to the extremity of the lever. In
this manner, the point of the spring which acts as a style is
cousiderably in front of the lever whose movements it is to
register. Let us suppose the lever to rise, and take the
position indicated by the dotted line in figure 98; while
traversing this space, it will have described an arc of a circle,
and its extremity will no longer be in the same plane as before,
but the elasticity of the spring will have carried the writing
point more forward; it will still continue, therefore, to be

Fig. 98.—Elastie point tracing on a smoked glass,
.
in contact with the plane on which it is to trace. Thus the
lever lengthens or shortens, as required, and its point
always presses on the plane. The surface on which the tracing
is received is a well-polished glass, and the spring which
forms the style is so flexible, that the elastic pressure which it
exerts upon the glass rubs it but shghtly.

The apparatus being thus arranged, it must be submitted
-to a verifying process, to ascertain if movements are faithfully
transmitted and registered.

For this purpose, arming the two levers of fig. 97 with
similar styles, we placed their points against ihe same piece
of smoked glass; we directed with the hand one of the levers
so as to trace any figure, to sign one’s name for instance ; the
other lever ought to trace the same figure, to reproduce the
same signature.

240 ANIMAL MECIIANISM.

It generally happens that the transmission is not equally
easy in both directions ; we perceive a slight deformity in the
transmitted figure, which is lengthened more or less both in
height and in width. This fault can always be corrected ; it
arises from the fact, that the membrane of one of the drums,
being more stretched than that of the other, obeys less easily.
We soon succeed, by various trials, in giving the same sensi-
bility to the two membranes, which is ascertained, whea we
find that the figure traced by the first lever is identical with
that of the second. :

Lxperiment to determine graphically the trajectory of the wing.
—The following are the modifications which allow us to apply
this mode of transmission to the study of the movements of
the wing of a flying bird.

As the apparatus must necessarily be of considerable weight,
we chose a large bird to carry it; strong full-grown buzzards
were employed in these experiments. By means of a kind of
corset which left both the wings and the legs at liberty, we fixed
on the back of the bird a thin piece of light wood on which
the apparatus was placed.

In order that the lever might execute faithfully the same
movements as the wing, it was necessary to place the Cardan
joint of this lever in contact with the humeral articulation of
the buzzard. Therefore, as the presence of the drums*by the
side of the lever did not permit this immediate contact, we
had recourse to a parallelogram, which transmitted to the lever
of the apparatus the movements of a long rod, the centre of
motion in which was very near the articulation of the bird’s
wing. ‘Then, in order to obtain perfect correspondence be-
tween the movements of the rod and those of the buzzard’s
wing, we fixed on the outer edge of the wing—that is to say,
on the metacarpal bone of the thumb of the bird, a very tight
screw clip, furnished with a ring, through which slipped the
steel rod, of which we have before spoken.

Vig. 99 represents the buzzard flying with the apparatus
just described; underneath it hang the two transmitting tubes
which are fixed to the registering instrument.

After a great many fruitless attempts and changes in the
construction of the apparatus, which, being too fragile, broke

241

‘Buyai sqt jo Ayu014.x9

94} Aq poqttosep sywoUTOAOU oT} JO [eUFIS oT} soATa Tory snguredde ong ayia Susy pavzzng—'gg ‘ong

242 ANIMAL MECHANISM.

at almost every flight of the bird, we succeeded in obtaining
satisfuctory results. During the whole of the bird’s flight the
registering lever described a kind
of ellipse. This ellipse, registered
on a plate having an advancing
movement from right to left, gave
figure 100. In order to under-
stand this figare, we must imagine
the bird flying from left to right
(as the tracing is to be read),
and rubbing the extremity of its
left wing against awall blackened
with smoke; the tracing which
its wing would leave under these
conditions would be identical with
that represented in fig. 100.
This curve is a kind of ellipse
spread out by the advancing mo-
tion of the plate which receives
the tracing. Except some trem-

D5

blings of the line, which arose
from the imperfection of the
apparatus, the trajectory of the
bird’s wing may be compared to
the tracing given under the same
conditions by a Wheatstone’s rod,
tuned in unison, and giving an
elliptical vibration.

Fig. 101 represents a tracing
of this kind.

Vhedetermination of the course
of the wing, with the different
phases of its velocity, is so im-
portant, that we resolved to verify
by various methods the reality
of this elliptical form. All our ex-

org

“BUI § p.itq v Jo yutod on} Jo Furowsy Twondry]— ‘oor

periments have furnished results
Which agree with each other; they have shown that birds of dif-
ferent species describe with their wings an elliptical trajectory.

MOVEMENTS OF THE WINGS OF BIRDS. 243

D'Esterno had already determined by his experiments that
this trajectory existed; and he has even figured, in his work,
the curve described ; but, in his opinion, the larger axis of
the ellipse would be directed downwards and backwards, which
is entirely opposed to the result of our experiments.

Fic, 101.—Ellipse formed hy a Wheatstone’s rod tuned in unison and
tracing on a revolving cylinder.

We remark also the unequal amplitude of ‘the strokes of
the wing from the commencement to the end of fig. 100.
This variation in size agrees with what we. have already
stated concerning fig. 96. This showed that at the com-
mencement of its flight, the bird gives stronger strokes with
its wing. It is at that moment, in fact, that it has to efttect
the maximum of work, in order to rise from the ground.
After this, it will only need to remain at the height which it
has attained.

244) ANIMAL MECIANISM.

CHAPTER V.

OF THE CHANGES IN THE PLANE OF THE BIRD’S WING 4T
DIFFERENT POINTS IN ITS COURSE.

New determination of the trajectory of the wing —Description of apparatus
—Transmission of a movement by the traction of a thread Instru-
ment and ap aratus to suspend the bird—Experiment on the flight of
a pigeon—Analysis of the curves—Description of the apparatus
intended to give indications of the changes in the plane of the wing
during flight—Relation of these changes of plane with the other
movements of the wing.

NEW DETERMINATION OF THE TRAJECTORY OF THE WING.

Tue simultaneous analysis of the changes in the plane of
the wing, and of the various phases of its course, would have
presented great difficulties, if we had not discovered a new
arrangement of the apparatus, which allowed us to examine,
at the same time, an almost infiuite number of different
inovements.

This simplification of the method consists in the employ-
ment of threads to transmit the movement of any point
whatever to the experimental apparatus, which in its turn,
sends it by the ordinary means to the registering instrument.

Description of apparatus.—Let fig. 102 be two lever-drums
connected together, similar to those already represented in
fix. 21.

The lever L belongs to the experimental apparatus, that on
which the movement to be studied is to act. On the frame
of this first instrument let us place an arm of bent wire, from
the extremity of which an india-rubber thread, F, will pass to
the lever L. From the same lever hangs a cord of twisted
silk, C C, to which is suspended a leaden ball.

Let us suppose the bull to be at its lowest position—at
the point A—the lever L occupies the place marked by a dotted
line, while in the registering instrument the air driven out
raises the lever L’, which traces the movement.

MOVEMENTS OF THE WINGS OF BIRDS. 245

Now let us raise the ball to the position B; the elasticity
of the india-rubber thread will cause the lever to rise. Thus
it is acted upon alternately by two forces, sometimes by the
traction exerted by the silk thread, which lowers it; at others,
by the retraction of the india-rubber, which re-acts as soon as
the tractile force ceases. Thus the lever will follow faithfully
all the movements which are given to the extremity of the
thread which draws it down.

Fi
eR
Soe FEE _
I if
“| <P)
T

Fic. 102.—Transmission of a to and-fro movement by means of a simple
traction-cord.

The lever L’, which is to trace on the cylinder the move-
ments transmitted to it, moves in an opposite direction to the
course of the cord CC. The tracing will thus be reversed,
and if it were important to obtain it in the same direction, it
would be necessary to turn the registering drum, so as to place
the membrane downwards.*

With two instruments of this kind, one acted upon by the

* As many instruments of this kind are required as there are move-
iments to be studied. But three connected levers will always be sufficient
to ascertain the movements of a point in space, since each of the posi-
tions of this point is defined when it has been determined with reference
to three axes at right angles to each other.

246 ANIMAL MECIIANISM.

vertical tractions of a thread attached to the wing of the bird,
and the other by the horizontal tractile force of a secon
thread also fastened to its wing, we can verify the experiment
which has furnished us with the trajectory of this organ, and
obtain with much greater accuracy the curve illustrating its
movements, ‘This we have perfectly succeeded in doing, as
we shall show further on,

But this is not all that we wislicd to obtain. We might
have made the bird carry the apparatus which we have just
described, and put it in communication with the registers by
means of tubes, as in the experiment represented in fig. 99.
But while sceking to render the analogies of the movements
of flight perfect, we wished also to discover a plan which
would be equally applicable to the living bird, and to every
kind of machine intended to represent artificially aerial loco-
motion.

In this project we must endeavour to copy Nature in her
functions, as the artist does in her form. We must give more
rapidity to movements which are too slow, and render those
slower which are too rapid, until they have absolutely the same
characters and the same mechanical effects as those of the
bird.

This incessant comparison requires us to place ourselves
under new conditions. ILitherto, our analytical studies have
been directed to a bird flying at liberty; for since we have
never been able to imitate flight exactly by mechanical
methods, it would be impossible to leave an artificial instru-
ment to itsclf; it would be broken at each experiment.

The comparisou of the movements of the bird with those
of imitative instruments does not require these movements to
he effected under the conditions of free flight. Provided that
the bird, although restrained in its movements, should flap
its wings with the intention of flying, we shall be able to
study these muscular actions with reference to their characters
of force, extent, and duration. A bird suspended by a cord
and allowed to flap its wings might, for example, be com-
pared with an artificial apparatus suspended in the same
manner.

We have tricd a less imperfect mode of suspension which

MOVEMENTS OF THE WINGS OF BIRDS. 247

allows the bird to fly under conditions almost normal, and
at the sume time will permit the artificial instruments to make
attempts at flight, without any fear of letting them full, if
the movements which they produce should be insufficient to
sustain them in the air. We will now describe this suspen-
sory apparatus.

There is a sort of frame-work of six or seven metres in
diameter, in which the bird moves continuously, being thus
able to furnish us with an observation of a circular flight of
long duration. We give the instrument a large radius, that
its curve, being less abrupt, should modify less the nature of
the movement which the bird may make. I{arnessed to some
extent to the extremity of a long arm which turns on a central
pivot, the bird ought to be as free as possible to go through
its movements of vertical oscillation. We shall presently see
that a bird passes through a double oscillatory movement in
a vertical plane for each revolution of its wings.

Arrangement of the frame.—The conditions to be fulfilled are
the following: in the first place, a great mobz.lity of the
instrumect, that the bird may have the least possible resist-
ance to overcome in its flight; then, a perfect rigidity of the
arm of the machine, to prevent any vibrations peculiar to
itself, which might render unnatural the movements executed
by the bird.

Fig. 103 shows the general arrangement of the apparatus.
A steel pivot, resting on a solidly-cast socket of great weight,
is placed on the platform of a photographic table. This table
is raised by means of rack-work, so that the operator, after
having arranged his apparatus so as to suit the experiment,
may place the platform sufficiently high for the instrument to
turn freely above his head.

The frame-work, properly so called, is a bow formed of a
long piece of fir-wood slightly curved. The string of this
bow is an iron wire, which is fixed by the middle to a cage
of wood traversed by the central pivot. Care is taken to
balance the two ends of the apparatus, by gradually adding
weights to the arm not carrying the bird which is the subject
of the experiment.

If wo did not take this precaution, the apparatus, as it

mitted at once to

tran

are Ss
flight becumes regular.

signals

fastened to the apparatus; three

is
placed in the centre. ‘lhe uperator collects the tracings at the moment that the

ngement of the instrument. A pigeon

1
register

MOVEMENTS OF THE WINGS OF BIRDS. 249

turns, would give lateral movements to the pivot on which it
rests, and to the base itself.

To furnish the bird with a solid point of suspension, pro-
tected not only from vertical oscillations, but from move-
ments of torsion, we have placed at each end of the instrument
across piece of wood, to the two extremities of which are
attached cords communicating with the ceiling of the room.
At this point is a revolving hook, which turns freeiy with the
machine.

Of the apparatus which suspends the bird. — Fig. 104 shows
the detuils of this suspension which binds the bird to the arm
of the instrument, while it confines as little as possible the
liberty of its movements.

Of the registering apparatus.—The transmitting tubes are
arranged along the arm of the instrument; they are fastened
to it throughout all its length, and end in a register which
carries three lever-drums tracing on the 1evelving cylinder.
The instrument in its rotation would cause the transmitting
tubes to roll round its axis, if the register to which they are
directed did not participate in the general rotation.

We sce in fig. 103 how this apparatus is arranged. The
cylinder is placed vertically above the axis of the instrument ;
the three levers trace upon it. The whole apparatus rests
on a tablet, which turns on the central pivot. We have here
well-known arrangements, in which several movements are
registered at the same time on the cylinder; it will, there-
fore, be useless to repeat the precautions which are to be
taken in the management of the apparattis, such as the exact
superposition of the tracing points, &c.

The movements of the wing are extremely rapid; they can
be registered only on a cylinder turning with great velocity ;
that which is employed in this experiment makes one revolu-
tion in a second and a half. ‘The shortness of the time at
our disposal to trace the movements of the bird compel us to
do so only at the precise moment when the phenomena which
we wish to observe are presented, whether it be the swiltest
flight, the gradual slackening of its speed, or the efforts
made at starting. If the three levers were to rub constantly
on the cylinder, we should soon have nothing but a confused

12

SM.

MECHANI

ANIMAL

250

ellipse of metal capable of oscillating freely in every
r the lowe f the el
. The suspensory apparatus is fix < of the piveon. The lever-
drum (1) receives the movements executed by the wing ina vertical direction. The lever-drum (2) receives those of
the horizontal movements.

MOVEMENTS OF THE WINGS OF BIRDS. 251

scrawl. It is indispensably necessary so to arrange the
instrument that the points of the levers should touch the
eylinder only at the moment when we wish to register the
phenomena, and to cease this contact after one, or at most
two revolutions of the cylinder, in order to avoid confusion in
the tracings.

We have recourse, for this purpose, to the arrangements
already made in our experiments upon walking.

Fig. 103 shows the experimenter at the instant when he
is about to take a tracing from the pigeon. Observing the
flight of the bird, he seizes the moment when it becomes
regular, and squeezes the india-rubber ball. The contact of
the levers is immediately produced, and the tracing is made.
After a second and a half he ceases to press it, the spring
removes the levers from the cylinder, and the tracing is over.

With a little practice it is very easy to ascertain the dura-
tion of the revolution of the cylinder, and to confine the
tracing to the necessary length.

This long description was necessary, as we were anxious
to make this apparatus understood, it being the most im-
portant of all, on account of its double function. We shall
have to employ it, not only in the analytical, but also in the
synthetical part of these studies, when we anal attempt to
represent the movements in the bird’ s flight.

New determination of the trajectory of a bird's winy.—A
pigeon was made use of in this experiment. It was a mile
bird of the variety called the Roman pigeon, very vigorous,
aud accustomed to fly.* Fig. 104 shows the arrangement of
the apparatus which we have used for the purpose of study-
ing its movements.

It is more especially to the humerus that we have directed
our attention, in order to obtain the movements of the wing in
space. or this purpose a wire is twisted round the bone,
holding it as in a ring, and furnishing by its free ends a firm
point of attachment outside the wing for other wires which
act on the experimental drums.

* This latter point is of great importance, for the greater part of the

birds in a dove-cot are of no use to us, on account of theirinexperience in
flight.

252 ANIMAL MECHANISM.

The movements of the two wings being perfectly symme-
trical in regular flight, we cause two wires, which pass sym-
metrically from the wings, to converge to each of the experi-
mental drums. Thus, drum No. 1, intended to give signals
of the elevation and depression of the wing, receives two
wires, each of which proceeds from one of the humerus bones
of the pigecn, at about 3 centimetres outside the articulation
‘of the shoulder. These wires rise and converge, aud are
attached to the point of the lever No. 1; while from the
same point proceeds an india-rubber tliread,* which serves as
a counter-spripg, and rises vertically to a hook above, which
holds it.

We have before secn (fig. 102) how the lever of the
experimental drum receives, under these conditions, all the
movements of elevation and depression executed by the
lhumerus of the bird.

Two other wires, each attached to the humerus of the
pigeon on each wing, and starting from the same point of the
bone to which were fastened the wires of drum No. 1, con-
verge also, turning backwards, and proceed to the lever of
drum No, 2. This is the drum which receives the movements
executed by the wing in the antero-posterior direction. ‘The
two drums send their signals by air tubes to the register
situated in the centre of the apparatus.

Experiment.—After having ascertained that the two levers
intended to trace have their points situated on the same
vertical, the pigeon is allowed to fly. The bird goes through
the movements of flight, and soon carries round with con-
siderable rapidity the instrument to which it is attached.
The operator, placed in the centre of the apparatus, has only
to follow for a few paces the rotation of the instrument.
During this time he holds in his hand the india-rubber ball,
and has only to compress it, in order that the two levers may
rest with their points against the blackened paper, and that
the tracing may commence. As soon as the flight is well
established, and seems to be carried on under satisfactory

* In fiz. 104 a spir spring has been substituted for this india-rubber
thread.

MOVEMENTS OF THE WINGS OF BIRDS. 253

conditions, he compresses the ball, and produces the tracing
represented in fig. 105.

Fic. 105.—Tracing of the movements of a pigeon’s wing. The upper line,
A P, shows the movements forwards and backwards. The lowcr line
H Bb, the movements up and down.

Interpretation of the tracings.—The curves are read from left
to right, like ordinary writing. The upper curve is that
described by the humerus of a bird in its movements for-
wards and backwards; the direction of these movements is
indicated by the letters A and P, which signify that all the
tops of the curves, as well as that at A, correspond with the
time when the wing has reached the most forward part of its
course ; the lower parts of the curves, on the contrary, indicate,
as well as that at the point P, the moment when the wing
has reached the hinder part of its movement.

The horizontal line which cuts this curve has been traced
in a previous experiment by the point of the lever at the
instant when the wings of the bird, kept motionless by an

254 ANIMAL MECHANISM.

assistant, may be considered as horizontally extended, tending
neither forwards nor backwards. ‘This line represents, there-
fore, to some extent, the zero of the scale of the movements
of the wing in its antero-posterior direction. The inspection
of the curve shows us also, that the pigeon’s wing was carried
more especially in the direction of the upper parts, similar to
the point A; in other terms, that the forward predomiuated
over the backward movement.

Fie. 106.—Superposition of the preceding curves on paper divided in milli-
metres. The two curves have a common direction with reference to the
axis of the abscissz.

The same explanations would apply to the lower curve
H P, which expresses the movements of the wing upwards
and downwards

In order to ascertain if the course of the pigeon’s wing in
the present experiment is apparently the same as that of the
buzzard recorded before, we have constructed the complete
curve of the wing during one of its revolutions, making use
for this purpose of the two partial curves of fig. 105.

The following is the method employed in this construction :

In order to give more facility to the measurement of the
positions of the different points of these curves, we have
copied them both on a paper graduated in ceutimetres and

MOVEMENTS OF THE WINGS OF BIRDS. 255

millimetres. We have traced in full line one of these curves,
that of the movements in the antero-posterior direction, the
course of which is indicated by the letters A and P; then we
have represented, by a dotted line, the curve of the upward
and downward motions with the letters H and B. We have
placed these two tracings over each other, so as to make the
zero-lines of each coincide. We have also taken care to
preserve the vertical superposition of the corresponding points
of each of these curves; we may therefore be certain that,
wherever any vertical line cuts the two curves, the inter-
sections correspond with the position which the humerus of
the bird occupies, at that instant, with reference to two planes
at right angles to each other. The intersection with the dotted
line will express, by the length of the ordinate drawn from
this point to the axis of the abscissee, the position which the
wing then occupies with reference to an horizontal plane; the
intersection with the full line will express the position of the
wing as referred. to a vertical plane.

This determination is realised in fig. 107 for the trajectory
of the wing, which has been constructed by successive points
in the following manner :—

Pity Be
Ni IGS SES008 SSSSE Eee es one. sees 4
208 BERG SEs CRERE eee OSE
=

Fic 107.—Constructed from the preceding curves. An arrow indicates the
direction of the movement. The separation of the dots expresses the
rapidity of the movements of the wing at the different parts of its
course.

256 ANIMAL MECHANISM.

Let there be two lines, # 2, forming the axis of tho
alscissee, and y y that of the ordinates. Let us assume, that
all which is above the line of zeros, in the full curve—that is
to say, that which corresponds with a movement in a forward
direction, ought to point to the right of the line yy. In-
versely, that all which is below the zeros, in the full curve,
will point to the left of the axis of yy. The position with
reference to this axis will be reckoned, parallel to it, by
means of millimetric divisions.

On the other hand, the different measurements taken on
the dotted curve (that which expresses the upward motion of
the wing) must point to the corresponding elevation, reckoned
above or below the line # #, according as these points in the
curve of the elevations are removed a certain number of
millimetres either above or below the zero line.

Let us take as our point of departure, in the construction
of the new curve, the point ¢ (fig. 107), chosen on the dotted
line, at one of the times when the wing has arrived at one of
its anterior limits.

This point, accordiug to the millimetric scale, shows us
that the wing is depressed 13 divisions beneath the horizontal
line. Let us follow the vertical line which passes through
the point ¢, till it meets with the curve of movement in the
antero-posterior direction: the intersection of this vertical
line with the curve shows us that the wing at this moment
had been carried forward 26 divisions; on the new curve,
therefore, the point a ought to be marked at a well-ascertained
position ¢, which will be found at the intersection of the thir-
teenth division below the axis # #, with the twenty-sixth to the
right of the axis y y, which according to what we have as-
sumed, corresponds with 26 divisions iu the forward direction.

‘Yo determine a second point in our curve, let us proceed,
in reading the tracings, oue millimetric division farther to
the right; we shall find, as before, the intersection of the
vertical at this point with the two curves, and we shall thus
have a second point in the new construction determined.

The series of successive points obtained in this manner
form a curve which slows the course of the wing; the arrow
indicates the direction of the movement.

CHANGES IN THE PLANE OF TIE BIRD'S WING. 237

By constructing thus the whole figure, we see that this
curve, after proceeding downwards and forwards, rises and
returns back again.

By comparing this figure with that which we have obtained
ly means of another apparatus (fig 100), on another kind of
Lird, and by examining the movement of another part of the
wing, we shall find striking ‘resemblances between the two
curves, which show that birds proceed in their flight by
movements which are almost identical. In fact, the bone of
the wing in each describes a kind of irregular ellipse, with
its greater axis inclined downward and forward. ‘The im-
portance of this determination is so great, that we trust we
shall be pardoned for the long and minute details of the
experiments which have furnished these results.

OF TILE CITANGES IN THE PLANE OF THE WING.

We have seen in Chapter I. that the wing of the insect is
subject to torsions under the influence of the resistance of the
air, and that the inclination of the plane of its wing is
changed at every moment. ‘These movements, which are
entirely passive, constitute the essence of the mechanism of the
insect’s flight; the wing, in each of its alternate movements,
acts on the resistance of the air, and gains from it a force
which is exerted on the membrane by the side of the main-
rib, thus serving to sustain the insect and propel it forward.
The structure of the bird’s wing does not allow the existence
of a similar mechanism. Its wing during its ascent does not
present to the air a resisting plane, because the feathers which
fold over each other would open to allow it to pass through.
The depr:ssion of the wing is therefure the only phase in the
flight of the bird which has any analogy with that of the
insect. Besides, the curve described by the point of the bird's
wing is sufficiently differeut from that of the insect, to prove
that their mechanical conditions are very dissimilar.

It was indispensable to determine by experiment the dif-
ferent inclinations of the plane of the bird’s wing at each
phase of its revolutions. In fact, to estimate the resistance
which the air presents at each moment of the flight, we must
know the two elements of this resistance: first, the angle

258 ANIMAL MECHANISM.

under which the plane of the wing strikes the air, and
secondly, the velocity with which it is lowered. Nothing is
more easy than to obtain the second data of the problem;
we can reduce them from the curve which represents the
position of the wing at each instant, a curve of which we
have an example in fig. 108, as obtained from a pigeon. But
the difficulty which presents itself, is to obtain the indication
of the changes which take place in the plane of the wing
during flight. For this purpose we have had recourse to the
following mechanism.

We have seen, in fig. 99, that a rod connected with a
Cardan universal joint, whose centre of rotation is near the
scapulo-humeral articulation, can be made to represent ac-
curately the circular movements of the wing. But Cardan’s
jvint, though it obeys the rotary motions of every kind which
are given to the rod, does not allow any movements of torsion
with reference to the axis of this rod.

Fic. 108.—Theoretical figure of the apparatus to investigate the torsion of
the wing.

Let fig. 108 be a kind of apparatus of this sort: we can
give the rod t t every kind of motion in the vertical or hori-
zontal direction; it will follow all the impulses which it
receives. But if we take hold of the extremity of the rod,
near the lever 7 which is perpendicular to it, and try to give
the lever a movement of torsion, as if we were t:uning a screw,
the Cardan does not allow this movement t)» be made, and the
rod resists the impulse brought to bear upon it. Let us
suppose that behind the Cardan joint, and on the prolonga-
tion of the rod t t, there is another cylindrical rod, p, turning
in a tube; this rod will turn under the influence of the torsion
exercised by the hand holding the lever J, and if the rod p
carries a lever l’, at right angles to it‘ and situated in the

cy)

CITANGES IN TIE PLANE OF THE BIRDS WING. 259

sime plane as l, we shall see that these levers correspond
with each other, and that every change of plaue undergone by
the first will be transmitted to the second.

Under these conditions, if we cause the lever / to signal the
changes of plane which the wing undergoes in the various
phases of its revolution, these changes will be communicated
to the lever UV’, which can in its turn act on an experimental
apparatus, and transmit the signal under the form of a
tracing. This is precisely the method which we have em-
ployed in our experiments. The lever / was placed upon the
wing of the bird, and was held in a horizontal position.
The lever Ul’, also horizontal, was fastened by a wire to the
lever of an experimental druin placed above it, and arranged
in the same manner as in the experiments described in the
former chapter.

When we caused the plane of the wing to oscillate, so as
to turn its upper surface more or less backwards, the registered
curve was depressed ; it rose, on the contrary, when we turned
the wing so as to carry ifs upper surfi.ce forwards.

Sulla difficulty presented itself. It was not possible to fix
the lever J at one point of the rod ¢¢; and, at the same time,
to render it immovable at a single point in the bird’s wing.
In fact, the Cardan joint, not having the same centre of motion
as the articulation of the wing, it tullowed that in the vertical
movements the rod slipped upon the wing. It was necessary,
therefore, for the lever l, while fixed to the feathers of the
bird, to glide freely on the rod in the direction of its length,
and yet that it should cause it to receive, under the torm of
torsion, all the changes of inclivation that are transmitted to
it by the wings of the bird. We see in fig. 109 how this
result has been obtiuined.

Let tt be the rod which is to follow all the circular move-
ments executed by the bird. This rod has in it deep
longitudinal grooves, which give its section the appearance of
astur; it glides freely in a tube which is applied to its
external surfice. But at one of the extremities of the tube is
a metallic sliding casting, the interior part of which is grooved
like a star, through which passes the rod whose grooves slide
in those of the star-shaped vpening. ‘Then the lever J is

260 ANIMAL MECHANISM.

soldered to this tube, and is able to move with it to any point
along the rod, thus allowing full liberty to the movements of
flight, while no change of plane can be effected without com-
municating a movement of torsion to the rod. .

After some experiments, it became necessary to make im-
provements in this apparatus. This, the lever / hada tendency
to get twisted on account of the displacement of the feathers
during flight; it was replaced (fig. 109) by a piece with three

Via. 109.—Actnal arrangement of the apparatus intended to experiment
upon the movements of the wing, and its change of plane.

movable levers, ) lb, turning in the same plane round a
common centre, like the blades of a fan. Tach of these little
branches terminated in a hook. After having attached the
sliding tube to the false wing of the bird, the extremity of
each of these three blades was tied to one of the long feathers
of the wing. ‘This ligature, made with india-rubber, gave
excellent results.

The lever / (fig. 109) was also defective on account of its
unequal action. In its stead was substituted a pulley of short
radius, placed on the rod prolonged behind the Cardan joint,
‘The thin cord rr, which was to transmit the torsions of the rod,
passed round the wheel of this pulley. In this manner the
rotation of the pulley, resulting from the torsion of the rod,
always faithfully transmitted this torsion to the exverimental
lever.

To put an end to this 1ong description of the. mstrument
intended to transmit the signals of the elevation and depression
of the wing, let us only say that the piece situated at the base
of the lever ¢ ¢ is intended to transmit the vertical and

CIIANGES IN THE PLANE OF TiIE BIRD’S WING. 261

horizontal movements by two systems of cords. For the
vertical ones, a cord v goes to the lever of the experimental
drum. ‘The cord h transmits to another apparatus the
movements in the horizontal, that is, in the antero posterior
direction.

Eaperiment.— A buzzard to which this apparatus has been
adapted is harn«ssed to the instrument and allowed to fly: we
obtain at the same time the three curves represented in
fig.110. With these three data, we can construct, not only the
trajectory of the wing, but the series of inclinations of its plane
at the different points of its course.

The curve traced with a full line corresponds with the
movements of the wing in an antero posterior direction. ‘The
point A, and those homologous with it, correspond with the
extreme anterior position of the wing; the point P with the
extreme posterior position, ‘The curve formed of interrupted
strokes indicates the relative height of the wing in space; the
point H corresponds with the maximum elevation of the wing,
and the point B with its greatest depression.

These two first curves enable us to construct, by means of
points, the closed curve* (fig. 111) representing the trajectory
of the buzzard’s wing. It is by this trajectory that we shall
determine the inclination of the plane of the wing at every
part of its elliptical course.

For this purpose, we must return (fig. 110) to the dotted
curve 8, which is the expression of the torsions of the wing at
different instants. The positive and negat.ve ordinates of this
curve correspond with the trigonometrical tangents of the
anglest which the wing makes with the axis of the body.t

* This curve is not always closed ; this is the case only when the flight
is extremely regular,

+ We must subtract algebraically from the angle found, a constant
quantity, the angle of 30° which the wing, during repose, makes with the
horizon.

~ We cannot positively affirm that this axis is horizontal ; it seems
rather that it is inclined so that the beak of the bird turns slightly
upwards. This inclination of the axis would necessitate a correction in
the absolute inclinations of the wing at the different points of its
revolution.

262 ANIMAL MECHANISM.

They enable us, therefore, to trace in fig. 111 a series of
lines, each of which expresses, by its inclination with respect

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pres nted to the lorizon at this same portion of its course,

CHANGES IN THE PLANE OF THE BIRD'S WING. 263

The direction of the movement of the wing is read from above
and forward, from H to Av.

Fig. 111 shows that the wing during its ascent assumes
an inclined position which allows it to cut the air so as to
meet with the minimum of resistance ; while in its descent,
on the contrary, the position of its plane is reversed, so that
iis lower surface turns downwards and slightly backwards.
It follows, that in its period of depression, the wing, by its
obliquity, acts upon the resistance of the air, and while raising
the body of the bird, carries it forward. We see, also, that

Fic. 111.—Inclinations of the plane of the wing with reference to the axis
(Ay) of the body during flight.

the inclination of the wing changes gradually, in the different
phases of its elevation and of its descent. Especially in this
latter phase, the influence of the air in shaping the course of
the wing is more evidently seen; it is, in fact, at the moment
when the rapidity of its depression attains its maximum that
we see the posterior edge of the wing turn up the morestrongly.

The wing, when it has reached the end of its descending
course, changes its plane very suddenly. The explanation of
this movement is very natural. As soon as the resistance of
the air ceases to raise the feathers, these, by their elasticity,
return to their ordinary position, which they occupy during all
the phase of elevation.

Even the ellipse which forms the trajectory of the wing cen

264 ANIMAL MECHANISM,

be explained by the resistance of the air. The muscular
apparatus of the bird, like that of the insect, has nothing to
do with the course of the wing; elevation and depression are
almost ail the movements that it can produce. But the
resistance of the air during the phase of descent gives rise to
the anterior convexity of the curve passed through, by means
vf a mechanism which we already understand. ‘The posterior
convexity which belongs to the ascensional phase is also
e xplained by the action of the air on the lower surface of the
wing, which it carries backward at the same time as it raises
it, W e must seek for the demonstration of this tleory in the
urtificial representation of these different movemeuts.

CHAPTER VI.

RE-ACTIONS OF THE MOVEMENTS OF THE WING ON THE
BODY OF THE BIRD.

Ne-actions of the movemeuts of the wing —Vertical re-actions in differcut
species ; horizontal re-actions or changes in the rapidity of flight ;
simultaneous study of the two orders of re-actions—Theory of the
flight of the bird—Passive and active parts of the wing—Reproduc-
tion of the mechanisin of the flight of the bird.

In order that we may follow, in studying the flight of the
bird, the same plan which las guided our researches on the
other kinds of locomotion, we must determine what are the
reactionary effects of each of the movements of the wing on
the body of the animal.

Two distinct effects are produced during flight: by one, the
bird is sustained in opposition to its weight; by the other, it
is suljected to a propulsive force which carries it from one
place to another. But do we find that the bird, when sus-
tained in the air, keeps at a constant level, or does it pass
through oscillations in the vertical plane? Does it not
experience, by the intermittent effect of the flapping of its
wings, rising and falling motions, of which the eye cau detect

RE-ACTIONS DURING FLIGHT. 265

neither the frequency nor the extent ? Again, does not the bird
advance in its onward course with variable rapidity? Shall
we not find in the action of its wings a series of impulses,
which give to its advancing course a jerking motion ?

These queries can be answered experimentally in the follow-
ing manner,

Since we have at our disposal the means cf sending the
signals of movements to a distance, and recording them by
tracings, when these movements are made to produce a pres-
sure on the membrane of a drum filled with air, we must
endeavour to reduce to a pressure of this kind the movements
which we desire to study.

The oscillations which can be effected by the bird in a hori-
zontal plane must be made to exert on the membrane of thie
drum pressures alternately strong or feeble, in proportion as the
bird mounts or descends. ‘The same kind of experiment must
be made on the variations in its horizontal rapidity.

The question has been already solved for the vertical
re-actious, hy means of the apparatus represented in fig. 28,
when we were treating of terrestrial locomotion; a slight
modification will allow us to employ the same method to
ascertain whether vertical oscillations are produced during
flight.

fic. 112,—Apparatus intended to transmit to the registering instiument a!l
tne vert.cal oscillations of the bird,

Vig. 112 shows the arrangement that we have adopted.
The mass of lead is applied directly to the membrane; some
wire-work protects the upper surface of the apparatus from
the friction of the feathers of the bird, which, without this
precaution, might sometimes affect the form of the tracing.

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RE=\CTIONS DURING FLIGHT. 267

After having convinced ourselves that the apparatus trans-
mits faithfully the movements which are communicated to it,
we connesi it with the registering instrument by means of a
long tube, and place it on the back of a bird, which is then
allowed to fly. Experiments made on many different species,
pigeons, wild ducks, buzzards, moor-buzzards, screech owls,
have shown that there are very varied types of flight with
respect to the intensity of the oscillations in the vertical
plane.

Fig. 113 shows the tracings furnished by different species
of birds. All these tracings, collected on a cylinder revolving
with a constant rapidity, and referred to a chronographic
tuning-fork vibrating 60 times in a second, enable us to
ascertain the absolute and relative duration of the oscillations
during the flight of different species of birds.

We find from this figure, that the frequency and amplitude
of the vertical oscillations vary much according to the species
ef the bird. In order to ascertain the cause of each of these
niovements with greater accuracy, let us register at the same
time the vertical oscillations of the bird, aud the action of the
muscles of the wing. If we make this double experiment on
two birds which differ much in their manner of flight, such
as the wild duck and the buzzard, we obtain the tracings
represented in fig. 114.

The duck (upper line) presents at each elevation of its
wing two energetic oscillations; that at b, at the moment when
the wing is lowered, is easy to be understood, as well as that
at a, at the moment that the wing begius to rise again. To
explain the ascent of the bird during the time of the elevation
of the wing, it seems indispensable to refer to the effect of
the child’s kite, to which we have before alluded. The bird
having acquired a certain velocity, presents its wings to the
air as inclined planes; an effect is immediately produced,
similar to the ascent of the hovering apparatus which trans-
form their acquired velocity into ascensional force. ‘The
flight of the buzzard shows also, but in a less degree, the
ascent which accompanies the upward movement of the
wing.

Determination of variations in the rapidity of fli, ht —The

268 ANIMAL MECHANISM.

second question which we have to solve relates to the deter-
mination of the various phases in the rapidity of fight. It
may receive its solution by the employment of the same
method. link the drum, loaded with a piece of lead, be placed
on the back of the bird so as to present its membrane in a
vertical plane—that is, at right angles to the direction of flight,

Fic. 114.—In the upper part we see, placed above each other, the muscular

tracing (see p. 232), and that of the vertical oscillations in a wild duck.

Under the undulation a, which shows the elevation of the wing, is seena
vertical oscillation; another is seen under #, the tracing corresponding
with the depression of the wing. In the lower balf of the figure are
tracings collected from a buzzard ; the oscillation at ¢, which corresponds
with the elevation of the winy, is less marked than that from the duck.

the apparatus would be insensible to vertical oscillations, and
would only give the signal of those which are made backwards
and forwards. Let us turn the membrane of the drum in
front; it is evident that if the bird quickens its speed, the
retarding influence of the inertia of the mass of lead will
produce a pressure on the membrane of the drum; the air
will be compressed, and the revistering lever will rise; while

RE-ACTIONS DURING FLIGIIT. 269

the slackening of the bird’s speed will cause a descent of the
lever by an inverse action.

Experiments tried upon the species of birds before men-
tioned, have furnished us with tracings analogous with those
of the vertical oscillations.

If it be true, as we have supposed, that the vertical
oscillation of the bird, at the moment of the ascent of the
wing, is due to the transformation of speed into elevation,
we shall have the means of verifying this supposition, by
collecting simultaneously the tracings of the vertical oscilla-
tions and those of the variations of rapidity.

Thus, by registering at the same time the two orders of
oscillation in the flight of a buzzard, we find that the phase
of depression of the wing produces at the same time the
elevation of the bird and the acceleration of its horizontal
swit.ness. This effect is the natural consequence of the
inclination of the plane of the wing at the moment of its
descent ; this we already know from having obtained it in the
flight of the insect. As to the elevation of the wing, it is
found that during the slight ascent which accompanies it, the
swiftness of the bird diminishes. In fact, the curve of the
variations of rapidity is depressed at the moment when the
bird rises. ‘This is, therefore, a confirmation of the theory
which we have ; ropounded concerning the transformation of
the horizontal rapidity of the bird into ascensional force.
Thus by this mechanism, the stroke of the descending wing
produces the force which will cause the two oscillations of the
bird in the vertical plane. It produces directly the ascent
which is synchronous with it, and indirectly prepares the
second vertical oscillation of the bird by creating rapidity.

Simultaneous tracing of the two orders of the escillations of the
vird.—Instead of representing separately the two kinds of
oscillation executed by the bird as it flies, it is more insti uc-
tive to seek to cbhtain a single curve representing together tlie
movements which the body of the bird makes as it advances
in space.

Tue method which we have employed to obtain the move-
ments of the point of the wing may, with certain modifica-
tions, furnish the simultaneous tracing of the two orders of

270 ANIMAL MECHANISM.

movement which we wish to investigate. For this purpose, the
two drums combined rectangularly must be connected with the
same inert mass.

Let us refer to fig. 97 (p. 237), where we see the two
levers connected together and communicating with each other
by tubes, which transmit to one all the movements executed
by the other. When we give the first lever any kind of
movement, we see it reproduced by the second lever in the
same direction.

Now, let each of these levers be loaded with a piece of lead,
and taking in our hand the support of the apparatus, let us
cause it to describe any kind of movement in a plane perpen-
dicular to the direction of the lever. We shall see that the
lever No. 2 exccutes movements of exactly an opposite kind.
In fact, since the motive force which acts on the membrane of
the drums is nothing more than the inertia of the mass of
lead, and the movements of this mass are always later than
those given to the apparatus, it is clear that if we raise
the whole system, the mass will keep the lever down, while
if we lower the instrument the mass will retain the lever
above; that if we carry it forward, the inertia will keep the
lever back, &c. Therefore, the lever No. 2, only going
through the same movements as No. 1, will give curves which
will be absolutely opposed to the movement which has been
given to the stand of the apparatus. This being assumed, let
us pass to the experiment; for this, let us employ the
app:ratus represented in fig. 99 on the back of the buzzard
as it flies ; let us remove the rod which received the movemeuts
of the wing, as well as the parallelogram which transmitted
them to the lever; we will only retain the lever fastened to
the two drums, and the contrivance which fixes the whole
instrument on the back of the buzzard; lastly, let us adapt a
piece of lead to this lever, and let the bird fly. ‘The tracing
procured is represented in fig. 115. The analysis of this
curve is at first sight extremely difficult; we hope, however,
to succeed in showing its signification.

Analysis of the curve illustrating the oscillations of the bird.—
This curve is described on the cylinder in the same manner as
in fig. 100, which shows the different movements of the point

RE-ACTIONS DURING

of the wing; the glass
plate moves from right to
left; the tracing must be
read from left to right.
The head of the bird is
turned towards the left,
its fheht is in the direction
pointed out by the arrow.

We may divide this
figure into a_ series of
portions by means of ver-
tical lines passing through
homologous points, whe-
ther we let fall these per-
pendiculars from the top
of the loops, or from that
of the simple curves, as
has been done at the points
a and e. Each of these
portions will enclose toler-
ably similar elements, with
the exception of their un-
equal development in the
different points of the
figure: let us neglect this
detail for the present.

It is evident that the
periodical return of similar
forms corresponds with the
return of the same phases
in a revolution of the bird’s
wing. The portion ae will,
therefore, represent the dif-
ferent movements of the
bird in one and the same
revolution.

Let us remember that in
the curve which we analyse,
all the movements are con-
rary to those really per-

formed by the bird. The

FLIGHT.

Fic. 115.—Simultaneous tracing of the two kinds of oscillations executed by a buzzard during flight.

272 ANIMAL MECHANISM.

two vertical oscillations of the bird, the greater and the
less, must thus be represented by two curves, of which
the summit will be placed downwards. It is easy to recognise
their existence in the large curve, a bc, and the smaller one
ede. The bird was, therefore, rising from a to b, descending
from b toc; it rose again from e¢ to d, and descended from
d toe.

But these two oscillations encroach on each other, which
produces the loop ed; the oscillation ¢ de partly covers the
first by turning towards the head of the bird. Since the
indications of the curve are in a direction contrary to the real
motion, this is a proof that the bird, at this moment, was
cither carried backwards, or at least slackened the rapidity of
its flight.

This figure, therefore, recalls all that the furmer experiments
have taught us concerning the movements of the bird in
space. We see from them, that at each revolution of its wing
it rises twice, followed by two descents; that these oscillations
are unequal; the larger one, as we know, corresponds with the
lowering of the wing, the smaller one with its elevation. We
see, also, that the ascent of the bird, while the wing is rising,
is accompanied by the slackening of its speed, which justifies
the theory that this re-ascent is made at the expense of tlie
velocity acquired by the bird.

But this is not all: fig. 115 shows us, also, that the move-
ments of the bird are not the same at the commencement as
at the end of its flight. We have already seen (figs. 95 and
100) that the strokes of the wing at its departure are more
extended; we see here that the oscillations produced at its
departure by the descent of the wing (shown at the left hand
of the figure) are also more extended. But theory enables us
to foresee that the oscillation of the ascent of the wing, being
produced by the velocity of the bird, must be very feeble at
the commencement of its flight, when the bird has, as yet, but
little rapidity. ‘This figure shows us that this is actually the
case, and that at the beginning of the flight, the second
oscillation of the wing (that which forms the loop) is but
slight.

We are now, therefore, in possession of the principal

THEORY OF FLIGHT. 273

notions on which may be established the mechanical theory of
flight.

From all these experiments we may deduce that it is
during the descent of the wing that the bird acquires all the
motive force which sustains and directs it in space.

Theory of the flight of the bird.—On this subject, as on
almost all those that belong to this discussion, nearly every-
thing has been already said; so that we must not expect to
find an entirely new theory arise from the experiments which
have been described. In the works of Borelli we find the
first correct idea of the mechanism of flight. The wing,
says this writer, acts on the air like a wedge. Developing
still farther the thought of the learned Neapolitan physiologist,
we should now say that the wing of the bird acts on the air
after the manner of an inclined plane, in order to produce a
re-action against this resistance which impels the body of the
bird upward and forward. This theory, confirmed by Strauss-
Durkheim, has been completed by Liais, who noticed the
double action of the wing; first, that which in the phase of
depression of this organ, raises the bird and gives it an im
pulse in a forward direction ; then, the action of the ascending
wing, which is guided in the same manner as a boy’s kite,
and sustains the body of the bird until the following stroke
of the wing.

We have been reproached for relying cn a theory which
had its origin more than two centuries ago; we much prefer
an old truth to the most modern error; therefore we must be
allowed to render to the genius of Borelli the justice which
is due to him, and only claim for ourselves the merit of having
furnished the experimental demonstration of a truth already
suspected.

But the theories which had been propounded up to the
present time neglected many important parts which experi-
ments reveal, and which we are about to endeavour to bring
clearly forward.

Thus, the manner in which the change in the plane of the
wing is effected in every part of the flight was necessary to
be known, in order to explain the re-actions which tend

13

274 ANIMAL MECHANISM.

always to sustain the body of the bird, sometimes by acceler-
ating the rapidity of its flight, sometimes by slackening it.*
Fig. 111 shows this change of plane.

As to the re-actions to which the body of the bird is sub-
jected, experiment has clearly demonstrated them; it has
furnished us with the means of estimating their absolute force.
We have seen that these re-actions differ according to the
species of bird which is observed. They are powerful and
sudden in birds which have a small surface of wing; longer
and more gentle in birds formed for hovering; the re-action
of the period of the re-ascent of the wing disappears almost
entirely in the latter kind.

If we could compare terrestrial locomotion with the flight
of birds, and assimilate alternate with simultaneous move-
ments, we might find certain analogies between the walk
of man and the flight of the bird. In both, the body is
urged forward by an intermittent impulse; man, like the
bird, raises himself by borrowing the necessary work from
the dynamic energy which he has acquired by his muscular
efforts.

As to the estimation of the work expended in flight, we
must, before we can undertake it, have a perfect knowledge
of the resistance which the air presents to surfaces of every
form, inclined at different angles, and possessing varied velo-
cities. We only know as yet the movements of the wings;

* We ought to beg the reader to remark that the inclinations repre-
sented in fig. 111 are referred to a line which probably is not horizontal
during flight. In fact, this line does not correspond with the axis of the
body of the bird, for it was suspended in the apparatus by a corset placed
behind its wings, and thus had its centre of gravity in front of the point
of suspension, which caused its beak to hang slightly down. In free
flight, on the contrary, the axis of the bird is horizontal—or rather turned
somewhat upward. Restored to this proper position, a fresh direction
would be given to each of the positions of the wing (fig. 111), which
would alter them all by the same number of degrees. Then, probably,
we should see that the wing always presents its lower surface to the air,
as the only one which can find in it a point of resistance. This supposi-
tion requires for its verification some fresh experiments, which we hope to
be soon able to make.

THEORY OF FLIGHT. 275

the resistance which they meet with in the air has yet to be
determined. Our experiments on this subject are still being
pursued. When once we have these two elements, the mea-
sure of work will be obtained from the resistance which is
presented to the wing by the air at every instant, multiplied
by the distance passed over. This will give us the measure
of work brought to bear upon the air.

For its horizontal advance the bird will be obliged only to
furnish the quantity of work equivalent to the resistance
presented by the air in front of it, multiplied by the distance
passed through. <A part of this resistance, namely, that
which is applied to the lower surface of the wing, is utilised
to sustain the bird, by the kind of action which we have com-
pared to that of a child’s kite.

It appears that this action is of primary importance in the
flight of the bird. In fact, among the researches on the
resistance of the air there is one which we owe to Mons. de
Louvrié, which seems to prove that if the wing make a very
small angle with the horizon, nearly all the work obtained
from the dynamic energy of the bird is employed to sustain
it; according to this writer, an angle of 6° 30’ would be the
most favourable to the utilisation of its energy. The im-
portant part played by the gliding of the wing upon the air
seems also proved by the shape of that organ. The wing
being alternately active when it strikes the air, and passive
when it glides through it, is not, in all its parts, equally
adapted to this double function.

When a surface strikes the air, it must move with rapidity
in order to find resistance. Thus the wing, turning around
the point by which it is attached to the body, shows unequal
and gradually-increasing velocity in different points according
as they are nearer to the body, so that being almost nothing
at the point of attachment of the wing, the velocity will be
very great at the free end.

Let us imagine the wing of an insect as large at the base
as at the extremity; this size would be useless in the part
nearest to the body, for the wing, at this point, has not suffi-
cient rapidity to strike the air with effect. Thus we find, in
the greater part of insects, the wing reduced to a strong

276 ANIMAL MECHANISM.

nervure towards its base. The membranous part commences
only at the point where rapidity of movement begins to be
of some use, and the membrane goes on increasing in breadth
till near the extremity of the wing. Such is (fig. 116) the
type of the wing essentially active—that is, intended oniy to
strike the air.

Fic. 116,---Wing of an insect.

In the bird, on the contrary, one of the phases of the
movement of the wing is, to a certain extent, passive; that
is to say, it receives the pressure of the air on its lower sur-
face, when the bird is projected rapidly forward by its
acquired velocity. Under these conditions, the whole bird
being carried forward into space, all the parts of the wing
are moved with the same rapidity; the regions near to the
body are as useful as the others to take advantage of the
action of the air which presses on them as on a kite.

Fic. 117.—Act.ve and passive parts of the Lird’s wing.

Thus, the base of the wing in the bird, far from being re-
duced, as in the insect, to a rigid but bare rib, is very wide,
and furnished with feathers and wing coverts which constitute
a large surface, under which the air presses with force, and
in a manner very efficacious to sustain the bird. Fig. 117
gives an idea of the arrangement of the wing of the bird, at
the same time active and passive.

The inner part, deprived of sufficient velocity, may he

REPRODUCTION OF MECHANISM OF FLIGHT. 277

considered, while it is being lowered, as the passive part of the
organ, while the external part, that which strikes the air, is
the active portion.

By its very great velocity, the point of the wing must meet
with more resistance from the air than any other part of this
organ; whence the extreme rigidity of the large feathers of
which it is formed.

The conditions of decreasing rapidity explain the flexibility
which becomes greater and greater in the feathers of those
parts of the wing nearer to the body, and at last the great
thinness of those at the base or passive part of the wing.

Let us add that the effect of the kite must be produced at
the base of the wing, even while the point strikes the air, so’
that the bird, as soon as it has acquired its velocity, would
be constantly lightened of part of its weight, on account of
this inclined plane.

The reproduction of the mechanism of flight now occupies the
minds of many experimenters, and we hesitate not to own
that we have been sustained in this laborious analysis of the
different acts in the flight of the bird, by the assured hope of
being able to imitate, more or less imperfectly, this admirable
type of aérial locomotion. We have already met with some
success in our attempts, which have been interrupted during
the last two years.

Winged apparatus has been seen in our laboratory, which
when adapted to the frame-work which had held the bird,
gave it a rather rapid rotation. But this was only a very
imperfect imitation, which we hope shortly to improve.
Already a young and ingenious experimentalist, Mons.
Alphonse Pénaud, has obtained much more satisfactory results
in this direction. The problem of aérial locomotion, formerly
considered a Utopian scheme, is now approached in a truly
scientific manner.

The plan of the experiments to be made is all traced out :
they will consist in continually comparing the artificial instru-
ments of flight with the real bird, by submitting them both
to the modes of analysis which we have described at such
length; the apparatus will, from time to time, be modified
till it is made to imitate these movements faithfully. For

278 ANIMAL MECHANISM.

this purpose we are about to undertake a new series of ex-
periments; some new apparatus is being constructed, which
will soon be finished.

We hope that we have proved to the reader that nothing
is impossible in the analysis of the movements connected with
the flight of the bird: he will no doubt be willing to allow
that mechanism can always reproduce a movement, the nature

of which has been clearly defined,

INDEX.

——_e——_-

Action and reaction, 109

Air, resistance of, changes plane of
insect’s wing, 197

Aliment, heating power of, 16

Animal motion, 27

Animals, high temperature of, 21

— warm and cold blooded, 23

Apophyses, cause of, 89

Automatic regulator of temperature,
25

B.

Béclard’s experiments on heat and

work, 17
Bernard on automatic regulator of

temperature, 25
Bertrand on birds’ muscles, 212
Biped diagonal, definition of, 154
B'rds, conformation of, 216

— curves in wing of, 210

— electrical experiment on

flight of, 231

— flight of, 209

— hovering of, 221

— large pectoral muscles of, 211

— M. de Lucy on, 222

— muscular force of, 213

— passades of, 220

— rapidity of muscular action

in, 214

— _ressource of, 220

— sailing flight of, 221

— stable equilibrium of, 216
Birds’ wings, compared to screw, 211
duration of elevation

and depression of, 229
stroke of, forward and

backward, 235
Blood, circulation of, 67

Bones, change in through age, 90
Borelli on locomotion, 103
— birds’ muscles, 212
— flight of birds, 273
—_— horse, 161
Buzzard, muscular force of wing of,
213

C.

Chronograph described, 122
Circulation of blood, variations in,
26
— — furrows the
bones, 87, 88
Climbing, 106
Club-foot, 96
Creeping, 105
Curnieu on Eclipse’s gallop, 167

1D)

Darwin’s natural selection, 79

Darwinists, suggestions to, 84

Davy on torpedo, 52

Development theory, 78

Diptera, manner of flight of, 208

Dromedary, paces of, 173

Dugés on movements of horse, 139

Duhamel’s chronographic tuning-
fork, 44

Duval, representation of horse by
zuotrope, 177

E.
Electric fishes, 51

280 INDEX.

Electricity, animal, 49
_ disappearance when te-
tanized, 50
— Du Bois Reymond on,
0

— mechanical work substi-
tuted for, 51
D’Esterno on flight of birds, 221

F.

Fibre, striped and unstriped, 28
— and tendon, 69
— inoldage replaced by tendon,
9

Force, what, 5 ‘
— allcan be reduced to motion, 8
— indestructible, 6, 13
— potential, 12, 14

Flight, see Wing.

of buzzard, 261

of birds, 209

of pigeon, 255

mechanism of, imitated, 277

sailing, of birds, 221

slight waste of substance in,
213

Frog, signals, 32

‘*Function makes the organ,” Guerin,
84

G.

Gorilla, skull in old and young, 90
Guerin on club foot, 97
— onchange of bones through
age, 90
— theory of function, 84

H.

Hartings on ratio of birds’ wings to
weight, 223, 224

Heat, animal, 19
— loss of, in external organs, 22
— mechanical equivalent of, 15
— unit of, 13

Helmholtz on contraction of muscles,
46

Helmholtz on lost time in muscular
action, 48
Herdenheim’s experiments on heat
and work, 17
Hirn on heat and work, 18
Homology of muscles, 73
Horse not projected into air, 156
— paces of, 139
— power, 68
— transition of paces of, 172
— various authors on, 144
— Vincent’and Goiffon on, 151
— zootrope figures of, 177
Hovering of birds, 221
Humerus, curvatures in head of, 92
— a contorted femur, 91

I.

India-rubber, change of heat into
work in, 39

J.

Joule on equivalence of force, 15

K.

Kaleidophone rod, tracing of, 191
-- — with wing ot
wasp, 193
Kangaroo, development of crural
muscles in, 71

L.

Lamarck’s development theory, 77
Latour on movement of bird’s wing,
212
Lavoisier’s theory of animal heat, 20
Levers in animal skeleton, 65
Liais on double action of bird’s
wing, 273
Life, organic acts of, 28
— of relation, 28
Locomotion, aerial, 180-277
— aquatic, 106
_ terrestrial, 102

=;

INDEX.

Lest time in muscle, Helmholtz, 43
Lucy, M. de, on wings of birds, 222
Lungs, not seat of combustion, 23

M.

Marey’s myograph, 32

Matteucei on torpedo, 52

Mechanical work, estimation of, 61

forms of, 60

Mechanism of. flight, reproduced,
Zin,

Modification of animals, 100

of men, 101

Momentum, divided between gun
and carriage, 110

Moreau on torpedo, 53

Motion, all force reduced to, 8

alternate in living motive
powers, 66 ,

Motors, living, dynamic energy of, 68

Movements, see Tracings

caused by muscles in
insect’s wing, 196

of snail, 105

of wing of birds, 226

insects, 195,
197

Muschelbroeck on torpedo, 52

Muscles, absorption of, from disease,

96

——

adaptation of, to function,
5

change of, by age, 99

by experiment,
101

fatty degeneration of, 97

harmony between form and
function in, 77

homology of, 73

in jaw of carnivora, 90

in man and ape, 75

large, slight contraction of,
62

lateral dilatation of, 36

long and short, 70

mechanical force in, 39

pectoral in birds, 72, 211

penniform, 70

use of, acquired by habit,
29

281

Muscles, work of, 47

Muscular current, negative varia-
tion of, 50

contraction, tone heard
in, 46

force of birds, 213
— of tissue, 64

shocks, 50, 51

system, variation in, 94

tissue, specific force of,
64

— wave, 35
speed of, 38

Myograph, explanation of, 31

N.

Nerve, function of, 41
Nervous agent, speed of, 42
Du Bois Reymond
on, 41
eentres command action
without the influence of
the brain, 29
tetanus, 45
Notation of paces, man, 134
horse, amble, 142
— gallop,165,
168, e¢ seq.
— trot, 144
— irresu-
lar, 156
— walk, 142,
163
synoptical table
of, 145

rule, 175

O.
Oscillation of body, 118
Oxidation of blood, 20
Ee

| Passades of birds, 220
| Penaud’s flight instrument, 277

252

Pettigrew, Dr., on birds’ wings, 210
Piste, definition of, 152

— of amble, 162

— of slow gallop, 167

— of Eclipse’s gallop, 167

— of trot, 157

— of walking pace, 162
Pline on stable equilibrium of birds,

216

R.

Reactions defined, 115
— instruments to show, 116
— of movements of wing of
birds, 264
of walking (man), 127
of leap, ditto, 131
of gallop, ditto, 131
of trot of horse, 153
of gallop, ditto, 165, 171
Regnault’s equivalent of heat, 15
Ressource of birds, 220
Reymond, du Bois, on muscular
shocks, 50
Rhythm of paces, 133
Running (man), 125

s.

Selection, natural, 81
Shoe, experimental, 113
Skeleton, action of aneurism on, 87
— variability of, 85
_ change of course and at-
tachment of
muscles, 89

_— — im, _ transmitted
to descendants,
94
— hollows worn by tendons
in, 86

Snail, movements of, 105
Stepcurves, 127

-— of horse’s trot, 153
gallop, 165
walk, 160
Stimulus of necessity, 83
Synthetic reproduction of move-
ments inman,137
in horse, 177

INDEX.

T.

Temperature of animals, 23
Tetanus, muscular, 45
— from strychnine, 46
—— heat developed in, 49
— Volta and Weber on ner-
vous, 45
Thermo-dynamies, 14
Torpedo, experiments on, 52
— lost time in, 56
Tracings, see Table of Illustrations.
— of walking pace (man),
115
— _ of running (man), 128
— of gallop (man), 131
-—- of hopping (man), 132
— _ of leaping (man), 131
— of movements of insect’s
wing, 190 et seq.
— of action of pectoral mus-
cles of birds, 232
— of flight of wild duck, buz-
zard, &e., 266
— of Wheatstone’s rod with
wing of wasp attached,
191
— of humming-bird moth,
191
— eompared with vibrations
of chronograph, 121
Traction, effects of, on skeleton,
89
Trajoatery. of pubis, 119
of bird’s wing, 234-240
Transitions i in paces of horse, 174

U.

Unit of heat, 13
— of work, 14

Wis

Veratrine, muscle under, 35

Villeneuve, Dr., on birds’ wings, 293

Vincent and Goiffon on horse, 151

Volta and Weber on nervous te-
tanus, 45

INDEX.

W.

Walking (man), 111

—

(horse), 142

Wing (bird’s)

action downward and back-
ward at each stroke, 235

active and passive parts of,
276

ascent of, like action of boy’s
kite, 273

analogy to human arm, 211

at each revolution of, bird
rises twice, 272

change of plane in, 244,
257

compared to screw, 211

curves in, 210

depression of, elevates and
carries forward the body,
269

descent of, gives all motive
force, 273

duration of elevation and
depression of, 228

frequency of strokes of, 227

Hartings on, 223

instrument to show change
in plane of, 258

inclination of, changes gra-
dually, 263

M. de Lucy on, 222

Louvrié, M. de, on angle of
plane of bird’s wing, 275

movements of, 226

ratio to weight, 222, 225

283

Wing (birds’)—continwed.

re-action of movements of,
on body, 264

— of wild duck,
&e., 267

trajectory of pigeon’s, 255

Wing (insects’)

act as inclined planes, 200

artificial representation of,
198

causes of movement of, 196

changes in plane of, 190-204

figure-of-8 movement of, 195

flexible membrane of, 208

flight instrument, illustrat-
ing, 206

frequency of movement of,
181-185

moves downward and for-
ward, 197

movements of, determined
optically, 187

propulsion of, from below
upward and forward, 204

shape of, 276

structure of, 196

trajectory of (Dr. Pettigrew),
201

mechanical, 60

unit of, 16

Z.

Zootrope, 137
Zuckung, shock of muscles, 30

THE END.

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book pretends to no special literary excellence, but is briskly written,
and may be read with interest. Some of its descriptions are very graphie
and picturesque, and, with its excellent illustrations, it is a travel-sketch
of much interest and value.’—N. Y. Evening Post.

“The famous cafions, the hot springs or geysers, the National Park,
the Indian agencies, the tribes of the Sioux, Crows, and other aboriginals ;
Indian figiting, the massacre of pleasure-parties in the National Park,
hunting, fishing, and the usual adventures of travel in a wild country, are
among the subjects treated.’"—V. Y. Home Journal.

“ An account of the summer rambles of a Methodist preacher in the
wondrous Yellowstone region, The numerous chapters are vivid pictures
of the journey to and through that enchanted land.’—J. Y. Christian
Advocate.

“This is a well-printed book of 179 pages, by a worthy and useful
Southern Methodist preacher—one of our brethren on the far frontier of
the new Northwest. There is much in the book to interest and instruct.
It is pleasant reading for a man; it would delight a boy with any soul in
him,.”’—Macon (Ga.) Wesleyan Christian Advocate,

D. APPLETON & CO., 549 & 551 Broapway, New York.

Wye OP ERole S

WILLIAM CULLEN BRYANT.

Illustrated 8vo Edition of Bryant’s Poetical Works. 100
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other Artists. 1 vol., 8vo. Cloth, gilt side and edge, $4.00; half
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The Song of the Sower. [Illustrated with 42 Engravings on Wood,
from Original Designs by Hennessy, Fenn, Winslow Homer, Hows,
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by our best Artists. Elegantly printed and bound, Cloth, extra
gilt, $5.00; morocco, antique, $9.00.

The Story of the Fountain. With 42 Illustrations by Harry Fenn,
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one handsome quarto volume. Printed in the most perfect manner,
on heavy calendered paper. Uniform with ‘The Song of the Sower.”
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A New Volume of the “ International Scientific Series.”

STUDIES IN SPECTRUM ANALYSIS.

By J. NORMAN LOCKYER, F.R.S.,

CORRESPONDENT OF THE INSTITUTE OF FRANCE, ETC.

With 60 Illustrations. - . - - 1vol.,12mo. Cloth, $2.50.

From the New York Evening Post.

“The peculiar excellence and high rank of all the preceding volumes of this
series is at once a guarantee of the high value and character of this. Mr. Lockyer
has in this work entitled himself to a place among the rare, good, industrious,
and every way faithful men of the times, who are so successfully disseminating
the highest and most advanced kinds of useful knowledge among the people.
These men are, par excellence, the uplifters and civilizers of humanity.”

From the New York Times.

‘*Many colored plates and woodcuts assist the eye in this pleasantly-written
little treatise. A certain amount of historical matter is interspersed here and
there. To Sir William Herschel, and the elder Draper, of New York, the author
vives the credit of the first steps in i ag co photography; but the telescope of

. M. Rutherfurd, of New York, says Mr. Lockyer, is the instrument of the future,
so far as stellar astronomy is concerned.”’

From the New York Evening Express.

“The study of spectrum analysis is one fraught with a peculiar fascination,
and some of the author’s experiments are exceedingly picturesque in their results.
They are so lucidly described, too, that the reader keeps on, from page to page,
never flagging in interest in the matter before him, nor putting down the book
until the last page is reached.”

From the Boston Gazette.

“Mr. Lockyer’s work on spectrum analysis is admirably adapted to instruct
the non-scientific reader, and to make him acquainted with the results of one of
the most important discoveries of the century.”

From the Philadelphia Weekly Times.

“Mr. Lockyer is one of the very foremost authorities in this important and
interesting department of scientific research. The difficulties of the subject are
in large measure relieved by an abundance of illustrations, and especially by the
colored plates and the remarkable reproductions of spectrum photographs.”

From the Providence Journal.

‘**Mr. Lockyer is a scientist who speaks with authority. He shows the mar-
velous agency of spectrum analysis, and tells us not only the constituents of the
sun, but clearly explains the process by which the result is reached.”

From the Baltimore Gazette.
‘*The freshest work upon this interesting subject.”

D. APPLETON & CO., 549 & 551 Broapway, New Yor«g.

TENT-WORK IN PALESTINE:

A Record of Discovery and Adventure.

By CLAUDE REIGNIER CONDER, R.E.,

OFFICER IN COMMAND OF THE SURVEY EXreDITION.

Published for the Committee of the Palestine Exploration Fund.

With 33 Illustrations by J. W. WHY MPER.

2 VoLs., 8v0. . 5 2 2

Crora, $6.00,

© ° °

CONTENTS.

THe Roap To JERUSALEM.
SHECHEM AND THE SAMARITANS.
Tue Survey oF SAMARIA.

THe Great PLAIN oF EspR#LON.
Tue Nazareto HILts.

CARMEL AND ACRE,

SHARON. :
Damascts, BAALBEx, AND Hermon.
Samson’s CountrY.

BETHLEHEM AND Mar Sua.
JERUSALEM.

Tus TempLte AND CALVARY.

JERICHO.

THe JornDAN VALLEY.

Hepron AND BrERSHEBA.

Tue Lanp oF BENJAMIN.

THe Drsert oF JUDAH.

THE SHEPHDAH AND PHILISTRIA,.
GALILEE,

THe ORIGIN OF THE FELLAHIN.
Lire AND HaBits OF THE FELLAHIN.
Tue Bepawin.

Jews, Russrans, AND GERMANS.
Tue Fertitity OF PALESTINE.

This book is intended to give as accurate a general description as
possible of Palestine, which, through the labors of the Committee of the
Exploration Fund, is brought home to us in such a way that the student
may travel, in his study, over its weary roads and rugged hills without
an ache, and may ford its dangerous streams and pass through its mala-
rious plains without discomfort.

D. APPLETON & CO., 549 & 551 Broapway, New York.

AM Shir

EXPERIMENTAL SCIENCE SERIES.

In neat 12mo0 volumes, bound in cloth, fully illus-
trated. Price per volume, $1.00.

Tus series of scientific books for boys, girls, and students of every age, was de-
signed by Prof. Alfred M. Mayer, Ph. D, of the Stevens Institute of Technology,
Hoboken, New Jersey. Every book is addressed directly to the young student, and
he is taught to construct his own apparatus out of the cheapest and most common
materials to be found. Should the reader make all tbe apparatus described in the first
book of this series, he will spend only $12.40.

NOW READY:

I.—LIGHT.

A Series of Simple, Entertaining, and Inexpensive Experiments in the Phenomena of
Light, for Students of every Age.

By ALFRED M. MAYER and CHARLES BARNARD.

II—SOUND:

A Series of Simple, Entertaining, and Inexpensive Experiments in the Phenomena of
Sound, for the Use of Students of every Age.

By ALFRED MARSHALL MAYER,

Professor of Physics in the Stevens Institute of Technology; Member of the National
Academy of Sciences; of the American Philosophical Society, Philadelphia ; of
the American Academy of Arts and Sciences, Boston ; of the New York
Academy of Sciences ; of the German Astronomical Society ; of
the American Otological Society ; and Honorary Mem-
ber of the New York Ophthalmological Society.

In AcTIVE PREPARATION.

III, Vision and the Nature of Light.
IV. Electricity and Magnetism.
Vv. Heat.
VI. Mechanics.
VII. Chemistry.
VIUl. The Art of experimenting with Cheap and Simple In-
struments.
D. APPLETON & CO., Pullishers, 549 & 551 Broadway, New York.

A thoughtful and valuable contribution to the best religious literature
of the day.

RELIGION AND SCIENCE.

A Series of Sunday Lectures on the Relation of Natural and Revealed
Religion, or the Truths revealed in Nature and Scripture.

By JOSEPH LE CONTE,

PROFESSOR OF GEOLOGY AND NATURAL HISTORY IN THE UNIVERSITY OF CALIFORNIA,
12mo, cloth. Price, $1 50.

OPINIONS OF THE PRESS.

‘¢ This work is chiefly remarkable as a conscientious effort to reconcile
the revelations of Science with those of Scripture, and will be very use-
ful to teachers of the different Sunday -schools.”—Dedrozt Union.

«Tt will be seen, by this résumé of the topics, that Prof. Le Conte
grapples with some of the gravest questions which agitate the thinking
world. He treats of them all with dignity and fairness, and in a man-
ner so clear, persuasive, and eloquent, as to engage the undivided at-
tention of the reader. We commend the book cordially to the regard
of all who are interested in whatever pertains to the discussion of these
grave questions, and especially to those who desire to examine closely
the strong foundations on which the Christian faith is reared.” —ZBoston
Fournal.

«¢A reverent student of Nature and religion is the best-qualified man
to instruct others in their harmony. ‘The author at first intended his
work for a Bible-class, but, as it grew under his hands, it seemed well to
give it form inaneat volume. The lectures are from a decidedly re-
ligious stand-point, and as such present a new method of treatment.”
—Philadelphia Age.

«©This volume is made up of lectures delivered to his pupils, and is
written with much clearness of thought and unusual clearness of ex-
pression, although the author’s English is not always above reproach.
It is partly a treatise on natural theology and partly a defense of the
Bible against the assaults of modern science. In the latter aspect the
author’s method is an eminently wise one. He accepts whatever sci-
ence has proved, and he also accepts the divine origin of the Bible.
Where the two seem to conflict he prefers to await the reconciliaticn,
which is inevitableif both are true, rather than to waste time and words
in inventing ingenious and doubtful theories to force them into seeming
accord. Both as a theologian and a man of science, Prof. Le Conte’s
opinions are entitled to respectful attention, and there are few who will
not recognize his book as a thoughtful and valuable contribution to the
best religious literature of the day.” —Mew York World.

D. APPLETON & CO., Publishers, 549 & 551 Broadway, N. Y.

APPLETONS’ AMERICAN CYCLOPADIA.

NEW REVISED EDITION.

Entirely rewritten by the ablest writers on every subject. Printed from new tyfe,
and illustrated with several thousand Engravings and Maps.

The work originally published under the title of THE New AMERICAN CycLoPpaDIA

was completed in 1863, since which time the wide circulation which it has attained in all

arts of the United States, and the signal developments which have taken place in eve
Pecnchs of science, literature, and art, have induced the editors and publishers to submit
it to an exact and thorough revision, and to issue a new edition entitled THE AMERICAN
CycLopzepia.

Within the last ten years the progress of discovery in every department of knowledge
has made a new work of reference an imperative want.

‘The movement of political affairs has kept pace with the discoveries of scierce, end
their fruitful application to the industrial and useful arts and the convenience and refine-
ment of social life. Great wars and consequent revolutions have occurred, involving
national changes of peculiar moment. The civil war of our own country, which was at
its height when the last volume of the old work appeared, has happily been ended, and
a new course of commercial and industrial activity has been commenced.

Large accessions to our geographical knowledge have been made by the indefatigable
explorers of Africa.

‘The great political revolutions of the last decade, with the natural result of the lapse
of time, have brought into public view a multitude of new men, whose names are in
every one’s mouth, and of whose lives every one is curious to know the particulars.
Great battles have been fought, and important sieges maintained, of which the details
are as yet preserved only in the newspapers, or in the transient public: itions of the day,
but which ought now to take their place in permanent and authentic history.

In preparing the present edition for the press, it has accordingly been the aim of the
editors to bring down the information to the latest possible dates, and to furnish an ac-
curate account of the most recent discoveries in science, of every fresh production in
literature, and the newest inventions in the practical arts, as well as to give a succinct
and original record of the progress of political and historical events.

The work was begun after long and careful preliminary labor, and with the most
ample resources for carrying it on to a successful termination.

None of the original stereotype plates have been used, but every page has been
printed on new type, forming in fact a new Cyclopedia, with the same plan and com-
pass as its predecessor, but with a far greater pecuniary expenditure, and with such
improvements in its composition as have been suggested by longer experience and
enlarged knowledge.

The illustrations, which are introduced for the first time in the present edition, have
been added not for the sake of pictorial effect, but to give greater lucidity and force to
the explanations in the text. They embrace ‘all branches of science and of natural his-
tory, and depict the most famous and remarkable features of scenery, architecture, ané
art, as well as the various processes of mechanics and manufactures. Although intended!
for instruction rather than embellishment, no pains have been spared to insure their

artistic excellence; the cost of their execution is enormous, and it is believed that they -

will find a welcome reception as an admirable feature of ‘the Cyclopedia, and worthy
of its high character.

This work is sold to subscribers only, payable on delivery of each volume. It is
completed in sixteen large octavo volumes, each containing about 800 pages, fully illus-
trated with several thousand Wood Engravings, and with numerous colored Litho-
graphic Maps.

PRICE AND STYLE OF BINDING.

In extra cloth, per vol. ...cccccueee $5.00 j Jn half russia, extra gilt, per vol. .$8 00
In library leather, per vol.........+ 6.00 | Jn full mor. ant., gilt edges, per vol.10.09
In half turkey morocco, per vol..... 7.00 | In full russia, per VOl.... 601.0004 + +%O.00

*,* Specimen pages of the AMERICAN CycLopp1A, showing type, illustrations, etc..
.. # -P 1 pag tne £ ’ gty
will be sent gratis, on application.

New York: D. APPLETON & CO., PUBLISHERS.

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