INVESTIGATIONS
ON MICROSCOPIC FOAMS

AND

ON PROTOPLASM

X?3

INVESTIGATIONS

ON

MICKOSCOPIC FOAMS

AND ON

PEOTOPLASM

EXPERIMENTS & OBSERVATIONS DIRECTED TOWARDS A SOLUTION

OF THE QUESTION OF THE PHYSICAL CONDITIONS

OF THE PHENOMENA OF LIFE

BY

0: BUTSCHLI

PROFESSOR OF ZOOLOGY IN THE UNIVERSITY OF HEIDELBERG

AUTHORISED TRANSLATION

BY E. A. MINCHIN, B.A. (OxoN.)

FELLOW OF MERTON COLLEGE, OXFORD

LONDON
ADAM AND CHARLES BLACK

1894

TKANSLATOK'S PKEFACE

IN bringing an English translation of this work before the
public, I feel that a word or two of explanation is due to
my readers. Many people regard the translation of French
or German scientific works as unnecessary, holding that
every student of science should have a knowledge of these
languages. Without wishing to controvert this opinion
generally, I may state the reasons which originally prompted
me to undertake this translation. In the first place,
the investigations here described are of so fundamental a
nature as to be of interest not only to workers in all the
various branches of Biology, and to physicists, but perhaps
even to those who are not professed students of science at
all. In the second place, this work, lying as it does for the
most part on the border-line between two sciences so
distinct as Physics and Biology, is full of the technicalities
of both these sciences, and is therefore by no means easy
reading in the original for a modern scientific specialist,
however great his knowledge of the German language.
For these reasons it seemed to me that a translation of
Professor Blitschli's valuable investigations might form an
acceptable addition to English scientific literature.

In preparing this translation certain German words
and phrases were found especially difficult to render into
English. Above all, this was the case with the two words

vi PROTOPLASM

" Entmischung " and " Ausbreitung," applied to the peculiar
physical phenomena described fully on p. 15 and p. 62 et
seq. respectively. Not being able to find English equiva-
lents for these words I applied to Lord Kayleigh, Sec. E. S.,
for advice, and with his kind help I have coined the word
desolution for " Entmischung," while " Ausbreitung " I have
rendered at his suggestion by the word extension or super-
ficial extension. There is no need for me to explain these
terms here, as that is done in the text at the places
indicated.

Protoplasm is conceived of in this work as having the
structure of a froth or foam in which minute droplets of a
watery liquid take the place of air in the bubbles of an
ordinary foam. Such a structure is termed by the author
" Wabenstructur," i.e. honeycomb structure ; the separate
vesicles, bubbles, or droplets of the foam are termed
" Waben," i.e. cells of a honeycomb. The latter word has
been rendered throughout by the term alveolus, and the
structure is generally termed alveolar. The most super-
ficial layer of radially directed alveoli, which gives the ap-
pearance of a striated border, has been termed by the
author the "alveolar layer" ("Alveolarschicht") par excellence.
In order to avoid confusion this has been rendered in many
places marginal alveolar layer, in other places simply
alveolar layer.

The plan has been followed of printing the book in two
types, in order that the student may be able to obtain first
of all a general idea of its contents, without entering into
details, by reading the portions printed in the larger type
consecutively.

Finally, it is my pleasant duty to express my thanks
for the assistance I have received in preparing this transla-
tion. Without Professor Eay Lankester's kind help the
work would never have been undertaken. To the Author

TRANSLATOR'S PREFACE vii

and to my friend Mr. Hatchett Jackson I am greatly
indebted for the trouble they have taken in looking over
the proofs, and for making many valuable suggestions and
corrections. My obligations to Lord Eayleigh have already
been stated.

E A. M.

OXFORD, January 1894.

CONTENTS

PAGE

INTRODUCTION ... 1

PART I

OBSERVATIONS ........ 5

A. Investigations upon Oil-Foams ..... 5

1. Preparation and Structure of the Foams ... 5

2. Some more exact Statements as to the Alterations in

Volume of the Drops of Foam under the Influence

of the surrounding Fluid . . . .38

3. Radiate Appearances in the Drops of Oil-Foam . . 41

4. Fibrous Structures in Drops of Oil-Foam . . .44

5. The Durability of the Oil-Foams . . . .46

6. The Phenomena of Streaming Movement exhibited by the

Oil-Foams ...... 47

7. The probable Explanation of the Streaming Movements

exhibited by the Drops of Foam . . .61

8. Streaming Movements exhibited by Drops of Foam in Cells 80

9. Remarks upon Frommann's Experiments on Drops of Oil-

Foam . . . ..... .82

B. Investigations upon Protoplasmic Structures . ... 85

1. Investigations upon Protozoa . . ' . .86

Suctoria ....... 87

Ciliata ....... 88

Flagellata . . . . . . . 91

Radiolaria. ...... 92

Heliozoa ....... 93

Marine Khizopoda with Calcareous Shells and Reticulate

Pseudopodia ...... 94

Gromia Dujardini, M. Schultze . . . . 101

Amcebse . .106

PROTOPLASM

PAGE

^Ethalium septicum (Fuligo varians) . . . Ill

Pelomyxa palustris, Greeff .... 116

2. On Protoplasmic Structures in the Bacteria and allied

Organisms ...... 117

3. Some Observations on the Streaming Protoplasm of Vege-

table Cells ...... 122

4. Observations on some Egg Cells . . . .124

5. Red Blood Corpuscles of Rana esculenta . . .127
6. . Observations on some Epithelial Cells . . .131

7. Peritoneal Cells on the Gut of Branchiobdella astaci, etc. . 136

8. Liver Cells of Rana esculenta and Lepus cuniculus . 140

9. Epithelium of the small Intestine of Lepus cuniculus . 142

10. Pigment Cells of the Parenchyma of Aulastomum gulo . 143

11. Capillaries from the Spinal Marrow of the Calf . . 143

12. Connective Tissue Cells between the Nerve Fibres of the

Ischiadic Nerve of Rana esculenta . . . . 144

13. Ganglion Cells and Nerve Fibres .... 145

PART II

GENERAL PART ........ 157

A. The Theory of the Net-like or Reticular Structure of Proto-

plasm ...... 159

B. Summary of Divergent Views ..... 177

1. The Theory of the Fibrillar Structure of Protoplasm . 177

2. The so-called Spherular Theory of Kiinstler . .184

3. The so-called Granular Theory of Protoplasm . .191

4. Attempts to explain the Reticular Structures as Pheno-

mena of Coagulation or Precipitation . . 201

The Nature of Colloid Bodies . . . .216

5. The Structure of Protoplasm is Alveolar or Honeycombed

(Foam-like) ...... 219

(a) Aggregate Condition of Protoplasm . . . 220

(&) Vacuoles . . . . . . 227

(c) External Surface of the Protoplasm . . . 234

(d) Alveolar Layer . . , . . .236

(e) Cell Membranes, Cuticulse .... 240
(/) Radiate Layer of Alveoli round the Nucleus . . 243

(g) Granular Enclosures in Protoplasm, and Corresponding

Position of Soot Particles in the Artificial Foams . 244
(h) Radiate Appearances in Protoplasm during Cell Division 246
(i) Radiate Appearances in Ova, etc. . . .251

(/) Striated Protoplasm of Epithelial Cells . . .254

CONTENTS xi

PAGE

(k) Fibrous Protoplasm ..... 255

(Z) Theories concerning the Causes of Radiate Appearances . 257

6. The Homogeneous Protoplasm and the Alveolar Theory . 262

7. The Phenomena of Protoplasmic Movement in their

Relation to the Alveolar Structure . . . 267

(a) Theories as to the Causes of the Phenomena of Movement 267
(ft) So-called Contractility . . . . .267

(c) Contractility of the alleged Reticular Framework . 269

(d) Objections to the Theory of Contractility . . 270
(«) Hypotheses of Hofmeister, Sachs, and Engelmann . 271

(/) Electrical Hypotheses of Velten and Fol . . . 279

(g) Leydig's View of the so-called Hyaloplasm . . 280

(h) Montgomery's Hypothesis . . . . 287

(i) Hypotheses relating to Surface Tension — ^erthold,

Quincke ...... 289

(/) My own View of the Explanation of AmcEboid Move-
ment ...... 307

On the Currents in the Water surrounding Amoebae,

etc. .317

(k) Independent Movements of Granules . . . 319
(Z) Causes of Internal Displacements in the Alveolar Proto-
plasm ...... 323

(m) Possibility of an Explanation of Muscular Contraction in

this Way . . . . ... 325

(ri) Rotational Currents in Plant Cells . . .327

LITERATURE ...:..,. 331

EXPLANATION OF THE PLATES . . . . . 341

INDEX . 367

LIST OF ILLUSTKATIONS

PRINTED IN THE TEXT

no. PAGE

1. Formation of foam in an oil-drop placed in water. The darker peri-

pheral zone represents the portion which has become frothy, while
the centre of the drop is occupied by clear homogeneous oil. NaCZ,
fragments of common salt ; v, vacuoles . . . .12

2. Diagram of the union of three lamellae of a foam in one edge, as seen

in optical section . . . . . . .27

3. Diagram representing an optical section of the superficial region of a

foam. The arrows a, 6, c, represent the tensions of three lamellse

at the surface ....... 33

4. Diagrammatic optical section of the greatly attenuated margin of a

drop of oil-foam . . . . . . .37

5. Diagram showing the course of the currents in a drop of oil-foam

placed in dilute glycerine, o, the upper, a, the lower side of the
drop; O, slide; D, cover glass '. . . . .48

6. Outline sketch showing one of the forms assumed by a large drop of

oil-foam in active movement. The pairs of dotted arrows repre-
sent centres of extension-currents . . . . .51

7. Outline sketches showing the forms assumed by a drop of oil-foam,

when warmed and moving actively, during a period of ten minutes.
Arrows to denote extension-currents . . . .53

8. Outline sketches of a drop of oil-foam under the influence of the

electric currents ; taken at intervals of five minutes, to show the
changes of form and movement consequent upon change of the
poles. The signs + and - denote the positive and negative poles ;
the arrows denote the extension -cur rents . . . .58

9. Diagram showing the system of extension-currents produced in a

drop of oil placed in water under the cover glass, when approached
on one side by soap solution. The arrows denote the currents.
m, the axial quiescent streak ; x, the posterior quiescent region . 62
10. Diagram showing extension -currents in a drop of paraffin oil under
similar circumstances, and also the currents in the surrounding
water 64

xiv PROTOPLASM

FIG. PAGE

11. Diagram of a drop of oil containing particles of lamp-black in sus-

pension, showing the position assumed by the lamp-black under

the action of extension-currents . . . . .69

12. Diagram showing the extension-currents produced in a drop of oil

when approached by a bent platinum wire, heated by means of an
electric current . . . . . . .72

13. Diagram showing the extension -currents produced in a drop of oil

in contact with a capillary tube containing soap solution . . 73

14. Diagram showing a method of obtaining circulatory extension-

currents in a drop of paraffin oil . . . . .74

15. The same as Fig. 5 . . . . . . .76

16. Diagram of a section through a drop of oil under the cover-slip when

free from pressure (A) and when compressed (B) . . . 78

17. Sketch of two streaming drops of oil-foam in closed cells . . 80

18. Diagram representing the true reticulum (a) with an exact focus,

and the false optical reticulum (&) with a higher focus . .215

19. Diagram of the currents set up in a drop of water on a slide, when

approached by ether on one side. To show the currents ivory
black has been mixed with the water .... 301

20. Diagram of a median longitudinal section through the drop shown

in Fig. 19 . . . . . . . .302

21. Diagram to show the currents in the growing pseudopodium of an

Amceba . . . . . . . .311

22. Diagram of muscle contraction ..... 325

23. Diagram of rotational streaming in plant cells . . . 328

LIST OF PLATES

PLACED AT THE END OF THE VOLUME
MLATE

I. Illustrations of the minute structure of the protoplasm and the pseudo-
podia of Gromia Dujardini M. Schultze.

II. The minute structure of the protoplasm and pseudopodia of Foramini-
fera (Figs. 1-6) and Amcebce (Figs. 7 and 8).

III. Illustrations of the pseudopodia of Foraminifera (Figs. 1-4) and the
body protoplasm of Acineta (Fig. 5).

IV. Illustrations of the minute structure of Foraminifera (Figs. 1 and 2),
Amcebce (Figs. 3 and 4), and Ciliata (Figs. 5-8), and of vegetable
protoplasm (Fig. 9).

V. Illustrations of the minute structure of the ova of a sea-urchin, Sphcer-
echinus (Fig. 1, a-c), of the protoplasm of Thalassicolla (Fig. 2, a
and b) and Ghiloinonas (Fig. 3), and of oil-foams (Figs. 4 and 5).

VI. The minute structure of oil-foams (Figs. 1 and 2) and of an epidermic
cell of Lumbricus (Fig. 3), a fat cell of Blatta (Fig. 4), and the epi-
dermis of Gammarus.

VII. The protoplasm of various tissue cells ; liver cells of the frog (Fig. 1) ;
peritoneal cell (Fig. 2), epidermis and cuticle (Fig. 3, a-c) of
Branchiobdella ; egg (Fig. 4) and ciliated cells (Fig. 5) of Hydatina;
pigment cell of Aulastomum (Fig. 6), and nerve fibre of Astacus
(Fig. 7).

VIII. The minute structure of the protoplasm of ganglion cells and axis-
cylinders from the frog (Fig. 1), calf (Fig. 2), and earthworm (Fig.
3) ; and of connective tissue cells from the frog (Fig. 4).

IX. The minute structure of capillaries, ganglion cells, and axis-cylinders ;
a capillary (Fig. 1), a process of a ganglion cell (Fig. 2), and an axis-
cylinder (Fig. 3) from the calf, and transverse sections of axis-cylin-
ders from the frog (Fig. 4, a-c).

xvi PROTOPLASM

PLATE

X. Blood corpuscles of the frog (Fig. 1, a and b) ; axis-cylinder, in trans-
verse section, of the rabbit (Fig. 2) ; pseudopodium of Actinosphwrium
(Fig. 3) ; structure of a thin lamella of oil-foam (Fig. 4) ; and draw-
ings to show the optical network, produced by intersection of dif-
fraction rings, between minute suspended droplets of oil (Fig. 5,
a-c).

XI. A thin section through the cuticle and hooks of Distomum.

XII. Pseudopodium of A ctinosphcerium (Fig. 1); protoplasmic filament from
a cell of Tradescantia (Fig. 2) ; section through cells of the intestinal
epithelium of Distomum (Fig. 3) ; stalk muscle of Zoothamnium (Fig.
4) ; and tentacle of Acineta in optical section (Fig. 5). For Fig. 6
compare the text, p. 179.

INTRODUCTION

IN the preface to the studies published by me in 1876,
upon the primary developmental processes of the ovum, cell
division, etc., I pointed out that the morphological method
of consideration, which had led to such brilliant results for
the comprehension of multicellular organisms, fails to be of
service to us when we attempt to penetrate deeper into
the essential nature of the elementary organism — the cell.
I expressed the view " that the phenomena exhibited by and
in the elementary organism could not assume an intelligible
form except through a knowledge of the physical and
chemical conditions of their origin and cessation." I also
attempted in this work, and, as I believe, for the first time,
to bring into requisition a property of fluid bodies, — namely,
surface tension, in order to explain the phenomena of the
division of the protoplasmic cell body, of which I had made
a careful study.

In the following investigations I believe I am able
to bring forward a contribution towards a more accurate
physical explanation of certain peculiarities of living matter
or protoplasm. Since it is far from my intention to enter
at present into detailed historical disquisitions upon the
question of the structure and nature of protoplasm, I will
only put forward here a few historical remarks upon my
own position with regard to this question, in order to indi-
cate the train of reasoning which led to the investigations.

In 1878 I found an opportunity for the first time
of expressing my opinion upon the alleged reticular struc-
ture of protoplasm, which had come more to the fore at

1

2 PROTOPLASM

this time through the works of Frommann, Kupffer, Heitz-
mann, and others. I remarked at that time that the facts
which had become known concerning this point " do not,
however, seem to me by any means so noteworthy and so
unconnected with former observations as was usually repre-
sented. From the protoplasm of many Protozoa in which
appear single scattered vacuoles there is a gradual transi-
tion to be found to completely alveolar or, what is the
same thing, reticular protoplasm, where the alveoli are so
densely crowded that their real protoplasmic walls take on
a honeycombed arrangement, which in optical section appears
reticular." I further remarked that in the hyaline cortical
layer and the pseudopodia of Ehizopods, we had before us
structureless homogeneous protoplasm. Thus, as far back as
1878, I represented the view that the reticular structure of
protoplasm described by various investigators was a honey-
combed or alveolar structure.

My extensive dealings with Protozoa of very various
groups, to which I had to devote myself during the follow-
ing years, gave me the opportunity for many an observation
upon protoplasmic structures, which more and more con-
firmed me in the view I had already expressed in 1878.
In the years 1884 and 18851 was first able to study more
thoroughly relations of this kind — in 1884 Noctiluca ; in
1885, a series of marine Ehizopods, Adinosplicerium, and
certain Ciliata. More definitely than before I expressed
my conviction that the so-called reticular structures should
be interpreted as honeycombed, and founded this conception
upon the proof of the indubitable honeycomb structure of
the so-called " alveolar layer." I also brought forward
proofs of the reality of the protoplasmic structures, the
resemblance of which to the products of the coagulation
and precipitation of various substances might awaken a per-
fectly justifiable suspicion as to whether they did not also
belong to the same category of phenomena. I soon found
occasion for engaging still more thoroughly in studies of this
kind, when in the years 1886-88 I undertook to do the
Ciliata for Bronn's Klassen und Ordnungen. In my own
studies upon this group I was able to avail myself of the

INTRODUCTION 3

assistance of two talented pupils, Dr. Schuberg and Dr.
Schewiakoff. In their works upon Ciliata(1886 and 1889),
which were carried on in continued collaboration with me,
they have brought forward in support of my conception,
essential contributions from within the limits of this group
of Protozoa. On the ground of their investigations, as well
as of others of my own, I was able in my description of
the Infusoria to give a somewhat broader and more detailed
exposition of my view (pp. 1317, 1392). The experience
gained up to this point had called forth the conviction that a
phenomenon of fundamental importance was before us ; a
conviction which I expressed at that time (18 8 8) in the1
following words : — " We are here confronted with a pheno-
menon of the same widespread occurrence and significance
as the building up of higher organisms from cells, without
possessing at the outset a guiding and explanatory idea, just
as was the case with the observers of cellular tissue before
the cell theory had been founded." Although convinced that
the structure of protoplasm was in general alveolar, I yet
thought it necessary at that time (p. 1392) to make a con-
cession to the theory of its spongy structure, inasmuch as I
admitted " that at times adjacent alveoli may break through
into one another, and thus a spongy structure would come
to be formed in places." This remark was particularly
inconsistent in the case of the endoplasm, since I at the
same time represented its nature as fluid, and such an
assumption excludes any idea of the kind.

As a proof, to a certain extent, of the significance which
the theory of the honeycomb structure of protoplasm
might possess for the conception of protoplasm as a whole,
I also described in 1888 the consequences which result
from it for the growth of protoplasm, by trying to show that
the difficulty in conceiving of growth by intussusception
could be got over upon the basis of my theory.

As is obvious from this proposition and from the view
quoted above from my work on Protozoa, I cherished the
idea, ever since the universal occurrence of such struc-
tures in protoplasm became clear to me, that in this
fact an essential reason was to be sought for many of the

4 PROTOPLASM

peculiar properties and activities of this substance. Accord-
ing to my conception the structure of protoplasm corre-
sponded to that of the minutest microscopic foams, with the
difference that the alveoli of ordinary foams contain air,
while protoplasmic foams contain a watery fluid. If such
microscopic foams were successfully manufactured, ought
they not to show certain peculiarities of protoplasm, and
could not an accurate study of them furnish an essential
contribution towards confirming or correcting my view ?
This question forced itself upon me more and more strongly.
Whether the results obtained in this direction might or
might not be favourable to my view, it was to be hoped in
any case that they would contribute to the clearing up of
the protoplasm question.

PAET I

OBSERVATIONS
A. Investigations upon Oil-Foams

1. Preparation and Structure of the Foams

THE reflections and considerations set forth in the preceding
pages impelled me to try if it were possible to produce
artificial foams of the fineness that I believed to exist in
the instance of protoplasm. Although it was scarcely to be
expected that such attempts would produce results at all
considerable, I thought nevertheless that something or other
of importance might possibly be attained by such a course.
Hence I sought to follow it up, as soon as time and
opportunity offered, on the completion of my work upon
Protozoa. Experiments of this kind could at first be little
better than a blind groping about, as it were, in the hope
of finding a possible starting-point from which advance
might be made in a more methodical and confident manner.
I began this attempt with a feeling of vague uncertainty,
such as the alchemists must have felt in their hopeless
experiments. This uncertainty was, as may be easily con-
ceived, heightened by the fact that I was setting foot in a
region in which I was very little at home, and the difficulties
of which were hence far beyond my ken. Still this
ignorance proved perhaps, if anything, serviceable ; with a
sufficient appreciation of the difficult problems of molecular

6 PROTOPLASM

physics in which I set myself to dabble, the experiments
would perhaps. have never been undertaken.

Various fruitless attempts were made first with different
kinds of emulsions, which led to no satisfactory results, since
they were not to be deprived of the character of an emulsion,
i.e. of minute drops suspended in a relatively abundant fluid
matrix. A foam of fine structure was, however, for the
first time successfully produced by the mixing of two fluids.
Without describing here the previous experiments that gave
no result, I will proceed to make a few remarks on the
attempts that were first successful. If a very thick solution
of commercial soft soap (potash soap) be shaken up thoroughly
with benzin or xylol, a fine emulsion is formed, since the
benzin distributes itself in the soap solution in drops
varying in size from those of moderate fineness to the very
minutest. If this emulsion be then left to stand, the lighter
benzin droplets rise to the surface, and become arranged,
through the thinning out of the layers of soap solution
between them, into a fine froth, just as bubbles of air rising
to the top of a soap solution collect gradually on its surface
into an ordinary lather. The description and explanation
given by Plateau for the latter case is without doubt also
suitable for the froth here described. The whitish foam,
in which benzin plays the part of air in an ordinary
soap lather, attains to a considerable degree of fineness, but
is not to be compared in this respect with the froths which
I obtained later in another way. I have not taken any
measurement of the average size of its meshes, since such
benzin foams are difficult to investigate, but they stand
somewhere on the boundary between the macroscopic and
the microscopic, since at least their larger meshes are visible
with the naked eye or with a weak lens. Nevertheless the
durability of froths of this kind is striking. I have kept
such a froth for two years now in a tightly-stoppered bottle
without its having essentially altered. Perhaps in the course
of time its meshes have become somewhat coarser, but its
original character has been completely retained.

Experiments of various kinds, especially electrical, which
I performed upon such benzin froths did not lead to definite

EXPERIMENTS WITH OIL 7

results. Drops of such a froth placed under benzin, on
quicksilver with which is connected one pole of an induc-
tion apparatus, while the other touches the drops, show a
distinct spasm at each closing or breaking of the current.
I do not, however, believe that this phenomenon is connected
with their frothy structure, but that it is to be regarded in
just the same way as the alteration in form of a drop of
water under similar conditions.

I was urged to further experiments in manufacturing
fine froths by Quincke's communications (1888) on the
diffusion of watery fluids through fatty oils. As is well
known, the above-named physicist was able to determine by
various experiments that such a diffusion may take place.
My experiments also, to be communicated in the sequel, are
in favour of this happening, or at least are not easily ex-
plicable without such a supposition.

Since Quincke made use of the experience he had obtained
with regard to the phenomena of movement, or, more properly
streaming, produced by relations of surface tension in fluids, and
particularly in oil-drops, in order to construct a hypothesis con-
cerning the phenomena of streaming in protoplasm, and took the
opportunity of occupying himself more specially with protoplasm
in general, it is permissible for me to state more exactly the
relations of Quincke's investigations to mine. As I have already
remarked, I took from Quincke's work the idea of using fatty
oils for the production of finely-structured foams, since I con-
sidered possible, as will be presently described, the conversion of
the oil into froth by the diffusion demonstrated by Quincke.
Moreover, I recognise willingly that Quincke's investigations
and hypotheses stimulated me to undertake experiments based
upon my own view of the structure of protoplasm, in order to
subject the correctness of my conception to a thorough test. On
the other hand, my experiments and ideas were, from the very
beginning, on an altogether independent footing, the outcome of
my experience with regard to the finer structure of protoplasm.
The idea of the alveolar structure of protoplasm guided me from
the commencement, and, as has been said, prompted the experi-
ments.

I have frequently in conversation communicated my views
upon the probable structure of protoplasm to my colleague, Prof.
Quincke, and emphasised the fact that certain properties of
protoplasm might well be connected directly with this structure,

8 PROTOPLASM

before he published his hypothesis of protoplasmic movement.
In his communication of 1888, Quincke still treats protoplasm as
a simple fluid, and nowhere speaks of its froth-like structure.
When he lays stress (1889), after the publication of my first report
(1889), on the frothy structure, I can only recognise in this
fact the influence of my experience, although he nowhere men-
tions this in his publication, which deals with protoplasm and the
phenomena of movement exhibited by it.

The train of reasoning which led to the experiments with
fatty oils was as follows. If a mixture of oil and very finely
ground down particles of a substance easily soluble in water,
be brought into water, the latter will enter by diffusion into
the oil. The fine particles of soluble substance will attract
the water and become converted into minute drops of a
watery solution. The closely-compressed drops are able to
convert the oil in which they are suspended into a fine froth
in this manner. Although this reasoning did not prove
perfectly correct, yet the experiments prompted by it led to
gratifying results.

Olive oil that had stood for a long time in a bottle in
the laboratory was first employed for the experiments. As
soluble substances, common salt, cane sugar, and potassium
nitrate were tried. The method pursued was as follows.
A very small quantity of the soluble substance, taken on the
tip of a knife, was pulverised as finely as possible in a small
mortar, and then rubbed up into a thick paste with a drop
of olive oil. Small or minute drops of this mixture were
placed on a cover-slip provided with wax feet at the corners,
and the cover-slip was then inverted over a drop of water
of sufficient size upon a slide. As a rule, the ordinary
Heidelberg tap-water was used, which contains relatively
little dissolved matter, but sometimes distilled water was
also tried. But since the experiments gave similar results
in both cases, the ordinary town water was used in con-
sequence exclusively. The wax feet on the cover-slip were,
as a rule, high enough for the drops of the oil mixture
to be in contact with the surface of the slide without, how-
ever, being compressed.

In the manner described, it was possible to convert the

FORMATION OF FROTH IN OIL 9

above-mentioned olive oil by means of either cane sugar or
common salt into a very fine froth, while the attempts with
potassium nitrate did not yield favourable results, and hence
were not further continued. The behaviour of the oil-drops
when brought into water is, as far as it was followed out,
somewhat as follows. Microscopic observation shows, in the
first place, that the pulverisation of the substance mixed in
with the oil is, in spite of all care, comparatively coarse,
and that, besides particles of the finest size, a considerable
number of coarse fragments are present in addition. A
watery fluid can soon be observed round these fragments in
the oil. Finer and coarser droplets appear, and not in-
frequently fragments of the enclosed substance are extruded
from the surface of the drop and dissolve in the sur-
rounding water ; or at times even the watery fluid that has
made its appearance in the oil pours out eruptively into the
surrounding water. The fact that a lively and fairly
regular exchange takes place by diffusion between the oil
mixture and the water is shown by the active streaming
movements of the latter, which can be well followed if Indian
ink is mixed with it. I have followed these movements to
some extent in some drops of oil mixture prepared with
common salt, and can report on them as follows. After
transferring the drop of mixture to the slide it is soon
observed that in the higher regions the water streams from
all sides towards the drop, and, on the contrary, in the lower
regions, i.e. on the slide itself, the water streams away from
the drop radially. These currents gradually become slower,
but can be followed for about twenty minutes, when they either
die down or continue very feebly. It was often observed
that the upper current, at first purely radial in direction,
gradually changed in such a way that at one region of the
drop an out-streaming current was formed even at the higher
level, while at other places the in-streaming currents con-
tinued, but had slightly altered their directions in consequence.

The above-mentioned streaming movements admit of an easy
explanation. The water immediately surrounding the drop takes
up salt solution, either by diffusion or by the direct emergence of
single particles, becomes specifically heavier thereby, sinks down

io PROTOPLASM

on to the slide, and spreading out upon it, streams in all directions
away from the drop, while in the higher regions it is replaced by
pure, specifically lighter water, which therefore streams from all
sides towards the drop. The correctness of this explanation is
confirmed by the fact that the same streamings are also obtained
by allowing concentrated salt solution and pure water to approach
one another under a cover-slip — a process which can be carried out
with the retention of a fairly sharp boundary between them.
The current in the water, which is directed towards the boundary,
goes on in the upper region, while in the lower region the current
flows away from it ; on the other hand, in the salt solution the
current towards the boundary is below, the current away from it
uppermost, since the salt solution of the intermediate region, having
become specifically lighter, continually ascends. The streaming
movements are distinct but fairly slow. Corresponding stream-
ings appear if glycerine is brought in contact with water.

After the drops of oil mixture, prepared in the manner
stated, have stood about twenty-four hours in a damp cham-
ber, they become completely opaque and milk-white. The
particles of soluble substance have vanished, but here and
there larger drops of fluid (vacuoles) are visible in the oil.
The closer investigation of drops that have thus become
opaque shows that they have become converted into a more
or less finely-structured foam throughout their entire mass.
On account of their opacity the drops must naturally be
pressed out into a thin layer, if it is desired to determine
their finer composition. Hence a more suitable method is
to clear them up gradually by addition of glycerine to the
water under the cover-slip, or rather by replacement of the
water by glycerine. One can then follow plainly the way in
which the clearing up gradually penetrates from the surface
of the drop into the interior, and finally, after a short time,
pervades the whole drop equally. The gradual clearance of
such a drop of oil-foam by glycerine is a sure proof that the
glycerine diffuses through the oil, so that its alveoli become
filled after a time with watery glycerine. In consequence
of this the froth-drop naturally becomes much more trans-
parent, on account of the diminution in the difference of the
refractive indices. I defer for the present the more detailed
description of the structural relations of foam-drops produced

PREPARATION OF OIL-FOAMS 11

in this way, from olive oil and sugar or salt, and will forth-
with proceed to discuss the further experiments which were
performed in order to manufacture such foams, and to
explain their formation.

The attempt to obtain similar drops of oil-froth with cod-liver
oil and common salt gave bad results, since only a defective foam
with large vesicles was formed. On the other hand, tolerably
good results were obtained with boiled linseed oil and common
salt. For certain reasons I experimented also on the behaviour
of a thick mixture made up with paraffin oil and common salt.
As was to be expected, no proper formation of foam took place
in the paraffin oil ; the salt, however, dissolved gradually with
formation of droplets, but very slowly. Hence diffusion of
water through the paraffin oil certainly takes place, although
very slowly.

It has been already pointed out above, that the original
train of reasoning which led to the experiments upon the
formation of foam in oil was not, as a matter of fact, com-
pletely confirmed. I demonstrated that the particles of
the substances mixed with the oil were relatively coarse in
spite of the finest pulverisation ; hence it seems impossible
to ascribe the alveoli or foam vesicles of a successful oil-
foam of this kind, as a rule of extreme fineness, to the
drops of fluid produced by the solution of the enclosed
particles. For this reason some other source of the forma-
tion of the finest droplets of watery fluid must be present
in the oil. To clear up this point I instituted a series of
experiments, to enumerate which is of no further interest,
since they soon led to the result that even in pure olive oil,
placed in similar drops in H20 under the cover-slip, numer-
ous very minute droplets of fluid very soon make their
appearance, causing it, at least in places, to become finally
quite opaque and 'of a minute foam-like structure. In a
few hours after setting up such a preparation, numerous
very fine droplets of fluid may be noticed in the oil ; these
drops increase continually in quantity, so that after one or
two days the drop has become quite turbid. In particular,
the lower edge of the drop, i.e. the edge of the surface by
which the drop rests on the slide, has then become quite

12 PROTOPLASM

black and opaque (in transmitted light), so that a dark
somewhat irregular margin completely surrounds the drop
like a girdle (see Fig. 1). The phenomenon does not per-
ceptibly proceed with greater
intensity or speed, if the olive
oil is heated beforehand for
some time on the water-bath
over sugar or common salt ;
hence, any solution of these
substances in the oil is with-
out direct influence. On the
other hand, the production of
froth takes place quite strongly,
rig. i. if some few crystalline fragments

of salt or sugar are enclosed

in the oil-drops. Drops of fluid then form as a rule round
the fragments of salt ; but curiously enough, this does not
occur at times round certain of the fragments, and moreover,
not round those of sugar. The oil-drop becomes frothy in
exactly the way described above, but this process appeared,
however, as has been said, to go on more intensely than in
the pure oil-drops (see Fig. 1). In the vicinity of the drops
of fluid, which had formed round the salt crystals, there
appeared to be in no way any special crowding of the froth
droplets, which were concentrated, as depicted, more es-
pecially in the marginal zone. The explanation of the
intense crowding of the droplets of froth in the lower
marginal region of the oil-drop may be somewhat as follows.
The formation of the droplets depends, without doubt, on
water being taken up into the oil, which takes place in a
way that will be treated more in detail later. As a
consequence, the formation of droplets will occur principally
in the marginal region of the oil, bordering on the water.
But since the droplets consist of a watery solution, and
hence are specifically heavier than the oil, they will sink
gradually in the oil-drop, and, as a result, collect principally
in the region of its lower margin. Since the droplets when
sinking press against one another, they cause, if the conditions
are suitable, the formation of a froth, in a similar manner

SOAP PRESENT IN THE OIL 13

to the ascending air-bubbles in a soap solution, or the earlier
described benzin droplets in a froth of soap and benzin.

Drops of almond oil and cod-liver oil, which were brought
into water, behaved in just the same way as the olive
oil already investigated. Cod -liver oil especially became
turbid very quickly and intensely, and turned completely
into a fine frothy structure in the lower region.

These experiments led me to suppose that the formation
of foam in oil-drops in water might depend on the presence
of small quantities of soap dissolved in the oil. The dissolved
soap strongly attracts water which diffuses into the oil, and
the watery solution of soap thus formed, not being soluble
in oil any longer, separates out in minute particles, which by
further absorption of H90 become minute droplets. This
hypothesis appeared also very probable, if not certain, from
special experiments directed to the point. It was not found
possible to deprive olive oil of its property of becoming
gradually turbid and frothy in H20, by heating it with
water and shaking it repeatedly ; indeed it is improbable that
oil can be thus completely deprived of such soap as it may
contain. On the other hand, the influence of soap in the
olive oil on the production of froth was shown very plainly,
when the amount of contained soap was increased by warm-
ing the oil for some time with Venetian soap, even though
the latter was not noticeably dissolved. A drop of such
oil, brought into water in the usual manner, begins to turn
frothy immediately; at the same time wave-like stream-
ing movements (superficial extension -currents) appear on
the surface, called forth by local extension -movements of
the soap. In a few hours the drop became quite frothy.
A similar result is obtained if a few particles of Venetian
soap are enclosed in a drop of pure olive oil, which is then
brought into H20 under a cover-slip. Such drops also im-
mediately show lively wave -like extension-currents, and
minute droplets stream out on all sides from the particles
of soap into the surrounding oil. After a few hours the
oil-drop becomes finely frothy throughout, therefore white
and opaque. I have not followed out this method of pre-
paring such oil-lathers more accurately, so that I cannot

I4 PROTOPLASM

say if it is as good as that described below, or possesses
any special advantages.

It is an interesting fact that white of egg exerts the same
influence as soap on the conversion of olive oil into froth. The
olive oil (a), used for the experiments hitherto described, was
allowed to stand some days over dried pulverised white of egg,
and then filtered off. Drops of this perfectly clear oil were brought
into water under the cover-slip in the way described. Numerous
extremely minute droplets of fluid appeared at once in the oil-
drop, which in a short time became turbid. Simultaneously it
took on the peculiar circulating streaming movements, described
below for drops of oil-foam in glycerine. A superficial current,
both from the upper and lower edges of the drop, streams out
radially from all sides, and runs towards its equator, where
the two streams coming from above and below meet, and pass
into a horizontal internal current, travelling from the equator
on all sides towards the centre of the drop. Here this in-
ternal current divides in all cases into an ascending and a de-
scending stream, which feed the two streams first described.
As shown later, this peculiar mode of circulation depends in
every case upon phenomena of extension which come into play
particularly at the upper and lower edges of the drop. Oil
treated in this way with white of egg becomes even after a few
hours totally turbid, and in places has a pronounced frothy
structure. Whether this effect upon the oil is due to the
white of egg itself, or whether it depends on a formation of
soap by the alkali in the white of egg, I leave undecided, though
the latter supposition seems to me the most probable. The
experiments described make it, however, very probable that the
conversion of the oil-drop into foam in the water depends on
its containing soap. Hence the extremely fine oil-foams pre-
pared as above described from drops of a thick mixture of oil
and common salt or cane sugar must also be considered from
this point of view. It is not the mere presence of small particles
of common salt or sugar in the drops that brings about the
formation of a foam, but the first origin of the fine droplets of
froth are rather to be referred to the soap naturally contained
in the oil. The fact that the formation of foam goes on much
more energetically and completely under these conditions may
be due partly to the sugar or salt in the oil producing a stronger
permeation of the oil by the water, and partly to the resulting
infiltration of the oil with numerous drops of salt or sugar
solution favouring the formation of the fine droplets of froth.

NATURE OF THE PROCESS 15

On the other hand, it cannot be well assumed that salt or sugar
furthers the formation of soap in the oil-drops.1

If my view as to the formation of froth in oil-drops is
correct, this process belongs to the category of phenomena
which Berthold, and after him Fr. Schwarz, have termed pro-
cesses of desolution? They understand by this the separa-
tion from one body of another dissolved in it under certain
conditions which remove or diminish the solubility of the
latter. Schwarz gives various methods of producing such
processes of desolution artificially, whereby the originally-
dissolved body, after being separated out from the so-called
" homogeneous mixture," appears in the form x>f drops or
vacuoles. Mastix or resin in weak alcohol, as well as the
precipitation membrane produced from soluble glue (Traube's
/3-glue) by a solution of tannin, are said to show these
vacuoles. For the resins mentioned, the phenomenon is
explained by the fact that they formed a homogeneous
mixture of two bodies, of which one is soluble in alcohol,
the other not; the precipitation membrane produced
from /3-glue consists of a modification which is soluble, and
another insoluble, in H20, and hence gradually exhibits
a process of desolution under the influence of water. It
is of interest that this process of desolution leads, in the
glue membrane, to the formation of frothy honeycomb-like
structures (so-called reticular structures), although here the
ground substance of the membrane certainly does not possess
a really fluid consistency. Finally Schwarz brings in the
" separating out of the fluid droplets of soap, which arise if
oil containing oleic acid is brought into a watery solution of
potassium carbonate, or disodic phosphate, or in weak am-

1 I cannot, however, refrain from referring to a circumstance which does
not harmonise well with the explanation attempted, namely, the fact that
even in drops of chemically pure oleic acid which were placed in water,
minute droplets appear after a little while, although not so plentifully as in
usual olive oil. If the oleic acid had stood twenty-four hours over pulverised
white of egg, the formation of droplets in water was considerably more
energetic and rapid, so that the deeper region of the drop became quite
turbid.

- For this term see the Translator's Preface.

1 6 PROTOPLASM

monia," as an example of similar desolution processes. My
interpretation of the formation of droplets in oil, obtained
quite independently, thus harmonises in essentials with
Schwarz's ideas. I can also cite as a good example of such
a process of desolution, connected with the formation of
frothy structures, the behaviour of the mixture of collodion
solution and clove oil usually employed for fixing sections
on the slide. This mixture, when spread out into a thin
layer on the slide, usually shows a beautiful finely frothy
structure after hardening and removal of the clove oil by
means of turpentine. By colouring the frothy collodion
membrane with aniline stains the structure can generally be
easily studied. Its great resemblance to the fine reticular
structures of protoplasm makes this method of sticking on
sections seem not without its dangers in investigations of
protoplasmic structures. What is the exact course the
process of desolution takes in this case I have not investigated
more closely, but probably the warming of the mixture, as a
result of which the solvent medium common to both the
collodion and the clove oil is driven off, leads to the
separating out of the latter in the form of minute droplets,
until the stiffened layer of collodion finally obtains the
frothy net-like structure.

After determination of the important influence of soap
on the formation of froth in the oil, it naturally fol-
lowed that the employment of a salt suitable for producing
soap, such as K2C03, would cause the process to go on much
more energetically and better. Experiments also showed
the correctness of this supposition. By such a method not
only were the most regular and finely structured froths
obtained, but also a series of important facts upon pheno-
mena of movement and other matters were ascertained in
drops of these froths.

With further experiments, however, it was soon found
that the nature of the oil is of great and all -important
influence upon the formation of good and finely-structured
drops of oil-lather. A fortunate chance had originally
brought into my hands an olive oil that had stood for a long
time in a little bottle, and which happened to be just in the

PREPARATION OF OIL 17

suitable condition for the success of the experiments.
When I made further experiments with freshly bought oil, I
only obtained very defective results. A long course of
experimentation then proved that the fresh yellow oil is, as has
been said, unfit for the experiments, but that one can pre-
pare good material from it, however, by long warming up to
50°-60° C. I heated small samples of unsuitable fresh oil
in flat watch-glasses in thin layers in a warm chamber,
such as we usually employ for embedding objects in paraffin,
and which is kept at a constant temperature of 54° C. The
yellow oil becomes by degrees quite colourless and of a
thicker consistency with continued heating. Under these
conditions the warming must always be continued eight to
ten days or longer, till the oil has attained the proper
consistency. Since commercial olive oil is in all cases very
variable in its nature, which moreover changes with the
age of the oil, the length of time that is necessary for
warming it cannot be determined once and for all, and it
can only be ascertained by repeated testings whether the
oil that is being warmed has gradually attained the right
consistency. Later I attempted to shorten the time of
warming by the employment of higher temperatures — a
method which also works well. Although I did not deter-
mine the point more exactly, the result of my experience
was, that, as a rule, heating the oil up to about 80° C. for
two or three days has the same effect as when it is done at
50° to 60° C. for eight or ten days.

As has been mentioned, the oil becomes considerably
thicker and more viscid during this process. I am further
of opinion that the right degree of consistency of the oil
is of special importance for the success of the experiments.
Oils that have become too thick give very good foams,
but they are unsuitable for the experiments to be described
hereafter, on the phenomena of streaming in the drops
of oil-foam, since the too great viscidity of the oil is with-
out doubt a hindrance to the streaming movements. Later
on I shall make a few remarks upon the special relations of
the froths prepared from oils that have been rendered viscid.

Oil that has become too viscid can in general be cor-

2

1 8 PROTOPLASM

rected by mixture with some that is too fluid. I have
usually improved to some extent my samples of oil in this
fashion.

I will not report here in more detail upon the numerous
experiments which preceded the discovery of the above described
method. Since it seemed an obvious hypothesis that the free
oleic acid mixed with the oil must be of influence upon the
formation of soap and froth, I attempted to improve the unser-
viceable ordinary oil by addition of a few drops of pure oleic
acid; but this addition, as well as that of a volatile oleic
acid (valerianic acid), proved quite useless. The attempt to
obtain a utilisable product by dissolving mutton-suet in the
olive oil met with just as little success ; nor was the olive oil
rendered any more serviceable after separation of the more
easily congealed glyceride by means of a freezing mixture.

As to other oils I experimented with almond oil, boiled
linseed oil, cod-liver oil, and refined bone-oil (watchmakers' oil,
so-called). All the oils mentioned are more or less serviceable
when they possess the proper consistency ; but since, however,
they offered no special advantages, I usually returned again to
olive oil. Furthermore, the manufacture of froth-drops with
Na9C03 and NH4NH2C02 was tried ; but the experiments were,
as a rule, more successful with K2CO3, on which account this
salt alone was finally employed. At the commencement I used
carbonate of potash finely pulverised, and freed as far as possible
from water ; later, however, I convinced myself that the experi
ments succeed better if the salt is slightly damp. Hence I
proceed now to breathe several times on the small sample of
salt, while pounding it in the mortar, till it is moderately damp,
and then to rub it up well with the drop of oil into a thickish paste.
This paste is immediately made further use of in the way described,
since after standing long it loses its valuable properties. Little
feet of paraffin serve for the support of the corners of the cover-
slip in these experiments, since wax, or cobblers' wax, becomes
friable under the action of the K2C03 solution, which is gradually
formed under the cover-slip.

The processes which go on while such a drop of paste placed
in water, is converted into foam are, as far as they can be
observed under the microscope, somewhat as follows. The
drops of the paste when in the water pass into more or less
violent undulatory movements, since here and there particles
of K CO pass from the paste into the surrounding water,

FORMATION OF OIL-FOAM 19

and quickly dissolve in it, and by their action on the oil
call forth, sometimes in one place, sometimes in another,
local extension-currents. At this period, and usually also at
the moment when the cover-slip with the drop of paste is laid
on the drop of water, a more or less considerable number of
small and minute oil droplets separate off from the drop of
paste, for which reason the latter generally becomes sur-
rounded by a zone of such little droplets. If the oil is well
suited to the production of foam, these little droplets become,
so to speak, instantaneously concerted into foam-drops, so
that it can be thus determined with some certainty if
the oil in question is in the smallest degree not quite
suitable. In the drops of paste there gradually1 appears an
increasing number of larger or smaller droplets of fluid, as a
result of which it becomes more and more opaque. From
time to time eruptions of such drops of fluid into the sur-
rounding water take place on its free surface, which are
naturally accompanied in their turn by superficial extension-
currents. These extension-currents doubtless also promote
the conversion of the drop into froth, since, as will be
shown later, violent extension -currents frequently bring
about absorption of the surrounding fluid in the form of
minute drops. In a relatively short time the drop of paste
becomes quite opaque and milky white in transmitted light.
With the extinction of the currents from the interior and of
the superficial extension-currents, the drop, which formerly
had more or less irregular and variable contours, rounds itself
off, for the most part, completely, and then finally remains
perfectly quiescent. This rounding off of the drop usually
takes place in a relatively short time — about one-half to one
hour. After about twenty-four hours the process is entirely
ended, and the drop is suitable for further investigation.

Naturally, with this conversion of the oil-drop into foam,
its volume increases considerably, upon which I shall make
more precise statements below in the proper place. As a
rule, during the process more or fewer bubbles of gas,
i.e. C02, appear in the drop, which are expelled from
the K2C03 by the free oleic acid ; later they gradually
vanish again. I do not, however, think that the forma-

20 PROTOPLASM

tion of C02 is indispensable for the success of the experi-
ments.

Successfully prepared drops are, as has been said, com-
pletely round, and, as follows from this, quite fluid. In
transmitted light they appear of an even dark-yellowish
brown, which was usually a sign to me that the process had
taken a favourable course. They are permeated by coarse
drops of fluid or vacuoles in more or less abundance, while
their evenly frothy general substance is much too finely
structured for its composition to be recognised under these
conditions. On the surface of such drops there collect, as
a rule, more or fewer fine granular structures, which are
probably a hard, not easily dissolved soap. They are of no
importance when they do not appear in too great quantity,
since they can, for the most .part, be washed away by
a current of water. Were the oil too fluid, and hence
unsuitable, foam is not evenly formed throughout the whole
mass of the drop ; sometimes it is only full throughout
of larger drops of fluid, without being properly frothy, while
at other times, between finely frothy portions, there are
to be found more or less homogeneous portions of oil. Of
course these relations can only be made out with sufficient
distinctness when the drops are strongly compressed.

Were the oil too much thickened it lost its fluidity in the
process, as follows from the fact that such drops did not
round themselves off, but retained more or less irregular contours.
Although I am not able to explain this phenomenon properly, I
must nevertheless call attention to it. It seems to show that on
thickening peculiar alterations in the oil take place which I am
not in a position to follow up further, but which, however,
are most important for the success of the experiment. If these
alterations exceed a certain measure, they prove harmful in turn.
As a proof, I may adduce the following. Very strongly thick-
ened and quite viscid cod-liver oil, rendered more fluid with
ordinary cod-liver oil, was made up into paste with K2C03
in the usual manner, and placed in water. At the com-
mencement the drop became quite finely frothy, but towards the
evening the foam had almost entirely broken up, and the next
morning had entirely vanished, all but a few very transparent drops
and some finely granular cloudy masses and threads. Also, the
froths manufactured from very viscid, thick olive oil, which had

APPEARANCE OF THE FOAM-DROPS 21

stood two months in the sun, showed themselves quite abnormal
in the fact that they were very transparent ; for their investiga-
tion no clearing up with glycerine was requisite. By remaining
longer in the weak solution of K2C03 under the cover-slip, these
froths were in like manner relatively quickly attacked and de-
stroyed, while those obtained from moderately thickened oil could
remain without harm in the solution for many days.

As I mentioned above, the extremely minute drops of oil that
are split off become frothy immediately. This fact naturally leads
one to suppose that the production of froth can also be brought
about by placing an oil-drop in a solution of K2C03. Experiments
proved successful, but slowly, with more concentrated solutions
of K2C03, although with a moderately strong solution the
drop was finally changed after some days into an even, fine
froth. A much more energetic formation of froth goes on in
solutions of from 1 to 2^ per cent. The drops when brought
into the solution become milk-white at once, and a circulatory
streaming is set up, similar to that which was described earlier
(see above, p. 14) for the oil-drops treated with white of egg
or soap. The edge of the drop gradually becomes darker and more
opaque, and sometimes retort-shaped processes project from the
surface, in which the very peculiar relations of the currents are
difficult to understand. By continued growth of the dark margin
of the drop, the whole drop finally becomes opaque. After twenty-
four to forty-eight hours the formation of the froth is completed ;
the froth is very fine and regular. Nevertheless, drops of oil-
lather obtained in such a manner proved from various experiments
unsuitable for the observation of the phenomena of streaming,
for which reason I did not continue to employ this method of
preparing foam. I should be inclined to think, however, that with
more elaboration it might develop into a very simple and good
method. It is interesting to note that the oil-drops which have
stood a longer time in a more concentrated solution of K2C03,
without having formed good froths, after being transferred to
water develop quickly into good froths, which harmonises well
with the explanation of froth production given above.

Successfully prepared drops of oil-lather are, as remarked,
completely milk-white in reflected light, and, if at all thick,
quite opaque in transmitted light ; smaller drops, on the
other hand, or larger ones pressed out into a thin layer,
appear brownish yellow in transmitted light. The frothy
structure can be studied without further trouble in the
smaller drops that split off, since they are sufficiently trans-

22 PROTOPLASM

parent. The larger drops require, as was said, clearing
up with glycerine. Although they then become very
transparent, it is nevertheless indispensable for the study
of their structure to compress them more or less strongly,
in order to be able to observe them in a very thin layer.
The thinner this is, the more clearly the structural relations
are shown.

After clearing up with glycerine, the drops are seen to
be diminished very considerably in volume, just as is a
mass of protoplasm under the same conditions. This very
circumstance is, in my opinion, decisive in determining the
structural condition of such drops as foam-like, aad not in
any way as bodies of a net-like or spongy structure. Since
the principal mass of the froths is oil, which is not itself
capable of swelling, the diminution of volume can only
depend on a process corresponding to the so-called plas-
molysis of plant cells. It can only be explained by the
fact that the mass of oil is honeycombed throughout by
numerous minute spaces quite closed off from the exterior,
and filled by a watery fluid, which, when subjected to
diffusion with glycerine, naturally give off more H20 to the
surrounding glycerine than it takes up of the latter. The
consequence will be, therefore, a plasmolytic decrease of size
of the spaces filled with watery fluid, and hence, also, of the
whole drop. For further details on this point see below.

As already mentioned, the microscopic investigation of
such froth-drops shows at once that, as a rule, they are more
or less abundantly filled throughout with larger drops of
fluid (vacuoles, up to '015 mm. in diameter). Very varying
relations are naturally met with in this respect ; occasionally
one obtains drops completely, or nearly completely, devoid of
the larger vacuoles, and which only consist of the finest
foam, while other drops are very full of vacuoles, so that
without closer investigation they appear to possess a coarsely
vesicular structure. Such froths often proved themselves
especially favourable for the phenomena of streaming.
The principal mass, which encloses the larger vacuoles, gives
the impression of an evenly and finely granular structure with
low magnification ; only when investigated with the best and

PROPERTIES OF FOAM 23

strongest systems (Zeiss Apochr. 2 mm., Ap. 1*30 and 1'40),
and by employing strong oculars (comp. Oc. 12 and 18), is
it seen for certain that we are dealing here with a very fine
foam-like structure. Such a very fine microscopic froth
does not, as a rule, appear any different from a macroscopic
soap or beer-froth. There is this difference, however ; the
microscope only represents clearly an image that falls in
one plane, and therefore only brings into view a plane section
through a froth of this kind. Moreover, there are still a
number of relations to be taken into consideration in con-
nection with the peculiarities of microscopic vision ; they
will be further discussed below. As a result, the microscopic
image of such a froth will appear as a meshwork or network,
the meshes of which are formed of the most varied kinds of
polygonal figures. Very numerous transitions from triangular
meshes to those with many angles will be found.

As is well known, a number of laws obtain for the
formation of microscopic froths which Plateau (1873 and
earlier) developed with exactitude, and which are chiefly
as follows. A froth represents a system of thin lamellae
of fluid, the arrangement of which is always such that
three lamellae meet at one edge, each making with its neigh-
bour an angle of 120°. Since each lamella, in con-
sequence of its surface tension, exerts a pull upon the
common edge in which they meet, it is clear, a priori, that
as long as the three lamellae have equal tensions — and this
is invariably the case in ordinary froths — equilibrium can
only be established between the three lamellae under the con-
dition stated. The edges in which the lamellae of froth touch
one another are connected amongst themselves in such a way
that three edges meet in a nodal point, so that the lamellae
form the most varied polyhedral figures, in which the rule
obtains that the angle, which every two neighbouring edges
form in the nodal point, amounts to 109° 28' 16" (see
Plateau, T. I. p. 315). If one attempts to build up a system
of lamellae under the conditions stated, and assumes an equal
length of edge in all lamellae that meet, a system is obtained
composed of nearly regular dodecahedra, a natural result,
since the dodecahedron comes nearest to the conditions to

24 PROTOPLASM

be fulfilled, with an inclination of 116° 33' 54" formed by
the surfaces meeting at one edge, and an angle of 108° which
the edges, that meet at one corner, form one with another.
A soap lather formed of bubbles as equal in size as pos-
sible, visibly consists mainly of dodecahedric alveoli. They
naturally can never, however, be regular dodecahedra, since
the figure is one that does not quite satisfy the conditions to
be fulfilled. Since, however, we are dealing with fluid
lamellae, this deficiency in the angles can easily be com-
pensated, and the condition of equilibrium established, if the
lamellae equalise the difference in the angles of contact, by
curving slightly towards the edges at which they meet one
another. As a natural consequence, only the angles formed
by the tangential planes of the curved surfaces at their edge
of contact amount to 120°. That such curvings of the
lamellae frequently occur in macroscopic froths, so as to
establish conditions of equilibrium, is shown at once by
observation ; similarly the edges are also frequently curved
in the same manner, in order to comply with the condition
that they should form at the nodal points angles of 109°
28' 16" with adjoining edges.

Considering what has been stated, it will readily be
understood that the alveoli of froth may form polyhedra of
the most various kinds, from tetrahedra to those enclosed by
the highest possible number of sides, and therefore that the
image of our microscopic froth will show polygons of very
different kinds. Nevertheless one condition [will always
obtain, that in a nodal point or an edge only three lines
meet one another, which may, however, enclose very variable
angles. The latter point depends, in the first place, on the
fact that in such fine microscopical froths as are under
consideration here, in which the breadth of the meshes
remains, as a rule, under '001 mm., it is not possible to dis-
tinguish in the microscopic image whether the three lines
radiating from a nodal point are the sections of three
lamellae meeting one another at one edge, or whether the
union of three edges is before us. Further, the section, of
the plane of the image may pass through the edge at which
the lamellae meet one another in any sort of way, or rather

MICROSCOPIC FOAMS 25

the edge by which they unite can be orientated in very
different ways with regard to the plane of the image. In
addition to this point there is the fact that in alveoli of such
small diameter, it is, of course, no longer possible to ascer-
tain whether the sections of the lamellae or their edges have
a slight curvature ; as a rule, it is as much as one can
expect if the meshwork can be at all plainly recognised.

This description shows, on the one hand, that, as has been
said, there may occur a great variety of alveoli, a possi-
bility which seemed at first doubtful, and on the other that
one must by no means expect to find angles of 120° or
109° everywhere, so that objections as to the regular frothy
nature of the drops described are not to be raised on this
account. Should there exist a doubt, however, as to whether
the fine meshwork is the image shown by a foam-like struc-
ture, it can easily be set aside by the fact that in such froths,
which are in one part more coarsely, in another part more
finely structured, a transition between the coarser portions
of the foam and the finest can be clearly traced. Since,
however, the former can be recognised with ease and
certainty as froths, this is a proof that the finest portions
also, in which only the network is distinguishable, must
possess the same structure. Still more decisive in this
respect are the results given by the investigation of defective
foams, or such as have been again disorganised by long
keeping, strong pressure, or tne addition of unsuitable fluids.
Such foams contain portions of homogeneous oil in which
are scattered singly droplets varying in size from the
coarsest to the very minutest. In these isolated droplets
of froth, even in the finest of not quite 1 //, in thickness,
it is possible to convince oneself that one is dealing with
more feebly refractile and, since they are always spherical,
fluid droplets. If the tube of the microscope be lowered
a little from the median sharp focus, they increase in
lightness, while by slightly raising the tube, on the
other hand, they become dark. It is further easy to
follow out how, by the gradually increased crowding
together of such very minute droplets, the portions
with a frothy structure originate, and in these in turn

26 PROTOPLASM

it is possible, by lowering and raising the tube, to
determine clearly the same state of things in the finest
meshes (see Photogr. I. and II.) I lay special stress on
this because, as we shall see later, pictures of a fine network
can also be produced by the microscope as optical delusions
when small, strongly refractile granules or spherules are in
close apposition to one another. On this account I must
at once lay emphasis on the fact that, as a rule, I failed to
demonstrate the presence of strongly refracting granules
or spherules of a solid nature in the froths, even with
polarised light, by which they appear perfectly dark when
the prisms are crossed.

The optical relations, just described, of the meshes or
alveolar spaces of the froths, are also definite evidence against
the assumption of a net-like or spongy structure, if such an
assumption still required any refutation after all that has
been stated. But since, however, it is a question of such
extremely fine microscopical relations, that the determination
is so difficult in many ways, attention may be drawn here
to yet another circumstance. We shall see later, that the
froths under the influence of induction shocks show distinct
bursting of their alveoli ; a similar effect can be also pro-
duced by the addition of certain fluids. It is possible to
follow out the way in which neighbouring froth vesicles
or alveoli suddenly burst into one another, exactly as they
do in macroscopic froths. When superficially-placed froth
vesicles suddenly burst to the exterior, the very small drops
of froth take on jerky, springing movements, which is easily
explained by the fact, that at the spot where such a vesicle
bursts the surface tension is suddenly very much decreased.
As a result of this the stronger pressure of the remaining
surface impels the whole drop of froth for a short distance
forwards in the direction of the radius passing through the
spot on the surface at which the vesicle burst.

In the investigation of the fine froths the attention is at
once arrested by the fact that the nodal points in which the
edges1 of three alveoli meet one another are always dis-

1 I speak here and in the sequel of the edges of alveoli, being indifferent as
to whether sections of lamellse or actual edges are to be understood thereby,

NODAL POINTS 27

tinctly thickened and appear darker. It is a consequence
of this that the froth appears with a low power, or with
cursory observation, to be composed of closely-packed fine
granules. The reason of this phenomenon must be chiefly
as follows. If one investigates in macroscopic froths the
union of three lamellae at one edge, or the union of six
lamellae at a nodal point, as the case may be, it is found
that here the lamellae do not simply meet one another, but
that the limiting surfaces of the neighbouring lamellae pass
into one another with a concave curvature (see Fig. 2). A
consequence of this must be, that the edges
are somewhat thicker than the rest of the
lamellae; but since the corresponding rela-
tions in the fine microscopic froths are
much too small for it to be possible to
make out distinctly the true form of these
nodal points, only a general appearance
of a rounded thickening of the nodal points must arise. If
the nodal points of macroscopic froths are studied more
closely, it is further very often seen that they are occupied
by minute air-bubbles, which often bulge them out more or
less into a swelling. This is interesting at once for the
reason that it shows that such small vesicles or bodies in
the froths collect at the nodal points, and further, because
it proves the possibility that in the microscopic foams the
nodal points may in part be thickened by the inclusion of
very small foam vesicles, no longer recognisable as such, which
cause them to stand out more strongly. Finally, yet a
third cause is to be mentioned, which produces the appear-
ance of dark nodal points in the framework of the meshes,
and to which I am now inclined to ascribe an essential
share in this effect. It has been already pointed out that
the optical appearance of the alveoli of the foam, i.e. bodies
of feebler refracting power enclosed in a more strongly
refractile medium, is of such a kind, that when focussed

since, as has been set forth above, this distinction cannot be drawn in prac-
tice. In any case, the three lines that are actually to be observed, which
meet together in the nodal points, are, as a rule, sections through three
lamellre, which meet at one edge.

28 PROTOPLASM

accurately in the middle, they appear moderately light;
with a slightly deeper focus, lighter ; but with a higher
focus, as darker round points. But since even in a
strongly compressed froth a number of layers of alveoli lie
one over the other, with even the sharpest focus, alveoli
must come into vision at the three foci named. Now if
there lies, as will often occur, an alveolus under a sharply-
fpcussed nodal point — one, that is to say, seen with a high
focus — it will produce the effect of making the nodal point
appear as a rounded dark spot, which with the slightest
lowering of the tube changes into a clear alveolus.

The appearance of the nodal points depends in part at
least on this circumstance, yet without doubt another
optical phenomenon must come into consideration. For if
a layer of froth be studied, one so thin that it is formed
only of a single layer of the minutest alveoli, the nodal
points are distinctly noticeable, provided that the alveoli
of the froth are/' not altogether too fine (see Photogr.
I.) It follows fwm this that the nodal points are shown
up even without a layer of other alveoli under them. If
the middle of the alveoli be sharply focussed, the nodal
points appear just as full as the edges of the alveoli, no
darker than the latter, but distinctly thickened, correspond-
ing to the explanation above of the way in which three
fluid lamellae meet one another. If now -the tube be
lowered in the slightest degree, the nodal points show up
as very dark points, resembling granules (see the Photogr.),
while the rims of the alveoli connecting them appear con-
siderably lighter, and the contents of the alveoli much
lighter still, of course. The appearance of dark granules
deposited in the nodal points is so strong that only the
complete absence of such granules in the finely drawn out
and apparently quite homogeneous marginal portion of such
a very thin layer of froth, or in other cases, the want of any
such granules in the parts of the oil that are not frothy,
puts an end to the idea of very minute granular depositions.
That we are here dealing with a special optical phenomenon,
and not with granular contents, or with a special structural
relation of the froths, is plain at once from the fact that

GRANULAR APPEARANCES

29

this phenomenon, as has been said, is only to be observed
by focussing somewhat below the middle line. An explana-
tion of it may be found in the following considerations. If
small, closely packed air-bubbles in a thick solution of gum
be studied under the microscope with a low power, by focussing
as sharply as possible on the equator of an air-bubble it is
seen that in the dark marginal zone, where each bubble
touches a neighbouring one, a clear spot of light makes its
appearance, so that in two neighbouring bubbles these spots
always stand exactly opposite. Nageli and Schwendener
have already (1865) made a theoretical investigation into
this phenomenon, and have referred it to the reflection of
light at the underside of the air-bubbles. If now the tube
be lowered slightly from the middle focus, the clear spots
decrease in brightness, but become, on the other hand,
broader, so that they traverse the whole dark marginal zone
as radial light bands ; simultaneously the bands of
neighbouring air-bubbles ms-h-vis to one another become
confluent, so that one obtains a land of clear net, which is
stretched out at the point of contact between the air-
bubbles. Now since in our froth lamella we have before us,
in the same way, very closely crowded droplets of a less
refractile fluid in one more strongly refractile, something
similar must take place. The clear, radial bands produced
by reflection of the light will be relatively very broad here,
since the diameter of the vesicles is very small. These
clear bands naturally fall on the middle portions of the
edges of the alveoli and make them lighter, while the nodal
points become no lighter, and hence appear relatively dark
by the effect of contrast.

I take this opportunity to state that in successfully
prepared good froths I could not demonstrate any granular
structures whatsoever, which by their deposition had in any
way added to the actual distinctness of the nodal points.
It was rarely that I observed in some froths rounded bodies,
more or less scattered, of about the size of a small alveo-
lus, and hence having nothing to do with the nodal
points.

Since the problem with regard to the true structure of

30 PROTOPLASM

the oil-foams was not so easy to solve as it might have
originally seemed, on account of the fineness of the micro-
scopic structure, and since, in particular, it was difficult to
decide, by simple observation, whether it was possible for
granular deposits to make their appearance in consider-
able quantity in addition to froth vesicles, I took great
trouble in various ways to find out a method of reducing
the froths again to some extent. Since, as has been men-
tioned, strong induction shocks call forth continued bursting
of the froth vesicles, I tried if it would be possible to obtain
the desired effect by long-continued action of the inter-
mittent current. The result was, however, a negative one.

Finally, chance led me, as is so frequent, the correct way.
If drops of foam, well washed out with water, be left to
stand undisturbed under the cover-slip without addition of
glycerine, the water gradually evaporates, and the drop of
froth thus coming into contact with the air gradually loses
its frothy nature again completely. • The water of the froth
vesicles slowly evaporates (or rather the latter burst, partly
from the contact of the air with the surface of the froth-
drop), and the soap left behind dissolves in the oil. Thus,
after some days the drops have again become as perfectly
clear and transparent as the oil originally employed for their
preparation. The smaller and the minutest drops then
show no trace of any deposits, even when viewed with
the strongest magnifications, while the large drops still
contain isolated small froth vesicles. Granular elements,
however, are either entirely wanting in the drops, or only
isolated granules are to be found, of medium size and
moderately strong refractile power. As has been said, when
they are present, they occur in such small quantity as not
to interfere in the least with the transparency of the drops.
Once I also saw fairly large clear crystals, approaching in
form to rhomboidal plates, together with needle-like crystals
in very limited quantity in the drops, as well as some gritty
bodies, which perhaps had arisen by strong compression
of such crystals.

From these results it can hence be concluded with
complete certainty that solid deposits do not occur to any

FLUIDITY OF OIL- FOAMS 31

considerable extent in the foams, and that, therefore, their
structure depends solely on their nature as foam.

This conclusion receives further confirmation from a very
interesting circumstance with regard to the perfectly clear and
transparent oil-drops that are obtained in the way described
from froths. If water is allowed access afresh to drops of this
kind, the smaller and the more minute ones become changed, as
if by a magic touch, instantaneously into the most beautiful drops
of foam again, with all the characteristic structural relations
described earlier. The larger drops also become frothy at once
down to a considerable depth, and in a relatively short time have
again acquired a frothy consistency throughout. This astonishing
behaviour may be explained by the fact, that with the drying
up of the froth-drops the soap l contained in the froth vesicles is
again taken up by the oil and dissolved, so that in this way a
drop of oil is formed richly impregnated with dissolved soap,
which, with addition of water, at once passes rapidly back into
froth again. If, therefore, we may see in this process, on the
one hand, a further confirmation of our views as to what goes on
in the formation of the froths, it offers, on the other hand, also
one of the finest examples of a so-called desolution process. From
all that has been stated, it can be concluded with perfect certainty,
that my view as to the structure of the froth-drops is well
grounded, and agrees with all the results of observation.

In successfully prepared froths the breadth of the finest
meshes varies between about '005 mm. and '001 mm. or
less. When such drops of froth remain undisturbed for some
weeks, the alveoli gradually become arranged in layers
corresponding to their relative sizes. The finest froth
collects in the uppermost layer, and further below it becomes
coarser and coarser. If the drop was defective in froth, so
that homogeneous oil was present in addition, the latter
gradually assumes the highest position in the drop. This
phenomenon naturally depends on the greater specific
gravity of the contents of the alveoli in comparison to
the oil, but offers, however, a further proof of the complete
fluidity of the froths as well as of their frothy structure,
since neither net-like nor granular structures could behave in
this way. One can, moreover, easily convince oneself of the

1 Or other unknown substances also, which assist in the formation of froth.

32 PROTOPLASM

fluid nature of the froths, a fundamentally important fact, by
pressing, inclining, or pushing them, by which it is proved
that well prepared foams are perfectly fluid, and flow scarcely
more slowly than the oil employed in their preparation.

A phenomenon of especial importance is exhibited by the
surface of successfully-prepared foams of even composition.
With moderate magnification they appear surrounded by a
delicate, somewhat clearer border. To the exterior this
border is limited by a sharp and rather dark line ; to the
interior, its limit in like manner appears fairly sharp, though
less so than externally. Investigation with the highest
magnification proves that this border is delicately and
minutely striated vertically to the surface (see Fig. 4,
Plate V., and the Photographs III. and IV.) The com-
parison with the system of alveoli of the neighbouring deeper
portions of foam, which are immediately within the border,
show in the clearest manner that we are only dealing with
the outermost layer of the alveoli, directed radially to the
surface, which gives rise to the border. From these results
it is also easy to understand that this border can only
come into prominence in a froth of composition as regular
as possible, for if the meshes are very irregular in size an
even border cannot well be formed.

The thickness of this border, which I have named the
alveolar layer, naturally depends on the size of the alveoli of
the foam ; if they are of considerable size, the border also
will be thicker. In the foams investigated by me the thick-
ness of the alveolar layer varied between about *0005 and
•005 mm.; alveolar borders so thick, however, were only
observed here and there in foams prepared with NaCl ; in
the fine ones prepared with K2C03 they were never thicker
than between '0005 and *0007 mm. Eecently, however, I
have frequently observed coarser foams of the latter kind
which possessed very fine alveolar layers (see Photogr. IV.)
of greater thickness.

The origin of the border is easily explained, since it is
only a consequence of the laws which the arrangement of
the froth lamellae obey. As has already been pointed out
several times, the froth-drops are completely fluid, so that

MICROSCOPIC FOAMS 33

they assume the shape of a spherical drop, if not acted upon
by any special influence, whether from within or from with-
out. Their surface will therefore be curved like that of a
sphere. Nevertheless, it is of course impossible for the
surface of such a froth to be a simple spherical surface ;
the tension of the lamellae, which attach themselves to
the surface, naturally tend to bring about a dipping in of
the surface at these points of attachment, so that each
alveolus or froth vesicle of the superficial layer projects
slightly over and above the general surface of the sphere, even
though with a very feeble curvature. As a matter of fact,
I could never observe this projection of the alveoli of this
layer with perfect distinctness in the finest froths, although
it often wore the appearance; on the other hand, in the
coarser ones it was very prominent (see Photogr. III.) At
the point of insertion of a lamella reaching to the surface,
the tensions a and & of the two external curved lamellae
(see Fig. 3), touching one another, come into effect, and
maintain an equilib-
rium with the ten-
sion c of the lamella
first mentioned. If
this most external
layer of froth is formed
of alveoli of equal size,
it is easy to see that

the lamellse of the external layer that reach to the surface
must all be placed vertically to it, so that equilibrium may be
established. Since, however, the three lamellae meeting one
another in one edge at the surface — or rather their tangen-
tial planes — must form angles of 120° each to each, at the
edge in which they meet, if both the external lamellae lie
nearly in the general surface of the sphere, then the lamella
reaching from the interior must be directed radially to the
surface, in order to form equal angles with both of them.

One question still requires consideration before we
proceed to further investigations. It was noticed that the
drops of oil-lather behave as an ordinary fluid, inasmuch as
when other factors are excluded, they assume a spherical

3

34 PROTOPLASM

form. But since one is accustomed to see macroscopic
froths in very varied forms, this point will require still some
explanation. The spherical form of drops of fluid can be
interpreted as a consequence of the capillary pressure
produced by surface tension, which, as is well known, is
always directed towards the centre of the curvature of the
surface, and is inversely proportional to the radius of the
curvature. Hence, a freely suspended mass of fluid will
only attain to a condition of equilibrium when the surface
tension is equal at every point, a state of stability only
realised in the spherical form. If we consider our froths of
microscopic fineness, and very regular composition, their
surface cannot be taken as the surface of a regular sphere,
although this fact is not sharply recognisable ; but we must
certainly assume, as I have already shown, that each of the
superficial alveoli projects with a feeble convexity. As a
consequence, the capillary pressure must be the same over
the whole surface if equilibrium is to be established. A
curvature of the surface differing in strength or in direc-
tion must doubtless exert an influence on the capillary
pressure, even though not directly, as at the surface of a
homogeneous fluid, but by alteration of the curvatures of
the single components, i.e. of the convex bulging surfaces
of the superficial alveoli. A more accurate study shows
that the more curved is the general surface, the stronger
must be the convex curvature of each individual bulging
surface, and vice versa. But since the total surface pressure
represents the sum of the effects of the pressures of each
single bulging surface, and their pressure becomes greater
towards the interior in proportion as they are more convex,
it follows that such a froth behaves in general as an ordinary
fluid, the pressure of which increases and diminishes with
the curvature of its surface. If this is the case, then such
a froth must assume the spherical shape as the one form in
which equilibrium obtains, and only show other shapes under
the influence of special external and internal forces.1

1 The above remarks can be represented more accurately in the following
manner. If the surface of the froth is level, the radially-directed lamellae of
the most external layer of froth will be vertical to the outer surface, and

ALVEOLAR LAYER

35

The fluidity of the described froths naturally demands
that the so-called alveolar layer should also be fluid.
Although the distinctness and sharpness with which it

hence parallel to one another. Under these circumstances the lines of section
ac and be, which the two tangential planes at the points of attachment (a and
b) of the two, neighbouring radial lamellse produce with the plane of the

a

Fig. I.

d
Fig. II.

paper, will form at their point of intersection an angle of 120°, as follows at
once from the triangle abc. If, however, the surface is curved, the two
neighbouring radial lamellae will not be parallel, but will form an angle /3 with
one another (see II.) Then it follows from the quadrilateral acbd, that the
angle which the two tangential planes include at c=120°-/3. Mutatis
mutandis, it follows in the same manner that with a concave curvature of the
whole surface, the angle included by the tangential planes = 120° + p. But since
the transverse measurement of the alveoli ab evidently always remains nearly
the same (in any case it does not increase, but, if anything, becomes smaller),
then as the angle c diminishes the radius of the segment of the circle described
in it becomes smaller, and hence the curvature stronger, and vice versa.
That with strong curvature of the surface the transverse measurement of the
alveoli must, as has just been pointed out, become less, but in no case greater,
follows from the following'considerations. Since, as is well known, the sphere
is that body which, with the same volume, possesses the smallest surface, a
portion of froth imagined as limited by plane surfaces will continually
diminish its surface during the transition into the spherical form, from which
it follows that this change of form is not accompanied by any tendency to
widen out the alveoli of the alveolar layer, but that they would rather tend,
on the contrary, to become narrower. The same reasoning holds, however,
also in the spherical rounding off of a portion of the froth, the surface of
which presented various degrees of curvature.

With regard to the question discussed here, it is of special interest to note
that Budde (Zeitschr. f. physik. Chemie, Bd. vii. 1891, p. 586) has recently
shown that fine emulsions of chloroform droplets, which arise by the
action of soda on a solution of chloral, show a distinct tension in relation to
the remaining fluid, and hence form a constant marginal angle with the wall
of the vessel.

36 PROTOPLASM

stands out in successfully manufactured drops might well
awaken the supposition that one is dealing with a skin-like
hard covering, yet more accurate investigation shows its
complete fluidity. It is quite astonishing to see how easily
such drops, together with their border, flow along, and how
the latter, in spite of its fluid nature, maintains itself
throughout. This again just shows that it owes its origin
to physical laws, which continue to act during the move-
ment of flow.

It is at once readily understood that the same conditions
which give rise to an alveolar layer at the surface of the
froths must bring about the formation of a similar radiate
layer round each of the more considerable vacuoles in their
interior. This is also entirely confirmed by accurate in-
vestigation of the froths (see Photogr. I.-III. and V.) Every-
where one notices round the vacuoles the finely striated
border, depending on the radiate arrangement of the lamellae
arranged closely round the wall of the vacuole. As a rule,
I only found a distinction between the external alveolar
layer and this border to the vacuoles to the extent that
the latter was usually not so sharply and distinctly marked
off from the neighbouring irregular alveolar substance as was
generally the case with the external alveolar layer.

It was mentioned above that the alveolar layer is
marked off from the external fluid by a sharp, dark border,
which appears like a delicate darker skin or pellicle. Since
ordinary drops of oil also appear, when sharply focussed, to
be limited by a corresponding delicate dark border, I am
convinced that this border limiting the alveolar layer is no
special structural feature, but only an optical phenomenon.

In the account given of the alveolar layer, emphasis was
laid on its formation out of very small alveoli quite regular
in size. In general it is a striking fact in the in-
vestigation of the froth-drops that their peripheral, and
therefore, of course, their entire superficial region, consists, as
a rule, only of very minute or small alveoli. Larger ones,
up finally to those so considerable in size that they merit
the denomination of vacuoles, make their first appearance at
some depth below the surface. This phenomenon shows up

APPARENT HOMOGENEITY 37

most distinctly in the photographs of these foams which
supplement this work (see Photogr. I.-IIL) Although I am
not able to give any plausible explanation for this state of
things, it seems to me not without significance, especially with
regard to similar phenomena in protoplasm. Even in the
drops of foam photographed in I. and II., which were
adhering to the underside of the cover glass, and hence were
drawn out to the smallest possible thinness, this phenomenon
shows up distinctly ; in fact, a progressive diminution of
size towards the edge can be observed in the alveoli. The
most external and thinnest marginal region of this adhering
drop at first gives the observer the impression of being made
up of quite homogeneous oil, and not of alveoli; and it
would of course be conceivable that with such a minimum
thickness of the layer of oil, the foam vesicles would be
pressed out of it, so that an outermost border of homo-
geneous oil would be formed. Very careful observation
shows, however, that this apparently homogeneous border
really exhibits very faint indications of frothy structure.
In the photographs this can be plainly recognised in places.
So far as the size of the alveoli in this apparently homo-
geneous external margin can be ascertained in the photo-
graph, it is about the same as the size of those in the more
sharply defined zone bordering on it.

On what does the fact depend of the alveoli of this
external margin being so pale and indistinct that it appears
all but homogeneous ? Since the layer of oil becomes
thinner and thinner towards the margin until it finally is
reduced to a minimum, it may for one thing depend upon
the fact that the delicate most external lamellae between
the vesicles of the foam become shallower and shallower, and
naturally at the same time fainter (see Fig. 4). Moreover,
the foam vesicles in the external zone,
which runs out quite flat, must them-
selves be very strongly compressed

from above downwards, and hence pressed strongly against one
another laterally, which necessarily causes an attenuation of
the oil-lamellaa between them to a minimum of thickness.
Both these factors taken together may explain, as it seems

38 PROTOPLASM

to me, why only traces of frothy structure are to be found
in the external margin.

Yet a further point may be touched upon at this oppor-
tunity. In the manipulation of these drops of foarn under
the cover glass, one has occasion to observe, if the drops stick
more or less to the glass, that fine lamellae or threads of the
frothy mass stretch across between drops squeezed apart.
I was able to observe fine lamellae of this kind, which con-
sisted of only a single layer of alveoli, in optical section,
when it could be seen most distinctly that, as was to be
expected, the partitions between the alveoli stand vertically
to the two surfaces of the lamella (see Fig. 4, Plate X.) In
the finest threads, which stretch out between neighbouring
drops and naturally break very soon and become retracted
into the contiguous portions of froth, I could not observe
any structure, and hence believed formerly that they were
only formed of the ground substance of the froth, i.e. oil.
But I have become somewhat doubtful on this point in
consequence of my experiences with regard to the scarcely
recognisable frothy structure of the greatly attenuated mar-
ginal portions of drops already described, and now prefer to
assume that such finely drawn-out threads also retain a
frothy structure, but that their structure .can no longer be
plainly observed from causes similar to those obtaining in
the strongly attenuated marginal portions. In every case
where such threads show even the slightest swelling, the
latter is always distinctly frothy, even if occasionally only
composed of quite a few alveoli.

2. Some more exact Statements as to the Alterations in Volume
of the Drops of Foam under the Influence of the sur-
rounding Fluid

Since it seemed to me of great importance for the correct
explanation of the froths, to determine somewhat more
accurately the alterations of volume already mentioned, I
recently performed some experiments which were directed
towards solving this question. For this purpose two narrow
glass strips of 0*20 mm. in thickness were fastened with

CHANGES IN VOLUME 39

paraffin on a slide parallel to one another. The layer of
paraffin between these strips and the slide was of excessive
thinness, as the strips were pressed firmly down on the
melted paraffin. The cover-slip with the drop of oil mixture
was then placed on the strips, and the water so far drawn
off from under it that the cover glass was firmly pressed
down upon the slips. Then the edges of the cover glass,
which rested on the glass strips, were firmly cemented with
melted paraffin from without. In this manner the distance
between the cover glass and the slide was kept sufficiently
constant, so that in the experiments to be described in the
sequel, errors of any kind, through pressure of the cover
glass on the drops, appear to be excluded.

Two preparations set up in this manner contained each
three drops of the oil mixture, which may be denoted by the
letters a, b, c, and d, e, f.

On the 28th May, at 11 A.M., immediately after setting
up the preparation, the drops showed the following diameters.
The sign (m) added to the numerical statement indicates
that the drop in question was not quite circular, so that the
statement represents the arithmetical mean of the greatest
and least diameter.

I. — Diameter of a = 0-720 (m)
6 = 0-488

c = 0-565

d = 0-385
e = 0-469
/= 0-803 (m)

At 6 P.M. on the same day the volume of the drops had
already much increased, and on the 29th May, at 10 A.M., it
had grown still more strongly, as shown in the following
table :—

28/5. 6P.M. 29/5. 10A.M.

II— Diameter of a = 1'336 (m) 1'605 (m)

6 = 0-951 (m) 1-084 (m)

c= 1-092 (m) 1-503

d = 0-707 0-784

e = 0-925 0-997 (m)

/= 1-388 1-481

40 PROTOPLASM

After the last measurement on 29th May, at 10 A.M. (see
Table II.), the preparations were thoroughly washed out with
semi-dilute glycerine, and then left to stand in this fluid.
After about an hour the drops had already become much
smaller. Since the drops e and / flowed together after a
short time, this preparation was not further taken into
account. The decrease of volume was further maintained,
so that the diameters of the three drops of preparation I.,
which had again become completely round, were, at 9.30
A.M. on the 30th, about as follows : —

III.— a = 0-899
b -0-572
c = 0-668

The glycerine was then washed out with water ; the increase
in size of the drops was quite visible in an hour's tune, and
their diameters on the following day, 1st June, at 11.30 A.M.,
had attained the following dimensions : —

IV.— a =1-747 (m)
b= 1-285 (m)
c= 1-567 (m)

As results from a comparison with Table II., the dimen-
sions of all three drops are now somewhat larger than at
first, which no doubt depends on the fact that originally
they were not formed in pure water, but in a weak K2C03
solution, which, like glycerine, naturally exerts an osmotic
effect.

Finally, on the 1st June, the water was once again
replaced by half-diluted glycerine. The drops now adhered
somewhat strongly to the glass, so that with the contraction
that took place they became more or less sausage shaped.
Their diminution in size was again speedily very striking,
and by the following day, 2nd June, at 10.15 A.M., they
shrank to the following dimensions : —

V.— a = 0-937 (m) [ + 0'038
6 = 0-609 (m) [ + 0-037
c = 0-673 (ro) [ + 0-005

RADIATE APPEARANCES 41

If one takes into regard the errors which necessarily
result from the somewhat irregular shape of the drops, the
agreement in the size of the drops with that which they
previously possessed in glycerine (see Table III.) is quite
striking. I have added to Table V. in square brackets the
differences of measurement as compared with Table III.
This reaches the maximum in one drop of 6 per cent. I do
not doubt that the repetition of the experiment would have
succeeded oftener still, but I had no occasion to continue it
further.

If the demonstrable and indubitable fluidity of the froth-
drops be taken into consideration, the observations here set
forth upon the plasmolysis of the drops, as the process may
aptly be termed, may serve to remove all doubts which could
be raised, and which have already been raised by Frommann
(see further below), as regards the frothy nature of the drops
prepared by me.

Since to many people the notion of a diffusion of watery
fluids through lamellae of oil is somewhat unusual, though the
experiments related here prove it occurs beyond a doubt, I
have also performed some experiments on this point with
aniline colours. If the drops are brought into a moderately
concentrated solution of methyl green in water, they are
coloured strongly greenish blue after about twenty -four
hours, and after forty-eight hours the colouring had even
gone completely through the larger drop (diam. about 1*5
mm.), though after twenty-four hours it still showed a white
centre. By pressing the drops more strongly it could be
plainly made out that the contents of the alveoli were
coloured green, and hence the solution of methyl green had
penetrated into the alveoli.

3. Radiate Appearances in the Drops of Oil- Foam

In good froths, which have stood quietly for some time,
a more or less pronounced radial striation can be not in-
frequently observed, as well beneath the whole surface, as
round the larger vacuoles of the interior. This radiate
appearance can usually be increased, or even produced, if,

42 PROTOPLASM

in a drop made transparent by half-diluted glycerine and
strongly compressed, a diffusional exchange of fluid be set
up, either by adding concentrated glycerine, or by the
addition of water. Concentrated salt solution has also been
occasionally employed with good results. As has been said,
after some time one observes in places, or in successful pre-
parations over the whole surface of the drop, fine radiate
markings directed radially to the surface, which penetrate
more or less deeply into the froth-drop, sometimes even
to a considerable distance. The radial striation often
appears especially well marked round the larger vacuoles
of the interior, and it then attains not infrequently an
extension equivalent to the diameter of the vacuole. A
closer microscopic investigation of this radiate appearance
shows, that it depends on the meshes or alveoli being dis-
posed one behind the other in a more or less pronounced
radial arrangement. I have convinced myself of this in the
clearest manner, and the photograph (VI.) of such a radiate
structure, which is in my supplement to this work, also
shows this to some extent, although unfortunately it was
taken from a very defective preparation, and has not itself
come out particularly well.

The conditions under which these radiate markings are
especially produced are of themselves a proof that diffusion
currents play a part in giving rise to them. I am not able
to give more precise information as to the manner in which
the influence of the diffusion is expressed by them, but it
appears to me certain, as has been said, that the diffusion
between the contents of the alveoli and the surrounding
medium, or the contents of larger vacuoles, is the primum
movens in the process.

A peculiar observation which I frequently made on oil-
drops appears to me to belong to this same category of
phenomena, and perhaps it throws further light on the
appearances already described in the foam-drops. In my
experiments I often used oil evenly mixed with a lamp-
black purified by extraction, with alcohol, or by heating to
the glowing point for some time. When drops of such an
oil were brought into water, it could usually be very

RADIAL STRIATION 43

plainly seen under the microscope that the particles of
lamp-black at the superficial region of the oil-drop, down to
a greater or less depth, arranged themselves after a short
time in rows, all directed radially to the free surface of the
drop. As a result the marginal zone presented a beautiful
radiate appearance to a greater or less extent. As has
been mentioned, this phenomenon appears in ordinary drops
of olive oil, usually with great distinctness. I obtained it,
however, still better and more distinctly when some particles
of anhydrous calcium chloride were enclosed in the oil-drops.
Crystals of nitre served in the same manner ; on the other
hand, the inclusion of drops of glycerine in the oil was not so
good. With enclosures of the kind named a radiate striation
could often be observed round the drops of solution of nitre
or calcium chloride, which had become formed round the
particles enclosed in the oil. The fact, therefore, that these
radiate appearances are also strengthened by the diffusion
processes, which are doubtless set up by the particles enclosed
in the oil-drops, appears to support the view expressed above
as to the cause of the striation in the drops of oil-lather.
If it were possible to introduce into the foam-drops particles
of some substance that attract water strongly, I think that
radiate appearances would appear much more marked. Un-
fortunately no means for effecting this have as yet been in
my power, since the drops break up on raising the cover
glass.

The very same radial striation can, moreover, be easily
observed in drops of paraffin oil mixed with fine lamp-
black, and it therefore does not depend directly on the
chemical quality of the oil. I have frequently repeated
of late the experiments with paraffin oil which were per-
formed at an earlier date, and have again observed radiate
appearances very well and very distinctly. Indeed I have
obtained the impression that they develop quicker and
better in paraffin oil than in olive oil. Since radiate
appearances can also appear under some circumstances as
optical effects round air-bubbles, I may lay special emphasis
on the fact that the radial striation in the oil or froth-
drops makes its first appearance gradually, and frequently

44 PROTOPLASM

reaches so far towards the centre as to set aside any doubt
as to the reality of what has been described.

The radiate arrangement of the particles of lamp-black
was first observed when I studied the action of the electric
current on the drops. Under the influence of the constant
current the radial striation as a rule appeared very soon ;
nevertheless I should not like to assume off-hand a closer
connection between this phenomenon and electrical pro-
cesses.

4. Fibrous Structures in Drops of Oil- Foam

In the ordinary drops of oil-foam, which showed well
the phenomena of streaming that are to be described later,
it was often observed that an appearance of fibres was
noticeable at the so-called centre of extension-currents, i.e.
at the spot where a current from the interior reaches the
surface and thence flows away superficially on all sides.
The fibres followed the paths of the currents in their course,
and hence resembled to some extent a bundle of sheaves
passing out from the interior to the surface, where they
spread out. This appearance was naturally not immut-
able, but became modified in details more or less, since the
spot in question was the seat of continuous streaming move-
ments.

If the very much thickened and exceedingly viscid olive
oil, already mentioned on p. 20, was worked up with K2C03
into froth-drops in the way known to us, there were formed,
as has been already described, finely structured foams of
great viscidity and transparency, but quite good in other
respects. Since, however, they take the shape of irregularly
lobed masses between the cover-slip and slide, and no longer
assume a spherical form like the ordinary well-prepared
froths, it is clear that they are no longer fluid, but rather
deserve to be termed of a solid nature, or at all events they
are in an intermediate condition of consistency to which the
term solid is more appropriate. This also follows from the
fact that these froth-drops do not show the slightest ten-
dency to streaming movements, and when squeezed or pressed
do not begin to flow. If they are drawn out by pressure

EFFECTS OF TENSION 45

into threads or bridges, which finally break through in the
middle, the broken halves of these threads certainly contract
to some extent, but they do not gradually flow back per-
fectly, as they ought to do in a fluid froth.

Any one who has followed out the gradual thickening of
the oil used will allow that in this process a sharp limit
between a firm and a fluid condition can be drawn just as
little as in the drying up of a solution of gum, but rather
that both conditions pass gradually one into the other.
Hence, for the foams just spoken of the consistence cannot
be stated with absolute definiteness.

If such foams, the microscopic character of which is on
the whole just the same as in the case of the more fluid
foams, be subjected to pressure or tension, e.g. by rapidly
drawing off the fluid under the cover glass, they naturally
become stretched and drawn out in certain places or regions.
Here and there portions of the foam are forced apart ; be-
tween the portions coarser or finer threads are stretched
like bridges. The very variable appearances that may
chance to be formed in this way scarcely require more de-
tailed description. It can be seen in them, however, that
wherever the action of such tensions makes itself felt,
fibrous structures appear (see Plate VI. Fig. 2, a, 6). In
the stretched threads, which are spread out like bridges, it is
naturally at once seen that the direction of the fibres
coincides with the direction of the pull to which they are
subjected. A more thorough microscopic investigation
leads, as was to be expected, to the result that the fibrous
appearance solely depends upon the extension and stretching
of the meshes in certain directions. Thus, for example,
one can often discern plainly in the fibrous bridges stretched
between two portions of froth, how the drawn out
fibrous framework of the bridge passes into the usual
irregular framework of the portions that are not stretched.
Not infrequently also, in the larger portions of froth pressed
out in this way, one remarks quite irregular and tangled
fibrous structures, which can easily be explained by the fact
that at these spots simultaneous or successive strains took
effect in different directions.

46 PROTOPLASM

The distinctness of this fibrous modification of the
alveolar structure in the froths described is naturally
only a consequence of the great viscidity of the substance
of their framework, which causes the meshes to persist
for a longer time in a state of tension. When the
framework is a more fluid substance, as in the ordinary oil-
lathers, a fibrous structure will also appear as the effect of
tension, but it will change again rapidly into the ordinary
condition. /If, however, the action of tension remains persist-
ently in Certain spots in the same direction, and the ground
substance is fairly fluid, fibrous structures will still possibly
come under observation. A case of this kind is that
formerly described in streaming froths, and we shall fre-
quently come across similar cases in the description of proto-
plasmic structures. It appears to me a point of a certain
degree of importance, that the froths described as having
a nearly firm framework show no marginal alveolar layer.
This fact appears to me quite intelligible, since the laws
which cause the formation of the marginal alveolar layer
only attain their full power under the condition that the
framework is a perfectly fluid substance.

5. The Durability of the Oil-Foams

The oil-foams can be kept for a relatively long time.
When put up in glycerine they show no noticeable change
for four to six w^eks. Then, however, the froths gradually
deteriorate, slowly becoming coarser in structure through the
bursting of the alveoli. At last, also, homogeneous portions
of oil, no longer of a foam-like structure, appear in them.
I have not followed out more closely the process of degenera-
tion in the froths.

We have, as yet, only studied the drops of foam under
the cover glass. If the cover glass be taken off, the drops
as such break up, since they are somewhat specifically
lighter than the surrounding fluid (H20 or glycerine), and
hence ascend to its surface. Here they spread out into a
thin layer, which, sending out numerous irregular processes,
breaks up into small drops. In breaking up, however, the

MOVEMENTS OF FOAM-DROPS 47

foam-like nature of the drops remains unchanged, even when
the preparation is left uncovered for a long time.

6. The Phenomena of Streaming Movement exhibited ty the
Oil-Foams

If successfully manufactured drops of oil-foam, obtained
from oil correctly prepared according to the above prescrip-
tion, be carefully washed out with water under the cover-
slip — an operation effected in the well-known manner, by
drawing water through with filter paper, and best done from
the two sides alternately, in order to remove any solid
particles adhering to the surface of the drop — then striking
processes of movement are at once set up in the drops. As
long as they remained in the weak solution of K2C03 they
were perfectly quiescent. The movements of the drops of
foam, when free from pressure and hence quite opaque, take
place in such a manner, that without any striking change of
shape, they creep somewhat rapidly backwards and forwards,
under the cover glass. At the same time, the direction of
movement changes fairly often, though it also happens that a
drop may retain for a long time, or permanently, the direction
of movement it has once taken up.

As has been said, the movements of progression were
frequently very energetic; thus, I once observed a drop
which in one minute traversed 0*45 mm. ; usually, however,
the forward movement was less rapid. When it was re-
marked above that these movements go on without particular
changes of form, the statement is so far correct, that the
changes are not very striking ; still, they are not wanting.
Frequently the drops become somewhat elongated in the
direction of the forward movement ; bulgings out of the edge
also appear here and there, which, for the most part, quickly
vanish again. A change of shape is therefore not wanting
—only, on the whole, it is slight. In spite of the great
opacity of the drops, it can be observed that lively streaming
phenomena take place in them. Every bulging out of the
edge is accompanied by a stream which starts from the
interior, and spreads out on the surface ; the creeping pro-

48

PROTOPLASM

n(\ I - i

1

V

I

cry ••••"I

gressive movements are without doubt in connection with

o

such streamings, although no definite conclusion on this
point can be obtained in the opaque drops.

To obviate any possible objection that pressing the
cover glass or anything of the sort may cause the move-
ments of the drops, I remark especially, that experiments
were also carried out with perfectly firmly fixed cover glasses,
which rested on strips of glass fastened with paraffin, and
that just the same results were then obtained.

If the water be slowly replaced under the cover glass by
semi-dilute glycerine, a system of very energetic circulating
currents is gradually set up in most drops, such as has
briefly been mentioned earlier for certain oil-drops (see Fig.
5). Thus, from the upper edge of the drop, which is in

J)

y///////M////M//////M//^ 0

Fig. 5.

contact with the cover-slip (D), as well as from the lower
edge, which lies on the slide (0), a superficial current,
streaming out on every side, travels towards the equator (a),
where the two streams unite and now pass inwards as a
common stream towards the centre of the drop ; from this
spot the centripetal stream bends upwards and downwards
into the two currents first mentioned. It may be observed,
however, in drops displaying such a streaming motion, that
frequently streams suddenly start here and there from the
interior towards the free edge, and disturb the circulation
described, though it usually soon regains the upper hand.
Small drops, however, which rest on the floor of the slide,
not infrequently show from the first another mode of
streaming, viz. an axial stream passes out from their in-
terior towards a point of the equator, spreads out here on
every side, and rushes along in the superficial regions towards
the hindmost point, where it gradually bends round again
into the axial forward stream. The mode of streaming last

MOVEMENTS OF FOAM-DROPS 49

described is, as a rule, connected with a forward movement
of the drop in the direction of the axial current. If such
drops are watched for some time, a slowing down of the
axial current, and the appearance of a new one, directed
towards another point of the edge, can often be observed,
upon which the drop naturally moves forward in the new
direction.

If the larger drops, which show the above described
circulatory streaming, are more or less pressed by the cover-
slip, an object best effected by pushing a splinter of a
moderately thick cover glass under the edge of the cover-
slip, removing the paraffin feet, and then drawing off the
glycerine as required, the phenomena of their streaming move-
ment gradually take on the character that has just been
described for the smaller ones. Although the currents
rushing from above and below towards the equator usually
continue for some time longer, there usually appear marginal
centres, from which the currents spread out ; a single such
centre in the moderately large drops, or frequently several
or many in the larger ones. The more or less energetic
streamings from these centres finally suppress the original
circulatory currents. The middle-sized drops, which develop
one such centre of extension-currents, take on, as a rule, an
elongate oval shape, for the most part with a slightly
widened anterior end, in which the centre of the extension-
currents is placed. At the same time, they move for-
ward energetically in the direction of the current which
passes along the axis to the edge where the streams spread
out. I have observed such drops, which in one minute tra-
velled about 0'12 mm. As I only took a few measurements,
it is not to be supposed that the measurement here given
has reference to a maximum of rapidity. We have to
deal here not merely with a displacement forwards of the
centre of extension, or with a stretching of the elongate
oval drop, but rather with a movement of it forwards
as a whole, like a simple amoeba. This can easily be
determined by simple observation, but may also be definitely
proved by marking the position of the anterior and
posterior end by means of a micrometer. I have already

4

50 PROTOPLASM

briefly described the processes of streaming in a drop
of this kind, which moves forward with a single extension
centre, and the figures, which will be given in the sequel
of corresponding streamings in oil - drops, furnish a
sufficient explanation of it. One point, however, still
requires brief mention. It is frequently seen that the
hinder end of such a drop takes no further part in the
streaming, and is also marked out from the rest of the drop
by its somewhat different glassy appearance. Particles of
dirt, or of lamp-black which has been mixed with the
glycerine, collect at the hinder end, without in the main
changing their position. From this it follows, that at the
hinder end a condition of relative quiescence prevails, and
that this region takes relatively little share in the streamings.
Later on, when discussing the similar streaming movements,
which can be called forth in ordinary oil-drops, we shall go
more closely into the state of things observable at the
hinder end of the drops.

Not infrequently a drop of the kind just described is
observed to run towards one of the strips of cover glass
employed as supports. Indeed, it would even seem as if any
drops in the neighbourhood of such a strip of glass have a
tendency to wander towards it. The drop then applies itself
more or less closely to the strip of glass, by the spot at
which the superficial streams spread out from a centre,, and
continues to stream quietly, with, as it seemed to me, even
increased force. Such a drop, however, was never observed
to come free again from the glass strip of its own accord.

It is even more curious when two drops run towards
one another. Neighbouring drops seem inclined to do this,
coming into contact with one another by the centres of
their extension - currents. The streaming then becomes
much stronger in both the drops ; this increase of strength
takes place, however, from reasons to be discussed later, even
before they directly touch one another. While the surfaces
of contact are visibly flattening out against one another, the
streaming is much intensified in both drops. It is note-
worthy how long a time passes before the drops flow
together all of a sudden. Although I took no accurate

MOVEMENTS OF FOAM-DROPS 51

account of this interval, I think I am not in error in
estimating it at some minutes. After complete union, an
entirely new centre of extension-currents is usually formed,
according to which the shape of the combined drop becomes
directed.

If a drop in its forward movement comes towards one at
rest, or approaches a relatively quiescent spot in the margin of
a larger drop, the approach of its centre of stream lines calls
forth a corresponding streaming in the second drop also.
I shall go into the explanation of this phenomenon below.

Larger drops usually form several or numerous centres
of extension - currents. In the accompanying Fig. 6 is

represented one of the finest examples of this kind which
came under my notice. The strongly pressed drop in
question had not less than eleven centres of streaming,
some of which had developed into long pseudopodium-like
processes. Such drops show, as was to be expected, no
actual forward movement as a whole ; on the other hand, the
actively streaming centres of the extension-currents usually
grow out like pseudopodia. Now since the streaming of
one or other of the centres frequently becomes gradually
slower and finally ceases, while, on the other hand, another
is developed more strongly, or even entirely new centres arise,
the result is that such drops show, as a rule, a striking
amoeboid change of form. In a relatively short time, after

52 PROTOPLASM

half an hour or an hour, a drop of this kind has altered
its shape very considerably. That drops of such large
size when under strong pressure move but little for-
wards as a whole, may partly depend also on the fact that,
having relatively large surfaces of contact with the cover
glass and slide, they meet with a proportionately large
resistance from friction. When a single one of their pseudo-
podial processes streams strongly forwards, as, for example,
the one denoted by b on Fig. 6, it may happen that, as it
continually grows farther out, without being followed by
the principal mass of the drop, it finally breaks off from the
latter, owing to the bridge connecting it with the main body
becoming more and more attenuated, until it breaks.
In this way the process mentioned, denoted by b in
Fig. 6, separated off soon after the drawing was fin-
ished, and then moved on as an independent drop in the
direction of its centre of extension-currents. Similar pheno-
mena of division, if it be wished to so term this case, have
often been observed by me in a similar manner.

It is frequently seen that a strongly streaming centre
of extension -currents gradually suppresses a neighbouring
weaker one. One of the lateral streams from the first
centre gradually overcomes the opposing current of the
latter, and thus finally brings by degrees the whole centre
to extinction.

Continuance of the Streaming Movements

Successfully manufactured drops show the described
phenomena of streaming for at least twenty-four hours, dur-
ing which time the streams gradually become weaker and
weaker, and finally cease. Frequently, however, I could follow
them for from forty-eight hours to three days. Finally, in May
1889, after several attempts, an oil was successfully combined,
which yielded drops of peculiarly good streaming powers. In
one of the preparations the largest drop of froth, made from
this oil on 28th May, still streamed distinctly, though
feebly, on the 3rd of June, so that in six days it had not
completely come to rest.

INFLUENCE OF TEMPERATURE

53

The fact that it was one of the largest drops which
showed this long continued streaming is a confirmation of
a phenomenon which was also plainly seen in studying
the smaller drops. Very minute drops, consisting of only
relatively few alveoli, as often occur (see p. 19) in the
preparations, were never seen by me to pass into the
condition of streaming. Larger drops of perhaps 0*05 to
O'l mm. diameter usually showed very fair streaming
movements, which did not, however, last long, becoming
extinct after one or a few hours. Streamings of such long
continuance as have been mentioned above can only be
observed in relatively large drops. The continuance of
the streaming stands therefore in direct relation to the
size of the drop, which harmonises well with the ex-
planation of the phenomena which we shall come to speak
of below.

Influence of the Temperature, etc., on the Streamings

If streaming drops are warmed on a Max Schultze's
hot stage up to 40° or 50° C.,1 it is easy to observe that

Fig. 7.

the streamings become much more quick and intense.
The same is true of their forward movements. In the same
way it may be observed how drops, which have already come

1 The temperature is of course somewhat lower than is shown by the
thermometer of the stage.

54 PROTOPLASM

to rest, begin to stream anew with heating, or that such
drops as were unwilling to stream well succeed in doing so
with a higher temperature. When several centres of stream-
ing are present, the drops show a rapid change of form, ac-
companied by the appearance of new centres and the dis-
appearance of earlier ones. An astonishing case of this kind
is figured by me in the accompanying Fig. 7 ; the period
of time in which the amoeboid change of form depicted
took place was not more than about ten minutes.

I was unable to ascertain any influence exerted by gravity on
the streaming movements. Preparations with streaming, and
usually somewhat strongly compressed drops, were placed verti-
cally by bending the microscope back, and observed for some
time in this position. The streamings appeared, however, to be
in no way distinctly influenced, and took place equally well
both in the direction of gravity as well as against it, or in any
other direction. Although these experiments are not free from
objection, yet I wished to mention them briefly.

I also instituted some experiments to determine the possi-
bility of any influence of light on the processes of movement.
These experiments were performed with drops that were not
pressed and which were in glycerine. The preparations were
placed near the window on a piece of black paper, and in ad-
dition the half of the preparation turned away from the window
was covered with black paper in such a way that at least one
of the drops was just half covered by the paper. Over the pre-
paration a glass vessel was then placed, of which the half turned
away from the window was covered by a black cloth. The few
experiments carried out up till now have shown no influence of
light. The drops sometimes wander into the light, sometimes
into the dark, most frequently the former. It was certainly
striking that for the most part their movements were more or
less in the direction of the light that reached them, i.e. either
towards the window or away from it ; but this result may also
be only a matter of chance, on account of the number of experi-
ments being too small to establish it.

Reaction of the Drops of Foam to Electricity

Since it seemed to me from the outset very important to
investigate the influence of electric forces on the phenomena
of streaming movement in the drops of foam, I have occupied

ELECTRICAL EXPERIMENTS 55

myself for a long time, and repeatedly, with this object. Un-
fortunately, however, I must confess that the results obtained
are not very satisfactory. This may depend partly on the
natural difficulties of the object, and partly also no doubt
on the inexperience of the observer in this subject. Although
therefore I must regret not being able to communicate more
definite and satisfactory results, I yet think that I ought
not to remain silent about them, even at the risk of what
is brought forward here being subjected to a severe criti-
cism from more competent authorities.

In my preliminary communication of 3rd May 1889 it
was reported that the froth-drops, when between the poles
of the constant current, showed streaming , movements
directed towards the negative side. Since, however, ordin-
ary oil-drops also under these conditions permitted the observa-
tion of feeble streamings, soon dying away, the circumstance
seemed in need of further explanation. Even at that time
I had an idea that the centre of extension-currents directed
towards the negative pole might possibly be only a con-
sequence of the free alkalis formed at the negative pole by
means of the electrolysis set up — an effect which would natur-
ally produce a centre of extension-currents directed towards
the negative pole as soon as they reached the surface of the
drop of foam or oil (on this point see below, p. 62). Now
since the glycerine, in which the drops of foam were investi-
gated, contains potash soap in solution, a possibility of this
kind ought certainly to be taken into consideration. More-
over, the water employed for diluting the glycerine is itself
not free from traces of alkaline salts. The reasons which,
in spite of this, caused me at that time not to ascribe the
negative stream to this cause I will not go into more fully
at present. My original experiments were of course per-
formed on slides, which were provided in the usual
way with electrodes of platinum foil, the electrodes being
about 4 to 5 mm. apart. In order to avoid the above-
mentioned source of error, in later experiments performed
in the course of the summer of 1889, I made use of small,
so-called non-polarisable brush electrodes, as invented by
Dubois Keymond, which, wetted with 1 per cent solution of

56 PROTOPLASM

common salt, are pushed inwards from both sides some way
under the cover glass, and act perfectly well, besides being
relatively easy to manipulate.

Since the negative stream did not make its appearance as
a rule until after the poles had been closed for two to five
minutes, this fact also pointed to its electrolytic origin.
This supposition seems to me to be proved with tolerable
certainty by further experiments, so that the idea of the
drops being influenced by the electric current, as was stated
at first, may be dismissed.

If ordinary drops of oil, placed in glycerine containing
some NaCl, be exposed to a constant current between
platinum electrodes on the slide, there appears almost imme-
diately, provided the amount of NaCl contained in the
glycerine be considerable, a powerful centre of extension-
currents on the negative edge of the drop, with formation
of soap. If the amount of NaCl in the glycerine is slight,
it takes some time for a feeble system of extension-currents
to be developed on the negative margin of the drop. Next
there usually follows again a condition of rest lasting a
short time, and then the action of the alkali soon begins to
take effect very energetically at the negative margin of the
drop. The drop falls into very violent streaming move-
ments, becoming transformed into beautiful, perfectly opaque
froth, so that I consider it possible to manufacture very
good foam in this way.

In order to follow out this point still further, I brought
drops of oil into the semi-dilute glycerine, which I usually
employed, having coloured it slightly with some neutral
litmus solution.1 Then, when the constant current was
passed through, employing a battery of five chromic acid
elements with platinum electrodes, there immediately ap-
peared a blue coloration at the negative electrode and
a red at the positive. The blue colour gradually spread
out in the form of a triangle, the base of which was at
the negative electrode, while its apex was directed towards

1 This solution I owe to Dr. K. Mays, who has already described the mode
of preparing it by means of the dialytic method. See Verh. des medic.-
naturJiisi Sereins, Heidelberg, K F. Bd. iii. p. 295.

ELECTRICAL EXPERIMENTS 57

the oil-drop, placed in the middle between the electrodes.
Shortly before the apex of the blue region reached the
margin of the drop, the first trace of the system of extension-
currents made itself noticeable at the edge of the drop.
After this negatively directed extension-current had lasted a
short period, a condition of rest followed for some time, — the
same phenomenon which has already been mentioned above,
and which was also as a rule observed under similar con-
ditions in drops of foam investigated in glycerine. The cause
of this transitory quiescent state was equally intelligible
under the arrangement of the experiment that was chosen.
For during the streaming of the drop the red acid fluid of
the positive side spread itself out in a peculiar manner com-
pletely round the drop, so that the latter was now surrounded
on the negative side as well by a narrow red zone, and the
blue triangle had entirely altered its form. In consequence
the cause of the negative streaming was removed, and it
died down. After a short time the blue zone approached
the drop again, and now called forth persistent negative
streaming movements, which, after interruption of the electric
current, became immediately weak, and soon died away.
The phenomenon described can be reversed at will by reversal
of the poles. The length of time involved up to the setting
in of the persistent negative current was, with electrodes
3 mm. apart, about five minutes.

If, moreover, one takes into consideration the fact that
with a slight acidulation of the glycerine by means of HC1,
and the use of non-polarisable brush electrodes, a negative
current could not be obtained, it is certainly a legitimate
conclusion, if all these considerations are taken together,
that the earlier described negative streaming of the
drops of foam depended solely on the electrolytic action
of alkali.

In further experiments on drops of foam, using pla-
tinum electrodes, it was soon proved, on the other hand,
that, in opposition to an earlier idea, immediately after
closing the current a moderately strong centre of extension-
currents made its appearance at the positive margin of the
drop; this fact was ascertained just as plainly and fre-

58 PROTOPLASM

quently with non-polarisable brush electrodes also. The same
phenomenon could be observed both in drops free from
pressure and in those strongly compressed ; and frequently
not only streaming but even movement forwards towards the
positive pole could be observed most plainly. I can by no
means say that the phenomenon will always be produced
with absolute certainty ; often the experiments succeed only
partially. But in quite a considerable number of cases the
phenomenon was so strikingly evident that I consider its
existence as proved. At the same time it was seen that
this positive streaming died away immediately or in quite a
short time after interruption of the electric current, and that
by change of the poles it could be produced again and again
and with great certainty, now on one side, now on the other.

4-

Fig. 8.

The foam-drops best suited to the experiments are such
as show no streamings of their own, or only very feeble ones,
since lively movements of their own act in all cases as
a check to those produced by electricity. Nevertheless,
even in vigorously streaming drops, the positive stream, with
movement towards the positive pole, was often called forth
successfully, and then with change of the poles a corre-
sponding stream was caused very regularly, almost without

ELECTRICAL EXPERIMENTS 59

exception. Drops that were streaming and creeping well
often showed most beautifully, when investigated with non-
polarisable electrodes, how under the influence of the stream-
ing caused by the electric current and the movement towards
the positive side connected with it, their shape changed in
a corresponding manner, similar to an Amoeba, which creeps
alternately in opposite directions. In the accompanying
Fig. 8 two consecutive forms of the same drop are depicted :
a shows the shape at 12.40 with the position of the poles
as indicated ; the peculiarly jagged hinder margin depends
on the adherence of the moving drop to the slide. At
12.41 the poles were changed; the new positive centre of
extension-currents made its appearance at *, and * at 12.45
the shape of the drop, as it now gradually moved towards the
positive side, was that of the figure I. The same alteration
of form and streaming, however, had been already produced
several times in this drop, so that the phenomenon figured
could not be a mere coincidence.

At all times in drops that are streaming independently
irregularities are met with, which depend principally on the
fact that spontaneous streaming movements, which have arisen
from other causes, disturb the regular course of events. On
this account it is certainly to be recommended, in a repetition
of the experiments, to employ stronger electric currents than
were at my disposal.1 This conviction impressed itself upon
me more and more in the course of my experiments, and I
certainly think that I should have obtained clearer and more
convincing results if I had worked with stronger currents.

In the course of these experiments it occurred to me that
it would be of interest to determine how ordinary oil-drops
behave with regard to the electric current, when they are
placed in glycerine in which some soap is dissolved. For it
is quite clear that the glycerine round the drops of foam
always contains some soap. As usual, finely divided lamp-
black was mixed with the oil-drops, in order to render
distinct any currents that might occur. In the investiga-

1 Use was made partly of a battery of five moderately large chromic acid
elements, partly of one of eight small Grove elements. The action of the two
was not essentially different.

60 PROTOPLASM

tions carried out with non-polarisable brush electrodes it was
shown that under these conditions a positive streaming
could be seen quite plainly, even if relatively feeble, in pure
drops of oil also. Similar experiments performed at earlier
dates with platinum electrodes had partly given the same
results, but had more particularly shown that fairly large
oil-drops in soapy glycerine obey distinctly the well-known
law that small suspended particles wander towards the
positive pole, which they do not do in pure glycerine.

Influence of Induction Shocks

Successfully prepared drops of foam placed in glycerine
were frequently exposed to the action of single moderately
strong induction shocks, from which, as a general result, the
following was fairly uniformly the outcome. The shocks
generally produce sudden and frequently most violent con-
vulsive movements, which extend in good drops over the
whole margin, but may appear more localised in those not
so good. In such convulsions the edge of the drop takes on
a more or less wrinkled appearance, and frequently shrinks
back to a not inconsiderable amount. As a rule, it can be
plainly observed that the shocks on closing the current
have much less effect than those on breaking it. If the
effect as a whole is weak, the shocks on closing frequently
produce no convulsions at all, while the shocks on breaking
still distinctly do so. When the experiments were con-
tinued for some time, the definite and invariable result was
that the convulsions become feebler, and often cease alto-
gether.

When vigorously streaming drops were exposed to
induction shocks, it could frequently be observed that the
streaming came to a stop for a moment, or even for as long
as a minute, starting again after this interval, and often with
increased strength. It is always streaming movements that
go on fairly at right angles to the direction of the electric cur-
rent, which are thus affected. Occasionally, though seldom,
streaming movements which had slowed down were sup-

EXTENSION-CURRENTS 61

pressed entirely, by the formation of a new centre of stream-
ing after a short time in their vicinity.

Several makings and breakings in quick succession always
produce a fairly energetic bursting of froth vesicles in the
interior of the drops — a phenomenon which naturally makes
itself still more obvious with the employment of the inter-
mittent current. By the action of the intermittent induction-
current, using non-polarisable brush electrodes, it could
be determined with certainty that, as a result, very violent
extension-currents appear at the two spots of the edge of the
drop, which face towards the poles. On interrupting the
current they soon die down, and on closing it they quickly
begin again. This phenomenon harmonises well with the
positive streaming observed with the constant current,
since in the intermittent induction-current the poles change
quickly, and hence the action of the positive pole must show
itself on each side.

7. The probable Explanation of the Streaming Movements
exhibited by the Drops of Foam

In order to arrive at an explanation of the peculiar and
long continuing phenomena of the streaming in the drops
of foam, we must first consider their structure again. As
has been remarked, they consist of a framework of very
minute lamella of oil, the meshes of which are filled by a
watery fluid. It follows from the method in which the
froths are formed, that this fluid must be a watery solution
of K2C03 and potash soap, formed by the action of
potash upon the free fatty acids of the oil, or it may be
upon the glycerides themselves. If the froth-drops have
been cleared up in glycerine, the alveoli then contain a
solution of glycerine containing soap and K2C03.

The streaming phenomena of the froth-drops take place
on the whole in the fashion of the so-called superficial
extension-currents (Quincke, 1888; emulsion movements,
Berthold, 1886 ; contact movements, Lehmann, 1888), which
arise regularly whenever the surface tension of a fluid (#),
placed in air, or in a second fluid (&), is locally diminished

62

PROTOPLASM

by bringing a spot in the surface of (a) into contact with a
third fluid (c), with which (a) possesses a lower surface
tension than with (b). This case arises, for example, if we
allow a weak solution of soap to approach one side of a drop
of oil, which is placed in water under a cover glass on a
slide.

This experiment is best performed by the method of
mixing lamp-black with the oil-drop and Indian ink with
the soap solution, or by colouring the latter strongly with
an aniline dye. It is then seen that at the edge of the
drop, shortly before the soap solution touches it, an energetic
system of radiating currents is set up, a system consisting of
an axial stream from the interior of the oil-drop, which
reaches the surface, and flows away on either side. In
their course backwards — that is to say, towards the spot at
the margin which lies diametrically opposite to the point of
contact between the soap solution and the edge of the oil
drop — the two down currents become continually slower.

Finally, they meet at the
hinder pole of the drop, to
gradually turn and pass
into the forward axial
current. Closely studied,
the relations of the currents
are somewhat as seen in the
accompanying Fig. 9, in

which the rapidity of the

*

local currents is roughly in-
dicated by the length of the
arrows. As the figure teaches us, at the hinder edge of the
drop there is a region x of almost complete quiescence, which
is roughly triangular in form, with the apex turned towards
the so-called centre of extension. The extent of this
quiescent posterior portion depends on the intensity of the
streaming; the stronger are the two streams rushing back-
wards on each side, the farther they reach towards the hinder
pole, and hence the more limited is the quiescent region x.
Intense currents reach finally even to the hinder pole itself,
and there meet. Then by the mutual interaction of the

Fig. 0.

MOVEMENTS OF OIL- DROPS 63

conflicting currents, there is formed only a narrow, axial,
relatively quiescent streak, which is continued forwards
through the entire axis of the drop, as far as the centre of the
stream lines. Such a median streak (m, see the Fig.) is
also, however, formed in the case when a more considerable
quiescent region is found posteriorly, and is then an imme-
diate continuation forwards of its forwardly-directed apex.
The conditions described become much more distinct by
addition of lamp-black to the oil. The further peculiar fact
is then shown, that the particles of lamp-black, which
were originally distributed evenly through the oil, gradually
vanish completely from the posterior quiescent region, as a
result of which the latter becomes transparent * and clear;
just in the same way the continuation of the portion xy
which we have termed the median streak m, is also quite
free from lamp-black. At times the lamp-black becomes
more especially collected on the border of the resting portion
x, so that two dark masses arise here.

Simultaneously, however, with these streaming processes,
the drop also shows a forward movement, when the ex-
periment succeeds well. The drop moves with more or
less speed in the direction of the soap solution approaching
it, and frequently 'creeps along for a considerable distance in
this manner. Usually this forward movement commences
at once on the soap solution touching the edge of the drop,
and then the latter bulges out strongly and suddenly
towards the soap simultaneously with the commencement of
the superficial extension-current. During the continuance
of the movement, the drop, as a rule, gradually assumes an
oval shape, with a somewhat pointed (i.e. more strongly
curved) anterior end and a broader posterior end.

At the same time that streamings are going on in the
drop, there are naturally others, also, in the surrounding
water, which can be observed in the plainest manner on
addition of Indian ink to the soap solution. It is then
seen that the soap solution flows backwards from the
point of contact with the oil-drop along the surface of the
latter, to the spot where the streaming in the oil-drop extends.
At this point the current bends outwards, so that a back

PROTOPLASM

current is gradually formed on each side in the surrounding
water, just as in the oil-drop (see Fig. 9). The locality of
this back current is marked by an aggregation of Indian
ink. By degrees, the dark curved line of Indian ink reaches
back to the advancing soap solution (see Fig. 10).

The physical explanation of the radiating currents de-
scribed here, which Quincke and others have studied under

rather different con-
ditions, is, according to
Quincke's interpretation
(1888), somewhat as
follows. Since the sur-
face tension at the
boundary between the
olive oil and the soap
solution is less than that
at the boundary between
the olive oil and the
water, the condition of
equilibrium in the ten-
sion on the surface of the
oil-drop must be dis-
turbed by contact with the soap solution on one side. Let us
conceive the tension of the surface to be represented by a
stretched elastic membrane. Then that part of the surface of
the drop which is in contact with the water must shrink
together to a certain extent, since its tension is greater than
the tension in that portion of the surface which is covered
by soap solution. Let us now imagine that under these
conditions the limiting layer between the oil- drop and the
surrounding fluid becomes torn and carried towards the
hinder end of the drop, a violent movement which will
naturally affect both the mass of oil and the surrounding
water with equal force, and cause, to a certain depth in both,
a similarly directed system of currents, leading away from
the point of contact or centre of extension. But with this
tearing away of the limiting zone between the oil and the
surrounding fluid, a new surface of oil comes into contact
with the surroundings. Since the thin layer of soap solution,

Fig. 10.

EXPLANATION OF THE MOVEMENTS 65

carried backwards by the so-called extension-current, im-
mediately dissolves, or at least becomes very quickly diluted
in the water surrounding the hinder region of the drop, the
condition of equilibrium immediately becomes disturbed again,
and in this manner a continuous extension-current results,
which flows backwards on all sides from the point of contact.
In such a manner the continued duration of such cur-
rents under the conditions given is well explained. On the
other hand, this mode of consideration does not seem to me
to account completely for the axial current, and still less for
the forward movement of the drop in the direction of the
axial current. Mensbrugghe (1890-91) also has already
expressed the strongest doubts as to whether the axial
forward current as well as the forward movement can be
effects of the surface tension, and looks upon them rather
as a result of chemical attraction between the soap
and the oil. It seems clear, in the first place, that
the axial stream is a simple consequence of the superficial
system of currents, which radiate out equally on both
sides from the centre of extension, and are continued
into the depth of the oil-drop. These two streams in their
passage backwards must produce, as the result of friction,
an eddy on each side within the oil mass, as is plainly
shown in Fig. 9, on p. 62, and the combined effect of these
two eddies appears as the axial current. Moreover, there
is an additional factor which aids in producing the axial
stream. When the oil-drop is in water, it will necessarily
assume a spherical form in consequence of the surface tension
being equal on all sides. Only under these conditions is there
equality on all sides of the internally -directed capillary
pressure. This pressure is to be regarded as the result of the
surface tension, taking effect in the normal to the curv-
ature of the surface, and inversely proportional to the
radius of curvature. If then by contact of the edge of the
drop with the soap solution the surface tension (i.e. the
tension acting on the surface) is lowered, this lowering neces-
sarily influences the shape of the drop. Since by diminution
of the tension the internally -directed pressure is also
lowered, the spot at the surface of the drop which is in con-

5

66 PROTOPLASM

tact with the soap solution must become more strongly
curved, i.e. arched forwards or bulged out, in order to main-
tain the equilibrium with the unaltered pressure of the
surface in contact with water. Since as a matter of fact
the internally-directed pressure is inversely proportional to
the radius of the curvature of the surface, this difference of
pressure will become equalised by stronger curvature of the
surface of the drop. We find then, both in Quincke's ex-
periments and in mine, that the drop actually assumes
the form corresponding. Now by the phenomenon of
extension the oil in the superficial region of the drop is
caused to stream backwards, and at the same time the
difference in tension at the surface of the drop continues
to exist. The consequence of this would be, that, in order
to equalise the constant diminution of the bulging out at the
centre of extension which is produced by the down currents,
the surface would continually bulge forwards, so that the
shape of equilibrium is maintained. This bulging forwards
demands, however, an afflux from within, which is supplied
by the axial current, and which strengthens the latter to a
certain extent.

Finally, there is the question whether the forward move-
ment of the drop in the direction of the soap, i.e. in the direc-
tion of the axial stream, can also be explained as a simple
result of the differences in the surface tensions of the oil-
drop. Quincke affirms it to be the case, since he supposes
that the capillary pressure, which is, as described,
stronger behind, drives the drop forwards in the direction
of the centre of the extension-currents, where the pressure
is least. I cannot agree with this view, since I cannot see
how this difference of pressure could produce more than the
alteration in the form of the drop which has just been
described. A continuous forward movement of the drop
could ultimately only be explained in this manner on the
assumption that the differences in surface tension became
continually greater. Lehmann, on the other hand (1889,
Bd. ii. p. 499), tries to refer the forward movement to the
friction between the superficial currents of the drop and the
surrounding fluid, as a result of which the freely suspended drop

EXPLANATION OF THE MOVEMENTS 67

is driven forwards. I think that the inadmissibility of this
view is fairly clear. If the forces which are the cause of the
streaming movements had their seat in the interior of the
drop, then such friction at its surface would be quite pos-
sible. As a matter of fact, however, this is by no means
the case, but the active forces take origin at the limiting
surface between the drop and the surrounding water, and
produce in the latter exactly the same streaming as they
also impart to the surface of the drop. Under these
circumstances, therefore, the possibility of friction between
the streaming surface of the drop and the surrounding water
appears excluded. Mensbrugghe believes, as has been re-
marked, that the forward movement, as well as lthe whole
phenomenon in general, depends on chemical attraction, which
produces, in opposition to the surface tension, forces of pres-
sure directed outwards towards the approaching soap. Un-
fortunately I am as little able to agree with this opinion,
since I convinced myself by numerous experiments that the
whole complex of phenomena can also be called forth in
the very same manner with a body so chemically unalter-
able as paraffin oil. Commercial paraffin oil was treated
with concentrated sulphuric acid at 100° C., and well
washed out, and then also showed just the same phenomena.
N"ow since it cannot be well assumed that paraffin oil
and dilute soap solution have any appreciable chemical
action one upon another, it seems beyond doubt that the
processes described must depend only upon purely physical
causes.

The explanation of the forward movement of the oil-
drop towards the soap solution may be sought, according to
my idea, in something of the following kind. By the
action of the extension-current some of the soap solution is
being continually drawn away from its point of contact with
the drop, and carried off to the hinder end of the drop.
For this soap solution abstracted in front a compensation
must be made by the neighbouring fluids, and this will of
course be effected by the general pressure within the fluid,
which works equally upon the soap solution, the water, and
the oil. The easiest way of representing such a condition is

68 PROTOPLASM

to imagine that the oil-drop is suspended in a fluid of the
same specific gravity. Now since, as we have seen, the capil-
lary pressure of the oil-drop necessitates its form remaining
the same, the oil-drop itself will take part in the replacement
of the soap solution that is flowing away backwards ; since of
course the pressure, which causes this replacement, works
equally upon water, soap solution, and oil-drop. Hence the
latter will wander into the soap solution or be to some
extent attracted by it in the same measure as the soap
solution streams backwards. For the rest, I think that it
should also be possible to explain the phenomenon by a more
accurate investigation of the force exerted by the lateral
pressure of the currents which come into play. These forces
must undergo alteration corresponding to the law that the
lateral pressure in streaming fluids is diminished by an
amount which is proportional to the square of the rapidity
of the streaming.

In agreement with the explanation here developed of
the progression forward of the drop, it may be noted that
this movement is in general not set up until the phenomena
of streaming reach a certain intensity. Slow or moderately
strong currents may continue a long time without the edge
of the drop moving forwards in the slightest. But when
the streaming attains to a certain intensity, the forward
movements become more and more distinct, since then the
forces are sufficient to overcome the friction that is always
present between the drop, the cover glass, and slide.

The superficial extension-currents described in the foregoing
pages can be produced in just the same manner by allowing dilute
solutions of KHO, NaHO, NH40, or K2C03 and Na2C03, to
approach the drop of olive oil instead of soap solution. The
efficiency of these materials depends in part on the alteration of
the surface tension which they occasion directly, in part and prin-
cipally upon the formation of soap, set up by their action upon
the free fatty acids of the oil. The soap thus formed at the
point of contact, and partly dissolved in the surrounding water,
has naturally the same effect as soap solution added directly.
Since, however, by the action of alkaline solutions on the oil-
drops, granules of a scarcely soluble soap are also formed, which
become partly collected on the surface of the drop, partly

EXTENSION-CURRENTS 69

scattered in the surrounding fluid, such experiments do not come
off so clearly and distinctly as those performed with soap. The
oil-drops rapidly become turbid by application of these solu-
tions, in consequence of numerous minute drops of fluid appear-
ing in them. These may partly arise in the way described
earlier, but may partly be thrust in from the surrounding fluid
by the violent streaming movements. Further, the fine granules
and droplets which appear round these oil-drops may be in part
very minute droplets of oil that have become split off. It was
shown that during the process (oil-drops + K2C03, 2 '5 per cent)
the fine drops of fluid, which gradually made the oil-drop turbid,
collected in the posterior quiescent portion x (see above,
p. 62, Fig. 9), as a result of which the latter soon becomes quite
turbid. Without doubt the fine droplets were gradually carried
to this region by the current, since the superficial streaming zone
of the drop also became turbid and frothy to a small depth.
Finally, the clear axial streak m, which in this drop was
similarly well marked, also became bordered on each side by a
narrow, frothy, turbid line, which no doubt took its origin from
the posterior region x. This behaviour of the fine droplets of
fluid in streaming olive oil-drops is the more peculiar since, as
has already been described, the fine particles of lamp-black mixed
with the drops behave quite differently, and do not penetrate into
the region x. That this difference is not a peculiarity inherent in
the particles of lamp-black themselves, follows from the fact that
in streaming drops of paraffin oil they behave in just the same
way as the droplets of fluid in the olive oil. Thus if a drop of
paraffin oil impregnated with lamp-black is thrown into energetic
streaming movements, lasting for some time, by means of soap
solution or other fluids, after a relatively very short period all
the particles of black collect posteriorly in the resting region x,
which in consequence (see Fig. 11) appears as a black triangle
that extends forwards more or less far
into the similarly black axial streak. The
remaining part of the drop usually be-
comes completely clear and almost quite
free from black ; here and there only does a
particle of black emerge from the region
x. into the streaming again. I have always
observed this phenomenon in the same Fig n

manner in the numerous experiments
performed with paraffin oil. In the streaming drops of foam
also, that were prepared from olive oil containing lamp-black,
the soot particles, curiously enough, showed a behaviour more as
in paraffin oil. In just the same way they collected abundantly

?o PROTOPLASM

in the resting region x, and formed a black axial streak, entirely
unlike their behaviour in a drop of pure olive oil. But so
complete a collection of the soot at the hinder end, as is peculiar
to the paraffin oil, did not occur.

I would merely point out here briefly that the currents in
drops of olive and paraffin oil were also reproduced, as was to be
expected, by numerous other fluids in a similar, though less
energetic, manner. Since a special study of these processes from
a physical standpoint was no part of my task, I only experi-
mented on some few fluids for my own information. Absolute
alcohol produces extension-currents in both the oils named, which
mostly last only a short time, but can usually be called forth
again by a repeated addition of alcohol. NaHO or NH40 produce
similar extension-currents in paraffin oil; in some experiments
with paraffin oil and NH40 performed in the year 1889, the cur-
rents lasted above a quarter of an hour. I have recently repeated
these experiments with paraffin oil and ammonia, and, as a rule,
obtained only feeble currents of short duration, but succeeded
finally in reproducing the phenomenon with the duration and
clearness earlier observed. Concentrated sulphuric acid produces
a powerful extension-current in both oils, which can be observed
very beautifully in olive oil in particular, and can, as it gradually
becomes feebler, be strengthened again several times by fresh
addition of sulphuric acid. No visible alteration of the olive oil
by means of the sulphuric acid is observable at first ; but if
the drop be washed out with .water its outer zone becomes
turbid. Probably, therefore, minute droplets of sulphuric acid
have been taken up which do not become distinct until
after addition of water. In both oils the appearance of the
extension-current caused by the sulphuric acid is preceded in the
drop by an exactly opposite current of short duration. This has
its centre in the margin of the drop farthest from the sulphuric
acid, and the down current passes towards the point of contact
with the acid. As has been said, this feeble current only lasts
a very short time, and makes its appearance before the sul-
phuric acid touches the edge of the drop. I shall try to show
below that this current has its cause in the rise of temperature
which follows when the concentrated sulphuric acid mixes with
the water.

It seemed to me of interest to try whether the experi-
ments described could also be reversed in the following
manner. The drop of oil is placed under the cover glass in the
fluid with which it shows the smaller surface tension. Then the
fluid with which it has the higher tension, namely water, is
allowed to flow to it on one side. In this case, according to the

EXTENSION-CURRENTS 7 1

theory, a reversed current must be set up, which is directed
towards the point of contact with the water. The centre of
stream lines must lie in the edge of the drop opposite to the
point of contact. Such a reversal of the experiments, however,
was not very successful when the drop was placed in soap solu-
tion, which seemed to adhere rather firmly to the surface of the
drop, so that the surface was surrounded by water before
actual contact took place ; but with alcohol, H2S04 and NH4O,
good results were obtained. It was thereby shown, especially
when alcohol was used, that the extension-current set up both
with paraffin and olive oil, was very markedly stronger than when
the drop was placed in water and approached by alcohol. For
the most part the current produced is even violent, and also lasts
for a fairly long time. If it becomes slower it can be strengthened
again several times by repeated afflux of water. During the pro-
cess minute globules of oil become split off in numbers from the
surface of the drop, and carried by the current to the hinder end
of the drop, i.e. to the end in contact with the water. Here they
collect, and gradually spread out again from this point in the
form of an arch on each side towards the end in contact with
the alcohol. They thus form a figure exactly corresponding
to that which has already been described above for the distribu-
tion of soot particles, or split off oil droplets (see above, Fig. 1 0, p.
64). When a drop of olive oil was used for the experiment,
numerous minute droplets of the surrounding fluid penetrated
into the oil, and quickly made it turbid.

An explanation for the much greater intensity of the exten-
sion-current under these conditions of the experiment can per-
haps be found in the fact that here the drop has a low
tension over a large portion of its surface, and a high
tension over a small portion ; while in the experiments first
described the conditions are reversed. If, as we assume, a
bursting of the surface layer of less tension takes place as a
consequence of the difference of surface tension, then Hie whole
phenomenon must of course be much more violent when a large
surface is burst in this manner, than when only a small surface is
dealt with.

The same reversal of the experiment can also be carried out
with drops of paraffin oil which are put up in concentrated sul-
phuric acid or ammonia. Afflux of water then produces the
reversed extension-current in the same manner. I could not,
however, observe an especial strengthening of the current in
these experiments. In the year 1889 some experiments made
with ammonia succeeded very well, but recently they have come
off badly.

PROTOPLASM

Attention has been drawn above to the peculiar pheno-
menon that, on the oil-drops being approached by concentrated
sulphuric acid, an extension-current of very short duration
appears at first at the opposite pole. Since I have had an
idea that this counter-current might be a consequence of the
warmth produced on one side by the mixture of the sulphuric
acid with water, I tried to clear up this point by some
experiments. If a drop of olive oil placed under a thin
cover glass in water be approached as close as possible,
without, however, touching the cover glass directly, by a
brass wire of 1*5 mm. thickness, heated red-hot, such a
counter-current towards the heated edge of the drop can be
produced very distinctly after some time. The experiment
succeeded much better still with a small apparatus which
Dr. C. Hilger had the great kindness to construct, con-
sisting of a very thin platinum wire with its two halves
bent parallel to one another, and heated to the glowing
point by the electric current. In this way the applica-
tion of warmth could be
concentrated at will upon
a given spot. On fixing
the wire so that its re-
curved portion was about
1 to 2 mm. away from the
drop, and then heating it
to a moderate glow, the
current described was
beautifully shown, and
lasted until the electric
current was interrupted.
The particles of lamp-black mixed with the oil were all
carried to the side that was warmed, which was the region
of quiescence, and thence they extended in the form of
an axial streak through the drop (see Fig. 12). It was
observed very distinctly that the rapidity of the superficial
current diminished steadily from the heated pole to the
opposite one — that is to say, in a manner exactly the reverse
of an ordinary extension-current, but in correspondence with
what should occur in a reversed extension-current. If then

Fig. 12.

EXTENSION-CURRENTS 73

in this current we are really dealing with a phenomenon of
extension, as appears to be the case, it would then of course
follow that the surface tension between water and oil when
warmed is greater than that between the two fluids when not
warmed. With regard to the influence of temperature upon
surface tension, it is known in general that the latter
diminishes with increase of temperature ; but these state-
ments only have reference to the surface tension with air.
That the process described should be produced secondarily
by streamings in the surrounding water I consider very
improbable.

The duration of the extension-currents described is, for
the most part, relatively short, when the experiment has
been arranged as prescribed, although the streamings
which are produced by means of soap solution in drops
of olive or paraffin oil not infrequently persist for hours,
during which the drops carry out extensive migrations.
Since, however, under these conditions, it is frequently
rather a matter of uncertainty whether some other causes,
such as pressure and the
like, may not produce
streamings in the drops, I
arranged an experiment,
which proved quite suit-
able, in order to obtain
streamings of long dura-
tion, as follows. A fine
capillary tube, partly filled
with soap solution, and
then sealed up at one
end, is pushed towards

a drop of paraffin mounted under a cover glass, until
it touches the drop directly and makes an indentation
in its margin. The extension -current then begins at
once, and, as the accompanying Fig. 13 shows, it assumes
a direction corresponding very well to the position of
the end of the tube. In a preparation of this kind I
followed the streaming from 1 P.M. to 7 P.M., and the next
morning at nine o'clock a slight streaming could still be

74 PROTOPLASM

observed. In such preparations it may be occasionally
observed also, that the oil-drop gets drawn deep into the
capillary tube by a decrease of temperature, without the
streaming suffering. In the thread of oil contained in
the capillary tube a forward current then runs axially
towards the soap, and a backward current runs superficially
on all sides out of the tube.

Finally, I will notice here certain other experiments which
were instituted with the intention of producing purely
circulatory streamings by means of extension phenomena.
If a thin strip of glass is fixed on a slide with Canada
balsam, and then a cover glass on this in the same
manner, a very shallow chamber, open on three sides, is
obtained. Then if, by means of a capillary tube, a drop of
paraffin oil is placed in this chamber at the edge of the strip

of glass, it spreads out here

IlililllllBiB to some extent between the

slide, cover glass, and strip of
The remaining space
under the cover glass is filled
with water (see the accom-
panying Fig. 14). If now soap
Fig. 14. solution is cautiously allowed

to flow along the edge of the

glass strip to the drop of paraffin oil, a one-sided extension-
current is set up in the latter, which, as the figure shows,
causes a simple self-repeating circulation. The explanation
of this phenomenon is naturally to be sought in the fact,
that the contact between the soap and the oil takes place
first at the point a, arid since this point only presents a free
edge of the oil-drop on one side, there can only be a one-
sided current formed, flowing away backwards, which must
result in a simple circulatory movement.

From the streaming processes hitherto described in the
oil-drops, it can be plainly recognised that the currents
in the drops of oil-froth spoken of earlier are of the same
kind, i.e. extension-currents, which are produced by local
diminution of the surface tension. As is evident from the
mode of preparing the foams, the substance which causes

STREAMING OF FOAM-DROPS EXPLAINED 75

this diminution of tension can only be soap, which spreads
itself out in solution upon the surface of the drop. Accord-
ing to the statements given above as to the origin and
structure of the foams, the fluid which fills their alveoli is a
watery (or after clearing them, a glycerine -containing)
solution of. soap. Both by diffusion and by bursting of
superficial alveoli, the soap solution in the contents of the
alveoli comes to the surface and produces extension-
currents. I should conclude that bursting of alveoli does
actually come into play from the fact that when the foams
are brought into water, local eruptions of some strength
frequently break out from the interior, and are accompanied
by strong superficial extension-currents. That such erup-
tions depend upon occasional bursting of single larger
vacuoles is beyond a doubt.

When we turn to details, an explanation ought first to
be given for the peculiar circulatory currents, which the
drops of foam, when free from pressure, usually show after
being transferred to glycerine. But first of all, a word as to
the influence of glycerine may not be out of place. As has
been already described above, the drops move about also in
water, whence it follows that glycerine does not produce the
movements. On the other hand, I quite believe that it
favours them to a certain degree, since, in particular, it
hinders, or at least considerably diminishes, the adhesion
between the drop and the glass. I am not inclined to
ascribe to the addition of glycerine any other influence upon
the movement.

The peculiar circulatory streaming which the drops of
foam show, as a rule, after transference to glycerine may be
explained, upon the basis of the results now obtained, in the
following manner. If the cause of the phenomena of stream-
ing is to be sought in the exudation of soap solution at
the surface of the drop, it being a matter of indifference
whether this takes place by diffusion or by bursting of
alveoli, it follows that if this exudation at the surface takes
place at first fairly evenly, there must be soap solution of
greater concentration formed in the narrow interstices which
remain between the surface of the drop and the cover glass

76

PROTOPLASM

(D) or the slide (0) (see Fig. 15) than at the equator of the
drop. Now, since soap solution of high concentration
diminishes the surface tension more strongly than that which
is more dilute, two centres of extension-currents will arise
at the two poles o and u, since here the surface tension is
lower — that is to say, the superficial layer of the drop will
flow from here towards the equatorial zone a. At the latter
region the streams meet, and thence turn horizontally
inwards towards the centre of the drop, where they naturally

rr

'a

J

a

Fig. 15.

bend round into the two axial currents caused by the
centres of extension o and u. Since the conditions re-
main constantly the same, as long as there is the same
difference in the concentration of the soap solution on the
surface of the drop, and since this is provided for by the
constant exudation of new soap solution and its continual
diffusion into the water, it is conceivable that the stream-
ing phenomena here described may endure for a very long
time.

On the same cause also depends essentially the pheno-
menon described above, namely, that a drop which is streaming
forwards with a marginal centre of stream lines, gradually falls
into more lively streaming, if it approaches one of the glass
strips which support the cover glass. In this case the strip of
glass lying in the way offers a hindrance to the diffusional
distribution of the soap solution, which produces the centre of
stream lines at the anterior end of the drop. Hence a relative
concentration of the soap solution is brought about, accompanied
by a strengthening both of the streaming and of the forward
progress. The same thing, however, will also take place, if one
drop approaches the surface of another, which then furnishes a
similar hindrance to the diffusional distribution of the soap solu-
tion as does the strip of glass in the former case. But under these
conditions the more concentrated soap solution which is formed

STREAMING OF FOAM-DROPS EXPLAINED 77

between the two drops will produce in the quiescent drop, when
they have come close enough together, a centre of stream lines
opposite to that of the approaching drop. I have often observed
this phenomenon, and am convinced that it is to be explained in
this manner, and not in any way by the friction of the streaming
fluid on the quiescent drop ; for the opposing centre of stream
lines in the quiescent drop makes its appearance when there is
a pretty considerable interval between the drops, and moreover,
the strength of its streaming is too great even at quite an early
period to be capable of interpretation simply as a phenomenon of
friction.

The equal action of two drops upon one another is
shown, of course, still more intensely when they advance upon
one another with their marginal centres of stream lines foremost.
For then the more highly concentrated soap solution, which is
present at the centre of stream lines of each drop, comes together
from the two sides, thus causing a still stronger concentration
between the two drops. As has been already described, it can
then be plainly observed how the streaming of two drops
moving towards one another is gradually strengthened. All
these circumstances bring about the result, that two drops which
have come fairly close to one another, as a rule soon flow to-
gether, if their centres of stream lines do not lie exactly upon
opposite sides.

It was not quite clear to me why the formation of
marginal centres of stream lines, in connection with forward
movement and amoaboid change of shape, did not usually
take place distinctly until the drops were somewhat strongly
pressed. The streaming is seen to continue without pressing
in the way already described, yet occasionally small drops
occur which, without the help of any pressure, develop a
centre of extension at their margin, and move about in a
lively manner. After being pressed, one or more marginal
centres of extension make their appearance, which gradually
entirely overcome the first mentioned streamings, and then
cause the phenomena already described. It is probable that
in drops which are not pressed the causes which give rise to
the two polar extension-currents have a much stronger effect
than in those which are strongly pressed. In the latter the
conditions causing a difference of surface tension at the poles
and at the equator become less and less. When, therefore,

78 PROTOPLASM

in a drop which is free from pressure (see Fig. 16, A), a
marginal centre of stream lines arises by the bursting of some
of the alveoli in the region of the equator a, it will gradually
be suppressed by the strong polar centres of extension ; the
more so, as the soap solution which exudes into the relatively
thick surrounding layer of fluid will spread abroad rapidly
by diffusion. In the drop which is under pressure (see Fig.
16, B) the polar currents become more and more feeble, and
since at the same time the surrounding layer of fluid is
much thinner, the soap solution dis-
charged by the bursting of some of
the marginal alveoli will spread
abroad much more slowly. This
reasoning seems to me to make it
to some extent intelligible how it is
p. 16 that centres of extension are gradu-

ally developed at the edge of com-
pressed drops, leading to the phenomena already described.1
All phenomena which we observe in the streaming froth-
drops, namely the posterior .resting zone, the axial streak,
and such like, have already come under our notice in
streaming oil-drops, and are to be explained in the same
way as in the latter.

The long continuance of the streaming in the drops of
oil-lather is explained by the fact, that they contain a con-
siderable store of soap solution in their alveoli, which is very
gradually used up during the movement, and as gradually
diffuses to the exterior. Since the froths after extinction
of their movement show no alteration of appearance, the
cessation of the streamings cannot be the result of an altera-
tion in structure ; it is rather the diminution of the soap

1 It would be very important to investigate the movements of froth-drops
suspended in the fluid quite free from pressure ; the more so as friction against
the slide and cover glass must essentially influence the movements of the
strongly pressed drops. Since the drops are specifically lighter than water,
such pressure could only be caused by mixing with them finely divided
particles of a heavy substance, e.g. sulphate of baryta. I think that such
experiments would not be hard \ to carry out and would yield important
results. Unfortunately I lacked t*he time for putting the point to the test
myself.

TEMPERATURE AND MOVEMENT 79

contained in the alveoli, and its absorption into the surround-
ing fluid, which must be the cause, and as soon as a complete
equalisation has taken place the streaming must be definitely
put an end to. Unfortunately I have not troubled to find out
whether, as is probable, one can produce new streamings in
drops which have streamed themselves out by replacing the
soapy glycerine around them with fresh glycerine.1 On the
other hand, I tried to stir up afresh drops which had come
to rest by bringing them into a 1 per cent solution of K2CO •
After the drops had remained some hours in this solution,
and had again become quite opaque, they passed a second
time into active streaming movements after being washed
out and having semi-dilute glycerine added to them ; the
alveoli had been again filled with soap solution. On the
other hand, a similar attempt to effect the renewal by means
of a 1 per cent solution of Venetian soap did not succeed
well, since the froth-drops were quite spoiled by it. I think,
however, that one might obtain better results with a more
dilute soap solution.

As we found before, a heightened temperature causes a
considerable increase in the intensity of the streaming and
in the forward movement. The cause of this phenomenon
is to be sought in the fact that the viscid oil becomes more
fluid at a higher temperature, of which fact it is easy to
convince oneself with viscid oil. The greater fluidity of the
oil will permit of not only an intenser current under the
action of an equal force, but also no doubt of the easier
bursting of the alveoli, which must favour the phenomena
of movement.

Mensbrugghe is of opinion (1890-91) that the strengthening
of the phenomena of movement by an increase of temperature
depends on a greater intensity of the chemical reaction, which
he assumes as the cause of the phenomena of streaming. For
this very reason he considers the explanation given by me as
erroneous. But although, as experience teaches, surface tension
is in general diminished by raising the temperature, this fact is

1 Since sending off the manuscript I have several times seen new stream-
ings arise as the result of adding fresh glycerine to drops which had ceased to
stream for a long time.

8o

PROTOPLASM

nevertheless without importance for the explanation attempted
by me. My explanation does riot deal with the absolute amount
of the surface tension, but with its differences at different spots
on the surface of the drop, and these differences may remain the
same even when the absolute quantity of surface tension is
diminished.

8. Streaming Movements exhibited by Drops of Foam
in Cells

With regard to the streamings of protoplasm within
plant cells, it seemed to me important to try what form the
streamings might take in froth-drops which were contained
in small closed spaces. This experiment was carried out as
follows. Moderately thin sections of elder or sunflower
pith were passed from absolute alcohol into chloroform, and
then into an oil suitable for the formation of froth. The
cell spaces of the pith became completely filled with oil in
the process. In order to drive off the chloroform entirely,
the oil was allowed to stand with the pith sections in a warm
case for some time at a higher temperature. The sections
soaked with oil were well washed out with water and brought

into a 1 to 2 per cent solution of
K2C03, either under the cover glass
or in a small test tube. After
twenty-four to forty-eight hours
the oil was milk-white, and of a
fine foam -like structure through-
out. The sections are again washed
with water, and finally freed from
any oil -foam adhering to them
externally by being brushed with a
paint-brush. They were then put
up in semi- dilute glycerine. In
successful preparations it is then observed that the oil-lather
contained in each of the pith cells is in lively streaming,
which persists for some hours. Since the glycerine dimin-
ishes the volume of the oil-lather, the cells are never
completely full, which disturbs the approximation to the
conditions of the plant cell (see Fig. 17). The phenomena

STREAMING IN CELLS 81

of streaming were essentially the same in all cells observed.
The contents always showed but a single centre of extension-
currents, situated, as a rule, at one end of the elongate cell,
more rarely, however, displaced slightly towards a lateral
wall, and very seldom occurring in the middle of one of the
longitudinal sides. Corresponding to this arrangement, the
axial current was, as a rule, directed longitudinally towards
the centre of extension, more rarely obliquely, and finally very
seldom transversely, to the long axis of the cell. In any
case the streaming was always a double-sided one, with a
flow on each side away from the centre of stream lines.
Nothing was ever observed of a rotational streaming, such as
occurs so commonly in vegetable cells. I lay especial stress
upon this point, since I had hoped I might possibly have
seen something of the sort take place under the conditions
given. Isolated cases indeed occurred where the current of
one side only passed a very short distance backwards, while
that of the other side ran round a larger part of the cir-
cumference of the contents. Although such a state of
things may be regarded as an approximation to rotation,
nevertheless I found, as has been stated, no proper rotational
streaming. It is not without interest to note that the
streaming in a large number of the cells was directed in
a similar sense ; yet here and there cells were seen with
the direction of the current reversed or different in some
other way.

If therefore the experiments as yet performed cannot
be exactly said to have yielded great results, yet their
further continuation and modification might ultimately lead
to conclusions upon certain phenomena of protoplasmic
streaming in closed cells. It is easily understood that
conclusions are possible only to a limited extent in the ex-
periments described, since the conditions within the plant
cell are without doubt quite different, as will be described
with more detail in a later section.

82 PROTOPLASM

9. Remarks upon Frommann's Experiments on Drops of
Oil-Foam

Frommann published in 1890 some communications
concerning experiments which he performed on drops of oil-
lather prepared according to my directions, and upon which
I feel myself bound to express an opinion. I must say
beforehand, however, that I am only able to do this with
some difficulty, since Frommann's statements are in great
measure insufficiently clear to me. I therefore take two
points in them, which at least go . to the root of the
author's case in his remarks directed against me. On p.
666 et seg/., Frommann tries to show that " in drops with
non-fluid contents" a perfect alveolar structure is no longer
present, and that both the walls of the alveoli and the outer
limiting layer of such drops are interrupted in many places
by gaps. Although Frommann unfortunately does not state
more accurately what he understands by " drops with non-
fluid contents," and how he manufactured them, I must
suppose that he means by the expression foams which are
manufactured from very much thickened and viscid oil,
such as I also have described above. Since such foams
spoil relatively quickly, and their framework of oil pos-
sesses at the same time a very tough consistency, I will by
no means dispute that during their gradual degeneration
gaps may appear in the walls of their alveoli, although I
never myself observed anything of the kind in the.
viscid and immobile foams investigated by me (see before,
pp. 20 and 44). As has been stated in the preceding
sections, I have principally directed my attention hitherto
to completely fluid foams, in which the formation of such
gaps is simply a physical impossibility. Frommann seems
inclined to dispute even this fundamental law of physics,
since he states on p. 667 : "Numerous gaps in the walls of
the vacuoles, leading to a disappearance of the vacuolar
structure, may also be obtained in drops of an emulsion
which is prepared without K2C03 merely by rubbing up a
drop of linseed oil with water. The drops prove to be
more or less regularly and thickly vacuolated, the walls of

CRITICISM OF FROMMANN 83

the vacuoles interrupted only here and there by gaps ; but if
the drops are spread out flat on a slide, the walls of the
vacuoles become torn in many places and are drawn out, so
that at intervals in the place of vacuoles there arises only
a framework of oil interrupted in many places by gaps,
some smaller, some larger." I will not enter here into the
obvious supposition as to what occasioned the origin of this
framework of oil, when the drop of linseed oil, with droplets
of water in its interior, was spread out on the slide. It is
sufficient for me to have shown by the above-made quotation
that Frommann actually puts forward the view, that between
neighbouring drops of water suspended in fluid linseed oil
gaps may exist in the fluid oil lamellae separating them,
without the partially continuous drops of water flowing to-
gether, and that similarly he entertains the opinion, that
a net-like framework consisting of fluid oil can remain
suspended in water. Since both these things are physically
impossible, Frommann must have seen gaps where none were
present. But this .fact makes us also very doubtful as to
his observations on the viscid froths, the more so as he gives
us no information as to the optical means by which his
investigations were carried on. We know, however, that an
accurate investigation of the froths requires the strongest
systems and oculars. Hence it appears to me that From-
mann has not recognised the finest portions of the froths at
all ; at least he speaks of the fact that between the vacuoles
of the froth-drops " a fine and faintly granulated substance
occurs everywhere, which very probably consists of oil in
a state of the finest emulsive division" (p. 665), or notices
on p. 667 "a pale, finely granular, or indistinctly granulo-
fibrillar material between the vacuoles." So far as I am
acquainted with the froths, this material can only have been
foam of the minutest structure, from which fact it is a
legitimate conclusion, that the investigations were carried
on with insufficient magnification.

I may take this occasion, however, to remark, that in
very thinly spread out marginal portions of foam, which
stick to the slide or the cover-slip, or even in very small
drops of foam, where it is often possible to see larger foam

84 PROTOPLASM

vesicles projecting beyond the edge, very sharp focussing
is not infrequently necessary, to recognise the excessively
thinned-out external wall of such foam vesicles.

When Frommann applies the experience which he obtained
on drops with " non-fluid contents," with regard to the gaps
alleged to occur in the wall of the vacuoles, in order to
support his view of the net-like structure of protoplasm, he
would seem to forget that the latter is to a great extent fluid.

Frommann also makes some communication upon the
phenomena of streaming in drops of foam, from which, how-
ever, I can only conclude that he never observed good
streaming movements. As far as I understand his com-
munications, all that he remarks upon this subject does not
refer at all to the drops of foam, but to the irregular
phenomena of streaming and movement, which are shown
by drops of a paste of oil and K2CO.}, when transferred to
water.

B. Investigations on Protoplasmic Structures

IN the description of the drops of foam, I have intentionally
avoided entering into what was the starting-point of my
experiments, namely, the imitation and possible explanation
of protoplasmic structures. In proceeding to this, I may
first point out the really striking resemblance to protoplasm
which is presented by successfully prepared drops of foam,
when they have been cleared up in glycerine and are suffi-
ciently compressed. Since the refractive index of their oily
framework is greater, even after being cleared in glycerine,
than that of the framework of living protoplasm, the impres-
sion made by the foam approximates more to that given by
protoplasm which has been killed and fixed. I have often
placed preparations of the foam before some of my colleagues,
who were themselves not inexperienced in the investigation
of protoplasmic structures, and were quite unbiassed in their
opinions, and asked them what they believed the object to
be which they were shown, and of the nature of which they
were quite ignorant. One of them guessed it to be an egg
cell, another thought it was Ehizopod protoplasm, or
something of the sort. Although the pictorial method of
representation does not fully succeed in reproducing the
impression made by the natural object, yet the close resem-
blance may be convincingly proved by a comparison of the
photographs of drops of foam, which supplement this work,
with those of the protoplasm of various cells, among which
I would especially draw attention to the photographs of
ganglion cells from Lumlricus (XIII.) and of ^thalium
septicum (XV., XVII.)

Although it was not part of my original intention to

86 PROTOPLASM

institute studies of my own upon the structure of protoplasm,
nevertheless I soon found myself forced to take this course.
I therefore made use of the time and opportunity which the
past two years have afforded me to collect further observa-
tions in this line, upon which I will first report briefly.
It should be noted at the outset that they were all carried
out with the aid of the best optical apparatus of the present
day, i.e. with the apochromatic objectives, 2 mm. Ap. 1/30,
and 1*40 of Zeiss, employed in combination with the
strongest compensating oculars 12 and 18. The large
amount of illumination given by the objective Ap. 1'40
permits perfectly well of the use of ocular 18.

The structural relations are in general so minute and
delicate that the employment of the strongest powers
seems altogether indispensable. When the daylight, as was
so frequently the case, was not sufficient, a good petroleum
lamp (Hinck's duplex -burner) was used as a source of
illumination, its light being concentrated on the mirror of
the microscope by a globe filled with water slightly coloured
with ammomacal solution of copper oxide. The Abbe's
condenser was used in some cases, but not in others, since I
frequently remarked, as I thought, that finer structural rela-
tions came out more clearly without it. Special attention
ought to be directed to regulating the strength of the illum-
ination of the object in such investigations, since it is
notorious that too intense an illumination obscures the details
completely. It is therefore very advantageous to be provided
with an iris diaphragm, and especially with the arrangement
permitting a vertical displacement of the illuminating
apparatus and of the ordinary diaphragm. I lay the more
stress on these points here, since I am convinced that many
results not in accordance with my own depend on insufficient
attention being paid to these particulars.

«

1. Investigations on Protozoa

Since the protoplasmic structures in even the highest
Protozoa can, in great part, tie made out very well in the
living condition, I prefer to describe these forms first.

STRUCTURE OF AC I NET A 87

Suctoria

The small Acinetan drawn from life on Plate III. Fig. 5
was first found by my pupil Herr Lauterborn in his fresh-
water aquarium. Since I did not make a closer study
with regard to its systematic position, I am unfortunately
not in a position to determine it more accurately. For the
most part, it recalls Claparede and Lachmann's Acineta
notonectw, which I referred to the genus Solenophrya in my
work on Protozoa (q. v. p. 1930) ; our form possesses, however,
in contrast to that of Claparede, a distinct, though very short
stalk, and did not live on Notonecta but was fixed to particles
of dirt. This small, very transparent Acinetan permits the
structural relations of the protoplasmic body to be made
out very clearly in the living condition. The protoplasm
is completely reticular, and the width of the meshes of the
reticulum is about the same through the whole body. The
nodal points are not excessively prominent. The most
external layer of meshes, that which lies under the somewhat
pellicle-like external border of the surface, is everywhere
directed radially to the surface, and thus forms a distinct
alveolar layer (alv). Similarly, a radiate border of the same
kind is also formed round the macro-nucleus (mn\ which lies
nearly in the centre of the body, as well as round the
apically placed contractile vacuole (cv). The latter lies at
some depth under the apex, opening by a relatively long
efferent canal, which passes downwards from the apex into
the protoplasm. The wall of this canal appears like a dark
pellicle, and in any case is somewhat thicker and denser than
the pellicle of the surface of the body. Small nodal points
in the wall of the canal form the points of attachment for
the adjacent meshes of protoplasm, which are disposed at
right angles to the canal. In the protoplasm of the body,
dark, strongly refractile granules are deposited, varying in
size from such as are very minute to others which are
coarser. These granules are more especially collected in
certain spots, e.g. in the neighbourhood of the contractile
vacuole. 'The largest of them show a somewhat broad,
dark border. In the case of the smaller, it can always be

88 PROTOPLASM

\

easily made out that they are lodged in the nodal points of
the protoplasmic meshwork. The anterior edge of the house
appears to pass directly into the pellicle of the anterior part
of the body projecting from the shell.

The living macro -nucleus (mn) also shows the reti-
cular structure very plainly, more so, in fact, than the pro-
toplasm, since the framework of the nucleus is rather
darker and its meshes are a little wider. The external
limiting contour of the nucleus is somewhat dark and
sharp, like the pellicle. The more external layer of nuclear
meshes bordering on it is directed radially to the surface,
and hence shows the relations of an alveolar layer. In the
nodal points of the nuclear framework numerous dark
strongly refracting granules can be made out, doubtless
chromatin granules.

I did not investigate the tentacles more closely, but I
was able on the same occasion to examine those of ToJeo-
plirya (PodopJirya) elongata, Clp. and L. Their optical
section gave the appearance represented on Plate XII.
Fig. 5. The central circle is the optical section of the
central canal, and the radially striated zone is a single
layer of meshes of protoplasm which forms the wall of the
tentacle.

Ciliata

On Ciliata I have recently made but few observations,
although, as was known from earlier researches, they are
especially suitable objects for the questions in view.

I observed the protoplasmic structure in the living condi-
tion very distinctly in a small, somewhat yellowish, undeter-
mined marine species of Vortwella, which was of common
occurrence on Ehizopod shells coming from Naples. If a
spot at the margin, slightly behind the peristoinial ridge of
the living Yorticella, be studied in optical longitudinal section
(Plate IV. Fig. 5), there is seen most externally the rather
thick, double contoured, dark pellicle (p), and below this
the clear alveolar layer (alv), the radial striation of which
shows up but feebly, though it is quite recognisable. Upon
this follows the internal reticular protoplasm with distinct

CILIA TA 89

nodal points containing dark, strongly refractile granules in
some abundance. Where the protoplasm borders on the
large vacuole (v), which I believe to be the contractile
vacuole, although I did not observe its pulsations, it again
forms a very distinct radiate layer, which is separated from
the vacuole by a dark margin. It is worthy of note that
here the layer of meshes following immediately under the
alveolar layer also shows a radiate arrangement. We thus
have the same state of things before us as has already been
described by Schewiakoff and myself for other Ciliata (see
Protozoa, p. 1264, and Schewiakoff, 1889).

The alveolar framework of the internal protoplasm was
in a state of incessant wave-like movement to a-nd fro, on
account of which the dark granules also appeared as if in a
state of vibration.

I was able, moreover, to convince myself of the reticular
nature of the living endoplasm in strongly compressed speci-
mens of Paramcecium caudatum and Stylonycliia pustulata,
as well as to make out the alveolar layer in the living
condition. The reticular structure of the protoplasm was
very distinct in preparations of Paramcecium bursaria, which
had been killed in a mixture of picro-sulphuric and osmic
acid, and had hence become dark -brown in colour. Plate IV.
Fig. 6 represents a small portion of the cortical protoplasm
with the thickly-packed zoochlorellae (z). Here the radiate
arrangement of the meshes round the surface of the zoo-
chlorellse is especially noteworthy.

In Paramcecium caudatum and putrinum, in Cydidium,
and also in Zoothamnium mucedo Entz, which I was able to
observe in Naples, I was struck by the fact that the entire
endoplasm is crammed with an immense number of minute
bodies. These bodies are present in such masses that be-
tween them only one or a few meshes of endoplasm remain
(see Plate IV. Fig. 7 of Stylonycliia, Fig. 8 & of Paramcecium
caudat.) They can be easily isolated by compressing the
Infusoria till they burst. I have not determined their size,
but reckon it at about I //, in diameter. In Zoothamnium
much larger ones also occurred. For the most part they are
roughly spherical, more rarely oval or elongated. When

90 PROTOPLASM

isolated they appear moderately refractile, with a rather
broad dark border and somewhat clear interior. It would
be difficult to say whether this border is a structural reality,
or only an optical phenomenon such as is shown by every
small globule. The bodies are remarkable for the intense
readiness with which they are coloured by eosin or gen-
tian violet, and with Delafield's hsematoxylin also they
can be tinged a light reddish colour. The protoplasmic
framework is tinged very little by any of the staining fluids
mentioned, most, however, by gentian violet dissolved in
aniline water.

It appears that the bodies described are of widespread
occurrence in the protoplasm of the Ciliata. Whether they
are in part identical with the singly refracting corpuscles
mentioned by Maupas appears to me doubtful. On the
other hand, they can certainly be ranked with the cell
granules described by Altmann.

In the above-mentioned Zoothamnium I devoted some
attention to the strongly developed stalk muscle, since, as
is well known, a fibrillar structure has often been ascribed
to the muscle thread of this genus. In the living condition
I could only observe a quite feeble longitudinal striation in
the thread. After death, however, the fibrillar nature shows
up very beautifully, and at the same time it is seen that
the fibrillse are connected in the transverse direction by
numerous delicate lines, so that the structure is one com-
posed of elongated meshes (Plate XII. Fig. 4).

I have already pointed out several times that the macro-
nuclei of Ciliata possess a very finely meshed structure.
On the occasion of the investigations on Paramcecium cau-
datum just described I was able to convince myself again
of the fact. If Paramcecia be killed with iodine- alcohol
(alcohol of 45 per cent tinged light yellowish brown with
iodine), and then stained as intensely as possible witli
Delafield's haematoxylin, and broken up into little frag-
ments in oil of cloves, particles of the protoplasm (Plate
IV. Fig. 8, a) are found intermingled with particles of the
macro-nucleus (Plate IV. Fig. 8, 6). The latter can easily be
recognised from the fact that their framework, very similar in

FLAGELLATA AND RADIOLARIA 91

other respects to the protoplasm, is more finely meshed and
coloured a stronger blue, and also -that numerous intensely
red granules are lodged in the nodal points. These granules,
which correspond to the chromatin granules observed by me
(1890) in numerous animal and vegetable nuclei by means
of the same reaction, are much smaller than those above
described in the protoplasm, and stain much more strongly.

Flagellata

Only a few have been occasionally studied by me. In
living Chilomonas paramcccium (Plate V. Fig. 3, hinder end)
I could observe with perfect distinctness the radially
striated alveolar layer under the rather thick and dark
pellicle (p), as well as the reticular structure of the adjacent
internal protoplasm. Preparations which were made with
osmic acid or iodine -alcohol, and stained in Delafield's
hsematoxylin, showed the alveolar layer and the reticular
structure of the internal protoplasm in just the same
manner, and in particular again permitted the determina-
tion of the fact that the meshes surrounding the nucleus
are directed radially to its surface. The alveolar layer
and reticular structure were also observed with just the
same degree of perfection in preparations of Cryptomonas.
In the same way too, in preparations of Euglence which I
studied casually, a relatively thin but distinct alveolar layer,
and a reticular endoplasm, frequently filled with larger
vacuoles, could be well seen. The results mentioned
harmonise well with the structural relations of these and
other forms of Flagellata which have been observed recently
(1889) and quite independently by Kiinstler.

As I have already remarked elsewhere (1890), there
are to be found in the endoplasm of Flagellata, when they
are killed with alcohol or iodine-alcohol and cautiously
stained with Delafield's hsematoxylin, larger or smaller
quantities of small granules stained an intense red. They
have been as yet especially observed in Chilomonas,
Cryptomonas, Euglena, Lepocindis, and Trachelomonas, and
agree closely both in size and colouring with the chromatin

92 PROTOPLASM

granules of the nucleus. I have already referred in an
earlier publication to the distribution of corresponding
granules in the protoplasm of the Bacteriacae, Cyanophycese,
diatoms, and certain thread algse. To the objects enumerated
before I can now add the beautiful diatom Surirella and the
alga Ckantrcmsia.

Radiolaria

In this group only the intracapsular protoplasm of the
large Thalassicolla nucleata was the object of investigation.
Since the material in stock derived from Naples was quite
unserviceable on account of its unsuitable preservation, I
could only investigate some old, and therefore not very thin,
sections of specimens which I had preserved myself in osmic
acid. As a matter of fact, I have hardly seen another object
which shows the meshed structure more plainly than the
intracapsular protoplasm of this Eadiolarian. Fig. 2, a, on
Plate V., gives a picture of it which is in no way schematised,
but as true to nature as possible. The great resemblance,
in fact the really striking agreement, between this picture
and the appearances presented by the artificial oil-lathers, is
astonishing. The nodal points of the framework stand out
very distinctly, and the radiate arrangement of the layer of
meshes bordering on the vacuoles or so-called albumen
spheres can everywhere be well seen. As is well known,
the intracapsular protoplasm' of Thalassicolla contains
numerous large vacuoles or " albumen spheres " (E. Hertwig),
some of which enclose concretions. In Fig. 2, &, Plate V., is
drawn a portion of a large vacuole of this kind, which con-
tains a concretion, while Fig. 2, a, represents the protoplasm of
one of the bridges between the large vacuoles. In the sections
investigated, the so-called albumen spheres showed no other
contents besides the concretions, and hence gave the impression
of ordinary large vacuoles. The width of the meshes of pro-
toplasm varies to some extent. Since a direct measurement
of such minute dimensions is somewhat difficult, I have
counted the number of meshes round one of the vacuoles
depicted on Fig. 2, a, and from the calculation of the circum-
ference of the vacuole I have fixed the breadth of the

HELIOZOA 93

meshes at about O'OOIO mm. The figure shows, however,
that meshes also occur of much smaller diameter.

Earlier observers have already found that the most
superficial zone of the intracapsular protoplasm, bordering on
the wall of the central capsule, is distinctly radially striated.
In the sections investigated this striation was also very
distinct, and at the same time it could be demonstrated
with certainty that it only depended on the arrangement of
the meshes in radiating series. This is plainly shown by
Fig. 2, b, which represents the striated protoplasm bordering
on the periphery of a large vacuole.

Heliozoa

As far back as 1885 I reported that the protoplasm of
the large Actinosphccrium exhibits the finely meshed struc-
ture well, after treatment with chrom-osmic-acetic acid, and
that in the pseudopodia also the same structure is plainly
recognisable. More recently I have found an opportunity of
investigating this form, as well as ActinopJirys sol. In both,
with the optical apparatus that is now obtainable, I was
able to convince myself easily as to the meshed structure
of the endoplasm in the living condition, and also to
observe the radiate layer of meshes distinctly present
round the food vacuoles of Actinophrys. The protoplasm of
the pseudopodia of Actinophrys appeared in part composed
of distinct longitudinal fibres. Moreover, this fibrillar
modification of the protoplasm could be followed through the
coarsely vesicular ectoplasm into the finely meshed endo-
plasm, and at the same time it could be demonstrated that
the fibrous tracts pass into the mesh work of the endoplasm.

In Actinosplmrium also the meshed structure of the
protoplasm of the pseudopodia could be made out even
in the living condition (see Plate X. Fig. 3). To do so is
naturally somewhat difficult on account of the continual
streaming movements. Since, however, the meshed appear-
ance shown by the protoplasm of the living pesudopodia is
in no way altered by killing with picro-sulphuric-osmic
acid, but only becomes sharper and plainer, this proves, as

94 PROTOPLASM

it seems to me, that the pseudopodia killed in this manner
show the normal structure. At the base of the pseudo-
podia the layer of protoplasm surrounding the axial thread
is several meshes in thickness, and diminishes to a single
layer of meshes towards the ends. For the rest, I have
not yet investigated more closely how the matter stands
with the finely attenuated external ends of the pseudopodia.
On killing with picro-sulphuric-osmic acid the protoplasm
of the pseudopodia frequently contracts itself up into
varicose swellings along the axial thread, as a result of
which the latter becomes quite denuded in places (see Plate
XII. Fig 1).

In the ectoplasm of the living Actinosphaerium I could
observe the meshed structure only very indistinctly, when
the surface of the large vacuoles was focussed. It appeared
most distinct in the obliquely sloping walls of the external
marginal vacuoles.

After treatment, however, with the osmic mixture
already mentioned, the meshed structure is everywhere easily
recognisable in the ectoplasm. Whether or not the ultimate
structure of the axial thread was similar, was a point
not successfully determined, though it occasionally appeared
to be so.

Marine Rhizopoda with Calcareous Shells and Reticulate
Pseudopodia

While staying at the Zoological Station at Naples in the
beginning of the year 1890, 1 had an opportunity of devoting
some study to the above-named Rhizopoda. As objects of
investigation use was made of representatives of the genera
Discorbitut, Planorbulina^olystomella, Cornuspira, and various
Miliolidce. I directed my attention principally to the
pseudopodia, but also investigated to some extent the proto-
plasm enclosed by the shell.

„ ! I will commence with the latter. If one of the Rhizo-
pods mentioned be burst by means of pressure, or broken
up with fine needles, it is easy to convince oneself that the

FORAMINIFERA

95

protoplasm which is set free has a very viscid consistency.
It becomes drawn out between the broken pieces of shell
into threads, which frequently stick to the glass or the
needles ; generally the protoplasm shows a very glutinous
consistency. In Discorbince the protoplasm set free in this
manner underwent in all cases immediately or very soon an
essential alteration, since it neither showed movements nor
had the threads that were stretched across any inclination
to contract themselves together into spherical forms. The
Miliolidce behave differently in this respect. Here the viscid
protoplasm becomes in like manner drawn out into thinner
or thicker threads, in which phenomena of streaming and
undulating movements are to be observed for a Jong time.
The protoplasm also of Miliolidce partially broken up can
still send out pseudopodia for a long time. All this serves
to prove that the protoplasm of these Ehizopods is much
more tenacious of life than that of Discorbina and many
others.

When Miliolidce are broken up, larger or smaller
portions of protoplasm are not infrequently separated off',
which immediately assume a globular shape and form larger
or smaller drops. These drops continue to show slight
amoeboid movements for some time ; at their periphery
wave-like up-and-down movements are exhibited, and thus
there is a continual, though but slight, change of shape
going on.

Such drops of protoplasm show with great distinct-
ness a clear alveolar margin, which is limited externally by
a somewhat strong dark border as by a pellicle. The thick-
ness of this alveolar layer I have estimated by various
measurements at about O'OOOG mm. On compressing the
drops more strongly the radial striation of the marginal
alveolar layer can be plainly recognised (Plate II. Fig. 5, 1).
The internal protoplasm following on this layer is very
opaque on account of the numerous colourless granules and
brown fat drops which it encloses ; yet it can be recognised
that it has usually a radially striated structure down to
some depth (see Plate II. Fig. 5, a). The resemblance of such
drops of protoplasm to the drops of oil-foam earlier described,

96 PROTOPLASM

which frequently show a radial striation of this kind, is very
striking, in addition to which the phenomena of movement
described also possess a great similarity to those exhibited
by uncompressed drops of foam in water. That the structure
of the internal protoplasm of the drops is a meshwork can
be recognised in spite of the deposits it contains, and at the
same time it can be determined that the radial striation
depends on the same arrangement of the meshes which has
been already frequently described.

Drops of this kind remained for about three-quarters of
an hour in the condition described. Then the alveolar
layer suddenly disappeared over a certain extent of the
periphery ; the protoplasm lying beneath it burst out
irregularly, and in all cases died immediately, since it
retained irregular outlines, and hence must have become of
a solid nature. The process of dying went on by fits and
starts over the whole drop, until, having passed entirely into
this condition, it appeared as an irregular lump, of much
greater extent than the original drop. In the lumps the
reticular structure was now shown with great distinctness.

In a squashed Miliolid the following very interesting-
phenomenon was displayed by the small, distinctly amoeboid
globules of protoplasm which were set free in great
numbers. The chief portion of the squashed mass de-
veloped a rich network of pseudopodia again ; as soon
as a pseudopodium came in contact with a globule of
protoplasm it immediately fused with it, so that in a com-
paratively short time the majority of the isolated globules
were again united with the principal body. This observa-
tion is evidence, on the one hand, in favour of the fluid
nature of the protoplasm, but on the other hand, is also not
unimportant for arriving at a decision with regard to the
pseudopodia, to which I shall return again below.

The protoplasm of the other Ehizopoda investigated also
shows, even in the living condition, quite a distinct reticular
structure, which becomes much clearer still after fixation
with suitable reagents and staining with gentian violet.
Very commonly portions of the network are to be met with
having a fibrous structure, which is a consequence of the

FORAMINIFERA—PSE UDO PODIA 97

arrangement of the meshes. That this is the case may also
be concluded from the fact that all the bridge-like tracts of
protoplasm stretching across between the broken fragments
of shell have distinctly the appearance of a fibrous network,
in which the direction of the fibres corresponds to the
direction of the tension. Plate II. Fig. 6 shows a portion
of a bridge of protoplasm from a Miliolid. The protoplasm
of the bridge was in active movement, streaming to and fro,
so that the network was continually being displaced. The
formation of a fibrous network, running in the direction of
the tension, could also be always distinctly observed when
portions of the protoplasm stuck to the slide or the cover
glass, forming pseudopodium-like edges as a result of the
protoplasm striving to contract itself into a globular form,
just as adhering oil-drops do in a similar case.

In the internal protoplasm of the Discorbince investigated
occur great quantities of orange red or brown fat drops,
which are viscid, since they become drawn out into the form
of spindles under pressure. On addition of 70 per cent alcohol
they partly flow together, but they dissolve easily in absolute
alcohol. Further there also occur small colourless granules
or droplets, which are frequently found in groups, as if
turned out in batches. In absolute alcohol they were
insoluble, in weak iodine solution they stained but slightly,
in acid Delafield's haematoxylin not very intensely. After
staining squashed Discorbince with eosin, there were to be
found coloured granules of various sizes in addition to others
such as those just described.

The study of the living pseudopodia of the above-
named Ehizopods everywhere confirmed the result already
gained with regard to the meshed structure of the proto-
plasm. Wherever larger masses of protoplasm make their
appearance in the pseudopodial network, as in the thicker
pseudopodia or in swellings of the finer ones ; at the so-
called web-like expansions, where a great number of threads
of the pseudopodial network unite ; and further in the rim-
like expansion of protoplasm which emerges from the shell
when pseudopodia are greatly developed, and which sends
out the pseudopodia — in all these places the meshed struc-

7

98 PROTOPLASM

tare is to be observed, although the continual rapid dis-
placements of the network render the observation difficult.
The thicker pseudopodial stems and the basal rim usually
have the structure of a fibrous network similar to the above-
described bridges of protoplasm. Naturally this fibrous
structure always appears more or less confused, but the meshed
structure is usually especially distinct in the webbed mem-
branous expansions. These are, as a rule, excessively thin,
since they are built up of a single layer of alveoli or meshes,
and therefore they also show the structure in the clearest
manner (Plate IV. Figs. 1 and 2). Fig. 1 represents such
a membrane of a Miliolid in the living condition ; Fig. 2,
on the other hand, that of a Discorbina after fixation with
vapour of osmic acid and very strong staining with Dela-
field's hsematoxylin. It is beyond doubt that in both cases
the observation yields exactly the same results. Since we
are dealing with a protoplasmic layer of excessive thinness,
the object is very faintly defined even in an intensely stained
preparation, and demands very careful attention and
study. In the figures the dark granules, staining intensely
with hsematoxylin, may also be noticed distinctly ; they
occur in great numbers, as is well known, in the pseudo-
podial network of these Ehizopods, and display the so-called
granular movement. Finally in Fig. 2 the nodal points
of the meshwork can also be made out very plainly.

The reticular structure shows up especially clearly in the
lumps of protoplasm, which, like the granules, are carried to
and fro on the fine pseudopodial threads. The distinctness
of their meshed structure seems to depend principally on
the fact that their protoplasm is in a condition of relative
quiescence, so that the meshwork undergoes no displace-
ments. It is remarkable that such lumps occasionally
adhere to the pseudopodia in a state of complete rest, while
the moving granules rush past them uninterruptedly.

The most difficult problem is presented by the fine
thread-like pseudopodia, the thickness of which can scarcely
be measured even when the highest magnifications are
employed, and which may be so attenuated in the peripheral
expansions of the pseudopodial network as even then only

THREAD-LIKE PSEUDOPODIA 99

to be visible as lines. No distinct meshwork structure is
to be found in these pseudopodia, but there occur, on the
other hand, at moderate, though, during life of course, always
at variable, intervals, darker points, like faint nodules, which
by their displacement along the pseudopodium are an
index of the streaming movements. In their company are
others which are certainly granules, as has been already
mentioned ; by the intense coloration which they assume in
haematoxylin they are proved without doubt to be special
structures. The question is whether the first-mentioned
nodule-like points are also granules of smaller size, or whether
they correspond in some way to the nodal points of the
meshwork. I was not able to answer this question with
certainty. The majority of the nodal points in the fine
pseudopodia are very similar to the nodal points of the mesh-
work. It might be imagined that a fine pseudopodium of
this kind is to be regarded as a row of elongated meshes of
the protoplasmic framework, and the nodal points as the par-
titions of the consecutive meshes. This idea seems, however,
scarcely permissible, since, in the preparations at least, the
points in the fine pseudopodia follow one another at inter-
vals, which correspond roughly to the usual breadth of the
meshes (Plate III. Figs. 1 and 2, Plate IV. Fig. 2). More-
over, other very peculiar phenomena can be observed in the
fine pseudopodia. Among them seems to me specially
important and noteworthy the not infrequent impression of
having observed that one or another of the granules, which
rush along the pseudopodium, travels away from it for a
short distance, and then fuses with it again. It strikes
me that I have frequently observed granules, which were
rushing along the threads, seated upon small and very
pale projections of greater or less height, elevated- some
distance above the threads, an observation which would
explain the fact that the granules can apparently leave the
threads. Moreover, at times pale vesicular structures were
observed, which rushed along the threads (Plate III. Fig. 1),
and near them small aggregations of protoplasm, consisting
of only a few meshes. Also by careful study of my best
preparations (Plate IV. Fig. 2) I could to some extent make

ioo PROTOPLASM

out in the pseudopodial threads indications of very delicate
expansions, which were occasionally distinctly composed of
a meshwork.

All these observations awaken the suspicion that the
ultimate nature of the darker pseudopodial threads, which
are only just visible, is not yet exhaustively made out, but
that they may yet possess extensions which are visible only
with the greatest difficulty. It is conceivable that the fine
pseudopodial threads really play the part of an axial thread,
such as occurs in the Heliozoa and to some extent also
in Eadiolaria, and that on this axial thread a thin and
scarcely visible coating of protoplasm is moving. Such an
idea obtains some additional support from the fact that
by rapidly killing the Ehizopods with the vapour of osmic
acid,1 or some other quickly acting reagent, the pseudopodia
can only rarely be preserved quite intact. Usually they
assume a varicose nature, since numerous and closely con-
secutive spindle-shaped aggregations of protoplasm form
on them. These aggregations, which show the meshed
structure distinctly, and sometimes a marginal alveolar layer
as well, are connected with one another by a fine thread, which
is for the most part quite structureless. I also frequently
obtained preparations in which this thread could be followed
right through the swelling. The similarity is very great
between such appearances and those presented by the pseudo-
podia of Heliozoa after death, when the protoplasm on
the axial threads runs together into varicosities. Although
therefore I cannot bring forward any certain proof of a
structure of this kind in the fine pseudopodia, nevertheless I
regard the hypothesis which I have suggested as worthy of
consideration. I only found out afterwards that M. Schultze
(1863) had already been led to the same supposition by
similar observations on the protoplasm of the Miliolidce.

1 The pseudopodial networks were best obtained in a state of fixation by
the method of bringing the slide with the Rhizopod in a small drop of water
very quickly into a glass vessel, the air in which was richly impregnated with
osmic vapour by heating a 1 per cent solution on the water bath. As has been
said, the pseudopodial network can be preserved in its full development in
this manner, but rapid killing with fluid fixing agents under the cover glass
also frequently gives good working results.

STRUCTURE OF GROMIA 101

If the pseudopodia are killed more slowly, the connecting
thread which has been described between the varicosities
becomes destroyed or drawn in, and the pseudopodium
breaks up into a series of little spheres of protoplasm, which
often permit its original course to be plainly traced. A
similar breaking up into isolated spherules would, moreover,
only come about in a thread consisting of viscid fluid if it
were liquefied rapidly. It would then necessarily break up
into a great number of small droplets.

Gromia Dujardini. M. Schultze, 1854

I had numerous opportunities of observing1 this very-
large and interesting Ehizopod in Naples. Together with
many other Ehizopods it was dredged on the coast of Capri,
from considerable depths. It kept alive for so long a time
that I was able to transport it to Heidelberg, and carry on
further studies there.

Although the shell structure of this Gromia presents
many peculiar relations, I will not enter more fully into
the matter here, since I did not make a special study of it.
Only, in order to comprehend the figures, it must be noted
that the region of the mouth may take on a slightly different
appearance, according as whether the protoplasm is issuing
abundantly from the mouth-opening, or is retracted com-
pletely into the shell. In the former case the oral region
projects like a nipple, as is represented on Plate I. Fig. 2.
In the latter case, on the other hand, although the mouth
opening usually appears very much narrowed, or even nearly
closed, the nipple-like projection is quite shallow and flat-
tened off (Plate I. Fig. 1). The fairly thick shell wall appears
finely and radially striated in optical longitudinal section. At
the anterior pole it gradually becomes stronger, until at the
mouth opening itself it reaches a considerable thickness.
Up to a certain distance from the opening the shell retains
the radially striated appearance in section (Fig. 1, &). The
thickest part of the oral region has, on the other hand,
quite another structure. It appears finely granulated in
the section (Fig. 1, a), and is marked off by a sharp,

102 PROTOPLASM

and for the most part slightly sinuous, line from the con-
tiguous striated portion. The oral nipple is formed from
this granulated portion and from the neighbouring thicker
striated portion of the shell, which, at the time when the
protoplasm forces its way out and widens the oral opening,
becomes raised up and pushed apart. I believe that the
peculiar nature of the opening serves to supply an elastic
closing apparatus, which of itself closes up the aperture
again after the protoplasm has flowed back.

As a rule the opening has sticking to it a mass greater
or less of various kinds of detritus, which at times may even
considerably exceed the animal in circumference. This
lump of dirt consists of particles of the most varied sorts,
which the Protozoon has collected together by its pseudo-
podia, and has gathered up in front of the oral aperture.
Since it can be not infrequently observed that pseud opodia
apparently take their origin direct from the edge of this
lump, I regard it as certain that the protoplasm extends
between the particles of the mass, holds it together, and
makes use of it as food. This circumstance is a great
hindrance to the investigation, since the aperture, and
especially the protoplasm issuing from it, is usually quite
covered by the dirt. If the mass be removed cautiously
the aperture usually closes at once, and even after keeping
the animal for a long time new pseudopodia are only rarely
sent out.

The protoplasm which fills the shell is completely
opaque, since it is packed full of large brown bodies
(Fig. 1, c) which long ago attracted the attention of M.
Schultze on account of their great resistance to various
reagents.

In specimens in which it was possible to watch the
pseudopodia being sent out, the process observable was as
follows. Through the more or less widely opened aperture a
mass of protoplasm emerges which quite fills it, and which has
a structure very distinctly composed of elongate meshes giving
the appearance of longitudinal fibrils. This is by no means
a bunch of pseudopodia projecting from the oral aperture,
as M. Schultze described it, but a continuous mass, with a

HYALINE PSEUDOPODIA 103

structure as above said. I do not, however, wish to deny
that occasionally a bunch of pseudopodia may fill the oral
aperture, but the rule is what I have just mentioned. In
the protoplasm passing through the oral aperture I have
often convinced myself in the plainest manner of the
meshed structure, and Fig. 1, Plate I. gives a picture of
it as true to nature as possible. From measurements I
reckon the longitudinal fibrillae to be about 1 //, apart.

The protoplasm that is issuing forth first heaps itself up
in front of the aperture into an irregular mass, which pre-
sents the appearance of a tuft composed of confused fibre-
like meshes. On Plate I. Fig. 2 a small tuft of protoplasm
is figured in longitudinal optical section, which plainly showed
the fibro-reticular nature of the protoplasm. Larger tufts of
this kind appear, as a rule, more confused, but permit it
to be determined by careful investigation that their struc-
ture is a fibre-like meshwork.

From this tuft the pseudopodia now take their origin,
being, as Schultze has already pointed out, usually com-
pletely hyaline and free from granules, and therefore showing
no trace of streaming. In specimens with richly-developed
pseudopodia they radiate out in every direction from the
oral region, or apparently from the mass of dirt, becoming
for the most part very long, and then also of great thick-
ness, and sending out numerous lateral branches which
usually come off at an acute angle. In very large pseudo-
podia the lateral branches, which may themselves branch
again, sometimes also come off at a right angle, and are so
numerous that the pseudopodium as a whole resembles a
pine-tree. Since it was not my intention to follow out into
details the general morphological relations of the pseudo-
podium, I will spend no more time over these matters, but
merely mention that I never noticed anastomosis between
neighbouring pseudopodia.

It is a striking fact that at times single pseudopodia
appear sharply elbowed in certain places, a character which
further increases the impression of stiffness which these
pseudopodia as a rule give.

As has already been pointed out, the pseudopodia appear

104 PROTOPLASM

\

completely structureless and glassy even with the strongest
magnifications. The only thing to be observed distinctly
in the stronger stems is a fairly thick dark border, appear-
ing like a pellicle, and below that a clear margin. The
two together remind one strongly of a marginal alveolar
layer. With regard to the peculiar nature of the pseudo-
podia, their origin from the tuft of protoplasm, with its
fibre-like meshed structure, deserves special consideration.
I have frequently convinced myself definitely that the
structureless protoplasmic mass of the pseudopodia arises
quite directly from the fibrous meshed structure of the
tuft. The protoplasmic structure of the latter can be
seen to become rapidly paler, and to finally completely
vanish (Plate II. Fig. 4). The fibrous structure can also
be occasionally traced as far as the basal region of the
pseudopodia. Hence it seems to me certain that the hyaline
protoplasm takes its origin directly from that which is
structured. The study of the living Gfromia, moreover,
furnishes still further proof for this immediate transition
between the two kinds of protoplasm. It was occasionally
observed that a hyaline pseudopodium was continued
distally into a protoplasmic swelling of fibrous meshed
structure, which exactly recalled the fibrous tuft at the
mouth of the shell, even in the fact that from it a larger
number of finer hyaline pseudopodia radiated out. This
observation furnishes, on the one hand, a greatly-desired
proof for the direct origin of the hyaline pseudopodia
from the fibrous protoplasm, while, on the other hand,
it proves just as definitely that the hyaline protoplasm
can pass again into that which has a fibro-reticular struc-
ture, for in no other way can the production of the struc-
ture in question, in the course of a pseudopodium, be well
explained.

There are still other observations which point to the
transformation which I have just mentioned, of the hyaline
protoplasm into that which has a meshed structure. In the
fine pseudopodia one occasionally observes at the sides
more or less irregular lumps of protoplasm, or even mem-
brane-like expansions, which appear distinctly reticulated.

HYALINE PSEUDOPODIA 105

They recall similar appearances which have been described
above in the reticular pseudopodia. But the clearest proof
of the sudden conversion of hyaline into reticulated proto-
plasm is furnished by what takes place during the retraction
of the pseudopodium. This process is always commenced
by the pseudopodium suddenly becoming limp and flabby,
and thrown into wavy curves. It may next, without further
noticeable alteration, gradually diminish in size, and finally
disappear entirely, or, not infrequently, it becomes bent
back towards the fibrous tuft, or towards other pseudopodia,
and then fuses with them. In other cases, on the contrary,
the following interesting process can be observed. The
pseudopodium, which has become wavy in outline, first
acquires a granular appearance, as darker points make
their appearance in its course. It then contracts into an
irregular form, and, pari passu, with this process it becomes
continually more distinctly reticular in structure, until it is
seated finally on the hyaline larger pseudopodium, like
one of the irregular reticulate protoplasmic masses already
mentioned, from which it took its origin. On Plate I. Fig.
3, a, is depicted a pseudopodium of this kind in process of
retraction, which has already become distinctly reticulate in
two places, and Figs. 3, b and c, represent two stages of the
retraction of the pseudopodial branch *, which became dis-
tinctly reticulated in the process, and fused with the reticu-
late process of the other side **, also probably a retracted
lateral branch, to form the reticulated terminal appendage
of Fig. 3, c.

If the fibrous tuft of the shell opening be pressed slightly
with the cover -slip, its fibro- reticular protoplasm easily
changes into protoplasm of a quite homogeneous appearance,
which protrudes from the tuft in the form of lobose
hyaline processes, but it undergoes a reticular modification
after a short time, whereupon the tuft obtains its normal ap-
pearance again. Within the shell also, whenever the proto-
plasm in the region of the aperture was slightly retracted
from the envelope, I frequently observed irregular, com-
pletely hyaline, amoeboid protoplasmic projections of this
kind. With these it was similarly possible to follow the

io6 PROTOPLASM

way in which they passed quite gradually into the fibro-
reticular protoplasm of the internal body.

If from the observations described it has become very
probable that the pseudopodia even when apparently quite
hyaline possess a reticular structure, which has only become
unrecognisable for certain reasons, this supposition receives
further confirmation by treatment of the pseudopodia with
reagents. Although it was not always possible to demon-
strate a structure with certainty in killed and stained
pseudopodia, nevertheless I obtained preparations which
showed it most plainly. Fig. 3, Plate II. represents a
thick pseudopodium, richly branched towards the end, which
was rapidly killed with the chrom-osmium-acetic mixture
and then stained with Delafield's hsematoxylin. Throughout
almost the whole pseudopodium it appears composed of
longitudinally running fibres, and the structure can be dis-
tinctly recognised as made up of meshes, especially towards
the base and the extremity of the pseudopodium. In the
thin pseudopodial ramifications, which radiate out from the
main stem, I was unable to find any structure ; like the
main stem, however, they everywhere show a dark, some-
what more strongly stained border.

Amoebce

On various occasions I have studied several representatives
of the genus Amoeba and the nearly allied Gochliopodium.
Since I directed my attention principally towards the struc-
tural relations of the protoplasm, and had no intention of
studying the forms observed from all points of view, I will
only report upon these questions in their proper connection,
and will not enter into detailed descriptions.

In the smaller Amcebce investigated, such as A. (Dactylo-
sphcerium) radiosa, Ehrb., in its various forms, and A. Umax,
the net-like meshwork of the granular internal protoplasm
or endoplasm can frequently be plainly recognised even in
the living condition. In living Amoebae also I was often
able to convince myself of the existence of a radiating layer
round the contractile vacuole and of a similar layer round

PROTOPLASM OF AMCEB& 107

the nucleus. A so-called ectoplasm of hyaline, apparently
structureless consistency, is not, as I have already pointed
out, by any means always present, but may be wanting in
places or altogether ; thus it was not to be found occasion-
ally in the large A. proteus, nor as a rule in A. Umax.
Since, however, in A. proteus it was not infrequently beauti-
fully distinct in places, and since also the pseudopodia of
this Amoeba usually showed, at least towards the end, the
character of such hyaline protoplasm, it seems to me to
follow beyond a doubt that the hyaline ectoplasm arises
here, as in Gfromia Dujardini just described, by modification
from protoplasm with meshed structure, and can also be con-
verted into the same again. The surface of ' the body,
whether formed of hyaline ectoplasm or of protoplasm
structurally composed of a distinct meshwork, always shows
a relatively thick and dark limiting border, which has the
appearance of a pellicle both in living and prepared speci-
mens. This border can also be traced in the pseudopodia,
becoming more delicate and pale towards their attenuated
extremities. Under the pellicle -like margin there runs a
clear narrow zone on which the reticular meshwork of the
protoplasm borders directly,- when a hyaline ectoplasm is
not developed. The pellicle-like limiting border, together
with the narrow clear zone, present exactly the appearance
of a marginal alveolar layer. I have no doubt that they
represent one everywhere, and do not depend in any way
on optical relations. But as yet I have not been able to
convince myself with certainty in living Amoebae as to the
radial striation of this marginal alveolar layer. On the
other hand, I was frequently well able to do so, I may
remark, in specimens preserved with picro-sulphuric-osmic
acid mixture or even with iodine - alcohol. On Plate
IV. Fig. 4 the radially striated marginal alveolar layer can
be seen very plainly in an A. actinophora Auerbach, be-
neath the similarly striated envelope here present, upon
which I shall have a few words to add later. That the
radially striated envelope itself does not represent the real
marginal layer of alveoli, follows from the fact that it is very
clear and pale, and that the marginal alveolar layer proper

io8 PROTOPLASM

which is placed beneath it, shows at its limit towards the
envelope the dark pellicle-like border, which in the absence
of such an enveloping layer forms the actual surface of the
Amoeba. In the same preparation the protoplasm with its
reticular meshwork can be seen most plainly below the
marginal layer of alveoli ; in o it is drawn as seen in surface
view. Eound the nucleus also the layer of radial meshes
stands out very prominently. The great sharpness and
darkness of the nodal points in the framework of the meshes
of the endoplasm depends without doubt upon the deposition
here of small strongly refracting granules.

Although the pseudopodia of Amoebse usually consist of
apparently structureless hyaline protoplasm, yet this is not
always the case. The moderately long radiating pseudo-
podia of A. radiosa were seen by me even in life to be
distinctly composed up to their extremities of a pale
meshwork, partly fibrous to some extent. At the ex-
tremities the structure becomes paler and paler, but yet
remains recognisable. At the same time the above de-
scribed marginal layer of alveoli was to be traced round the
whole of the pseudopodia, although its structure could not
be made out. A. radiosa, however, frequently passed into
conditions in which it exhibits large quantities of apparently
hyaline protoplasm. Thus it not infrequently passes from
the forms just described, with pseudopodia of moderate
length and fair thickness radiating out on all sides, into a
very flat and spread out condition with spiky, pointed
pseudopodia, arising principally from the flat and expanded
margin. This margin consists of nearly hyaline protoplasm,
in which the meshwork structure can only be recognised with
difficulty. Finally, I found in the same water from which
the A. radiosa came, a considerable number of a small
Amoeba of a very peculiar form and mode of locomotion.
As a rule it had somewhat the form of an open fan, moving
with the convex edge of the fan directed forwards, and
formed by a fairly broad hyaline margin, upon which
followed protoplasm which showed a beautiful reticular
structure, making up the pointed end of the fan, and
containing the nucleus and the contractile vacuole. I

PROTOPLASM OF AMCEB& 109

have frequently observed this Amoeba, and for a long time
regarded it as a peculiar species, until I noticed one day
that a specimen, by throwing out a number of radiating
pseudopodia, passed into the typical form of A. radiosa.
Hence, I now have no doubt that it is only one of the
forms under which the very protean A. radiosa may appear.

In one Amoeba, which had an elongated form during
movement, several finger-shaped pseudopodia of moderate
length are formed, as a rule, at the anterior end, and, pari
passu, with the movement of the Amoeba forward in a
straight line in the direction of its long axis, these pseudo-
podia travel backwards and are gradually retracted. Now
as long as the pseudopodia are at the anterior lend, they
appear, as a rule, homogeneous and structureless, but after
they have travelled backwards they become distinctly reti-
cular throughout, even up to the outermost margin. Hence
the same phenomenon would seem to be repeated here that
we observed in the retraction of the pseudopodia of Gromia
Dujardini. The pseudopodia of this Amoeba showed in the
preserved condition (picro-sulphuric-osmic mixture) a very
pretty reticular structure usually up to the extreme tips,
and the marginal layer of alveoli could at the same time be
seen with great distinctness (Plate II. Figs. 7 and 8).

In the year 1878 I first drew attention to the fact that
A. Blattce, not uncommon in the end gut * of Blatta orientalis,
offers one of the best examples of fibrous protoplasm. In
this organism investigation in the living condition shows
the protoplasm to be very distinctly fibrous, and the fibre-
like appearances follow the direction of the movements. For
this point I will refer my readers to the description formerly
given by me. In recent times I have had the opportunity
of again observing this interesting Amoeba, but unfortunately
was unable to study it in detail. Still, I am able to complete
my former description in one point, namely, that the ap-
parent fibrillae are here also not disconnected, but united
into a network. If the Amoeba be followed in its move-
ments, it is easy to convince oneself that the fibrillar
appearance is only a consequence of the tensions caused by

1 Proctodseum.

i io PROTOPLASM

the streaming. This can be seen most beautifully at the
hinder end of an Amoeba of this kind when it is creeping
after the manner of an A. Umax. Corresponding to the
axial forward stream towards the anterior end, an axial
tract of fibrillse traverses the Amoeba, radiating out poste-
riorly into a tuft as a consequence of the protoplasm of the
hinder end being drawn in from all sides into this forward
current.

That radially disposed protoplasm may, moreover, occur
occasionally in other Amoebse is shown by the following
casual observation. In one of my preparations of A. actino-
phora, I found an elongated specimen, one end of which was
modified into a clear rim-like expansion. Although the
characteristic envelope of A. actinophora could not be demon-
strated with certainty in this specimen, nevertheless I
consider it probable that it belonged to the species in
question. The broad margin (Plate IV. Fig. 3), which
without doubt represented the end of the Amceba occupied
in forward movement, was radially striated in the most
beautiful manner in its entire depth. Although the structure
of the margin was relatively pale, it could nevertheless be
most plainly made out that it was the result of a radial
arrangement of the alveoli. The protoplasm bordering on
the margin towards the interior appeared very sharply
reticulated with very dark nodal points, resulting from the
deposition of fine granules. I think the assumption,
that this beautifully radially striated margin was repre-
sented in life by an apparently hyaline border, is all the
more permissible from the fact that Gruber (1882) depicted
on his Plate XXX. Fig. 17, an Amceba actinopJwra with a
similar border, in which a radial striation is faintly indicated.

Since Greeff has recently again doubted (1891) the
emptying to the exterior of the contractile vacuole of
Amoebae, I may notice that these studies gave me the
opportunity of observing very clearly, in several of the
Amoebae investigated, how the vacuole does not disappear
until it is in direct contact with the surface, and that during
the process it collapses from within towards the exterior.
Hence I have no doubt that it is emptied to the exterior.

P LAS MODI A OF sETHALIUM in

As is well known, the endoplasm of Amoebae contains, for
the most part, numerous granular contents of very various
sizes. Whenever I was successful in making out clearly the
position of these granules in the meshwork of the proto-
plasm, I always found them deposited in the network itself,
never, on the contrary, in the clear contents of the meshes.
The granules constantly show an undulating, almost a
dancing movement, frequently reminding one in the latter
case of molecular movements. This proves in any case that
the internal protoplasm is relatively very fluid. At all
events the framework is in a state of continual undulating
movement.

JEthalium septicum (Fuligo varians) l

It was only after the manuscript of the present work was sent
off that I found an opportunity of investigating the protoplasm of
^Ethalium, an object of so great and so long a recognised import-
ance for the study of living substance. I must regret that I
had not already paid before a closer attention to this organism,
for, as regards the protoplasm question, it is one of the most
instructive with which I am acquainted. Hence, it seems
justifiable to make in this place a brief supplementary report
as to some observations on the protoplasm of this Myxomycete.

Unfortunately, I have only as yet made a cursory study of
the living protoplasm, but I shall try, as soon as possible, to
make up for this deficiency. The protoplasm, fixed in the way
described above, with the picro-sulphuric-osmic mixture, shows
the alveolar structure more distinctly and beautifully than do
the majority of the objects described before. This is partly
connected with the fact that it is very easy to obtain plasmodia
of jEthalium in so thin a layer that they vie with the thinnest
sections. Now, since the processes of manipulation that are
performed in embedding and cutting do not in any way render
the structures more but rather less distinct (as I convinced
myself in yEthalium, of which I also made sections), it is obvious

1 These observations on the protoplasm of ^thalium and Pelomyxa were
made by the author after the text of this work had been finished and sent to the
press. In the original German edition they were placed in an Appendix at
the end of the work, but in the present edition these, as well as other
additions of the Appendix, have been inserted in the text in their proper
places.

ii2 PROTOPLASM

that layers of protoplasm of such thinness, as are formed here
and there by the plasmodia of Myxomycetes, are objects especi-
ally suited for investigation. In order to obtain a good pre-
paration, it is best to proceed as follows. Some slides are
thoroughly wetted and placed upon the tan, which should
be in a large damp chamber in the dark. It is then neces-
sary to wait until some plasmodia creep on to the slide and
have spread themselves out in a very fine layer. Of course,
only the thinnest and most branched networks should be chosen
for preparations. Or, on the other hand, plasmodia which are
creeping about on the walls of the vessel, or elsewhere, can be
simply scraped up with a scalpel, and the lumps of protoplasm
kept on damp slides in a damp chamber in the dark. I found
almost always that after about twenty-four hours, such lumps
of protoplasm had spread themselves out again into very
beautiful networks. It is now only necessary to keep the slide
in question for some time in a vertical position within a damp
chamber, so that the superfluous water may run off as far as
possible, and then to transfer it to picro-sulphuric-osmic acid or
some other fixing fluid. When the water has been as far as
possible removed from the slide in the manner stated, without,
however, the plasmodium being dried up, the latter, after fixation,
adheres quite firmly to the glass. If too much water has
been left behind, the plasmodial network easily separates off,
which renders further preparation very difficult. Plasmodia that
are adhering well can, after fixation, be played upon by a strong
spray from a flask without becoming loosened. Of course the
preparations can be stained as desired, but all the observations
described in the following were made upon unstained plasmodia,
which after being washed were put up in water.

In such preparations the alveolar structure of the protoplasm,
as I have often described it above, can be seen most beautifully.
In the plasmodial network places may be found of such thinness
that they are only formed of a single layer of alveoli. Places of
this kind are of course especially suited for study, and show all
the phenomena which we have observed above in similar thin
layers of oil-lather. Without entering into a detailed descrip-
tion, I refer to the Photographs XV. and XVI., XVII., and
XVIII. and XIX. Photograph XV. shows a small lobed projec-
tion at the edge of a plasmodium, which in the prepara-
tion is torn across close to its origin, probably because the
principal mass, from which it arose, contracted strongly. In
as accurate a focus as possible, such as was chosen in Photo-
graph XV., the frothy framework is distinctly noticeable in
the whole of the internal and thicker portion of the lobe. The

PLASMODIA OF &THALIUM 113

nodal points of the framework stand out very prominently in
many places. Towards the edge the framework becomes paler
and more finely meshed. Finally, a broad, apparently quite
homogeneous border forms the exceedingly attenuated edge
of the lobe, of which the outer, very delicate limiting contour
is only just visible. But by careful examination distinct traces
of foam-like structure can still be made out in the photograph in
this apparently hyaline margin. In many cases, however, I saw
this structure still better than in the present photograph, for
which reason I do not doubt that an apparent absence of
structure in the margin only depends on the faintness and fineness
of the framework, which is caused by the excessive thinness of
the margin. We shall soon see that a further fact of importance
is in favour of this assumption.

Photograph XV. should now be compared with Photograph
I., in order to convince oneself of the striking resemblance of
the two in all the points mentioned.

We may now consider Photograph XVI., which represents
the same lobe with a slightly higher and less sharp focus, and
hence shows the false reticular image, which will be discussed
more accurately and its origin examined into on p. 210 et seq.
The distinctness of this false network here is quite striking ;
it is also obvious that it must be considerably more prominent,
since it appears much darker than the true network does when
sharply focussed. Moreover, Photograph XVI. has come out
much better than XV. Now, with Photograph XVI. compare
Photograph II. of the above-mentioned oil-foam in a correspond-
ing focus, from which it is plain that in this respect also there is
complete agreement between them. Hence, from the observations
that have been adduced, no other conclusion can be drawn than
that identical relations are here before us — that is to say, the
structure of the protoplasm of Milialium, like that of the oil-
foams, must consist of a more strongly refractile alveolar frame-
work, which encloses in its cavities less strongly refracting
contents.

Photograph XVI. permits the corresponding faint structure
to be made out much more plainly also in the margin than is
the case on Photograph XV. with a sharper focus. This is
easily intelligible, since the false reticular image is darker than
the true one, and hence stands out more prominently. This
circumstance, which in like manner holds good for the oil-lather
on Photograph II., may be taken as a sufficiently sure proof that
the margin has just the same structure as the interior of the lobe.

As a further confirmation of what has been stated, I have
added two photographs, XVIII. and XIX., at correspondingly

ii4 PROTOPLASM

different foci, which exhibit a larger portion of a very thin
layer of protoplasm from the interior of a plasmodial network.
The photographs were taken with a lower magnification (Obj. 4
mm.), but this is quite sufficient to make out the characteristic
structure.

Finally, I refer to the very successful Photograph XVII.,
which in like manner shows an extremely thin portion from the
interior of a plasmodium (Obj. 4 mm.). Where the protoplasm
is thicker in this picture, the structure becomes, of course, more
indistinct ; moreover, the protoplasm is much more opaque in
these places, principally on account of the large quantity of darker
enclosures, varying from the finest to the much more coarse. In
the photograph these enclosures can also be noticed very plainly in
the thin places, and are plainly to be distinguished from the nodal
points of the honeycombed framework. In some places the layer
of protoplasm is interrupted by rounded gaps, so common in
the network of the plasmodium. Towards the edge of such a
gap the structure becomes fainter or even disappears entirely ;
here the edge thins out in a manner similar to the lobes of proto-
plasm described above. But even within the continuous thin layer
of protoplasm, one sometimes comes across places where the struc-
ture is quite faint, till finally only indications of it are to be
noticed. These are extremely thinned out portions in which gaps
may come to be formed by dehiscence later on.

Photograph XVII. shows, however, yet another very
interesting fact. When more accurately examined, one
notices in the protoplasm quite a number of rounded, rather
dark bodies. These are nothing more than the numerous cell-
nuclei, which in such thin places can be seen distinctly without
further preparation. With reference to the structure of these
nuclei, I will only remark that, as a rule, they contain a central
nucleolus-like structure, from which a nuclear framework, con-
sisting of simple radiating trabeculse, stretches across to the wall,
so that in fact they possess a structure such as I have already
frequently described for small nuclei. In some places it can be
seen quite beautifully in the photograph that the meshes of the
protoplasmic framework are directed radially to the surface of
the nucleus, as has already been described above in the case of
other objects.

After what has been remarked heretofore it scarcely needs to
be pointed out especially that the radiate layer of alveoli is not
wanting at the surface of the plasmodium. It usually shows up
most clearly at the edges of the gaps which so frequently inter-
rupt the plasmodium, granted, however, that the edges are not
too thin, so as to prevent the structure from being quite visible

PLASMODIA OF &THALIUM 115

up to them. Unfortunately no such spot is present on Photo-
graph XVII., but nevertheless the radiate layer of alveoli is quite
recognisable as a clear border to some gaps.

The plasmodium further shows us with particular distinct-
ness the frequent transition from the usual honeycombed into
the fibrous structure. Wherever strands of protoplasm are
stretched across like bridges between neighbouring branches —
that is to say, in general wherever the protoplasm is subjected
to a strain or tension, the structure appears fibrillar-alveolar, the
direction of the fibres running constantly in the direction of the
tension, and hence in bridges, for example, always parallel to
their long axis. In such fibrillar bridges and strands the radiate
alveolar layer can also be always plainly traced at the surface.

Bridges of this kind are often so attenuated in the middle
that they consist of only a single series of alveoli, and at last,
indeed, nothing more is to be seen of any structure, and they
resemble the very fine pseudopodia described already in the
Rhizopoda.

At the end of the plasmodial network which is occupied in
creeping forwards, protoplasm quite hyaline in appearance and
free from enclosures is usually to be observed during life. It
can easily be established that here we are not dealing with a
very thin and hence apparently structureless layer. This
hyaline protoplasm at the anterior end is, on the contrary, for
the most part very thick, and corresponds to the homogeneous
border at the anterior end of Amcebce. After fixation it proves,
in like manner, to be distinctly and finely alveolar, and at times
also finely radially striated : the layer of radiate alveoli can also
be plainly recognised at its surface. I will, however, return again
below to the question of the reality of its structure.

Fine plasmodia dried up on the slide in the air still show the
honeycombed structure distinctly in thin places when examined
in air ; with a higher focus also the image of the false network
can be made out beautifully. I set especial value upon this
observation, as I have already pointed out before (1890) for the
similar case of Bacteria. For since after drying up there can
certainly be no question of coagulation or precipitations, the
visibility of the structure in desiccated protoplasm may be taken
as a definite indication that it must also be present in the living
condition, and is not a product of the media of fixation.

I have made use of such dried plasmodia for deciding a
further question, which is especially important. It is well known
that there is as yet a lack of any sure proof as to the nature of
the contents of the protoplasmic alveoli, although in my idea
everything is in favour of its being a watery solution. Now if

ii6 PROTOPLASM

well-dried plasmodia be brought for twelve to twenty-four hours
into olive oil, and then the oil be washed off carefully with hot
water, the investigation of such preparations in water teaches us
that the alveoli of the protoplasm are filled, in many places at
least, with oil. The preparations become still more instructive if,
after the oil is washed off, they are placed for some time in 1 per
cent osmic acid, which turns the oil brown. That the oil actually
fills the alveoli of the protoplasmic framework in many places
can be made out very plainly in thin portions, since the contents
of the alveoli now show a considerably stronger power of
refraction than the framework, whilst before the reverse was the
case. With a rather higher focus the contents of the alveoli
that are filled with oil now appear very clear and bright, while
the framework becomes very dark, and hence much sharper and
more distinct than in places not filled with oil. As the tube of
the microscope is raised the stronger refraction of the contents
of the alveoli can be definitely established, since during the
process the contents of each one becomes a diminishing, glitter-
ing point, while the less refractile framework becomes darker.
I possess a photograph of the alveolar framework filled with oil
which shows this exceedingly well. The faint framework can
also be recognised with sufficient distinctness in the neighbouring
parts that are not filled with oil, and in this way it is still more
definitely shown that here is really a case of the alveoli being filled
with oil.

As has been remarked, I hold these results to be especially
important, since they markedly support my view, that the
alveolar contents are a watery solution. For if in dried or fixed
protoplasm the contents can be replaced by oil, the conclusion
is incontestable, and refutes more particularly the view of
Schwarz, discussed below on p. 205, who explains the contents
of the alveoli as being identical with the substance of the frame-
work, only rather less refractile.

Pelomyxa palustris, Greeff

By the kind help of my respected friend and colleague
Blochmann, I obtained during the past winter a considerable
quantity of this highly interesting Ehizopod from Eostock. I
made use of the opportunity to study the nature of the proto-
plasm, in addition to other observations. I must state, to begin
with, that Pelomyxa, as I have already pointed out before
(Protozoa, p. 99), in the normal condition possesses no cortical
protoplasm or ectoplasm. At times hyaline portions, usually of

STRUCTURE OF BACTERIA 117

very limited extent, make their appearance as small processes or
lobes on the surface. As the result of maltreatment, on the
other hand, whether from pressure or from the action of chemical
substances, there develops, as a rule, a layer of protoplasm of
this kind over the whole surface, which gradually disappears
again when these influences cease.

A clear border below the limiting contour of the surface is
always very plainly noticeable even with lower powers ; on the
other hand, I have not succeeded as yet in observing with
certainty any radial striation of this border, which in other
respects possesses all the characters of an alveolar layer. In the
rest of the protoplasm also I was not able to recognise distinctly
a fine alveolar structure during life ; the well-known coarsely
frothy structure of the protoplasm of Pelomyxa cannot, of course,
be placed on a level with the minute foam-like structure. If,
however, small and rather compressed individuals be rapidly fixed
with picro-sulphuric-osmic acid under the cover-slip, the entire
protoplasm shows the finely honey combed structure especially well,
and the alveolar layer usually shows up on the surface with a
distinctness and sharpness such as I have hardly seen elsewhere.
The radiate layer is shown just as beautifully round the numerous
nuclei. Also in the hyaline, and in any case very fluid proto-
plasm, which under the above-mentioned circumstances makes
its appearance at the surface, the radiate layer of alveoli and
the honeycombed structure can be made out excellently after
fixation.

The protoplasm of Pelomyxa possesses an especial tendency
to break up into a great number of spherical drops before its
final death. Each of these drops shows a beautiful layer of
radiate alveoli at the margin after fixation.

2. On Protoplasmic Structures in the Bacteria and
allied Organisms

In a work which appeared in the commencement of the
year 1890, I tried to show that Bacteria and Cyanophycem
possess essentially the same structure, and that in both there
could be demonstrated a nucleus of considerable size and
with a beautiful alveolar structure, which at least in the
larger forms of Bacteria, and universally in the Cyano-
pliycece, was surrounded by a thin layer of protoplasm
of alveolar structure. I would have contented myself with
simply referring here to that work as a proof that these

u8 PROTOPLASM

organisms, while showing the greatest simplicity of structure
in many respects, also permit the alveolar structure of living
matter to be made out in them ; and I might perhaps have
further pointed out that Kiinstler also (1889) quite inde-
pendently, by staining with Noir de Collin, observed, in the
body of a Bacterium termed by him Spirillum tenue, the
same alveolar structure which I demonstrated by somewhat
different methods in Spirillum undula, Ehrb., and a number
of other Bacteria ; if Alfred Fischer, in a work on TJie
Plasmolysis of the Bacteria, had not in the meanwhile
raised some objections to the interpretation of the structure
of Bacteria and Cyanophycece which I based upon detailed
studies. I feel myself bound to consider these objections
more closely. As a matter of fact, his objections seem to
me to lack cogency, and on that account I would have
gladly left them to be contradicted by the decision of some
third person of judgment and experience in this department
of knowledge ; since, however, in the eyes of so many people
the right seems to lie on the side of that person who has
spoken the last word, and the importance of facts formerly
advanced becomes forgotten, through each person scarcely
finding time to master his own limited province at all
thoroughly, I have made up my mind to refute in this
place the somewhat peculiar method of argument adopted
by Herr Fischer.

Fischer has not in any way troubled himself to study
from his point of view any one of the forms investigated by
me, nor one of the typical large Bacteria, upon the investi-
gation of which I based my description. He has not even
examined the Oscillarice, which are always accessible to any
one, in the least according to the methods suggested by me.
Nevertheless he considers himself quite justified in declaring
my views as to the structure of the organisms in question
to be quite erroneous, on the ground of some experiments
upon the plasmolytic contraction of the contents of certain
bacterial cells. What I described as a radially striated
layer of protoplasm of alveolar structure in the large
Bacteria, such as Chromatium okenii and Opliidomonas jenensis,
as well as in the numerous Oscillarice investigated, is

STRUCTURE OF BACTERIA 119

according to him nothing else than the protoplasm which
has remained sticking to certain points of the cell wall after
plasmolytic contraction of the contents, and has become
drawn out into threads or rays. It is therefore also im-
possible to speak of a special central body or nucleus in
these organisms, and that which I regard as such is nothing
else whatever but the central mass of the contracted cell
protoplasm.

Whoever reads the interpretation put upon my observa-
tions, an interpretation which makes my qualifications for
investigating such objects appear in rather a dubious light,
might perhaps arrive at the obvious supposition that Fischer
in his studies on the plasmolysis of the contents of the
bacterial cell had observed the occurrence of some such
process as he declares to be the source of my errors. It is,
however, to be sought in vain. He has observed nothing
more than the contraction of the contents of the cell under
the action of certain solutions ; in his pictures we look in
vain for any trace of structural relations. The whole of his
interpretation of the appearances described by me is therefore
hypothetical, and is only based upon the experience that in the
plasmolysis of " ordinary plant cells " single threads of proto-
plasm " not at all infrequently " remain sticking to the wall
of the cell, and according to Fischer are continued into the
pores of the cell wall. So far as I am aware, this phenomenon
is by no means of common occurrence in the plasmolysis of
" ordinary plant cells," but is the exception. As a rule,
the contents contract on all sides without any such formation
of threads, and whenever they occur, they make their
appearance for the most part very irregularly here and
there.

If it thus appears, from what has gone before, quite inadmis-
sible and absurd to try to refer the radiate alveolar layer of
protoplasm, observed by me quite regularly both in the large
Bacteria and in Oscillarice, to a phenomenon of such abnormal
occurrence in the cells of higher plants, this is shown still further
by a series of other facts. Fischer asserts, as has been said, that
all the conditions described by me are deceptive appearances
resulting from cells altered by plasmolysis, and supports his con-

120 PROTOPLASM

tention by the fact that I have investigated material fixed in
alcohol, which easily becomes more or less plasmolysed. Had
he spent more time in attentively reading my work (which only
laid claim to the importance of a preliminary communication), it
would not have escaped him that I by no means used alcohol
only for preservation, but employed at the same time various
most excellent fixing media, such as picro- sulphuric acid, both
with and without osmic acid, chrom-osmium-acetic acid, osmic
acid vapour, etc., and that all these different media lead to
the same results essentially. If I usually employed weak
alcohol, with moreover, for the most part, an addition of iodine,
as a means of fixation, this was done because I had convinced
myself that it gave the same results as the remaining media, and
at the same time offered the advantage that staining methods
came off better and more characteristically in materials so fixed.
I can also certify that with proper application of this means of
fixation no plasmolysis is set up, but on the contrary there is
frequently, as I remarked, rather a tendency for the membrane
to burst with partial effusion of the contents.

I consider it, however, quite unnecessary to spend any
more time over these things, since Fischer's quite unwar-
ranted objections can be contradicted without difficulty by a
series of facts which were just as accessible to him as to
me, and which he himself ought therefore to have taken
into consideration, had he thought it necessary to be
better informed upon these questions, before he delivered
judgment upon them. As is well known, the central body
or nucleus of the Oscillarice had already been observed by
E. Zacharias before me, and at a later date this investi-
gator followed up this matter further independently, but at
the same time as myself. Whether Fischer knows of
Zacharias's work or not remains uncertain, since he nowhere
mentions it. In any case, Zacharias is as convinced as I
am, that the Oscillarian cell contains a central colourless
body of considerable size, and with peculiar properties.
Whether this body is to be interpreted as a nucleus or not,
is another question ; in any case, it is satisfactory that both
Zacharias and myself have obtained desirable results which
agree sufficiently on this point. I can be quite content if
Zacharias recognised this body as the forecast of a nucleus ;
for in that case it is also the representative of the nucleus

CENTRAL BODY OF BACTERIA 121

of higher cells, the light in which I consider it. Whether
it possesses all the properties of the latter or not, is a
question which requires further investigation, and moreover
it does not seem to be absolutely necessary for this to
be the case. The central body of the Oscillarice is thus,
according to the observations of both Zacharias and myself,
which moreover are anticipated by the statements of some
earlier authors, to be observed in the cell quite plainly, even
during life, as a colourless central portion ; just in the same
way I pointed out a similar visibility of the corresponding
central body of Chromatium okenii, and that, as a matter
of fact, it may even be observed in Bacterium lineola
while living. This being so, how any one can presume to
defend the assertion, that the central body is only the
central mass of the cell contents contracted by plasmolysis,
is to me inscrutable, and it certainly offers a proof of the
strange manner in which arguments are frequently carried
on at the present day. If we consider further, that, as
Zacharias and I showed at some length, the central body is
marked out both by especial tingibility and by its behaviour
towards digestive fluids, the untenability of Fischer's asser-
tion becomes more and more beyond doubt. Last but not
least, an additional point which is capable of absolute proof
comes to our help, which I did not lay stress upon formerly,
since it seemed to me impossible to raise the objection
under consideration. In Chromatium okenii, as also in
Oscillarice, I frequently had opportunity to observe, in my
preparations, cells in various stages of plasmolysis, i.e. cells
in which the contents had more or less shrunk away
from the cell membrane. In such specimens it could be
determined in the most definite manner that, as the result
of the plasmolysis, the entire radiate alveolar protoplasm had
separated itself from the membrane, with a sharp, smooth,
limiting surface. Of Chromatium in particular, I have found
specimens in which the entire contents were retracted
strongly from the membrane, and which, nevertheless, showed
most beautifully both the protoplasmic cortex and the central
body. Even in Bacterium lineola it was possible to observe
similar conditions with certainty.

122 PROTOPLASM

As I believe that by means of the foregoing expose I
have sufficiently refuted and characterised Fischer's objec-
tions, I consider it unnecessary to enter closer into the
further attacks which he directs against my interpretation of
the smaller Bacteria as central bodies deficient in protoplasm,
or at least very poor in it.1 Since my line of argument is in
effect a simple consequence from the results which followed
from the investigation of the large Bacteria and Cyanophycea,
it may rightly be persisted in, if the objections raised by
Fischer against the correctness of these observations are
shown to be erroneous and unwarranted. That this, however,
is the case will, I hope, have become sufficiently clear.

3. Some Observations on the Streaming Protoplasm of
Vegetable Cells

Without having gone deeply into this subject, I have
nevertheless investigated casually some of the well-known
objects which show well the so-called rotational streaming
of the protoplasm, such as the hairs on the stamens of
Tradescantia virginica, the stinging hairs of Urtica urens, and
hairs of a Malva sp. The results were essentially the same
throughout. Almost always a very beautiful structure as of
longitudinal fibrillse can be observed in the long drawn out

1 I seize the opportunity of correcting an error which has slipped into my
work on Bacteria. On p. 34 the remark was made, that earlier observers
had already occasionally compared Bacteria to the nuclei of higher
organisms on account of their intense tingibility, and this was done, to
my knowledge, by Klebs (Allgem. Pathologie, 1887, Bd. i. pp. 75, 76) more
especially. Professor Hiippe had the kindness to point out to me that it was
he himself who at a somewhat earlier date had already enunciated this com-
parison (Hiippe, Die Formen der Bacterien, Wiesbaden, 1886, pp. 94, 95), a
correction which I here gladly make. As I was only able to give a short
preliminary account of my studies on Bacteria, by reason of the work which
forms the subject of the present writings, I lacked time to search carefully
through the so extensive literature of Bacteria. I therefore followed Ernst in
the statement in question, who made the same remark on p. 44 of his work.
Besides, this historical question has no very important bearing, since both
Hiippe and Klebs considered the relations indicated by them of the Bacteria
to the nuclei of true cells, as quite uncertain, and did not ascribe to them
any very great significance.

PROTOPLASM OF PLANT CELLS 123

strands of protoplasm that traverse the cell sap in various
directions. In these strands the fibrillse always run parallel
to the direction of the long axis, i.e. to the direction in which
the strand is stretched. In favourable spots it is possible to
convince oneself even in the living object, that one is not
dealing with isolated fibrillse, but with fibriUse connected into
a meshwork. The structure is everywhere the same as
that which we met with in the stronger pseudopodial stems
of the Khizopods. Of course, the observation is also
considerably hindered here by the continuous displacements
and alterations of the extended meshwork.

In general I found the appearances more distinct in the
hairs of Malva and Urtica than in Tradescantia*. Where
the streamings have temporarily slowed down, or especially
where portions of the protoplasmic strands have come to rest
for a time, one obtains especially favourable opportunities
for studying the meshwork, which alters its structural
character distinctly in the slight aggregations of protoplasm
arising from stoppage of the currents. It then passes from
the fibre-like meshwork into the ordinary reticulate mesh-
work, and vice versa portions with such a net-like meshwork
can be observed to pass over into the fibrous condition, when
they become drawn out into strands again. Fig. 9, Plate
IV. represents the marginal portion of a streaming proto-
plasmic strand of Malva, into which another strand opens
laterally ; in the latter the streaming has come to a stop at
the point of junction with the former. Hence this slightly
swollen spot appears distinctly composed of a reticulate
meshwork, while on the other hand the continuation of the
strand, as also the strand that is streaming, exhibit to per-
fection a structure of fibre-like meshes. In Malva, as
occasionally also in other objects, I further convinced
myself completely that the structure of the protoplasmic
strands, after killing with proper reagents, such as alcohol,
picro-sulphuric acid, etc., undergoes no alteration, apart from
the fact that it becomes sharper and more distinct. Oppor-
tunity is frequently offered of making observations on
threads of protoplasm drawn out to extreme fineness, in
which nothing is to be observed in the way of structure. On

124 PROTOPLASM

the other hand, wherever these threads possess swellings
the reticulate structure can be plainly recognised. On
Plate XII. Fig. 2, a structureless thread of this kind is
depicted with a distinct reticular swelling. The coming to a
decision as to the ultimate structural relations of the thinnest
threads is hindered by the same difficulties which we have
already discussed for the finest pseudopodia of the Rhizopods.

In the thin layer of protoplasm lining the internal wall
of the cell membrane as a continuous layer, the reticular
structure is very pale, and only to be made out with diffi-
culty, which is not to be wondered at when the excessive
thinness of this layer1 is taken into consideration. Here
also, however, it is to be observed in surface view. After
treatment with suitable reagents it shows up very plainly.
Since, as we have seen, the places where the structure
is more distinct in life undergo no alteration through
the reagents employed, we have every right to consider the
reticular structure of the thin layer of protoplasm lining the
cell wall as a normal phenomenon, although it only becomes
perfectly distinct after treatment with reagents.

In general my observations upon the structural relations
of the streaming protoplasm of the vegetable cell, both in
life and after treatment with reagents, prove its almost
complete agreement with that of the reticulose Rhizopods,
which have also a marked similarity in their mode of
movement.

4. Observations on some Egg Cells2

In order to begin here also with observations on the
living object, I will first mention that the ripe ova of the

1 Although I have as yet been unable to observe in optical section the
reticular nature of this layer of protoplasm clothing the wall, I am never-
theless of the opinion that it can only possess the thickness of one layer of
meshes.

2 A few remarks upon some methods of investigation, employed in the
following studies, may not be out of place here. Coloration with so-
called iron-hsematoxylin was frequently employed and carried out by bringing
the objects or sections first into a light brown watery solution of ferrous
acetate ; and then, after washing out, they were stained in a J per cent

PROTOPLASM OF OVA 125

very transparent Eotifer Hydatina senta show a reticulate
meshwork most distinctly after a little pressure. At the
same time it may be determined that the surface of the egg,
under the thin vitelline membrane, is formed of a layer of
alveoli with beautiful radial striation, which is bounded ex-
ternally by a very dark and fairly thick border. Strongly
compressed ova, of which the protoplasm is squeezed to
bursting, show the reticulate meshwork structure exceed-
ingly clearly, with strongly refracting granules, varying in
size from minute to much coarser ones, deposited in the
nodal points (Plate VII. Fig. 4). Since the protoplasm of
the ovum passes into a state of lively flowing movements as
soon as it is squeezed, it follows therefrom that it' is com-
pletely fluid.

Very fine sections through eggs of Sphcerecliinus granularis,
which have been preserved in picro-sulphuric acid and then
tinged brown in 1 per cent osmic acid, show the composition

watery solution of hsematoxylin. One obtains in this way extremely
intense staining, varying from blue to dark brown, which is very
necessary for the thinnest sections (1 yu). This method also gives certain
differentiations of colour. Frequently, however, in order to obtain the most
intense possible staining for very thin sections, aniline colours, especially
gentian violet in aniline water, were used. The so-called acid hsematoxylin,
so often spoken of, is greatly diluted Delafield's hsematoxylin, to which some
drops of acetic acid are added, until the colour becomes distinctly red. This
mixture gives especially good nuclear stains, which show in particular the
colour differentiations of the nuclear contents described by me above. In
order to prepare the thinnest sections, I cover the cut surface of the objects
embedded in paraffin with a thin skin of celloidin before cutting them ; this
method succeeds very well for obtaining sections of 1 /*, or even considerably
thinner. The investigation of the sections was first done in water, since the
delicate protoplasmic structures naturally show up much more plainly in the
feebly refracting water than in resins or the like. For the first investigation,
therefore, this method is much to be recommended, although any one ex-
perienced in these matters can usually make out the structures in prepara-
tions mounted in Damar or Canada balsam also. The distinctness of the
images is, however, so much greater in water that the use of that medium is to
be strongly recommended. As has been remarked, the most intense staining
is scarcely sufficient in the investigation of such fine sections, the more so as
even with it the protoplasmic framework proper only stains extremely slightly,
so that strong solutions of the stains seem almost indispensable for the recog-
nition of such delicate structural elements. A section of about 0'5 to 1 n
through an object which after staining with iron hsematoxylin appears
absolutely black, is yet so faintly coloured that further staining on the slide
is often necessary.

126 PROTOPLASM

of the protoplasm very distinctly as a fine reticulate mesh-
work. The sections were further stained on the slide with
Delafield's haematoxylin, as a result of which the true proto-
plasmic framework was, as usual, only very feebly tinged or
not at all. The relatively dark coloration, which the proto-
plasm takes on in haematoxylin, depends in the main much
more on the numerous fine, strongly staining granules which
are lodged in the nodal points of the framework.

On the surface of the yolk a radiate alveolar layer can
be made out plainly (Plate V. Fig. 1, 6), and the eggs which
were investigated after the second cleavage also showed the
layer of alveoli very plainly on each side of the surfaces of
contact of the two segmentation spheres.

From the investigation of eggs during the process of
segmentation it was shown that the radiating appearances
of the so-called asters or suns only depended on the arrange-
ment of the meshes of the protoplasmic framework. This
can be demonstrated even in entire ova killed with picro-
sulphuric acid (Plate V. Fig. 1, c), but of course much more
clearly and better in sections cut as thin as possible. The
similarity is very great between the arrangement of the
meshes and that formerly described in the radiating proto-
plasm of the central capsule of Thalassicolla. On Plate V.
Fig. 1, &, a fine section is figured through one of the suns of
the nuclear spindle of a dividing ovum. The section passes
a little obliquely with reference to the axis of the nuclear
spindle, which makes its appearance in the next section, and
shows a distinct equatorial nuclear plate. In the centre of
the sun or aster the so-called polar or central body, which
is relatively strongly stained, may be noticed. It seems
to consist of three vesicles provided with strongly stained
walls. This central body lies in the clear, quite unstained
central area of the radiations (" sphere of attraction,"
Beneden ; " archoplasma," Boveri), which in its turn is
again enclosed by the rather intensely stained and radiating
external protoplasm. The central area also is radiately
disposed throughout. The central body is immediately sur-
rounded by a zone of small extent composed of an irregular
mesh work of protoplasm, which passes directly into the

BLOOD CORPUSCLES OF THE FROG 127

radiate mesh work of the large portion of this region. That
this radiate protoplasm is really composed of a reticulate
meshwork can be demonstrated quite plainly. The proto-
plasm of the central area passes again immediately into
the more strongly stained radiating external protoplasm.
In this section the radiate arrangement of the external
protoplasm was less strongly pronounced than is the case as
a rule, but was nevertheless to be seen clearly in many
places. As I have already pointed out above, the stronger
tingibility of the external protoplasm certainly depends on
the numerous strongly staining granules which are lodged
in it, and not on an alteration in the nature of the real
framework. In order to show this fact quite plainly in the
figure, the section should, of course, have possessed the thick-
ness of only a single layer of meshes. But these sections
were not so thin (about 0'002 mm.), for which reason the
external mass of protoplasm still shows an apparently diffuse
staining.

Sections through the ovarian eggs of Barbus fluviatilis
preserved in Mliller's Fluid, especially those through larger
eggs, show the fine meshwork most distinctly, as also a
well-developed radially striated layer of marginal alveoli,
1 fju in thickness, under the egg membrane. In the largest
eggs the radiate markings reach about four or five times
deeper, which permits the supposition that we are con-
fronted here by conditions similar to those obtaining in the
peripheral zone of the protoplasm of the central capsule
of Thalassicolla. Eadiately striated protoplasm frequently
occurred also round the germinal vesicle of the larger ova,
which could be seen to owe its arrangement to a special
arrangement of the meshes. The meshed structure of the
protoplasm and the marginal alveolar layer could also be
recognised in the ovarian eggs of Dreissensia polymorpha,
on examination of some older sections, though not quite
so plainly as in the eggs first mentioned.

5. Red Blood Corpiiscles of JRana esculenta
On the occasion of some investigations upon the struc-

128 PROTOPLASM

ture of the nuclei of these cells I was also able to make out
some facts as to the structural relations of their protoplasm.
Since, in the investigation of these nuclei, I was making use
of hsematoxylin to obtain the differential stain described by
me on a former occasion (1890), which can only be dis-
tinctly shown in material preserved in alcohol, the observa-
tions to be described were undertaken upon blood corpuscles
which were preserved in iodine-alcohol of 40 per cent, then
stained in acid haematoxylin, and mounted in Damar. As
in a large number of blood corpuscles prepared in this manner,
the external form proved to be faultlessly preserved, and as
from many experiments carried on directly under the cover-
slip with iodine alcohol, it was known that this reagent gives
good preservation of the finest structural details of the pro-
toplasm, I have not the slightest fear that the somewhat
unusual method of preservation produced abnormal altera-
tions in the blood corpuscles.

On careful examination of a large number of well-pre-
served blood cells it may be recognised at the outset that they
are enveloped at their surface by a pellicle-like membrane
fairly thick and even distinctly double contoured (Plate X.
Fig. 1, p\ beneath which runs a clear border distinctly
radially striated (alv). This border can be followed quite
easily both in the surface view of the blood corpuscle (Fig.
1, a) and in optical median longitudinal section (Fig.
1, V). In the latter view particularly it may frequently be
seen very beautifully. The pellicle-like envelope together
with the radially striated border, represent, without doubt,
an external layer of alveoli of similar structure to that
which we described above in living Vorticellse, for example.
Beneath the marginal alveolar layer there can be seen in
surface view a girdle-like zone of finely -meshed internal
protoplasm, which, however, only attains from about J to J
the width of the transverse radius of the corpuscle (g).
This zone becomes still plainer in the optical median sec-
tion, when it is seen that the internal protoplasm only
forms a marginal ring or ridge (g), which passes down
on to the flat surfaces of the corpuscle ; but here it very soon
thins out, so that the flattened sides throughout the greater

BLOOD CORPUSCLES 129

part of their extent are composed of the marginal layer
of alveoli only, which comes into close contact with the
central nucleus. The blood corpuscles possess, in addition,
an internal cavity filled with cell sap, in which I occasionally
observed indications of isolated radial tracts of protoplasm ;
I have not, however, followed up this point more closely.
Studying the surface of the corpuscle by accurately
focussing its superficial aspect, it may be observed that the
network of the alveolar layer is more or less fibrous in
nature, as is represented for a small portion of Fig. I, a, at o.
The cell nucleus (n) shows a very distinct, rather delicate
framework of meshes, which stains a beautiful blue with the
method of preparation mentioned. In the nodal 'points of
this nuclear framework numerous chromatin granules of a
red colour are lodged, as I have briefly described already
on a former occasion (1890). As the figure shows, the
meshwork of the nucleus is much more open than that of
the entirely unstained protoplasm, and is distinguished from
the latter, therefore, not only in colour, but also in struc-
ture. Since this is also so distinct and clear in many other
cases, it seems difficult to understand how it is that the
theory of a direct transition between the framework of the
protoplasm and that of the nucleus is continually finding
new adherents.

Although it is impossible for me to enter here into the exten-
sive literature upon the subject of blood corpuscles, I must con-
sider some more recent observations, without setting up any
pretence to completeness thereby. Leydig mentioned as early
as 1876 the spongy structure of the red blood corpuscles of
Triton : " Here also there passes out from the nucleus, in radial
distribution, a fine network of threads towards the periphery of
the cell." The figure of the network, which he depicted in 1885
within the blood corpuscles, is, however, much too coarse, and can
scarcely represent the true network.

Frommann also observed, as far back as 1880, a reticulate
structure in the red blood cells of Salamandra maculosa, but was
of opinion that the protoplasm of the blood corpuscles was
originally quite homogeneous, and only became differentiated into
a network under the influence of an induction current applied
to it.

130 PROTOPLASM

Reticular structures, such as are described above, I find best
described by Pfitzner (1883), especially when the figures pub-
lished by him in 1886 are brought into comparison. The
radiating fibre-like structure was also then partially indicated.
The cell membrane mentioned by Pfitzner corresponds to the
pellicula. The threads of the network, according to him, sink
into this skin, and this, as a matter of fact, they do.

After I had commenced my investigations in June 1890, and
had already reported briefly upon the presence of a marginal
layer of alveoli (1890, 1892), there appeared a communication
of Auerbach which agreed in many points with my statements.
Auerbach had also observed the alveolar layer, but had not seen
its radial striation. He interprets it as a cell membrane. It is
interesting that in double staining with eosin and aniline blue it
becomes coloured blue, while the protoplasm bordering on it
stains red. Auerbach furthermore noticed the cavity in the blood
corpuscle, but regarded it as a colourless and structureless
protoplasm, which he terms medullary substance, in contradis-
tinction to that which I regard as the sole protoplasm, which
is termed by him cortical substance. The reticular structure of
the protoplasm, which he observed after treatment with picric
acid, he looks upon as an artificial product, as a vacuolisation, in
fact, from which it seems to him a little strange that his medul-
lary substance, which is at all events much richer in water,
shows no such vacuolisation. All my experiences with regard
to the fixation with picro-sulphuric acid (I did not use pure picric
acid) of distinctly structured living protoplasm, speak against this
explanation of the net-like structure. Apart from many other
differences, my observations also contrast essentially with those
of Auerbach in regard to the distribution of the protoplasm, or
cortical layer, as he terms it. This he describes as spreading out
under the whole surface of the corpuscle as a layer of even thick-
ness, as is evident from an optical longitudinal section figured by
him. This section must, however, have been taken from a de-
formed corpuscle, since it does not represent its true shape, and
shows the nucleus separated by a thick layer of the so-called
cortical substance from the marginal layer of alveoli on each
side, a disposition which directly contradicts what I have
observed.

Although I have not made this subject a matter of special
study, I would nevertheless state my belief that the central
hollow of the blood corpuscles is in reality a cavity contain-
ing cell sap, which, moreover, as has already been pointed
out above, is probably traversed by delicate strands of proto-

EPITHELIAL CELLS— GAMMARUS 131

plasm, just as in plant cells. That my description is not
exhaustive in the latter respect is obvious from the fact that
the nucleus must, in any case, be marked off from the
central cavity by a delicate layer of protoplasm, although I
have not been able as yet to observe any such with cer-
tainty.

6. Observations on some Epithelial Cells

Since it was known to me from former experience that
the epithelial cells of the gill lamellae of Gammarus pulex
show a protoplasm very distinctly striated longitudinally
even in the living condition, I chose this object in order to
obtain further light upon the nature of its minute structure.
Both the investigation of freshly cut off gill lamellae, as well
as of small and unhurt living animals, showed that the
structure is not made up of fibrils, but is a distinctly reticulate
meshwork. Fig. 5 on Plate VI. shows the optical section
through the epithelium of a freshly cut off gill lamella,
such a section as can be well seen at the edge of a
lamella. Externally there is the relatively thin cuticle (c).
Under this comes a delicate pale border, the significance of
which was not clear to me. Then comes finally the pro-
toplasm of the epithelial cells, with a very beautiful reticu-
late meshwork structure. As has been said, it can be
clearly made out that the striation only depends upon the
arrangement of the framework of the meshes. The cell
boundaries were not to be made out distinctly in the optical
section, while they were most conspicuous in the surface view
of the gill lamellae. Immediately round the nuclei of the
epithelial cells there can be seen fairly distinctly a modifi-
cation of the striated structure caused by the layer of
meshes directly surrounding the nucleus being arranged
radially to the surface of the nucleus.

In surface views, also, of the epithelial cells the net-like
structure can be observed very beautifully during life ; but
from this aspect it naturally does not appear striated but
irregularly reticular. The two epithelial layers of the
two surfaces of the gill lamella are connected with one

132 PROTOPLASM

another, as is well known, by peculiar pillars, which pass
vertically through the blood space of the lamella. In an
optical transverse section of them these pillars appear as
elongated structures which contain numerous nuclei, and
consist of beautifully reticulated protoplasm, on the surface
of which (towards the blood space) a distinct radiate alveolar
layer is formed. The optical longitudinal section of such a
pillar shows that it is traversed in the middle by a distinct
transverse line of demarcation, and that the pillar consists
of beautifully striated protoplasm composed of a meshwork,
just as are the ordinary epidermic cells of the gill lamellae.
The nuclei lie in the deeper region of the pillar, near the
line of demarcation already mentioned. As far, therefore,
as I can give an opinion as to the nature of the pillar from
a merely cursory investigation, I believe that it is formed
by the growth of epithelial cells towards the interior,
which, starting from the two surfaces of the gill lamella,
meet in its median plane. It is not quite clear to me why
I saw no cell boundaries in the optical transverse section of
the pillar in spite of its containing numerous nuclei, while
the cell boundaries on the surface of the gill lamella can be
traced very plainly. A more accurate investigation of sec-
tions of the gill lamellae will, however, easily determine their
structural relations.

" The striated nature " of the epithelial cells of the gill
lamellae of Asellus was observed by Leydig as far back as
1855. He pointed it out again in 1864, and represented the
relations somewhat more accurately in 1878 (Asellus, Porcellio,
and Gammarus). It seemed to him that the striation depended
upon "longitudinal canals or lacunes" traversing the proto-
plasm. In surface view the cells appeared as if bored through
by very minute, closely approximated holes. E. Hertwig,1 in
1879, mentioned the striated nature in Gammarus. The pillars
or trabeculse, briefly described above, which traverse the blood
space of the lamella, were also noticed by Leydig in 1878,
and he seemed to be of the opinion that they consist of chitin.
In the middle of the blood space fat is described as occurring, into
which the trabeculse extend, a fact of which I observed nothing
whatever. It should be added, however, that he only speaks

1 Der Organismus der JRadiolarien, Jena, 1879, p. 112.

EPITHELIAL CELLS— HYDATINA 133

quite briefly of the gills of Gam'marus in the description of a
figure referring to it.

An opportunity of making some studies upon the Eotifer
Hydatina senta enabled me to observe the very beautifully
striated and fibrillar nature of the protoplasm of the large
cells which carry the cilia of the two ciliated circles of the
wheel organ. The cells of the posterior circlet are especi-
ally well suited for this observation. Both in animals
subjected to pressure, as well as in such as had been
narcotised with hydroxylamine, it is very easy to con-
vince oneself as to this structure in the epithelial cells. As
far as I could see the entire protoplasm is not differentiated
into fibrils, but only a middle layer, from which the cilia
arise externally. The higher and deeper layers, on the other
hand, have the structure of an irregular reticulate meshwork,
and at the same time contain numerous peculiar elongate
or somewhat kidney-shaped bodies, which are very closely
packed in the framework, and remind one greatly of Bac-
terioids (Plate VII. Fig. 5). The fibrils of the middle
layer run down deep into the large cell until they approach
the conspicuous nucleus, without, however, reaching the
base of the cell. They are very distinctly knotted, and
closer observation demonstrates with certainty that the
nodes of neighbouring fibrils are connected by delicate
transverse threads. The structure is thus seen to consist
of a meshwork so disposed as to give a striated appearance,
and not to be really fibrillar.

The surface of the cell is limited (at least where the
cilia arise) by a radially striated border, possessing to some
extent the characteristics of an alveolar layer. The striae of
this border are direct continuations of the fibrillse, and pass,
on the other hand, immediately into the cilia externally.
In photographs which I have taken of such cells, I further
notice at their inner circumference a fairly distinct alveolar
layer, as well as a radiate layer of meshes round the
nucleus.

The anterior circlet of cilia consists, as is well known, of
a number of tufts of cilia. To each of these tufts corre-

134 PROTOPLASM

spends a bundle of fibrillae in the underlying cell, which
can similarly be well observed in the living condition.

In the investigation of the living Hydatina I also ob-
served the meshed structure very plainly in the protoplasm
of other cells, of which I will give a brief account. It
showed up most plainly in the cells of the so - called
gizzard, accompanied by the appearance of very pronounced
nodal points in the framework, an appearance, however,
which is partly called forth by granules deposited in it. On
the surface of each cell the radiate layer of marginal alveoli
was very distinct. In the cells of the gastric glands a
marginal alveolar layer could also be made out. The pro-
toplasm of these cells was either merely a reticular mesh-
work, or else a meshwork arranged in striae. In the latter
case the striation was directed towards the spot at which
the gland opened into the mid gut. Especially in the neigh-
bourhood of this spot the reticular structure could always be
observed very plainly, which partly depends on the fact that
numerous granules are lodged in the nodal points. We are
dealing here, no doubt, with the secretion products of the
gland, which are collected abundantly in the framework of
the protoplasm in this region.

The meshwork structure frequently appeared especially
distinct in the two peculiar strands which ascend for-
wards and obliquely outwards from the end gut. Whether
these strands are glandular, or are a kind of suspensoiy liga-
ment for this portion of the gut, I will not venture to
decide. Finally, the cells of the foot gland show in many
places the reticular structure fairly well, though not so
clearly as the last-mentioned histological elements.

Very thin transverse or longitudinal sections through the
body wall of Lumbricus terrestris show very beautifully the
longitudinally striated structure of the epithelial cells which
are not modified into gland cells ' (i.e. indifferent or support-
ing cells — Plate VI. Fig. 3). I will not go more specially
into the way in which the glandular and supporting cells
are arranged with regard to one another, since that has
already been recently described in detail elsewhere. Fine
longitudinal sections through the supporting cells (see the

EPITHELIAL CELLS— LUMBRICUS 135

figure) show veiy plainly the meshwork of the protoplasm
arranged to form longitudinal striations. In the nodal
points of the meshwork very small granules are lodged,
which can only be seen with difficulty. In material pre-
serred in iodine alcohol and stained with acid Delafield's
hasnatoxylin, it can, however, be made out plainly that
these granules are tinged reddish. Corresponding to their
small size the colour is naturally not very intense, but still
quite recognisable. Since the chromatin granules of the cell
nucleus also show the red coloration excessively plainly
with this method of staining, in sharp contrast to the blue
tinge of the framework, the granules of the nucleus and of
the protoplasm may be directly compared, and their great
similarity in staining and in other respects established.
I have no doubt that both are nearly allied structures, and
that here conditions are presented to us similar to those
which have been described already for Flagellata, Diatoms,
etc. (see above, p. 91). I would particularly emphasise the
fact that the nuclei of the epithelial cells of Lumbricus ter-
restris show the distinction between the staining properties
of the framework and of the chromatin granules with special
distinctness, just as well as, in fact even more distinctly than,
I saw them in CyanopkycaK, Euglcna:, etc. The nuclei of the
gland cells also show the same relations, but their frame-
work is arranged rather more densely, and in a different
way from that of the supporting cells. It is very similar to
that of the nuclei of Euglenoids, which I described briefly on
a former occasion (1890-91).

In the longitudinal section of a supporting cell figured
on Fig. 3, Plate VL, it can be farther observed fairly well
that the layer of meshes following directly under the
cuticle forms a kind of radiate alveolar layer, inasmuch
as it is marked off from the internal meshwork by a fairly
straight line, which of course only depends on the fact that
this most external limiting layer consists of meshes nearly
equal in size. It can further also be seen pretty clearly
that the layer of meshes surrounding the nucleus is arranged
radially to the surface of the latter.

In tangential sections which pass through the outermost

136 PROTOPLASM

zone of the epithelium, and therefore have not as yet passed
through the body of the gland cells, but only through their
efferent tubules, which run up between every two contiguous
supporting cells, it is possible to make out in addition the follow-
ing state of things. Each transverse section of a supporting
cell is surrounded by a very beautifully developed radiate layer
of alveoli, distinguished by staining strongly in hsematoxylin.
The alveolar layers of contiguous cells are in direct contact,
so that their pellicles form only a single sharp dark limiting
line. Every efferent tubule of the gland cell is therefore
surrounded by the alveolar layers of two neighbouring cells,
which here separate from one another to a slight extent, in
order to form the lumen of the tubule. The protoplasm of
the supporting cells shows a beautiful reticulate meshwork
in transverse section, sometimes with a slightly radiating
arrangement.

7. Peritoneal Cells on the Gut of BrancJiiobdella astaci, etc.

In very fine transverse sections of specimens of this
worm preserved in picro-sulphuric acid, I have observed the
protoplasmic structure very plainly, especially in the cells
mentioned above, but also in numerous other cells of the
body. Fig. 2, Plate VII., represents a section through a
cell of this kind, which was stained intensely on the slide
with gentian violet in aniline water. The thickness of the
section may have been at most 1 //,, but was without doubt
still less, since the investigation shows definitely that not
more than a single layer of the framework of the meshes
appears in the section. The appearance offered by the
nucleus represents, therefore, a transverse section through it.
As is shown by the figure, the protoplasmic framework
stands out with excessive distinctness, and is distinguished
by having numerous very intensely stained granules lodged
in its nodal points. It can be seen definitely, however, that
by no means all the nodal points of the framework contain
granules, but that fairly extensive regions of the framework
are quite free from them. In colouring and appearance no
distinction can be made out between the granules of the

CELLS FROM BRANCHIOBDELLA, ETC. 137

protoplasm and those of the nucleus. The protoplasmic
framework appears almost entirely unstained, and hence
very pale. The figure gives a picture of its arrange-
ment which is as true as possible to nature, not a diagram.
The meshes were drawn in exact correspondence to nature,
as far as they could be traced. The gaps in the framework
depend, therefore, partly on the meshwork not being distinct
enough in places to permit of an accurate drawing, and partly
on the existence of real gaps, which depend in their turn on
the presence of large vacuoles, or here and there on local
ruptures which are so easily brought about in the preparation
of such thin sections.

The meshed structure of the protoplasm was further
observed by me in the cells of the intestinal epithelium
of Branchiobdella, only that here the meshes are directed
longitudinally, and hence the protoplasm shows longitudinal
striations. The inner ends of the cells possess a cuticular
border, which stains very intensely, and is frequently
distinctly striated. Finally, these ends carry numerous
threads resembling cilia, which seem to bore through the
cuticular border. The protoplasmic framework is in like
manner stuffed quite full of intensely stained granules.

The epidermic cells of the skin also show a beautiful
reticulate meshwork, with large quantities of strongly
stained granules in the nodal points (Plate VII. Fig. 3, a).

In favourable sections of the cuticle, which did not stain
in the slightest, it may be seen to consist of several layers,
the height of which is about equal to the diameter of an
alveolus of the framework of the cells of the epidermis.
Each of the layers is distinctly vertically striated (Plate VII.
Fig. 3, a), and therefore presents more or less the appearance
of an alveolar layer. In other parts of the cuticle, on the
contrary, the alternating layers differed somewhat, one being
light, the other dark, and thus the total appearance being
somewhat as represented in Fig. 3, b. In surface view the
cuticle appears, as shown in Fig. 3, c, diagonally striated with
distinct dark nodal points. From these observations it
seems to me obvious that a meshed, or rather alveolar,
structure appertains to the cuticle also, and that therefore

138 PROTOPLASM

it might well have arisen by modification of the alveolar
framework of the cells of the epidermis.

I take this opportunity to remark, that the much
thicker cuticle of Pkascolosoma elongatum also frequently
shows the same structure and very plainly either in trans-
verse or longitudinal section ; only, corresponding to its
greater thickness, the number of its layers is much more
considerable.

Cuticle and so-called hooks of Distomum liepaticum. — In
very fine sections of specimens of this Trematode preserved
with picro-sulphuric acid, and then stained very intensely
with iron-hsematoxylin, the following details can be made
out as to the structure of the cuticula. The whole cuticle
stains very intensely, the cuticle proper more violet, while
the hooks lying in it stain a beautiful blue. The external
half of the cuticle shows, however, a rather more dirty violet
tint, and the inner portion more bluish violet, which depends
without doubt on large quantities of granules, staining a deep
blue, and lodged in it. The whole cuticle has a distinct
reticular meshed structure, in which the framework has a
somewhat blue tint, the intervening matrix, on the other
hand, appearing violet, for which reason the colour is violet
as a whole (Plate XI. Fig. 1). In the hooks the case is
otherwise, from the fact that the intervening matrix is also
coloured blue, so that they appear blue throughout. The
surface of the cuticle is formed of a very distinct dark
border of a blue colour, appearing like a pellicle, under
which extends a somewhat lighter, radially directed layer of
meshes, which possesses entirely the characters of a marginal
alveolar layer. The external half of the cuticle shows in its
remaining parts an irregular framework of meshes, which
obtains the appearance of radially directed fibres the more
it approaches the internal half, this character being quite
pronounced in the latter region. In addition, numerous
granules, stained a very intense blue, are lodged in the
nodal points of the framework of this deeper portion.
Since these nodal points, and therefore the granules also, lie
one behind the other, in more or less distinct rows, in conse-
quence of the fibrillar arrangement of the meshwork, the

CUTICLE, ETC., OF DISTOMUM 139

fibre-like structure of the deeper layer of the cuticle stands
out very prominently.

The hooks also show very plainly the structure of a
meshwork, and, moreover, of one that is modified into
longitudinal fibres throughout its whole extent, upon which
fact depends its longitudinally striated appearance. Blue
granules are also deposited in its framework, although not
very abundantly. Numerous lacunar spaces, resembling
longitudinal clefts, appear in the substance of the hooks.
The latter do not project out freely above the cuticle, but
are completely embedded in it, being clothed up to their
pointed external ends by a cuticular covering which gradu-
ally thins out more and more. On the other hand, the
internal ends of the hooks project beyond the inner limit of
the cuticle into the body. Between the circular and longi-
tudinal muscles a protoplasmic framework extends, which
carries numerous granules, stained deep blue, in its nodal
points. Although I could not make out completely to what
cellular elements this framework properly belongs, and
especially whether the so-called gland cells, which appear so
abundantly under the musculature, do not in some way
belong to it, I would nevertheless draw attention to the fact
that the fibrous trabeculse of the framework of the cuticle
are continued quite distinctly into the protoplasmic frame-
work extending between the musculature. It seems to me,
therefore, to follow with certainty that the cuticle, together
with the hooks, has arisen by direct modification of a proto-
plasmic framework, although the actual origin of this
covering of the Trematode body appears still as doubtful as
ever.

Very remarkable relations are shown also by the peculiar
and thick, so-called lacillar lining or cuticular border of the
epithelial cells in the gut of this worm. The epithelial
cells have a very distinct meshwork, arranged to form
longitudinal fibres, and closely packed with blue granules,
on which account it is relatively dark. The deep bacillar
lining stains only a dirty light blue colour. If this lining
be studied in the thinnest possible tangential sections through
the epithelium (that is to say, in reality transverse sections

HO PROTOPLASM

through the lining and the epithelium cells), for which
opportunity is often given by longitudinal sections of the
animal, the following peculiar structure can be seen (Plate
XII. Fig. 3). The lining consists of rather thick and
darkly stained rounded or oval bodies, which vary to some
extent in diameter. These bodies have a distinct meshwork
structure, and carry numerous strongly stained granules in
their nodal points. They appear connected with one
another by a paler, less strongly stained meshwork, which,
however, also carries scattered granules in its nodes. After
this composition has been made out in tangential sections,
it is also possible to observe a corresponding state of things
in longitudinal sections through the cuticular border. The
more strongly stained portions appear in longitudinal section
as conical bodies, which are united by a paler intervening
alveolar meshwork. Since these conical bodies, which are
pointed towards the inner surface of the lining, are not quite
of equal length and thickness, they appear to differ somewhat
in size in a tangential section, as the figure shows.

8. Liver Cells of Eana esculenta and Lepus cuniculus

Since liver cells have been made use of so often for
studies on the structural relations of the protoplasm, I
investigated them in the thinnest possible sections. The
pieces of liver in question were hardened in the picro-
sulphuric-osmic acid mixture, and then stained with iron-
hsematoxylin in the manner described. The thickness of the
finest sections must certainly have been under 1 //,, and
therefore, in any case, would not have been above the
medium thickness of a mesh of the protoplasmic frame-
work.

Sections prepared in such a way through the frog's liver,
and, for the most part, stained still further on the slide
with iron-hsematoxylin or vesuvin, show at once a very
beautiful net-like protoplasmic framework in the clearest
and most convincing manner, of which P]ate VII. Fig. 1,
and also Photograph VIII., give a representation. I
expressly point out that the figure was drawn with all

LIVER CELLS— FROG AND RABBIT 141

care, and is in no way a schematic representation. The
actual protoplasmic framework again appears very pale and
little stained: its apparently strong coloration in thicker
sections depends rather on the deposition of numerous
intensely stained granules in the nodal points of the net-
work. Although these granules, as has been said, are
present in great abundance, it is not by any means every
nodal point that is provided with them. On the contrary,
one frequently observes fairly extensive portions of the
framework which are free from them. The true nodal
points nevertheless stand out fairly prominently. If also
a somewhat fibrous composition of the meshwork is to be
seen in places, it was at all events never very pronounced
in the preparations studied by me, and the thinness of the
sections excludes every possibility of interpreting the struc-
ture, as in any way the result of separate fibrillae being
glued together or superposed upon one another. This
possibility is still further set aside when we see that the
protoplasmic framework here presents also the same
peculiarities which we have met with so frequently. If the
limits of the cells be more closely investigated (for which
purpose, of course, the thinnest and best portions are to be
chosen), it may be plainly seen that the two most external
layers of meshes of cells that border upon one another
are placed vertically to the line of limitation. Even in
Photograph VIII. this comes out plainly in places. The
line that marks the limit between two cells is always
stained very darkly, which in part, at least, may depend
on the abundant deposition of strongly stained granules.
In any case, however, a pellicle-like modification of the most
external lamella of the meshwork is also present. As Fig.
1, Plate VII. shows, this line of limitation had also fre-
quently a distinct zigzag outline, corresponding to the con-
tiguous meshes of the two limiting layers ; at times they
appear quite interrupted in places, so that the protoplasmic
frameworks of neighbouring cells pass directly into one
another. Since, however, to trace out in detail the relations
that obtain at the boundaries of the cells is, for the
present, beyond the scope of the task which I have under-

142 PROTOPLASM

taken, I only gave quite a cursory consideration to the
matter. I will, therefore, only state briefly that the dark
line of demarcation sometimes appears rather thicker,
and may then itself appear to have a meshed structure ;
it should, however, be taken into consideration, that slightly
oblique sections through the limiting lamella might produce
appearances of this kind, although I do not wish to deny
their reality altogether off-hand.

Just as we are able to demonstrate an alveolar layer at
the surface of the liver cells, so it is not infrequently pos-
sible to convince oneself that a radially arranged layer of
meshes occurs round the nuclei.

The sectional width of the meshes of these liver cells I
am inclined to estimate at about 1 p.

Sections of pieces of rabbit's liver prepared in a corre-
sponding manner showed the reticular structure of the
protoplasm in the same way and very beautifully. In
addition to cells, of which the protoplasmic framework was
pale and finely structured, exactly as has just been described
in the frog, there also occurred some with a considerably
coarser and hence much more distinct structure. In these
cases the trabeculae of the meshwork were also much thicker
and darker than usual. Photograph IX. gives a fairly good
representation of such cells. I contented myself at the time
with ascertaining the meshwork structure of the protoplasm
of these cells, without entering more especially into the
numerous points of detail still to be solved.

9. Epithelium of the small Intestine of Lepus cuniculus

Pieces of the small intestine of the rabbit, after being
hardened in picro-sulphuric-osmic acid and strongly stained
in iron-hsematoxylin, show the structure of the epithelial
cells very beautifully in thin sections. As in all cells of
similar structure, we have also to deal here with a mesh-
work modified into a longitudinally fibrillar structure with
numerous strongly staining granules lodged in the nodal
points. As far as I investigated the structure of the
protoplasmic framework, it agreed entirely in essential

PIGMENT CELLS, CAPILLARIES, ETC. 143

points with that which has already been described above for
the cells of the epidermis for Lumbricus. I think, there-
fore, that a more detailed description may be omitted, and
content myself with a reference to Photograph X., which,
however, both as regards the goodness of the section and
the success of the photograph, still admits of being con-
siderably surpassed.

10. Pigment Cells of the Parenchyma of Aulastomum gulo

I draw attention to these brown pigment cells observed
by me casually, chiefly from the fact that they show the
meshwork structure especially clearly and distinctly, and
moreover, permit the relations of the pigment granules to
the framework to be made out particularly well. The cells
investigated were obtained casually when making prepara-
tions of isolated muscle cells. The maceration of small pieces
of the body wall of Aulastomum was performed in 10 per
cent iodine alcohol, and lasted two days. Plate VII. Fig. 6
gives a picture, as true to nature as possible, of a small
portion of the protoplasmic framework of an isolated cell.
The very small pigment granules are always lodged in the
nodal points of the framework, yet on. account of their
staining properties it can be seen very plainly that by
no means all the nodal points contain such deposits. With
regard to other points, I think the figure requires no further
explanation.

11. Capillaries from the Spinal Marrow of the Calf

In maceration preparations of the spinal cord of the
calf, one frequently obtains isolations of rich networks of
the finest capillaries. If one investigates more closely the
finer structure of one of these capillaries (Plate IX. Fig. 1),
it can be seen to possess a very thin protoplasmic wall, in
which here and there large nuclei (n) are lodged. These
nuclei cause, wherever they occur, a projection of the wall
into the lumen of the capillary.

In an optical longitudinal section of the wall it may

144 PROTOPLASM

be seen to have a reticular structure, and to consist only of
a single layer of meshes. Correspondingly, the walls of
the meshes are placed perpendicularly to the inner and
outer limiting lamellae of the wall. At the nucleus, the
layer of meshes splits into two, so as to surround it both
externally and internally by a thin layer of protoplasm,
the meshes of which are placed vertically with regard to the
nucleus and to the limiting lamella. If the surface of the
wall of the capillary be focussed (o), a confirmation of the
meshed structure is obtained, which, of course, can be seen
in this aspect also. The result is that, corresponding
to its extension in a longitudinal direction, the capillary
consists of a meshwork modified into a fibrous structure.
Whether or not the protoplasm belonging to the individual
nuclei is separated by cell boundaries I was unable to
determine in preparations of this kind, and I have not
followed up this point more thoroughly.

Ley dig has noticed quite correctly, as far back as 1885 (p. 15),
that the cells of the blood capillaries (gills of Salamandra) consist
in section of a single layer of alveoli, and hence appear striated.
Only he draws the dark wall of the alveoli very thick, and the
clear intervening spaces very narrow. From this observation,
however, he wishes to infer that the thin plate-like body of these
cells is porous. "Under some circumstances the fine pores
might widen into larger openings, and thus permit the passage
through of blood corpuscles." That this view, which would lead
to consequences physiologically untenable, is also unjustifiable
anatomically is evident from the description given above.

12. Connective Tissue Cells between the Nerve Fibres of the
Ischiadic Nerve of Rana escidenta

In teased - up preparations of the ischiadic nerve,
numerous elongated spindle-shaped connective tissue cells
are obtained isolated, which are interpolated between the
nerve fibres. By successful isolation it can frequently
be seen that these cells are connected lengthways like a
chain, as is shown in Fig. 4, a, Plate VIII., the protoplasm
passing directly from one into the other. The cells have a
somewhat different aspect, according to the view in which

GANGLION CELLS 145

they are studied. That is to say, they are flattened to some
extent in a direction at right angles to their longitudinal
extension (Fig. 4, c). The nucleus shows an elongated oval
or sausage -like symmetrical shape when seen from this
flattened side, and is always surrounded with a border
formed by a single layer of meshes of protoplasm. At the
ends of the nucleus the protoplasm is continued into the
narrower portion of the cells, where it assumes a more or
less longitudinally fibrillated structure. In the width of
that portion of the cell which is drawn out like a band
there do not, however, occur more than about three meshes.
In the aspect in which the cells usually show them-
selves, namely, at right angles to that already nientioned,
as seen when lying along the isolated nerve fibres, the
nucleus is asymmetrical (Plate VIII. Fig. 4, 6) and makes
the cell bulge out strongly on one side. This bulging out,
so far as I have paid attention to the matter, which is
beside my main subject, is always situated in the depression
formed at one of Eanvier's nodes in the nerve fibre, and
quite fills it up. The thread-like portion of the cell
appears to be a single mesh thick in this aspect, and there-
fore shows the same relations as have already been described
in the walls of the capillaries. On the flat side of the
nucleus I could trace out the simple layer of protoplasm
distinctly. Whether a similar protoplasmic envelope occurs
also on the convex side was not to be made out with
certainty ; nevertheless I do not doubt the fact of its
occurrence.

13. Ganglion Cells and Nerve Fibres

Ganglion Cells

I have isolated in various ways ganglion cells from the
spinal cord of the calf and from the ventral nerve cords of
Lumbricus terrestris and Astacus fluviatilis, and have always
convinced myself in the clearest manner that their structure
is a fibrous meshwork. Since there are already in exist-
ence a considerable number of sufficiently good figures that

10

146 PROTOPLASM

represent such structural relations in ganglion cells, I do
not for my part consider it necessary to give more. I will
only refer here to the very successful photograph (XIII.) of
a very thin section of a ganglion cell of Lunibricus, which
permits the reticulate meshwork to be made out very plainly.
The preparation was stained with iron-hsematoxylin, which
also rendered distinct the numerous strongly stained granules
lodged in the nodal points of the network. These granules
can also be observed quite plainly in isolated and unstained
ganglion cells of this worm. In the latter I first observed
a perfectly definite radiate layer of alveoli at the surface of
the cell, as is depicted on Plate VIII. Fig. 3. Photograph
XIII. also shows this layer very well in places. That
the radiate layer of meshes occurs also round the conspicuous
nucleus of the ganglion cell, can be definitely seen in
isolated cells from the calf (Plate VIII. Fig. 2).

As I have already pointed out, the fibrous or fibrillar
nature of the protoplasm only depends on the arrangement,
or rather on the extension and elongation, of the meshes.
There is indeed very often an appearance as if stronger and
thicker fibrils or " runners " (Frommann) passed through the
meshwork. In my opinion, however, this only depends, on
the one hand, upon the fact that the tracts of the frame-
work are more distinctly prominent according to the extent
to which they are ranked in a straight line one behind the
other, and on the other hand upon the close packing of the
granules, of which we have before seen clear examples.

The processes arising from the ganglion cells always
have the structure of a meshwork forming distinct longi-
tudinal fibrils. In Fig. 1, Plate IX., I have represented the
structure of a broad protoplasmic process of a ganglion cell
of the calf, which was most especially clear and distinct.
I reckon the breadth of the meshes at about 0'8 yu,. The
structure of such protoplasmic processes is always clearer
and sharper than that of the axis-cylinder to be described
later, which may well be the result of deposits of granules.

For the view of Nansen (1886), namely, that nerve tubules
enter into the ganglion cell, spread themselves out as fibrous
tracts in its reticulate protoplasm, and finally emerge again, I

GANGLION CELLS— NANSEN' S VIEWS 147

have found no evidence of any kind in support, and regard this
opinion as incorrect. Nansen thinks that the protoplasm of
the ganglion cells is composed of two different kinds of con-
stituent elements — first, of the reticulate so-called spongioplasma,
which extends from the fibrous neuroglia sheath into the
ganglion cell ; and secondly, of the true nerve tubules, which,
as has been stated, penetrate through the processes into
the ganglion cell, and emerge again in the same manner. Every
such primitive nerve tubule is supposed to be enveloped in a
delicate sheath of spongioplasma, which is in direct connection
with the reticulate spongioplasma of the ganglion cell. As has
been said, I consider this view, viz. that the ganglion cell is
built up of two different elements — a view which, if correct,
would separate this structure from the typical cell series — as
in no way warranted. Nansen's view is supported chiefly
on the relations of the ganglion cells observed in Homarus and
some other animals. Here bundles of such nerve tubules are
said to be found cut through in sections at the periphery of the
cell or even scattered through its whole body, which are dis-
tinguished from the spongioplasmic ground substance by their
lighter appearance, and are proved to be transverse sections
of bundles of such nerve tubules by their distinct reticular
structure, resembling the peripheral nerve fibres, which are in
like manner interpreted as bundles of the same kind.

Now it seems to me beyond a doubt that Nansen is deceived
with regard to this supposed bundle of nerve tubules, and
that they were nothing more than larger vacuoles, which not at
all infrequently make their appearance in the protoplasm of
ganglion cells. In the cells of the ventral nerve cord of
Lumbricus I have frequently observed a large number of such
vacuoles, and other observers also, e.g. Rohde (1887), have found
them commonly in Polychsetes, especially in the periphery of the
cell. Rohde believes they should be regarded as collections of
the ground substance, termed paramitome, of the protoplasm. In
Lumbricus Nansen also has frequently seen these vacuoles, but is
inclined to explain them as cross sections of nerve tubules.
The correctness of my interpretation of these supposed bundles
obtains still further support from the fact that Nansen himself
has frequently pointed out their resemblance to vacuoles. The
apparent reticulation of these vacuoles is well explained from
the fact that if not focussed very sharply, at one time the
reticulate meshwork of their floor, at another that of their roof,
comes into view, giving the erroneous idea of reticulated contents.
If it was really a matter of bundles of nerve tubules which
passed through the so-called spongioplasma, they ought then to

148 PROTOPLASM

appear with relative frequency cut longitudinally or obliquely in
the sections, of Avhich, however, very little is to be made out in
Nansen's figures.

With regard to the alleged composition of the ganglion cells,
i.e. of spongioplasma and nerve tubules, it may further be
pointed out that Nansen was quite unable to demonstrate such
a composition directly in by far the greatest number of cases.
The greater number of the ganglion cells investigated by him
consisted of a dense tangle of such nerve tubules, and the
reticulation of their protoplasm hence depended on the cross
sections of numerous thickly - packed tubules, together with
their delicate sheaths of spongioplasma. Since, however, as I
shall further explain when describing nerve fibres, the assumption
both of nerve tubules and of their spongioplasmic sheath is
untenable, there is left for ganglion cells of this kind only the
simple and most natural interpretation still remaining, namely,
that the reticulation of their substance does not depend upon
special relations peculiar to nerve cells, but is the ordinary
reticulate meshwork of the protoplasm, which merely exhibits
modifications that can be in great part explained from the
peculiarities in form possessed by these cells, and their being
drawn out into processes. It is far from my intention to deal
in detail here with the extended literature upon nerve cells. I
merely thought it necessary to go rather more specially into the
work mentioned, which in essential points approaches so near to
my results.

Nerve Fibres

If pieces of the ischiadic nerve of the frog be investigated
by teasing, after having been preserved in very various
reagents, such as picro-sulphuric acid, picro-sulphuric-osmic
acid, Miiller's fluid, or weak alcohol (45 per cent), the
following can be made out (with or without staining) as to
the minuter structure of the axis-cylinder as a whole. It
is always distinctly composed of longitudinal fibrils, which
are about 0'6 to 0'7 p apart. Since the thickness of the
axis-cylinder varies, the number of the fibrillse is naturally
subject to change. I have seen axis-cylinders of such fineness
that their width only contained four fibrillae. The apparent
fibrillse are always finely punctate, i.e. they exhibit at
fairly regular intervals, which are slightly farther apart than

AXIS-CYLINDERS 149

the amount of their breadth, darker spots or points, which
give the impression of faint node-like swellings.

Closer observation, particularly of such preparations as
were coloured subsequently in the usual manner with gold
chloride, shows in the plainest manner that the fibrillse do
not by any means run side by side in complete isolation
from one another, but that they are connected by numerous
pale threads crossing from one to another. These threads
always arise from the nodal points of the fibrillae already
mentioned. The structure of the axis-cylinder is proved,
therefore, in the clearest manner to be a reticulate mesh work,
with somewhat elongate meshes arranged with tolerable
regularity in a consecutive series, following the longitudinal
direction of the nerve fibre (Plate VIII. Fig. 1, a, &).

Since it has occasionally been asserted that the fibrillar
nature is limited to the external surface alone of the axis-
cylinder, I must particularly lay stress on the fact that the
same image can be observed both with a surface focus and
in an accurate optical section of the axis-cylinder. There
can, therefore, be no doubt of the fact, that the axis-cylinder
possesses the structure mentioned throughout its entire mass.
In connection with this, there is the transverse section to
be considered, which we shall shortly describe, and which
completely confirms the same fact.1

1 I take this opportunity of being permitted to say a few words upon
Apathy's remarks (1891) with regard to my preliminary communication upon
the foam-like structure of protoplasm, and the corresponding structures of
nerve and muscle fibres. I forego examining more closely here Apathy's view
as to the structure of the axis-cylinder, since a complete solution of the
question will not be possible until Apathy's full work is to hand, with its
illustrations. On the other hand, I cannot but state that his objections have
not shaken in the least my conviction as to the correctness of my statements.
Apathy is willing to allow, on the one side, that foam -like structures are
widely distributed in protoplasm, and has, in fact, often convinced himself
of the fact. This, he says, is, moreover, nothing new, but was discovered
by numerous investigators before me. In consequence, it was quite un-
necessary that I should spend so much time and trouble in order to make it
probable that the reticular structures so often described in protoplasm ought
to be interpreted as in reality alveolar or foam-like structures ; although to
my knowledge no one has put forward this idea earnestly before me.

Nevertheless, however, Apathy believes' that the reticular structures
described by me, and later by Schewiakoff, in the contractile elements of

ISO PROTOPLASM

The structural relations described can naturally be
observed most clearly in isolated axis-cylinders, such as one
frequently obtains by teasing. On the surface of such
cylinders there occasionally appeared to be present a radiate
alveolar layer consisting of a single layer of meshes, which
in surface view was distinguished by the simple net-like
character of its meshes from the fibrous meshwork of the
enclosed portion. Since, however, I only rarely observed
this quite plainly, I do not lay any stress on the point.

On the other hand, I was frequently able to convince
myself quite definitely in such isolated axis-cylinders that the
apparent fibrillae sometimes divide, or rather, that in places
where the axis-cylinder becomes thinner (see Plate VIII.
Fig. 1, &), the fibrillee decrease in number. This seems
perfectly natural if we regard the substance of the axis-
cylinder merely as a modification of the ordinary net-like
meshwork of protoplasm. The greatly narrowed portion
of an isolated axis-cylinder, drawn in Fig. 1, &, corresponds
most probably to the region of a ring-like constriction, where,
in fact, according to most observers, the axis-cylinder be-
comes transitorily narrowed. With reference to this point,

muscle cells, are all to be set aside as artificial products, since, according to
his view, the muscle fibril is a completely homogeneous secretion-product of
the protoplasm, which has nothing to do with its structure.

He even goes so far in this respect as to declare that ' ' Biitschli's methods
of investigation present every possible means of producing an alveolar structure
in an otherwise homogeneous colloid substance by swelling." I do not call
to mind that I have employed any other methods than the usual ones, or than
those used, at all events, by Apathy himself.

To interpret as artificial products, resulting from the swelling of colloid
substances, the structures described by Schewiakoff and myself in the con-
tractile elements of Arthropod muscles, certainly astonishes me greatly. Such
an idea would not be very much out of place as regards the irregular structures
of ordinary protoplasm ; but to apply it to such regular structures as
those of the contractile elements is somewhat strange. Without, however,
entering here into a further defence of our discoveries against Apathy's
assertion, I may be permitted to refer to Schafer's work (1891, 1892, and 1893),
and which at any rate confirms independently a great part of our observa-
tions, even if it interprets what has been seen in a different way.

A discussion of the conceptions as to protoplasm expressed by Apathy in
the memoir referred to, and of the attacks which he takes the opportunity of
directing against my theory, may, I think, be omitted, since the author's course
of reasoning remains unintelligible to me in many ways, besides that many
points emphasised in it appear to me of quite subordinate importance.

AXIS-CYLINDERS IN SECTION 151

however, I must state unhesitatingly that, after having
studied many such constrictions, I have observed, as a rule,
no narrowing of the axis-cylinder, but have been, on the
other hand, able to trace it as a strand of even and equal
thickness right through the constriction.

I obtained preparations just as beautiful, in fact simply
splendid, showing the structure described in the axis-
cylinder, by making macerations of the spinal cord of the
calf. The macerations were done partly in 10-15 per cent
alcohol, stained yellow with iodine, partly in Muller's fluid.
In these axis-cylinders, which, as is well known, can be
particularly easily isolated on account of their lacking the
sheath of Schwann, I have seen quite plainly1 that the
meshes are not rectangular, but, as was to be expected,
somewhat polyhedric, so that the apparent fibrilke do not
run absolutely straight, but are lines with slight zigzag
bends (Plate IX. Fig. 3).

If now one takes into comparison the appearances shown
in cross sections of the axis-cylinder of the frog, the structure
already found is still further explained. The sections were
made from material treated either with picro-sulphuric
or picro-sulphuric-osmic acid, and had the thickness of about
1 p. They were partly stained in Delafield's haematoxylin,
partly with iron-hsematoxylin, or in gold chloride as well,
and were examined in water or methyl alcohol. In such
preparations it may be made out in the plainest manner that
the axis-cylinder does not at all show the dotted appearance
of sections through isolated fibrils, but has a very beautiful
net-like meshwork in cross section (see Plate IX. Fig. 4, a-c,
and the Photographs XL and XII.). The nodal points of
the network stand out very prominently as a rule, and it
also seems as if some fine granules were lodged in them.
It is further of especial interest that the most external layer
of meshes in the network are here again distinctly directed
vertically to the surface of the axis-cylinder, and that the
internal meshwork is by no means always quite irregular, but
frequently exhibits a structure as of fibres running either
perfectly straight, or slightly sinuously. The meshes are
arranged just as we have frequently observed in other

152 PROTOPLASM

objects, in definite tracts one behind the other, from which
arrangement arises the fibrous structure.

I have observed very plainly exactly the same structure
of the axis-cylinder in cross sections through the ischiadic
nerve of the rabbit, prepared in a corresponding manner.
Fig. 2, Plate X., gives a figure of such a preparation drawn
with a camera lucida, taken from a section as thin as possible,
which only showed fragments of the nerve.

Since in cross sections of the ischiadic of the frog some
peculiarities can also be observed in the sheath of Schwann,
I will describe them briefly. The sheath always stains very
intensely with Delafield's haematoxylin, while the axis-
cylinder, on the other hand, remains very pale. It can now
be plainly observed that the substance of the sheath has a
meshwork structure, consisting, in fact, of a single layer of
meshes, the walls of which are directed vertically to the
surface of the sheath (Plate IX. Fig. 4, a-c). At a spot
where a nucleus is lodged in the sheath it becomes thickened,
increasing at the same time to two layers of meshes, one
of which then encloses the nucleus internally, the other
externally, so that it comes to lie in the protoplasm. We
thus find exactly the same relations as have been already
described for the cells of the capillaries, and for the peculiar
connective tissue cells of the ischiadic nerve.

As I did not make a special study of the substance of
the medulla, I will merely remark briefly, that a net-like
meshwork can be made out in it very well, both in entire
isolated fibres, after treatment with picro-sulphuric-osmic
acid, and in longitudinal and transverse sections of them.
Just in the same way I have always found a dark sheath very
distinct round the axis-cylinder, as is especially well shown
in Photograph XIV. As to the relations of the two
sheaths to one another, and to the medullary substance, I
can only express an opinion by the way, that these three
parts may well form together a single whole.

NER VE FIBRES-CRA YFISH 1 5 3

Fibres of the Nerve going to the Chela of Astacus
fluviatilis

If fibres of this nerve are isolated by being teased
up after maceration in iodine alcohol, it is possible to de-
monstrate, especially in those of medium size, structural
relations which correspond completely to those of vertebrates.
In the first place, they also possess a sheath, which agrees
in all points with that of Schwann in the fibres of the
ischiadic nerve. In optical section the sheath appears rather
dark and glossy, permitting its composition out of a single
layer of alveoli to be seen very beautifully (Plate VII. Fig.
7, s). Also, by sharply focussing the surface, the somewhat
irregular net-like structure of the sheath can be recognised
very plainly (os) ; in places, however, its superficial structure
may also appear as a mesh work giving the appearance of
longitudinal fibres. In the sheath there are large elongate
nuclei (ri), which project outwards only to a slight extent,
but more strongly into the interior of the fibres (V). Just
as has been described in the case of the sheath of Schwann,
the layer of meshes composing the protoplasm of the sheath
divides in the vicinity of the ends of the nucleus into two,
so that the internal and external surfaces of the nucleus are
distinctly covered each by a layer of alveoli. In the thicker
fibres, however, the sheath also appears to become stronger,
sometimes to the extent of two or three layers of meshes.
In such thicker fibres the axis-cylinder did not quite fill up
the sheath, while this was always the case in thinner ones.

Now, although the structure of the axis-cylinder is very
pale, it can still be made out clearly that it agrees com-
pletely with that already described for the vertebrates.
The longitudinal fibrillae are here also distinctly linked with
one another by means of threads connecting them across
(Fig. *7, /), and they show the nodal points at the places of
union between the fibrillse and the cross threads very
beautifully.

The examination of cross sections of such nerve fibres
proves that a distinct net-like meshwork exists in the axis-

154 PROTOPLASM

cylinder, such as Nansen has already discovered and figured
very well in Homarus and other Crustacea, for which reason
I need only refer to the figures given by him.

In the literature there are two works, as far as I : am aware,
in which results have been attained that approach very closely to
mine, namely, the investigations of Nansen (1887) and Joseph
(1888). I therefore think I ought to point out particularly that
I only subsequently came to know of these works, and thus
attained the same results in an unbiassed manner. Both
investigators observed the reticulation quite plainly in fine
transverse sections of the nerve fibres : Nansen in numerous
invertebrate animals, Amphioxus and Myxine ; Joseph, on the other
hand, in the medullated fibres of a number of vertebrata. The
latter author, moreover, got one step farther than Nansen, since
he also found, in longitudinal sections through axis-cylinders pre-
served in osmic, the fibrillae frequently connected by cross threads.
Nansen has never observed anything of the kind, but on the
contrary has set up a view concerning the structure of the axis-
cylinder which is incompatible with the existence of such cross
threads. In agreement with Leydig's views (1885) as to the true
nervous significance of the hyaloplasm, i.e. the clear intervening
matrix of the framework of ganglion cells and protoplasm gener-
ally, Nansen arrived at the idea that the axis-cylinder consists
of numerous fine tubules about 1 /A in diameter, which are
formed of a "viscous," clear, structureless substance. Each
primitive tubule is supposed to be surrounded by a thin
sheath of spongioplasm. Now since the primitive tubules
would be closely compressed in the formation of an axis-cylinder
or of a corresponding nerve fibre, their spongioplasmic sheaths
are united into a framework, since the spongioplasm is not to be
regarded as "a quite firm and non-adherent substance." The
spongioplasmic framework that had arisen in this manner would
appear, therefore, in cross section as the reticulation described.
I can agree with Nansen to this extent, that I consider it proved,
from the comparison of longitudinal and transverse sections, that
we are not dealing with isolated fibrils in the axis-cylinder, but
with a honeycomb-like structure, the edges of which appear in
longitudinal section as the supposed fibrillse. On the other hand,
the longitudinal sections show perfectly clearly that the
cavities of this honeycomb certainly cannot be filled by con-
tinuous tubules, for they are divided by cross threads into
numerous chambers arranged in a row, one behind the other.

Although it cannot of course be proved with absolute cer-
tainty by simple observation that these cross threads are parti-

THEORIES OF NERVE STRUCTURE 155

tions which divide up the longitudinal cavities, and not threads
merely, yet this seems to follow with great probability from the
indubitable fact that the apparent longitudinal fibrillse represent
a honeycombed structure. When we then further see that the
structure of the nerve fibre corresponds entirely to the structure
of ordinary fibrous protoplasm, and at the same time are able to
render probable, from a whole series of reasons, the fact of
alveolar structure of protoplasm, it seems to me that the inter-
pretation of the cross threads as partitions is proved to be the
only plausible one. If we further take into consideration the
great agreement between the structure of the processes of
ganglion cells and that of the axis-cylinder, and also the fact
that axis-cylinders may pass directly, in their entire mass, into
ganglion cells, it seems to me certain that the axis-cylinder is
nothing but a strand of protoplasm, the structure of which has
become modified into a fibre-like meshwork in correspondence
with the modification which tracts of protoplasm generally
undergo when stretched out lengthways, and which is, as a rule,
distinguished from ordinary protoplasm, including that of the
ganglion cells, by its feeble staining powers in the usual colour-
ing media. The latter circumstance may, however, depend
principally on the small number and the fineness cf the granules
deposited in it, which are generally the cause of intense tingi-
bility in protoplasm.

Although Joseph (1888), as has been remarked above, reached
a step farther in observation, he remained, to my mind, far
behind Nansen in the interpretation of what had been seen. In
his view the reticulation observed both in transverse and longi-
tudinal section of the axis-cylinder is a framework which is a
direct continuation of that of the medullary sheath. We are
thus concerned with a supporting framework to the axis-
cylinder ; the true nervous substance would be the intervening
substance, just as Nansen also supposed. Now, although
Joseph naturally found this substance always homogeneous and
structureless, he yet thinks it possible to maintain the unten-
able view that it is in reality fibrillar. On this view the fibrilla-
tion in the axis-cylinder observed by M. Schultze and so many
others would belong to this intervening substance ; treatment
with osmic acid is supposed to be* unsuitable for rendering the
real nerve fibrillse visible. I think, however, that every one will
allow that the longitudinal fibrillse seen by Joseph are the same
that M. Schultze and his successors termed the fibrillse of the
axis-cylinder, the more so as osmic acid was just the reagent
most in favour for demonstrating these fibrillse. I therefore
consider Joseph's assumption of a special kind of nervous fibrillse,

156 PROTOPLASM

which run in the matrix, filling the supposed framework of the
axis-cylinder, to be quite untenable, the more so as he never
convinced himself of the existence of such fibrillse. To enter
into the dispute as to whether the substance of the framework
of the protoplasmic axis-cylinder, or the enchylema itself, is the
true nervous substance, seems to me quite superfluous in this
place.

Although Leydig (1885) speaks occasionally of a spongy
structure in the nerve fibres (especially in Aulastomum and
Lumbricus), he yet openly defends the view that the axis-cylinder
of the fibres of vertebrates is structureless, that is to say, that it
consists of structureless so-called hyaloplasm ( = enchylema), which
collects in the centre of the medullated fibres, while the reticular
spongioplasm forms the medullary sheath round the axis-
cylinder.

A passage in Dietl (1878, p. 95) may well be taken to indicate
that he had seen the net-like connections of the so-called nerve
fibrillae in invertebrates, while denying their existence in verte-
brates. It is difficult, however, to become quite clear on this point,
yet I consider this interpretation of Dietl's statements as correct.

Heitzmann also (1883, p. 296) speaks of a "delicate net-like
structure " in the axis-cylinder of vertebrates, but apparently
has not paid sufficient attention to these relations, since in
opposition to Schultze and others he denies the longitudinal
fibrillar structure. He therefore cannot raise any claim to be
considered seriously in this question, the less so also as he gives
no figures.

PART II

GENERAL PART

ALTHOUGH I have devoted much time to the study of the
numerous works upon the structural relations of protoplasm,
it seemed to me at first, after much reflection, almost advisable
not to enter into a critical and historical examination of the
subject, but to simply communicate my observations and
the conclusions drawn from them. On the one hand, this
subject has already frequently been treated in great detail
from the point of view of its gradual development; on the
other hand, I am somewhat doubtful as to the value of
detailed expositions of this kind, especially in a question
which is as yet so little ripe for final treatment; besides
which, the great productiveness of the present time puts
every one's power of assimilation to a severe test, so that
brevity appears to be the ideal to be striven after.

Nevertheless, even at the risk of not being read, I
made up my mind, after all, to give a compressed summary
of the gradual development of the structural question. I
have, as already stated, worked conscientiously through the
works accessible to me, so far as I was able, without, how-
ever, wishing to set up any claim to completeness ; this is,
as a matter of fact, scarcely possible, especially for more
recent times, in which such floods of literature have been
poured out dealing with the subject. Since, moreover, we
are in no way concerned with reporting carefully upon
every single work in which anything is said concerning the

158 PROTOPLASM

structure of the protoplasm of some cell or other, but only
with trying to obtain information upon the different views
as held by their chief exponents, and the most important
grounds brought forward in support of them, no appreciable
harm will arise from this incompleteness.

A. The Theory of the Net-like or Reticular Structure
of Protoplasm

As is well known, the first observations upon the peculiar
structures in the protoplasm of certain cells were made at
a very early period. If we leave the muscle cells out of
consideration, as has been done throughout this work,
observations upon ganglion cells and the so-called axis-
cylinders were what first brought peculiar structures into
notice.

As far back as 1837 Eemak found (p. 39, footnote) that
the axis-cylinder of the medullated nerve fibres of vertebrates
(Eemak's so-called primitive band) appeared to be composed
of very minute fibres, which occasionally showed nodular
thickenings in their course. In 1843 he discovered the
fibrillar structure of the axis-cylinder of the large nerve
fibres in the ventral nerve cords of Astacus flumatilis, but
was not quite certain whether this fibrous strand was the
equivalent of the. axis-cylinder of the vertebrate nerve fibre.
In 1844 he expressed himself more definitely upon this
homology, and at the same time demonstrated the fibrillar
nature of the ganglion cells of the crayfish, while Will in
the same year also observed a concentric striation in the
ganglion cells of Helix pomatia.

Since it is not our intention to describe in detail the
further development of the question of the structure of
ganglion cells and nerve fibres, we will confine ourselves to
noting that, especially through the works of Eemak (1852),
Stilling (1856), Leydig (1862 and 1864), Walter (1863),
Deiters (1865), and above all, those of M. Schultze (1868

160 PROTOPLASM

and 1871), the doctrine of the fibrillar structure of proto-
plasm of nerve cells was confirmed and further developed.

Frommann, who, as far back as 1864 and 1865, occupied
himself with the careful investigation of the fibrous struc-
ture of ganglion cells, and chiefly sought to show that the
fibres of the protoplasm arise from the nucleus and nucle-
olus, came in 1867 to the conviction that the fibrous
structures were not only a specific peculiarity of nerve cells,
but probably formed a universal peculiarity of protoplasm.
Since his work of 1 8 6 7 is unfortunately not accessible to me,
my judgment is limited to what he himself (1884) and others
have reported on the subject. As has been said, Frommann
had, on the one hand, observed similar fibrous structures,
taking their origin from the nucleus, in numerous other
kinds of cells also, but he further occasionally remarked
filamentous connections between the granules of the proto-
plasm, and similar ones between those of the nucleus.
Supported by these observations, the question seemed to him
even then worthy of consideration, whether a network
might not unite the granules of the protoplasm, and whether
the latter might not themselves be merely the nodal points
of such a network. Although, therefore, Frommann in 1867
had not, properly speaking, by any means observed the
reticular structure of protoplasm, yet the real merit is
due to him of having pointed out the possibility of such a
structure, and of having at the same time recognised the
structural relations already discovered in ganglion cells, as
being probably a universal peculiarity of protoplasm.

Simultaneously and independently J. Arnold (1865 and
1867) had also observed fibres united into a network in the
ganglion cells both of the sympathetic and of the spinal
column, and had seen fibres running out on various sides from
the minute granules of the protoplasm. He also laid stress
on the connection of these fibres with the nuclear corpuscles,
or rather with the fibres of the nucleus.

Fibrous or striated structures had, however, already been
seen at quite an early period in certain epithelial cells.
Friedrich in 1859 described the striated structure of the
ciliated cells of the Ependyma ventriculorum of man. In

OBSERVATIONS ON VARIOUS CELLS 161

1866 a corresponding structure was also recognised in the
ciliated cells of the gut of Anodonta by Eberth and Marchi,
and it was shown most convincingly that there was an
actual differentiation of the protoplasm in question.
Marchi was able to observe a similar fact in the cells of the
ciliated epithelium of the labial tentacles and the gills of this
mussel. Since that time numerous observers have estab-
lished the fact that a striation is widely distributed in
ciliated cells, if not present universally. Special mention
should be made of the works of Stuart (1867), Arnold
(1875), Eimer (1877), Nussbaum (1877), Engelmann
(1880), Gaule (1881), and Frenzel (1886).

Even before these observations upon the cells of ciliated
epithelia had been collected, Leydig had already, in 1854,
drawn attention to the fact that the non-ciliated epithelial
cells of the gut of Isopods had a similar longitudinal stria-
tion. Henle (p. 53) and Pfluger observed in 1866 a
partial fibrillation in a longitudinal direction of the proto-
plasm of the epithelial cells clothing the efferent ducts of
the salivary glands of vertebrata. At a later period numer-
ous investigators, especially Pfluger (1869 and 1871), and
Heidenhain (1868, p. 21; 1875), occupied themselves
in extending these observations. It was established thereby
that the striated structure of protoplasm is a phenomenon
of very widespread, in fact one might say of almost universal
occurrence in the columnar epithelial cells of the skin,
intestine, and numerous glands.

As has been remarked above, Frommann and Arnold had
really only observed more or less isolated filaments, which
here and there showed a net-like union. Frommann's more
far-reaching supposition was a hypothesis, the correctness of
which could only be proved by future observations. The
works that appeared soon afterwards were evidence of the
correctness of this supposition. Pfliiger found (1869) that
the protoplasm of liver cells was fibrillar, and in his detailed
work the structure is even represented as a beautiful fibrous
network, since the fibres are made to anastomose with one
another. It is interesting also to find that he expresses
himself to the effect that the fibrillar axis-cylinders, which

11

162 PROTOPLASM

are stated to be in direct connection with the liver cells,
expand into these cells by anastomosis of their fibrillae. The
networks drawn and described are rather coarse, as was in
general the case with all the early observations upon proto-
plasmic structures ; on which account we can only be dealing
in all these observations with a part merely of the true
structure, that is to say, in all probability with a coarsely
vacuolar structure in certain protoplasms — a point which
cannot now be decided with certainty in many cases.

In 18*70 Kupffer described the protoplasm of living
follicle cells of the egg of Ascidia canina as having a
beautiful reticular structure, and was also able to see that
the most external meshes, as well as those round the
nucleus, had a radial arrangement. He regarded the struc-
ture as a breaking up of the protoplasm into " vesicles." I
estimate the diameter of the alveoli figured at about 2 yu,, for
which reason it is probable, even if not quite certain, that
he observed the true protoplasmic structure.

In 1873 I described the flat epidermic cells of the
Pilidium as having a fine net-like structure in surface
view ; the study of the optical section showed that this
depended on a finely-chambered or alveolar structure of the
protoplasm. Although more accurate measurements of the
structural relations were unfortunately not made, never-
theless I am of opinion that this was not the real minute
structure of the protoplasm, but a coarser one produced by
vacuolisation.

In proceeding to criticise briefly the important works
published by J. Heitzmann in 1873 upon the structure of
the protoplasm and the cell — in fact, of the whole organism
—I find myself in rather a difficult position. For if one
takes into consideration the degree of perfection which had
been attained by optical apparatus at the commencement of
the year 1870, and further, the great difficulties presented
by the very objects, namely, small Amoebae, which Heitz-
mann made the basis of his views upon the structure of proto-
plasm, it is difficult to overcome a certain amount of doubt
which arises with reference to his observations. Heitzmann
found a reticular framework in the protoplasm of small

HEITZMANN—FROMMANN 163

Amoebae during life; also in that of the colourless blood
corpuscles of Astacus, Triton, and man, and in colostrum
corpuscles. With regard to the observations upon blood
corpuscles, I am certainly of opinion that Heitzmann, as
also Frommann afterwards, has partly taken post-mortem
appearances, of the nature of vacuolisation, for normal reti-
cular structures ; a proof of this is his statements concern-
ing the alleged differentiation or new formation of nuclei
in these blood corpuscles under the eye of the observer.
For there can be no doubt in the mind of any experienced
observer that this is simply a case of the nuclei becoming
distinct, as happens regularly after death.

As for Amoebae, I am inclined to believe that in the
same way Heitzmann observed forms in which the proto-
plasm was thickly vacuolated, for I consider it scarcely
possible that he was successful in tracing out in the living
object the true reticular structure in the protoplasm of
Amoebae with his optical apparatus. It is also very
apparent from Heitzmann's description that he schema-
tised and speculated in a most lively manner, since he
extended the mere indications of reticular structure seen
by him to the whole protoplasm. I therefore cannot but
ascribe a strongly hypothetical character to his work of
1873, which, moreover, received its punishment in not
obtaining the consideration it deserved. In addition to this,
Heitzmann forthwith expanded his observations upon the
reticular structure of protoplasm into a theory concerning
all living matter, which frequently clashed strongly with
the facts. His description of the origin of reticular proto-
plasm by vacuolisation from the so-called primitive compact
living matter, was altogether hypothetical, and the alleged
proofs were undoubtedly entirely uncertain. His efforts to
show that protoplasm, nucleus, nucleolus, and even inter-
cellular substance, were merely modifications of the one
living matter, and that therefore there was an easy transi-
tion from one to another, stood in opposition to a great
number of well-established experiences, quite apart from the
lack of any substratum of fact upon which such far-
reaching conclusions might be built up. Hence these

1 64 PROTOPLASM

comprehensive and very dogmatic assertions could only
be of harm to Heitzmann's theories, however much they
might be proved to be correct by later observations.
In the same way the attempt to eliminate the cell entirely
as an elementary unit in the building up of organisms,
could only increase the hostility of his opponents. Since
we must discuss more closely later on the theory of the
structure of protoplasm, developed by Heitzmann as far
back as 1873, and again, with greater detail, in 1883,
we may content ourselves in this place with these remarks.

In 1875 Frommann also, in the investigation of the
blood corpuscles of Astacus, arrived in many points at the
same results as Heitzmann. Although Frommann certainly
observed fine networks in the living blood cells, even if
they are not very apparent in his figures, yet it appears to
me just as certain that the alterations he claims to have
seen in the two kinds of blood corpuscles — the gray ones
and the so-called granular cells — were nothing more than
post-mortem appearances. Thus I consider it beyond a
doubt that the blood corpuscles figured by him on Plate
XV., Figs. /, g, h, k, p, and Plate XVI., a-g and k-v, were
dead, and that therefore the vacuolisation of the yellow
granules of the granular cells, described already by Heitz-
mann, the formation of granules and networks from them,
and finally the alleged new formation of a nucleus in
the granular cells — that all this only depended on the
gradual death of the cells. In the ganglion cells also of
the crayfish Frommann was now able to clearly convince
himself of the existence of a reticular structure, and he
declared that the protoplasmic granules in them were only
the nodal points of the network. With regard to the rela-
tions between the framework of the nucleus and that of the
protoplasm, Frommann, as before, was essentially in agree-
ment with Heitzmann, since he energetically defended their
direct connection, just as Arnold also had clone already.

In the same year, 1873, in which Heitzmann described
the reticular structure in the protoplasm of Amoebae, the
botanist Velten, who also worked in Vienna, communicated
the results of his observations on the streaming protoplasm

VEL TEN-KUPFFER—SCH WALBE 1 65

of the vegetable cell. More plainly than by Heitzmann
there is shown in Velten's communication the influence
upon the Vienna biologists of the work published by Brucke
in 1861, in which is set forth the necessity of an organisa-
tion in the protoplasm, i.e. of its being made up of more
solid and more fluid parts. Velten found the living pro-
toplasmic strands, which traverse the cell sap (more particu-
larly in Cucurbita pepo), to be frequently of a finely fibrillar
structure, the spaces between the fibrillse showing the same
low power of refraction as the cell sap. His interpretation
of his observations is as follows. The protoplasm is made
up of a system of fine canals filled with watery fluid, which
are quite shut off from the cell sap, and traversed frequently
by " transverse partitions." The configuration of the chambers
so formed is " constantly altered by the movement of the
protoplasmic walls." The granules of the protoplasm are
to be found in or on the walls, not in the intervening
fluid. It may happen, however, under abnormal conditions,
that granules get into the latter, where they then exhibit
lively molecular movements. Velten pointed out particu-
larly that this canal system of the protoplasm was in no way
to be confused with " a spongy framework." While in
1873 he believes he has observed these structural relations
only in cells subjected for some length of time to weak
induction-currents, in 1876, when he also gives a figure,
this is no longer definitely stated. His statements as well
as the figure given in 1876 prove quite definitely that Velten
really had observed the fibrillar structure of the living and
streaming protoplasmic strands, and had also seen plainly
the net-like connections of the fibrillse. It appears, however,
natural and beyond all doubt, that he could only have
seen distinctly a few strands and threads of the meshwork,
and has therefore made the width of the meshes much too
great — a fact which, as remarked already, is equally true of
the older observations.

Kupffer observed in 1874 the reticular structure of the
protoplasm quite plainly in the salivary glands of Periplaneta
orientalis, both in the fresh condition and after treatment
with the most various reagents. Since the width of the

166 PROTOPLASM

meshes was about 0*002 mm. after treatment with concen-
trated caustic potash, in which the network swells up, he
very likely had the true protoplasmic structure before
him. He found the epithelial cells of the efferent ducts to
be of a longitudinally fibrillar structure. It seemed to him
certain in the case of this object that the granulation of the
protoplasm could be referred to the reticular structure. In
1875 he extended his investigations more especially to the
liver cells of the Yertebrata, and saw in them a net-like frame-
work, which frequently became more compact round the
nucleus. As before, he found that the structure could be made
out even in the fresh condition, and only became more dis-
tinct under the action of reagents. In fact, he thought he had
observed slow movements in the threads by warming the
fresh liver cells on the slide.

I think it would lead us too far if we tried to follow
out step by step the gradually increasing confirmations of
the reticular structure of protoplasm. In the following
lines, therefore, I will proceed more cursorily, and only lay
especial stress upon the more important and extended
observations.

In 1876 Schwalbe became an adherent of the theory of
reticular structure from his own observations on the colour-
less blood corpuscles of the crayfish, Triton, and various
ganglion cells. He also traced these structural relations in
objects as fresh as possible, and arrived at the important
opinion, which was enunciated here probably for the first
time, that the structural relations of the nerve cells
observed by M. Schultze and his predecessors depend on
regular arrangement of the trabeculse of the network.
"From all this it is obvious that isolated fibrillse are not
to be assumed in ganglion cells," was Schwalbe's conclusion
from his experiences. It is further of interest to note that
he considered net-like connections of the fibrillse of the
axis-cylinder as quite possible.

In the same year Trinchese also described the net-like
structure of the protoplasm of various cells on the occasion
of the anatomical investigation of an opisthobranch (Cali-
phylla), and of the connective tissue corpuscles of the frog

STRASSBURGER— KLEIN 167

from preparations. Since the width of the meshes described
is on the whole rather great (0*0027 mm. in the figure
provided with a scale of measurement), and the contents of
the meshes themselves are drawn as being finely punctate,
it seems rather doubtful if the true protoplasmic structure
was seen.

Doubts may also be raised with respect to the net-like
structures described by Strassburger (1876) in the proto-
plasm of vegetable cells. Both in his treatise on protoplasm
and in the second edition of his book on cell formation and
cell division, it is almost exclusively the coarser vacuolated
structures which are described as reticular. This follows
with tolerable certainty from the size of the meshes, the
width of which varies, as a rule, from 0'005 to O'Ol
mm., though occasionally sinking to 0'0015 mm. The
fact, therefore, of Strassburger having occasionally seen
the true meshwork of the protoplasmic structure, is cer-
tainly by no means excluded. But one thing appears
especially noteworthy, namely, that he especially remarks
(Zellbildung,p. 217) that the net-like structure of the proto-
plasm is in reality a " dividing up of the protoplasm into
chambers, in which the cavities of the chambers are filled
by a more or less concentrated solution of albumen." The
distinction which he seeks to draw in his treatise on proto-
plasm between vacuoles and chambers in the granular proto-
plasm is not quite clear to me. Vacuoles are said to be
drops of a watery fluid in the protoplasm, but the chambers,
on the other hand, are formed by the protoplasm filling up
the cell fluid in the form of thin plates connected like a
network. This conception of the reticular structure seems
to me the more remarkable from the fact that Strassburger
gave it up soon afterwards, and in its place adopted the idea
of a net-like or spongy structure.

As we have seen that Schwalbe had already tried to refer
the peculiar structural relations of the ganglion cells to their
reticular nature, it is especially interesting to note that Eimer
in 1877 brought the longitudinal striation of the ciliated
cells of various objects into connection with the special
arrangement of the usual reticular meshwork. That is to

1 68 PROTOPLASM

say, he observed distinctly that the longitudinal fibrillse
were frequently connected with one another into a net-
work.

As has been indicated above, as far back as 1878 I
expressed the opinion that the reticular structures described
might be alveolar, or in other words, that protoplasm has a
froth-like composition.

In two memoirs of the years 1878 and 1879 Klein
confirmed the net-like structure of protoplasm for very
many cells of Vertebrates, and declared himself in favour
of Frommann's and Heitzmann's views with regard to many
points. This was especially the case with regard to the
intimate connection and transition which both he and the
latter authors assume between the framework of the
nucleus and the protoplasm. Indeed he goes so far as
to believe, with Strieker, that fusion frequently takes
place between the nucleus and the protoplasm, especially
in the colourless blood corpuscles. The nucleus is only a
portion of the cell protoplasm marked off by a perforated
membrane. This agrees essentially, as has been said, with
the views developed by Heitzmann and Frommann. Although
I do not wish to assert that everything which Klein describes
and figures is really the true protoplasmic structure (which
is frequently very doubtful, especially in the case of gland
cells), yet this is the case in many of the structures
described. Like Eimer, he made out quite correctly the
fact of the longitudinal striation being only a modification
of the ordinary reticular structure.

In opposition to these observations, Arnold (1879), in a
discussion of the investigations upon cell structures which
had been made up to that time, expressed himself as still
doubtful upon the fundamental question whether filament-
ous or reticular structures were present, in protoplasm or
not ; " whether the nuclear filaments are connected with one
another ; whether such a relation exists between the fila-
ments of the body of the cell ; to what extent the reticular
arrangement of the filaments can be regarded as generally
typical ; and whether, finally, an invariable connection exists
between the filaments of the nucleus and those of the pro-

SCHMITZ FRO MM ANN 169

topla§m ; these are questions which still require the most
careful observation in order to obtain a final answer." At
the same time Arnold confirmed the existence of filamentous
structures in the cells of numerous tumours.

On the botanical side Schmitz (1880) came forward to
support energetically the universal distribution of the re-
ticular structure of protoplasm. He observed it in material
preserved with concentrated picric acid. It can be affirmed
with great certainty that Schmitz had not seen the true minute
structure of protoplasm, but only more coarsely vacuolated
structural appearances, just as Strassburger had done. For
instance, he describes the original protoplasm as being
in general finely punctated, and the reticular structure as
first arising in this. The frequently repeated remark that
the cell sap cavity arises by flowing together of meshes of
the protoplasmic network also expresses the same view.
Schmitz is, however, of the opinion that the punctation
of protoplasm which is not distinctly reticular is only the
optical expression of a very minute net-like structure, and
that, therefore, both the modifications of protoplasm pass
one into the other. On the other hand, he tries to refute
any interpretation of the structures observed as phenomena
of coagulation, or artificial products of any other kind.

Frommann published, from the year 18*79 onwards, a
series of communications on his further studies of proto-
plasmic structures, which it would take too much time to
even enumerate here. They extended to various cells of
the animal body, such as cartilage, ganglion cells, epidermic
cells, and blood corpuscles, as well as to various vegetable
cells. In 1884 he brought together the greater part of these
investigations, and set them forth with increased accu-
racy. We will, therefore, attempt to give a rather more
exact account of the opinion which Frommann has formed
upon the ground of his numerous studies, with the help of
his description of 1884. It must first be pointed out that
he found reticular structures everywhere in the protoplasm
investigated. The network or framework was not, however,
one connected together on all sides and at all points ; on the
contrary, isolated portions of it frequently occurred. As a

i?o PROTOPLASM

rule, it was very changeable, since spontaneous and con-
tinual alterations took place in it. Fusions of filaments and
granules of the network were frequently to be observed, but
on the other hand the nets might also break up into granules.
Indeed it could even be observed that all the structured
portions might vanish transitorily, so that the protoplasm
became quite homogeneous. In the reverse way such homo-
geneous protoplasm could change back into reticular by
reappearance of the framework. By fusions such as have
been mentioned above, the walls of vacuoles, and even
entire nuclei, were formed. In this way he again supported
the view here that nuclei might arise under the influence
of the induction-current, or spontaneously, in the proto-
plasm. As before, he maintained the direct connection
between the framework of the nucleus and the protoplasm.
The nuclear membrane is said to be interrupted by finer or
coarser gaps for the passage through it of the filaments of
the network. In fact, it is really, on the whole, only a
thickening of the framework. In the same way the sur-
face of the cell is not surrounded by a continuous layer or
lamella of the framework, but limited in the same manner
as the surface of the nucleus.

The view of Schmitz with regard to the nature of vege-
table protoplasm was adopted soon afterwards by Eeinke
and Eodewald (1881 and 1882) for the protoplasm of
jEthalium septicum, and supported by further proofs. From
experiments which they made by compressing the objects,
both investigators concluded that the protoplasm of the
^Ethalia, especially that of the fructifying cakes which collect
on the surface of the tan, consisted of a firm ground
substance and a fluid enchylema. They succeeded in
obtaining 6 6 per cent of fluid enchylema by forcibly pressing
it out, while the substance of the framework remaining
behind formed a solid and rather dry cake. With a centri-
fugal, however, it was not possible to separate the two
substances. On the ground of these and other experiments,
they assumed the presence of a spongy framework of plastic
and contractile nature in the protoplasm, which was
permeated by the fluid, albuminous enchylema, and shut

STRASSBURGER—LEYDIG 171

off from the exterior by a thin enveloping layer formed of
the substance of i the framework. Eeinke is inclined to
admit that the spaces filled by the enchylema " become
partitioned off here and there by delicate diaphragms of the
substance of the framework," in which statement we may
perceive an approach to the theory of an alveolar structure.
In the figures which were added by Kratschmar to the
work of 1883, the reticular structure of the protoplasm of
^Jthalium is represented rather fine and indistinct, but is
quite recognisable.

From the year 1882 there come a few more contribu-
tions from other observers. Thus Freud again confirmed
the presence of net-like anastomosing fibres in the ganglion
cells of Astacus fluviatilis without, however, having seen the
real minute protoplasmic network ; he therefore gave his
complete adherence to Schwalbe's conception of the structure
of ganglion cells. Paladino found reticular structures in the
cells of the endothelium of the Arachnoidea, and Schmidt
in the cells of the pancreas.

Strassburger also now (1882, Zellhaute) came into
agreement with the more recent results of observation,
namely, that the structure of protoplasm was reticular,
but in the work which he published at the same period
upon the processes of division in the cell nucleus, etc., he
represented the protoplasm as a tangle of short twisted
fibres, after the manner of Flemming. Externally it was
supposed to be enclosed by a so-called " cuticular layer "
(Hautschicht), which arose by narrowing or obliteration of
the meshes of the framework, just as Schmitz had already
assumed.

1883 brought with it two works of great importance
for the problem in hand ; first, the extensive investigations
of Leydig, which comprised observations upon very numerous
histological objects, and were amplified by a work that
appeared in 1885 ; and secondly, the investigations of
E. van Beneden, which were confined to the sexual organs
and sexual products of Ascaris megalocephala.

Leydig was able to observe distinctly the reticular or
spongy structure of the framework everywhere, both in fresh

172 PROTOPLASM

and fixed protoplasm. The so-called protoplasmic granules
were in great part merely the nodal points of the frame-
work, but there were frequently also numerous granules of
various kinds present, which lay originally, at least, in the
substance of the framework. The fact that the striated,
radiating, and confused fibrous structures, which were
frequently observed in the protoplasm of certain cells, were
only modifications of the spongy framework was quite
certain in his opinion, and was clearly proved by their
frequent transitions into ordinary protoplasm. In conse-
quence of this view, which was only occasionally slightly
shaken by his referring to vacuolar protoplasm (1885,
footnote on p. 2), he arrived, like Frommann, at the opinion
that the surface of the protoplasm must be porous, and
interrupted by finer or coarser gaps, which were subject to
great change in shape and size. He therefore conceives of
the surface of the cell as porous, somewhat in the same way
as that of a bath sponge. With this is connected the
fact that the intervening substance or contents of the frame-
work— his " hyaloplasm " — must be " soft, clear, and semi-
fluid," and in any case not capable of being mixed directly
with the surrounding water, since he ascribes to it certain
curious peculiarities, as a further consequence of the concep-
tion just discussed. Thus the hyaloplasm is supposed to
" creep out, as it were," from the framework, and form the
pseudopodia of Protozoa or other cells ; it would further
form in a similar manner (1) the sensory bristles, knobs or
hooks, the auditory setae, the visual rods, and the real nervous
substance in general ; (2) the contractile material of cilia and
muscles; (3) the homogeneous substance of the cuticular
layers ; and (4) certain secretory masses.

From this conception it follows at once that Leydig
sees in the hyaloplasma the real living, contractile, and
nervous substance, while the framework — his spongioplasma
— must only perform the function of support. But he
did not remain perfectly consistent with himself, since in
1885, p. 105, he believes he has seen the cilia on the
epithelial cells of the olfactory mucous membrane of the cat,
arising as processes of the spongioplasma, and on p. 161

VAN BENEDEN— CARNOY 173

lie even ascribes to the cilia a composition of both kinds of
protoplasm.

Since we shall frequently have to discuss Leydig's views
again later on, this short exposition of his opinion will suffice
for the present.

E. van Beneden, in his investigation of the protoplasmic
structure of ova, etc., of Ascaris, was at first, at any rate, on
what is in my opinion the right tack, since he was inclined
to refer the net-like structure of the protoplasm to the exist-
ence of numerous vacuoles, and pointed to Actinosphccrium
and similar forms for comparison (p. 82). But he was
doubtful whether the vacuoles which produced the reticular
structure were entirely shut off from one another/ In the
further course of his work, however, this view was with-
drawn altogether, and in its place another appeared, which
seems to have been put forward as the result of the study
of the interesting structure of the spermatozoa. Here, as in
the general part dealing with protoplasmic structures, van
Beneden consistently terms the fibril the structural element
of protoplasm. The protoplasm is said to consist of nodular
fibrils and an intervening substance. The fibrils are
orientated in the three directions of space, and their nodal
points, which represent actual thickenings, are connected
by finer fibrillse. In this way there results a " protoplasmic
trellis work " (treillage). The fibrils are contractile, and
hence the framework is capable of alteration. It would
appear doubtful whether the intervening matrix is identical
with the contents of the larger vacuoles ; if this is the case,
a special wall with extremely narrowed meshes must be
formed round the vacuole, just as Heitzmann and Schmitz
had already assumed.

Pfitzner, in 1880, when giving an account of the epi-
thelial cells of the salamander larva, described a meshwork
in the protoplasm which at the surface of the cell passed
distinctly into the radially striated border; and in 1883 he
gave a good description of the reticular structure of the red
blood corpuscles of Amphibia, publishing later (1886) a
most excellent figure. At the same time he developed his
theoretical views as to the origin of such structures, which

174 PROTOPLASM

were supposed to be of two kinds, the one " passive," i.e.
such as are produced by vacuolisation, the other " active,"
the result of the granules becoming grouped into filaments
or nets. It will be sufficient here to have mentioned this
view, since in the sequel we must return to it in more
detail.

Without taking special notice of the occasional descriptions
given by Affanasiew and Langley of reticular structures in
liver cells, we proceed at once to the extended investigations
which Carnoy in 1884, 1885, and 1886 published upon
the subject of protoplasm. Since with regard to the struc-
ture his standpoint is entirely that which was developed by
Heitzmann, and which has been reverted to essentially in
the views of Schmitz, Leydig, and van Beneden, it does not
require to be set forth in detail here. Living protoplasm
was but little investigated by Carnoy ; hence he nowhere
discusses the very important question how the occurrence
of apparently quite homogeneous protoplasm is to be ex-
plained on the general hypothesis of the reticular structure.

Carnoy also recognises the fact of fibrous and radiate
structures having originated by modification of a perfectly
reticular structure. The framework is definitely regarded
by him as solid, or at least very viscid, and contractile ;
the intervening matrix, on the other hand, is supposed
to be "hyaline and viscous." Nevertheless I certainly
believe that Carnoy also has partly mistaken coarsely
vacuolar structures for the real fine protoplasmic structure ;
this is quite evident from the fact that he identifies
the network of coarse trabeculse in the protoplasm of
Noctiluca with the finer protoplasmic framework, and
regards the cell sap of this Protozoon as equivalent to the
enchylema or intervening matrix of protoplasm. Moreover,
I also infer this from the fact that Carnoy frequently
represents the enchylema finely granulated, which leads one
to conclude that at times he only saw the coarser network,
and regarded the finer one as granulations. In opposition
to Leydig, he incorrectly makes out the granular contents of
the protoplasm to be located always in the enchylema,
which is supposed to frequently contain even the coarser

APPARENT RETICULAR STRUCTURES 175

deposits. Since Carney's investigations of 1885 and 1886,
upon the cells of numerous Arthropods, and the sexual
products of Nematodes, did not make any essential altera-
tions in his fundamental conceptions, but rather confirmed
them for these objects in every way, there is no need to
go more specially into these later works.

As has been stated already in the Introduction, in
1885-86, when giving a description of the reticular
protoplasmic structures of Noctiluca and some Rhizopods,
I defended the standpoint I had already taken up in 1878,
namely, that we are not dealing with a reticular, but with
an alveolar or froth-like structure.

As far back as 1882 Flemming had expressed the
opinion, with regard to the reticular structure described by
Klein in certain gland cells (especially the goblet or
mucous cells), that the relatively coarse reticular structure
of the secretion masses of these cells have in any case nothing
to do with the true minute structure of protoplasm, I
must declare myself entirely of this opinion. The com-
parison of various works which have appeared since upon
this subject — such as the investigations of Schiefferdecker
(1884), List (1885, 1886), Paulsen (1885, 1886), Zerner
(1886) — is altogether in favour of this view. From these
results it seems to me beyond doubt, as has been said, that
we have to deal here with coarsely vacuolated structures,
the origin of which from the finely reticular protoplasm of
the original gland cells is still in need of being further
cleared up. The descriptions of List especially, make it
quite clear that the so-called stalk of the cells still consists
of the original finely reticular protoplasm ; the theca also
seems to be merely a continuation of the latter. The chief
question of which a solution is required may be stated as
follows : does the mass of the secretion, with its coarsely
reticular structure, arise by direct modification of the original
protoplasm, or is it a secreted vacuolar mass ?

As has been pointed out several times already, it is
frequently, in fact as a rule, very difficult to decide, whether
the reticular structures described by earlier observers were
really the minutest protoplasmic structures, or whether they

i?6 PROTOPLASM

depended on coarser vacuolisation. Since both have a very
similar appearance, it is only possible to arrive at a true
decision on this point by a knowledge of their actual
dimensions, since we found throughout that the meshes of
the true protoplasmic structures scarcely exceed 1 p in
width. I am, therefore, obliged to consider the reticulum,
for example, drawn by Sedgwick (1886) in the egg of
Peripatus capensis as a coarser one which does not cor-
respond to the true structure of protoplasm, since the
width of the meshes is frequently drawn very coarse, and
even in the finest parts does not sink below 2 /*. I believe,
therefore, that in this as in many similar cases the trabeculse
of the so-called reticulum would themselves display the finer
protoplasmic structure. With regard to the general concep-
tion of the protoplasmic network Sedgwick approaches most
closely to Heitzmann and Frommann.

As for Protozoa, Schuberg (1886) for Hursaria, etc.,
Btitschli and Schewiakoff (1887 and 1889) for numerous
Ciliata, and Fabre-Domergue (1887) for the same order,
have in recent times been more especially deserving of
notice. With regard to the views of Kunstler (1882 and
1889), who followed out carefully the reticular structure
in the Flagellata, they must be gone into more closely
farther on. In histology, moreover, so many statements lie
scattered about in various works, that it does not seem
advisable to bring them together in full. Only Nansen's
work (1887) upon the reticular structure of ganglion
cells, which has already been discussed above (p. 147),
may here be referred to again.

B. Summary of Divergent Views

1. The Theory of tJie Fibrillar Stricture of Protoplasm

IN opposition to the theory of the reticular framework
of protoplasm, some investigators still hold fast to the con-
ception which was so prevalent at an earlier period of the
investigations, namely, that we have to deal with fibrils
which are isolated, or at least only occasionally connected
secondarily, in the intervening matrix of protoplasm. In
fact, we have seen already that not a few authors of the
works described briefly in the foregoing section speak of
fibrils of protoplasm, though at the same time admitting that
these fibrils anastomose as a rule in a net-like manner, even
if they occasionally occur isolated.

The assumption of a fibrillar structure in protoplasm ob-
tained the most definite support in Flemming's book of 1882.
The earlier works of Frommann, Arnold (1879) and Schleicher
(1879, upon the composition of the protoplasm of cartilage
cells), can also be regarded as to a certain extent precursors
of such a conception. Schleicher especially gave a most
definite denial to the alleged existence of reticular structures
in the protoplasm of cartilage cells, in opposition to Heitz-
mann and others, but frequently observed, on the contrary,
isolated filaments in their living protoplasm.

It cannot indeed be asserted that Flemming affirms
definitely the fibrillar nature of protoplasm ; his standpoint is
rather a sceptical one towards Heitzmann, Klein, and others.
Thus he admits a net-like connection of the filaments of the
protoplasm as " fully possible for many objects, but can,
however, find no certainty for the fact" (p. 58). The

12

i?8 PROTOPLASM

objects seemed to him to be too much on the border-line
of visibility to obtain a definite decision. In any case, from
his numerous observations he was more inclined to the
assumption of a fibrillar structure, and also considered the
multiplicity of the structures too great to class them all
together under the conception of a continuous reticular
framework (p. 64), which seemed to him unproven and
improbable. That the so-called protoplasmic granules were
only the nodal points of a reticular framework hence seemed
to him in like manner not proved. On the other hand,
Flemming considered it certain that protoplasm shows
as a rule a filamentous structure, although the temporary
appearance of homogeneous protoplasm might be quite
possible. Such protoplasm would originate by " the filaments
. . . approaching until they came in contact, and perhaps
becoming fused for a time" (p. 66). The so-called inter-
vening matrix, or his " interfilar mass," he regards as possibly
fluid, but it might also possibly be " a yielding solid," since
after reagents it sometimes appeared finely granular. I
think, however, that the fine granulation of the so-called
interfilar mass was in most cases the actual fine reticular
structure, which he never definitely observed.

It may, however, be asked how Flemming, so careful
an observer, and provided with the best apparatus, could
frequently declare that he was " never " able to convince
himself for certain of the reticular nature of protoplasm,
and hence felt doubtful about it. I think, ho.wever, that,
both from his chief work of 1880 and from his treatise of
the same period upon the structure of the cells of the spinal
ganglia, the conclusion may be drawn that Flemming reposed
rather too much confidence in certain apparatus that were
new at that time, namely, the Abbe's condenser. In both
memoirs passages can be found from which it is obvious
that Flemming as a rule conducted his investigations
with very " bright " light from the Abbe's condenser, and
without any diaphragm (see p. 43 ; spinal ganglion cells,
p. 15), and he cherishes the view that the images obtained
by such means quite determine the point. With " worse
light," however, he saw the reticular pattern of the

CRITICISM OF FLEMMING 179

protoplasm. I must say I think that Flemming was in
error when he regarded the image obtained with a bright
light and widely open diaphragm as the more correct ; for,
as has already been pointed out frequently by others, the
distinctness of the structures suffers very much from intense
illumination, which of course receives a natural explanation
from the fact that with a strong illumination our eye is no
longer able to distinguish the relatively slight differences of
light and shadow.

I am therefore not at all of Flemming's opinion, that the
net-like connection of the filaments or fibrillae which becomes
apparent on diminishing the illumination is a result of the
image becoming indistinct, so as to produce the effect of the
filaments which run over one another appearing connected
together. As a rule, it certainly cannot be asserted that the
microscopic image is rendered less distinct by diminish-
ing the illumination ; on the contrary, any one can easily
convince himself that it thereby becomes much more
distinct and sharp. In any case the filaments running at a
higher or lower level could not lie simultaneously in the
plane of distinct vision, while net-like connections of the
threads in the same plane of focus can frequently be
demonstrated with the utmost certainty. All these reasons
place it beyond a doubt in my mind that Flemming's dislike
to the idea of a reticular framework is to be referred in the
main to a false estimation of the correctness of the micro-
scopic image.

To this must be added a further reason, which I will
proceed to discuss rather more in detail. In studying
the reticular framework, a more or less confused fibrous
structure is usually very prominent. This depends on the
fact that now in one place, now in another, some of the
walls of the meshes are arranged for a greater or less
distance in a series one behind the other to form a sinuous
line, and thus give the impression of lines of some length.
Now it can be shown easily that the eye is better able to
observe delicate lines when they are long than when they are
short, so that the greater the distance for which the tracts of
the network have a linear arrangement in rows, the plainer

i8o PROTOPLASM

they become. On this, therefore, depends also the fact that
the pronounced fibrous structure of the ganglion cells, and the
striations of the epithelial cells, axis-cylinder, etc., were dis-
covered at such a relatively early period, while the reticular
structures were not discovered till much later. If a system
of long parallel lines be drawn at equal distances apart,
and joined together by vertical, irregularly arranged con-
necting lines of equal thickness, as shown in Fig. 6,
Plate XII., the following fact can be observed from a con-
sideration of the drawing. When the figure is looked at
from a moderate distance, so that it can be plainly discerned,
and then the interval between it and the eye gradually
increased, a distance is finally reached in which only the
long parallel lines can still be plainly distinguished, while
the cross connections, on the contrary, have disappeared from
the vision of the observer.1

Just the same state of things is presented by the micro-
scopic image of an axis-cylinder, which gives in my opinion
a sufficient explanation of the fact, that the longitudinal
fibrillse were discovered here at such a relatively early
period, while their cross connections were not seen till
so late, and even now require to be studied carefully and
to have their structure rendered very distinct, if they
are to be clearly observed. The same fact is true, however,
of the protoplasmic reticulum generally. If a drawing of such
a structure be made, at a certain distance the true filaments
of the reticulum will become more indistinct, and finally only
the thicker and darker nodal points will remain, provided
they are sufficiently darker than the filaments of the net-
work, so as to produce, of course, the appearance of granula-
tion. If, however, certain tracts of the network are ranked
one behind the other in a line for some distance, they will
remain distinct for a correspondingly longer time, and one

1 It is also possible to observe at the same time the vanishing of the longi-
tudinally directed shorter lines, from which, as has been said, it follows that,
other conditions being equal, the distinctness of the lines varies with their
length. The observations described are just as successful, in fact even
better if anything, if the figure be approached gradually from a greater
distance.

ALLEGED OCCURRENCE OF FIBRILS 181

obtains the appearance of isolated filaments in a granular
matrix.1

The same objections which I have just raised against
Flemmiug's view of the fibrillar structure of protoplasm,
must of course also apply to the corresponding descriptions
of earlier and later investigators. For ganglion cells H.
Schultze (1878) and Kohde (1887) declared themselves of
this opinion. In the same way Pfeffer (1886) and Pfluger
(1889) have assumed the fibrillar structure, without, how-
ever, having brought forward any investigations of their
own upon this point. Pfluger especially expressed himself
very plainly. The gelatinous condition of the cell contents
represents according to him "a mixture of an absolutely
fluid with an absolutely solid material." The solid substance
is supposed to be partly granular, and partly, on the contrary,
at any rate in its chief mass, a feltwork of very minute
filaments (p. 30).

Of a similar opinion is Ballowitz (1884), who in like
manner believes protoplasm to consist of interwoven, con-
tractile filaments, which are not, however, connected together,
while Eabl (1889) adopts this conception to the extent
of assuming the presence of isolated fibrils at certain
times at least, especially during the division of the cells,
when they appear in the form of radiating systems. In the

1 In his most recent work (1891, Archiv. f. mikroskop. AnaL, Bd. xxxvii.
p. 736) Flemming expresses himself as follows upon protoplasmic structures :
" I am one of those who, reasoning from visible phenomena, assume a real
formed structure in the cell, even though it may not be fixed or permanent,
and who cannot agree with the opinion that the cell is an emulsion, and the
fibres that can be made out in it only the expression of streaming movements."
A more detailed discussion of this casual expression of opinion, in so far as it
would have reference to my conceptions, seems to me unnecessary, since the
whole of the present work may be taken as a fundamental contradiction of it.
Only the uncertainty of such expressions as " formed structure," which "is
not fixed or permanent," may here be pointed out. I hope that Flemming
will convince himself in these matters also of the correctness of my views in
principle, just as he has with regard to the question of nuclear division. I
must not omit to point out the fact that he frequently speaks of reticular
fibres in protoplasm in the work cited, but in his figures he depicts tangles
of undulating fibrillfe without distinct net-like connections, just as he has
usually done. That this in no way corresponds to the reality is sufficiently
obvious already from the investigations of my predecessors.

182 PROTOPLASM

resting condition of the cell, however, these fibrils are
supposed to be connected together in a network, as is
also the case with the nuclear framework.

Finally, the fibrillar structure has found an eloquent
defence in a work of Camillo Schneider which has appeared
recently (1891). Since the considerations urged by him
are especially directed against my conception of proto-
plasmic structures, I must examine them rather more in
detail. Schneider has investigated partly the same objects
as I myself studied, viz. the eggs of sea-urchins and Ascaris,
Vorticellce, Triclioplax adlicerens, etc. He finds everywhere
in the protoplasm twisted fibrils of the same thickness
throughout, without a trace of nodular thickenings ; in fact
it even appears to him not impossible that the entire cell
may consist of a single enormously twisted filament. The
investigations were undertaken with Zeiss ^ homogeneous
immersion, while I worked, as has been said, with the
Apochromatic 2 mm., Ap. 1'30 and T40, of Zeiss, and the
oculars 12 and 18. Now if Schneider thinks himself in a
position to assert (p. 5) that " an alveolar framework or a
net-like connection of the filaments is as a matter of fact
not present in Strongylocentrotus in the ova investigated," I
must for my part reply just as definitely that both are
present, and that Schneider gives an entirely false repre-
sentation of the microscopic image. I will not appeal to the
fact that the great majority of observers, and among them
quite a number of the first rank, represent the same opinion
as myself with regard to the microscopic appearance, but I
prefer to subject the figures given by Schneider to a brief
criticism. He remarks (p. 2) with regard to them that
those first executed did not represent the framework quite
correctly, and refers to the explanation of the figures with
regard to this. Here I find it stated only for Fig. 19,
" Framework drawn very accurately." The figure represents
a section through a spermatogonium of Ascaris. By careful
study one will find in this figure quite a number of reticular
connections of fibrils, in fact they are even figured as forking.
This appears still more strikingly in Fig. 21, of which it
is stated that the framework is drawn correctly only in part ;

SCHNEIDER— FA YOD 1 83

here there is hardly anything to be seen of fibrils, but
only a continuous reticular framework. Finally, Fig. 14
shows quite a distinct network, but it is affirmed of it that
it " represents the framework as it appears from superficial
observation, without taking regard to the isolation of the
fibres at the points where they cross." Now it is quite
certain that the figures referring to Ascaris must be the
later and more accurate ones, since those which are pub-
lished of the egg of Strongylocentorotus are diagrams such as
never occur in nature. I think I shall be quite certain of
the assent of all observers who have ever studied such
things attentively, when I assert this definitely. The
schematisation of these figures, especially that of Fig. 9,
is carried to such an extent that the single fibrils, which
are frequently drawn connectedly of a length nearly half
that of the diameter of the egg, for the greater part cast
shadows, and therefore stand out in prominent relief. On
the whole, however, I must take exception to Schneider's
figures, inasmuch as, with few exceptions, they give an
utterly false idea of the actual relations, since they show
the fibrillae light and the intervening substance on the other
hand quite dark, although, as a matter of fact, the state of
things is exactly the reverse of this, as has been stated not
only by me but by all other observers with the single
exception of Kiinstler, and as is shown of course in the
plainest manner in every photograph.

I will enter later on into the difficulties, in fact the
impossibilities, which stand in opposition to such a view
as that which Schneider brings forward. This especially
holds good for the formation of vacuoles which takes place
so frequently in protoplasm, the walls of which Schneider
supposes to be produced from the fibrils, which are connected
by a special cement in order to effect this.

From all these considerations I have not the least doubt
that Schneider's view is altogether erroneous, and that he
has not taken the fibrillar structure of protoplasm from the
objects, but has construed it into them.

In conclusion, I must say yet a few words with regard
to the remarkable view which Fayod (1890) has developed

1 84 PROTOPLASM

concerning the structure of protoplasm. According to his
experience, which is founded principally upon the investi-
gation of vegetable cells, protoplasm and nucleus consist of
long, hollow, spirally twisted fibrils, the so-called " Spiro-
fibrillae." Several of such fibrils are supposed to be usually
" twisted in such a manner that they form the walls of
hollow strings, which are again twisted in their turn." The
last -mentioned "hollow strings" are termed by Eayod
" Spirospartse." The cavities of the Spirospartge and Spiro-
fibrillse are said to be filled in the normal condition by
" granular plasma." Spirospartse pass from the protoplasm
into the nucleus and vice versa, and also can frequently be
traced from one cell into a neighbouring one, so that " the
cell loses its value as a morphological and physiological
unit."

These results were obtained in vegetable cells, chiefly by
injection with quicksilver, by which method Fayod believes he
filled the cavities of the Spirospartae and Spirofibrillse with
metal. In animal cells, which he also investigated, he made
use, as a rule, of other means. I need scarcely state that,
supported by the results of my. investigations, I must deny
Fayod's statements altogether. It could only be a matter of
clearing up what it was exactly that this investigator injected
with quicksilver, for there can be no question that it was
not protoplasmic fibrils. Since I was not in a position to
repeat Fayod's experiments myself, I will not attempt to
express a supposition on this point. But in order to point
out the character of Fayod's views, I may refer to his remarks
upon the blood of vertebrates. Fayod thinks he has con-
vinced himself that the " blood plasma " also consists of
Spirofibrillse, and that they penetrate here and there into the
" Hsematoblasts." In this case it may be taken as suffi-
ciently clear that Fayod has mistaken coagulations of fibrin
for Spirofibrillse.

2. The so-called Spherular Theory of Kunstler

In the year 1882 Kjiinstler developed a most peculiar view
with regard to the structure of the protoplasm in a number

KUNSTLER'S OBSERVATIONS 185

of Flagellata which he had studied closely. According to
his observations, it consists of numerous protoplasmic
spherules ("spherules protoplasmiques "), which, placed in
close apposition to one another, build up the protoplasm, as
cells build up a cellular tissue. That an analogy of this kind
was of great significance for the origin of Kunstler's con-
ception of protoplasm may be plainly seen in the descrip-
tion given by him. Every such protoplasmic spherule
is supposed to consist of an external dense and firm wall
with fluid contents; it is therefore, properly speaking, a
vesicle. In consequence of this structure, protoplasm
frequently appears to be composed of closely packed
vacuoles of the minutest size, separated inter se by very
delicate partitions of a denser nature (1882, p. 86).

Although this conception might well excite some surprise
at the outset, in the form, i.e., in which Kiinstler brought
it forward, and in combination with his peculiar views on
the anatomy and biology of the Flagellata, which would raise
these Protozoa to the rank of highly complicated beings,
still it appeared very probable, all things considered, that
observations upon the reticular structure of protoplasm had
led him to these peculiar interpretations of its nature. Hence
in 1883 (Protozoa, p. 681) I expressed myself to that effect.
More recent observations of my own upon certain Flagellata,
as well as the beautiful and in many respects important studies
which Kiinstler has recently (1889) devoted to this group,
place it beyond all doubt that I was perfectly in the right
when I gave this interpretation to the statements made by
Kiinstler in 1882. In his last work Kiinstler gives a great
number of very good representations of the honeycomb
structure of the protoplasm, chromatophores, nuclei, etc., of
these Protozoa — in fact, he believes, as formerly, that he can
observe signs of such a structure even in the flagella, which
I have never yet succeeded in doing. Thus, as regards
matters of fact, there is a pleasing agreement between
Kiinstler and myself, except on one point, which I must say
I find in many respects very difficult to explain. In 1882,
and again also in 1889, Kiinstler states that the manner
in which he has drawn the honeycomb structure in his

i86 PROTOPLASM

figures, does not really correspond to its natural appearance.
In his figures he depicts it, as a rule, just as has been done
by me as well as by the many observers of the reticular
structure of protoplasm, but he declares that in reality
the contents of the alveoli appear dark and their walls light.
Thus on p. 454 (1889) he says the honeycomb struc-
ture consists " of vacuoles which are enclosed on all sides by
a thick white (' plus blanche ') substance, which in pre-
parations stains less, and contains a more strongly staining,
darker, and probably fluid substance " (contents of the
alveoli or enchylema). I must confess that to me these
statements, which directly contradict both my experiences
and those of all former observers, seem scarcely explicable.
With too high a focus the contents of each alveolus give
the*appearance of a dark point, as has been described already
in the case of the oil-foams (see above, p. 25), yet it seems
to me hardly possible that this circumstance should have
led Kiinstler to his view. The statement with regard to the
greater staining power of the contents of the alveoli is also
inexplicable to me. Since, however, I am in complete
agreement upon this point with all other observers of the
so-called reticular structure, I think I may leave alone
these contradictory statements of Kiinstler.

Kiinstler takes this opportunity to admit (p. 454) that
my comparison of the structure of protoplasm with the struc-
tural relations of a foam gives " une idee assez exacte de ce
que 1'observation microscopique directe revele." Although,
as has been said, he gladly accepts this comparison, yet in
a footnote he combats very energetically my attempts to
explain or illustrate protoplasmic structures with the help
of artificially produced foams. Since his remarks on this
question may serve as a prototype for similar objections,
willed in the course of time will certainly be put forward
in opposition to my efforts, I take the liberty of quoting
them here in fu11. " Si, pour la simplicite avec laquelle elle
fait saisir cette structure, j'accepte volontiers la comparaison
faite par Blitschli eni^e la constitution de la mousse de savon
et celle du protoplasma; il n'en saurait etre de meme de ses
experiences re'centes sur ^s emulsions, d'apres lesquelles il

KUNSTLER'S CRITICISMS 187

pretend expliquer cette structure par le melange de deux
liquides. Quelques spe'cieuses que puissent paraitre ses
donn^es, je m'eleve centre cette interpretation. Le proto-
plasma est une substance vivante, hautement structured, dont
la constitution est le resultat d'une Evolution particuliere,
qui ne saurait avoir rien de commun avec ces mixtures.
Comparer ces deux ordres de faits me parait aussi inutile, au
point de vue de la comprehension re'elle de cette structure,
que de comparer une Me'duse a une ombrelle, une Oursin a
une pelote d'e'pingles, ou certains Bryozoaires a de la dentelle.
Ce sont la des jeux d'hasard, amenant des apparences plus
ou moins analogues sans qu'il y ait aucun autre point
commun."

On the ground already mentioned, it may be worth
while to subject the unfavourable opinion expressed in this
passage with reference to my experiments to a more detailed
criticism. . The quintessence of Klinstler's train of reasoning
is, as he himself says, that protoplasm is a " living, highly
structured substance, the constitution of which is the result
of a special development" As regards, in the first place,
the significance of protoplasm as " living " substance, I am
naturally as strongly convinced of this as Ktinstler himself ;
on the other hand, our paths evidently diverge when it comes
to explaining the peculiar manifestations of activity which
distinguish protoplasm and make it a living, as opposed to
a not-living substance. Since Kiinstler begins his refutation
of my views by laying emphasis on the fact that protoplasm
is living, he evidently belongs to that not inconsiderable
number of biologists who eagerly carry on investigations
upon life and its products, and yet do not welcome a suc-
cessful attempt to get nearer to the actual causes of the
phenomena of life, i.e. an explanation of it as due to the inter-
action of physical and chemical forces under definite condi-
tions. The veil of secrecy and the mysterious obscurity,
which at the present time still hang over these processes,
are the very incentives whereby investigators of this kind,
whom I have met with frequently before, are drawn towards
the study of the phenomena of life ; in fact they not
infrequently spur them on to obscure the processes and

1 88 PROTOPLASM

relations, and make them still more mysterious, by intro-
ducing complications and false analogies with higher forms
of development. This endeavour was very apparent in
Klinstler himself in his earlier work on the Flagellata. To
the same category belong also the scientists that crop up
from time to time, who have "a preference for paradoxes,
who feel a secret horror of all simple and straightforward
solutions of the problem, who in fine are only content
when they think they have found as extraordinary an
explanation as possible, directly contradicting all other
experiences.

Any one who takes exception, at the outset, to all
attempts to explain the various phenomena of life, on the
ground that such attempts are devoid of importance, because
not made upon the living body or upon protoplasm,
renounces at once all possibility of an explanation of these
processes ; he shows that he does not take their explanation
seriously, but thinks it more correct to regard vital pheno-
mena as the outcome of a secret and mystical cause, which
it is not permissible to touch upon. Whoever, on the
other hand, does not share this point of view, will as little
as myself be of the opinion that I had prepared living-
protoplasm by means of my experiments, but will admit
that bodies were successfully manufactured which not only
possess a great similarity to living protoplasm in their
structural relations, but also offer certain peculiarities which
hitherto were only to be observed in the same manifestation,
and for the same length of time, in living protoplasm. To
bring these results to bear upon the explanation of the
phenomena exhibited by living protoplasm seems to me not
only permissible, but even imperative.

Now Klinstler explains protoplasm not only as a living,
but also as a " highly structured " substance. In so far as
this statement has reference to structural relations actually
observed, and not to such as are supposed to be hidden from
us, and to be necessarily connected with the mysterious life
of this substance, I can by no means agree with it. Proto-
plasm, as far as our knowledge extends, is in no way more
highly structured than the foams artificially manufactured

OIL-FOAMS AND PROTOPLASM 189

by me ; and if it must of necessity possess a very high
degree of complexity, it may be confidently predicted that
this complexity is to be sought in the province of chemistry,
as I have already attempted to explain elsewhere (1891).
Finally, according to Kunstler, protoplasm must be "the
result of a special development, which can have nothing in
common with the mixtures prepared by me." Now I think
that Kunstler would find it difficult to reply if he were
asked for a more precise account of this special mode of
development, of which protoplasm is the result. I regret to
say that I, at least, know nothing definite concerning any
developmental history of protoplasm, although I am, of
course, greatly interested in it. So far as I have heard,
there has been much talk about the growth of protoplasm,
and some hypotheses concerning it have been put forward,
which, however, only deal with the mode in which complete
molecules or micellae of protoplasm are added to those
already in existence ; but, as I have said, I know nothing
of any special mode of development of protoplasm which
could be adduced in opposition to the validity of my
attempts to explain certain phenomena of protoplasm.

Now, finally, I may be permitted to say a few words
as to the illustration, not conceived in the best of taste,
which Kunstler brings in at the conclusion of his remarks
upon my comparison between artificial froths and proto-
plasm. This comparison is supposed to be just as " use-
less " as that " of a Medusa with an umbrella." Of course
if it was to be inferred that the Medusa consisted of the
framework of an umbrella, covered over with silk, linen, or
some other material, then the use of this metaphor would
not be at all inadmissible, even if the Medusa was manu-
factured by nature from special materials, while the
umbrella was made in X. and Co.'s workshop in the usual
way. But unfortunately this is not the case; a Medusa
has no more internal resemblance to an umbrella than a
professor of Bordeaux to a statue. Were the resemblance
between artificial foams and protoplasm of a corresponding
character, I should then, of course, have every reason to strike
my colours. The affair, however, is not so bad as all that.

190 PROTOPLASM

If I may keep to the above simile of two umbrellas, the
differences and resemblances between protoplasm and the
artificial foams may be summed up as follows. Protoplasm
from nature's workshop is essentially of exactly the same
structure as the artificial protoplasm from Butschli's work-
shop, only the former enjoys the agreeable advantage that
the substance of its framework is not olive oil, but the
peculiar substance of protoplasm, and its enchylema also
contains many substances which the latter does not possess.

Any one who denies that the phenomena to be observed
in the foams may be compared with those exhibited by
protoplasm, and may be used for an explanation of them,
may also assert with as much reason that everything which
has hitherto been stated with regard to the combustion of
organic substances in the metabolism of the animal machine
is useless, for the animal lives, and consists of a substance —
protoplasm — which is peculiar in the highest degree, while
all processes of combustion, as we know, go on in not-
living material and without the co-operation of protoplasm.

Klinstler has, however, as was said, adopted my view
as regards the general appearance of the structure of the
protoplasm. Yet he does not think it necessary to give
up entirely his earlier idea of protoplasm being composed
of hollow spherules. Thus he tries to render it probable
that the lamellae which form the walls of the alveoli may
split occasionally, so that single alveoli become isolated as
spherules through the appearance of an intervening fluid
matrix. This possibility he attempts to demonstrate,
more especially by means of observations upon the proto-
plasm of a Eoraminiferan with a peculiar shell, which has
been dealt with already in two works dating from 1888.
Without entering more closely into these observations, I
should like merely to express my conviction that the little
vesicle-like bodies, which Klinstler observed either singly
or united into groups in the endoplasm of this Foramini-
feran, and described as almost fluid and granulated, have
certainly not arisen in the manner alleged by him, through
isolation of the alveoli of a protoplasmic network which
existed before. My own observations of a former date, as

THE GRANULAR THEORY 191

well as those recently repeated by me, on the protoplasm
of marine Khizopoda, rather tend to show that such bodies
occur very commonly as deposits in the protoplasm of these
Protozoa, and certainly have nothing to do with the alveoli
of the distinctly honeycombed protoplasm which is also
present. That Kiinstler's vesicles were nothing more than
the similar granules or deposits of such frequent occurrence
in the protoplasm of Rhizopods, seems to me to follow
beyond all doubt from his remark that in well-nourished
Foraminifera these granules are the seat of the red colora-
tion. It is, however, a matter of common knowledge that
the seat of the red coloration is formed, as a rule, by
droplets of fat, which are impregnated with pigment in
solution, as is obvious from their being readily soluble in
alcohol ; on the other hand, it is probably also due some-
times to bodies of the nature of Zooxanthellse, as I attempted
to show in 1886 in the case of Peneroplis. But in any
case we are not justified in referring these deposits, as
Klinstler wishes to do, to the isolation of originally con-
nected alveoli of protoplasm ; his few observations are also
certainly insufficient to support an assumption so difficult
to comprehend. I am inclined to see in it an abortive
attempt to rescue some portion of his statements of 1882, as
to the protoplasm being composed of vesicle-like spherules.
But after the detailed expositions in the earlier portions of
this work, it is not necessary for me to state more precisely
why I regard this view to be erroneous now just as before.

3. TJie so-called Granular Theory of Protoplasm

As is well known, the earliest view with regard to the
constitution of protoplasm was that it consisted of a viscid
or slimy ground substance, in which numerous granules
were embedded. These granules, which from a long time
back have been considered as an indispensable constituent,
so to speak, of protoplasm, were distinguished by the
term protoplasmic granules from other granular contents
lodged in the protoplasm, upon the chemical nature of
which, as fat, starch, pigment, etc., it is possible to arrive

192 PROTOPLASM

at some understanding. After they had been christened
" Microsomes " by Hanstein in 1882 they obtained to
some extent the right of entry, as it were ; for anything
that is called by a Greek name at once seems to many people
to be much better known, and as something which must
be definitely reckoned with.

With the gradual extension of the theory of the reticular
structure of protoplasm the view developed, that a great
portion of these protoplasmic granules were merely the nodal
points of the network, although the adherents of this theory
of course pointed out frequently enough the occurrence of
granular deposits in protoplasm. There was also no lack
of attempts to refer the protoplasmic structures observed to
a special arrangement of the protoplasmic granules.

Martin, as far back as 1882, developed the latter view
very consistently. Protoplasm consists, according to him,
of a ground substance, the so-called "gangue protoplas-
matique," and of granulations deposited in it. The ground
substance is supposed to be the true contractile matter.
The granulations embedded in it may now either (1) lie
without any regular arrangement whatever in the ground
substance, as, for example, in leucocytes and numerous other
cells ; or (2) they may be arranged in longitudinal rows
one behind the other, from which a striated structure arises
in the protoplasm, as, for example, in ciliated epithelial
cells ; or (3) finally, a breaking up of the ground substance
or " gangue protoplasmatique " into " rods or cylinders " may
take place, each of which contains in its axis a row of such
granules ; this condition is said to have been evolved in
numerous gland cells, as well as in smooth and striped muscle
cells ; it is the cause of their longitudinal striation, or rather
their fibrillar nature.1

Finally, Martin also discusses the question, whether the
granulations of the protoplasm might not perhaps be living

1 Heidenhain in 1875 had already tried to refer the striation of the inter-
nal region of the pancreas cells to the deposition of fine tubules in the ground
substance of the cell. Into these tubules the granules of the protoplasm
were able to penetrate, for which reason the latter often appear arranged in
rows.

PFITZNER'S THEORIES 193

structures, and comes to the conclusion that this view,
already originated by Be*champ (1867), may well be the
correct one. His remarks upon this are as follows : " La
granulation proteique du protoplasme est peut-etre un
eldmen t vivant, line cellule, dont la vie et la fouction
re'guliseraient et speciferaient dans un sens physiologique
determine, 1'etre complexe, que nous ddsignerons encore sous
le nom de cellule simple ou primitive." His grounds for
this assumption are the great resemblance of the granulations
to micrococci.

Pfitzner also tried to demonstrate theoretically in 1883
that the structures of protoplasm have arisen from the
arrangement of the granules in series. In fact this idea
seemed so obvious, that the radiating phenomena in division
have since their first discovery usually been referred to the
protoplasmic granules being arranged in rows. As has
already been mentioned above, Pfitzner distinguishes
between the active and passive structures of protoplasm.
By the latter he understands reticular structures produced
by vacuolisation. He is of the opinion that the majority of
the protoplasmic structures hitherto described belong to
this category. Active structures, on the other hand, would
be such as are produced by attraction and repulsion of the
small particles which are suspended in the protoplasm.
Pfitzner conceives of these particles as viscid, and the
ground substance in which they are found as fluid. If
attraction prevails, the particles flow together into larger
drops, as, for example, in fat cells, where they fuse into fat
drops of considerable size. If, on the other hand, repulsion
prevails, the minute particles become evenly distributed in
the ground substance, as, for example, the pigment granules
in pigment cells. But when repulsion and attraction are
equal, the particles only come into contact, and range them-
selves alongside of one another, as a result of which certain
structures arise if the particles refract the light more strongly
than the ground substance. The form assumed by the
filamentous framework, which is built up by the serial
arrangement of the granules, depends on the " intensity of
the attraction." When it has a certain strength, each par-

13

194 PROTOPLASM

tide has the power of " binding " two neighbouring particles ;
then filaments are formed. If, however, a particle is able
to bind three others, networks arise. As examples of such
active structures, he considers those of the nuclei and the
fine protoplasmic structures, which he himself described in
the red blood corpuscles of Amphibia (see above, pp. 130 and
173).

I think I scarcely need point out that in these specula-
tions Pfitzner did not go upon actual physical grounds, but
that the forces of attraction and repulsion brought into play
were specially invented for this service. One point, how-
ever, I should like to emphasise particularly. In Pfitzner's
passive reticular structures the framework is of course the
true protoplasmic substance become reticular from the
formation of vacuoles. But in active structures, on the
other hand, the contents of the network, or the intervening
matrix, would be the true original protoplasm. My view,
on the contrary, regards both structures as essentially the
same.

Brass (1883-85) is also of the opinion that the reticular
structures occasionally observed by him were formed by a
serial arrangement of the granules. Kultschitzky (1883)
had the same idea with regard to the striations in the
sensory cells of Gaudry's corpuscles, and Schiefferdecker
(1887) with regard to the fibrillar structure of ganglion
cells. Moreover, Vejdowsky (1888) drew from his inves-
tigations on the formation and development of the eggs of
Rhynclielmis, the conclusion that protoplasm is originally
quite homogeneous and structureless (p. 19); that then
very minute granules make their appearance in it, which
" begin to group " themselves ; " rather later there arise
from these granules, especially in the neighbourhood of
the nucleus, filaments running irregularly and crossing
repeatedly " — " thus arises the reticulum of the Cytoplasma "
(p. 20). In the course of the segmentation of the egg also,
Vejdowsky believes he has frequently seen reticular proto-
plasm becoming homogeneous, and differentiating again
into structured. He therefore sees in the structures of
protoplasm and cells, "products of the processes of nutri-

ALTM ANN'S VIEWS 195

tion, assimilation, and growth" (p. 119), produced by
differentiation of the primitively structureless, homogeneous
protoplasm. I think I need hardly point out that the so-
called protoplasmic reticulum which Vejdowsky describes
in the ripe ova of Rhynchelmis, is not a real protoplasmic
structure, but a coarse protoplasmic framework which
remains free of yolk. He himself was also forced to this
assumption (p. 120), without, however, being able to find
the true protoplasmic structure in this reticulum. On the
other hand, he certainly has observed a great deal of the
real protoplasmic structure in the so-called attraction spheres
at the ends of the nuclear spindles, periplasts as he terms them.
Finally, since 1886, Altmann has made thorough studies of
the protoplasmic granules, in the course of which he has
arrived at views similar to those already originated at an
earlier period by Bdchamp, and especially by Martin. It is
an incontestable merit of Altmann's to have proved that in
protoplasm there occur probably quite universally numerous
granules, capable of being strongly stained with certain
aniline colours. On the other hand, he decidedly goes too
far in his conclusions concerning these so-called " granula,"
as well as in the theory of the constitution of protoplasm
founded upon them.

If we wish to give an account of Altmann's views and
their merits, we must first trace their gradual development
for a little, since they have undergone certain modifications
in the course of time. In 1886 Altmann first brought
forward the proof that the protoplasm of almost all cells
contained granules, which he himself first discovered in a
number of cells. It is rather a motley collection which is
here brought together under the head of granules. First come
the chlorophyll granules of the vegetable cell ; then pigment
granules of all kinds, the granulations of the plasma cells
(Waldeyer), of leucocytes (Ehrlich), the granules of the
pancreas, liver, and other gland cells, the eleidin granules
of cornified cells, and the yolk granules or yolk discs of the
protoplasm of the egg, are all included here. On the ground
of Altmann's later work we can also count fat granules and
fat drops, which are supposed to be produced by modification

1 96 PROTOPLASM

of the granules through " storing up of fat." The granules
are embedded in a " jelly-like substance," and play the most
important part in the phenomena of life exhibited by
protoplasm. As far back as 1886 Altmann pointed out
their analogy with Bacteria, which were supposed to be
certainly not cells. The great, and indeed determining
importance, which in 1886 he ascribed to them as the real
agents in carrying on and bringing about the processes of
metabolism, shrinks more into the background in his later
works. For instance, the assumption which he set up in
1886, that they were the means of transferring oxygen, is
at a later time no more to be found. This omission is
no doubt in connection with the fact that the alleged
activity of the granules was based, in any case, on their
supposed relation to chlorophyll granules ; but since the
latter structures no longer appear among the granules in
1890 as the result of Altmann becoming gradually convinced
that such a conception was untenable, this side of the activity
of the granules was necessarily made less of.1

The matrix of the protoplasm chiefly plays a part,
according to Altmann, in affording a vehicle for the physical
phenomena of life. In 1886 and 1887 he still admits
the existence in this matrix of special fibrils, which have
nothing to do with the granules. Thus in 1886 he asserts
that the axis-cylinder consists of fibrils, between which the
granules lie in rows. In 1887 he allows the occurrence of
fibrils and networks in the protoplasm in like manner, but
now they are to be derived from arrangements of the granules
in rows, in the same way as the filamentous Bacteria form
connected threads composed of numerous single individuals.
It sounds, at least to zoologists, very confusing, that Altmann
should call these threads formed by serial arrangement of
the granules " Nematodes."

1 Zimmermann in two of his works has studied Altmann's method of in-
vestigating granules in the vegetable cell. He seems, however, in opposition
to Altmann, to by no means regard the granules observed in them as
identical things. I am also unable to find in Zimmermann anything in favour
of regarding the chlorophyll granules and leucoplasts as "granula." Since
these structures themselves for the greater part possess granular contents,
there can be no question of any such comparison.

HIS OBJECTIONS TO A FRAMEWORK 197

In 1890, finally, he retains only the fibrils, while the
networks are attributed to erroneous observations. The
apparent reticular structure is explained as a delusive
appearance depending on the fact that the closely packed
unstained granules have been overlooked, and have been
interpreted as the spaces of a meshwork. I think I need
only say a little here concerning this view. Altmann
extends it in like manner to the nuclei, the structure of
which is supposed to correspond exactly to that of the
protoplasm. The reticular framework of the nucleus is also,
according to his idea, a deception. But any one who has
seen the granules of the nucleus and of the protoplasm in
the unstained condition, when they are, of course, just as
visible as when stained, knows that they are denser and
darker structures, with a high power of refraction, which,
therefore, could not be confused with the clear meshes of the
protoplasmic network by any observer at all experienced.
On the other hand, in the investigations set forth above, we
have come across granules sufficiently often, and have always
found that they lie in the framework of the protoplasm.
In staining experiments with very various aniline colours,
etc., it was always shown in the plainest manner that the
meshes of the network remain colourless, while the proto-
plasmic framework assumes only a feeble coloration. It is
the granules alone which stain intensely in the protoplasm.
For confirmation of this fact, sections are of course required
which have only the thickness of one or two meshes. The
alleged coloration of the spaces of the meshes, which earlier
observers affirmed frequently, is to be attributed to the
thickness of their sections, and can be explained without
difficulty ; in fact it follows necessarily, if our view of the
alveolar structure of protoplasm is to be regarded as correct.

But how, it will be asked, could Altmann have com-
pletely overlooked, on his part, the framework of the
protoplasm ? The explanation of this seems fairly obvious.
He himself recommends investigating the preparations with
" an open cone of illumination," i.e. under conditions which
cause all the more minute and pale structural elements,
that are stained but little or not at all, to become simply

198 PROTOPLASM

invisible, as has already been thoroughly discussed above
(p. 1*79). If we examine one of Altmann's figures, as, for
example, the pigment cell depicted on Plate I. (1890),
which is supposed to represent to a certain extent the
typical structure of the cell, the remarks just made will
become still more obvious. We miss throughout this figure
any distinct limiting contour to the cell. Frequently little
aggregations or strands of pigment granules may be noted,
which lie entirely isolated, without any connection with the
rest of the cell. Hence it may be inferred very definitely,
that Altmann has in reality only observed the granules,
and has overlooked, on the other hand, the protoplasmic
framework.

A similar result is obtained, moreover, if we pay atten-
tion more especially to the alleged formation of fibrils by
arrangement of the granules in rows. In most of the figures
it can be plainly made out that the fibrils do not consist at
all of closely packed granules, but that clear spaces intervene
between the granules. Only in very few cases relatively are
the fibrillee drawn as continuous red lines, which lie rather
scattered in the . cell. I put aside the latter cases, with
regard to which I will assume that the continuous fibrils
would prove to consist of granules when more closely
studied, and will linger for a moment over the more
frequent instances of the kind first mentioned. In my
opinion, these observations are in favour of just the very
thing which Altmann wishes to deny, namely, that some-
thing must be present which maintains the rows of granules
in their arrangement ; in favour, that is to say, of the
presence of a t fibril distinct from the granules, or rather
of a fibril-like tract of the meshwork of the protoplasmic
framework.

For the reasons enumerated I must conclude that Alt-
mann's objections to a reticular framework of protoplasm are
futile.

Although it lies beyond the scope of the task we have
undertaken to examine more closely the importance which
Altmann ascribes to the granules, yet I must not pass this
over altogether, since a few critical remarks on this point

BACTERIA AND CELL GRANULES

199

would seem not out of place on this occasion. Altmann
considers the granula or cytoblasts, as he also terms them,
to be really living, and as homologous with Bacteria. We
seek in vain for any decisive proof of this view, for the
oft -asserted proliferation by division is nowhere proved.
That they are able to continue living outside the proto-
plasm, and more especially to increase, is indeed directly
denied by him, in opposition to Bdchamp. In 1890 the
function which, according to Altmann and his pupils, they
perform in the metabolism of fat is cited finally as a proof
of the vitality of the granules. Although this point does
not seem to me by any means sufficiently clearly estab-
lished, I will not go into it farther, since I am inexperienced
in this line. But as long as individual constituents of the cell
are not seen to persist when isolated, nor are distinct living
phenomena observed in them, it is very dangerous to speak
. of their life as something which they possess in themselves.
They are so far living, as long as the opposite is not proved,
in that they are parts of a living organism, so that the
granula may therefore be living in the same way as the
nucleus, even though they no longer betray any sign of life
after isolation.

Are we then to regard the granula as homologous on
the whole with Bacteria, as Altmann assumes, to derive
them phylogenetically from Bacteria, and hence to look
upon the so - called matrix of the protoplasm, with
Altmann, as a kind of zooglsea jelly ? I think this is not
permissible. I argue quite apart from the fact that the
genetic connection between the numerous granular contents
of the very various kinds of cells, which Altmann unites as
granula, has first still to be proved. I depend rather on
the observation made by myself and others, that the Bac-
teria in like manner contain granula, and, moreover, granula
which we are completely justified in regarding as equivalent
to the chromatin granules of cell nuclei. Besides these,
however, there may be special granules, showing different
relations, in the Cyanophycece, which agree so closely
with the Bacteria. And why does not Altmann also
regard the sulphur drops of numerous Bacteria as granula ?

200 PROTOPLASM

The chromatiu granules of the nuclei are regarded by him
as being quite certainly " granula," hence he will be obliged
to admit that Bacteria may themselves contain granula.
However, I have sufficiently set forth my views with regard
to Bacteria in another place (1890), to which I may
refer the reader, and I consider that I have there also
refuted Altmann's view that the Bacteria are non-nucleated
primitive organisms of a peculiar kind, comparable to the
granules of the nucleus and the protoplasm. The Bacteria,
according to my conception of them, are partly comparable
to the nuclei of higher animals, without any clearly demon-
strable trace of protoplasm apart from the cilium, and
partly, on the other hand, to nuclei, with a scanty envelope
of protoplasm. Still less, however, is Altmann's assertion
justified that many other Protista also, e.g. Sarcodina, are
non-nucleated, and that we may, to some extent, compare
the process of formation of a nucleus with the encystation
of such a monerous Sarcodine, as a process in which a portion
of the original protoplasm becomes encapsuled as a nucleus,
while another portion remains persistent round the nuclear
capsule as the protoplasm of the cell. Unfortunately Alt-
mann has omitted to specify by name any case of encyst-
ment in Protista which might appear to him to serve as a
commencing nuclear formation of this kind. I am inclined
to believe that what he had in his mind was not true
encystment, but something like the structure of the Eadio-
laria or the shell-bearing Ehizopoda. Since, however, in all
these cases, as also in the true encystment of the Protista,
nuclei are known with sufficient certainty to be present, the
entire comparison does not, on the whole, prove what it is
intended to.

On the other hand, however, it is quite possible that,
among the strongly staining granules of the protoplasm,
there are in reality bodies which can be homologised with
Bacteria, so-called Bacteroids, as they have been termed,
which have been frequently demonstrated in vegetable and
animal cells. I had already at an early date pointed out
that the numerous granules which fill the endoplasm of the
Ciliata reminded me strongly of Micrococci, and with regard

THE FRAMEWORK AN ARTEFACT 201

to this point I can also further adduce an observation which
Dr. Safftigen made in my laboratory in the summer of 1890
upon Epistylis galea. As is well known, the ectoplasm of
this form, as of Vorticdlina generally, contains numerous
rounded, rather strongly refractile structures, which Ley dig
once regarded as nuclei. Now the fact can be established
that these granules, which I regard as identical with those
mentioned above in Ciliata, were found at times in a state
of rapid proliferation by division, which of course greatly
supports the interpretation of them as Bacteroids.

Since it seemed to me of importance to investigate the
Bacteroids discovered at an earlier date in certain animal
cells, with a view to their relations with the framework of the
protoplasm, I have carefully studied, for my own benefit,
Blochmann's sections through the cells of the fat body of
Blatta orientalis, which were filled with such bodies. It
was thus established that the Bacteroids, strongly stained
by Gram's method, lay embedded in rather a scattered manner
in a very pale, but distinct reticular, protoplasmic framework
(Plate VI. Fig. 4). Besides the Bacteroids, no granular con-
tents of any kind are present in the protoplasmic framework.
The nuclei, and more especially their chroma tin granules, are
stained very intensely.

As to the works of Zimmermann (1890 and 1891),
Mitrophanow (1889) and Luckjanow (1889), who agree
more or less with Altmann in their conception of proto-
plasm, I think I need not enter into them more specially
after the above discussion.

4. Attempts to explain the Reticular Structures as Phenomena
of Coagulation or Precipitation

It is really surprising that the question whether the so-
called structures of protoplasm are not produced by the
coagulation or precipitation of albuminous bodies during the
process of preparation, should not have been thoroughly dis-
cussed at an earlier period. That this was not done probably
depends on the fact that the investigators who worked at
this subject upon zoological lines were just those who, even

202 PROTOPLASM

in early times, occupied themselves with the study of the
living object, in order to ascertain the existence of structures
in living protoplasm. Since, moreover, the living nuclei
frequently showed still more distinct structures of a similar
kind, it seemed all the more justifiable to regard the exist-
ence of the protoplasmic structures during life also as a
certain fact.

As is well known, some later observers, as more especially
Berthold, Er. Schwarz, and, in connection with the latter,
also Kolliker, have disputed the idea that reticular structures
are present in living protoplasm. In their opinion they are
artificial products, so far as they do not depend upon patho-
logical vacuolisation, i.e. appearances artificially produced by
precipitation or coagulation of the protoplasm. Berthold,
who first expressed this view in 1886, has come forward
again, as is well known, with good arguments, and in a very
praiseworthy manner, to vindicate the fluid nature of pro-
toplasm, which was taken for granted almost universally at
an earlier period. It possesses, according to him, the char-
acter of an emulsion, i.e. it is a mixture of two or more
fluids which are insoluble in one another, or only soluble to
a limited extent. Of course it was also quite in accordance
with his view for solid secretions in the form of granules or
crystals to appear in the protoplasm. Berthold seeks very
correctly to refer the emulsive character of protoplasm to
the so-called processes of desolution, which have already been
briefly explained above, and were found to be the true
efficient cause of the formation of oil-foams. When Ber-
thold terms his conception of protoplasm, and, more particu-
larly, his statements as to its fluid nature, a hypothesis
merely, I think he is too sceptical in this respect. I shall
try to explain later on, as I have already done before, that
the fluid nature of more ordinary protoplasm follows very
definitely on the contrary from all the phenomena observed.
It will then also be discussed how the view gradually
developed that protoplasm could not be fluid, or that it
must at least be a mixture of solid and fluid parts. If
then Berthold, by reason of his view of the fluid and emul-
sive nature of protoplasm, got so far as to deny a reticular

BER THOLD—SCHWARZ

203

framework altogether, his attitude is quite intelligible, for a
framework of this kind could only be imagined as a firm
structure, and the alleged fluid nature of protoplasm would
of course have been quite irreconcilable with such a view.
For a sponge soaked full of liquid, as one would have to figure
to oneself from the current views upon the reticular framework
of protoplasm, could not possibly exhibit the phenomena of
a fluid. Nevertheless, Berthold could not deny the appear-
ance of filaments in protoplasm, and, in fact, he has himself
observed them frequently since 1882 in living vegetable
protoplasm. On the other hand, he denies that these threads
are connected into a network, and that they form a continu-
ous framework ; he believes that, with regard to this' point,
he must rank himself with Flemrning, who represented the
same opinion. What these filamentous " torulous " struc-
tures in protoplasm really are, is not clear from Berthold's
discussions. As far as I am able to come to a decision on
this point, he places them in the same category as the
granular and other contents, which are separated from the
fluid ground substance of the protoplasm by processes of
desolution. On this point, however, he would depart widely
from Flemming's view, to an agreement with whom he attaches
great importance. On the whole, however, it is clear that
if filamentous solid bodies occurred in such quantities in the
protoplasm, as is the case according to Flemming, for instance,
and numerous other observers, the fluid character of the
protoplasm would certainly be completely lost. For if we
represent to ourselves a heap of solid filaments, which
are connected by layers of fluid about 0*5 to 1 //, in thick-
ness, the adhesion between the fluid and the filaments
must, without doubt, have the effect of causing the entire
lump of filaments to assume, at most, the character of a
plastic body, while protoplasm presents the nature of a
viscid fluid. For the rest, Berthold (p. 62) admits
that in protoplasm occasionally "products of differentia-
tion or precipitates may occur in the form of a fine
framework," although he himself never observed anything
of the kind.

Opinions in many respects similar, only more indefinite,

204 PROTOPLASM

are expressed by Fr. Schwarz (1884) upon the reticular
structure of protoplasm.

What his conception of protoplasm really is, does not
appear to me sufficiently clear from his extensive treatise.
He declares (p. 130) that all authors are agreed upon the
point " that protoplasm consists of solid and fluid parts,"
from which it is to be concluded that he, in like manner,
supports this view. On the other hand, however, he speaks
also of the " semi-fluid " nature of protoplasm. Now, since
he denies in the most definite manner that the firm sub-
stance of protoplasm appears in the form of a framework,
he comes to the conclusion that protoplasm must be a
" mixture, which in external appearance is homogeneous, but
seems nevertheless to admit the possibility of the single
substances being variously distributed" (p. 130). On p.
125, also, it is said with reference to the investigations of
Eeinke and Eodewald, that " there might be a homogeneous
mixture, of the framework and the enchylema," which was
not to be separated by the action of centrifugal force. But
what this " homogeneous mixture " may be in reality is not
clear to me. If protoplasm is supposed to consist of solid
and fluid parts, they could only be indistinguishable if they
possessed exactly the same power of refraction. But since
it is inconceivable that such a thing should occur universally,
it is incomprehensible to me how Schwarz arrives at the
statement (p. 130) that it is never possible to convince
oneself of the presence of a framework in living protoplasm
— an assertion which was the more unjustifiable because
numerous investigators even before Schwarz had convinced
themselves of its existence. Unfortunately Schwarz, while
talking about protoplasm in quite a general manner, has
by no means taken into consideration the numerous observa-
tions on the zoological side. He appeals, indeed, to Flemming,
without, however, appreciating or paying more special atten-
tion to what is communicated by him.

What he himself has described in the way of filamentous
protoplasmic structures in vegetable cells were, in my
opinion, as a rule nothing of the sort, but merely networks
of minute trabeculoe of protoplasm which traverse the cell

FRAMEWORK PRESENT IN LIFE

205

sap, or at times also form the lining of the cell wall.
The real intimate structure of protoplasm, on the contrary,
he has not observed, for which reason it becomes explicable
how he arrived at the idea that the filamentous proto-
plasmic structures gradually passed into the trabeculae of
the protoplasm which usually traverse the cell sap of the
vegetable cell. A cursory study of the protoplasmic struc-
tures described in such numbers in animal cells would
necessarily have taught him that there are filamentous
structures which pervade the entire protoplasm, and which,
therefore, in no way permit of the interpretation attempted
by Schwarz.

I think, however, that in the face of the numerous proofs
brought forward both in this and earlier works that not only
filamentous, but also reticular substances are frequently to
be observed in living protoplasm, the interpretation of them
as products of coagulation or precipitation requires no
further refutation. It has already been shown above that
the fibrillar structure of protoplasm always proves, when
accurately studied, to be a modification of the reticular
structure ; therefore, as I have already explained earlier,
the existence of the so-called reticular structure can be
inferred with a high degree of probability, if not with
certainty, from the demonstration of fibrillar structures in
living protoplasm.

In opposition to the attempts to set aside the structures
as artificial products, it would seem worth while to give a
brief review of former observations which have demonstrated
structures in living protoplasm. Of course these statements
are not all of equal value, since occasionally without doubt
deceptive appearances or post-mortem alterations of the
protoplasm may have been seen such as may occur quite
easily, especially in the case of the cells of higher organisms
detached from their natural environment.

That the structures of ganglion cells can be recognised
even in the freshest possible condition, has been confirmed
by the majority of observers since the time of M. Schultze
(1863), namely, by Schwalbe (1876), Arnold (1879), Dietl
(1878, for Helix), Freud (1882), Leydig (1883), and

2o6 PROTOPLASM

Frommann (1879-84). In living cartilage cells, filamentous
or reticular structures have been described by Flemming
(1870), Frommann (1879, 1880), and Schleicher (1879).
For colourless blood cells, Frommann (1875, 1880), Schwalbe
(1876), and Ley dig (1885) have affirmed the presence of
reticular structures, and Strieker (1890) has recently
photographed them from life, by which photograph Schafer
was converted from the opinion he held for so many
years, namely, that reticular structures were not present
in leucocytes. In the salivary corpuscles Strieker (1880)
described a trabecular framework. Moreover, there are
numerous assertions concerning the existence of striations in
epithelial cells in the living condition. Heidenhain observed
them in 1875 in fresh pancreas cells, Strieker and Spina
noticed striated structures in the fresh cells of the skin
glands of Amphibia (1880), JSTussbaum (1887) in fresh
cells from the intestine of Anodonta, Ley dig (1885)
frequently confirmed the striated structure in fresh epithelial
cells of insects, and Carnoy (1885) expressly declares that
the reticular framework is to be made out plainly in the
living cells of insects. As is well known, Kupffer had
already described in 1870 a reticular framework in the
living follicle cells of the Ascidian ovum, and in 1874
in the cells of the salivary gland of Blatta ; he also saw
the reticular structures of liver cells, though more faintly,
in the fresh cell.

In streaming vegetable protoplasm, Velten had already
(1873 and 1876) found the structures described above, and
Frommann also (1879) had frequently seen them there
beyond all doubt, even though many things which he
describes (especially in 1884) must have been pathological,
since he often investigated the cells for quite a long time
in sugar water; in fact he describes processes in them
similar to those which have been already mentioned, and
interpreted as pathological, in the case of the blood corpuscles
of the crayfish. On the other hand, the assertion of Schwarz,
that " these local reticular structures observed by Frommann
were nothing else than precipitates which separated out in
certain places " (of course in the cell sap), " and which later

SCHWARZ >S VIEWS 207

became vacuolated," seems to me to go too far, and to be in
the main unfounded, since in any case there certainly could
be no question of precipitates within the cell sap.

Finally, we must mention further, that van Beneden
(1883) also convinced himself that the most important of
the structures described by him in the sexual products of
Ascaris were to be observed while still in the living condition.

In Protozoa, which are especially important for the
structure of living protoplasm, Biitschli (1887), Fabre
(1887), Schewiakoff (1889), and others, have traced the
living structures.

Taking into consideration all that has been enumerated,
which could certainly be further increased by a more
conscientious search through the literature, as well as,
on the other hand, the further proofs which I have com-
municated in this work, it may well be asserted that the
structures in question are frequently to be observed quite
plainly in the living condition, and therefore cannot be
any 'artificially produced appearances of precipitation or
coagulation.

Now Schwarz allows reticular or filamentous structures,
which can be precipitated or fixed, in the case of the nuclei
and chlorophyll bodies, but denies them, on the other hand,
in the case of protoplasm ; and why ? He asserts, in fact,
that in the fixed framework of the protoplasm, a chemical
difference between the framework and its contents is not
demonstrable. The contents of the meshes stain in the same
manner as the meshes, and therefore also consist of a
coagulable substance. The difference between the frame-
work and its contents only consists in a slight difference
of density ; both are said to consist of plastin. The
contents of the meshes is said not to be a fluid (p.
131); this contrasts very strongly with the descrip-
tion given on p. 140 of the same framework in fixed
protoplasm, where it is stated " the cavities " (i.e. those of
the framework) "are for the most part filled with fluid, but
may, under certain circumstances, also be filled with a less
dense substance." I must say I think Schwarz would find
few to agree with his view of the chemical similarity between

208 PROTOPLASM

the framework and its contents, and I can only, as before,
assert in the most definite manner that in the thinnest
sections, or with the intensest staining, I could never obtain
any coloration whatever of the contents of the meshes or
intervening matrix. As I have remarked before, the in^
vestigation of thicker sections, or even of whole layers
of protoplasm, as was the method of Schwarz in all cases,
proves nothing at all in this respect ; for even if only a few
layers of alveoli were superposed upon one another, it must
naturally give an appearance as if the intervening substance
also possessed a fainter colour, because both above and below
a mesh which is exactly in focus there lies a quantity of
coloured matter which affects the light transmitted. Exactly
the same holds good, in my opinion, for the reticular
precipitates prepared artificially by Schwarz, for which also
he assumes a homogeneous or granulated ground substance
composed of the same material. If Schwarz saw precipita-
tion films, which were originally homogeneous, becoming
afterwards granular and reticular, I assume, until further
light has been thrown on the subject, that it was nothing
to do in this case with structures which became formed
within the homogeneous film, but it was a matter of deposits
that appeared subsequently in the form of granules, networks,
and crystals.

I will not follow up this subject further, since as yet I
have but few observations at my command upon reticular
precipitates and coagulations. Yet I agree completely with
Schwarz that coagulated drops of white of egg, as also a
precipitate of ferrocyanide of iron (from rather concentrated
solutions), appear very finely reticular, and possess great
resemblance to protoplasmic structures. In the case of a
precipitate of Prussian blue, it can scarcely be doubted that it
is only the result of a serial arrangement of minute stained
granules, and the same will also probably hold good for the
precipitates of colloidal bodies.1 With regard to this, and
also with reference to protoplasmic structures generally, it
seemed to me of importance to test in what way very

1 Upon this point see the Appendix at the end of this chapter (pp. 216-
219 infra) for the changed opinions which I now hold.

FALSE NETWORK BETWEEN GRANULES 209

minute granules behave which are lying closely packed
together in a liquid, or which have been dried up on a
slide; that is to say, what appearance they present with
high magnifications.

If some Chinese ink, rubbed up into rather a thick
paste, or else some sepia of the same consistency, which has
been removed from the ink sac, be spread out on a cover-slip
in a thin layer and allowed to dry, and then a cover-slip
placed over it with damar, the thin layer of ink or sepia,
when studied with the highest powers, looks as follows.
A very finely meshed but distinct network is to be seen, the
nodal points of which seem to be formed by the very
smallest particles of ink or sepia (Photogr. VII.). It
is evident that the phenomenon does not depend on the
soluble matter of the ink having been dried up with it, and
having formed the reticular tracts between the ink granules,
from the fact that it is possible, after drawing the cover-slip
with the ink on it through a flame several times, to treat
it for a long time with water, concentrated hydrochloric acid,
caustic soda, alcohol, and ether, etc., without the appearances
being changed. Moreover, the ink or sepia when suspended
in water also shows the reticular appearance distinctly,
provided it is not, as usually is the case, in a state of violent
molecular movement. If one investigates the ink rubbed
up with water under the cover glass, it can be observed that
wherever a bubble of air is shut in between the slide and
the cover glass, a very thin layer of ink is found between
the air and the cover glass. In this thin layer of fluid no
molecular movement takes place, and there one can see very
plainly that the ink granules show reticular connections.

Just the same appearances are also obtained by slightly
blackening a cover glass over a flame and mounting it in
damar.

By these experiments it is shown that closely apposed,
and very minute granules also present the appearance of a
network. That the granules of the thin dried-up layer of ink
are closely packed, however, follows from the fact, that after
treatment with acids, etc., the layer frequently comes away
partly as a continuous membrane. On what, then, does the

14

210 PROTOPLASM

appearance of a network depend, which may be of such con-
sequence for our studies on protoplasm ? It is certain that
the granules are often actually directly connected to one
another ; one can convince oneself of this fact by rubbing up
a small quantity of ink with glycerine jelly and mounting it,
and also by moistening a little of the soot on a slightly
blackened cover glass with oil and investigating it. Granules
can then frequently be seen to be connected together, and
apparently united by a dark, short filament, giving rise to a
dumb-bell shaped structure. I regard, however, the latter
phenomenon as to a great extent an optical one, the
explanation of which will not be further attempted here.
If one examines fine drops of oil, such as can be easily
produced by shaking up olive oil with weak soda solution,
one notices also that two drops in close contact when
sharply focussed seem to pass into one another directly by
means of a dark bridge at their point of contact. It is self-
evident that in this case a real connection does not exist,
sinc'e otherwise they would necessarily flow together.
We must, I think, put a similar value upon the above-
mentioned dumb-bell shaped figures of the adherent ink
granules. The network described, however, can only in part
depend upon this connection of the ink granules. In the
main it may depend upon another optical phenomenon.

If single isolated quiescent ink granules be studied in
glycerine jelly or oil, it may be seen that each granule, when
focussed as sharply as possible, so that it appears dark and
sharply contoured, is surrounded by a clear area, which has
a breadth of about the diameter of the granule, or rather
more, and is marked off from the rest of the field of vision
by a rather darker, dull border. This is the so-called
diffraction area, which is seen in the microscopic image
round all bodies of greater or less refracting power, and
which by Nageli and Schwendener (1877, pp. 230-236) was
referred partly to the direct reflection of the incident light
at the edge of the body in question, partly to the interference
of this reflected light with the light which comes through
unreflected. If one slightly raises or lowers the tube of the
microscope, the granule disappears, but in both cases the

THE OPTICAL NETWORK EXPLAINED 211

area remains visible as a light circle. Now, if two or more
granules of ink are lying close together, and the tube be
raised or lowered, the granules pass into a network of just
as many meshes as there were granules originally. The
explanation of this appearance must be sought in what
has- been pointed out above, that instead of the granules
appear clear diffraction circles, which partly overlap one
another and by their dark edges produce the appearance of
a meshwork. Now since in the examination of a layer of ink,
such as has been described above, there are numerous granules
not in sharp focus which must present the appearance of
such a network produced by the diffraction circles, I think
that the reticular appearance depends essentially oh the
last-mentioned optical phenomenon.

The formation of net-like structures just described, which
possess no reality, but depend only upon optical phenomena
connected with the peculiarities of microscopic vision, has
been followed out by me still further, since a knowledge
of them, which has hitherto been quite neglected, must be
exceedingly important for estimating the value of reticular
structures, and may indeed render it a matter of doubt
whether all reticular structures are not on the whole only
due to optical phenomena. It was for these reasons that I
discussed the question in detail above, and, as I believe,
settled definitely whether the appearance of reticular struc-
ture in the foams depended in reality upon their frothy
nature or not, since the possibility that dense granular
deposits might produce the appearance of a reticuluni was
not to be lost sight of.

If one prepares an emulsion of oil-drops as minute as
possible by shaking up a little olive oil with 1 per cent
solution of caustic soda, and examines it in a thin layer with
the strongest magnifications, the following facts may be ob-
served. If the layer of fluid is thick, all the droplets are
found in violent molecular movement ; but if the glass be
pressed down more strongly by drawing off fluid, the larger
drops are held still, and round them collect groups of the
smallest drops, which are now in like manner quiescent. By
focussing accurately the median plane of these droplets it is

210 PROTOPLASM

appearance of a network depend, which may be of such con-
sequence for our studies on protoplasm ? It is certain that
the granules are often actually directly connected to one
another ; one can convince oneself of this fact by rubbing up
a small quantity of ink with glycerine jelly and mounting it,
and also by moistening a little of the soot on a slightly
blackened cover glass with oil and investigating it. Granules
can then frequently be seen to be connected together, and
apparently united by a dark, short filament, giving rise to a
dumb-bell shaped structure. I regard, however, the latter
phenomenon as to a great extent an optical one, the
explanation of which will not be further attempted here.
If one examines fine drops of oil, such as can be easily
produced by shaking up olive oil with weak soda solution,
one notices also that two drops in close contact when
sharply focussed seem to pass into one another directly by
means of a dark bridge at their point of contact. It is self-
evident that in this case a real connection does not exist,
sinc'e otherwise they would necessarily flow together.
We must, I think, put a similar value upon the above-
mentioned dumb-bell shaped figures of the adherent ink
granules. The network described, however, can only in part
depend upon this connection of the ink granules. In the
main it may depend upon another optical phenomenon.

If single isolated quiescent ink granules be studied in
glycerine jelly or oil, it may be seen that each granule, when
focussed as sharply as possible, so that it appears dark and
sharply contoured, is surrounded by a clear area, which has
a breadth of about the diameter of the granule, or rather
more, and is marked off from the rest of the field of vision
by a rather darker, dull border. This is the so-called
diffraction area, which is seen in the microscopic image
round all bodies of greater or less refracting power, and
which by Nageli and Schwendener (1877, pp. 230-236) was
referred partly to the direct reflection of the incident light
at the edge of the body in question, partly to the interference
of this reflected light with the light which comes through
unreflected. If one slightly raises or lowers the tube of the
microscope, the granule disappears, but in both cases the

THE OPTICAL NETWORK EXPLAINED 211

area remains visible as a light circle. Now, if two or more
granules of ink are lying close together, and the tube be
raised or lowered, the granules pass into a network of just
as many meshes as there were granules originally. The
explanation of this appearance must be sought in what
has- been pointed out above, that instead of the granules
appear clear diffraction circles, which partly overlap one
another and by their dark edges produce the appearance of
a meshwork. Now since in the examination of a layer of ink,
such as has been described above, there are numerous granules
not in sharp focus which must present the appearance of
such a network produced by the diffraction circles, I think
that the reticular appearance depends essentially on the
last-mentioned optical phenomenon.

The formation of net-like structures just described, which
possess no reality, but depend only upon optical phenomena
connected with the peculiarities of microscopic vision, has
been followed out by me still further, since a knowledge
of them, which has hitherto been quite neglected, must be
exceedingly important for estimating the value of reticular
structures, and may indeed render it a matter of doubt
whether all reticular structures are not on the whole only
due to optical phenomena. It was for these reasons that I
discussed the question in detail above, and, as I believe,
settled definitely whether the appearance of reticular struc-
ture in the foams depended in reality upon their frothy
nature or not, since the possibility that dense granular
deposits might produce the appearance of a reticulum was
not to be lost sight of.

If one prepares an emulsion of oil -drops as minute as
possible by shaking up a little olive oil with 1 per cent
solution of caustic soda, and examines it in a thin layer with
the strongest magnifications, the following facts may be ob-
served. If the layer of fluid is thick, all the droplets are
found in violent molecular movement ; but if the glass be
pressed down more strongly by drawing off fluid, the larger
drops are held still, and round them collect groups of the
smallest drops, which are now in like manner quiescent. By
focussing accurately the median plane of these droplets it is

212 PROTOPLASM

shown beyond a doubt that they are in mutual contact.
This is especially shown by the fact that the larger drops
which are apposed to one another are distinctly flattened at
the surface of contact. Eound each drop the above-men-
tioned clear diffraction ring is to be seen, which is distinctly
marked off by a darker border from the rest of the less
brilliantly illuminated field of vision. If the tube be
lowered just a little, the droplets dimmish in size and become
dark, as is the rule with strongly refractile drops ; at the
same time the image of the larger ones becomes dis-
tinctly polygonal, which confirms what has been remarked
above concerning their direct contact and mutual flattening
(see Plate X. Fig. 5, a, l>). The images of the droplets
now no longer touch one another, but are separated by
light intervening spaces. These intervening spaces are dis-
tinctly crossed by faint, moderately dark filaments, which
unite the dark images of the droplets to one another. In
this way quite an exquisite network comes to be formed,
with nodal points of considerable thickness. The meshes of
this network are always triangular, the trabeculae for the
most part very fine, but occasionally also much thicker.

The origin of this network is easily explained if one
studies attentively the most external drops of such groups.
It is then seen that the diffraction ring with its dark border,
described above, is present round each of the droplets ; but
since the dark borders of neighbouring diffraction rings run
into one another, and at the same time pass across adjacent
droplets, the connecting filaments are shown to be portions
of the dark borders of the diffraction rings. As long as a
border of this kind coincides with an adjacent droplet it is no
more visible. The thicker connecting filaments also admit
of a simple explanation. In the smallest droplets, as a rule,
the dark borders of two neighbouring diffraction rings fall
so close together that they give the appearance of a common
connecting filament between the two drops. If, on the other
hand, two such borders are farther apart, a dark connecting
bridge of greater thickness comes into view, since the whole
intervening space between these adjacent borders appears
darker. As a rule, each one of the triangular meshes of the

FALSE NETWORK IN FOAMS 213

network is lightened by the superposed diffraction rings of
three adjacent drops. In the case discussed, however, the
space between two adjacent droplets, which are a small
distance apart, is only illuminated by two diffraction rings,
and therefore appears a little darker — an appearance which is
strengthened by contrast with the neighbouring clear meshes.
The origin of the thicker bridges can, for example, be very
distinctly observed, when a series of small drops is apposed
to the surface of a large one (Fig. 5, c, Plate X.).

The observations which have just been described are a
warning to exercise the greatest caution in forming con-
clusions about reticular protoplasmic structures ; a great deal
of more detailed investigation is necessary in order to test
the earlier observations with a view to determining the
reality of the structures described.

We have seen how reticular appearances of this kind
arise in strongly refracting droplets which are thickly
crowded together in a medium of less refracting power ; the
same thing can be shown, however, when we are dealing
with closely packed droplets of less refracting power in a
more strongly refractile medium, as in the earlier described
oil-froths, for example. If a very thin layer of such a froth
be investigated, not exceeding in thickness one layer of
alveoli, exactly the same phenomenon can be observed if one
places the focus a little above the exact median plane. With
a high focus the image of every less strongly refractile
droplet changes, as is well known, into that of a darker
point or granule. Eound each of these points, however, there
exists just such a diffraction ring as round the droplets of
stronger refraction, and these diffraction rings with their
borders then also produce just the same reticular appearance
with dark nodal points as has been described above.
Photograph II. reproduces this false reticular appearance
very beautifully, while Photograph I. shows the same spot at
a focus slightly below the median one.

From these results it is certainly to be concluded that
in the microscopical observation of a thicker layer of such a
foam, there must be indications in many places of the
image of the false network mixed up with that of the real

214 PROTOPLASM

one, because here and there portions of the froth are in too
high a focus, and hence show the false reticular image. In
future any fine network in which the meshes are triangular
throughout must in general be regarded with suspicion,
and cannot be considered as the true structural image
without sure proof. As has been said, it follows from
what has been set forth above, that the meshes of this mock
network must always be triangular. Although I have
devoted much thought to the point, I at least am unable to
find anything to support the idea that quadrangular or
polygonal meshes may arise in this way. Of course the
circumstance must be taken into account that from various
reasons individual connecting filaments may appear less dis-
tinctly marked out, and therefore may easily be overlooked,
in which way meshes may be formed which are apparently
polygonal.

In any case it is impossible that there could be formed
in the way described modifications of the network which
would give the appearance of longitudinal fibrils, such as
are so frequently shown by the protoplasmic framework,
especially with such distinct transitions to the usual reticular
framework.

From the arguments adduced I consider that the possi-
bility of the protoplasmic framework owing its origin to' an
optical phenomenon of this kind is quite excluded. But there
are still other facts that prove this. As we saw, the reticular
appearances described arise when the drops or granules are
in close contact, or when there is an extremely small
interval between them. Now, if the protoplasmic network
depended upon corresponding relations, the close apposition
of the granules or droplets would necessarily be evident in
any case with a proper focus, and therefore the image would
be essentially different in such a focus. This, however, is
never the case. Hence in my opinion the protoplasmic
structure cannot be produced by close apposition of
granules. It may, however, on the contrary, very well be
the Consequence of a close, froth-like crowding together of
feebly refracting droplets, for such a structure gives, as has
already been shown, the appearance of a network, whether

FALSE NETWORKS IN PROTOPLASM 215

focussed clearly or not ; only the two appearances are rather
different. The accompanying diagrammatic figure shows
the relations of these two reticular images to one another,
the real one (a) in sharp focus, and the optical one (b)
with a higher focus. The distinction between them lies in
the fact, that the former has a wider and
more irregular mesh, the latter, on the
other hand, is denser and more regular,
appearing in particular more as if striated
diagonally. Now if we are able to show
that in very fine sections of protoplasm,
which have at most the thickness of one
or two alveoli, the two different reticular images are actually
to be observed, this may perhaps furnish the surest proof that
the structure is really present as asserted by me, that is to
say, that the meshed structure of the protoplasm depends
upon the deposition in it of feebly refracting droplets, which are
so crowded together as to form a froth-like structure. Now
this is as a matter of fact the case. Both in fine sections
through liver cells and elsewhere, I was at an early period
struck by this strange phenomenon, without knowing its
explanation, and I may well say that at that time it
gave me many a mauvais quart d'heure. There can be
noticed, as I have said, two reticular images, one with a
rather deeper focus, which even at an early period I was
able to decide was alone that of the exact focus, and
then, a second one which comes into view with a higher
focus, and is if anything more distinct than the first one,
appearing finer and more striated, and thus corresponding
exactly to that which is demanded both by observation upon
the oil-foams and by theoretical considerations.1

The discovery of the optical reticular images, which I
did not make until nearly at the end of my investigations,
of course disturbed me very much at first ; indeed for some
time I even considered the whole of my views, as to the
reticular structure of protoplasm generally, to be entirely
exploded, until, as has been described, I gradually found, by

1 For further remarks on the false reticular image exhibited by protoplasm
see the description of sEthalium above, pp. 111-116.

216 PROTOPLASM

penetrating more deeply into the subject, that these obser-
vations were even of a kind to furnish additional proofs
for the correctness of my theory.

The Nature of Colloid Bodies l

The problem of the nature of coagulated albumen and other
coagulated colloids must now receive, as has already been pointed
out above, quite a different solution from me from that which
I gave at the time of completing this manuscript (summer of
1891). At that time I had not myself accurately investigated
this subject, as I also remarked. Since, however, it is an especi-
ally important one, I attempted to obtain more detailed informa-
tion upon this point after concluding the present work. That
this has not been done till now is scarcely a matter to be
regretted by me, but rather to be regarded as a fortunate
circumstance, for I think that, probably, all the investigations
communicated in the present work would have been left undone
if I had taken this question in hand earlier.

To be brief, the result of the investigations hitherto under-
taken by me upon the nature of coagulated white of egg, and
of coagulated commercial gelatine, is, that they present all the
phenomena which we have recognised in this work as characteristic of
the structure of a fine foam. I will not describe my experiments
and observations more in detail in this place, since it will be
necessary to bring them out later more fully, and accompanied
by photographs of the most important relations. I will only
mention that coagulated white of egg and gelatine have a very
beautiful, finely honeycombed structure, and since the false
reticular image can be seen distinctly with a higher focus,
the alveoli possess less refractile contents, probably consisting of
a watery fluid in the honeycombed framework. In both the
radiate alveolar layer can be plainly made out, both on the
surface and round the larger vacuoles of the interior. In all
parts which during the coagulation are subject to a pull or a
tension, a fibrillated alveolar structure is shown, frequently
magnificently developed, and agreeing completely with the
corresponding structures of protoplasm. It is also frequently
possible to see in the interior of such coagulated masses radiating
appearances which quite rival those of protoplasm.

So far the appreciation of the relations of the coagulation
products in question offers no special difficulties for any one who

1 An addition made by the author in April 1892 after completion of the
manuscript.

FOAM STRUCTURES IN COLLOIDS 217

is acquainted with the optical appearance of finely frothy
structures, and has more especially become sufficiently an
expert by the study of coarser foam structures. On the other
hand, great difficulties may be presented by the question as to
what conclusions are really to be drawn from these results.
Those who, like Berthold, Schwarz, and Kolliker, deny generally
the existence of structures in living protoplasm, will of course
be inclined to look upon the above results simply as a confirma-
tion of their view that the alleged structures only owe their
origin to processes of coagulation of this kind. In answer to
this I must declare afresh that their opinion is untenable in view
of the numerous cases in which the structures are distinctly
demonstrable in living protoplasm. Only for such protoplasm,
as in life appears quite hyaline, would their interpretation of
the structures which appear in the fixed condition be possible.
But it should first be decided with sufficient clearness what
significance properly attaches to these foam structures of
coagulated white of egg and gelatine. The subject still lies in
obscurity. Two opposite possibilities confront one another here.
Either fluid albumen and watery gelatine are homogeneous
bodies in the sense of a solution, and at the moment of coagula-
tion undergo a process of desolution with formation of froth, just
as we have above become acquainted with an instantaneous forma-
tion of foam in suitable oil-drops ; or these bodies are not homo-
geneous in the sense of solutions in the uncoagulated condition,
but are very fine foam structures, of which the two components
possess such similar powers of refraction that their structure is
not recognisable. The frothy structure of their coagulation
products would, in this case, not be a new formation, but it
would merely be a case of their being rendered distinct, owing
to the frothy framework undergoing an alteration, that is to say,
becoming strongly refractile, and hence distinctly visible. Which
of these two possibilities is the correct one, it is impossible to
decide off-hand.

On the whole, I am more inclined, at the present time, to the
latter view, without, however, being able to prove it satisfactorily,
or to overcome certain difficulties which stand in the way of the
assumption that it is correct.

The following points are, in my opinion, in favour of the
assumption. As I have already pointed out, a layer of radiate
alveoli can be observed plainly in coagulated albumen and
coagulated gelatine. The gelatine was not brought into the
coagulating fluid until it had stiffened to a jelly. Now, since the
formation of a typical radiate alveolar layer is connected with
the fluid aggregate condition, the development of such a layer in

218 PROTOPLASM

the coagulation of solid gelatine jelly is difficult to understand ;
on the other hand, it is intelligible of itself, if we suppose that
the foam structure already existed in the uncoagulated fluid
condition, and became visible by coagulation.

The exceedingly distinct fibrillated alveolar structures alluded
to (supra) must lead us to the same supposition. These structures
are obtained when filtered albumen is sprinkled by means of a
paint-brush into a drop of picro-sulphuric-osmic acid on the slide.
The coagulated threads, which one commonly obtains by this
method, show, as a rule, as has been said, a very beautiful
fibrillated alveolar structure in their longitudinal direction.
Now it seems to me most difficult to assume that the fibrillar
structure of such threads is first produced by tension of the
already coagulated albumen; on the contrary, I regard it as
more probable that the fibrillar structure had already been pro-
duced before the coagulation by the drawing out of the fluid
white of egg into threads.

If we further consider that the energetic power of swelling
exhibited by albumen and gelatine would gain very much in
intelligibility on the supposition of a frothy structure, and that
in addition there is the fact that gelatine, at least during the
process of taking up water, becomes more or less opaline, and
that watery fluid can be squeezed out of gelatine jelly by strong
pressure, it appears to me that there is some evidence in favour
of the second of these possibilities. I will not omit to point out
that neither in the fluid nor in the dried albumen, and still less
in gelatine jelly, was any trace of structure to be made out.
But it is noteworthy, that in drops of fluid albumen mounted in
paraffin oil I was able to observe an indication of an alveolar
layer, and even of its radial striation. I put no great value upon
this observation^ because it requires repeated investigation, and
deceptions are very possible.

Now whether the question that has been raised will be
decided in the future in this sense or in another, nevertheless it
seems to me at the outset to be of interest, that the foregoing
investigations have led me to a conception of the jelly-like
distensible and coagulable bodies, which harmonises well
with the opinion expressed by a physicist of experience in
this subject. For Quincke has expressed himself upon this
point (1890, p. 207) to the following effect: "In the same
way I believe gelatinous substances, such as glue and other
jellies, should be regarded as fluids in which there are numerous
invisible thin partitions of firm or fluid lamellae." l I may be

1 As I see from Lehmann's Molecularphysik (Bd. i. p. 525 et seq.), similar
views with regard to the physical constitution of the jellies have already been

PROTOPLASM A MINUTE FOAM 219

allowed, at this opportunity, to refer also to the fact that a
physicist such as Quincke names bodies of this nature " foams "
without hesitation, when they are composed of two fluids. I
point this out because, as is well known, it has been brought
forward against me from several sides that I make an incorrect
use of the word foam ; that is to say, that the foams described
by me should more correctly be termed emulsions of two fluids.

5. The Stricture of Protoplasm is Alveolar or Honeycombed
(Foam-like)

After having set forth briefly the various views held upon
the structural relations of protoplasm, we must finally pass
on to place upon a stronger basis the opinion which I have
represented for some time, and which I am seeking to
establish more firmly by means of the present investigation.

This view culminates essentially, to express myself as
briefly as possible, in this, that protoplasm has a structure
such as we have seen and thoroughly studied in the
artificially produced drops of oil-lather, that is to say, it
has a foam-like structure.

It will therefore be my first task to set forth the reasons
which make it probable or certain that the spongy frame-
work commonly assumed to exist, or fibrils connected in a
net-like manner, cannot be present in protoplasm. For
there is no need of any special discussion to show that the
decision between these two possibilities cannot be reached
from the microscopic image alone. The minuteness of the
structures renders it impossible to make out off-hand whether
the reticular appearance observed corresponds to a spongy
framework or an alveolar meshwork, since the microscopic
image, as has been said, must in such minute structures be
the same in both cases.

expressed before by physicists. For instance, Guthrie (1875 and 1876) seems to
have put forward the same view in the main as that represented by Quincke.
Lehmann himself is also inclined to an opinion of this kind, in the chapter
cited upon the jellies, even though he supposes they have a spongy instead
of a frothy framework. It is not quite intelligible to me, however, how with
such views with regard to the physical nature of jellies, he can interpret in
a following chapter "the phenomena of swelling as due to chemical combina-
tions " (that is to say, of the body that swells) " with the solvent medium."

220 PROTOPLASM

(a) Aggregate Condition of Protoplasm

In order, however, to approach this question, we must
first of all come to a decision with regard to the aggregate
condition of protoplasm, since the solution of the question
turns essentially upon this preliminary inquiry. The point
has notoriously been much disputed, and an opinion has
even been expressed that one cannot properly speak at all
of an aggregate condition of protoplasm, in the same sense
as of that of a homogeneous body (Briicke, 1861), for the
very reasons that protoplasm is not a homogeneous body,
but a mixture of solids and fluids.

I would gladly avoid entering into the historical aspect of
this question, but it does not seem possible to discuss the
problem clearly without such a brief review. The older
observers were notoriously fairly united in their conception of
protoplasm as a slimy, rather viscid fluid. This view was
essentially established by the studies of prominent investiga-
tors, especially in the fifties and sixties, during which period
the protoplasm question awakened a lively interest. Max
Schultze's investigations on the protoplasm of E-hizopods and
vegetable cells and their phenomena of movement (1854-63),
on whose side Haeckel (1862, p. 90 et seq.) ranked himself as
the upshot of his extended labours on Rhizopods, Radiolaria,
etc., and finally the studies of Kiihne (1864) upon protoplasm,
especially confirmed this view. The principal support for it
was obtained from the relations of the phenomena of streaming
movement which gave the observer the impression of a sub-
stance in a state of flux, and therefore fluid ; and further
from the flowing together of protoplasmic processes, the taking
up of solid particles into the interior of the protoplasm, and the
tendency of isolated portions of protoplasm to assume a spherical
form.

A reaction against this conception was started as far back as
1861 by Briicke. Briicke disputed a priori the possibility of
fluid protoplasm being able to carry on all the complicated
functions of the cell. The cell, or more properly its protoplasm,
must therefore possess, in addition to its molecular structure, a
"special structure" or "organisation." Hence all protoplasm
must consist of solid and fluid portions. To inquire into the
condition of the protoplasm in the aggregate would therefore be
really just as absurd as to discuss the same question in reference

THE "ORGANISATION" OF PROTOPLASM 221

to a jelly-fish. Briicke brought forward facts, in so far that he
tried to interpret the protoplasmic streamings in the hairs of
Urtica not as simply the streamings of a liquid, but rather as
giving the impression that the protoplasm, " or the contractile
cell body, contained a fluid which streamed through it and
contained numerous small granules." So far, therefore, as it is
possible to understand the ideas briefly thrown out by Briicke,
one may well assume that he imagined to himself in the proto-
plasm a firm contractile framework steeped in fluid, just as was
described later by Heitzmann,

That Briicke's view, although it was disputed by Max Schultze
(1863), found approval is obvious from the fact that the
assumption of solid and fluid parts in protoplasm became more
and more widely spread. Although de Bary (1862) denied
Briicke's view of the processes of streaming in protoplasm, he
believed it necessary to accept his opinion upon the organisation
of the cell. Cienkowsky (1863), from a study of the plasmodia
of Myxomycetes, arrived in like manner at the assumption of a
thicker hyaline ground substance, capable of contraction and
expansion, and of a fluid granular substance. How he repre-
sented to himself the mutual relations of the two substances in
the building up of the protoplasm, remains, however, rather
obscure, the more so as it follows from his description that he
regards the contractile ground substance also as fluid. How
could we in any other way understand the expression on p. 414:
" The plasmodium thus gives an indubitable example of a fluid
stage in the development of an organism " ! Although de Bary
(1864) disputed this distinction of two substances in the plas-
modium, a contractile and a fluid, and regarded it with Kiihne
as contractile throughout its whole mass, he yet assumes a
similar difference, inasmuch as he admits local differences in its
" cohesion, fluidity, and mobility," which, moreover, were subject
to frequent change. The plasmodium is supposed to consist
therefore only of one substance, but its physical character is
frequently liable to local variation. The protoplasm of these
Protista is said to possess a "soft consistency," but in any case
they would be "in no way bodies in the least of a fluid, trickling
nature."

Hofmeister, who in 1867 called protoplasm a "viscid mixture
of various organic substances, or a thickish slime," and often
makes use of the physical properties of fluids to explain the
behaviour of protoplasmic bodies, yet declared himself, as far
back as 1865, and again also in 1867, in favour of a special
organisation of protoplasm. He remarks on p. 8 that every
attempt to obtain a conception of the phenomena of protoplasmic

222 PROTOPLASM

movement must have as a postulate " an organisation of th<
protoplasm," " a peculiar structure in it, which differs essentially
from the aggregate condition of viscid fluid bodies in the faci
that the molecules of the protoplasm are capable of being un
equally displaced in different directions." Of this allegec
postulate of every explanation he makes, however, no use what
ever, either in considering the phenomena of the structure, or o
the movement of protoplasm; the hypothesis evolved by hin
with regard to protoplasmic movement contains no mentioi
of it.

In opposition to these efforts, it must be of special interest t<
us that two observers so experienced in physical matters ai
Nageli and Schwendener both in 1865 and later in 1877
especially point out the "viscid nature " of protoplasm, somewha
like mucilage ; it may then, of course, possess an organisation wit]
impunity. They derived their proofs chiefly from the flowing
together that may frequently be observed in protoplasmic bodies
and the behaviour of swarm spores when they happened to fo
torn in pieces.

Briicke's views soon found further defenders. In 187(
Hanstein expressed himself to the same effect. It seemed also t<
him quite unthinkable that from a fluid substance a structur
should have been produced which was organic, and " therefor
different in itself." For the rest, his ideas of protoplasm at tha
time were rather obscure. He ascribes to it " a soft and plastic
and yet viscid and formed and self-forming condition." It wa
said to contain besides fluid parts, " soft solid " ones as well ; i
was not a substance but an organism.

But it was Yelten especially who in his works (1873-76
tried to collect further proofs for Briicke's conception. For hin
also it was an established fact (1873) that protoplasm possesse<
in any case a complicated organisation, and was not a homogeneou
fluid. But how he really represented the matter to himself i
not quite clear. In 1876 he declares that protoplasm is com
posed of solid and fluid parts. Thus on p. 138 it is said tha
"in protoplasm we have a more or less coherent body, possessing
the solid aggregate condition, which last may be temporarily
exchanged for that of fluid substance." If the latter limitatioi
makes the view first pronounced rather obscure, the following
passage (p. 130) adds still further to the obscurity, where it is sai(
" that protoplasm contains solid and fluid parts side by side in th<
smallest particles of space." Velten's view is partly based upoi
structures observed by him (see above, p. 165), partly upon thi
peculiarities of the phenomena of streaming. He makes sincen
efforts to reconcile with his view the tendency of protoplasm t<

OTHER VIEWS AS TO ITS NATURE 223

assume a spherical form, which had been pointed out by the
adherents of the theory of its flmd nature. When this phenomenon
occurs normally, it was said to depend upon the peculiar organi-
sation of the solid particles of the framework ; he thus intro-
duced a mock explanation in the place of a natural one.
For the most part, however, the assumption of the spherical form
was to be referred to an abnormal state of the protoplasm, which
would hold good for the rounding off which takes place in plas-
molysis, the spherical form of drops of protoplasm that have
oozed out, and so forth. In these cases the protoplasm is
supposed to become usually more watery ; the framework, of solid
particles of protoplasm breaks up, but may subsequently re-
generate itself. Just as little does he allow the spherical form
of vacuoles to hold good as a proof, since the formation of
vacuoles takes place in the abnormal condition — an assertion
which betrays a certain amount of inexperience in these matters.
It cannot at any rate be asserted that Velten has based his view
upon sufficient grounds.

Hanstein in 1880 and 1883 set forth in still more detail the
views he had already expressed in 1870. It appears from them
that he had taken up to some extent the opinion already ex-
pressed by de Bary with regard to the protoplasm of the Myxo-
mycetes. The " fluid " as well as the non-fluid parts of which
protoplasm is composed are supposed to be " forms of the same
im>tni>1<ixtiu, which only differ from one another in the amount
of water they contain " (1880, p. 163). The partitions formed
by the non-fluid protoplastin, which is deficient in water, within
and around that which is fluid, are explained by him as some-
times viscid, sometimes solid. The fluid part he termed ench>/l< inn
(1882), the hyaline ground substance of the entire protoplasm,
hyaloplasma, and the granules lodged in it the microsomes. His
enchylema is, therefore, in its turn equal to hyaloplasma + micro-
somes. There is no need to point out specially that the use,
which at a later period was made of the term enchylema, has
nothing to do with the original meaning of this term in Hanstein.

We now turn to the numerous observers who have described
filamentous or reticular structures in protoplasm. From the
foregoing account we have learnt that theoretical deductions,
as well as observations and speculations upon the phenomena
of movement, had already necessitated the assumption, and
finally the discovery, of such a structure. I think there is no
necessity to go through the views of the numerous observers
of filamentous or reticular structures in detail, as they have in
part been indicated already. It is sufficient to point out
that the majority have more or less plainly declared that they

224 PROTOPLASM

represent to themselves the filaments or the network as com-
posed of a firm substance. When the fundamental laws of
physics were consulted, it was impossible for it to be other-
wise, since the permanent existence of such structures was
only thinkable if they consisted of a solid substance. Besides
this, numerous investigators held the idea that the phenomena of
contraction, or changes of form generally, such as protoplasm
shows, could only be produced by solid bodies. On the other
hand, it was at the same time pointed out that protoplasm
behaved very like a fluid. Thus Strassburger, who still upheld
the reticular structure of protoplasm, remarked (1882, p. 232)
that it was " soft or semi-fluid " ; that it agreed in many of its
peculiarities with a colloid, but still more closely, on the other
hand, with a fluid, " for it has a tendency to assume the spherical
form in a condition of stable equilibrium." Such terms as
soft, solid but yielding, jelly-like, semi-fluid, recur continually
here and there. Those authors, however, express themselves in
the most definite manner who assume, like Pfliiger (1889), that
protoplasm is composed of "absolutely solid and absolutely
fluid " parts.

I had, for my part, expressed myself already in 1876 (p. 203)
to the effect that "in spite of the objections that are raised
against the idea, there are the most cogent arguments for sup-
posing that protoplasm obeys the fundamental laws of a fluid
mass." My conception of the structure also gave me no reason
for departing from this view. In 1886 Berthold in his valuable
book again took up the doctrine of the fluid nature of proto-
plasm, which had fallen very much into discredit. He did not,
however, try to really support it by direct proof, but laid it down
as a hypothesis upon which to base his observations and specu-
lations upon the structure and upon the phenomena of the move-
ment of protoplasm, in order to show the probability of the
hypothesis by the ease with which the problem could be worked
out.

What position Schwarz (1887) really takes up with respect
to the question of the aggregate condition of protoplasm, is not
quite clear to me from his work, as I have already pointed out
above. As is well known, he denies the reticular framework,
and speaks of a "semi-fluid aggregate condition" of the cytoplastin
(p. 131). On the other hand, he says on p. 136: "In the
cytoplasma no preformed networks and frameworks are present,
but a part of it may modify itself into filaments and strands. In
consequence of this I must assume that the cytoplasma is a
mixture in which, under certain circumstances, a separation can
take place of more rigid, viscous, and more fluid dissolved

PROTOPLASM A VISCID FLUID 225

substances." Hence, under certain circumstances, a framework
of a firmer nature can make its appearance. Since Schwarz, on
p. 139, declares that his results agree with those of Berthold,
I must certainly assume that he conceives of this "mixture,"
which the cytoplasm is in his opinion, as a fluid one. Such
expressions as " semi-fluid " are too vague to be taken definitely
into account.

I had myself in 1887 advocated the fluid nature of the
endoplasm of the Infusoria, and, in this connection, also that
of the greater part of other protoplasm, which throughout
behaves in a similar manner (p. 1392). I drew attention
more especially to the constantly spherical form of the
vacuoles that appear in protoplasm, a fact which would prove
that both the contents of the vacuole and the surrounding
protoplasm are fluid throughout. In Protozoa there is
such frequent opportunity for observing vacuoles of different
kinds — food vacuoles, contractile vacuoles, and ordinary
fluid vacuoles — that no one can be in doubt as to their
regular appearance in normal protoplasm. It is, however,
just as certain, and as plain, that all these vacuoles assume
the form of a spherical drop when they are not hindered by
solid bodies to which they adhere, or by mutual pressure,
streamings, or any other kind of special force which is act-
ing upon them. From this positive experience, which is
just as capable of proof as any other physical fact, there is
only one conclusion to be drawn, namely, that expressed
above, that the contents of the vacuoles, as well as the
protoplasm surrounding them, must be fluid. In addition
we know definitely with regard to the contents of the
food vacuoles that it is water. But all other vacuoles exhibit
just the same appearance and behaviour, for which reason
their contents must in like manner be a watery, very dilute
solution. We know further that vacuoles may flow together,
and in this process behave - in exactly the same way as any
two drops of water in viscid oil. The study of the contrac-
tile vacuoles, which unfortunately have received very little
attention from many investigators who have given vent to
opinions upon such things, gives us the most beautiful
instances of such fusions, and the consequent rounding off

15

228 PROTOPLASM

protoplasm have, however, rather different views with regard
to the limitation of the vacuoles. In the first place, none of
them have really given any account of why the vacuoles
should always be spherical, although the rigidity of their
framework was yet necessarily admitted. In general the
structures in question are regarded as larger collections of
fluid in certain regions of the framework, which is thereby
thrust apart. These views only vary on the point as to
whether the contents of the vacuoles are to be considered
as identical with the general contents of the matrix of the
alveolar framework, or as differing from it. Thus Heitzmann
has termed the vacuole " a lake in the middle of the proto-
plasmic body" (1883). Now, if the framework is rigid, it
is not at all apparent why the vacuole when unrestrained
should always possess a spherical, and not a more or less
irregular outline. But it remains still more inconceivable
how the adherents of the framework theory can speak of a
flowing together of vacuoles, since this is simply impossible.

If the vacuole is only a collection of fluid in certain regions of
the framework, there must exist, originally at any rate, a connec-
tion between the contents of the vacuole and the intervening
matrix. That such a connection, however, cannot be permanent
is proved not only by direct observation, which always shows a
distinct and continuous limiting margin to the vacuole, but also
by the common experience, that the cell sap cavity of vegetable
cells, which is in reality nothing more than a very large vacuole,
frequently contains a coloured fluid, while the enchylema of the
protoplasm is completely uncoloured. This, as well as other
observations, make it unconditionally necessary that the contents
of the vacuole should be shut off from the enchylema by a closed
lamella. In this way Schmitz (1881) had already assumed that
the origin of the vacuoles was due to the formation of " a special
continuous limiting layer " round the cavities of the framework.
But this would only be possible, if the framework contracts,
by closing its meshes to form a continuous membrane round
the vacuole. Van Beneden also arrived, in 1883, at similar
views. If, he declares, the contents of the vacuole is identical
with the inter-fibrillar substance, the wall of the vacuole must
possess a lattice-like structure with extremely narrow meshes.
He therefore imagines in any case that this wall arises by con-
traction of the framework. Leydig (1883), who derives the

VACUOLES AND THE FOAM THEORY 229

vacuoles from " enlargement and flowing together " of the cavities
of the meshes of the framework, seems to think that they are
usually not definitely shut off from the enchylema. At least he
remarks that they seldom obtain a definite lining by condensa-
tion of the trabecular framework (p. 143). Finally Heitzmann
also (1883) developed similar views. According to him the
vacuoles always possess a special wall, which is built up in the
form of a so-called " membranous layer." By such a membranous
layer he understands a delicate closed membrane, which is thus
formed. From the nodal points of the network, which as a rule
only send out a few filaments of the meshwork, such a number
of threads radiate out in one plane that they fuse into a con-
tinuous layer, while the nodal points at the same time disappear.
Now, since the membranous layers formed by neighbouring
nodal points become united into a continuous layer, there arises
a continuous envelope round the vacuole. Frommann also states
(1890, p. 10) that the vacuoles possess "for the greater part a
delicate pale or somewhat shiny membrane." He even seems
to regard this membrane as solid, since he remarks that the
growth of the vacuoles " takes place by fusion of neighbouring
vacuoles, accompanied by a tearing or liquefaction of the mem-
brane," or by osmosis.

Finally C. Schneider (1891), whose views upon the fibrillar
structure of protoplasm we described above (p. 182), has also
discussed the formation of the vacuolar wall. He believes that
he is able to find his fibrillae even in the vacuolar wall. In this
place they are united by a special cementing substance into a
membrane. What Schneider regards as the fibrillse in the wall
of the vacuole is certainly nothing else than a surface view of
the layer of alveoli which borders on the vacuole.

We have seen in the foregoing to what assumptions the
representatives of the framework theory are forced in order
to explain the closed vacuolar wall. If we further imagine
to ourselves the apparatus of mysterious forces which bring
about the condensation, or even the closure, of the meshes
of the framework round the vacuoles, and on the other
hand reproduce the usual condition of the network after
the disappearance of the vacuole, it would seem clear that
the correct explanation will be attained with some difficulty
on this theory.

On the other hand, the alveolar, or foam theory of
protoplasm explains the actual phenomenon, and the be-

230 PROTOPLASM

haviour of the vacuoles, in the simplest manner, by the
physical laws of fluid masses. We can completely grasp
the reason why every vacuole must be surrounded by a
continuous pellicle-like border, which shuts it off from the
neighbouring layer of alveoli. We understand their spherical
form, their occasional flowing together, etc., in the easiest
manner ; but we can comprehend a great deal more,
which the framework theory is unable to explain. That is
to say, we can understand why each vacuole is surrounded
by a radially arranged layer of alveoli, as has been shown
above in a series of examples. For this point the frame-
work theory is not able to furnish a solution.

I must not leave entirely without mention in this place a
theory of the vacuoles which has sprung up on botanical grounds,
and has found numerous adherents among botanists, namely, de
Vries's Tonoplast Theory. De Vries is, as is well known, of the
opinion that the vacuoles are just as much independent organs of
the cell as the cell nucleus, the chromoplasts, and other things.
The vacuoles are the products of so-called tonoplasts, certain small
bodies which build up strongly osmotic substances within them-
selves, and in this way swell up to vacuoles. The vacuoles always
possess, it is supposed, a special, independent membrane, distinct
from the rest of the protoplasm, which arises from the tonoplasts,
and is to be regarded as the true active and living part of these
structures. Admitting the correctness of this view, the difficulty
would arise of explaining the continuous limitation of the
vacuole. I regard, however, de Vries's theory as on the one hand
unproved, in fact improbable, and on the other hand I consider
the origin of the vacuoles to be completely intelligible without
the tonoplast theory.

In the first place, there is a lack of any substratum of fact for
the assumption of tonoplasts. No one has ever seen them in the
non-vacuolated condition ; there is therefore a necessity for other
grounds upon which to justify the assumption. Among such it
would of course be decisive to show that the vacuoles were only
formed like the nucleus or the chromoplasts, by multiplication
on the part of bodies like themselves. Now de Vries is actually
of the opinion that this multiplication always occurs. What,
however, he brings forward (1886) in the way of facts cannot
be regarded as the slightest proof of an independent multipli-
cation of the vacuoles, but would rather seem to be entirely
a case of constriction of larger vacuoles into smaller ones

VACUOLES—THE TONOPLAST THEORY 231

in plasmolysis and similar processes, in which it is evident
that the division of the vacuole is effected by the surrounding
protoplasm. Also what Went communicates later (1888) in this
respect is not convincing. For the proof that vacuoles become
constricted in two is not sufficient ; it ought rather to be proved
that this is effected by the proper and independent wall of the
vacuole, and not by means of the surrounding protoplasm. It is
just this point, however, which Went is not able to make clear.
He even says himself on p. 318, "the wall of the vacuole is so
thin that for the most part it is not visible," nevertheless he
thinks it may be assumed " from analogy " that it takes an
active part in the division. On p. 319 it is remarked: "It
hence seems to me (!) that the wall of the vacuole plays an
active part. This point must, however, be made clear by
later investigations." This point is, however, just the most
salient one in the whole question concerning the so-called
division of the vacuoles, and has, therefore, in spite of his
assertion to the contrary, not been solved by Went. Just as
little, moreover, has Went proved that the vacuoles never appear
as new formations, as he asserts. His investigations, as well as
those of de Vries, only extend, as is shown by the figures, to
relatively large coarse vacuoles. Now since new vacuoles are
originally at any rate exceedingly minute, their statements prove
nothing in this respect. What can, however, be proved, in such
subtle questions, by figures so coarsely schematic on the whole
as are those which accompany the works of de Vries and Went ?
Whoever has studied at all closely the contractile vacuoles of
Protozoa cannot doubt for a moment that new vacuoles con-
tinually make their appearance, which do not owe their first
origin to the division of formerly existing ones. This had
already been for a long time proved to a certainty when de Vries
and Went undertook their investigations.1 Moreover, Pfeffer has

1 In recent times Kiinstler (1889) has come forward energetically in defence
of a " more resistant membrane " being present round the contractile vacuole
of Flagellata, especially in the genus Cryptomonas. Both on theoretical
grounds, and from the special relations of the contractile vacuole of that genus,
he regards this conclusion as unquestionable. Without entering here into
details, I can only refer to the much clearer relations existing in Infusoria
(see on this point my book on Protozoa), in which the origin of the contrac-
tile vacuoles by fusion of numerous small ones has so often been proved,
that the presence of a special and constant membrane seems quite impossible.
Since a corresponding origin of the contractile vacuole has also frequently
been observed in Flagellata, it is impossible that the relations should be other-
wise here, unless the structure termed contractile vacuole in Cryptomonas
corresponds in some way to the reservoir of Euglenae, which I regard as quite
improbable.

233 PROTOPLASM

recently produced vacuoles artificially in the protoplasm of
Myxomycetes by introducing small crystals of asparagin and
other soluble matters into it, so that counter evidence seems to
be presented from this side also.

What de Vries brings forward with regard to the independent
wall belonging to the vacuoles seems to me in any case little
suited to prove its existence. In the normal vacuole he has seen
nothing more than the limiting margin, which is easily explained
on our view ; on the other hand, he and Went have observed
often enough how vacuoles flow together and become rounded
off again after their fusion. This, however, presupposes absolute
fluidity in the membrane, if for once we admit its existence.
And how does it harmonise with this view when de Vries
(1886, Dros., p. 33) says, " This wall must, like living protoplasm,
be exceedingly extensible and elastic, and impermeable to
colouring matters " ? Membranes extensible and elastic, but at
the same time fluid, are not very conceivable. Pfeffer (1886)
has therefore remarked very correctly, that the assumption of
de Vries that the wall of the large central vacuole of the
plasma cells was stretched elastically to a high degree, is very
improbable, since nothing can be seen of it in cutting through
the cell. Now de Vries has chiefly tried to prove his view of a
peculiar membrane belonging to the vacuole by plasmolytic
experiments on Spirogyra. Under the influence of a solution
of 1 0 per cent KN03 + Eosin which was used for these experi-
ments the vacuole with its wall was said to contract strongly,
and to remain living for a long time, while the protoplasm
quickly dies. The latter conclusion is drawn from the protoplasm
soon becoming stained with eosin, while the colouring matter
does not diffuse into the contents of the vacuoles, thus proving
the living condition of the wall. Now I have already remarked
above that the figures of de Vries are very coarse and
diagrammatic, and give no sort of information as to finer rela-
tions, on which account I consider it an admissible supposition
that the author has not carefully occupied himself with
finer microscopical details. It also seems to me not impossible
that the interpretation of the microscopic image given by de
Vries both here and in Drosera (1886) is incorrect. De Vries
gives us in fact no clue as to what is in reality present between
the wall of the strongly contracted vacuole and the frequently
only very slightly contracted thin utricle of protoplasm. I
should suppose that between the two lies a very strongly
vacuolated protoplasm. I imagine in my own mind that through
the action of the KNO3 solution water is drawn out of the vacuole,
and it therefore becomes considerably diminished in size, but at

PROOFS OF THE FOAM THEORY

233

the same time the protoplasm bordering on the vacuole becomes
strongly vacuolated, and in this way the space between the
apparent wall of the vacuole and the external part of the proto-
plasmic utricle is formed. Therefore the supposed wall of
the vacuole may be explained as a thin layer of the proto-
plasm immediately surrounding the vacuole, which is forced
apart from the remaining protoplasm by vacuolisation. It is
not inconceivable that under these conditions the vacuole with
its surrounding protoplasmic wall may occasionally become
entirely isolated. In the same way the apparent wall of the
vacuole, as being the most internal part, may well remain living
the longest ; but another circumstance may also be in part
responsible for the non-penetration, for a long time, of the
eosin into the cell sap, namely, that it becomes stored up in the
external protoplasm.

As has been said, I am unable to agree with either the
tonoplast theory or the view of the existence of a special
membrane proper to the vacuoles. All that can be admitted
in the latter respect is only that the pellicle-like limiting
border of protoplasm round the vacuole may possibly undergo
certain changes under the influence of the contents of the
vacuole, just as the external limit of the protoplasm under-
goes changes under the influence of the surrounding medium.1

1 With regard to this modification of the limiting layer of protoplasm
round the vacuole and at the external surface, i.e. the so-called " protoplasmic
membrane " of Pfefifer and others, the more recent observations and views of
Pfeffer (1890) agree very well with my ideas. I am only doubtful whether
the so-called protoplasmic membrane possesses the importance for osmotic
processes which Pfeifer ascribes to it ; on the ground of which processes Pfeffer
was really first led to assume its existence ; they are now also supposed by
him to prove its presence, even when direct observation shows nothing of it
for certain. It seems to me rather that the protoplasm as such can well
produce these osmotic processes and their peculiarities, the more so since we
have found that it presents a system of the finest lamellae, the spaces of which
are filled with watery fluid. Pfeffer (1890, p. 238) also considers this possi-
bility, which I have always held to be the most probable, but arrives at the
conclusion ' ' that for the protoplasmic membrane a greater resistance to per-
meability \i.e. than that of ordinary protoplasm] is required, for this reason,
that the imbibition fluid of the protoplasm apparently also contains materials
in solution, which do not pass out by exosmosis." Although this "appar-
ently," upon which Pfeffer's argument rests, does not seem to me quite incon-
ceivable, I yet hold to the idea that the state of the case has been essentially
altered by the theory of the foam-like structure of the protoplasm, which this
work attempts to prove. That which Pfeffer terms imbibition fluid and ap-

234 PROTOPLASM

(c) External Surface of the Protoplasm

Considerations quite similar to those which we have put
forward with regard to the vacuoles also hold good for the
external surface of the protoplasmic body. Consistent
adherents of the framework theory, such as Leydig (1883
and 1885) in particular, did not shrink from the assumption
that the outer surface of protoplasm, the surface of the cell
in general, was not formed of a continuous layer of substance,
but that it was " porous," in keeping with the spongy
structure of the protoplasm. Thus Leydig says (1885, p.
15) the outer surface of the cell is always porous, " inasmuch
as it consists of a meshed framework and an intervening
matrix enclosed by it." Even in 1883 he asserted the
same thing. In this respect his interpretation of the thin
stratum of alveoli, forming a single layer only in the cells
of the capillaries, appears characteristic, since he explained
them as porous (see above, p. 144). This strange conception
of Leydig's is, moreover, intimately connected with his view
of the importance of the intervening matrix as the true
living substance of the protoplasm, according to which, in
fact, the intervening substance was supposed to creep out of
the framework in the form of the pseudopodia. For this
purpose it was of course necessary that the surface should
not be covered by a continuous layer of the framework.

Frommann also was constrained to put forward similar views
for naked protoplasm. Thus he remarks (1880), with regard to

parently conceives of as a fluid which permeates the protoplasm evenly and
continuously, is open to an essentially different interpretation on the ground
of my investigations. This imbibition fluid is in reality the enchylema
contained in the alveoli, and since it is always shut off by very fine lamellae
of protoplasm, the conditions of osmosis are always present even when the
external protoplasmic membrane does not exist or does not possess the sig-
nificance ascribed to it. If one supposes, however, with Pfeffer, that this
imbibition fluid is one permeating the protoplasm continuously, it must of
course be assumed that a special protoplasmic membrane exists at the
surface, which controls the osmosis of the imbibition fluid. As has been
said, however, I do not regard this assumption as inevitable, but it seems
to me that the protoplasm as such, i.e. the lamellse of the alveolar framework,
suffice for the explanation of the osmotic processes.

THE LIMITING SURFACE OF PROTOPLASM 235

cartilage cells, that a few filaments (so-called limiting filaments)
of the framework occur on the surface, but no continuous mem-
brane of condensed protoplasm.

On the other hand, Heitzmann had from the first (1873),
although not persistently, represented the surface of the proto-
plasmic framework as shut off by a continuous membrane of the
skeletal substance. Later (1883) he discusses this point in more
detail, and derives the membrane, in the same manner as that of
the vacuoles, from the formation of a so-called " membranous
layer" (see above, p. 229) from the framework.

On the botanical side the matter has received rather different
treatment. The idea had notoriously prevailed among botanists
for a long time that the protoplasm must be limited towards
the exterior by a special cuticular layer (Hautschicht), which was
distinguished by its properties from the rest of the protoplasm.
This cuticular layer has often been directly observed, i.e. the most
external non-granular hyaline protoplasm, which we usually term
ectoplasm in Protozoa, was termed the cuticular layer. The
assumption of an ever-present, even if not directly visible
cuticular layer, was, however, first founded upon the osmotic
experiments of Pfeffer and others, which in the former's opinion
could only be explained on the supposition of such a protoplasmic
membrane possessing special osmotic peculiarities.

Schmitz, who was the first on the botanical side (1881) to
study accurately the reticular structure of protoplasm, thinks it
may be assumed that the cuticular layer is specially distinguished
by its more narrow meshed structure from the remaining proto-
plasm. Strassburger also (1882, Zellhaute) was inclined to agree
with this view, but is of opinion that the meshes of the cuticular
layer of protoplasm could also become completely obliterated
(p. 195). Upon this anomalous structure of the cuticular layer
its peculiar osmotic properties might well depend. On pp. 235,
236, he speaks quite definitely of the fact that he assumes the
" anatomical meshes," i.e. the meshes of the reticular structure,
to be quite closed in the cuticular layer, and that in it the so-
called molecular network is more stable, and the molecules have
a more definite arrangement. If the cuticular layer is wanting
on occasions, " then the granular protoplasm might contract the
meshes at its surface, and take on the function of the cuticular
layer." In 1884 Strassburger also explains the nuclear mem-
brane as a corresponding cuticular layer of the protoplasm, and
remarks upon this point (p. 104) that, "like every cuticular
layer " it is " produced by narrowing of the meshes " from the
network of the cytoplasm.

Schneider (1891), a consistent representative of the theory

236 PROTOPLASM

of the purely fibrillar structure of protoplasm, derives a continuous
limiting membrane to the protoplasm in the same way as has been
already described for the membrane of the vacuole, namely, by a
cementing together of the fibrils by means of a special cement
substance.

For the rest, the majority of investigators who have occupied
themselves with protoplasmic structures do not, as a rule, touch
more closely upon the question of the formation of the outer
surface of the protoplasm.

Prom what has been brought forward it follows that
the representatives of the supporting framework theory
require special assumptions to explain the limitation of
the framework towards the surrounding medium ; for the
facts of the matter are not as Leydig represented them, but
every observation tends to show that a continuous non-
porous limiting margin always covers the surface of the
protoplasm. Now since protoplasmic bodies can often be
burst by pressure or cut in pieces at will, and then still
show again a sharp continuous border at their surface
— an experiment which has in fact been done so often, both
on the animal and vegetable side, that it seems unnecessary
to bring forward special examples here — the adherents of
the supporting framework theory are forced to assume either
that mysterious forces immediately close the exposed meshes
again and again, or that this closure is effected by a
formation of cementing substance, etc.

Such assumptions are, as has been said, entirely un^
necessary for the alveolar theory. According to it the
constant presence of a pellicle-like continuous border is a
direct consequence of the supposed structure, and every
drop of protoplasm that is separated off finds itself in
exactly the same conditions again as the original proto-
plasmic body, and will therefore in like manner possess a
limiting border.

(d) Alveolar Layer

We now come to a further relation of the highest
importance witb regard to the external limiting layer of the
protoplasm, which in my opinion is sufficient to decide the

THE MARGINAL ALVEOLAR LAYER

237

question in favour of the alveolar theory. I have before
shown that especial relations exist at the surface of the
protoplasm, since the alveoli of the outermost layer are
always directed vertically to the surface, in consequence of
which the thin radially striated layer, termed the marginal
alveolar layer, comes to be formed. I have demonstrated this
marginal alveolar layer in quite a number of cells, etc., and
may further add that Schewiakoff and myself have further
proved its existence both in smooth and transversely striped
muscle cells (1890, 1891).

It has, however, further been shown that this alveolar
layer is in no way a special kind of membrane at the
surface of the cells, for it occurs in the same manner 'also
round the drops of protoplasm that are formed by crushing
either Miliolids or Gromia Dujardini.

On the other hand, we also found that a marginal layer
of alveoli is always marked out at the surface of artificial
drops of foam, and we were easily able to explain to our-
selves how and why it must always make its appearance
there. This agreement between the oil-lathers and proto-
plasm I regard as a proof that an agreement also exists in
their remaining structure. At any rate I am not aware in
what way the theory of a supporting framework would give
an explanation for the appearance of the alveolar layer ;
in any case it would need for this purpose, like every theory
built up on a false foundation, certain subordinate hypotheses,
by which means it would prove itself afresh to be im-
probable.

Since the marginal alveolar layer must be, according to our
conception of the structure and physical nature of protoplasm,
of quite universal occurrence, we must inquire for ourselves
whether there are any statements in the earlier literature which
justify the supposition. Kupffer as far back as 1870 figured
the outermost meshes in the follicle cells of the Ascidian ovum
as distinctly directed vertically to the surface. Since, however,
as was pointed out above (p. 162), it is rather uncertain whether
the alveolar structure of these cells is not a coarse vacuolisation,
it remains rather doubtful whether we have here a real alveolar
layer. Just as little can it be definitely determined whether
the radially striated wall which he described in 1874 in the so-

238 PROTOPLASM

called inner capsule of the salivary gland cells of Blatta is a true
alveolar layer ; but if so it is in any case a rather strongly
modified one.

That the radially striated cuticular layer, which first
Sachs and later Strassburger (Zellbildung und Zellihdlung, 2nd
edition, 1876) described in the Zoospores of Faucheria, must be
included here, has already before been pointed out by me. I
estimate the thickness of this layer from Strassburger's figures
(1876, Protoplasma) at about 3 //,. That is rather much for an
ordinary alveolar layer, since its thickness depends on the width
of the protoplasmic meshwork, which does not as a rule con-
siderably exceed 1 p. The Ciliata, however, furnish us with
numerous examples of similar thick alveolar layers ; in fact in
Bursaria truncatella it even reaches the thickness of 8 /A. There
can therefore be no question that this layer may be subject to
certain modifications, which is perhaps connected with the fact
that it becomes more or less rigid, and then undergoes a special
growth accompanied by considerable heightening of the meshes.
I will enter rather more closely into this question presently.
Strassburger without doubt gave a more correct judgment upon
the alveolar layer of Faucheria originally than he did later, since
he at first ascribed a chambered structure to it and brought the
striation into relation with the radially directed walls of the
chambers. At a later period he gave this view up again, and
referred the striation to minute rods, for which reason he* com-
pared the structure with the Trichocysts of Infusorians (p. 14).
The rods were regarded by him as essentially supporting
structures for the cilia.

It was incorrect, however, when I formerly stated (1889)
that Strassburger had also observed a radially striated alveolar
layer in plasmodia. What he saw there (1876, Protoplasma) was
in any case only protoplasm drawn out into filaments, which in
the shrinking which accompanied death remained sticking to the
outer membrane, which was perhaps the alveolar layer. He
himself interprets his observations in a similar manner.

Van Beneden (1883) figures a very beautifully developed
alveolar layer in the epithelial cells of the papillae at the lower
end of the oviducts of Ascaris megalocephala. It is remarkable
that two such layers, an external lighter one and beneath that a
darker one, should occur. The state of things is therefore
similar to that in certain Ciliata (Forticella, see above, p. 88, and
Nassula\ or they remind one also of the envelope together with
the alveolar layer in Amoeba actinophora (Plate IV. Fig. 4),
Cochliopodium, and similar forms with a shell envelope resembling
the alveolar layer. For this reason I think that these rela-

THE ALVEOLAR LAYER AND CELL MEMBRANES 239

tions can be similarly explained, i.e. that a primitive alveolar layer
becomes a firm membrane as the result of chemical alteration,
which leads as a consequence to the development of a new
alveolar layer beneath it, since according to the already described
laws governing foam, the layer of alveoli bordering on a rigid
membrane must always assume the character of an alveolar layer.
In Ley dig's work (1885) I can only definitely assert the radially
striated border of the epithelial cells of the lingual glands of
Pelobates to be a true alveolar layer. The outer radial zone of
the epithelial cells of Salamandra maculosa is, on the other hand,
much too thick to be regarded as an alveolar layer. This is also
obvious from the later description of these cells by Tangl
(1887). Pfitzner (1885) has also observed this border. It is
probably a case of the meshes of the whole of this zone being
radially arranged, by means of which the alveolar layer of
course becomes more indistinct. Carnoy (1884) has quite
certainly observed the alveolar layer, especially in the cells of
the intestine of Asellus, but his description is rather obscure.
The so-called membrane also, which he figures and describes
(though without structure) in the testicular cells of Lithobius, with-
out doubt belongs here. Now Carnoy considers the above-
described layer at the surface of the cells as a cell membrane,
and holds the view generally that all cells possess such a mem-
brane. I think, therefore, that he must have observed frequently
similar structures, and has regarded all these structures as cell
membranes. As a matter of fact he has later (1885) also
observed in the amceboid motile testicular cells of insects such a
membrane, which was said to show a reticular structure, and to be
occasionally raised up in places. Finally, in 1886, he described
in the segmentation of Nematode eggs a so-called cell plate,
which, travelling from without inwards, was found later on in the
plane of separation of the two blastomeres, and within which
the splitting of the cells then takes place. I am inclined to
think that Carnoy is wrong when he assumes that the segmenta-
tion of the Nematode eggs goes on in two ways, i.e. first by
means of constriction, and secondly, by splitting in the interior
of this cell plate. It seems to me rather that he has overlooked
the peculiar process of the so-called flattening of the seg-
mentation cells after their constriction, and has regarded
the closely appressed cells as stages of division by splitting.
This alleged cell plate, however, which can hardly have anything
to do with what is usually termed a cell plate, is a double
alveolar layer in structure, just such as I have also observed
at the limit of the appressed blastomeres of the eggs of the sea-
urchin. Carnoy derives later from the two separated layers of

240 PROTOPLASM

this cell plate the membranes of the cell. Yet he draws no
distinct alveolar layer on the free surface of the segmentation
cells, although it is certainly present here in like manner. That
it is more plainly noticeable in the parts of the cells which
border upon one another seems natural, since it possesses in this
situation double the thickness, and is therefore more striking.
Of course it is no concern of mine to try to clear up the matter
without new investigations of my own upon the objects in ques-
tion. I hope, therefore, that these conjectures will not be
misunderstood.

(e) Cell Membrane, Cuticulce

Since we have just seen that Carnoy without doubt deals
with our marginal alveolar layer universally as a cell
membrane, and Frommann also later (1890) refers the
alveolar layer of the Infusoria to the cell membranes with-
out one word in justification of this course, I must say a
few words on this point.

The reasons for which the alveolar layer of the Infusoria
cannot be placed among cell membranes in the usual sense
have been set forth at length by me before (1887, p. 1268).
The chief reason is that this layer is just as easily destroyed
or rendered fluid by pressure, as the rest of the proto-
plasm from which it shows no essential difference with
regard to tingibility and chemical properties, as far as this
has been investigated. Besides this its behaviour in
division must be taken into account, when it follows the
body like an external layer of protoplasm, and during the
fusion of Infusoria in conjugation. All this proves that the
alveolar layer of Infusoria cannot be directly compared with
an isolated, resistant membrane, of the kind which we are
familiar with in typical cell membranes. Their general
properties show that they must consist of a substance
agreeing essentially with the rest of the protoplasm, which
can have only undergone slight chemical modifications in
them. On the other hand, we can trace the alveolar layer
even down as far as amoeboid protoplasmic bodies, in which
there can no longer be any question of a cell membrane.
Although, therefore, I am not inclined to allow that a mar-

CELL MEMBRANES AND CUTICLES 241

ginal alveolar layer in general should be classed as a cell
membrane, since, neither in the physical nor the histological
sense, is it originally such, yet I consider it probable that
it may frequently develop, as the result of solidification,
into a firm membrane, which can be termed a cell
membrane.1

The grounds for this assumption are, in the first place,
that there is no doubt that at least the outer limiting
lamella of the alveolar layer, which in Protozoa I termed
the pellicle, has often, as a matter of fact, become of a firm
consistence. We must always admit this where definite
forms of cells occur, which are other than spherical, since
they are not possible without the surface being of a firm
nature. That the whole alveolar layer may become firm is
a legitimate conclusion, from the circumstance that in
certain Ciliata and in Nassula a second radiate layer occurs
beneath it, which may sufficiently prove the firmness of
the outer one. The radiate arrangement of the trichocyst
layer (cortical protoplasm) in Urocentrum and Paramcecium
also depends in part upon similar reasons.

Further there are well-formed resistant chitinous shells,
which have been isolated from the protoplasmic body, and
which possess the characteristic structure of the alveolar
layer. This has been longest and best known for the shell
of Arcella ; similar but more flexible shells are also found
in Cocliliopodium and probably some other Rhizopods.2 I
consider it very probable that these honeycombed envelopes
are derived directly from an alveolar layer. It was further
shown above that the cuticle also of Phascolosoma and
BrancJiiobdella consists of several or even numerous layers,
of which each one has somewhat the structure of an alveolar

1 Thin flat cells in which the whole body consists for a considerable
distance of only a single layer of alveoli (see above, the cells of the blood
capillaries, and the connective tissue cells of the ischiadic nerve), prove con-
clusively that not all cells can possess a cell membrane in Carnoy's sense. In
such cells this simple layer of alveoli plays in itself the part of a marginal
alveolar layer on both surfaces, and this fact proves most definitely, in my
opinion, that the ordinary marginal alveolar layers also belong to the proto-
plasm, although they may assume the character of firm cell membranes.

2 In the same way also in Flagellata, such as Trackelomonas.

16

242 PROTOPLASM

layer, so that we could explain the origin of such stratified
cuticles by the consecutive formation of several successively
hardened alveolar layers. As has been pointed out, I
hence consider it very probable that, as Carnoy and From-
mann assume, cell membranes and cuticles might arise by
hardening of the outermost layer of protoplasm, i.e. of the
marginal alveolar layer. The suggestions of both these
investigators as to the actual method in which the process
takes place, namely, hardening and chemical modification of
the framework, filling up of the meshes with cellulose or
solid nitrogenous substance, seems to me at the present
moment too hypothetical and uncertain for us to enter more
closely into the subject.

On the other hand, I cannot in any way agree off-hand
to regard all membranous envelopes of protoplasmic bodies
in general in the same way. I am obliged rather to allow
that membranes of this kind can also arise by actual secre-
tion, i.e. by means of a substance which emerges at the
surface of the protoplasm and hardens to an envelope.
Thus I have already, at an earlier period, discussed
accurately the reasons which make such an origin very
probable for the cyst envelopes of the Ciliata (Protozoa, p.
1659). I will only refer here to the fact that certain
Ciliata rotate actively by means of their clothing of cilia
during the formation of this envelope, which, in my opinion,
makes it quite impossible to imagine that this envelope
arises by direct modification of an external layer of proto-
plasm. The same thing also appears very probable for the
shells of the Ciliata, and possibly also those of numerous
Flagellata. We may also observe many stages of transition
between gelatinous coats and firm enveloping membranes,
which, in like manner, point to the same interpretation ;
for the gelatinous coats are most certainly actual excretions,
as far as we have an accurate knowledge of their origin.
Moreover, we have now set foot in a region that really
scarcely admitted of being investigated with profit before
the nature of the protoplasm itself was accurately discovered.
I hope that the further development of the view of the
structure of protoplasm which has been set forth by me.

RADIATE LAYER ROUND THE NUCLEUS 243

will prove fruitful also for these questions, and that in fact
it may even be possible to obtain experimentally in oil-
foams many results explanatory of these matters.

By the foregoing discussion I think I have explained
how the wide, in fact in all probability universal, occurrence
of the alveolar layer testifies entirely in favour of the foam
theory, since its origin can be explained by this theory,
while the framework theory gives us no help in under-
standing it.

(/) Radiate Layer of Alveoli round the Nucleus

The case is just the same with the appearance" of a
similar radiating layer round the nucleus. In the descrip-
tive part a series of examples were given of this. Heitz-
mann (1884) also everywhere figures very distinctly such a
radiate layer round the nucleus. I think, however, it may
be well assumed that it was constructed by him schematic-
ally rather than actually observed. Such a radiate arrange-
ment of the meshes round the nucleus was indicated by
Kupffer in 1870. Whether the clear area which Ley dig
(1883) frequently observed round the nucleus, and which
was said to be traversed by radiating continuations of the
framework, represents in part at least this radiate layer,
seems to me doubtful ; at any rate it was then in most
cases considerably widened by shrinkage of the nucleus.
On the other hand, Klinstler (1889) has represented the
radiate arrangement of the meshes towards the surface of
the nucleus in Cryptonwnas perfectly well, and at the same
time was the first to observe that the outermost layer of
the much finer meshes within the nucleus itself is also
directed radially to its surface. In Chilomonas I have
also observed very plainly the radiate arrangement of the
protoplasmic meshes with regard to the nucleus. Now, this
phenomenon is again explained very simply on our concep-
tion of protoplasm. For the very form of the nucleus
shows at least in many cases that its surface at any rate
must be of firm consistence.

Since it is not my intention to go here into the question

244 PROTOPLASM

of the nuclear membrane, I will not examine how this firm
surface of the nucleus is composed or takes origin. If, how-
ever, as cannot be doubted, the surface of the nucleus is
actually firm, then the layer of alveoli of the protoplasm
bordering on it must necessarily be arranged radially to it,
and numerous discoveries confirm this, as has been said.
Only one must not expect to see anything for certain of
these things in shrunk or otherwise deformed nuclei. I
will not attempt to show further in this place that the
outermost radiate layer of the so-called nuclear framework
must be regarded from the same point of view, since in
this work it is not my intention to touch on the general
relations of nuclei. We find, however, a further confirmation
of our theory in the existence of this radiating layer round
the nucleus ; it can also be predicted with certainty that round
every solid body which makes its appearance in the proto-
plasm, the same phenomenon will repeat itself, although I
have not as yet found any opportunity of paying attention
to this point.

Since, therefore, we have found important grounds for
the correctness of our view of the froth-like nature of proto-
plasm, in the aggregate condition of the protoplasm, and in
the appearance of the radiate layer round vacuoles, nuclei,
and on the surface of the protoplasmic body, I must here
once more draw attention to the very great general simi-
larity between foams produced artificially and protoplasm.
Since the figures and photographs give sufficient confirmation
of this assertion, it will not be necessary to discuss the
point more fully. I only point out more especially the
agreement in the size of the alveoli in both instances, and
enter briefly into their similarity in other points.

(g) Granular Enclosures in Protoplasm, and Corresponding
Position of Soot Particles in the Artificial Foams

In describing the structure of protoplasm we found it
the rule throughout that granular enclosures always lie
in the framework, and in fact in the nodal points of the
alveolar meshwork. Now I have tried to discover how the

GRANULES IN FOAMS AND PROTOPLASM 245

froth-drops behave in this respect. When finely divided
lamp-black is mixed witli the oil from which the drops are
prepared, it may be noticed that in the drops of foam the
fine particles take up exactly the same position with rela-
tion to the foam, that is to say, that they lie in the nodal
points of the meshes. It follows from that, as would have
been supposed from the general relations of foam structure,
that the finest granules at least, if they possess a recognis-
able size, are forced into the nodal points.1 Thus this

1 I have subsequently found that Plateau (1882) has also made an observa-
tion which in like manner confirms the aggregation of solid granules in the
corners and nodal points of the alveoli of foam. If some spores of Ly co-
podium are scattered on a thin lamella of glycerine containing soap in solu-
tion, which is stretched out on a wire ring, and then the lamella is placed
under a bell-jar, the spores gradually all become carried towards the periphery
of the lamella, i.e. to the spot where it is fixed to the ring of wire. The
granules wander, therefore, as Plateau tried to prove, to the region where the
lamella is fastened to the ring by concave curvatures. Hence in a system
of lamellae the granules will collect at the edge, or at the nodal points,
where, as has been described before, the lamellae similarly pass into one
another with concave curvatures. With regard to the ultimate explanation
of the phenomenon the work of Plateau itself should be consulted. Since it
seemed to me of no small importance with reference to the protoplasm ques-
tion to obtain as certain a decision as possible of the question as to how solid
granules behave in macroscopic foams, I recently performed with this object
some experiments which easily and completely confirmed the supposition.
If a durable froth be made in a flask by blowing air by means of a glass tube
into a suitable fluid (soap solution mixed with glycerine or extract of soap-
wood), and at the same time there be mixed with the fluid not too small a
quantity of poppy-seeds or some other suitable fine-grained seed, the little
seed grains are taken up in great quantity into the framework of the soap
lamellae. By far the greatest number lie in the plainest manner at the nodal
points of the framework ; a smaller number at the edges, and only an occasional
seed grain is to be found perfectly isolated and contained free in a lamella.
Not infrequently also a nodal point contains a group of grains, or an edge
a series of them, one behind the other. When the bubbles burst it can be
plainly seen how the grains immediately travel back again to the nodal
points. These experiments with macroscopic foams confirm, therefore, as
has been stated, our hypothesis in the most definite manner. If some
rubbed-down carmine be taken instead of seed grains, one finds the same
relation in respect to the coarser grains. It is interesting to note, how-
ever, that the finest carmine granules also collect by preference at the
nodal points, so that the latter appear red, while the edges and lamellae are
colourless. All these observations present a certain interest, since they show
us that the nodal points of the framework may appear darker or show other
peculiar relations under certain conditions, even without larger or recognis-
able granules being lodged in them. For in protoplasm it may also happen,

246

PROTOPLASM

peculiarity of protoplasmic structure is also easily and surely
explained on the basis of the foam theory, while I am not
able to understand how, by means of the theory of a support-
ing framework, it could be shown why the granules always
take up their position in the nodal points of the framework,
and do not appear in the course of its meshes.

(h) Radiate Appearances in Protoplasm during Cell
Division

For a further and an important point of agreement be-
tween artificial foams and protoplasm we refer finally to the
radiate appearances which may appear in both, and which
can be demonstrated to depend upon the same structural
relations, i.e. upon the more or less pronounced arrangement
of the alveoli into consecutive rows in certain directions.
As I showed before, the radiate appearances of the artificial
foams very probably depend upon diffusion processes in
them ; that is to say, the alveoli arrange themselves in series
in the direction of the diffusional exchange, and to a certain
extent in the direction of the diffusion currents if this
expression is permitted. This experience agrees very well
with the conclusions at which I arrived many years ago
with regard to the significance of radiating phenomena in
protoplasm.

As far back as 1874 I found that round the contractile
vacuole of the large Amoeba terricola, during the process
of diastole, a very beautiful and fine striation, radiating out
on all sides, could be observed in the protoplasm. When I
occupied myself later with the radiate phenomena which, as
a rule, make their appearance during cell division at the
poles of the nuclear spindle, I concluded, partly on the
ground of this earlier experience, partly from the appear-
ances in the protoplasm during cell division, that the suns
at the poles of the nuclear spindle owe their origin on the

that granular deposits are contained in the framework, which cannot, on
account of their minuteness, be plainly made out, just as, in fact, it is often
impossible to decide definitely in the case of the visible granules whether
they occur singly or whether they are groups of minuter granules.

RADIATE APPEARANCES IN CELL DIVISION 247

whole to the same processes, which also produce a sun round
the vacuole of Amoeba terricola. Since the last-mentioned
radiate appearance only exists during the growth of the
vacuole, i.e. while the vacuole is drawing in water from the
surrounding protoplasm, I concluded that the striation was
an optical expression of this process. I had thus arrived
at that time at an interpretation of the process, which was
confirmed fifteen years later by observations upon the
drops of oil-lather. Now since the radiate phenomena in cell
division completely correspond in appearance with the stria-
tion round the contractile vacuole, the conclusion seemed
obvious, that a corresponding migration of fluid and soluble
matter in the protoplasm was also the cause of the appear-
ances in the former case. Only at that time I thought it
necessary to assume that in this process a diffusion took
place in the reverse direction from the clear central area of
the suns into the protoplasm on all sides, from which of
course the appearance of striation would result in like manner.
This train of ideas was confirmed, as has been said, by the
observations upon oil -drops, for, as I explained before,
radiate appearances arise in them both when diffusion is
set up from the drops into the external medium, and when
it is caused in the reverse direction from the latter into
the drops. The striation therefore only presupposes the
existence of such a diffusion movement, it being a matter
of indifference whether it prevails in the one or the other
direction.

In recent times our knowledge of the origin of the
radiate appearances in division has, as is well known, been
considerably extended. It has been shown that they are
not produced by the nucleus or the protoplasm itself, as I
assumed even in 1876, but they are in connection with
certain peculiar corpuscles, which are permanently present
near the nucleus in the protoplasm, the so-called central
bodies. The protoplasmic rays are always formed round the
central bodies, whether they have already become noticeable
in the resting cell, or whether they only gradually develop
at the commencement of the division round the central
bodies. These facts only recently discovered necessitate of

248 PROTOPLASM

course the modification of our former conception of the stria-
tion, inasmuch as we have to seek in the central bodies those
structures which by their action on the protoplasm produce
the formation of the asters. According to our view, how-
ever, this action consists in the fact, that the centrosome
attracts the matters dissolved in the enchylema, or the
enchylema itself partly, as the case may be, in the same
way as a hygroscopic substance attracts water, and that the
diffusional migration set up in this way produces the
appearance of rays. That this view finds further support in
the facts, follows from the observations of Boveri, who
showed that in the case of Ascaris megalocepTiala the central
bodies, which are very small in the resting condition of the
cell, gradually increase to a considerable extent during the
formation of the asters, and diminish again in the same way
afterwards.1 This observation proves directly that the
central bodies take up matter from their surroundings, at
the expense of which they grow in size. This observation
therefore, as has been said, harmonises very well with the
theory proposed. There remains only the question,
whether we can also express any opinion upon the
clear central area of the suns, in which the central body
lies, the so-called attraction-spheres of van Beneden, or the
archoplasm of Boveri (periplast, Vejdowsky, 1888). This is
not possible directly. There is, however, a physical pheno-

1 The investigations of Vejdowsky, so interesting in many respects, but in
my opinion not quite continuous, and therefore in part erroneously inter-
preted, upon the process of segmentation of the ovum of JRhynchelmis, seem
to prove a very considerable increase in the size of the central body during
the formation of the spindle. Since Vejdowsky" probably overlooked the
central bodies, on account of their smallness, during the resting condition, he
interprets them as the forecasts of new attraction-spheres, his so-called "peri-
plasts," which arise, at least in the first cleavage cells, endogenously within
the pre-existing periplasts. From a comparison of his results with those of
van Beneden and Boveri, etc. , it may, as has been said, be safely concluded
that Vejdowsk^ is wrong in making the central body, observed in the
swollen condition, pass over into the later periplasts or attraction-spheres.
It seems to me not without interest that Vejdowsky figures stages in the
division of the central body which recall karyokinesis, and hence the opinion
given by me elsewhere (1891), that the central bodies may perhaps corre-
spond to the micronuclei, with karyokinetic division, of Infusoria, receives
a certain amount of support.

RADIATE APPEARANCES DUE TO DIFFUSION 249

menon which possesses a certain similarity with the forma-
tion of these arese. It is well known that round rapidly
growing crystals of coloured substance which are separating
.out from a saturated or supersaturated solution, there
frequently arises a distinct area which is coloured slightly
or not at all. This is explained by the fact, that the
rapidly growing crystal attracts the dissolved substance of
the surrounding fluid more quickly than it can travel by
diffusion from the surrounding fluid. The formation of
such an area is, for instance, always to be observed when a
crystal grows in a saturated solution by means of so-called
globulites, i.e. minute drops of strongly supersaturated solu-
tion. Then there is always found round the nucleus a cleUr
area free from such globulites, which depends on the fact
that the globulites are gradually dissolved in the solution
already rendered dilute by the formation of the crystal
(see on this point Lehmann, Molecularpliysik, Bd. i. pp. 319
and 726 et seq.). Now in a similar manner to the grow-
ing crystal the central body draws to itself substances from
its surroundings, and if this attraction goes on rapidly, it
may happen, as in the growth of the crystal, that the diffu-
sion from the surroundings does not furnish a supply with
sufficient rapidity, in consequence of which the relative
degree of concentration is disturbed in a certain area, and
in this region chemical alterations can be effected. Whether
these alterations, as in the case of the globulites, may
eventually manifest themselves by the solution of granules
and their attraction to the central body, I leave an open
question. This certainly does not seem impossible, since the
central bodies increase with every division of the cell, and do
not diminish in mass, thus undergoing a gradual growth. If
we consider, however, that the tingibility of the protoplasmic
substance is often very considerably impaired by relatively
slight influences — I will only cite in this respect the char-
acteristic red coloration of the chromatin granules of the
nucleus and protoplasm by hsematoxylin which I have
described, a reaction which almost always fails after previous
fixation with acids — it may also be considered possible that
the slight, or rather the special tingibility of the central

250

PROTOPLASM

area may also be the effect of chemical alterations which are
produced by the central body.1

Although I consider this explanation only quite hypo-
thetical at present, nevertheless I thought it best not to omit
it, since I am convinced that we shall get no farther in these
matters by means of speculations upon attractions and con-
tractions, or with the help of micellar and molecular
theories, but that we must rather .risk the attempt to ad-
vance upon the basis of the known phenomena of molecular
physics. In any case I think that by means of this work
I shall establish the conviction that in living matter there
are no mysterious forces at work, but only those which
also prevail in the organic world.

My interpretation of the radiating appearances which are
visible during division is, however, still further supported by
the fact that similar appearances are to be seen quite un-
connected with division. I have already referred before

1 See with regard to the questions here discussed a memoir by the author
entitled "Ueber die kiinstliche Nachahmung der karyokinetischen Figur"
(On the Artificial Imitation of the Karyokinetic Figure) in the Verhandl. d.
nat. med. Vereins Heidelberg, 1ST. F., T. V., Heft 1, where new observations
have led him to somewhat changed views. It is shown that in a foam of
gelatine and oil which has been warmed, a very distinct radial striation ap-
pears on cooling round little air-bubbles enclosed in it. The same occurs in
the case of air-bubbles enclosed in the foam-like structures shown by albumen
when coagulated by heat, and in coagulated gelatine (vide supra, p. 216). Each
such bubble may lie in a clear space, which passes into the sun-like system
of rays. This appearance is due to the contraction of the air-bubble on cool-
ing, which causes a tension or pull to be exerted on the surrounding mass.
The tension is directed from all sides towards the centre of the bubble, and
modifies the foam-like structure into a system of rays. When two such sys-
tems cross each other a spindle-like figure results.

Hence the explanation of the radiate appearances round the centrosome
must be somewhat as follows. The centrosome does not diminish in volume
like the air-bubbles described above, but is known to increase in size during
the formation of the aster. This increase can only be due to its absorbing
fluid from the surrounding protoplasm. If it be supposed that the centrosome
becomes chemically combined with the fluid it absorbs, it will increase in size
to a less extent than the surrounding protoplasm diminishes by loss of the fluid
given up to the centrosome. Then the centrosome will form the middle point
of a portion of the protoplasm which is contracting and diminishing in size
as a whole, and this protoplasmic area will exert radially directed tensions
upon the remaining protoplasm and produce radiate appearances, just as in
the case of the contracting air-bubble.

RADIATE APPEARANCES IN OVA

251

to the appearance of rays round the contractile vacuole of
Amoeba terricola. More recently I was able with v.
Erlanger (1890) to observe the same thing round the
contractile vacuole of Actinobolus. In the same way I
found it also in Nydoiherus} I need scarcely remark that
this striation is not to be confused with the radiately
arranged affluent canals of the contractile vacuole. I
only point this out here because Frommann (1890, p. 11)
seems to have fallen into this very error when he says
with regard to this phenomenon : " In many Infusoria and
in Amceba terricola there radiate out from the circumference
of the contractile spaces a number of lacunae (!) into the
surrounding parenchyma (!) of the body, into which the
parenchymal fluid (!), laden with products of metabolism, is
forced by the pressure (!) of the water taken up into the
body, and is thus guided to the vacuole." As is proved by
the continuation of this passage, Frommann has simply
confused the radiating protoplasm round the vacuole with
the so-called radial canals, which occur moreover in other
species, so that one is quite justified in saying of the passage
quoted that it contains as many errors as there are clauses.

(i) Radiate Appearances in Ova, etc.

It is notorious that radiating appearances are a very
common phenomenon in the protoplasm of egg cells. I will
only recall here the observations of Leydig (1872) and
Eimer on Eeptilian eggs, of van Beneden (1876), Flemming
(1881, 1882) and Frommann on Echinoderm eggs, of
Eauber (1883) on the eggs of Triton, the trout, and the

1 It is interesting that Frenzel in like manner has recently, in a so-called
Amoeba cubica, observed a very well developed radiate striation round the
contractile vacuole. This discovery appears the more important, since it
forms, after nearly twenty years, the first confirmation of my observation
which was achieved, as it would seem, quite independently, i.e. without
knowledge of my earlier observations. It is to be hoped that rather more
attention will now be given to this important phenomenon than has been
done during the relatively long time it has been known. (See J. Frenzel,
" Untersuchungen liber die mikroskopisehe Fauna Argentiniens," Arch. f.
mikr. Anat., Bd. xxxix. 1891, p. 9, Plate I.)

252 PROTOPLASM

alligator, of Carnoy (1880) on the egg of Cyprinus, and of
van Beneden on the ovurn of Lepus cuniculus (1880) and
Ascaris megalocepkala (1883). In most of these cases it is
only a superficial cortical zone of the protoplasm of the
ovum which shows the radial striation ; the same is usually
the case, as we have already described, in the central
capsule of Thalassicolla and many other Eadiolaria. Such a
radial striation can therefore hardly be brought into con-
nection with the centrosome, situated as it is in all cases in
the vicinity of the nucleus, for the radial striation, which
has the centrosome as its starting-point, is always character-
ised by being most distinct in its neighbourhood and
becoming more indistinct with increased distance from it,
since it first makes its appearance close to the centrosome
and commences to spread out centrifugally. The above-
mentioned radiate striation of the ova, on the contrary, is in
general most distinct at the surface of the cell, and
diminishes in sharpness towards the centre, which, as has
been pointed out, it never reaches as a rule. From this
fact we must certainly conclude that the cause of the
radiation has its seat at the surface of the egg cell, i.e. that
diosmotic processes between the surrounding medium and
the surface of the ovum produce the phenomenon. In har-
mony with this is the fact especially emphasised by van Bene-
den, and observed by him in Ascaris megalocephala, namely,
that the radiate striation is not concentrated upon the often
excentrically placed germinal vesicle. I would further point
out that the drops of oil-lather often show the same appear-
ance, which, from all that we know, owes its origin without
doubt to such processes.

There are, however, also radiating appearances in the
interior of the protoplasm, which, as far as we can judge of
them, are not produced by central bodies, or at least are not
exclusively caused by them. It is well known that the
radiating appearances which arise during fertilisation round
the male and female pronucleus, usually spread out evenly
and on all sides round these nuclei, although it is quite cer-
tain from recent observations that they are originally pro-
duced from the central bodies. If, however, this were also

SYSTEMS OF RAYS ROUND THE NUCLEUS 253

exclusively the case at a later period, that is to say, after the
two nuclei have become closely apposed, it would not be
possible for a system of rays streaming out evenly on all
sides to be developed round them ; there would rather have
to be two such systems indicated if the radiation was
exclusively caused by the centrosomes, as is in fact actually
the case in division. I think, therefore, that the nuclei
themselves take part in the production of rays, which
harmonises well with the fact that the two pronuclei during
the formation of the radiating suns grow to a considerable
extent, and therefore absorb material from their surround-
ings.

That the nucleus can also cause by itself the formation
of a system of rays centred upon it, seems to me from
some other facts very probable, even if not certain. I
refer especially with regard to this point to the observations
of Schewiakoff (1887), which were controlled by me, upon
the division of Euglypha. Here, there appears round the
nucleus, while passing into the spirema stage, a regular
radiate striation on all sides, having nothing to do with
the two polar suns, which do not develop until much later,
after the first system of rays has disappeared again. Now it
is a very suggestive fact, that the nucleus during the exist-
ence of this striation increases its volume two or three
times, and therefore must take up a considerable quantity of
fluid from the surrounding protoplasm. The formation of
this system of rays round the strongly growing nucleus of
Euglypha again confirms therefore our view of the cause and
significance of the striation. It may be not improbable that
similar striations appear still oftener round the nucleus.
Heuser has seen the same phenomenon round the vegetable
nucleus in the spirema stage. I may refer further to the fact
that, according to Strassburger's observations, a regular
system of rays spreading out on all sides makes its appear-
ance during the so-called free cell formation in the embryo
sack of Phanerogams, which is to be regarded in just the
same manner as the cases described above.1

1 Whether the appearance of rays, which Vejdowsky (1888) described
round the centrally placed germinal vesicle of the ripe ovum of Rhyn-

254 PROTOPLASM

(/) Striated Protoplasm of Epithelial Cells

That the radiate appearances are not always caused by the
central body seems to me further to follow from the fact
that there is no sharp distinction between them and the
striated appearances which epithelial cells exhibit so often,
perhaps even universally. Both depend, as I have already
explained before, upon the same cause, i.e. upon a regular
arrangement of the alveoli. Now this arrangement of the
alveoli in parallel rows has no relation either to the nucleus
or to any central body that may be present, but it always
runs parallel to an axis of the cell, which is directed
vertically to its outer surface. Since, however, there is no
obvious reason for regarding the striated structure of the
alveolar framework of these cells as a consequence of strain
or tension in the direction of the striation, since the same
striation is shown also by cells which are shorter in the
direction of the axis than in one -at right angles to it, and
the fibrous appearance sometimes does not extend through
the whole cell, it may be assumed that in these cases the
longitudinal striation depends in the same manner as a
rule upon diffusion currents. The fact that such diffusion
currents are usually present in epithelial cells and
especially in gland cells, and that then they must take the
direction indicated by the longitudinal striation, scarcely
requires any further elucidation, whether these currents
move towards the exterior or towards the interior of the cell.
As has been said, I therefore consider it most probable that
the striation of the epithelial cells depends in general upon
the same cause as the appearance of radial striation.

On the other hand, there are a large number of cases
in which protoplasm exhibits striated alveolar structures,

chelmis, is to be included here, remains an open question, inasmuch as a
central body is certainly present in the vicinity of the germinal vesicle. If,
however, the rays are regularly centred round the germinal vesicle as
Vejdowsky alleges, I consider it certain that they are produced by it. There
is no inherent difficulty in supposing that at one time the nucleus, at another
time the central body, may be the cause of radiating appearances, or that
occasionally both may manifest at the same time an activity of this kind.

FIBRES IN FOAM AND IN PROTOPLASM 255

that cannot be regarded in this manner, but where the
phenomenon demonstrably depends upon the effect of tension
or upon being stretched.

(k) Fibrous Protoplasm

In the description of the pseudopodia of Rhizopods, and
of the trabeculae and bridges of protoplasm which traverse
the cell-sap of plant cells, etc., we have always found that
these strands of protoplasm have a fibrous alveolar structure,
and it can also be shown that in Rhizopods bridges of
protoplasm drawn out by direct tension always assume this
structure. Now it cannot be doubted that in the formation
of pseudopodia and of protoplasmic bridges in the cell-sap
a tension is exerted which draws or spins them out ; the
formation of such bridges or pseudopodia only depends in
general upon the effect of energetic tension which is exerted
at their free ends, as shall afterwards be explained more
accurately in the case of the coarser pseudopodia at least.
In such forms as Amceba blattce it can be plainly observed
during life that the extremity which is progressing (the
anterior end) draws towards itself an axial stream of proto-
plasm, and that in this stream a most beautiful fibre-like
differentiation is visible, which spreads out radially towards
the posterior end, where the current receives affluent
streams on all sides. In the same way the fibrillae can be
plainly traced bending round forwards in the direction of
the current. On the whole, as has already been shown for
the foam-drops, the state of things can be described by
saying, that if the alveolar framework is sufficiently viscid,
a stretching of the alveoli in the direction of the current
takes place, s'ince as a matter of fact the existence of the
current always presupposes tensions in this direction.

Now since I have further shown that very viscid drops
of foam show plainly the fibrous alveolar structure under
pressure or tension, it cannot well be doubted that the last-
mentioned category of fibrous alveolar structures owes its
origin to the same causes.

256 PROTOPLASM

We have come across, however, a considerable number
of fibrous alveolar structures which cannot be brought into
direct connection with the streaming phenomena of the
protoplasm, but which certainly might depend upon similar
causes. Here in the first place stands the fibrous alveolar
structure of the axis cylinder, as well as of the elongated
connective tissue cells which have been described between
the nerve fibres of the ischiadic, the fibrous structure of the
cells of the capillaries and of the processes of the ganglion
cells, and finally, also the more or less confusedly fibrous
nature of the protoplasm of the ganglion cells them-
selves. In these cases we are always concerned with proto-
plasmic bodies which have grown out very strongly in
certain directions, to which the course of the fibres of the
meshwork invariably corresponds. We must therefore
imagine that we are dealing with a viscid alveolar mesh-
work, which is stretched in a definite direction by the
growth of the cell. I am able to further support this
by the fact that the processes of the very richly
branched connective tissue cells, which occur between the
longitudinal muscle cells of Lumbricus terrestris, also show
the fibrous alveolar structure very beautifully, just like the
pseudopodia of Ehizopods. The confused fibrous structure
which appears chiefly in greatly branched ganglion cells,
probably has its cause in the fact that during the outgrowth
of the numerous processes the action of tension is exerted in
various directions upon the protoplasm, which is indeed
plainly expressed also in the fact that the fibrous structures
of the processes always penetrate more or less deeply into
the cell, and here combine with one another in the most
various ways. On the other hand, however, it is by no
means necessary to exclude local tensions set up within the
protoplasm of the cell itself, which further complicate the
structure. There are many examples of such protoplasm
with a confused fibrous structure. I will here only refer to
a very good one, namely, the protoplasm of the large
medullary sacs of Ascaris lutnbricoides and the medullary
substance of its muscles generally.

A question of fundamental importance is raised, however,

THEORIES CONCERNING RADIA TE APPEARANCES 257

in the descriptions of these structures, namely, how we are
to regard the aggregate condition of the substance of the
alveolar framework in their case. If they exist j" -i-
manently, it seems quite certain at the outset that their
alveolar framework must be rigid, or at least so viscid that
it only alters its configuration, in obedience to the laws of
fluid foams, with extreme slowness. In any case it seems
beyond a doubt that structures of this kind cannot
exist permanently if we have to deal with fluid substances
forming the framework and the contents of an alveolar
meshwork, which is itself free in a surrounding fluid. The
matter, however, is not simple here, but the form of all these
protoplasmic bodies proves at once that they must be
surrounded by a firm membrane. Moreover, these cells are
so connected in the interior of the organism with others, or
even with undoubtedly solid parts, that their form will
become fixed accordingly. Now how a viscid foam, which is
enclosed in a firm elastic envelope, will behave during ten-
sion of this membrane, does not seem to me quite easily
decided A priori; in fact, so far as the laws of foam forma
tion have been investigated, it seems to me even possible
that it would be converted into a foam with elongated
meshes, and would persist as such if the meshes were not
too much stretched.

In opposition, therefore, to my former assumption (1891)
I think we must admit it to be possible that these per-
manently fibrous alveolar structures of the axis cylinder,
etc., may be of a viscid nature.

(1) Theories concerning tlie Causes of Radiate Appeara

Very various views have in the course of time been set up
with regard to radiating protoplasmic structures, the prob-
able cause of which we have above sought to refer to processes
of diffusion. I think there is no need to enter into a detailed
discussion of all the opinions, but I will confine myself to the
description of the principal points of view that have been taken
up with regard to this matter. At first of course the idea was
put forward that the radiate appearances in cell division must be
due to a kind of attraction which was exerted by the poles of
the nuclear spindle upon the particles of protoplasm, or more

17

258 PROTOPLASM

particularly upon its granules, such as the so-called yolk granules
of the protoplasm of the ovum. Just as fine particles of iron
group themselves round the poles of a magnet in peculiar sys-
tems under the influence of its attraction, it was thought that
the attractive action of the centres of the rays took effect in some
way also upon the protoplasm and its particles. To such ideas
were inclined Fol (1873), myself (1874), Strassburger (1875), O.
Hertwig (1875), and many later investigators, who cannot be
enumerated individually here. Auerbach, on the other hand,
had in 1874 expressed the view that the appearance of rays was
produced by the nuclear fluid streaming out into the protoplasm.
In 1876, when I brought forward my view, which I still uphold
even at the present time, and with much better grounds than
formerly, it was particularly pointed out that I could not, with
Auerbach, regard actual currents as the cause of the appearance
of radiations, but rather processes which we can now best denote
as migration of substances by diffusion.

Anton Schneider, at a later date (1883), derived the radi-
ate appearances in like manner from the nuclear fluid. The
nucleus, which had become amoeboid, "obtained the power of
sending out processes and rays " (p. 75). This was said to be
an "amoeboid property." It then follows from his further
description that Schneider also certainly regarded the nuclear
fluid as forming the rays.

The idea that streamings in the interior of the protoplasm were
the cause of the appearance of rays was also maintained by Fol
(1879, pp. 251-256), and was especially based by him on the
accumulation at the clear central arese, as well as on the
growth of the pronuclei in fertilisation, and of the young
nuclei after division, in the same way as the opinion I had
already (1876) expressed upon the significance of these central
arese. Fol supposed that currents, in part centrifugal, in part
centripetal, produced the radiating appearances. But it was
not a question of nuclear fluid streaming outwards during these
processes, as Auerbach believed, but of currents of the proto-
plasm itself. In any case the phenomena were supposed not to
depend on an arrangement of the yolk granules, since the fila-
ments of protoplasm passing between the rows were much too
broad for that. His including me on this occasion among the
representatives of the hypothesis of attraction and polar orienta-
tion of the yolk molecules is an error to be regretted, since I had
refuted, as I have said, the hypothesis of attraction in 1876, and
had attempted an explanation which agreed with Fol's later one
in a series of essential points. The so-called central arese, or
attraction centres, as Fol terms them, he believes to be caused

MARK— KLEIN— VAN BENEDEN 259

by a mixture of two substances, one of which was derived from
the nucleus, the other from the protoplasm.

Mark, in 1881, criticised the views of earlier investigators
upon the cause of the aster formation very ably indeed, without,
however, expressing a definite opinion himself upon their signi-
ficance. Thus he remarks, on the one hand (p. 533), "While I
concur with Hertwig in the belief that there is an attractive force
exerted upon the vitelline protoplasm which emanates from the
centre of radiation," and, on the other hand (p. 530), "I do
not claim that there is absolutely no transfer of substance to and
from the centres of attraction. On the contrary, I believe the
phenomena are, on any other assumption, unintelligible ; but it
seems to me that the formation of a clear area, and the existence
of radial striations, are far from commensurate, and that to claim
that the rays are only the optical expression of currents is to
associate as cause and effect two things which have not neces-
sarily any such connection with each other." The view expressed
by me he also regards not as a real explanation, but more as a
description of the phenomenon. I can only accept this criticism
to the extent that I did not indeed give an explanation in the
mechanical sense, which, however, was not my intention, but I
think, on the other hand, I established certain conditions under
which the phenomena make their appearance. For the rest,
Mark has understood my view very correctly, and since this was
not always the case I will quote here his remarks upon this
point (p. 530) : "Biitschli's opinion that the asters are the optical
jxpression of a physico-chemical alteration of the protoplasm
smanating from the central area is probably incontrovertible.
A.t least there is a physical alteration of the protoplasm, and
t first becomes apparent at the centre of the star ; but this is
•ather a description than an explanation of the appearance."

Klein had already (1879 (2), pp. 416, 417) casually expressed
ihe opinion that the striations round the poles of the dividing
nucleus only depend on a particular arrangement of the proto-
alasmic network, since the nuclear network probably contracts
luring the nuclear division, and draws the protoplasmic fibres
Cowards itself. It is strange that Klein did not come to exactly
Jhe reverse idea, which would have corresponded much more to the
arocesses actually taking place, and which, therefore, soon came to
)e held. Nevertheless, we must recognise that he first pointed
>ut the probable origin of the radiation by rearrangement of the
Drotoplasmic framework. Flemming, in 1879, while he admitted
/he mechanical connection of the two processes brought into asso-
iation by Klein, was yet inclined to regard the matter as not so
imple. In 1881 he pointed out in Toxopneustes that the radia-

260 PROTOPLASM

tion certainly did not depend on the arrangement of the yolk
granules, but that it was a " transitory " protoplasmic structure.
It could also be traced in places where there were no yolk
granules.

Van Beneden, in 1883, recognised that in the ovum of Ascaris
the appearances of radiation arose throughout from radial ar-
rangements of the framework in certain places. Since he
regarded the supposed fibrillar reticular framework as the true
contractile substance, he therefore as good as stated that this
radiating arrangement of the otherwise irregular fibrillse must
depend on their contractions, although he did not say so in so
many words.

Leydig arrived at the same opinion as to the origin of
the sun-like figures by special arrangement of the framework
(1883, p. 144). In 1885 he particularly pointed out that he had
convinced himself of the correctness of this view by means of
his own investigations upon the eggs of Ascaris megalocephala.
Flemming, also, had in the meanwhile expressed himself to the
effect that the radiation was probably founded upon an " arrang-
ing and centring of the felt work of the cell substance." At the
same time he correctly criticised and refuted the opinion of
Anton Schneider referred to above. Finally, Carnoy (1884),
Frommann (1890), and other observers, came forward in support
of the view that derives the radiations from the radial arrange-
ment of the framework, so that it may now well be termed the
one which enjoys the most universal recognition. In addition
there is the fact that van Beneden, after renewed study of the
so-called systems of asters or rays, which he investigated in
company with Neyt, has come to the opinion that by contraction
of their moniliform fibrillse, which took origin from the proto-
plasmic trellis work (treillis), they mechanically caused both
nuclear and cell division. The structure of such a moniliform
fibril of the aster was supposed to be comparable to that of the
muscle fibrils, for which reason their contractility was rendered
probable. The so-called central corpuscles, which in van Beneden's
work were first proved to occur in the cell near the nucleus
even in the resting condition, only played in these processes the
part of supporting organs for the contractile fibrils of the aster,
among which were also reckoned the whole of the fibres of the
nuclear spindle, just as is usually done now, in spite of numerous
observations to the opposite effect, and indeed of contradictory
experiences of his own. At about the same time Boveri arrived
at a very similar conception of the part played by the fibrils of
the systems of rays in division — in fact he even asserted that the
fibrils, or archoplasmic filaments as he termed them, could, by

BO VERI—RABL—FOL

261

reason of their " power of lengthening and shortening themselves,
be characterised as muscular fibrillae, and all the laws that obtain
for muscles might be applied to them " (ii. p. 99). After such
an opinion it seems astonishing when Boveri defends (ii. p. 80)
on the other hand the view, or at least declares it to be the most
probable one, that the fibrils of the aster do not permanently
exist as such in the protoplasm, and that they are not, as van
Beneden and others correctly recognised, produced from the
meshes of a framework existing in the protoplasm, but that they
are first formed ad hoc by connection of the otherwise separate
microsomes of the archoplasma. As far as I understand Boveri,
he seems to represent the view that it is especially the microsomes
of the so-called archoplasma, i.e. of the so-called central areae,
that produce the filaments, which then commence to grow from
the archoplasm outwards into the surrounding protoplasm by
elongation. I scarcely think that any one will be strongly in
favour of this view, according to which alleged muscle fibrils
arise at one time from the union of microsomes, and at another
time break up again into such bodies.

Rabl (1889) has recently fallen in with the interpretation of
the systems of rays as contractile fibrillae, which play in cell
division the part assigned to them by van Beneden. He assumes
that the framework of the cell protoplasm and nucleus is per-
manently centred round the central corpuscle — a view which is
in fact favoured by observations upon the radiate arrangement of
the protoplasm round the central bodies of certain resting cells.
He is further inclined to believe that the reticular framework
of the protoplasm is transformed into fibrils during division, like
those of the nucleus, by a breaking up of the cross connections of
the filaments ; consequently the systems of rays only consist of
isolated fibrils, which later become modified again into networks
by the formation of anastomoses.

Finally, Fol has attempted recently (1891) to demonstrate in
the egg of the sea-urchin a different mode of formation for the
radiations which appear primitively round the sexual nuclei and
the segmentation nucleus derived from them, and for the so-
called suns or asters at the poles of the nuclear spindle. The
former are stated to depend only on the arrangement of the yolk
granules and of the " tracts of sarcode " by which they are sus-
pended. The true asters, on the other hand, are formed of
actual rays, i.e. fibrillae which are just as distinct and capable of
being isolated as the connective tissue and muscular fibrils. I
am unable to agree at all with this view, either from my own
observations, or from the experience of other investigators. The
possibility of isolating the fibrils is not, in my opinion, in any

262 PROTOPLASM

way decisive in this matter, since tracts of the hardened alveolar
meshwork may quite well be isolated by teasing like fibrils in
certain places. I think that possibly special accumulations of the
granules in certain radial tracts may have been the cause of the
distinction laid down by Fol.

Although I am willing to admit that the course of the
phenomena in the division of the nucleus and the cell har-
monises fairly well with the theory set up by van Beneden
and Boveri concerning the contractile nature and action
of the so-called fibrillae of the systems of rays, I am not
inclined to consider my explanation of these processes as
improbable on that account. Apart from the structure of
the protoplasm not being, as a matter of fact, spongy or
fibrillar, a great number of important facts, which have been
detailed above, are in favour of it. It will be the subject of
a special investigation, based on the results of this work, to
discover whether there are not other points of view for
the processes occurring in cell and nuclear division, which
bring them into unison with my view of the significance of
the systems of rays. I entirely put aside for the present
the hypothetical, and in itself inexplicable, contractility of
the fibrils, since I shall treat of this point more in detail
later. On the other hand, I should like to point out that I
still consider the opinion developed by me at an earlier date
(1876) upon the forces that come into action in cell division
to be the probable one, at least in principle.

6. TJie Homogeneous Protoplasm and the Alveolar Theory

As we have frequently pointed out in the descriptive
portion of this work, the living protoplasm of certain
organisms occasionally appears entirely homogeneous and
structureless in parts, without even a trace of granular
contents. Gromia Dujardini in particular supplied us with
a good example of this, in its often very large pseudopodia.
The pseudopodia and the so-called ectoplasm of the fresh-
water Ehizopods, however, very often show the same condi-
tion, as has often been pointed out by earlier investigators.

HYALINE AND ALVEOLAR PROTOPLASM 263

The fact is therefore beyond doubt that living protoplasm
occasionally exhibits no trace of alveolar structure.

Among the representatives of the framework theory some
have not discussed this difficulty at all, while others have tried
to cope with it in various ways. Heitzmann (1883) thinks the
apparent homogeneity of such protoplasm can be explained by
the fact that the meshes of the framework are so strongly
stretched and widened that their nodal points vanish entirely,
».«. pass into filaments of the framework which at the same time
become no longer visible on account of their attenuation. This
view obtained a certain amount of support from the fact that it
is just those pseudopodia which are stretched out, or to a certain
extent pressed out over the surface, that often appear homo-
geneous ; and it therefore harmonised with Heitzmann's view, to
be discussed later, as to the causes of pseudopodial formation.

Frommann was also quite aware of the existence of homo-
geneous protoplasm. Since he cherishes the idea, as has already
been described, that the frameworks can be dissolved in the
protoplasmic matrix just as easily as they can be formed
anew in it, this phenomenon did not in his opinion present any
essential difficulty. Flemming (1882), on the other hand, had
rather a different conception of the matter. He considers the origin
of homogeneous protoplasm possible by the filaments becoming
densely crowded together or being temporarily fused.

Leydig (1883, 1885) was the representative of an essentially
different view. As has already been discussed on a former
occasion, the homogeneous protoplasm of the pseudopodia of
Rhizopods was the same in his opinion as the structureless
matrix of the protoplasm, his so-called hyaloplasm, which was
supposed to have the power of creeping out of the stiff frame-
work of the spongiaplasm.

This summary practically exhausts the opinions expressed
upon this point, which in any case has a very important
bearing upon the protoplasm question. As has been said, the
majority of the representatives of the theory of a framework or
of fibrillae have not approached the question at all. Kiinstler ako
has expressed no opinion upon it In the same way I do not
find any discussion of it in Altmann's granular theory, though
such a discussion would have great importance, since granules
are certainly wanting in homogeneous protoplasm.

As has frequently been pointed out in the descriptive
part of this work, it can be demonstrated with certainty
that the apparently homogeneous protoplasm of the pseudo-

264 PROTOPLASM

podia and cortical layer of Khizopods is produced from
alveolar protoplasm, and is capable in like manner of re-
conversion into it. The investigation of the pseudopodia
of Gromia Ditjardini furnished a decisive proof of this fact.
Moreover the fibrous alveolar structure, which is distinctly
exhibited by these apparently homogeneous pseudopodia here
and there after suitable fixation and coloration, is a sure
proof that they do not lack the honeycombed structure, but
only that as the result of special conditions it is no longer to
be observed in life, nor even to a great extent after fixation.
Hence arises the question whether it is possible to supply
a more or less plausible explanation for the disappearance
of the structure. At an earlier date (1890) I had already
suggested, as a possible explanation of this phenomenon,
that the alveoli became widened, whilst there was a con-
sequent thinning out of their walls to such a degree of
fineness that they ceased to be visible. I also pointed
out upon physical grounds that a foam, which as a matter
of fact manifests a great similarity to solid bodies in
its appearance, would do so the more the thinner its walls
became. I did not see until later that this suggestion also
obtains a certain amount of support from the observations of
Mensbrugghe (1882) upon the tension of thin fluid lamellae.
Mensbrugghe has shown that the tension of these lamellae
increases when their thickness sinks below a certain limit,
and that the lamellae then behave as firm elastic membranes,
whose resistance to further stretching constantly increases
(see on this point Lehmann, Molecularpliysik, Bd. i. p. 257).

This would agree with the fact that the homogeneous
protoplasm which occurs in Ehizopods seems to possess a
greater viscidity or firmness than the more fluid and
distinctly reticular internal protoplasm. It is usually
sought to explain this fact by ascribing a somewhat greater
density to the homogeneous ectoplasm — a notion which,
as a matter of fact, obtains no support from its optical
appearance.

From Plateau's calculations on soap-bubbles, it follows
that the thickness of the lamellae of macroscopic soap-foams
may be very small. From the interference colours which

EXPLANATION OF HYALINE APPEARANCE 265

they exhibit he could establish the fact that the thickness of
the fluid lamella at the summit of a soap-bubble may sink
to O'OOOl mm. A lamella of such thinness nevertheless
exhibits great durability, since it maintains itself under
favourable circumstances for many days (Bd. ii. pp. 4, 5).
Hence there is theoretically nothing to oppose the notion
that the walls of the microscopic alveoli of protoplasm might
under certain circumstances become thinned out to invisi-
bility. To effect this a comparatively slight attenuation
would be quite sufficient, since when they are visible in the
living condition they are already so delicate and faint that,
if attenuated to a relatively small extent, they would dis-
appear from vision.

This interpretation of the apparent homogeneity and
absence of structure in certain protoplasms is to a certain
degree strengthened by the observations that have already
been briefly described upon artificial froths. I pointed out
above that in a froth-drop sticking to the cover glass or slide,
the structure at the edges, where the drops spread out into a
perfectly flat thin layer, becomes so faint and indistinct that
it is at last no longer recognisable (p. 38 ; see Photographs
I. II.). The perfectly gradual diminution of distinctness
towards the edge, as well as slight traces of structure which
are still visible even in the apparently homogeneous edge,
prove that the nature of the edge is not really homogeneous,
but is also alveolar, and that the structure has merely
become too faint and delicate to show up distinctly any more.
I formerly tried to refer this phenomenon to the great
tenuity of the marginal border, and it is not without
importance in this respect that the homogeneous pseudo-
podia, as well as the homogeneous marginal layer of Rhizo-
pods, are mostly portions of the protoplasm which are very
thinly spread out upon the surface over which they are
creeping, although homogeneous protoplasm certainly occurs,
for which this statement does not hold good.

In any case this discussion may serve to show that
the occasional transition of alveolar protoplasm into that
which is apparently quite homogeneous, is quite compatible
with the theory, and that on the ground of this fact no

266 PROTOPLASM

exception can be taken to it. On the contrary, I Lave
described above a number of facts with regard to Gromia
Dujardini from which it follows quite necessarily that
homogeneous protoplasm also possesses an alveolar structure,
for otherwise it would not be explicable how it could arise
so suddenly from alveolar protoplasm, or how, on the other
hand, it could be again converted into the latter.

In this phenomenon it remains for the present still unex-
plained why the granular contents of the interior do not
penetrate into the homogeneous protoplasm. There is no
intrinsic reason why this should be so. Schwarz (1887)
has observed that granules which are suspended in a viscid
fluid usually keep at a certain distance from the surface,
and hence he thinks that the hyaline non-granular marginal
protoplasm, such as is often seen in vegetable cells also
(the so-called " Hautschicht " of the botanists), may be
referred to this physical phenomenon. Apart from the fact
that I never observed the phenomenon described by Schwarz
in my numerous experiments on oil-drops with which finely-
divided lamp-black had been mixed, I cannot accept this
explanation for the further reason that in Amcebse one
frequently notices that when the marginal border is wanting
the granules penetrate as far as the surface, or at least as
far as the alveolar layer, which could not well take place if
the explanation given by Schwarz was correct. On the
other hand, however, from the fact that non-granular homo-
geneous protoplasm as soon as it passes into the alveolar
condition becomes distinctly granular (that is to say, that
the nodal points of the alveolar framework which have now
become visible, impart this character to it), the view already
stated may be proved with certainty, namely, that the granular
appearance of the protoplasm depends to a great extent on
the alveolar structure, since both the nodal points and the
optical properties which have already been pointed out in
the case of artificial foams cause the same appearance
in them.

MOVEMENT AND CONTRACTILITY

267

7. The Phenomena of Protoplasmic Movement in their
Relation to the Alveolar Structure

(a) TJieories as to the Causes of the Phenomena of Movement

In my review of 1891 I had already pointed out that
the great similarity between the phenomena of movement
of the foam-drops and the simpler locornotory phenomena of
protoplasmic structures, is further evidence for the correctness
of my view with regard to the structure of protoplasm. For
these and other reasons it therefore seems necessary that we
should give some attention to these relations ; that is to say,
that we should consider rather more closely both the
phenomena of movement and previous attempts to explain
them.

(b) So-called Contractility

For a long time back the view has been consciously or
unconsciously held that all the phenomena of movement
exhibited by protoplasmic bodies are to be referred to the
same fundamental property. Under these circumstances it
was natural that the form of movement hitherto most
familiar to us, namely, the contraction of muscle protoplasm,
should be claimed as this fundamental property, and an
attempt be made to derive all phenomena of movement from
it. Since, therefore, the older attempts to explain the pheno-
mena of streaming and movement in simple protoplasmic
bodies as the result of electrical or chemical forces, etc.,
did not lead to a successful issue, it was thought that the
key to the comprehension of these protoplasmic movements
was to be found in the so-called contractility of protoplasm,
which itself was not to be further explained. From the
facts of the genetic development of organisms it might
perhaps have been predicted that a correct explanation ought
rather to take the opposite path, since the typically con-
tractile protoplasmic structures are undoubtedly not the
most primitive, but have developed at a much later stage.
The solution of the problem would, as has been said, have

268 PROTOPLASM

appeared a priori more hopeful, if the explanation of the
so-called sarcode or protoplasmic movements had been
chosen as the starting-point, and contraction proper had
been treated as a special or subordinate case, which attains
its full development under certain conditions.

Investigation was, however, pursued, as has been re-
marked, in the opposite direction from the fifties onwards,
since it was thought necessary to make use of contractility
as a general property of protoplasm for the explanation even
of the processes of movement and the streamings of simple
protoplasmic bodies, such as Ehizopods, protoplasm of plant
cells, etc.

Amongst those who took up this standpoint were both
M. Schultze (1863) and his opponent Reichert (1862, 1863),
Briicke (1861), Cienkowsky (1863), de Bary (1862 and
1864), Haeckel (1862, p. 90 et seq.), Kiihne (1864), and
numerous others.

If the process of movement in an Amosba, or the process
of streaming in the protoplasm of a plant cell, was to be
explained on the basis of contraction, it was, of course,
necessary to assume some kind of organisation in these
protoplasmic bodies which would offer a certain analogy
to the organisation of higher organisms, since obviously the
whole mass could not be contracted evenly if phenomena of
locomotion and streaming were to be brought about. The
contraction then was confined chiefly to a cortical layer of
the protoplasm, which, like a layer of integumental muscles,
was supposed to set the remaining protoplasm in movement
by local contraction, or to this contractile and therefore
changeable cortex a contractile framework or felt work was
superadded, which traversed the entire protoplasmic body
(Briicke, 1861; Cienkowsky, 186 3, etc.). In general, however,
the adherents of the contraction theory scarcely made any at-
tempt to explain or to analyse at all more accurately the loco-
motory phenomena of simple protoplasmic bodies on the basis
of their theory. They contented themselves rather with
referring in a general way to contractility as the cause. If
they had gone more accurately into the individual cases, the
untenability of the theory would have been earlier apparent.

CONTRACTILITY OF THE FRAMEWORK

269

(c) Contractility of the alleged Reticular Framework

As has been mentioned, Briicke had already actually
postulated a contractile internal framework of firmer con-
sistence for the explanation of the phenomena of movement
and streaming in protoplasm. When, therefore, Heitzmann
in the seventies had described the reticular framework of
protoplasm, he concluded at once that it was a contractile
framework of this kind, by alterations in which all the
movements of protoplasm could be explained. In his
opinion this framework alone is contractile ; the intervening
matrix, on the contrary, is a " non-contractile fluid." Dur-
ing the contraction of the framework the filaments which
connect neighbouring nodal points shorten, owing to the
latter at the same time swelling and approaching one
another. In accordance with this view Heitzmann was
forced to imagine that the substance of the filaments is
absorbed by the nodal points as they swell. When the
framework is relaxed the reverse process takes place. In
addition to this Heitzmann further assumes the occurrence
of a condition of extension of the framework, which arises
by a squeezing out of the intervening fluid of one region of
the protoplasmic body, which is contracted, and its being
driven into another, thereby causing the framework to
become stretched beyond the normal condition. As a
result of this expansion of the meshes the filaments
are said to become greatly elongated, the nodal points
reduced to the vanishing point, and the whole meshwork
finally so attenuated that it becomes quite invisible, as in
the pseudopodia of Amoebae, etc. The protrusion of the latter,
as well as phenomena of protoplasmic movement in general,
he thus explains by a local stretching of the framework
in this manner as the result of local contractions.

Most of the adherents of the framework theory were, on the
whole, in agreement with Heitzmann, to the extent at least that
they in like manner considered the framework, or the fibrillse
of the protoplasm, as the contractile elements, and sought in them
the seat of the locomotory phenomena, changes of form, processes
of division, etc. A more precise analysis of the processes was-

270 PROTOPLASM

not undertaken by any of the investigators whom we shall
shortly mention. The perfectly natural idea, that phenomena
of contraction were only conceivable in solid substances, was, to
a certain degree, the determining one in this conception ; it
was not, as a rule, definitely expressed — only in Reinke (1881,
ii. p. 96) do I find a direct reference to it — yet this train
of reasoning at any rate formed the chief ground for con-
sidering the framework, conceived of as being solid or at least
very viscid, as the contractile substance. The following authors
professed themselves more or less definitely as being of the
opinion which has just been mentioned: Schleicher (1879),
Klein (1879), Reinke and Rodewald (1881 and later), van
Beneden (1883 and later), List (1884), Carnoy (1884), Marshall
(1887), Fabre (1887), Ballowitz (1889), Boveri (1889), Rabl
(1889), and many others.

In more recent times, as we have seen, some authors
even went so far as to ascribe the properties of muscle fibrils
to ordinary protoplasmic fibrils (see above, p. 260).

(d) Objections to the Theory of Contractility

Even at quite an early period strong objections have
been raised to the contractility theory, which were directed
just as much against the older conception of it as against
the turn which it took under the influence of the frame-
work theory.

With regard to the movements of Amrebae and plasmodia,
Wallich (1863) had already drawn attention to the import-
ant fact, quite decisive as to the untenability of the con-
traction theory, that the commencement of a current does
not take place in the interior or at the hinder end of the
Amoeba, and then advance from this region towards the
portion of the surface that was streaming forwards, as would
be required by the contraction theory, but that, on the con-
trary, the current first makes its appearance in exactly the
opposite manner at the surface that was moving forwards,
and from thence gradually extends backwards. De Bary
(1864) also found this observation confirmed in plasmodia,
to this extent, that he certainly observed such currents,
which he termed centripetal; but in addition, he believed

IMIUBITION THEORIES

271

he had also observed so-called centrifugal currents moving
in the opposite direction, which would agree with the
contraction hypothesis. He thus saw himself forced to
assume causes of two kinds to explain the two streams ;
the former would arise by an " expansion " of the peripheral
protoplasm at the edge of the plasmodium, the latter, on
the contrary, by a contraction of it.

Hofmeister (1865, 1867) and many recent investigators
have seen the streams in plasmodia and Amoebae always arise
at the forwardly moving edge. For my own part I drew
attention to this fact in 1873 for the large Amoeba tcrricola,
and for this reason declared myself opposed to the contrac-
tion theory. Hofmeister (1865 and 1867) was also able
to convince himself that in the hair cells of Tradescantia
the currents extend from before backwards.

This observation caused him to turn against the con-
traction theory just as Nageli and Schwendener (1865) had
also done. The latter authors remarked with reference to
protoplasmic streamings in plant cells that contractility
really explained nothing, the more so as this conception
was obscure and unintelligible for protoplasmic bodies.
Under such circumstances streamings could only arise
according to the analogy of a blood circulation. We see
also, as a matter of fact, that the further development of
the contraction theory did necessitate this idea.

(c) Hypotheses of Hofmeister, SacJis, and Engelmann

Hofmeister, therefore, attempted to found a special
hypothesis of protoplasmic movements, and in particular of
the protoplasmic streaming in plant cells, the identity of
which with those of Ehizopods was recognised on all sides.
He thought (1865) that these phenomena of streaming
might be referred to the very varying power of imbibition
of the protoplasm, which was chiefly manifested in the play
of the contractile vacuoles. With regard to the contractile
vacuoles, however, he held erroneous ideas. The individual
" particles " of protoplasm were supposed to possess a very
different and varying power of imbibition. If this power

272 PROTOPLASM

possessed by the particles within the protoplasmic body
were to increase constantly in a certain direction, the water
would necessarily be set in movement in this direction,
since it would be attracted by the particles with the greater
power of imbibition; thus a streaming movement would
be brought about, with which an increase in the volume
of the particles with stronger powers of imbibition would at
the same time be connected. In 1867 he put the latter
point more in the foreground, without, however, basing the
actual explanation of the streamings on it, which was given
in just the same way as in 1865. In 1867 Hofmeister
more specially declares that, as a result of the increase or
decrease in the thickness of the envelope of water round
each molecule of protoplasm endued with different powers of
imbibition, changes of place must be produced in the mole-
cules, and their middle points brought closer together or
carried farther apart. Although he now remarks that this
conception of the alteration in the position of the molecules,
as the result of different degrees of imbibition, is completely
sufficient for the " demonstration " (" Versinnlichung ") of the
" mechanics of protoplasm," yet, in the further course of his
description, he gives exactly the same explanation of the
currents again which he had already put forward in 1865,
where he speaks, indeed, of the above-mentioned water
currents, but does not try to refer the streaming movements
to alterations of this kind in the position of the molecules.

Hofmeister, when he thought that the mechanics of
protoplasm could be interpreted by the idea that the watery
envelopes of the molecules possess a variable thickness, had
yet overlooked one important point, namely, the observed
fact that a muscle cell when it contracts becomes thickened
in correspondence with its shortening, which his hypothesis
in the form put forward by him was not able to explain.

Sachs also (1865) came forward as an opponent of the
contraction theory in the case of vegetable protoplasmic
movements. He regards Hofmeister's theory as admissible
in general, but in need of still further elaboration in order
to lead to a clearer understanding, since it did not explain
the actual causes of the varying imbibition of the particles

SACHS-ENGELMANN 273

of protoplasm, which is supposed to bring about the pro-
cesses of movement. Sachs attempted, therefore, to com-
plete the theory in this direction by introducing a number
of further hypotheses, which gave it such a complicated
form that there was little hope at the outset of arriving
in this direction at a clearer comprehension of the pro-
cesses. He bases his view upon four assumptions with
regard to the nature of the molecules, or rather molecular
complexes, of the protoplasm: (1) That they must possess
a definite, but not spherical form ; (2) that they mutually
attract one another in proportion to their mass and
their distance apart ; (.'3) that each molecule possesses a
strong affinity for water, which, however, decreases more
rapidly with distance than does the attraction of the mole-
cules for one another, so that each molecule is surrounded
by a relatively thick envelope of water ; and (4) that the
molecules, in addition to their general attraction for one
another, also possess so-called directive forces, which depend
upon their form, i.e. a sort of polarity, and that these forces
tend to bring the molecules into certain definite positions
with regard to one another. By the combined effect
of all these forces and conditions, a state of unstable
equilibrium of the molecules to one another is produced,
the consequence of which is that any local disturbance
in it immediately spreads throughout the entire mass. He
is of opinion in particular that as soon as the distance
between two molecules is increased through any circum-
stance, their watery envelopes become thickened by attrac-
tion of water from the neighbouring " molecular inter-
stices," and thus a streaming movement is set up which is
continued backwards from the point towards which it is
directed. If, now, it is to be admitted, on the ground of
the hypothesis put forward, that by an increase in the
distance between two molecules their watery envelopes are
able to grow, as the result of a diminution in the hindrance
which the mutual attraction of the molecules opposes to this
growth in thickness of the water envelopes, it is yet in no
way intelligible, as far as I am able to judge, why these
molecules should then necessarily absorb water from the

18

274 PROTOPLASM

neighbouring ones, for the water envelopes depend on the
force of the affinity for water possessed by the molecules
remaining in statu quo; and since this force is not
disturbed or altered in the adjacent molecules, I do not
see how a current of water can be brought about in the
manner alleged. I am hence of opinion, both from these and
other reasons, that a comprehension of the most simple proto-
plasmic movements is not to be arrived at in the way
which Sachs considers possible, and still less so in the
case of the more complicated instances of pseudopodial
development, etc.1

In 1879 Engelmann put forward the hypothesis that
the cause of the phenomena of movement exhibited by
protoplasm was to be sought in the contraction of its
minutest particles, the so-called " Inotagmas," which are to
be conceived of as " combinations of molecules." These
inotagmas are supposed to possess an elongated form when
in a state of rest, and during the contraction following upon
stimulation to approach a spherical form more or less.
Their contraction itself is supposed to depend upon an
alteration in their state of turgidity, since it is prob-
able that with increased turgidity they would tend to
shorten, or on the other hand, after giving off fluid, to become
stretched again. The latter assumption, therefore, brings
Engelmann's theory near to that of Hofmeister and Sachs
to a certain extent, from which it differs essentially with
regard to the mechanical explanation of the processes of
movement. I am, however, of the view that Engelmann's

1 A special micellar theory of the movements of protoplasm was also
developed by the botanist C. Kraus in 1877. I think I need not discuss it
here more particularly, but will content myself with the remark that Kraus
starts from the assumption that the attraction of the micellae, both among
themselves and for the water of their envelopes, depends on the relation of
their volume to their surface. With diminution of the volume of the
micellae their mutual attraction diminishes more rapidly than their affinity
for water ; hence the protoplasm becomes more watery. During the increase
in size of the micellae, on the other hand, their mutual attraction would
increase to a relatively greater extent, which would necessitate an approxima-
tion of their middle points, and at the same time a contraction, which would
be able to produce phenomena of movement, changes of shape, processes of
division, formation of vacuoles, etc.

THE "INOTAGMAS"

275

theory does not justify the expectations of its founder, and
I will attempt to explain this rather more fully.

Engelmann wishes to refer the spherical form assumed
by naked protoplasmic bodies, consequent upon stimulation,
to the fact that all the inotagmas become spherical at the
same time, that is to say, become contracted, as a result of
which " the surface attraction which they exert upon one
another, that is to say, the cohesion of the entire mass, must
become sensibly equal everywhere and in all directions."
He thus introduces a new assumption, namely, that the
mutual attraction of the inotagmas in the resting condition
is different in different directions, corresponding to their
elongated form, without, however, paying closer attention
to this subordinate assumption. Now even if, as postulated
by the above explanation of Engelmann, the mutual attrac-
tion of the inotagmas becomes equal everywhere and in all
directions, there will, in my opinion, only result a tendency
towards the spherical form if the protoplasm at the same
time obeys the general laws of fluid bodies ; and the cause
of this tendency to a spherical form can only be, as Engel-
mann himself also formerly assumed, the surface tension,
which, with equal cohesion throughout, only attains to
equilibrium under this condition.

If the mass be not fluid, it seems self-evident that the
rounding off of the inotagmas and the equality of their
cohesion cannot produce a tendency to a spherical form,
but at most slight alterations of form. If, on the other hand,
the mass is fluid, the same point really holds good, only
then, as soon as the cohesion becomes equal on all sides,
the surface pressure necessarily produces the spherical form.
If we imagine to ourselves an irregularly-shaped Amceba,
or even the richly-branched pseudopodial network of
many Sarkodina and Myxomycetes, it is, in my opinion,
quite inconceivable how these structures should contract
into a spherical form merely as the result of the inotagmas
becoming rounded off, and of their mutual attraction being
equalised on all sides ; for these processes, as has been said,
could only produce certain alterations in form, since there is
no reason at all for the assumption of a spherical form as

276 PROTOPLASM

a whole as long as the surface tension does not come into
play.

The formation of a simple pseudopodium of an Amoeba,
Engelmann thinks, can be referred to " a general contraction
of all the inotagmas of the portion of the hyaline cortical
layer which is bulging forwards." To me, however, the origin
and gradual elongation of a larger pseudopodium does not
seem to be intelligible in this manner. If we assume that
the inotagmas of the hyaline cortical layer are all directed
parallel to the surface of the region in question, of the body
of the Amoeba, and if we then imagine them contracted to the
fullest extent, so that they become greatly thickened in a
direction at right angles to the surface,1 there will of course
result a thickening of the cortical layer of the portion of the
surface in question, which may produce a moderate bulging
forward of it, but with that the process will have reached its
limit. For since we know that the cause of the elongation
of the pseudopodium, and of the current that passes through
the protoplasm, has its seat at the tip of the pseudopodium,
and that here, at all events, the contraction of the inotagmas
reaches its maximum at the commencement, a further con-
traction does not seem to be possible at this spot. The
theory, therefore, gives indeed an explanation for the first
slight bulging forwards, but is not able to explain the
further growth of the pseudopodium. For it seems inadmis-
sible that the inotagmas in question should continually
contract further. If, on the other hand, it was thought
necessary to assume in some way that the layer of con-
tracted inotagmas at the tip of the pseudopodium finally
became ruptured and the protoplasm lying beneath, which
had come to the surface, now contracted in its turn, this view
would also seem to be inadmissible, quite apart from the
improbability of such assumptions, since a rupture will not
in any case occur at the spot where contraction is taking

1 Although Engelmann makes no exact statements with reference to the
power possessed by the inotagmas of becoming shortened or thickened, yet it
seems to me beyond a doubt, that he must imagine the degree of shortening
to be a relatively moderate one, namely, of about the same extent as he has
become acquainted with from the shortenings that can be observed in mns-
/ cular contractions.

CRITICISM OF ENGELMANN 277

place. Now if we consider that many simple Amcebce move
forward for long distances at a time in exactly the same
way that a pseudopodium is protruded, i.e. that they
really represent a single creeping pseudopodium, this fact is
still more definite evidence than the case upon which we
based our argument above, against the complete applica-
bility of Engelmann's explanation. There is also the
further fact, that while it explains the stream of protoplasm
forwards into the pseudopodium, it does not account for the
lateral back currents at the ends of the pseudopodium.

Engelmann believes, however, that the formation of
pseudopodia is produced by other causes still. He is, with
de Bary, of the opinion that pseudopodia can be pressed
forwards, and streaming movements set up, also by a vis It
tergo, which depends on local contractions. Finally, he does
not wish to refer the origin of the fine filamentous pseudo-
podia to contraction, but on the contrary to relaxation of
contracted rows of inotagmas. The latter explanation, the
mechanical representation of which in itself presents very
great difficulties, if one thinks of the considerable length
to which pseudopodia of this kind frequently attain, may
also be rejected for the reason, that it is improbable in the
highest degree that the development of pseudopodia, in
which very gradual transitions can be traced so beautifully
in the Rhizopod series, should owe its origin to two com-
pletely opposite causes.

Just as unsatisfactory as the explanation of the forma-
tion of pseudopodia it seems to me is Engelmann's view as
to the causes that produce rotational currents in plant cells.
He says on this point (p. 378): "A current of this kind
must be brought about when the inotagmas of the layers in
motion are, on the whole, orientated with their longitudinal
axes parallel to the direction of movement, and the spontan-
eous stimulation continues to move forward in tliis direction.
The motile protoplasm then creeps upon the non-motile
layer of the wall just as the foot of a snail upon the
substance beneath it."

In opposition to this explanation it may be urged that,
in the first place, there is certainly a continuous connection

278 PROTOPLASM

and a gradual transition between the non-motile layer of the
wall and the streaming protoplasm, and that therefore the
relations are here, as a matter of fact, essentially different
from the case of a snail's foot, which moves upon a firm
substance completely separated from itself. Further, if the
relations were as supposed, one would expect to observe in
the rotating protoplasm something of the wave of con-
traction that would move forward, which would, of course,
be marked out towards the cell-sap cavity as projections, just
in the same way as distinct waves of contraction are to be
traced in the snail's foot. Finally, the observation of these
streaming processes teaches us quite definitely that there
is certainly no creeping substance present in the way in
which Engelmann's explanation supposes, but that we are
dealing with a substance which is flowing — a fact which can
be traced very plainly in the movements, displacements,
torsions, etc., which the particles contained in the streaming
protoplasm go through.

Hence, as has been said, the hypothesis of Engelmann
also seems to me to give no satisfactory idea of the causes
and mechanical relations of protoplasmic movements, just as
little as the two before-mentioned molecular hypotheses were
able to do. On the whole, I believe that, as Berthold has
declared already, nothing profitable is to be obtained by
setting up peculiar molecular hypotheses to explain certain
processes in the organic world. At any rate it seems to me
much more promising and satisfactory to seek for the causes
and conditions of these processes among the known physical
forces than to have recourse to special molecular forces
constructed ad hoc. It is only necessary to call to mind,
for example, the complication of the assumptions made by
Sachs — and those of Engelmann are in like manner very
complicated, since he also postulates an increase and decrease
of the attractive forces of his inotagmas corresponding to
the decrease and increase of their water of imbibition, that is
to say, of the watery envelopes of the inotagmas — in order
to convince oneself that it would be difficult to attain to
satisfactory explanations in this direction.

ELECTRICITY AND MOVEMENT 279

(/) Electrical Hypotheses of Vclten and Fol

The opinion frequently expressed by older observers,
namely, that protoplasmic movements depend upon elec-
trical forces, was defended again by Velten in 1876.
According to him it is electrical forces, which reside in,
and take origin from, the individual cells, that cause the
streamings. Velten supported this supposition, and his
view cannot be termed anything else, since he is not able
to elucidate either the origin or the mode of action of these
forces in bringing about protoplasmic movements, by his
observations upon the effect of strong induction-currents on
plant cells after death. Under these conditions he was able
to call forth streamings and rotations in the dead contents,
or rather on their granular enclosures (starch granules, etc.),
which were very similar to the natural streamings of proto-
plasm. The fact that we are dealing with phenomena
in dead cells, and further also the possibility that these
processes of movement produced by strong electric currents
might be in part at least the result of a considerable
increase in temperature in the cellular tissue subjected to
the currents — which Velten does not take into account at
all, although he himself estimated the rise of temperature
at 65° or more, — this fact in itself makes the value of these
observations seem very little for forming an opinion upon
the streaming phenomena of living protoplasm. It was
without doubt in consequence of this that Velten's view
met with no support at all. Eeinke in 1882, by means of
a series of interesting experiments, sought to directly contra-
dict the basis of Velten's supposition, namely, the presence
of electric currents crossing one another in the cell, in the
same way as Becquerel (1837) had already undertaken to
do by means of other methods in the case of Chara. Eeinke
showed, for instance, that the closely approximated poles of
a strong electro-magnet, between which are brought cellular
filaments of Chara or Nitdla, or hairs of Urtica, suspended
freely in a drop of water, exert no directive influence upon
the position of the filaments. If electric currents really
moved in cells with flowing protoplasm, it might have

280 PROTOPLASM

\

been expected that the cells would have assumed a definite
position with regard to the poles of the magnet. But, as has
been said, there was nothing to be seen of this. The magnet
also proved without effect upon the arrangement of the
strands of protoplasm and the streaming of the granules in
the hair cells of Tradescantia, etc., a fact which in like
manner confirms the absence of electric currents.

For the sake of completeness it should be further
mentioned here that Fol (1879) set up a hypothesis as to
the connection of protoplasmic movements with electric
forces, which was not, however, raised above the rank of a
supposition, since it did not enter at all into details. Fol's
view and its significance may be made clear most simply by
means of the following quotation : " Si nous supposons une
pile electrique dont chaque element soit de la grosseur d'un
de ces granules que le microscope devoile au sein du sarcode
sous formes de petits points grisatres, la quantite totale
d'electricite* produite dans une pile de quelques millions de
ces elements reunis en tension pourra etre considerable
sans qu'il se degage aux extremites de la pile une quantite
d'electricite bien appreciable a 1'aide de nos galvanometres.
Neanmoins, suivant la maniere dont cette force se repartit a
la surface de chaque granulation, un mouvement imprime a la
premiere particule d'une serie pourra se propager de 1'une
a 1'autre et produire un deplacement mecanique conside-
rable " (p. 269).

(g) Ley dig's View of the so-called Hyaloplasm

Even at an early date there was a hypothesis framed
which sought for the actual living substance, and therefore
also the seat of movement, in the intervening matrix, the
so-called Enchylema. Leydig, the principal representative
of this view, had rather strange ideas concerning the matrix,
his hyaloplasma, which may be briefly indicated, since they
are of course the essential conditions for the possibility of
such a conception. He evidently had the greatest difficulty
in forming an opinion as to the nature of this hyaloplasm,
as can be proved by the following passage taken from his

THE HYALOPLASM OF LEYDIG 281

memoir of 1885 (p. 43). It runs thus : " We know that the
hyaloplasm contains throughout an abundance of water — in
fact, as far as the perceptions of our senses are concerned,
hyaloplasm and water may run into one ; they form, if we
may assist ourselves with the expression, a solution. Where,
then, is the line to be drawn between water and hyaloplasm,
a line which it is nevertheless necessary to assume ? "

In spite of this evident lack of any idea at all definite
as to the nature of the hyaloplasm, Leydig did not hesitate
to regard it both as " the primary motile substance "
(p. 152) and also as the nervous, etc., although he was not
even quite certain whether lymph might not be identical
with hyaloplasm and with the homogeneous nerve sub-
stance, which was also supposed to be merely hyaloplasm.
Since Leydig's assumption, as has been pointed out, was
based principally upon the supposition that the axis-
cylinders consisted of such homogeneous and structure-
less hyaloplasm, for which very reason the hyaloplasm was
supposed to be the real nervous and generally active
substance, this view of course falls to the ground, when
it is proved that the axis - cylinders possess just the
same honeycombed structure as the rest of the protoplasm.
Even with the modification which Nansen (1887) has given
to Leydig's view, the latter is no longer tenable, since, as we
saw, the assumption that the axis-cylinders are composed of
continuous hyaloplasmic nerve tubules is incorrect, because
the hyaloplasm, or in our terminology the enchylema, is
really discontinuous, and distributed in the substance of
the axis-cylinder in the form of numerous chambers or
alveoli separated by delicate partitions. If, however, this
view is correct, it seems absolutely necessary to consider the
substance of the framework as the substratum of nerve
conductivity, for it alone extends continuously through the
axis-cylinder, and is therefore in a position to be instrumental
in conduction. The arguments brought forward by Pflliger
(1889) against Leydig's view seem to me also important.
Pfluger remarks that this assumption is improbable from the
fact that the nerve fibres are only stimulated by currents
directed longitudinally, and not by those directed transversely,

282 PROTOPLASM

for which reason the fibrillse must be the really active and
irritable components. This observation also seems con-
sistent with our view relative to the constitution of the
axis-cylinder, since the cross connections which we have
found are throughout discontinuous, and are therefore
essentially distinct from the longitudinally directed tracts of
the framework. Pfltiger further declares it to be unthink-
able that images of memory, such as we must ascribe to the
ganglion cells of the brain, could be retained by a fluid
substance such as the" hyaloplasma ; rather that this would
only be possible in a solid substratum. So far as a concep-
tion of these things is generally possible in the present time,
his conclusion seems to me perfectly justified. Now, since
my interpretation of the structure of the ganglion cells
quite admits of their framework becoming partially or
entirely firm, it can be brought very well into harmony
with these physiological requirements.

We have already learnt before that some investigators,
such as Brass (1883 and 1885), Schafer (1887), and Eohde
(1890 and 1891), have ranked themselves more or less
definitely on the side of Leydig's hypothesis. Schafer alone,
however, in more recent times has attempted to support the
opinion alleged by further investigations. In white blood
corpuscles of Amphibia, after fixing and staining, he believes
he has convinced himself that the pseudopodia are always
structureless and homogeneous, while the rest of the corpuscle
appears more or less distinctly reticular. At the same time,
the homogeneous substance of the pseudopodia stains very
little or not at all, and is thus sharply marked off from the
strongly staining reticular substance of the rest of the
corpuscle. In these results Schafer sees, as has been said,
a decisive proof of the correctness of Leydig's hypothesis.
He also especially declares the derivation of the apparently
homogeneous protoplasm of pseudopodia, etc., from that of an
alveolar structure — an idea expressed by me in 1890, and
followed up more thoroughly in the present work — to* be very
improbable and contrary to experience. Since the other
arguments, which are in opposition to the hypothesis of
Ley dig and Schafer, are not touched upon at all in Schiifer's

CRITICISM OF LEYDIG AND SCHAFER

283

dissertation, I need merely confine myself here to a brief
discussion of the objections set forth above. My view, that
the alveolar structure is not wanting even in apparently
homogeneous protoplasm, but is only no longer traceable
owing to the fineness of the walls of the alveoli, is held by
Schafer, as has been remarked, to be contradicted by the
alleged sharply -defined limit between the reticular and
the homogeneous protoplasm. With regard to this point I
may simply refer to the investigations upon the apparently
homogeneous pseudopodia of Amcebcc and of Gromia Dujardini
which are described in an earlier part of this work. More-
over, I may lay especial stress on the fact that, in the
pseudopodia investigated by me, I never observed a snarp
boundary between the reticular and the apparently homo-
geneous protoplasm, but could always see a transitional zone
both in life and in preparations. In fact, it may frequently
be observed in the pseudopodia, that the structure becomes
fainter at the extremity, or even becomes indistinct before
reaching the extremity, which causes the latter to appear
homogeneous. I do not believe, moreover, that the pseudo-
podia of the blood corpuscles investigated by Schafer behave
differently in this respect ; on the contrary, even in Schafer's
Fig. 4 (1891, 1893), it can be seen in many places that the
reticular structure gradually becomes blurred towards the
lobed or rim-like pseudopodia, and insensibly passes into them.
If in other places a very sharp limit seems to exist between
the homogeneous protoplasm and the reticular central
portion of the corpuscle, this can be explained by circum-
stances of another kind. Schafer specially mentions that
the homogeneous substance of the pseudopodia, which in
accordance with his view he regards as enchylema (hyalo-
plasm) which has crept or flowed out, stains much more
feebly than the granular reticular central protoplasm, and
that therefore the two must also differ chemically, i.e. that
the strongly staining spongioplasmic framework can only be
present in the reticular portion. Now we have frequently
found that the spongioplasmic framework, i.e. the framework
substance of the alveolar protoplasm, stains, as a rule, very
feebly, and that the apparently intense coloration of it,

284 PROTOPLASM

which can be obtained so often, is always, upon more exact
investigation, to be referred to the granules which it usually
lodges in great abundance. Now, since we know that the
granules, also very numerous in Amoebae, do not pass into
the hyaline protoplasm of the pseudopodia, its feeble staining
powers are explained easily by this fact. This explanation
will, at any rate, hold good for the white blood corpuscles,
since granules are, in like manner, present in them in
abundance. An apparently very sharp limit between the
darkly stained reticular central protoplasm and the hyaline
protoplasm of the pseudopodia may, however, in addition to
being caused by this circumstance, be also an illusive
appearance due to the fact that the real origin of a pseudo-
podium which is creeping flat upon an underlying surface,
may be covered, to some extent, by a bulging out of the
more or less raised central portion of the corpuscle. This
frequently occurs in the case of Amoebae creeping upon a
flat surface. Under these circumstances a sharp boundary
between the substance of the pseudopodia and the central
protoplasm is then, of course, apparently visible, since
the origin of the pseudopodium cannot be plainly traced in
objects of such small size.

I think, however, that it is scarcely necessary to discuss
these objections more in detail, but that it will be sufficient
to refer to the above described observations upon the sudden
conversion of the apparently homogeneous protoplasm of the
pseudopodia into reticular protoplasm, which the hypothesis
of Leydig and Schafer is altogether unable to explain, while
it is perfectly compatible with my view. As has been said,
I consider my view with regard to the homogeneous proto-
plasm to be the more probable for these reasons, which
were developed by me in 1890, without Schafer having paid
any heed to them. There is furthermore the additional
fact, to which I will again call attention here, that as evi-
dence against the Leydig and Schafer hypothesis, which of
necessity assumes the existence of a spongy framework, there
are, of course, all those arguments which have already been
enumerated above against the possible existence of such a
framework. Schafer expresses himself rather indefinitely

ROHDE— STRUCTURE OF GANGLION CELLS 285

with regard to the aggregate condition of the actual spongio-
plasmic framework when he says (i. p. 175), "It is firmer
than the hyaloplasm (but perhaps not actually solid), and
is, in all probability, highly extensile and elastic." But a
highly elastic substance which is not actually of a solid
nature seems to me to be a physical impossibility, which
we cannot well make use of to found a hypothesis upon
living matter.

In recent times Rohde has specially come forward as a
very zealous adherent of Leydig's theory. His investiga-
tions upon the nervous elements of the Annelids convinced
him also that the hyaloplasm alone must be the nervous
element, and that the spongioplasm, on the contrary," per-
forms functions of support exclusively throughout the entire
nervous apparatus. I think that the reasons for the
opposite view, which have been enumerated already, are
not shaken in the least by the investigations of Rohde, and
on that account I will not try to discuss them more thoroughly
here, the less so as his last work (1891) only became
known to me after the completion of my manuscript. I might,
however, point out the fact that the fibrillar structure of
ganglion cells, nerve fibres, etc., which Rohde alleges, does
not exist in the sense in which he interprets it. Rohde
takes up, in fact, about the same position as Flemming.
In opposition to him I hold my view of the structure of
ganglion cells, etc., to be entirely correct, and I think I am
the more justified in doing so as Rohde, in a photograph
of a section through one of the so-called peripheral ganglion
cells (Plate VII. Fig. B), has furnished, in my opinion, a
very valuable proof of the correctness of my view.

The photograph in question shows the honeycombed
structure of the protoplasm very plainly almost everywhere,
and enables us to make out exceedingly well how the appear-
ances of fibres and striations arise solely by a modification
of the alveolar framework. If one compares this photograph
with the drawing of one of these cells which Rohde gives at
the same time (Plate VI. Fig. 12), it is very obvious not
only how little the latter corresponds to nature, and to
what a high degree it is schematised, but also that the drawing

286 PROTOPLASM

does not contain many details of structure which the photo-
graph represents very well. In this regard I may refer, by way
of example, to the nucleus alone, the contents of which are
described and depicted as granular, while the photograph
shows distinctly that the granules are lodged in a honey-
combed framework. I regard, therefore, as has been said,
Eohde's photographs, as well as those of a ganglion cell from
an earthworm which accompany the present work, as good
evidence of the alveolar structure. The photograph in
question teaches us still more, however. Rohde describes
and figures the fibrillse of the ganglion cells as being of
very different thicknesses, and asserts that in certain zones of
the protoplasm very strong fibrils make their appearance,
while in other regions there are only very fine ones. In a
former section I have already pointed out that the stronger
fibrils, or " runners " (Reiser), so often described, are quite
certainly only the result of densely deposited granules. Now
Rohde's photograph, already mentioned, also seems to me to
bring forward the strongest proof in favour of this explanation,
for it can be plainly made out in it in many places that
the apparent stronger fibrillae arise by a more or less dense
crowding together of such granules, and it can further be
seen with the same distinctness that the differences between
the five zones of protoplasm which Rohde distinguishes
depend in the main, at any rate, upon differences of the
degree to which they contain granules lodged in them, to-
gether with, however, special modifications of the framework
here and there. On the other hand, the width of the meshes
does not seem to me to be subject to any very considerable
amount of variation in the different zones. The fact that
the zones, with very numerous granules, appear in general
more finely structured, may rather depend essentially on all
the nodal points being sharply marked out by the granules
lodged in them, while in the zones poor in granules many
nodal points are so pale that they are only slightly promi-
nent, or even partly left out in the photograph.

Now since, as has been said, I find in this photograph of
Rohde's an involuntary support for my interpretation of the
structure of ganglion cells and of protoplasm generally, I

MONTGOMERY ON AMCEBOID MOVEMENT 287

consider it the less necessary to contradict again the
doctrine, accepted by Eohde also, of the nervous nature of
the hyaloplasm, since it must appear untenable in and for
itself, as soon as the correctness of the view concerning
protoplasmic structure, put forth by me, is admitted.

Qi) Montgomery's Hypothesis

I must say a word or two, in passing, relative to the
hypothesis developed by Montgomery (1881 and 1885)
with regard to protoplasmic movements. It is not easy to
obtain a clear idea of this view, since its founder has con-
ceptions of protoplasm and of the forces at work in it, which
depart completely from what are usual ; in fact they are on
the whole difficult to grasp. Without wishing to attempt a
more exact proof of this assertion, I content myself with a
reference to the following sentence, which concludes Mont-
gomery's work of 1881, and contains, as it were, his con-
fession of faith with regard to living matter. " Itself sem-
piternal, an indivisible specific totality, bringing back the
past to the present, it is in opposition throughout all time
to the remainder of transitory nature. It, the living sub-
stance, is in the world the truly permanent, and not the
dead formless matter." Starting from such conceptions,
which recall strongly the past times of the nature-philosophy,
Montgomery arrives at the strange view that ordinary
physical forces play on the whole no part in protoplasm, and
that the living substance is in fact governed only by chemical
forces. For this reason, according to him, it is out of the
question to talk of an aggregate condition of protoplasm.
If any definite idea is to be connected with these assertions,
it seems to me to follow from them that Montgomery con-
ceives of the entire protoplasm of an organism, in fact even
the whole body of a higher animal, as would appear from
certain of his applications, as a large chemical molecule,
which is in a state of constant decomposition and recon-
struction, within which also only chemical forces exert their
activities and not the usual forces of molecular physics.

Montgomery's hypothesis concerning the processes of

288

PROTOPLASM

movement is hence also a chemical one. The movements
of an Amoeba which is flowing in a simple manner are
supposed to proceed as follows. At the anterior end of the
Amoeba, under the influence of the external medium, a
decomposition of the hyaline protoplasm is continually taking
place, a " disgregation," as he calls it ; in consequence
the hyaline protoplasm of the anterior end shrinks together
and becomes granular, being at the same time carried
towards the sides and finally towards the posterior extremity.
This granular shrunken protoplasm then gradually re-enters
the current, to become again restored, under the influence
of nourishment, to the former condition of hyaline proto-
plasm, its natural condition. During this process of recon-
stitution, however, it " stretches," and this stretching, which
has its seat chiefly at the anterior end of the Amoeba, where
the hyaline margin occurs, is the cause of the forward
movement and, of course, of the streaming generally. The
continual play of disgregation and reconstitution thus causes
the streaming of the Amoeba and similar protoplasmic
movements. Montgomery tries to extend this hypothesis to
explain also the contraction of muscles, but I will not
attempt to represent here his views with reference to this
point.

Frommann has recently (1890) pronounced a very
shrewd critique upon Montgomery's hypothesis ; elsewhere I
have not seen it made the subject 'of earnest criticism, either
favourable or otherwise. I think that I may also omit any
discussion of it, the more so because, in my view, it is, in
the first place, altogether hypothetical, being in fact, as is
even asserted at the outset, not based at all upon physical
forces. Moreover, I am of opinion that, even if we accept
the postulates that are made, the regular protoplasmic
movements of Amoeba or of plant cells could never be
brought about by the alternate action of shrinking and
stretching which is asserted to occur. The fact, moreover,
that any explanation is lacking as to why the protoplasm
should, as a matter of fact, shrink after decomposition, and
should stretch when reconstituted, need not be brought for-
ward by me here as an objection.

SURFACE TENSION HYPOTHESES

289

(i) Hypotheses relating to Surface Tension — Berthold,
Quincke

It has already been occasionally pointed out here and
there, that in bringing about protoplasmic movements the
phenomena of the so-called surface tension of the fluids may
play a part.

Hofmeister attempted, as far back as 1867, to interpret
the so-called rounding off of drops of protoplasm, which
has often been regarded as a phenomenon of contraction,
as a property identical with the tendency to assume a
spherical form in ordinary drops of fluid, that is to say, as
an effect of the surface tension.

Engelmann also, on the ground of his idea that proto-
plasm becomes fluid by electrical stimulation, arrived (1869)
at the view that the forces which cause the contraction of
protoplasm "may be just the same as those which tend
to make every non- spherical free drop of fluid become
spherical " ; that would, of course, be the surface tension.
He is, with Hofmeister, completely convinced of the fact
that contractions, in the ordinary sense, are not the cause of
movements, and agrees entirely with the view of the latter
oncerning the extension of the currents backwards. At
later date, however, Engelmann did not recur again
> this, in my opinion, very correct idea, but developed, as
e have seen, a theory of movement based on essentially
;her grounds.

In 1876 I tried to make use of surface tension
ypothetically as the efficient cause in the explanation of
ill division. As I have already remarked, I regard the
xplanation given then as still suitable in its main points,
ud indeed as having become considerably more probable
rom recent observations with regard to the great part played
y surface tension as an important cause of the processes
f movement in protoplasm. Since the time when I first
rrived at the conviction that this property of fluid bodies
lust be of pre-eminent importance for the explanation of
be changes in form exhibited by fluid protoplasm, I have

19

290 PROTOPLASM

always kept this problem in view ; and the firm conviction
that there was in this direction a prospect of arriving at a
comprehension of protoplasmic movements was one of the
main incentives of the investigations described in this work.

In 1880 Eindfleisch published his ideas upon the
supposed causes of protoplasmic movements, which have
certain points in common with the view that surface tension
comes into play in this process. Eindfleisch adopted the
theory of the reticular framework of protoplasm, and sought
to show that the intimate interpenetration of two different
substances, i.e. the framework and the intervening matrix,
which follows from such a structure of protoplasm, was of
fundamental importance for the origin of processes of
movement. His hypothesis asserts that the adhesion of the
two interpenetrating substances forms the active principle
in the origin of processes of movement ; alterations of their
adhesion necessarily produce small movements, the sum
total of which bring about the observed effect. He tries to
support this assumption by reference to the phenomena of
movement in fluids. For instance, he refers to the movements
which a drop of glacial acetic on a slide, or a fine layer of
oil on water, shows when warmed. In these cases, however,
there is no doubt that surface tension is the cause of the
changes of form and phenomena of movement, so that it
may well be supposed that Eindfleisch had in reality
imagined this to be if anything the efficient cause. Besides,
it scarcely requires any special discussion to show that no
explanation is possible in the way indicated by him, since
the hypothesis of a reticular framework, which nevertheless
must be fluid, in order to exhibit changes of form and
phenomena of movement under the assumed conditions, does
not seem possible.1

In the year 1886 Berthold arrived at the view that the
protoplasmic streamings in vegetable cells had their cause in

1 It may be mentioned here quite briefly that Geddes (1883) developed a
hypothesis which seeks to refer amoeboid movement and the contractions of
striped muscles- to the so-called phenomena of aggregation, such as Darwin
observed in the protoplasm of insectivorous plants. Geddes's view is not,
however, perfectly intelligible to me.

PROTOPLASMIC STREAMING— BERTHOLD 291

local alterations of the surface tension between the fluid
protoplasm and the cell-sap. Weber in 1855 had already
pointed out the similarity between the streamings observed
in certain drops, and produced by surface tension, and the
protoplasmic streamings in plant cells. It is without doubt
a great merit on the part of Berthold to have recognised
correctly the importance of these relations, and to have
ventured an attempt to follow them up consistently. Even
in 1865 Niigeli and Schweudener had very rightly declared
that the true seat of the motor forces in the streamings of
plant cells must be the surface of the protoplasm turned
towards the cell-sap ; on the other hand, they formed an in-
correct judgment upon the state of affairs, inasmuch as they
considered that this movement of the surface of the proto-
plasmic body obtained its point of support in the surrounding
water, " just in the same way as a bird in the air or a fish in
the water," and that in this way the forward movement took
place. They concluded, therefore, that the adjacent cell-sap
must always be in a condition of streaming " in an opposite
sense to " the movement of the protoplasm. This erroneous
idea, founded upon incorrect views as to the nature of the
streamings, was especially contradicted by Velten (1873),
who showed that the movement of the adjacent cell-sap, as
far as can be judged from the fine granules occasionally
occurring in it, always took place in the same sense as that
of the protoplasm. From these undisputed observations it
also follows with certainty that the streaming of the proto-
plasm reaches as far as its limit on the side of the cell-sap,
a fact which may also frequently be directly observed, so
that no resting skin-like layer exists at this spot. It seems
to me quite impossible to assume with Wakker (1888),
who also observed this movement in the cell-sap, that the
protoplasmic streaming sets the membranous layer lining the
cell-sap vacuole or cavity in rotation by means of its fric-
tion ; especially if we consider that in cell-sap cavities, which
are spanned by bridges of protoplasm, such displacements
of the vacuole would necessarily be very obvious.

According to Berthold's hypothesis it is a case of differ-
ences in the surface tension, at the limit between cell-sap

292 PROTOPLASM

and protoplasm, which produce the streaming movements
in the plant cell. In this point I think Berthold has hit
the mark ; on the other hand, I cannot consider as satisfac-
torily grounded his efforts to explain, by means of these pro-
cesses, isolated cases of movement in vegetable protoplasm.
The very important case of the so-called rotation of the
protoplasm in a constant direction remains, in my
opinion, unexplained. For the remarks that Berthold makes
upon this point on p. 118 can scarcely be considered as
a sufficient explanation. He thinks that the rotational
streaming has gradually arisen from numerous irregular
streamings, such as occur in the so-called circulation, in
the following way. " The stronger currents will gradually
suppress the weaker, and draw them along in their
direction, and thus in the struggle for existence (!) only a
single rotational current will be left remaining among them,
for only in this way would the principle of least resistance
be satisfied." Berthold further supposes that a special
increase of the fluidity of the protoplasm is a condition
for the development of the simple rotatory current. An
explanation such as the above can hardly be considered
a physical one, although Berthold means to give one of this
kind, for such principles as tho " struggle for existence " are
here quite inadmissible and do not explain anything. A
system of numerous streams will always remain as such
when the causes persist which produce them ; if no change
takes place in the causes, a single stream cannot possibly
be formed. With regard also to the principle of least
resistance I am very sceptical, since I freely confess that
I do not quite understand what Berthold really pictures
to himself by it. In order to explain rotation currents
on the ground of Berthold's hypothesis, which, as I have
said, I regard as the only correct one, even after all the
observations of my own which are detailed in this book, it
is necessary to show why, when, and in what way there
arises a single powerful current of this kind, which, as we
have already been convinced by the streamings in the foam-
drops, can suppress feeble local streams with perfect ease by
gradually removing the cause of their origin ; and we must

AMCEBOID MOVEMENT— BERTHOLD 293

further show how, above all, it comes about that this current
only attains development on one side, for, as we saw before,
every extension - current radiates out on all sides from
the place of its origin. Later on it will be a subject of
inquiry whether it is possible to find an explanation for the
one-sided nature of the rotational stream. For the rest,
Berthold has clearly recognised that the weakest point of his
explanation of the circulatory streamings consists in the fact
that in them true centres of extension, such as the
hypothesis postulates, are scarcely to be made out with
certainty. He seeks the cause of this fact in the thinness of
the protoplasmic lining of the wall, but I hardly think that
the matter is to be cleared up thus.

It is curious, however, that Berthold is of the opinion
that the movements and streamings of Amoebae and plas-
modia do not depend on the same causes that produce
the streamings of the protoplasm of plant cells, although the
forces that are at work are the same in principle. He
believes that it is not extension -currents, depending on
local diminution of surface tension, and the forward
movements that appear in consequence, such as our
drops of oil or foam show under suitable conditions,
which form the cause of amoeboid movement, but that
the protoplasm of the Amoeba behaves in much the same
manner as a fluid which spreads out upon a solid
body. In order, therefore, to be able to understand
Berthold's view with regard to these processes, it is neces-
sary to pay a little attention to the conditions of the
spreading out of fluids upon solid bodies. Quincke, upon
whose views Berthold supports himself, has attempted in
1887 to give a theoretical foundation to the proposition
that the spreading out of fluids upon solid bodies is
governed by the same conditions which also determine the
spreading out of one fluid upon the surface of another, or
rather upon the limiting surface of two others. He holds
it admissible to assume that even at the limit between a
fluid and a solid body, in fact even at the surface of a solid
body, a surface tension exists, and that it is the ratio of the
magnitudes of the three surface tensions, i.e. of the surface

294 PROTOPLASM

tension of the fluid which is brought upon the solid body
(«2), of that of the limiting surface between this fluid and
the solid body (a12), and of that of the solid body (a1),
which determines the spreading out of the fluid ; that is
to say, that the latter will continually spread out, if
ai — ai2>a2- Now, if we are not dealing, as was supposed
in the above case, with the surface of a solid body (1)
which is bounded by air, but with a surface covered by a
fluid (3), so that the fluid (2) is brought upon the limit-
ing surface between the solid body (1) and the fluid (3), the
spreading out of (2) will take place here theoretically when
the condition is fulfilled that «13 — a12>«23- The theory
further requires that in any drop of fluid which does not
spread out upon the surface of a solid object, its surface
should form, at each point of its line of contact with the
latter, a constant marginal angle with the surface of the
solid object — an angle which is independent of the geometrical
form of the surface of the drop, and is only dependent on
the ratio of the three surface tensions which act at every
point of the line of contact.

These theoretically -obtained determinations have only
been partially confirmed by experience. Thus, for example,
the marginal angle of a drop of water adhering to a glass
plate does not remain constant if water be gradually drawn
away from the drop ; the area which the drop covers
remains the same, while its volume diminishes, and at the
same time the marginal angle becomes smaller, while
theoretically it ought not to change, or at the most it might
increase, if one takes into account the decreased height of
the drop. Quincke was just as little successful in causing
an essential change in the marginal angle of an adhering
drop of this kind, by altering the surface tension a23 (or a2),
by means of placing some oil on the drop, though he
succeeded perfectly with drops which were lying on the
surface of a fluid. In any case these results seem to
indicate that in adhering drops relations come into play
which are not yet sufficiently known to us ; for which
reason- it seems very unsafe to make Quincke's theory the
basis of a hypothesis relative to the phenomena of movement

CRITICISM OF BERT HOLD

295

of Amoebae, and to class the latter as adhering drops of this
kind, as Berthold does. His hypothesis starts, as has been
said, from the view that the Amoeba adheres to the solid
substratum of the underlying surface and, being a fluid drop,
is subject to the above-mentioned conditions, in accordance
with which its marginal angle must also remain constant
as long as the chemical composition of the protoplasm is
constant.

Now if, at a point of the edge of the Amoeba, a chemical
alteration takes place, whereby a lowering of the surface
tension (a12) between the protoplasm and the underlying
surface is brought about, or, as Berthold usually expresses
it, the adhesion between the substance of the Amoeba "and
the substratum is increased, there then results an extension
of this margin, until the marginal angle is sufficiently
diminished, to compensate for this change of the surface
tension or of the adhesion. If we have already reason
to doubt this explanation, on account of Quincke's ex-
perience to the effect that surface tension has no
influence upon adhering water drops, there are in
addition a considerable number of further points which, in
my opinion, are evidence against it. In the first place,
I consider it incorrect to suppose that Amoebae really
adhere to the solid substratum. I do not entirely dispute
the fact that local adhesions at the hinder end, or occasion-
ally also in the pseudopodia during their retraction, may
come under observation. On the other hand, I consider
it certain that an extensive adhesion is absent. Any one
who has been frequently occupied with Amoebae knows that
even very feeble currents of water are usually sufficient to
wash them away from the surface on which they are creep-
ing, while really powerful forces would in any case be
necessary for this, if an actual adhesion existed. In
addition to this there is the fact that some Amoebae, which
certainly do not adhere, but swim freely in the water,
develop pseudopodia, and their power of changing their
shape is in 110 way impaired.1

1 A very suitable object upon which to convince oneself of the non-
adherence of very motile Amoebse is Pelomyxa. With some good motile

296 PROTOPLASM

Finally it is known that many Amoebae can to some
extent send out their pseudopodia free into the water, so that
Berthold sees himself constrained, in the case of the forma-
tion of pseudopodia of this kind, which in other respects is
precisely similar to that of creeping pseudopodia, to accept
the old theory of the pressure brought about from behind by
local contractions, and thus to assume two entirely different
causes at the same time in order to explain amoeboid move-
ment.

Berthold finds a proof of the correctness of his hypo-
thesis with regard to amoeboid movement in the well-known
phenomena of movement shown by drops of water ad-
hering to a glass plate, if some ether or alcohol is brought
near them at their edges. As is well known, the drops
retreat from the ether or alcohol. Berthold thinks that
this phenomenon is to be explained in exactly the same
way as he supposed amoeboid movement to be, that is
to say, by the marginal angle of the drops becoming
increased on the side towards the alcohol, since the sur-
face tension is greater between water mixed with alcohol,
and glass, or rather its adhesion is less; and he believes,
as has been said, that the conditions are the same as
in the Amoeba, for which he postulates, in like manner, polar
differences of adhesion, i.e. a preponderance of adhesion
at the pole which is advancing forwards. Now, in the
first place, I regard the explanation given by Berthold of
the drop of water retreating from alcohol, etc., as only
partially correct. Its edge shrinks back on the approxima-
tion of the alcohol with an increase of the marginal angle,
and this may rightly be referred to the cause alleged by
Berthold. But with this shrinkage the movement would be
exhausted, and a continuous retreating movement, or, in other
words, a spreading out of the edge turned away from the
alcohol, would not be intelligible, since, after a corresponding

specimens in a watch-glass, it is easily proved by slightly inclining the glass
that they do not adhere to it. On the slide it is possible to displace an
actively-streaming Pelomyxa by means of a light touch with a fine glass
rod. Only the hinder end, which in Pelomyxa, as in other Amoebae, is dis-
tinguished by special peculiarities, sometimes adheres to a slight extent.

CRITICISM OF BERT HOLD

297

increase in the marginal angle, a condition of equilibrium
would be established. The retreat or progression of the
drop must therefore have another cause, which has, in fact,
long been known. Since the alcohol greatly lowers the
surface tension of the water drop towards the air, a violent
extension-current is of course set up at once on the surface
of the drop, which has, as its consequence, a transfer of
fluid of the drop from the alcohol edge to the opposite one.
Here the alcohol rapidly evaporates again, for which reason
the extension-current persists, in the same way as we have
already seen similar currents persist for a long time. By
this continual flowing away of liquid from the edge of the
drop nearest the alcohol, it is caused to shrink away befbre
the alcohol.1

Berthold has paid no attention to these necessary and
so often described currents, and hence has also not noticed
that they are direct evidence against his explanation of
amoeboid movement. For instance, if we wish to apply the
phenomenon of the retreating drop to an Amoeba, we should
be obliged, on the contrary, to imagine that we had an
adhering drop of alcohol or some other fluid of relatively

1 A drop of this kind adhering to glass and retreating before alcohol, moves
therefore in exactly the opposite manner to that in which a drop that is sus-
pended in a second fluid, or at least is only very slightly adherent, would move
forwards under the same conditions ; for we know of old that the lowering of
the surface tension at the free surface of such a drop produces a forward
movement in the direction from the centre of the drop towards this point of
the surface. That this phenomenon is not exhibited in an adhering drop of
water is in any case a consequence of adhesion and of its being in air.
Even when the drop of water is in a fluid, and adheres strongly, the relations
may take a similar course. In my experiments with drops of oil and oil-
foam, I sometimes made the strange observation that in spite of the existence
of an energetically streaming centre of extension, they did not, as usual,
move forward in its direction, but in precisely the opposite direction.
Hence the course of events was exactly the same as for the drops of water, on
the supposition, that is to say, that the oil streaming away from the centre
of extension was not sufficiently replaced by the current streaming towards
it ; and in this way a continual abstraction from the drop at the extension
centre, and a continual addition to it at the opposite margin, was going on,
which produced a progression of the entire drop away from the centre of
extension. Formerly I was unable to explain this phenomenon satisfactorily ;
I now think that 'I was dealing with drops which adhered strongly, and for
which the relations were similar to those for water drops on a glass plate
when approached by alcohol.

298 PROTOPLASM

low surface tension, which was brought into contact on one
side with water or another fluid of higher surface tension ;
since water is less volatile than alcohol, the experiment
could not be carried out in the same manner as the reverse
one. Now, if the adhesion was increased, or, in other
words, the surface tension of the drop towards the glass was
diminished, by the surface of the drop of alcohol taking up
water on one side, so that this edge of the drop spread itself
out with diminution of the marginal angle, then, by reason
of the difference of tension on the free surface of the drop,
which would necessarily result, a superficial extension-
current would at once arise, whose centre of course
would be situated at the opposite edge of the drop. If
this current was continuous, as would of course be the
case if the polar difference of the surface tensions in the
drop was maintained — that is to say, if water was more
volatile than alcohol, — a movement forwards of the drop
towards the side of the water would be the natural con-
sequence.

From these reflections it seems to me obvious that, if
amoeboid movement had as its cause what Berthold ascribes
to it, a system of currents ought to be set up in an Amoeba
exactly the reverse of what actually exists. The currents
should flow away from the hinder end of an Amoeba on
each side and carry protoplasm to the anterior end. But
since it is notorious that the streaming takes exactly the
opposite course, I consider Berthold's hypothesis unsuitable.
Now, Berthold has well remarked that the currents in an
Amoeba run, in the main, just as if an extension-current
existed as the result of the surface tension being diminished
at the anterior end, as is the case in our drops of oil or oil-
foam. Nevertheless, he considers it incorrect to accept this
obvious hypothesis as a means of explaining amoeboid move-
ment. He is more inclined to think that the successive
spreading out of protoplasm at the anterior end of an
Amoeba takes place with considerable force, and that
thereby not only the axial up current, but also the back
currents on each side, are to be explained. In opposition
to this idea I must point out that it seems to me quite

CRITICISM OF BERT HOLD

299

impossible to explain both the back currents and the
regular circulation of the protoplasm as a whole in a simple
Amoeba by means of such a spreading out at the anterior end,
and all the less since we have found that the theory
necessarily demands an exactly opposite current.

Against the admissibility of the explanation which I
have put forth, Berthold finds an objection of great moment
in the fact which he claims to have established, namely,
that in the water surrounding an Amoeba, after mixing
carmine with it, no system of currents was to be observed
at its anterior end such as is required by the explanation.
With reference to this point I may remark that I regard
the observation of such currents as very difficult, when the
extent, for the most part very slight, of the currents of
Amoebae is taken into consideration, and that, therefore,
in the meanwhile, I still regard their presence as possible.
Unfortunately I have hitherto delayed inquiring into this
question myself.1 Yet I may refer to an observation which
shows that the apparent absence of currents in the surround-
ing water is not decisive with regard to the correctness of
the explanation. In small drops of oil, which were yet
considerably larger than most Amoebae, and which crept and
moved about very energetically under the influence of
surface tension, I could not demonstrate the existence of
currents of any kind in the surrounding water, with which
Indian ink had been mixed. This observation astonished
me very much at the time, since such currents are always
very distinct and strong in the vicinity of large oil-drops.
Hence, without attempting to explain the reasons of this
deviation from the rule, it seems to me of sufficient
importance to diminish the difficulties raised by Berthold's
objections.

If, however, we take our stand upon Berthold's hypo-
thesis, the complete absence of any phenomena of streaming
in the surrounding water would be just as strong evidence
against his explanation as against that put forward here.
Since Berthold's hypothesis is founded exclusively upon
the alterations of surface tension which are caused by

1 See Appendix at the end of the next section (pp. 317-319 infra).

300 PROTOPLASM

chemical changes at the anterior end of the body of an
Amoeba, extension-currents must necessarily arise, as I have
pointed out already, at the surface of the body of an
Amoeba, in connection with these changes. Hence, if
Berthold denies generally the existence of any currents in
the water surrounding an Amoeba, this is, in my opinion, just
as strong evidence against his own theory as against the one
brought forward here. I hardly think he could be of opinion
that the chemical changes in the protoplasm only extend to
the under side of an Amoeba, i.e. to its adherent surface,
since he regards the entire hyaline protoplasm of the
anterior end as that which is chemically changed. In any
case, however, this change must extend to the edge of the
adhering surface, and here come into contact with the sur-
rounding medium, so that differences of surface-tension
would necessarily exist in this region, and cause currents to
be set up. But, as I have already explained in discussing
the drops that retreat from alcohol, I consider it as on the
whole impossible that forward movements can be brought
about by such a change in the adhesion without accom-
panying differences of tension in the free surface of the
drop. On the contrary, such a change would only give rise
to a single alteration in the shape of the drop.

On the ground of the foregoing explanations, therefore,
I must regard Berthold's explanation of amoeboid movement
as unsuitable, at least in so far as it has been possible for
me to rightly understand his train of argument.

It seemed to me, however, of interest to test more
accurately, by means of experiment, the relations of the
system of currents in the drops of water, which are
theoretically postulated as necessary during their retreating
movements. It was thereby proved, after some unsuccess-
ful experiments, that the phenomena take in the main just
the course that was assumed above. In order to convince
oneself of this fact, it is best to proceed by placing drops of
water on a glass plate cleaned as well as possible, and then
causing a capillary tube, of not too great fineness, or a glass
rod, with ether, to approach their margin. If some ivory
black has been mixed with the drops, it can be observed

MOVEMENTS OF ADHERENT DROPS

301

even with the naked eye, or with a lens of low power, that
on the approach of the ether just the same phenomena of
streaming are set up in the drop which we formerly described
in detail for oil-drops, the tension of which had been lowered
at one spot by soap or something of the sort. The currents
are very violent, so that the eddies (A) arising on each side
are shown with great distinctness. When the drops flee
from before the ether, their edge, which is turned towards

Ether

Fig. 19.

the ether, is at first rather straight, and later even concave,
and with this change in the shape of the edge changes in
the currents are also apparent, which modify the original
appearances to some extent. An actual movement away
from the ether arises most easily when the drops are very
shallow ; deeper drops show the streamings and the shrinking
back of the edge turned towards the ether most excellently,
but the movement not so well.

If a more exact knowledge of the phenomena of streaming
within the drops be required, it is necessary to study the
relations existing in smaller drops under the microscope.

302 PROTOPLASM

Since the currents, as has been said, go on exceedingly
energetically, the appearances to be observed in such drops
with slight magnification are particularly beautiful, and very
suitable to complete our knowledge gained in another
way with regard to streamings in oil-drops. The appear-
ance presented by an energetically streaming drop is in
general that represented in the preceding Fig. 19. One
recognises in it at once the two eddies (A) which we
have already found before, but in addition to these some
secondary eddies may also be observed (B and C), the
positions of which, and their relations to the principal
eddies, can be plainly made out from the figure, so that I
will not enter into a further explanation of them here.
One phenomenon, however, of particular interest, appears
between the two principal eddies, and is especially dis-
tinct when the latter are placed rather far apart in the
direction of their breadth. It can then be remarked that a
dark and rather broad band is stretched between them, which
depends on the fact that in the interval between the two
eddies another eddy corresponding to the thick band extends
through the whole drop. Since this eddy is seen from

Fig. 20.

above, it necessarily appears as -a dark streak. This pheno-
menon is explained by the fact that in the whole breadth
of the drop the relations are essentially the same as are seen
on the two sides as it were in longitudinal section. A
median longitudinal section of the drop, of which a direct
view unfortunately is not to be obtained, would therefore
show something of the appearance represented in Fig. 20.
The sum of all the eddies which extend transversely through
the drop hence appears as the dark band. Since there is
a condition of relative quiescence in the interior of these

MOVEMENTS OF ADHERENT DROPS

303

eddies, colouring particles usually collect in them, especially
the coarser ones, which form a dark streak in the middle of
the band ; sometimes also these particles may be distributed
at quite regular intervals in the dark band. The peculiar
transverse line (Z) between the two eddies, which is in
continuation laterally with the secondary eddies (B), can
also be explained at once from the nature of the streaming
in the median longitudinal section. As we found in the
drops of paraffin oil, so also in the streaming drops of water
the black mixed with them for the most part gradually
collects in the posterior quiescent region, and from here
enters the forward current again.

Now if the ether be so closely approximated to the drop
as to cause its edge to shrink away, so that it finally flees
from it — which cannot be done so well with drops of water
mixed with black as with pure drops — the following process
is in the main exhibited. By the edge shrinking back
and becoming straighter and therefore broader, the median
forward current increases in breadth, and the two eddies (A)
become quite separated from one another. It then appears
as if there was only one very violent eddy in motion at the
edge, passing above from the margin to the opposite edge
of the drop, but soon descending downwards and rushing
towards the edge in proximity to the ether again. This is
the vortex current, which we have already become acquainted
with in the form of the dark transverse band. Only at the
most external portions of the edge of the drop are the eddy
(A) and the lateral back currents into the forward current
still to be seen. It can be easily explained how these
currents owe their origin to the fact that the ether now
exerts its action violently upon a broader portion of the
margin.

I will take this opportunity of remarking that, in the
well-known experiment, so frequently performed, of ap-
proximating a drop of ether to the surface of some water,
whereby a noticeable depression is produced in it under
the ether, or if the layer of water be very shallow, the
bottom of the vessel is even laid bare, the same vortex
movements can easily be demonstrated if ivory black be

304 PROTOPLASM

mixed with the water. If the layer of water is fairly
shallow, but not so much so as to be broken through by the
depression, and if the black has already collected to some
extent upon the bottom, it may be observed, on approximat-
ing a rod dipped in ether, that the colour is completely
removed from a ring -like zone corresponding to the
periphery of the rod, and at its inner edge is densely massed
in a black ring immediately under the rod. That is to say,
by the vortex current at the bottom of the vessel returning
towards the rod the colouring matter is all carried inwards,
and remains lying at the spot where this vortex current
ascends upwards again.

As to .the explanation of the retreating movement, however,
it results from these observations that the retreat must depend
upon the back currents in the drop being in excess of the
forward currents ; but this can only be due to the adhesion of
the drop, which offers a hindrance to the forward current which
goes on in the deeper layer. As a proof of this fact there
is also the observation, which has already been mentioned
above, that the retreating movement is especially pronounced
when the drops are very shallow. In any case, however,
all these observations confirm the view that the movements
of Amoebae cannot take place in this way.

Berthold, however, is willing to admit, as has been
already remarked above, that pseudopodia are occasionally
sent out by forces acting from within, somewhat in the
same manner as was supposed by the older observers,
namely, by contraction of the hinder part of the body of the
Amoebae (p. 102). Contractions of this kind may be pro-
duced by changes in the condition of imbibition of the
protoplasm (pp. 102 and 105). Finally, Berthold adds to the
three hypotheses already mentioned, concerning the causes
of protoplasmic movements, yet a fourth, in order to explain
the origin of fine filamentous pseudopodia, which rise up
free into their surroundings ; for which no one of the three
detailed is sufficient. Since Berthold's ideas of these
processes can scarcely be described briefly, on account of
the uncertainty of the forces brought into the problem,
I refer the reader to his memoir, and will confine my

QUINCKE'S HYPOTHESIS

305

remarks to a few words upon this, in my opinion, quite
untenable hypothesis. The forces which Berthold draws
upon to explain the development of the fine pseudopodia,
are of a chemical nature, namely, those which are sup-
posed to come into play during the solution of a solid
body, as exerting attractions between its molecules and those
of the solvent medium. Forces of this kind are supposed
to exert their activity between the surrounding medium and
the particles of the protoplasmic body, and, upon the supposi-
tion that its surface tension is very low, to be sufficient to
spin it out into fine pseudopodia. As can easily be seen,
this hypothesis recalls to some extent that of Mensbrugghe
described earlier (p. 65) with respect to the cause of the
pseudopodium-like outgrowths of oil-drops. I think, how-
ever, that Berthold's hypothesis is built upon much too
uncertain a basis, i.e. takes forces into account which are
altogether too hypothetical and uncontrollable for us to take
them earnestly into consideration. If Berthold's interpreta-
tion were correct, one might well expect that pseudopodium-
like processes would be seen to radiate out from a thick,
coloured gum solution, upon which water was poured,
which is by no means the case.

In any case, however, it would seem in the highest
degree improbable that protoplasmic movements should
have four different causes; it may rather be postulated
with some certainty that a common cause must lie at the
root of them all, even if it is not yet possible at the present
time to refer all the modifications to this cause.

In 1888 Quincke developed, in connection with his
observations upon superficial ex tension- currents as the result
of local diminution of surface tension, certain views upon
the explanation of the protoplasmic streams in plant cells,
etc., which agree in the main with the first hypothesis given
by Berthold. In its details, however, Quincke's explana-
tion seems to me untenable, since he has not sufficiently
taken into consideration the state of things that actually
exists in the vegetable cell. Quincke has the following-
idea of the structure of a plant cell. The protoplasmic
lining which occurs under the cell membrane consists of

20

306 PROTOPLASM

(1) an external "protoplasmic utricle," (2) the hyaline cuti-
cular layer (Hautschicht), and (3) the granular protoplasm.
The so-called protoplasmic utricle is supposed to be an
immeasurably thin, fluid oil membrane, for the most part in-
visible. Without Quincke's making any definite statement
with regard to the fact, it may be assumed that he was led to
suppose the existence of a so-called protoplasmic utricle by
the protoplasmic membrane of Pfeffer and others. Now the
streamings are supposed to arise from the formation of a
saponaceous compound (the so-called albumen soap) produced
by the action of the albumen of the cuticular layer upon the
fatty acid set free, by the action of oxygen, from the oil of
the protoplasmic utricle. This soap produces local diminu-
tions of surface tension on the inner side of the protoplasmic
utricle, and thus calls forth extension - currents. Let us
pause for a moment over this fundamental conception with
regard to the streamings which Quincke has put forth.
I do not think that it appears admissible, and in the first
place, chiefly from the following reasons. According to
Quincke's view the region in which the streamings take their
origin is situated close under the cell membrane, namely, at
the boundary between the immeasurably fine oily utricle and
the cuticular layer. Now it is known quite for certain, and
has often been demonstrated, that the most external layer of
protoplasm, which touches upon the cell membrane, is beyond
doubt quiescent in a large series of cases, and in fact that, as
in Cham, for example, the entire chlorophyll-bearing cortical
layer of the protoplasm is in a state of rest. A similar
condition is also shown by the Ciliata with cyclosis of
the endoplasm, where in the same way the cortical
protoplasm and the ectoplasm are in a state of rest, while
the internal protoplasm streams. In these cases it is
impossible that the seat of the movement should be found
at the internal surface of such an external utricle of oil,
but there is every reason, on the other hand, for believing
that, as has already been stated above in connection with
the views of Nageli, Schwendener, and Berthold, the cause of
movement has its seat at the limiting surface between the
protoplasm and the cell-sap. In the cyclosis of Infusoria,

AMCEBOID MOVEMENT

307

in which a cell-sap is wanting, special relations are in any
case presented which cannot be gone into until later on.
In addition to this difficulty, which, as it seems to me, alone
suffices to prove the untenability of Quincke's explanation,
there is yet a further one, namely, that since the cuticular
layer is everywhere in close contact with the oily utricle, it
does not in my opinion seem very clear why local extensions
of the so-called albumen soap should arise, since the formation
of albumen soap should go on along the whole surface of
contact between the cuticular layer, which is everywhere
albuminous, and the oily utricle.1 Hence these suppositions
scarcely seem to supply the conditions for the appearance of
definite and often quite one-sided streaming movements.

Since also the principles from which Quincke starts in
his explanation do not seem to me to be adequate, it would
be unnecessary at the outset to discuss more accurately the
explanations which he gives for special cases, such as cir-
culatory streaming, development of pseudopodia, etc.

(/) My own View of the Explanation of amoeboid
Movement

At the commencement of this chapter it was pointed out
that I should consider the possibility of an explanation,
which my conception of protoplasm furnishes in the case of
the simpler phenomena of movement at least, as a confirma-
tion of the correctness of the interpretation which has been
attempted of its structural relations.

In passing on to attack this question more closely, I
must remark at the outset that in spite of all my efforts
such an explanation seems at present feasible only for
amoeboid movement in the strict sense, while other modifi-
cations of it, especially the formation of the fine pseudopodia
of numerous Sarkodina, obtain no explanation.

The movement of simple Amoebae, such as A. guttula,
Umax, and blattce, and Pelomyxa, is so exceedingly similar

1 It could only be assumed in some way that oxidation, and hence the
appearance of free fatty acid, took place locally in the oily membrane.

308 PROTOPLASM

to the streaming drops of oil-lather described before — in fact
so entirely their exact counterpart in all important points —
that I am completely convinced of the agreement of the
forces at work in the two instances. In these Amoebae also
we find an axial stream which passes through the axis
towards the progressing anterior end, there bends round on
each side, though certainly in other directions also,1 flows on
the exterior of the body for usually a relatively short distance
backwards, and then comes to rest. The axial stream draws
protoplasm to itself from all sides at the posterior end, and
in the same measure that this protoplasm from behind passes
into the current, the quiescent lateral protoplasm is carried
farther backwards, and then by degrees passes into the axial
stream again. The single essential difference, which is usually
shown between such Amoebae and streaming drops of oil-
foam, is this, that the extension-current of the anterior
end for the most part only extends, as has been said, a
comparatively short distance backwards, and that it comes
to rest relatively quickly. In the drops of oil-froth, how-
ever, the extent of the current in question also depends, on
the one hand, upon the intensity of the forces at work, on
the other hand, upon the viscidity of the oil. It can often
be observed that feeble extension-currents are only continued
a little way towards the hinder end, so that the conditions
become quite similar to those of the Amoebae described. I
am hence convinced that the explanation of the phenomena
of streaming in these Amoebae must be the same as that we
put forth for the froth-drops.

If we wish to apply the explanation given for foam-
drops to the phenomena of movement in Amoebae, it will be
necessary, in the first place, to examine into the nature of
protoplasmic substance a little. The aggregate condition has
already been briefly considered above, from which it resulted
that both the framework and the intervening substance must

1 It is easy to convince oneself in Pelomyxa of the fact that the back cur-
rent at the progressing anterior end, or at the tip of a pseudopodium, as the
case may be, goes on over the entire free surface, and not merely at the two
sides, where it usually conies into view. With a suitable focus it can
always be plainly seen that the back current stretches over the whole free
surface.

THE NATURE OF PROTOPLASM 309

be fluid. It is clear, as well from all the observations which
we collected upon this point as from our theoretical concep-
tion and explanation of protoplasmic structure, that the in-
tervening substance must be interpreted as a watery solution.
With this interpretation Reinke's investigations, upon the
enchylema that may be squeezed out from dZthalium septicum,
are completely in harmony. With reference to the framework
substance our view requires, in the first place, that it should
be a fluid substance insoluble in water. It is clear that
this substance contains albuminoid bodies. From the most
recent observations it becomes more and more probable that
the principal component of the framework substance is
an albumen compound related to the nucleins, the so-called
plastin. Reinke has interpreted the plastin, first clearly
recognised by him, in ^Jthalium septicum, and forming
according to his calculation 27*4 per cent of the protoplasm
when dried in air, as a combination of albumen and
nuclein, possibly further accompanied by a number of mole-
cules of a fatty acid belonging to the stearic or oleic acid
series. In any case it results from these and numerous
micro-chemical observations of more recent times (compare
especially the works of E. Zacharias and Fr. Schwarz) that the
foundation of the framework substance is not an albuminous
body in the ordinary sense. All that we know of the pos-
sible nature of this substance is indeed very little, but
nevertheless enough for it to be not inconceivable to us that
it is insoluble in water, a fact still more intelligible if
Reinke's supposition, as to molecules of fatty acid entering
into its constitution, receive further confirmation. A series
of reflections, based upon an entirely different foundation
from Reinke's, led me to suppose, quite independently of his
speculation, which I did not know of till later, that the
chemical basis of the framework substance must be
formed by a body which has arisen from a combination
of albuminoid and fatty acid molecules. Since, as has
been said, it appears quite possible for such a body to
be insoluble in water, I hold the assumption of an oily
membrane or something of the sort, which would protect
it against the action of water, to be unnecessary ; yet it

310 PROTOPLASM

must be admitted, on the other hand, that, with the
supposition of such a chemical composition for the sub-
stance of the framework, the appearance of an oil membrane
as the result of the decomposing action of water is rendered
possible.

If the protoplasmic framework is composed of a body of
this kind, it is quite intelligible that local differences in
surface tension must produce phenomena of movement
similar to those which have been observed in the drops of
oil-froth. It is only a question whether the enchylema also
seems suited to play the part which pertains to it. With
reference to this point it is now specially important that,
according to the observations of Eeinke and Eodewald, the
enchylema has an alkaline reaction, which is observable in
the fluid squeezed out. That protoplasm as such has an
alkaline reaction, has been noted by a series of observers,
among whom I specially mention Fr. Schwarz. Eeinke and
Eodewald think they may conclude that the alkalinity
of the enchylema is produced by NH3 or NH4NH2C02.
Schwarz disputes this view, and attempts to show that com-
pounds of alkalies with protein bodies probably cause
this phenomenon. The possibility that saponaceous com-
pounds may be the cause of the reaction has not been
hitherto taken into consideration. Now whether the alkaline
reaction of the enchylema depends upon the one or the other
of these causes, the mere fact that there is such a reaction,
as well as that fats are probably never wanting in proto-
plasm, and that it is not, on the other hand, improbable that
fatty acids enter into the composition of the framework
substance, render it very possible indeed that the enchylema
must also contain saponaceous compounds in solution ; that
is to say, that it is perfectly capable of playing the part
which pertains to it, according to our conception of the
processes of movement. Since it may seem very premature
to speculate upon so obscure a subject as the connection
of the chemical processes in protoplasm, I content myself
with these remarks.

The explanation of the processes of movement in
Amcebse is to be found, therefore, to my mind, in corre-

MOVEMENTS OF AM(EBA? 311

spondence with the interpretation of the phenomena of
streaming movements in the drops of foam, in the fact
that, by the bursting of some of the superficial alveoli,
enchylema is poured out upon the free surface of the proto-
plasmic body, where it produces a local diminution of
surface tension, and in this way sets up an extension
centre together with forward movement.1 In this way
are explained not only simple amceboid movements, from
which we started, but also more complicated movements
and changes of form by means of finger-shaped pseudo-
podia. The formation of such pseudopodia takes place
with phenomena of streaming movement corresponding
perfectly to those which go on throughout the body -of an
Amoeba which streams in a simple manner; in these
pseudopodia it is therefore merely a matter of local extension-
currents, reaching over a short distance only.

In AmcebiB, however, an additional circumstance seems
to come into play, as has already been pointed
out above, which has the effect of produc-
ing a limitation in the extension -currents.
In the formation of a finger-shaped pseu-
dopodium of Amoeba proteus (Fig. 21) it
can be seen that the current which traverses
the axis of the pseudopodium and flows
away on all sides from its tip, comes to rest
at a very short distance behind the tip — a circumstance
which in any case is extremely favourable to the rapid

1 A. G. Bourne has pointed out, in an investigation that has recently
appeared upon the newly-discovered Pelomyxa viridis, that the alveoli or
"vesicles," observed by him in the protoplasm of this Rhizopod, do not burst
in the movement, or rather in the development of pseudopodia ; he thinks
that this observation opposes my view as to the causes of amceboid movements.
In answer to this I must state explicitly that the "vesicles" described by
Bourne certainly have nothing whatever to do with the true alveoli of the
protoplasm. They are spherical structures filled with green contents, and
their considerable size must alone exclude a comparison with the true alveoli
of protoplasm. Of the true, and very much finer protoplasmic structure,
Bourne has observed nothing. What these green "vesicles" really were
I will not here further inquire, though in spite of assertions to the contrary
made by the discoverer of Pelomyxa viridis, it is difficult, if all the other
known relations are taken into account, to suppress the notion that they are
nothing more or less than Zoochlorellre.

Fig. 21.

312 PROTOPLASM

outgrowth of the pseudopodium, in contradistinction to the
relations that obtain in the drops of foam, since the
protoplasm that has come to rest is heaped up and the
pseudopodium grows in this way. These relations, as
well as those of the simply streaming Amoebae, evidently
seem to indicate that it is only at the anterior end of the
Amoeba, or at the extremities of the pseudopodia, as the case
may be, that sufficient fluidity exists for the extension of the
current, and that farther back, on the contrary, in all
probability by the action of the surrounding medium, the
surface soon becomes more viscid, and the current hence
dies down rapidly. That the surface of the body of the
Amoeba, and in particular the pellicle, is of a membranous
nature, has indeed often been pointed out, and follows with
tolerable certainty from other peculiarities.

In this respect the state of things at the posterior end
of many Amoebae must be taken into special consideration.
It is notorious that this end frequently bears a tuft -like
bundle of fine processes, which have often been compared
to pseudopodia. This tuft, however, certainly bears no close
relation to real pseudopodia, but is a phenomenon which
almost regularly accompanies the retraction of pseudopodia,
as can often be very well demonstrated in A. proteus, for
instance. In an Amoeba which simply streams along, in
which the hinder end is in fact in a continual state of
retraction, so to speak, the tuft must naturally attain a
special development in this region. If the retraction of a
pseudopodium be followed, it may be noticed that it gradually
becomes covered with short papillar processes, which
pari passu with the diminution of the pseudopodium become
narrowed into fine processes, or even become, in part, split
up into such, so that finally a tuft of fine processes remains
in the place of the pseudopodium. These processes then
fuse into a small eminence, which gradually becomes flattened
down and passes into the general protoplasmic mass of the
body. If numerous pseudopodia are drawn in at the same
time, a considerable portion of the surface of the Amoeba
may be covered with such tufts.

The most probable explanation of this phenomenon which,

EXPLANATION OF THE MOVEMENTS 313

as has been said, so especially characterises the posterior
end, is, judging from the course it takes, somewhat as follows.
As has been remarked above, it is very probable that
the surface of the body of the Amoeba is formed by a
viscid membrane-like layer. The backward flow of the
pseudopodia, like the gradual retraction of the hinder end
of the Amoebae that moves forwards in a simple manner,
depends, in my opinion, only upon the cessation of the
forward current, and the flowing back of the protoplasm
towards other directions. During this process the pseudo-
podium or the hinder end diminishes continually in size,
and meanwhile the viscid external layer cannot flow
together rapidly enough to keep pace with this diminutioh,
in consequence of which it is thrown into folds, which
appear as papillose processes. The whole phenomenon gives
just the appearance of a viscid, membrane-like layer, which
shrinks into folds on account of the gradual emptying of its
contents. With continued emptying of the contents these
folds become more numerous and fine, so that the com-
pletely shrunken layer is finally attached in the form of a
tuft-like bundle of fine processes. These processes or folds
then become closely apposed, and finally stick together.
Meanwhile they are removed from the action of the external
medium, which, as we supposed, is the cause of the cuticle-
like toughness of the superficial layer ; this removal, as well
as the influence of the interior of the Amoeba, which now
makes itself felt upon the tuft, has the effect of gradually
making it become fluid ; and the folds or processes fuse in
the above-described manner, whereupon the product of the
fusion and the rest of the protoplasm finally flow together.

That the origin of the tuft is really due to shrinkage
of the membrane-like external layer is also probable from
the fact that by treating Amoeba proteus with fairly concen-
trated NaCl solution (4 per cent), the same papillar
processes can at once be produced over the whole surface,
accompanied by considerable shrinkage of the Amoeba, and
in this case the processes certainly arise by folding of the
external layer, as a result of a decrease in the volume of its
contents. With 0'02 per cent caustic potash I also saw

314 PROTOPLASM

exactly similar appearances arise over the entire surface.
Moreover, it has been known for a long time back that the
formation of fine processes can also be effected by salt
solution over the whole surface of certain Amoebae ; processes,
that is to say, such as usually compose the posterior tuft.
The following observation, which I made casually upon
Amoeba proteus, is also evidence for the correctness of
the explanation here attempted of the formation of the
tuft. A specimen, which had been treated for a long time
with 0*05 per cent solution of caustic potash, suddenly
burst at a spot, as one frequently observes. Thereupon
the internal protoplasm flowed out, and the membrane-like
envelope shrank up together very much, at the same time
assuming the bristly appearance of the tuft over its whole
extent. As has been said, this observation seems to prove
for certain not only the existence of the tough membrane-
like enveloping layer, but also the great probability of my
explanation as to the formation of those fine processes or folds.
The bursting, here described, of the Amoeba, together with
the flowing out of the relatively fluid internal protoplasm,
may frequently be observed under the action of various
reagents, and also under a long-continued action of the con-
stant current ; on the other hand, a shrinking of the
enveloping layer in its whole extent, which has just been
described, I only saw once in this manner.

Hence if we are constrained to admit the existence of a
tough, membranous layer on the surface of numerous
Amoebae, the question is then raised, in what way this layer
becomes liquefied at the anterior end, or rather at the spots
where the pseudopodia develop ; for there can be no doubt
that it must be liquefied. In this process may be traced
a result of external local stimuli which concern the
Amoeba. That such stimuli must in the last instance
be the cause of the movements, and of the development
of pseudopodia, is beyond doubt. Nevertheless I do not
think that the liquefaction is in direct connection with this
fact, but that the outflow of enchylema, which is produced
by the bursting of some of the alveoli, is the primary cause
of the liquefaction of the superficial layer. This is, in fact,

DIFFICULTIES OF THE THEORY 315

quite natural, inasmuch as the internal protoplasm, which is
subject to the action of the enchylema, is quite fluid, for
which reason it does not seem an unwarrantable assumption
that the viscid external layer would also become liquefied
again if it was temporarily removed from the influence of
the water by a spreading out of enchylema on its outer
surface.

If, as I think, we have found in this interpretation of
amoeboid movement an explanation which is both very
probable and harmonises well with the observations upon the
froth-drops, it should nevertheless not be ignored that the
same explanation cannot be applied off-hand with good
results to fine reticulose pseudopodia. It is, of course,
quite conceivable that here also thicker pseudopoclia may
possibly develop in the way described, but on the other
hand I willingly admit that the explanation of filament-
ous pseudopodia, frequently of excessive fineness, cannot
be reached in this way. It is sufficiently obvious, from
the description which has been given before, that in these
pseudopodia other and special relations come into the
problem, which are not as yet satisfactorily cleared up.
I refer in this respect more especially to the behaviour of
the long filamentous pseudopodia during their retraction.
It is well known that during this process they for the most
part become suddenly relaxed in a peculiar manner, and
even occasionally assume a zigzag or spiral form. Although
we are not able to explain this peculiarity off-hand, it may
be taken, as has been said, as a proof of the fact that there
are here other peculiar conditions lying at the root of the
matter.

It has already been shown above that Berthold's
attempt at an explanation of these fine pseudopodia,
which are also frequently raised up free in the sur-
rounding medium, is in no way satisfactory. Just as little
satisfactory is the explanation given by Quincke. The latter
seeks to refer the origin of pseudopodium-like bridges and
threads of protoplasm, such as so frequently traverse the
cell sap of plant cells, to the formation of firm threads of
albumen at the boundary between his protoplasmic utricle

316 PROTOPLASM

(oil membrane) and the cuticular layer. These firm threads
of albumen are supposed, on their part, to arise by the
action of oxygen upon the dissolved albumen, which, as
Quincke has shown in the case of egg albumen, forms a firm
membrane-like envelope under the action of this gas. The
firm threads of albumen which have arisen in this manner are
supposed to be torn loose by the streaming movements and
to be carried into the interior of the cell, where they form
an internal framework traversing the cell sap. As they are
torn loose the filaments take with them an envelope of oil
from the oil membrane. In consequence the protoplasmic
masses are then free to move upon these oil-covered fila-
ments by means of extension-currents, in the same way as
the protoplasm of the wall moves upon the external oil mem-
brane. In the same manner Quincke thinks the fine pseudo-
podia of Sarcodina may also be explained, since he remarks
(p. 641): "The pseudopodia appear to be just such thin
filaments of albumen covered with oil, along which solid
albuminous granules are carried up and down by periodic
extension movements, just as in the interior of the plant cell."
Although there is, perhaps, much to be said for this concep-
tion in the case of the explanation of the so-called granular
movement on the pseudopodia, yet it in no way explains
the formation of the fine pseudopodia themselves. For
both their gradual development and the formation of
bridges and filaments of protoplasm in the cell sap of plants,
which, according to the statements of many trustworthy
observers, frequently develop just like the pseudopodia of
Sarcodina, make it impossible to refer their origin to the
breaking loose of solid threads of albumen, which the
streaming movements displace as pseudopodia.

As far as Quincke's interpretation, which we have just
quoted, of the pseudopodia themselves is concerned, it may
perhaps be justifiable to a certain extent, inasmuch as we
have already seen that the study of the pseudopodia had
long ago led M. Schultze, and again myself also recently, to
the supposition that possibly a firm thread may form the
axis of the pseudopodium — a supposition to which their
analogy with the state of things in the Heliozoa adds

CURRENTS CAUSED BY AMCEB^ 317

weight. It is well known that R Hertwig succeeded in
rendering probable the existence of such an axial thread
for some Radiolaria also.

As has been remarked, however, I regard it as still pre-
mature at present to think of a final explanation for the
formation of the fine pseudopodia, for we cannot, unfor-
tunately, say even for a moment that we have obtained a
satisfactory conception of the relations between their struc-
ture and movement, which must, however, be indispensably
the preliminary stage of any explanation. Hence, however
convinced I may be of the fact that to the explanation
attempted by me of the protoplasmic movements of Amcebcc,
etc., there attaches a further and essential significance for
the processes of movement exhibited by protoplasm gener-
ally, I am equally convinced, on the other hand, that it
would be very difficult to work out the explanation of the
numerous special cases which exist on the basis of that
principle at the present time, or at any rate that their
explanation could only be achieved by the help of numerous
subordinate hypotheses, which would considerably diminish
the probability of the explanation. I therefore consider it
not worth while to pursue this uncertain path with earnestness,
but hope that with a renewed study of the processes of
movement, which we shall probably not have to await very
long, in connection with the ideas put forward here as to the
probable causes of those processes, more sure foundations of
fact may be discovered for the solution of these questions.

On the Currents in the Water surrounding Anwbce, etc.1

I have already expressed my regret that I did not earlier
test the important question as to the existence of currents
in the water surrounding a moving Amoeba. Having recently
had an opportunity in an object so excellent for this purpose
as Pelomyxa, I must say that the ordinary small Amcebce offer
very little occasion for the solution of this question. Now
although during frequent observation of the processes of move-
ment in Pelomyxa I invariably was astonished by the per-
fectly complete agreement of its movements, even in detail,

1 An addition made by the author in April 1892.

318 PROTOPLASM

with those of the drops of oil-lather, I was necessarily the
more astounded when it was shown by observation of the
Pelomyxa creeping in water, with which Indian ink or ivory
black had been mixed, that currents, directed in the same sense
as the superficial protoplasmic streaming movements, do not, as
a matter of fact, exist in the surrounding water. If the stream-
ing movements of the Pelomyxa are not very powerful, it really
does appear as if no currents at all went on in the surrounding
water, as stated by Berthold. If, however, one observes closely
the anterior end of a Pelomyxa streaming forward very ener-
getically, or a pseudopodium which is developing powerfully,
it can be made out that currents do exist in the surrounding
water, but, strange to say, currents which run in exactly the
opposite direction to what was expected, and which do not
pass along in the same sense as the superficial back current at
the anterior end, but in a reverse direction, that is to say, they
rush towards the anterior end, i.e. towards the supposed centre
of extension. Considering the importance of the matter, I have
not left it to be judged by the eye, which might easily be
deceived, but have definitely traced the existence of these
currents with the ocular micrometer. I will take this oppor-
tunity to state again, that in streaming drops of oil -foam of
larger size I have frequently convinced myself of the presence of
currents running in the same sense.

I do not underrate the consequences of these results. They
necessitate the admission that the explanation of amoeboid
movement brought forward by me above is inadequate, i.e. that
in it there must at least be one discordant point, in which
Amwbce behave differently from the drops of oil -foam. I have
already remarked that the study of the movements of Pelomyxa
shows in other respects so complete a similarity to those of the
oil-foam drops — apart from the divergence that has been pointed
out — that I cannot doubt as to the identity of the forces in
operation in both cases. Unfortunately I am not in a position
to give an explanation of this difference off-hand. In any case
all that I can suppose is somewhat as follows. Perhaps the
behaviour which we have described in the Pelomyxa points to
the fact that the surface of the protoplasmic body is enveloped
by an extremely fine, viscid layer of a chemically different
nature, such as Quincke has assumed in the oil membrane, and
that further the forces of tension which are at work make their
appearance, as he supposes, at the limiting surface between this
membrane and the protoplasm below. Under these conditions
it may perhaps be imagined that the backward current which
is necessarily present may go on in the internal zone of this fine

MOVEMENTS OF GRANULES 319

membrane, bordering on the protoplasm, while in its external
zone, as is equally necessary, a stream runs forward to the
anterior end, which is alone that which makes itself felt in the
surrounding water, and thus causes the current that is so
strangely reversed in the latter. It is a question whether we
are justified in assuming double currents, running one upon the
other, in a membrane of such extreme tenuity as that postulated
must be. In this respect I would like just to refer to the
following observation, which I made as far back as the seventies
on the occasion of studies upon cell division, when I was induced
to occupy myself a good deal with phenomena of surface tension.
In the extremely thin membrane of large soap-bubbles it is
possible to produce very violent streaming movements by ap-
proximating volatile substances, such as NH3, alcohol, etc., i.e.
by disturbance of the tension, without the membrane bursting.
In this process, in spite of the thinness of the membrane,
currents must pass one over the other, afferent and efferent
currents, otherwise the thin membrane would burst at once. If,
however, it was a question of an oil membrane, such as Quincke
assumes, it would not be possible at all for it to burst under the
given conditions, since its tension at the surface bounding it
towards the surrounding water must in any case be considerably
greater than that at the surface which limits it towards the proto-
plasm, for which reason it could not be made to burst from this
side. I must therefore regard the double currents in a thin
fluid membrane of this kind as being quite within the bounds
of possibility.

For the rest, some advance may probably be made at this
state of the question by means of suitable experiments.

(k) Independent Movements of Granules

Certain points in the problem of protoplasmic move-
ments must, however, I think, be briefly touched upon now.
Amongst them the question of the relations of the so-called
protoplasmic granules to the streaming movements seems to
me one of the most fundamental. It is notorious that the
movements of protoplasm have frequently been estimated
only by the movements of these granules which have
served to a certain extent as indices of the streaming move-
ments of the protoplasmic ground substance. In keep-
ing with this there exists an almost universally occurring

320 PROTOPLASM

idea that the granules possess no power of movement of
their own, but are only carried about by the streaming
movements of the protoplasm, upon or in which they are
lodged. Berthold also represents this view, which has been
current since M. Schultze.

When I was following out the phenomena of movement
exhibited by these granules, as they can be plainly observed
in plant cells (Tradescantia hairs, for example), I was
involuntarily forced to the idea that their movements could
not be in any way passive, in the sense that they were
simply carried along by the streams of protoplasm as sus-
pended corpuscles, but that they must, in a certain sense,
be of an active nature, i.e. that the cause of movement
must reside near or within the granules themselves.
Although this idea was always aroused, as has been
remarked, by the consideration of vegetable cells and
Sarcodina, I could not come to any decision upon this
question in objects of this kind, which at the same time
exhibited lively protoplasmic movements. Only by the
study of a peculiarly favourable object, which recently came
into my hands, was a sure proof at last obtained that such
an automatic movement of the granules must, as a matter of
fact, take place. This object is a large diatom of the genus
Surirella. At the limiting surface of its protoplasm turned
towards the cell sap there are numerous granules in a state
of incessant movement to and fro in the most various
directions, which have already been mentioned before as
chromatin-like granules (p. 91). It seems a point of very
special interest that these motile protoplasmic granules
are only to be met with in this organism at the surface
of the protoplasm by which the latter is limited towards
the cell sap, while I was not successful in finding corre-
sponding granules in the interior of the protoplasm. It is
also shown beyond a doubt, by tracing their movements
more accurately, that they glide along the limiting surface
of the protoplasm, and partly, at any rate, project from the
protoplasm into the cell sap. Now since, as I have already
briefly described in another place (1891), the protoplasm of
this diatom is itself in a state of relative quiescence, as can

"SLIDING MOVEMENT"— ITS CAUSE 321

be distinctly demonstrated by the stability of its reticular
and radiating structures, it follows that the granules must
possess a movement of their own, and that it is impossible
to suppose that they are being carried along by streams of
the protoplasm.

This conception of granular movement is not so new as it
might appear from the widespread belief in the contrary view.
Nageli at any rate has described, as far back as 1855, a
granular movement quite corresponding to that here
described on the inner surface of the primordial utricle of
Desmidiacece (Closterium in particular) ; he has termed it
"sliding movement" (Glitsclibewcguwj). The movement
also of the granules on the inner surface of the prptoplasm
in Achlya, where the cell sap is traversed by protoplasmic
filaments, as frequently occurs also in Surirella, is regarded
by Nageli in just the same manner. This so-called sliding
movement has later been comprised as a subordinate case of
general protoplasmic movement (so also Berthold, 1886, for
instance), in which the streaming movements of the proto-
plasm are very feeble and irregular. Since, at an earlier date,
when protoplasmic structures had not been accurately traced,
it was impossible to decide with certainty whether the move-
ment of the granules was caused by the general streaming
movements of the protoplasm or not, there was much to be
said for the view, which subordinated the particular case to
the more general phenomenon. Since, however, we are now
able to convince ourselves, as has been said, that the proto-
plasm as such does not take any share in the movements of
the granules in Surirella by means of any noticeable stream-
ing movements or displacements, this explanation falls to the
ground. On the ground of his observations upon the so-
called sliding movements, Nageli, and with him Schwen-
dener (1865), held fast to the view that the protoplasmic
granules must also possess an automatic power of movement
in circulation and rotation, and that the seat of the motor
forces was to be looked for in the granules themselves.
Originally, in 1855, Nageli thought of hydro-electric forces,
but later (1865) he preferred to assume that the so-called
sliding movements, and hence, of course, the cause of the

21

322 PROTOPLASM

automatic movements of the granules in general, was a
molecular movement modified by adherence to the proto-
plasm.

Velten (1876) held that it was quite uncertain whether
the granules moved actively or passively, and has dealt
with this question thoroughly in his memoir " Activ oder
Passiv" ((Esterreich. Man. Zeitung, 1876, No. 3).

Although by reason of my own observations I must rank
myself altogether on the side of Nageli's view of the auto-
matic movement of the granules, in so far as they are
situated on the inner or the outer surface, as the case may
be, which limits the protoplasm, I am nevertheless unable
to share his opinion concerning the alleged cause of their
movement. I incline rather to the belief that the view
expressed by Quincke with regard to this cause, so far as it
concerns the independent movement of the granules, comes
the nearest to the truth. The granules, situated upon the
limiting surface of two liquids — a viscid one, the protoplasm,
and a more fluid one, the cell sap — move in all probability
from the same cause from which pieces of camphor move to
and fro continually on the surface of water.1 The cause in
question is that the granules continually effect a change in
the surface tension at the limiting surface of the two liquids
in their vicinity, as a result of which they of course move
towards the direction in which the surface tension is
heightened. With this change of tension feeble currents on
the outermost superficial layer of the two liquids are of
course connected, which, however, being very transitory and
feeble, only penetrate a small distance inwards, and therefore
do not call forth actual streaming movements in the proto-
plasm. I am of opinion that the assumption of a universal
occurrence of such automatic granular movements would set
aside many difficulties which have hitherto been raised in the
explanation of protoplasmic movement. The sudden stoppage
of these movements, their frequent reversal, the movement of
granules on the finest filaments of protoplasm in exactly
opposite directions, and finally, the frequent phenomenon of

1 Compare for these and numerous allied phenomena, van der Mensbrugghe,
1869, more especially.

INTERNAL MOVEMENTS 323

granules overtaking one another on very minute filaments —
all these are phenomena which, as I believe, can be under-
stood much more easily on the assumption of such an
automatic power of movement, than on the hitherto current
supposition that the movement of the granules is due solely
to the general streaming movement of the protoplasm.

(I) Causes of Internal Displacements in the Alveolar
Protoplasm

A further problem would be whether, on the same prin-
ciple, corresponding granules in the interior of the proto-
plasm could also carry on movements. I do not v consider
this possibility as excluded. Since the protoplasm, ac-
cording to our conception, is a system of very minute
lamellae of fluid, in which the cavities of the meshes are
filled by another fluid, the enchylema, it is very possible
that important consequences may result in this way affecting
the internal movements of protoplasm.

In such a system of fluid lamellae, as soon as the tension
of a lamella is altered, an influence must be exerted upon
the arrangement of the system. If the tension of a lamella,
which meets two others, in the way earlier described, at
angles of 120°, is raised, the lamella in question must contract
or shorten, so that the two lamellae will meet at an angle which
is less than 120°, and the resultant of their tensions now
maintains a state of equilibrium with the increased tension
of the first lamella. In the opposite case, with lowering of
the tension of the first lamella, there will, of course, be an
increase in its size and an enlargement of the angles of the
two others. That these theoretical assumptions can be
proved to be correct by means of experiment has already
been shown by Plateau (vol. i. pp. 368-370), who succeeded
in bringing about in the lamellar framework obtained by
dipping a wire cube into a glycerine solution of soap, both
contraction-like shrinkings and, on the contrary, enlarge-
ments of the central lamella, as the result of altering its
tension both by differences of temperature and by bringing
it upon other fluids of greater or less tension. Under

324 PROTOPLASM

these circumstances it seems certain, therefore, that in
foam-like protoplasm local alterations of the tension of
certain lamellae must produce immediate changes in the
shape of the alveoli, such alterations of tension being caused
either by the granules of the protoplasm or by something
else. In this way it becomes very probable that the
granules, if they possess the properties attributed to
them, may also give occasion to phenomena of movement in
the interior of the protoplasm, but that numerous other
causes also, which produce a change in the tension of
certain lamellse, are able to take effect in a similar manner.
For it is to be expected that every chemical change
in the protoplasm of the lamellae, as well as in the contents
of individual alveoli, will alter the tension of the lamellae,
and that in this way changes of shape and consequent
displacements of the alveoli must continually take place.

It seems to me therefore very probable that the irregular
undulating movements to and fro, which are to be observed
in nearly all protoplasm, depend on the causes which have
been named, and that, in fact, they are inevitable, so to
speak, if the conceptions which I have developed with
regard to protoplasm are admitted to be correct.

Whether these internal processes of movement, to which
I have already referred in 1888 (see Protozoa, p. 1397),
can also develop into regular streaming movements, seems
to me doubtful ; nevertheless I would not altogether deny
this possibility in the case of the phenomena of streaming
movement in the endoplasm of Ciliata. Since there is in
these forms no cell-sap cavity, which in plant cells, as we saw
above, is of great importance for the appearance of extension-
currents, we are in this case only able to indicate the mouth
opening as the region where such currents originate, since it
is here that the endoplasm usually comes into contact with
the surrounding water. Although I do not consider it
possible that an extension-current, starting from this point,
and as a rule only taking effect upon one side, is sufficient
to explain the circulation of the endoplasm of the Ciliata, I do
not wish to enter more thoroughly into the point, since so to
do could not be productive of much result without a special

MUSCULAR CONTRACTION 325

study of the individual cases. The streaming seems to
take the simplest course in Didinium. Here an extension-
current starting from the internal opening of the oesophagus
would explain the circulation, if it appeared on the whole
possible to refer the streaming movements of the endoplasm
of Ciliata to an extension-current of so simple a nature.

(m) Possibility of an Explanation of Muscular Contraction
in this way

On the other hand, I should like to point out that
the above-discussed causes of the changes in shape, and the
displacements in the alveolar framework, seem to me to
indicate a future explanation of the contraction of muscle
fibrils. Although it
is not my intention,
as has already been
remarked before, to
enter more closely in
this work into muscle
cells, the structure of
which requires much
more accurate clearing
up before a satis-
factory explanation of
their contraction is
to be thought of,
I will nevertheless

refer briefly to this case.1 Let us imagine as simple a
muscle fibril as possible, consisting only of a single row
of protoplasmic alveoli arranged one behind the other, which
are enclosed in the usual protoplasm, the sarcoplasm, of
the muscle cells. The accompanying Fig. 22 is intended
to represent a short extent of such a muscle fibril (//),
together with the contiguous sarcoplasm, in longitudinal

1 In 1888, in my Protozoa, p. 1317, I had already pointed out the possi-
bility of an explanation of muscular contraction, in the way which is set forth
rather more accurately in the sequel here.

326 PROTOPLASM

section. Let us also imagine that a chemical change of the
enchylema suddenly takes place in the sarcoplasm enclosing
the fibril, as a result of which the tension is raised at
the boundary between the enchylema and the protoplasmic
lamellae : this change must influence the system of lamellae
as follows. In the transverse lamellae ss of the sarcoplasm
the tensions of both their limiting surfaces are heightened,
while those of the lamellae mm are only increased on the
outer side, where they border upon the enchylema of the
sarcoplasm. Hence the higher tension of the lamellae ss
will result in their contraction and diminution in size ; but
at the same time the lamellae mfm! of the fibril, since their
tensions are not changed at all, must increase in size or
stretch, since the lamellae mm bordering upon them have their
tensions heightened. Hence in any case the nodal points
xx} y, and z must be displaced outwards from the centre of the
alveolus towards the sarcoplasm. The cross section of the
alveolus xyzx will therefore assume somewhat the shape
which the figure xfy'zfx' drawn in dotted lines represents, in
which process it is to be expected that the side x'y' will
form a convex surface towards the centre of the alveolus,
since only under these conditions is a state of equilibrium
possible between the tensions of the lamellae which meet in
the nodal points a/ and y'. In the same way, however, it
is also to be expected that during this process the alveolus
as a whole will widen in the transverse direction, which,
since its internal volume must remain the same, can only be
brought about by the height of the alveolus diminishing.
Now since this will take place under the conditions given
for all the alveoli of the muscle fibril, it will follow
that the slight shortenings of these alveoli will be
summed up, and in this way will bring about a considerable
shortening of the muscle fibril as a whole. If the cause of
the difference in tension vanishes again, the former con-
dition must naturally be reverted to in the opposite way.

Without entering more closely here into the finer
structure of the muscles, it will be understood that the same
effect will come about when it is not a question of a fibril
of the simplest kind, as was supposed, but of a plate-like

CURRENTS IN PLANT CELLS 327

fibril, or rather a contractile column, which consists of a
single layer of alveoli ; the same action will be manifested
in the same way, if the column consists of a double layer of
alveoli. The conditions are less favourable if the muscle
column is more than two layers of alveoli in thickness,
because the alveoli are no longer all in contact with the
sarcoplasm.

I think I have shown in the foregoing that, on the basis
of our conception of protoplasmic structure, the possibility is
conceded of an insight into the mechanics of muscle con-
traction. I am of course far from regarding what has been
put forward as a theory of this process. I see only a guide-
post, as it were, in the direction of a future theory, which
will require the joint labours of many to follow it u^ or set
it aside, as the case may be. Yet there appears to me to
be one further point, in the supposition put forth above,
which is worthy of special consideration. As is becoming
more and more evident from recent observations upon
the structure of muscle cells, a peculiar interpenetration
of two substances, i.e. of the contractile elements and the
so-called sarcoplasm, is especially characteristic of them. I
am not aware that any one of the views that have been
held hitherto upon the mechanics of contraction gives an
idea of the significance of this peculiarity, while we see, on
the other hand, that the hypothesis set forth above is able
to explain this very point to a certain extent.

(ri) Rotational Currents in Plant Cells

As we remarked before in discussing Berthold's views,
the so-called rotational streaming movements, which occur
fairly commonly in plant cells, are especially difficult to
comprehend. It has already been declared above that I am
unable to agree with the remarks of Berthold upon the
origin of this process. Although I have not studied this
subject thoroughly myself, nevertheless it seems to me
worth while adding a few remarks upon this point ; that is
to say, to discuss the possibility, at least, of explaining this

328

PROTOPLASM

phenomenon by means of extension -currents which have
their seat at the boundary between the cell-sap and the
protoplasm of the wall. We found before that it is possible
to set up such a rotational current in an oil-drop, if by means
of proper precautions care be taken that the extension-
current only attains to development upon one side (see
above, p. 74). Of course this phenomenon presupposes that
there is, as a matter of fact, only a single powerful centre
of extension -currents present in a state of permanent
activity, which produces the current ; for as I have already
explained earlier, I cannot regard as correct Berthold's idea
of the origin of such a rotational current by the conflict of
numerous currents. If we now assume such a centre of
extension -currents in a definite position, as the cause of the
rotational current on the inner surface of the protoplasm
lining the wall, the question arises, why the current in this
case is developed only on one side, and
thus leads to rotation. In reference to
this point Quincke (1888) has already
remarked that it must occur if, by means
of solid particles or by a partial rigidity of
its surface, an obstacle to the development
of the current on one side is present. In
our earlier described experiment the glass
surface, to which the oil -drop adhered, is
the obstacle. Hence if we assume that
on the inner surface of the protoplasm
lining the wall of a cell, somewhere
at the surface of one end, near x (see
an obstacle is present in the form of
bridge, stretched out over the proto-

Fig. 23.

Fig. 23), such
a narrow solid
plasm of the surface of this end, then an extension-current,
the centre of which is placed along one side of this solid
bridge, will naturally become a one-sided rotational current,
circulating in the cell in the direction of the arrows.
The question now is whether, arrangements really exist which
make it probable that conditions of this kind are realised in
rotation currents. I am only aware of one case to refer to
in this respect, which at least yields the possibility of such

CHARA-STRUCTURE OF CELL 329

an arrangement — I mean the state of things in the Charce.
As is well known, there exist in the protoplasm lining the wall
of the elongated thread-like cells of these algae two so-called
interference streaks, which pass along the longitudinal sides
of the cells opposite to one another, and in which the
chlorophyll-free protoplasm is. in a resting state. Since the
neighbouring protoplasm is in energetic streaming movement,
it must be assumed that the protoplasm of these streaks is
of a firm consistence. Now if, as seems quite possible, a
rigid bridge was stretched from the ends of these interference
streaks to the surfaces at the extremities of these cells (see
Fig. 22), then the conditions would be to some extent
realised which we postulated for the origin of the rotational
current. Whether a similar state of things can be made
probable in other cells also with rotational currents, remains
of course an open question. Nevertheless one further difficulty
may be considered here, which we meet with in the explana-
tion attempted for the rotational current of the Charce. It is
to be expected that under the suppositions we have made
the current might go on unaltered even after plasmolytic
separation of the protoplasm from the cell wall. It is,
however, well known that a long Chara cell can be con-
stricted by ligatures in several places, and that when this
is done, after a temporary pause a regular rotational current,
corresponding to the original one, appears in each of the
constricted portions. As has been said, this phenomenon
presents new difficulties. Of course the two interference
streaks also become constricted by the ligatures, and thus
at the ends of the constricted pieces of the cell the required
bridges are to a certain extent furnished by these streaks.
Since, however, these firm bridges, as is easily intelligible,
need not penetrate the whole lining of protoplasm, but
ought to be present only at its inner surface, in order to bring-
about a rotational current in the required manner, the
previous conditions could not be simply renewed by bending
together of the interference streaks, if at least, as is
probable, these streaks traverse the whole lining of proto-
plasm. Now whether we may picture to ourselves interrup-
tions of the interference streaks as already present from the

330 PROTOPLASM

outset in places, or whether after the constriction of the cell
the state of things that exists at the ends of the normal cell
is quickly restored at the ends of the constricted pieces, as
the result of a kind of regeneration, all this may remain an
open question, in order not to multiply further the number
of assumptions and possibilities.

However indecisive the results may be which we have
obtained with regard to the explanation of the rotation cur-
rents, it is nevertheless obvious from the preceding discus-
sion that this case appears, under certain conditions, to
admit of an explanation based upon our conceptions of the
structure and the motor phenomena of protoplasm.

A few words in conclusion to this work. Unfortunately
this Memoir has, while in course of preparation, consider-
ably exceeded the limits originally prescribed for it, although
I have taken pains to be as brief as possible, even at the risk
of being somewhat difficult to understand in those questions
which have hitherto lain beyond the province of biologists.

It gives me great pleasure to seize the opportunity of
expressing my heartiest thanks to all those who have helped
me in this work by their kind assistance. To my esteemed
colleagues at Heidelberg, Professors Askenasy, Horstmann,
Kuhne, and Quincke, I am greatly indebted for much advice,
and also to a great extent for assisting me with books and
apparatus. I am similarly obliged to the juniors in my
Institute, especially to Herrn Blochmann, von Adelung, von
Erlanger, Hilger, Lauterborn, and Schewiakoff, for much
assistance in the course of the last few years. During a
short stay at the Zoological Station at Naples in the year
1890, the work I had in hand was greatly promoted by
the most friendly attention to my wants.

All those whom I have named I beg again to accept of
my most cordial thanks.

LITEKATUEE

SINCE it is by no means my intention to bring together a com-
plete list of all writings that deal with the structural relations
of protoplasm, only those works are cited in the following to
which direct reference is made in the text. More exhaustive
lists of literature are to be found in Arnold (1879), Flemming
(1882), and Frommann (1890).

ALTMANN, R., Studien iiber die Zelle. 1. Heft. Leipzig, 1886.

Die Genese der Zellen. Beitrage zur Physiologic. C. Ludwig gewidmet.

Leipzig, 1887. p. 235.

Zur Geschichte der Zelltheorien. Leipzig, 1889.

— Die Elementarorganismen und ihre Beziehurigen zu den Zellen. Leipzig,

1890. 21 Plates.
APATHY, St., Ueber die Schaumstractur, hauptsachlich bei Muskel- und

Nervenfasern. Biolog. Centralblatt. Bd. XI. 1891. pp. 78-88.
ARNOLD, Fr., Handbuch der Anatomic des Menschen. Bd. I. 1844.
ARNOLD, J., Ueber die feineren Verhaltnisse der Ganglienzellen in dem Syni-

pathicus des Frosches. Archiv f. patholog. Anat. Bd. 32. 1865.

p. 1. Taf. 1.
Ein Beitrag zu der feineren Structur der Ganglienzellen. Archiv f.

patholog. Anat. Bd. 41. 1867. p. 178.
- Ueber feinere Structur der Zellen unter normalen und patholog.

Bedingungen. Archiv f. patholog. Anat. Bd. 77. 1879.
AUERBACH, L. , Ueber die Blutkorperchen der Batrachier. Anatom. Anzeiger.

1890. pp. 570-78.
BALLOWITZ, E. , Ueber die Verbreitung feinfaseriger Structuren in den Geweben

und Gewebselementen des thierischen Kbrpers. Biolog. Centralblatt.

Bd. 9. 1889.
DE BARY, H., Ueber den Bau und das Wesen der Zelle. Flora, 1862. pp.

243-51.

Die Mycetozoen. 2nd Ed. Leipzig, 1864.

BECQUEREL, A. C., Influence de relectricite sur la circulation du Chara.

Compt. rend. T. V. 1837. pp. 784-88.
BENEDEN, E. van, Contribution h. 1'histoire de la vesicule germinative et du

premier noyeau embryon. Bull. Ac. roy. Belgique. (2) T. 61. 1876.

332 PROTOPLASM

BENEDEN, E. van, Recherches sur la maturation de 1'oeuf et la fecondation.

Arch, de biologie. T. IV. 1884. pp. 265-640. 20 Plates.
et A. NEYT, Nouvelles reclierches sur la fecondation et la division mitos.

chez 1'ascaris megaloc. B. A. roy de Belgique. 14. 1887. pp. 215-95.

6 Plates.

BERTHOLD, G., Studien iiber Protoplasmameclianik. Leipzig, 1886.
BOURNE, A. G., On Pelomyxa viridis sp. n., and on the vesicular nature of

Protoplasm. Quarterly journal of micr. sc. (N.S.) Vol. 32. 1891.

pp. 357-74. PI. 28.
BRASS, A., Biologische Studien. I. Die Organisation der thierischen Zelle.

I. u. 2. Heft. Halle, 1883-84.

BRUCKE, E., Die Elementarorganismen. Sitzb. d. K. Akad. Wien. Bd. 44.

II. Abth. (Jahrg. 1861.) 1862. pp. 381-406.

BUTSCHLI, 0., Einiges liber Infusorien. Archiv f. mikrosk. Anatomic. Bd.
9. 1873. p. 658. Taf. 25-26.

Einige Bemerkungen zur Metamorphose des Pilidium. Archiv f.

Naturgesch. 1873. Bd. 1. p. 276. Taf. 12. Figs. 1-2.

Studien iiber die ersten Entwicklungsvorgange der Eizelle, die Zell-

theilung mid die Conjugation der Infusorien. Abhdl. der Senckenberg.

naturf. Gesellsch. Bd. X. 1876.
Beitrage zur Kenntniss der Flagellaten und verwandter Organismen.

Zeitschrift f. wiss. Zoologie. 30. 1878. pp. 205-281. Taf. XL -XV.
— Einige Bemerkungen iiber gewisse Organisations verhaltnisse der sog.

Cilioflagellaten und der Noctiluca. Morphol. Jahrb. 1885. Bd. X.

pp. 529-77. 3 Plates.
Kleine Beitrage zur Kenntniss einiger mariner Rhizopoden. Morphol.

Jahrb. Bd. X. 1886. pp. 78-101. 2 Plates.
Die Protozoen. Bronn's Klass. u. Ordnungen des Thierreichs. 2nd Ed.

1881-89.
Miissen wir ein Wachsthum des Plasmas durch Intussusception anneh-

men ? Biolog. Centralblatt. Bd. VIII. 1888. pp. 161-64.
Ueber die Structur des Protoplasmas. Verhandl. des naturhist. -medic.

Vereins zu Heidelberg. N. F. Bd. IV. 3. Heft. Sitzg. v. 3. Mai 1889.

Nachtrag ib. Sitzg. v. 7. Juni 1889.

Ueber zwei interessante Ciliatenformen und Protoplasmastructuren.

Tagebl. d. 62. Vers. deutsch. Naturf. u. Aerzte zu Heidelberg, 1889. pp.
265-67.

Weitere Mittheilungen iiber die Structur des Protoplasma. Verhandl.

d. naturhist. -medic. Vereins zu Heidelberg. N. F. Bd. IV. 4. Heft.

Sitzg. v. 11. Juli 1890.
- Ueber den Bau der Bacterien und verwandter Organismen. Leipzig,

1890. 1 Plate.
Ueber die Structur des Protoplasmas. Referat. Verhandl. der deutschen

zoologischen Ges. zu Leipzig, 1891. Leipzig, 1891. pp. 14-29.
— u. SCHEWIAKOFF, W., Ueber den feineren Bau der quergestreiften Muskeln

von Arthropoden. Biolog. Centralblatt. Bd. XI. 1891. pp. 33-39.
CARNOY, J. B., La biologie cellulaire. Liege, 1884.
La cytodierese chez les Arthropodes. La cellule. T. I. Fasc. 2. pp.

191-440. 1885. 8 Plates.
La cytodierese de 1'oeuf. 2. partie. La cellule. 1886. T. III. Fasc.

I. 91 pp. Pis. 5-8.

LITERATURE 333

CIENKOWSKY, L. , Zur Entwicklungsgeschichte der Myxomyceteu. Jahrb. f.

wiss. Botanik. Bd. III. 1863. pp. 325-37.

- Das Plasmodium. ibid. Bd. III. 1863. pp. 400-441. Taf. 17-21.
DIETL, M. J., Die Gewebselemente des Centralnervensystems bei \virbellosen

Thieren. Berichte des naturwiss. Vereins zu Innsbruck. Bd. VII.

Jahrg. 1876. 1878. pp. 94-109.
EBERTH, C. J., Zur Kenntniss des feineren Baues der Flimmerepithelien.

Archiv f. patholog. Anat. Bd. 35. 1866. pp. 477-78.
EIMER, Th. , Untersuchungeu iiber die Eier der Reptilien. Archiv f. mikr.

Anatomie. Bd. 8. 1872. pp. 226-43. Taf. 11-12.
Weitere Nachrichten iiber den Bau des Zellkerns und iiber Wimper-

epithelien. ibid. Bd. 14. 1877. p. 94. Taf. 7.
ENGELMANN, Th. W., Beitrage zur Physiologie des Protoplasmas. Archiv f.

d. gesammte Physiologie. Bd. II. 1869.
Physiologie der Protoplasma- und Flimmerbewegung. Handworterbuch

der Physiologie, herausgeg. v. Hermann. Bd. I. 1879. p. 341.
Zur Anatomie und Physiologie der Flimmerzellen. Archiv. f. d. ges.

Physiologie. Bd. 23. 1880. p. 505. Taf. V.
FABRE-DOMERGUE, P., Sur la structure reticulee du protoplasma des

infusoires. Compt. rend. T. 114. 1887. pp. 797-99.
Recherches anatomiques et physiologiques sur les infusoires cilies. Ann.

d. sc. natur. (7. s.) Zoologie. T. V. 1888. 144 pp. 5 Plates.
FAYOD, V. , Ueber die wahre Structur des lebendigen Protoplasmas und der

Zellmembran. Natunvissensch. Rundschau. V. Jahrg. 1890. pp. 81-

84. With Woodcuts.
FISCHER, Alfr., Die Plasmolyse der Bacterien. Ber. d. k. sachs. Ges. d.

Wiss. Math.-physik. Cl. 1891. pp. 52-74. 1 Plate.
FLEMMING, W., Zellsubstanz, Kern- und Zelltheilung. Leipzig, 1882. 8

Plates.
Vom Bau der Spinalganglienzellen. Beitr. z. Anat. u. Embryol. als

Festg. f. J. Henle. Bonn, 1882. pp. 12-24. Taf. 2.
Ueber Bauverhaltnisse, Befruchtung und erste Theiluiig der thierischen

Eizelle. Biolog. Centralblatt. Bd. III. 1884. p. 641.
FOL, H., Recherches sur la fecondation et le commencement de 1'henogeiiie

chez divers animaux. Mem. soc. phys. d'histoir. nat. Geneve. T. 26.

1879. 10 Plates.
Le quadrille des centres, un episode nouveau dans 1'histoire de la

fecondation. Arch. d. sc. phys. et. nat. 3. per. T. 25. 1891.
FRENZEL, J., Zum feineren Bau des Wimperapparates. Archiv f. mikrosk.

Anatomie. Bd. 28. 1886. pp. 53-77. Taf. VIII.
FREUD, S., Ueber den Bau der Nervenzellen und Nervenfasern beim Fluss-

krebs. Sitz.-Ber. der Wiener Ak. 1882. Bd. 85. 3. Abth. pp. 9-46.

1 Plate.

FRIEDREICH, N., Einiges iiber die Structur der Cylinderzellen u. Flimmer-
epithelien. Archiv f. patholog. Anat. Bd. 15. 1859. p. 535.
FROMMANN, C., Ueber die Farbung der Binde- u. Nervensubstanz des Riicken-

marks durch Arg. nitric, u. iiber Structur der Nerveuzellen. Archiv f.

patholog. Anat. Bd. 31. 1864. pp. 129-150. Taf. VI.
Zur Structur der Ganglienzellen der Vorderhorner. Arch. f. patholog.

Anat. Bd. 32. 1865. pp. 231-235. Taf. 7.

334

PROTOPLASM

FROMMANN, C., Unters. liber die normale u. patholog. Anatomic des Rucken-

marks. Jena, 1867.
Zur Lehre von der Structur der Zellen. Jenaische Zeitschr. f. Medic.

u. Naturw. 1875. Bd. IX. pp. 280-298. Taf. 15-16.
Ueber die Structur der Knorpelzellen v. Salamandra maculosa. ibid.

Bd. 13. 1879. pp. 16-29.

Ueber die Structur der Ganglienzellen der Retina, ibid. Bd. 13.

1879. Sitzber. pp. 51-57.

Weitere Beobachtungen liber netzfbrmige Structur des Protoplasmas,

des Kerns und des Kernkorperchens. ibid. Bd. 14. 1880. Sitzber.
pp. 31-35.

Ueber die Structur der Epidermis und des Rete Malpighi an den Zeheii

von Hiihnclien, etc. ibid. Bd. 14. 1880. Sitzber. pp. 56-58.

Ueber die spontan wie nach Durchleiten inducirtir Strbme an d. Blut-

zellen v. Salam. mac. u. an d. Flimmerzellen v. d. Rachenschleimhaut
des Frosches eintretenden Veranderungen. ibid. Bd. 14. 1880.
Sitzber. pp. 129-140.

Differenzirungen u. Umbildungen, welche im Protoplasma der Blut-

korper der Flusskrebses theils spontan, theils nach Einwirkung inducirtir
electrischer Strome eintreten. ibid. 1880. Sitzber. pp. 113-124.

Zur Lehre von der Structur der Zellen. Jenaische Zeitschr. f. Naturw.

Bd. 14. 1880. p. 458 bis 465. Taf. 22.
Ueber die spontan u. nach indue. Stromen eintret. Differ, u. Umbild.

in d. Blutkorpern v. Flusskrebs, etc. ibid. Sitzber. Bd. 1881. 9. Dec.

Ueber Structur, Leberiserscheinungen u. Reactionen thierischer u.

pflanzlicher Zellen. ibid. Bd. 16. Sitzber. 1882. pp. 26-45.

Unters. liber Structur, Lebenserscheinungen u. Reactionen thierischer u.

pflanzlicher Zellen. ibid. Bd. 17. pp. 1-346. 3 Plates. 1884.
Veranderungen, welche spontan u. nach Einwirkung inducirter Strome

in den Zellen aus einigen pflanzlichen u. thierischen Geweben eintreten.

ibid. Bd. 17. 1884. Sitzber. pp. 78-84.
Ueber die Epidermis des Hlihnchens in der letzten Woche der Bebriitung.

ibid. Bd. 17. 1884. pp. 941-950.
Zur Lehre von der Bildung der Membran der Pflanzenzellen. ibid.

Bd. 17. 1884. pp. 951-954.
Ueber Veranderungen der Membranen der Epidermiszellen u. der Haare

v. Pelargonium zonale. ibid. Bd. 18. 1885. pp. 597-665. 2 Plates.
Ueber Verander. der Aussenwrandungen der Epidermiszellen v. Euphorbia

cyparissias, palustris u. inauritanica. ibid. Bd. 20. 1886. Suppl.

Sitzber. pp. 74-90.

Beitrag zur Zellenlehre. Anat. Anzeiger. 1886. pp. 208-211.

Beitrage zur Kenntniss der Lebensvorgange in thierischen Zellen. ibid.

Bd. 23. 1889. p. 389. Taf. 24.
(1) Zelle. 1890. In Real -Encyclopedic der ges. Heilkunde. Edited

by A. Eulenburg. 2nd Ed.
(2) Ueber neuere Erklarungsversuche der Protoplasmastromungen u.

liber die Schaumstructuren Biitschli's. Anat. Anzeiger. 1890. pp. 648-

652 u. pp. 661-672. 4 Woodcuts.
GAULE, J., Das Flimmerepithel von Aricia foetida. Archiv f. Anat. u. Ph.,

phys. Abth. 1881. p. 153. Taf. 3.

L1TERA TURE 335

GEDDES, P., A hypothesis of cellstructure and contractility. Zool. Anzeiger.

Bd. VI. 1883. pp. 440-445 (also Pr. R. Soc. Edinb. VII. pp. 266-292).
GREEFF, R., Ueber den Organismus der Amoben, insbesondere iiber Amv<-

senheit motorischer Fibrillen im Ectoplasma von Ambba terricola.

Sitzber. d. Ges. z. Bef. d. ges. Naturw. Marburg, 1890. pp. 21-25.

Ueber die Erd- Amoben. ibid. 1891. Nr. 1. pp. 1-26.

GRUBER, A., Beitrage zur Kenntniss der Amoben. Zeitschr. f. wiss. Zoologie.

Bd. 36. 1882. p. 459. Taf. 30.

HACKEL, E., Die Radiolarien. Berlin, 1862. p. 89 et seq.
HANSTEIN, J. v., Die Bewegungserscheinungen des Zellkerns in ihren Bezie-

hungen zum Protoplasma. Sitzber. d. niederrh. Gesellsch. Bonn, 1870.

Sitzber. pp. 217-233.
Das Protoplasma als Trager der pflanzlichen u. thierischen Lebensver-

richtungen. Heidelberg, 1880.
Einige Ziige aus der Biologie des Protoplasmas. Botanische Abh.

Hera\isgeg. v. Haustein. Bd. 4. Heft 2. Bonn, 1882.
HEIDENHAIN, R., Beitrage zurLehre von der Speichelsecretion. Studien des

physiol. Instituts in Breslau. Heft 4. 1868. 4 Plates.
- Beitrage zur Kenntniss des Pancreas. Arch. f. d. ges. Physiol. Bd.

X. 1875. p. 557. Taf. V.

HEITZMANN, J. , Untersuchungen iiber das Protoplasma. I. Bau des Proto-
plasmas. Sitzber. der K. Akad. d. Wiss. Wien. M. ph. Kl. Bd. 67.

Abth. 3. 1873. p. 100. (Also 1883. pp. 20-37.)

— II. Das Verhiiltniss zwischen Protoplasma u. Grundsubstanz im Thier-
korper. ibid. p. 141 (1883. p. 119).

— III. Die Lebensphasen des Protoplasmas. ibid. Bd. 68. Abth. 3.
1873. p. 41 (1883. p. 47).

— Mikroskopische Morphologic des Thierkorpers im gesunden und kranken
Zustande. Wien, 1883.

HENLE, J., Handbuch der systematischen Anatomic des Menschen. Bd. II.

1866.
HOFMEISTER, W., Ueber die Mechanik der BeAvegungen des Protoplasmas.

Flora, 1865. pp. 7-12. (Read in 1864 at the meeting of naturalists in

Giessen. )

— Die Lehre von der Pflauzenzelle. Leipzig, 1867.
JOSEPH, M., Ueber einige Bestandtheile der peripher. markhaltigen Nerven-

faser. Sitzber. K. Ak. Berlin f. d. J. 1880. p. 1321.
KLEIN, E., Observations on the structure of cells and nuclei. Part I. Quart.

journ. micr. sc. (N.S.) Vol. 18. 1878. pp. 315-339. PI. 16.

(1) Part II. ibid. Vol. 19. 1879. pp. 125-175. PI. 7.

(2) On the glandular epithelium and division of nuclei in the skin of

the newt. Quart, journ. micr. science (N.S.) Vol.19. 1879. p. 417.

PL 18.

KOLLIKER, A., Handbuch der Gewebelehre. 6th Ed. Bd. I. 1889.
KRAUS, L., Die Molekularconstruction des Protoplasmas sich theilender u.

wachsender Zellen. Flora, 1877. p. 529.
KUHNE, W., Unters. iiber das Protoplasma u. die Contractilitat. Leipzig,

1864.
KUNSTLER, J., Contribution a 1'etude des Flagelles. Bullet, soc. zool. de

France. 1882. 112 pp. 3 Plates.

336 PROTOPLASM

KUXSTLER, J., Nouv. contributions a 1'etude des Flagelles. Bullet, soc. zool.

de France, 1882. pp. 230-36.
La struct, reticulee du protoplasma des infusoires. Compt. rend. Ac.

Paris. T. 114. 1887. pp. 1009-1011.
Structure vacuolaire ou areolaire. Bullet, soc. zool. France. T. XIII.

1888.
Les elements vesiculaires du protoplasme cliez les Protozoaires. Compt.

rend. Ac. Paris. T. 106. 1888. pp. 1684-86.

Recherches sur la morphologic des Flagelles. Bullet, scientifique de

France et de la Belgique. T. XX. 1889. pp. 399-515. PI. 14-22.

KUPFFER, C., Die Stammverwandtschaft zwischen Ascidien u. Wirbelthieren.
Archiv f. mikr. Anat. Bd. 6. 1870. pp. 115-172. Taf. 8-10.

Ueber Differenzirung des Protoplasmas in den Zellen thier. Gewebe.

Schrift. des naturw. Ver. f. Schleswig-Holstein. Bd. I. 1875. p. 229.

Ueber die Speicheldrusen der Periplaneta (Blatta) orientalis u.

ihren Nervenapparat. Beitrage z. Anat. u. Physiol., als Festgabe fur
C. Ludwig, 1874. pp. 64-82. Taf. IX.

LEHMANN, 0., Molekularphysik. 2 Vols. Leipzig, 1888-89.

LEYDIG, Fr. v., Lehrbuch der Histologie des Menschen u. der Thiere. Frank-
furt, 1854.

Vom Bau des thierisclien Korpers. Tubingen, 1864.

Ueber Amphipoden u. Isopoden. Zeitscher. f. wiss. Zoologie. Bd. XXX.

1878. Suppl. Taf. IX. -XII. p. 225.

Untersuchungen zur Anatomic der Thiere. Bonn, 1883. 5 Plates.

Zelle u. Gewebe. Bonn, 1885. 6 Plates.

LIST, J. H., Ueber Becherzellen u. Leydig'sche Zellen. Archiv f. mikr. Anat.
Bd. 26. pp. 543-552. 1 Plate.

Ueber Becherzellen. Archiv f. mikr. Anat. Bd. 27. 1886. pp. 481-

588. 6 Plates.

Ueber Stmcturen von Drusenzellen. Biolog. Centralblatt. Bd. 6.

1886. pp. 592-596.

LUKJAXOW, S. M., Ueber die Hypothese von Altmann betr. die Structur des

Zellenkernes. Biolog. Centralblatt. Bd. 9. 1889.
MARCHI, . ., Beobacht. iiber Wimperepithel. Archiv f. mikr. Anat. Bd.

2. 1866. p. 467. Taf. 23.
MARK, E. L., Maturation, fecundation and segmentation of Limax campestris.

Binney. — Bullet, of Mus. of Comp. Zool. Vol. VI. 1881. p. 173.

4 Plates.
MARSHALL, C. F. , Observations on the structure and distribution of striped

and unstriped muscle in the animal kingdom, and a theory of muscular

action. Quart, journ. micr. sc. (N.S.) Vol. 28. 1887. pp. 75-107.

PI. 6.
MARTIN, H., Recherches s. la str. de la fibre muscul. striee et s. les analogies

de struct, et de fonction entre le tissu muscul. et les cellules a batonnets

(protoplasma striee). Arch. d. physiol. norm, et pathol. 1882. pp. 465-

510. PI. XII.
MENSBRUGGHE, G. van der, Sur la tension superficielle des liquides, consid.

au point de vue de cert, mouvements observ. a la surface. Mem. cour. et

mem. des sav. etrangers Ac. Roy. Belgique. T. 34. 1869. 67 pp.

Sur la propriete caracterist. de la surface commune a deux liquides.

LITERATURE 337

soumis a leur affinite mutuelle. I. -III. Bullet. Acad. roy. de Belgiquc

(3 S.) T. XX. 1890. p. 32. PL XX. p. 253. T. XXI. p. 420.

1891.
MITROPHANOW, P. M., Ueber Zellgranulationen. Biolog. Centralblatt. Ud.

9. 1889.
MONTGOMERY, E., Zur Lehre von der Muskelcontraction. Archiv f. d. ges.

Physiol. Bd. 25. 1881. pp. 497-537. Taf. 9.

Ueber das Protoplasma einiger Elementarorganismen. Jenaische

Zeitschr. f. Naturw. 1885. pp. 677-712. 1 Plate.

NAGELI, C., Die Glitschbewegung, eine besondere Art der periodischen Bewe-

gung des Inhalts in Pflanzenzellen. Pflanzenphysiol. Unters. Heft I.

1855. pp. 49-53.
u. SCHWENDENER, Das Milcroskop. 1st Ed. Leipzig, 1867. 2nd

Ed. 1877.
NANSEN, F. , The structure and combination of the histolog. elements of the

central nervous system. Bergen's Museums Arsberetning for 1886.

Bergen, 1887.
NUSSBAUM, M., Ein Beitrag zur Lehre v. der Flimmerbewegung. Archiv f.

inikr. Anat. Bd. 14. 1877. p. 390. Taf. 27. Fig. 2.
PALADINO, G., Dell' endotelio vibratile nei mamiferi ed in generale di alcuni

dati sulla fisiologia delle formazioni endoteliche. I. Giornale inter-

nazionale delle scienze mediche. Anno IV. 1882. (See also Arch.

ital. de Biologie. III. 1883.)
PAULSEN, E., Ueber die Driisen der Nasenschleimhaut, besonders die Bow-

man'schen Driisen. Archiv f. mikr. Anat. Bd. 26. 1885. p. 307.

Taf. 10-11.
Bemerkungen iiber Secretion u. Bau von Schleimdrusen. Archiv f.

mikr. Anat. Bd. 28. 1886. pp. 413-415.
PFEFFER, W., Kritische Besprechung von de Vries, " Plasmolytische Studien

iiber die Wand der Vacuolen." Nebst vorlaufigen Mittheilungen iiber

Stotfaufnahme. Bot. Zeitschr. 1886. pp. 114-125.
- Aufnahme von Anilinfarben in lebende Zellen. Unters. aus dem

botanisch. Institut zu Tubingen. II. 1887. pp. 179-331. 1 Plate.
I. Ueber Aufnahme u. Ausgabe ungeloster Korper. II. Zur Kenntniss

der Plasmahaut und der Vacuolen nebst Bemerkungen iiber den Aggregat-

zustand des Protoplasmas und iiber osmotische Vorgange. Abhandl. der

mathem. physik. Klasse der K. sachs. Gesellsch. der Wissensch. Bd.

XVI. II. 1890. 2 Plates.
PFITZNER, W., Beitrage zur Lehre vom Bau des Zellkerns und seinen

Theilungserscheinungen. Archiv f. mikr. Anat. Bd. 22. 1883. pp. 616-

688. 1 Plate.

Zur pathologischen Anatomic des Zellkerns. Archiv f. pathol.

Anatomic. Bd. 103. 1886. p. 275. Taf. V.

PFLUGER, E., Die Endigung der Absonderungsnerven in den Speicheldriisen.

Bonn, 1866. 3 Plates. See also Archiv f. mikr. Anat. Bd. V. 1869. p.

193 u. 199.
Ueber die Beziehungen des Nervensystems zur Leber- u. Gallensecretion.

Archiv f. d. ges. Physiologic. Bd. II. 1869. pp. 190-192.
Ueber die Abhiingigkeit der Leber von dem Nervensystem. ibid. p. 459.

Taf. 2-3.

22

338 PROTOPLASM

PFLUGER, E., Die Speielieldriisen. Strieker's Handbuch der Lehre von den

Geweben. Leipzig, 1871.

Die allgemeinen Lebenserscheinungen. Bonn, 1889. Rectoratsrede.

PLATEAU, J., Statique experimentale et theorique des liquides soumis aux

seules forces moleculaires. 2 Vols. Gand et Leipzig, 1873.
Quelques experiences sur les lames liquides minces. Bullet. Acad. Roy.

Belgique. (3 S.) T. 2. 1882. pp. 8-18.
QUINCKE, G., Capillaritatserscheinungen an der gemeinschaftlichen Oberflache

zweier Fliissigkeiten. Poggend. Ann. d. Phys. u. Chemie. Bd. 139.

1870. pp. 1-88. 1 Plate.
Ueber den Randwinkel und die Ausbreitung von Fliissigkeiten auf festen

Kbrpern. Annal. d. Physik u. Chemie. (N. F.) Bd. II. 1877. pp.

145-94. 1 Plate.
Ueber periodische Ausbreitung von Fliissigkeitsoberflachen und dadurch

hervorgerufene Bewegungserscheinungen. Ann. d. Physik u. Chemie.

N. F. Bd. 35. 1888. pp. 580-642. 1 Plate.
- Ueber Protoplasmabewegung und verwandte Erscheinungen. Tagebl.

der 62. Vers. deutscher Naturf. u. Aerzte zu Heidelberg, 1889. pp.

204-7.

RABL, C., Ueber Zelltheilung. Anat. Anzeiger. 1889. pp. 21-30.
RATJBER, A., Neue Grundlegungen zur Kenntniss der Zelle. Morphol. Jahrb.

VIII. 1882. pp. 233-338. 4 Plates.
REINKE, J., Kreisen galvanische Strbme in lebenden Pflanzenzellen ? Archiv

f. die ges. Physiologic. Bd. 27. 1882. pp. 140-51.

u. H. RODEWALD, Studien iiber das Protoplasma. Untersuch.

aus dem botan. Institut der Univ. Gbttingen. 2. Heft. 1881. I. Die
chemische Zusammensetzung des Protoplasmas von Aethalium septicum,
von Reinke u. Rodewald. pp. 1-70. II. Protoplasma-Probleme, von
Reinke. pp. 79-182. III. Der Process der Kohlenstoffassimilation im
chlorophyllhaltigen Protoplasma, von Reinke. pp. 187-202.

u. Z. KRATZSCHMAR, Studien iiber das Protoplasma. 2. Folge. Unter-
such. aus d. bot. Laboratorium d. Univ. Gottingen. Berlin, 1883. p. 76.
1 Plate.

REMAK, R., Neurologische Notizen. Froriep's Neue Notizen aus d. Gebiet
d. Naturkunde, etc. Bd. 3. 1837. p. 216.

Ueber den Bau der Nervenprimitivrohren. Archiv f. Anat. u. Phys.

1843. pp. 197-201.

Neurologische Eiiauterungen. Archiv f. Anat. u. Physiol. 1844.

RINDFLEISCH, E., Eine Hypothese. Centralbl. f. d. medic. Wiss. 1880.

Nr. 45. pp. 801-7.
ROHDE, E., Histologische Untersuchungen iiber das Nervensystem der

Polychaeten. Zoolog. Beitrage herausg. v. A. Schneider. 2 Bd. 1887.

pp. 1-81. 1 Plate.
Histologische Untersuchungen iiber das Nervensystem der Hirudineen.

Zool. Beitrage herausg. v. A. Schneider. Bd. III. I. , 1891.
SACHS, J., Handbuch der Experimentalphysiologie der Pflanzen. 1865.
SCHAFER, E. A., The structure of the animal cell. Brit, medic, journ.

1883. Vol. 2. pp. 226-29.
(1) On the structure of amoeboid protoplasm with a comparison between

the nature of the contractile process in amoeboid cells and in muscular

LITER A TURE 339

tissue, and a suggestion regarding the mechanism of ciliary action.
Proceed, of the Roy. Society, London. Vol. 49. pp. 193-98. 1891.

(2) SCH AFER, E. A. , On the minute structure of the muscle-columns or sarco-

styles which form the wing -muscles of insects. Prelimin. note. Proc.
Roy. Soc. London. Vol. 49. 1891. pp. 280-86. Pis. 4-5.

(3) On the structure of cross - striated muscle. Internat. Monats-

schrift f. Anat. u. Physiol. Bd. VIII. 1891. pp. 178-238. PI.
15-17.

- and E. R. LANKESTER, Discussion on the present aspect of the cell
question. Nature. Vol. 36. 1887. p. 592.

Sen FAVIAKOFF, W., Ueber die karyokinetische Kerntheilung der Euglypha

alveolata. Morphol. Jahrb. Bd. 13. 1887. pp. 193-258. 2 Plates.
Beitrage zur Kenntniss der holotrichen Ciliaten. Bibliotheca zoologica,

herausg. v. Leuckart u. Chun. Heft V. 1889. 7 Plates.
S< HIKFFERDECKER, P., Zur Kenntniss des Baues der Schleimdriisen. Archiv

f. mikr. Anatomie. Bd. 23. 1884. pp. 382-412. 2 Plates.
SCHLEICHER, W., Die Knorpelzelltheilung. Archiv f. mikr. Anatomie. Bd.

16. 1879. p. 248. Taf. 12-14.
Nouvelle communication sur la cellule cartilagineuse viv. Bull. A. R.

Belgique. (2) 47. 1879.
SCHMITZ, Fr., Untersuchungen iiber die Structur des Protoplasma und der

Zellkerne der Pflanzenzellen. Sitzber. d. niederrh. Ges. f. Natur- u.

Heilk. zu Bonn. 1880. 42 pp.
SCHNEIDER, Ant., Das Ei und seine Befruchtung. Breslau, 1883.

- C., Ueber Zellstructuren. Zoolog. Anzeiger. 1891. Nr. 355-56.
4pp.

Untersuchungen iiber die Zelle. Arbeiten des zoolog. Instituts Wien.

Bd. IX. Heft 2. 1891. 46 pp. Taf. 1-2.
SCHUBERG, A., Ueber den Bau der Bursaria truncatella, mit besonderer

Beriicksichtigung der protoplasmatischen Structuren. Morphol. Jahrb.

Bd. XII. 1886. pp. 333-65. 2 Plates.
SCHULTZE, H. , Achsencylinder und Ganglienzelle. Archiv f. Anat. u. Phys.

Anat. Abth. 1878. p. 259. Taf. 10.

— M., Der Organismus der Polythalamien. Leipzig, 1854.

— Das Protoplasma der Rhizopoden und der Pflanzenzellen. Leipzig,
1863.

— Allgemeines iiber die Structurelemente des Nervensystems. In Strieker's
Handbuch der Gewebelehre. 1871.

SCHWALBE, G., Bemerkungen iiber die Kerne der Ganglienzellen. Jen.

Zeitschr. f. Med. u. Naturwiss. Bd. X. 1875. p. 25.
SCHWARZ, Fr., Die morphologische und chemische Zusammensetzung des

Protoplasmas. Colm's Beitrage zur Biologic der Pflanzen. Bd. V.

1887. 8 Plates.
SEDGWICK, A., A monograph of the development of Peripatus capensis.

Studies from the morphol. laboratory in the Univ. of Cambridge. Vol.

IV. P. 2. 1888. (Also in Quart, journ. micr. sc. (N.S.) Vol. 26.

1886. pp. 175-212.)
STRASBURGER, E., Zellbildung und Zelltheilung. 2nd Ed. Jena, 1876.

— Studien iiber das Protoplasma. Jenaische Zeitschr. f. Naturwiss. Bd.
IX. 1876. p. 395. 1 Plate.

340 PROTOPLASM

STRASBTTRGER, E., Ueber den Theilungsvorgang der Zellkerne und das Verhalt-
niss der Kerntheilung zur Zelltheilung. Arcliiv f. mikr. Anat. Bd. 21.
1882. p. 476. 3 Plates.
— Ueber den Bau und das Wachsthum der Zellhaute. Jena, 1882. 8 Plates.

STRICKER, S., Photogramm eines farblosen Blutkorperchens. Arbeit, aus
Instit. f. allg. u. exp. Pathol. Wien 1890. 3 pp. 1 Plate.

und SPINA, Untersuchungen iiber die mechanischen Leistungen

der acinosen Driisen. Wiener medicin. Jahrbucher. 1880. pp. 355-96.

STUART, A., Ueber die Flimmerbewegung. Diss. Dorpat, 1867. Also

Zeitschrift f. rationelle Medicin. Bd. 30. 1867.
TRINCHESE, S., Anatomia della Caliphylla mediterranea. Mem. d. accad. d.

scienze d. istituto di Bologna. (3 S.) T. 7. 1876. pp. 173-191. 2 Plates.
VEJDOWSKY, Fr., Entwicklungsgesch. Untersuchungen. Heft I. Reifung,

Befruchtung und die ersten Furchungsvorgange des Rhynchelmis-Eies.

Prag, 1888. 166 pp. 10 Plates.
VELTEN, W., Bewegung und Bau des Protoplasmas. Flora, 1873. pp. 81, 97,

and 113.

Physikalische Beschaffenheit des pnanzlichen Protoplasmas. Sitzb. d.

Wiener Akademie. Math.-phys. Kl. Bd. 73. pp. 131-51.

Einwirkung stromender Electricitat auf die Bewegung des Protoplasmas,

auf den lebendigen und todten Zelleninhalt, sowie auf materielle Theil-

chen iiberliaupt. Sitzb. d. K. A. d. Wiss. Wien. Math.-phys. Kl. Bd.

74. I. Abth. 1876. pp. 293-358. 1 Plate.
DE VRIES, H. , Plasmolytische Studien iiber die Wand der Vacuolen. Pringsh.

Jahrb. f. wiss. Bot. Bd. 16. 1885. pp. 463-598.
Ueber die Aggregation im Protoplasma von Drosera rotundifolia. Bot.

Zeitung. 1886. pp. 1, 17, 33, 57. 1 Plate.
WAKKER, J. H., Studien iiber die Inhaltskorper der Zelle. Jahrb. f. wiss.

Botanik. Bd. 19. 1888. pp. 423-92. Taf. 12-15.
WALLICH, G. C., On an undescribed indigenous form of Amoeba. Ann. and

mag. of nat. hist. (3.) Vol. 11. 1863. p. 287. PI. 8.— Further

observations, ibid. pp. 365 and 434.
On the value of the distinctive characters in Amoeba, ibid. Vol. 12.

1863. pp. 111-151.
WEBER, E. H., Mikroskopische Beobachtungen sehr gesetzmassiger Beweg-

ungen, welche die Bildung von Niederschlagen harziger Korper aus Wein-

geist begleiten. Poggendorff's Annalen f. Phys. u. Chemie. Bd. 94.

1855. pp. 447-59. Taf. VI. -VII.
WENT, F. A. F. C., Die Vermehrung der normalen Vacuolen durch Theilung.

Jahrb. f. wiss. Botanik. Bd. 19. 1888. pp. 295-353. Taf. VII. -IX.
ZERNER, Th., Ein Beitrag zur Theorie der Driisensecretion. Wiener medic.

Jahrb. 1886. 4. Heft. pp. 191-200.

341

EXPLANATION OF THE FIGUKES *

SINCE I have prepared the figures for the most part without the aid
of the camera, under the erroneous impression, as was afterwards found,
that by its help delicate protoplasmic structures could not be, recognised
with certainty, I often have no sure means of determining the magni-
fication in cases where direct measurements were not taken. In general,
however, the figures relating to protoplasmic structures are drawn with
a magnification of about 2500 to 3500 diameters, as is proved by those
in which the magnification was actually determined. As I have said,
I convinced myself at a later period that, in preparations of sufficient
clearness, the protoplasmic structures can be drawn quite well by the
help of the camera, using Zeiss's 2 mm. and Oc. 18 ; to which fact
Fig. 2 on Plate X. bears witness, for example. Since the size of the
alveoli varies within relatively narrow limits, that is to say, between
0-5 to 1 /u,, the magnifications can be determined fairly well from this
fact. Whenever it is not stated otherwise, the figures are all done
with Zeiss's Apochr. 2 mm., Ap. 1'30 or T40, and the Comp. Oculars
12 or 18.

1 A n Atlas of 19 Microphotographs in connection with this Work can be
obtained from Professor Biitschli, Zoologisches Institut, Heidelberg, by send-
ing the sum of five shillings.

343

DESCRIPTION OF PLATE I

344

PLATE I

All the figures relate to Gromia Dujardini M. Schultze.

Fig. 1. Oral region of a specimen with completely retracted protoplasm, and
the opening nearly closed, a, the finely granulated, non-striated portion
of the shell, which chiefly forms the nipple-shaped elevation when the
aperture is open (see Fig. 2). b, the portion of the shell which is radially
striated in optical section. The protoplasm in the opening of the shell
has a very distinct and longitudinally fibrillar, alveolar structure, c,
the large brown bodies contained in the protoplasm, x about 1000.

Fig. 2. Aperture of a living specimen, from which a moderately large tuft of
protoplasm has emerged ; the protoplasm shows very distinctly a honey-
comb-like structure, and sends out a number of fine hyaline pseudopodia.

Fig. 3, a. A pseudopodium in process of retraction, showing the alveolar
structure distinctly in two places, while the rest still appears quite
hyaline.

Fig. 3, b-c. Two consecutive stages in the retraction of a pseudopodium.
The fine lateral branch * on Fig. 3, b, has already become relaxed and
wavy, and it contracted rapidly, becoming distinctly alveolar in the
process. It then united with the alveolar eminence ** to form the
alveolar appendage at the end of the pseudopodium in Fig. 3, c.

M'LAOAN ACUMMINC.LITM (DIN?

345

DESCRIPTION OF PLATE II

346

PLATE II

Figs. 1-4 relate to Gromia Dujardini M. Schultze.

Figs. 1 and 2. Two drops of protoplasm, appearing hyaline during life,
which had been set free by pressure from the protoplasm of the oral
aperture of a specimen ; after treatment with picro-sulphuric acid and
staining with Delafield's htematoxylin. Both the drops show the alveolar
layer very distinctly.

Fig. 3. Large pseudopodium with numerous fine branches. Quite hyaline
during life. Figured after fixing with picro-sulphuric acid and staining
with Delafield's haematoxylin. The fibrillated alveolar structure very
distinct throughout almost the whole pseudopodium.

Fig. 4. Point of origin of some thick hyaline pseudopodial stems from the
protoplasmic tuft of the aperture. Note how the fibrillated alveolar
nature of the tuft partly extends even to the commencement of these
pseudopodia, here becoming less and less distinct, and finally vanishing
entirely.

Fig. 5, a-b. Margin of a living drop of protoplasm, isolated by pressure from
a Milliolid. It shows a very beautiful alveolar layer and a well-developed
radial striation of the peripheral protoplasm generally. 5, b, a small
portion of the margin more strongly magnified, in order to represent the
alveolar layer more accurately.

Fig. 6. Living bridge of protoplasm, which was stretched across between
the fragments of a squashed Milliolid. It had a distinctly fibrillated
alveolar structure, and was at the same time in a constant state of
undulatory streaming movement.

Figs. 7-8. Pseudopodia of Amoeba Umax after treatment with picro-sulphuric-
osmic acid. The alveolar structure is perfectly distinct as far as their
extremities, as also the alveolar layer.

< LAGAN k CUMMINC.LITH. EMN*

347

DESCRIPTION OF PLATE III

348

PLATE III

Fig. 1. Portion of fine pseudopodium, during life, of Polystomella.

Fig. 2. The same of C&rnuspira.

Fig. 3. The same of Discorbina.

Fig. 4. Thicker pseudopodial stem of a living Rotalina, with a very distinct
fibrous alveolar structure.

Fig. 5. Small Acincta (see the text, p. 87) from fresh water. Living. The
structure of the protoplasm only partly filled in. g, the wall of the
envelope ; alv, alveolar layer ; mn, macronucleus ; cv, contractile vacuole
with the very distinct efferent canal ; a;, dark bodies in the -protoplasmic
framework.

349

DESCRIPTION OF PLATE IV

PLATE IV

Fig. 1. Membrane-like expansion, with a very distinct structure, from the
pseudopodial network of a Milliolid. Living.

Fig. 2. Similar expansion from the richly developed pseudopodial network
of a Discorbina, which was killed rapidly by being placed in the vapour
of heated osmic acid and then stained with Delafield's hsematoxylin. The
drawing was made as true to nature as possible, without being schema-
tised in the least.

Fig. 3. Marginal portion of a fresh-water Amoeba, which was not determined
with certainty, but was probably referable to Amoeba (Cochliopodium)
actinophora, although the envelope was not distinct. At the broader
end the alveolar protoplasm becomes very beautifully radially striated.
A more precise determination of this form was impossible, since it was
only observed in a fixed preparation. Picro-sulphuric-osmic acid, damar.

Fig. 4. Amosba actinophora Auerbach (probably more correctly referred to
Cochliopodium, H. and L.) Picro-sulphuric-osmic acid, damar. Only a
portion of the margin, with the radially striated envelope (h), repre-
sented. Beneath this the distinctly alveolar protoplasm, of which the
most external layer immediately under the envelope has developed into
an alveolar layer (ah), o, the alveolar protoplasm in surface view, n, the
nucleus, with a very large nucleolus of a honeycombed structure, and a
framework arranged radially to the membrane.

Fig. 5. Small living Vorticella sp. from the Mediterranean. A small portion
of the edge in the region of the contractile vacuole in optical section.
p, pellicula ; alv,^ alveolar layer ; beneath that the distinctly alveolar
protoplasm, in which the most external layer of alveoli is directed radially
to the alveolar layer. At the same time, a similar arrangement of the
alveoli at the surface of the large vacuole (v), which was probably the con-
tractile vacuole, is very distinct. Numerous strongly refracting granules
in the endoplasm.

Fig. 6. Surface view of a small portion of the cortical protoplasm of Para-
mcecium bursaria Ehb. sp. with numerous zoochlorellos (z). Picro-
sulphuric-osmic acid, damar. The vertical position of the very distinct
alveoli of the cortical protoplasm, with regaro^ to the zoochlorellcc, is very
striking.

Fig. 7. Stylonychiapustulata'Eh'b. Small portion of the alveolar endoplasm
with corpuscles, strongly stained with eosin, lodged in it.

Fig. 8, a-b. Paramcecium caudatum Ehb. Killed with iodine - alcohol ;
then very strongly stained in Delafield's hsematoxylin, and transferred
to oil of cloves, and there broken up. 8, a, small fragment of the
macronucleus, showing beautifully the alveolar structure, and the fact that
the small chromatin granules, stained red, are lodged in the nodal points.
8, b, small fragment of the endoplasm with the larger, eosinophilous gran-
ules in the nodal points of the alveoli ; the latter stain slightly reddish
in hsematoxylin.

Fig. 9. Two living strands of protoplasm from the hair cells of a Malva sp. ;
in the strand on the left the streaming has stopped, for which reason
the structure here appears irregularly alveolar ; in the neighbouring
strand, on the other hand, which is in a state of streaming movement,
it appears distinctly fibrillar.

;.'-v

• v

I & CUHHINC.LITH (DIN*

351

DESCRIPTION OF PLATE V

352

PLATE V

Fig. 1, a-c. Eggs of Sphcerechinus granularis Lam.

Fig. 1, a. Thin section (about 1 to 2 /*), passing slightly obliquely to the axis
of division, through the so-called attraction sphere of an egg which was
in the act of dividing in two. In the centre is the centrosome, which
seems to consist of three closely apposed vesicular granules. Picro-
sulphuric acid, Delafield's hsematoxylin, damar.

Fig. 1, b. Thin section through the surface of a similar ovum, showing very
plainly the alveolar layer (alv), and the honeycombed structure of the
protoplasm lying beneath it.

Fig. 1, c. Striated protoplasm during division from an entire ovum in pro-
cess of division, which was investigated in water after treatment with
picro-sulphuric acid.

Fig. 2, a-b. Thalassicolla nucleata Hxl. Section through the central
capsule. Osmic acid, Canada balsam. 2, a, part of the intracapsular
protoplasm with two vacuoles or albumen spheres. 2, b, part of the
superficial, radially striated intracapsular protoplasm, bordering on an
albumen sphere, x about 3100.

Fig. 3. Hinder end of a living Chilomonas paramcecium Ehb. Both the
alveolar layer (alv) and the honeycombed endoplasm are very distinct.
In the latter lie the large amylum granules (am), p, pellicle.

Fig. 4. Optical section of the marginal portion of a drop of oil-foam prepared
from olive oil and NaCl, with a very distinct and relatively high alveolar
layer (alv). Seibert TV, x 1250.

Fig. 5. Foam prepared from olive oil and cane sugar. A small part of the
meshwork, projected with the camera lucida. x 1200.

353

DESCRIPTION OF PLATE VI

354

PLATE VI

Fig. 1. Foam prepared from olive oil and Nad. A small part of the mesh-
work. Camera lucida, x 1800.

Fig. 2, a-b. Foam prepared from very much thickened olive oil and K2C03 ;
very viscid. Drawn out by compression of the cover glass into strands,
which show the fibrillated alveolar structure very beautifully. 2 a, a
strand with low magnification. 2 b, a small part of this strand with
greater magnification, showing the honeycombed structure distinctly.

Fig. 3. Lumbricus terrestris L. Longitudinal section through a supporting
cell of the epidermis. Iodine-alcohol, acid hsematoxylin, daraar.
c, cuticle. In the nucleus the framework, stained blue, is very distinct,
with red chromatin granules lodged in it, and a nucleolus similarly
stained. In the meshwork of the protoplasm there are similarly
stained red granules, which, however, are smaller, and hence more
difficult to observe.

Fig. 4. A small portion of a cell from the fat body of Blatta orientalis L.
Stained by Gram's method, with subsequent staining withvesuvin. The
large cavities (/) have arisen by fat drops becoming dissolved. b, the
vividly stained Bacteroids, which are distinctly lodged in the pale mesh-
work of the protoplasmic bridges.

Fig. 5. Optical section through the epidermis (margin) of a living gill lamella
of Gammarus pulex de G. c, cuticle. The striated alveolar structure of
the protoplasm can be distinctly recognised.

m m

. .

355

DESCRIPTION OF PLATE VII

356

PLATE VII

Fig. 1. Very thin section through the liver of Rana esculenta. Picro-
sulphuric-osmic acid, iron-hsematoxylin, water. Region at which three
cells meet. Protoplasmic structure and alveolar layer very distinct,
x about 3500.

Fig. 2. Very thin section through a peritoneal cell of the gut of Branchiob-
della astaci Od. Picro-sulphuric acid, gentian violet, water. Thickness
of the section at most about equal to the diameter of a single mesh of
the protoplasm. The granules in the nucleus (ri) and protoplasm very
strongly stained. Drawn as accurately as possible.

Fig. 3, a-c. 3, a, very thin section through the cuticle and epidermis cell of
Brancliiobdella astaci, showing the structure of the cuticle (c) distinctly.
3, b, section through cuticle of rather different nature. 3, c, surface view
of the cuticle.

Fig. 4. Protoplasm of the strongly compressed living ovum of Hydatina
senta Ehb. The alveolar structure here exceedingly distinct.

Fig. 5. Protoplasm of the living cells of the posterior circle of cilia of
Hydatina senta, from a spot where the protoplasm has not got a fibrillated
alveolar structure.

Fig. 6. Small part of the protoplasm of a pigment cell of Aulastomum gulo
M. T. Isolated after maceration in iodine-alcohol (10 per cent). The
dark granules in the nodal points of the meshwork are the pigment
granules.

Fig. 7. Small portion of an isolated nerve fibre of the nerve of the chela of
Astacus fluviatilis. Maceration in iodine - alcohol (about 10 or 15 per
cent), s, the sheath in optical longitudinal section with the nucleus (n)
lying entirely embedded in it. n', the lateral boundary of the nucleus,
drawn elsewhere in optical section, os, the structure of the sheath in
surface view. /, optical longitudinal section through the axis-cylinder.

r~ is

i
:

357

DESCRIPTION OF PLATE VIII

358

PLATE VIII

Fig. 1, a-b. Isolated axis-cylinder from the ischiadic nerve of Rana esculenta.
Fixed with pier o- sulphuric acid, followed by alcohol, and finally stained
in the usual way with aurichloride of potassium. 1, a, with remains of
the medullary sheath sticking to it. 1, b, probably from the region of
a constriction. Optical longitudinal section. 1, a, x about 3300, 1,
&, x about 2700.

Fig. 2. Nucleus, with surrounding protoplasm, of a ganglion cell from the
spinal cord of Bos taurus (juv). Macerated in iodine-alcohol (10-15 per
cent). Shows distinctly the vertical position assumed by the alveoli
directly surrounding the nucleus with regard to its surface.

Fig. 3. Small portion of the margin of an isolated ganglion cell from the
ventral nerve cord of Lumbricus terrestris, showing the alveolar layer
distinctly. Maceration in iodine-alcohol (10 per cent).

Fig. 4, a-c. Isolated connective tissue cells from the ischiadic nerve of Rana
esculenta, 4, a, several connected cells under low magnification. 4, &,
single cells under stronger magnification in lateral view. 4, c, the same
in surface view. Picro-sulphuric-osmic acid, n, nucleus.

--

359

DESCRIPTION OF PLATE IX

36o

PLATE IX

Fig. 1. Small portion of an isolated capillary from the spinal cord of So
taurus (juv) in optical longitudinal section, n, two nuclei of the wall.
At o the surface structure of the protoplasm of the cells of the wall is
depicted for a short distance. Maceration in iodine-alcohol (10-15 per
cent).

Fig. 2. Broad protoplasmic process of a ganglion cell from the spinal cord
of Bos taurus (juv}. Fibrillated alveolar structure very distinct. Macera-
tion in iodine-alcohol (10-15 per cent), x about 2000.

Fig. 3. Isolated axis-cylinder of the gray substance of the spinal cord of Bos
taurus (juv}. Optical longitudinal section. Maceration in iodine-alcohol
(10-15 per cent), x about 4400.

Fig. 4, a-c. Transverse sections of medullated nerve fibres from the
ischiadic of Rana esculenta. Picro-sulphuric acid. Fat removed with
alcohol and ether. Stained partly with hsematoxylin, partly with gold
chloride. 4, a, transverse section between two constrictions. 4, b,
transverse section in the region of a constriction. 4, c, transverse
section through a nucleus (n) of the sheath of Schwann. s, sheath of
Schwann. a, so-called sheath of axis-cylinder which was in part very
distinct. In 4, c, the sheath of Schwann is probably rather abnormally
distorted.

DESCRIPTION OF PLATE X

362

PLATE X

Fig. 1, a, 6. Red blood corpuscles of Eana esculenta, iodine-alcohol, acid
hsematoxylin, damar. Only the nuclei stained. 1, a, view of the
broad side. At o a small part of the surface and structure of the proto-
plasm is depicted. In the rest of the figure the equatorial optical
section is represented. 1, b, view of the narrow side, optical median
section. In both views the alveolar layer (alv) is very distinct, g, the
limit of the protoplasm towards the cavity of the blood corpuscle. In
the nucleus (?i) the framework stained blue with the red chromatin
granules can be plainly recognised, p, pellicle.

Fig. 2. Transverse section through an axis-cylinder, rather distorted in
outline, from the ischiadic of Lepus cuniculus. Picro-sulphuric-osmic
acid, iron-hfematoxylin, water, x 4000. The somewhat irregular
transverse section was chosen because it was extremely thin (at most 1 /*),
and hence showed the structure very plainly.

Fig. 3. Small part of a living pseudopodium of Actinosphcerium eidihornii
Ehb. a, the axial thread, surrounded by the distinctly alveolar proto-
plasm, which contains numerous strongly refractile granules.

Fig. 4. Foam prepared from olive oil and sodium chloride. An out-
stretched lamella of foam, made up of a single layer, which it was
possible to study in optical section. Unfortunately I have not taken
accurate note of the special conditions under which this lamella was
observed, for it is clear that it could only exist in this manner under
peculiar relations, and for a short time, since the foam in question was
quite fluid.

Fig. 5, a-c. Very small droplets of olive oil, and which are obtained by
shaking up some oil with 1 per cent soda solution. The droplets are in
close apposition to one another. Focussed slightly below the horizontal
equatorial plane of the drops, so that the apparent network produced
by the diffraction circles which is stretched out between the droplets
is seen very plainly. Diaphragm drawn far down. In Fig. 5, a, a few
small drops lie apposed to a large one, of which only a part of the
edge is drawn. In Fig. 5, c, a number of minute droplets are similarly
closely apposed to the margin of a very large one, so that the relations
become rather peculiar. With reference to the interpretation of these
remarkable appearances compare the text, pp. 211 et seq. Zeiss Apochr.
2 mm., Oc. 18.

DESCRIPTION OF PLATE XI

364

PLATE XI

Fig. 1. Small portion of a very thin longitudinal section through the cuticle,
and one of the hooks occurring in it, of Distomum hepaticum L. /, the
hook, a, the dark, pellicle-like border of the cuticle ; beneath this a
layer, &, corresponding to an alveolar layer. Then follows the very dis-
tinctly alveolar outer stratum, c, of the cuticle, passing internally into
the fibrous portion, d, which contains numerous granules. Below the
cuticle are cross - sections of the circular muscle fibres, e, which are
embedded in a fibrous alveolar protoplasm. Picro -sulphuric acid, iron-
haematoxylin, water. Obj. 2 mm. 1'40, Oc. 18. Cam. luc. x 3275.

/'/,/// XJ

H« L»CAN i CUMMiNO.LITH,

365

DESCRIPTION OF PLATE XII

366

PLATE XII

Fig. 1. Part of a pseudopodium of Actinosphcerium eichhornii Ehb., after
treatment with picro -sulphuric acid. The protoplasm has become partly
contracted in a varicose manner on the axial thread, a, so that the latter
is laid bare in places.

Fig. 2. A very fine protoplasmic filament from a cell of a stamen of Trades-
cantia virginica. The filament becomes swollen up in its course, and the
swollen portion has a very beautiful alveolar structure, while the fine
filament does not permit any such structure to be made out. Unfortu-
nately I have not noted whether this drawing was made from a living or
a fixed object ; the latter alternative is, however, more probable.

Fig. 3. Surface section through the bacillar border of the epithelium
cells of the gut of Distomum hepaticum. Picro - sulphuric acid, iron-
hsematoxylin, water, a, the transverse sections of the more darkly-
stained conical bodies, distinctly alveolar and deposited in a mass of
alveoli more feebly stained and poorer in granules. Z. Apochr. 2 mm.,
Oc. 18. Cam. luc. x 4000.

Fig. 4. Small portion of the so-called stem filament or muscle, after fixation,
of Zoothamnium mucedo Entz; very distinctly made up of a fibrous
alveolar structure. Z. Apochr. 2 mm., Oc. 12.

Fig. 5. Optical section through a tentacle of Podophrya elongata Clp. and
L. The central circle is the tentacle canal, the wall of which is formed
by a layer of alveoli of protoplasm. Z. Apochr. 2 mm., Oc. 18.

Fig. 6. Compare the text, p. 179.

•

•--

, fnr

c

/

V •

INDEX

ABBE condenser, use of, for investigat-
ing protoplasmic structures, 86,
178

Achlya, movement of granules in (Na-
geli), 321

Acineta sp., structure of, 87, 88

Acinetan (Tokophrya), tentacles of, 88

Actinophrys sol, protoplasm of, 93, 94

Actinosphcerium, protoplasm of, 93, 94

Adherent drops and amoeboid move-
ment, 293-296

Adhesion a cause of protoplasmic
movement (Rindfleisch), 290 ; in
relation to amoeboid movement,
293-296

^Ethalium septicum, protoplasm of,
111-116 ; observations of Reinke
and Rodewald upon enchylema of,
170, 171

Aggregate condition of protoplasm,
220-227 ; of fibrous protoplasm,
257

Air -bubbles in gum solution, optical
phenomena shown by, 29

Albumen, nature of, 216-219 ; soap
(Quincke), 306 ; spheres of Tha-
lassicolla, 92

Alcohol, drops of water retreating
from, 296-305 ; iodine, for fixa-
tion, 90

Alkalinity of enchylema, 310 ; Reinke
and Rodewald's experiments, 170,
171

Almond oil, for preparing oil-foams,
13

Alterations in volume of foam-drops,
38-41

Altmann's views on the structure of
protoplasm, 195-200

Alveolar layer in oil-foams, 32-36 ; in
protoplasm, 236 - 240 ; physical
explanation of, 33 ; fluid nature

of, in oil-foams, 35, 36 ; in rela-
tion to cuticles and cell-mem-
branes, 240-242 ; layer similar to,
round vacuoles in oil-foams, 36
(see under Radiate Layer infra) ;
in Acineta, protoplasm, 87, nu-
cleus, 88 ; in plasmodia of JEtha-
lium, 114, 115 ; in Amcebce, 107,
108 ; in axis-cylinders, 150 ; in
Bacteria, etc., 118-122 ; in blood
corpuscles (frog), 128; in Chilo-
monas, etc., 91; in ciliated cells,
etc., of Hydatina, 133, 134 ; in co-
agulated colloids, 216 ; in epithel-
ial cells (Lumbricus), 135 ; in
ganglion cells, 146 ; in liver
cells, 141, 142 ; in drops of
protoplasm of Miliolidce, 95 ; in
ova of Barbus fluviatilis and
Dreissensia, 127, of Hydatina,
125, and of Sphcer echinus, 126 ;
in Pelomyxa, 117 ; in Vorticella,
88

Alveolar nature of colloids, 216-219 ;
of protoplasm, 219 et seq. ; of
hyaline protoplasm, 262-266
protoplasm, internal displacements

in, 323-325

theory of protoplasm in relation to
movement, 267 et seq.

Alveoli of microscopic foams, pro-
perties of, 24, 25 ; size of, 31 ; in
oil-foams, arrangement of, 31, 37 ;
elongation of, causing fibrous ap-
pearances, 45 ; bursting of, under
electricity, 26 ; vertical position
of, in lamellae of oil -foam, 38 ;
marginal layer of, see Alveolar
Layer ; of protoplasm, contents of,
310; size of, 93, 95, 127, 142,
146, 148, 176, 238, 341 ; in
jEthalium, 115 ; Klinstler's views

368

PROTOPLASM

on, 186 ; of muscle cells in
relation to contraction, 326 ;
arrangement of, producing stria^
tions in ova, 251-253 ; in epi-
thelial cells, 254, 255 ; in fibrous
protoplasm, 255-257 ; radiate ar-
rangement of, 246-253 ; radiate
layer of, round nucleus and vacu-
oles, see Radiate Layer infra.

Amoeba Uattce, fibrous structure of
protoplasm, 109, 255 ; terricola,
radiate appearances round vacuole
of, 246, 247

Amcebce, currents in water surrounding,
317-319; Heitzmann's observa-
tions on, 163 ; movement of, see
Amoeboid Movement ; non-adher-
ent, 295, 296 ; structure of, 106-
111

Amoeboid movement, explanation of,
307-317; Berthold's views on,
290-305 ; Engelmann's theory,
276, 277 ; Leydig's theory, 172,
280 ; Quincke, 305-307 ; Mont-
gomery's hypothesis, 287, 288 ;
in foam -drops, 47-54; in foam-
drops, under action of electric
currents, 58, 59

Angles in microscopic foams, 23-25

Annelids, structure of nerves in (Rohde),
285-287

Apathy, criticisms on the foam theory
of protoplasm, 149 (footnote)

Apparatus, optical, used for investigat-
ing protoplasm, 86

Arcella, shell of, 241

Archoplasm, 248, 249 ; structure of,
in Sphcerechinus, 126

Arnold, observations on ganglion cells,
160 ; on reticular structures in
protoplasm, 168

Artificial foams, see Oil-Foam ; light for
microscope, 86

Ascaris lumbricoides, confused fibrous
structure in muscles and cells of
medullary sacs, 256

Ascaris megalocepJiala, Boveri's observa-
tions on, 248 ; alveolar layer in
egg of, 238 ; sexual elements of,
173, 182, 252

Ascidia canina, follicle cells of, 162

Astacus fluviatilis, ganglion cells of,
145 et seq.', structure of chela
nerve, 153-156

Asters in egg of SpJwer echinus, 126

Attraction-spheres, 248, 249

Auerbach on blood corpuscles of frog,
130 ; views on radiate appear-
ances in protoplasm, 258

Aulastomum gulo, pigment cells of, 143

Automatic movements of granules in
protoplasm, 319-323

Axial thread in pseudopodia of Actino-
sphcerium, 94 ; of M iliolidce, etc.,
100

Axis-cylinder, structure of, 148-156 ;
fibrous structure of, 256 ; micro-
scopic image of, 180

BACILLAR lining of cells from intestine
of Distvnium, 139, 140

Bacteria and granules, Altmann's views,
199-201 ; Martin's views, 193 ;
structure of, 117-122

Bacterium lineola, central body of,
visible in life, 121

Bacteroids in ectoplasm of Epistylis
and fat bodies of Periplaneta,
201 ; bodies like, in ciliated cells
of Hydatina, 133

Barbus Jiuviatilis, ovarian ova of,
127

Benzin and soap solution, foam pro-
duced from, 6

Berthold, desolution processes, 15 ; on
the fluid nature of protoplasm,
224 ; on granular movements, 320 ;
on the nature of protoplasm, 202,
203 ; on streamings in plant cells
and amoeboid movement, 290-
305

Blatta orientalis, see Periplaneta

Blood corpuscles (white) of Amphibia,
(Schafer), 282; (red) of frog,
127-131 ; Frommann's observa-
tions on, 164

Bodies in endoplasm of Ciliata, 89,
90

Border, striated alveolar, see Alveolar
Layer

Bourne on Pelomyxa viridis, 311
(footnote)

Boveri on fibrillse in the aster and
radiate appearances in protoplasm,
261 ; observations on eggs of
Ascaris, 248

Branchiobdella astaci, structure of cells
from, 136, 137 ; cuticle of, 137,
241

Brass on reticular structures, 194

Briicke on the contractile framework
of protoplasm, 268 ; on the "or-
ganisation " of protoplasm, 220,
221

Brush electrodes, use of, 55

Bursaria truncatella, alveolar layer of,
238

CALF, capillaries of, 143, 144 ; ganglion
cells of, 145 et seq.

INDEX

369

Caliphylla, Trinchese's observations on,
166

Camera lucida, for making drawings of
protoplasm, 341

Cane sugar, for producing foams, 8

Capillaries from spinal marrow of calf,
structure of, 143, 144 ; fibrous
structure of, 256

Carnoy, alveolar layer observed by,
239 ; on reticular structures in
protoplasm, 174 ; on radiate ap-
pearances in protoplasm, 260

Cartilage cells, Schleicher's views on,
177

Cell division, radiate appearances dur-
ing, 246-251
membranes, 240-243
plate in nematode eggs, 239

Central bodies, see Centrosomes '

Central body (nucleus) of Bacteria, etc.,
118-122

Centrosomes, 246-251 ; structure of,
in egg of Sphcerechimcs, 126

Chantransia, granules in protoplasm,
92

Chara, streaming of, 306, 329, 330

Chemical forces in pseudopodia (Ber-
thold), 304, 305 ; in moving oil-
drops (Mensbrugghe), 65, 67 ;
hypothesis of protoplasmic move-
ment (Montgomery), 287, 288 ;
nature of protoplasm, 309, 310

CMlomonas paramcecium., structure of,
91 ; radiate layer round nucleus,
243

Chlorophyll granules, Altmann's views
on, 195, 196

Chromatin granules, Altmann's views
of, 199, 200; in epithelial cells
of Lumbricus, 135 ; in macro-
nucleus of Paramcecium caudatum,
91 ; in nucleus of blood corpuscle
of frog, 129

Chromatium okenii, structure of, 118,
121

Cienkowsky, on the fluid nature of
plasmodia, 221

Cilia of cells from ffydatina, 133,
134

Ciliata, structure of, 88-91 ; cyclosis
in endoplasm of, 306, 307, 324,
325 ; cyst envelopes of, 242

Ciliated epithelium, Elmer's observa-
tions upon, 167 ; observations of
Friedrich upon, 160 ; of Eberth
and Marchi, 161

Circulatory currents produced in oil-
drops, 74 ; in plant cells, 327-
330 ; Berthold's views on, 292 ;
Engelmann's views on, 277

Clearing up of foam-drops with glycer-
ine, 10, 22

Closterium, movements of granules in
(Nageli), 321

Coagulated albumen, structure of, 216-
219

Coagulation a cause of reticular struc-
tures, 201-219

Cochliopodium (Amoeba), 106-111

Cod-liver oil, for producing oil-foams,
11, 13

Collodion and clove oil, resemblance to
protoplasm, 16

Colloid bodies, nature of, 216-219

Common salt, for producing foams, 8, 11

Condition of protoplasm in the aggre-
gate, 220-227

Connective tissue, fibrous structure of,
in Lumbricus, 256 ; cells from
ischiadic nerve of frog,' 144, 145

Continuance of streaming movements
in foam-drops, 52, 53 ; cause of,
78, 79

Contractile vacuole of Amcebce, 110 ;
of Amoeba terricola, 246, 247 ; of
Acineta, 87 ; of Vorticella, 89

Contractility of protoplasm, 267-271 ;
of the framework, 269-271

Contraction of muscles, explanation of,
325-327

Criticism of Altmann, 195-201 ; of
Berthold, 202, 203 ; of the con-
tractility theory, 270, 271 ; of
Engelmann's theory of movement,
275-278 ; of Flemming, 178-180 ;
of Frommann on oil-foams, 82-84 ;
of Kiinstler, 187-191 ; of Ley dig's
and Schafer's hyaloplasm theory,
283, 284 ; of Schwarz, 207, 208 ;
of tonoplast theory (de Vries), 232

Cryptomonas, granules in endoplasm,
91 ; radiate layer round nucleus,
243

Currents in plant cells, 327-330 ; in
soap-bubbles, 319 ; in water-drops
retreating from ether, etc., 300-
305 ; in water surrounding
Amoebae, 317-319 ; of extension,
see Extension Currents

Cuticles, 240-243 ; of Branchiobdella,
137 ; of Phascolosoma, 138 ; of
Distomum, ib., 139

Cuticular border of cells from intestine

of Distomum, 139, 140
layer of Strassburger, 171, 235 ; in
plant cells, Quincke, 306

Cyanophycece, structure of, 117-122

Cydidium, bodies in endoplasm of, 89

Cyclosis of endoplasm in Ciliata, 306,
307, 324, 325

24

370

PROTOPLASM

Cyst envelopes of Ciliata formed by

secretion, 242
Cytoblasts of Altmann, 199

DE BARY on currents in plasmodia
and on contraction, 270, 271 ; on
the nature of protoplasm, 221

Desmids, movements of granules in
(Nageli), 321

Desolation, definition and examples of,
15

De Vries, tonoplast theory of vacuoles,
230-233

Diatoms, movements of granules in
protoplasm of, 320

Dietl on nerve structure, 156

Diffraction area, 210

Diffusion of watery fluids through fatty
oil, 7, 8 ; of oil through watery
lamellae, experiments to prove, 41 ;
a cause of radiate appearances in
oil-foams, 41-44, in protoplasm,
246-253

Diminution of volume in oil-foams
after clearing with glycerine, 22,
38-41

Discorbina, protoplasm of, 95 ; pseudo-
podia of. 98

"Disgregation " of protoplasm (Mont-
gomery), 287, 288

Displacements, internal, in protoplasm,
323-325

Distomum hepaticum, cuticle, etc., of,
138, 139

Dodecahedric figures in a regular foam,
23, 24

Drops of water retreating from ether or
alcohol, 296-305

Durability of oil-foams, 46, 47

EARTHWORM, see Lumbricus

Eberth on structure of ciliated cells of
Anodonta, 161

Ectoplasm of Amcebce, 107, 109 ; of
ActinospJicerium, 94 ; of Epistylis,
granules in, 201 ; of Pelomyxa,
116

Eddies in water-drops retreating from
ether, etc., 300-305

Egg cells, their structure, 124-127 (see
Ova)

Eimer, observations on striation of
ciliated cells, 167

Electrical experiments on benzin

froths, 6

explanations of protoplasmic move-
ment, 279, 280

Electricity causing bursting of alveoli
in oil-foams, 26 ; reaction of foam-
drops to, 54-61

Electrolysis causing negative stream-
ings in foam-drops, 54-57

Embryo sac of Phanerogams, radiate
appearances in, 253

Emulsion of oil-drops showing a false
network between the droplets,
211-213

Emulsions, experiments on, 6

Enchylema, nature of, 309, 310 ;
original definition of, by Hanstein,
223 ; of ^Ethalium, Reinke and
Rodewald on, 170, 171 ; Kiinst-
ler's views on, 186 ; Ley dig's views
on, 172, 280, 281 ; of muscles,
effect on contraction, 325-327 ;
Schwarz's views on, 204, 207

Enclosures in protoplasm and oil-foams,
244-246

Endoplasm of Amoebae, containing
granules, 111 ; of Ciliata contain-
ing minute bodies, 89 ; of Ciliata,
cyclosis in, 306, 307, 324, 325 ;
of Flagellata, granules in, 91 ;
of Foraminifera, 191 ; of Infusoria
fluid, 225 ; reticular structure of,
in Paramcecium caudatum, Sty-
lonychia pustulata, etc., 89

Engelmann, hypothesis of protoplasmic
movement, 274-278 ; on surface
tension and protoplasmic move-
ment, 289

Epidermic cells of Lunibricus, 134-136

Epistylis galea, granules in ectoplasm,
201

Epithelial cells, observations on, 131-
136 ; striated protoplasm in, 254,
255 ; of small intestine of rabbit,
142, 143

Ether, drops of water retreating from,
296-305

Euglena, granules in endoplasm, 91

Euglypha, nuclear division of, 253

Experiments upon diffusion as cause of
radiate appearances in foam-drops,
41-44 ; to prove diffusion of oil
through watery lamellae, 41 ;
electrical, on benzin froths, 6 ;
upon changes of volume in oil-
foam drops, 38-41 ; on currents
of Chara, 329, 330 ; on currents
in soap-bubbles, 319 ; on drops of
water retreating from ether, etc.,
300-305 ; electrical, upon drops
of oil-foam, 54-61 ; with emul-
sions, 6 ; Frommann's, on drops
of oil-foam, 82-84 ; to prove in-
fluence of soap in producing oil-
foams, 13 ; upon the influence of
temperature upon the movements
of foam-drops, 53, 54 ; upon in-

INDEX

371

fluence of gravity, 54 ; of light, #>.;
on movements of foam -drops,
47 - 54 ; on oils suitable for
oil-foams, 18 ; on position of
enclosures in foams, 245 footnote ;
on production of foam in oil, 11,
12 ; of Reinke and Rodewald on
enchylema of jEthcdium, 170, 171 ;
on streaming movements of foam-
drops in cells, 80, 81 ; on super-
ficial extension-currents, 61-80

Extension-currents, 13, 48, 49, 61-64 ;
methods of producing, 68-73 ; in
foam-drops produced by electri-
city, 55-60 ; negative currents, 55,
57 ; positive currents, 57-60 ; in
Ciliata, 324, 325 ; in plant cells,
306, 327-330; in pseudopodia,
308

External surface of protoplasm, 234-
236

FALSE (optical) network in plasmodia
of jEthalium, 113 ; between sus-
pended granules, etc., 209-216

Fat bodies in endoplasm of Forami-
nifera, 191 ; in protoplasm of
Mttiola, 95 ; in Discorbina, 97

Fat body of Periplaneta, Bacteroids in,
201

Fatty acids in protoplasm, 309 ; oils,
, diffusion of watery fluids through, 7

Fayod on structure of protoplasm, 183,
184

Fibrillar theory of protoplasm, 177-
184 ; protoplasm in ciliated cells
of Hydatina, 133 ; in pseudopodia
of Actinosphcerium, 93 ; in con-
nective tissue cells, 145 ; of
ganglion cells, 146 ; structures in
colloids, 216 ; appearances in
streaming protoplasm of plant
cells, 122, 123

Fibrils of muscle, structure of, 325-
327 ; in axis-cylinders, 148-156 ;
in the aster, theories of van
Beneden and Boveri, 261, 262 ; in
protoplasm, Altmann's views
upon, 196, 197

Fibrous protoplasm, 255-257 ; in
plasmodia of jEthalium, 115 ; of
Amoeba blattce, 109, 255 ; in blood
corpuscle of frog, 129 ; of Milio-
lidce, 97

structures in drops of oil -foam,
44-46

Filamentous pseudopodia, 315 ; of
Miliolidce, etc., 97-101

Fischer, Alfred, on the structure of
Bacteria, etc., 118-122

Flagellata, structure of, 91, 92, 185,
186

Flemming on hyaline protoplasm, 263 ;
on protoplasmic structure, 177-
180 ; on reticular structures in
protoplasm, 175 ; on radiate
appearances in protoplasm, 259,
260

Fluid nature of alveolar layer in oil-
foams, 35, 36 ; of microscopic
foams, explanation of, 34 ; of oil-
foams, 31 ; of protoplasm, 220-227

Foam produced with emulsion of ben-
ziu or xylol and soap solution, 6 ;
experiments on, 7 ; false network
in, 213-216 ; position of granules
in, 244-246 (see Oil-Foam)

Foam-drops in cells, streaming move-
ments of, 80, 81 ; explanation of
streaming movements in, 74-80 ;
Frommann's experiments upon,
82-84 ; resemblance to protoplasm,
85

Foam-like nature of protoplasm, 219
et seq. ; of colloid bodies, 216-
219

Foam theory of protoplasm, in relation
to its movement, 207 et seq. ;
Kiinstler's criticisms upon,'l 86- 1 9 1

Fol, electrical theory of protoplasmic
movement, 280 ; views on radiate
appearances in protoplasm, 258,
261

Foraminifera, bodies in endoplasm of,
(Kiinstler), 190

Framework of protoplasm, nature of,
309 ; supposed to be contractile,
269-271 ; Altmann's objections to,
197, 198 ; Berthold's views on,
202 ; Schwarz's views, 204, 207 ;
its existence during life, 205
theory and external surface of proto-
plasm, 234-236

Frenzel on radiate striation round
vacuole of Amoeba cubica, 251
footnote

Freud, observations on ganglion cells,
171

Friedrich on structure of ciliated cells,
160

Frog, blood corpuscles of, 127-131 ;
connective tissue cells from, 144,
145; liver cells of, 140-142;
nerve fibres, 148 et seq.

Frommann, experiments on drops of
oil-foam, 82-84 ; observations on
blood corpuscles, etc., 164 ; on
blood corpuscles of Salamander,
129 ; observations on structure of
ganglion cells, 160 ; observations

372

PROTOPLASM

on reticular structures in proto-
plasm, 169, 170 ; views upon limit-
ing surface of protoplasm, 234
on limiting membrane of vacuoles
229 ; on hyaline protoplasm, 263
on radiate appearances in proto-
plasm, 251, 260

Fuligo varians — ^Ethalium septicum,
111-116

GAMMARUS PULEX, epithelium of gill
lamella, 131-133

Ganglion cells, structure of, 145-148,
256 ; Arnold's observations on,
160 ; Frommann's observations
on, 159 ; Schwalbe's observations
on, 166

Gas bubbles appearing in oil-foams, 19

Gelatine, nature of, 216-219

Gland cells (goblet cells), structure of,
175; in stomach of Hydatina, 134

Globulites, 249

Glycerine, for clearing up foam-drops,
10, 22 ; dilute solution of, for
causing movements in foam-drops,
48

Goblet cells, structure of, 175

Granular appearances in oil-foams, 20,
27-30 ; contents in endoplasm of
Amosbce, 111 ; theory of proto-
plasm, 191-201

Granules, their position in protoplasm
and foams, 244-246 ; and hyaline
protoplasm, 266 ; their influence
on protoplasmic movement, 323-
325 ; false network between, 209-
211 ; movements of, in cell sap of
plants, 291 ; independent move-
ments of, 319-323 ; in Trades-
cantia and Surirella, 320 ; sliding
movements of, in Desmids (Nageli),
321 ; Velten's views, 322 ; ex-
planation of, 322, 323 ; in proto-
plasm of Acineta, 87 ; (pigment)
in cells of Aulastomum, 143 ; in
axis-cylinder, 151 ; in endoplasm
of Ciliata, 89, 90 ; of Flagellata,
91 ; in ganglion cells, 146 ; in
' cells of Hydatina, 134 ; in liver
cells, 141 ; in epithelial cell of
Lumbricus, 135 ; in protoplasm
of Miliola, 95 ; in filamentous
pseudopodia, 99 ; absent in
pseudopodia of Gromia, their
sudden appearance, 103 - 106
absent in the oil - foams, 26
Altmann's views upon, 195-200
Martin's views, 192, 193 ; Pfitz-
ner's views, 193, 194 ; Vejdow-
sky's views, 194, 195

Gravity, its influence upon streaming
movements of foam-drops, 54

Gfromia Dujardini, structure of, 101-
106 ; hyaline pseudopodia of, 262,
264

H^BMATOXYLIN for staining, 90, 91,
124 footnote; for staining blood
corpuscles of frog, 128

Hanstein, rnicrosomes, 192 ; on the
nature of protoplasm, 222, 223

Heat, influence of, on the movements
of foam-drops, 53, 54 ; producing
unequal surface tension and ex-
tension-currents, 72

Heidenhain, observations on epithelial
cells, 161

Heitzmann, alveoli round nucleus
figured by, 243 ; observations on
protoplasmic structure, 162-164 ;
on the contractile framework of
protoplasm, 268 ; on hyaline pro-
toplasm, 263 ; views upon limiting
surface of protoplasm, 235 ; on
nerve structure, 156 ; on vacuoles,
228, 229

Heliozoa, structure of, 93, 94

Henle on structure of epithelial cells,
161

Hertwig on epithelial cells of Gam-
marus, 132 ; on radiate appear-
ances in protoplasm, 258

Hofmeister on the currents in plas-
modia, etc., and on contractility,
271 ; on the nature of protoplasm,
221, 222 ; on protoplasmic move-
ment and " imbibition," 271, 272 ;
on surface tension in protoplasm,
289

Homogeneous border, apparent, in oil-
foams, 37

protoplasm in 6rm?w'a,103-106; in re-
lation to the foam theory, 262-266

Hooks of Distomum hepaticum, 138,
139

Hiippe on resemblance of Bacteria to
nuclei, 122 footnote

Hyaline cuticular layer in plant cells

(Quincke), 306

protoplasm, 262 - 266 ; of Amcebce,
107, 109 ; in plasmodia of jEtha-
lium, 113, 115
pseudopodia of Gromia, 103-106

Hyaloplasm of Hanstein, 223 ; of
Ley dig, 172 ; in relation to move-
ment, Leydig's views on, 280-287 ;
in relation to the foam theory,
262-266

Hydatina senta, ciliated and other cells,
from, 133, 134 ; ova of, 124, 125

INDEX

373

IMBIBITION theories to explain proto-
plasmic movement, 271-278

Imitation of karyokinetic spindle, 250
footnote

Increase in volume during formation of
foam in oil, 19

Independent movements of granules,
319-323

Induction shocks causing bursting of
alveoli in oil-foams, 26 ; influence
of, upon foam-drops, 60, 61

Infusoria, see Ciliata

Ink, apparent network between gran-
ules of, 209-211

" Inotagmas " of Engelmann, 274

Interference streaks in cells of Chara,
329, 330

Intertilar mass of Flemming, 178

Internal displacements in protoplasm,
323-325

Intestinal epithelium of Branchiobdella,
137

Intracapsular protoplasm of Thalassi-
colla, 92

Investigation of protoplasm, 86

Iodine-alcohol for fixation, 90, 91

Iron-hsematoxylin, use of, 124 footnote

Ischiadic nerve of frog, 148 et seq.

JOSEPH, views upon structure of axis-
cylinder, 154, 155

KARYOKINESIS, 246-251

Karyokinetic spindle, imitation of, 250
footnote

Klein on radiate appearances in proto-
plasm, 259 ; on reticular structures
in protoplasm, 168

Kolliker's views on protoplasm, 202

Kratschmar on reticular structure of
jEthalium, 171

Kraus, theory of protoplasmic move-
ment, 274 footnote

Ku'hne on the fluid nature of proto-
plasm, 220

Kiinstler, spherular theory of proto-
plasm, 184-191 ; on vacuolar
membranes, 231 footnote; radiate
layer of alveoli figured by, 243

Kupffer, alveoli round nucleus observed
by, 243 ; follicle cells of Astidia
canina, 162 ; observations on egg
of Ascidia, 237 ; observations on
the structure of the cells of the
salivary gland of Periplaneta and
on liver cells, 165, 166

LAMELLA of fluid, experiments on

tension in, 323, 324
Lamp for microscope, 86

Lehmann on the physical constitution
of jellies, 218 footnote; explana-
tion of movements in oil-drojs,
66, 67

LepocincliSi granules in endoplasm, 91

Lepus cun^c^dus, see Rabbit

Leucocytes, structure of (Schafer), 282

Leydig, alveolar layer observed by,
239 ; clear space round nucleus
figured by, 243 ; on blood cor-
puscles of Triton, 129 ; on epi-
thelial cells of Gammarus, 132 ; on
hyaline protoplasm, 263 ; on the
hyaloplasm in relation to move-
ment, 172, 280-287; on limiting sur-
face of protoplasm, 234 ; on the
limitation of vacuoles, 228, 229 ;
on radiate appearances in proto-
plasm, 260 ; views on reticular
structures in protoplasm, 172 ;
on structure of axis-cylinder, 156 ;
on structure of capillaries of
Salamander, 144 ; on structure
of epithelial cells, 161

Light, its influence upon streaming
movements of foam-drops, 54

Linseed oil, for producing oil-foams,
11

Lithobius, alveolar layer in testicular
cells of, 239

Litmus solution, experiment with, for
proving electrolysis in foam-drops,
56

Liver cells, Kupfler's observations on,
166 ; of frog and rabbit, 140-142

Lumbricus terrestris, epithelial cells
from, 134-136; fibrous structure
of connective tissue cells, 256 ;
ganglion cells of, 145 et seq.

MACRO -NUCLEUS of Acineta, 87, 88 ;
of Paramcecium caudatum, 90, 91

Mcdva, protoplasm of, 122 et seq.

Marchi on structure of ciliated cells of
Anodonta, 161

Mark on radiate appearances in proto-
plasm, 259

Martin, theory of protoplasmic struc
ture, 192, 193

Matrix of protoplasm, Altmann's views
on, 196, 199

Membrane of cell, 240-243 ; of vacuoles,
228-230

Mensbrugghe, explanation of increased
movement in oil-drops when heated,
79, 80 ; on the tension of thin
fluid lamellae, 264 ; theory as to
the cause of the movement in
oil-drops, 65, 67

Mesh work shown by microscopic foam,

374

PROTOPLASM

23, 25 ; arrangement of, causing
fibrous appearances in oil-foams,
45

Method of preparing oil - foams, 8,
16-18

Methods of producing extension -cur-
rents, 68-73 ; of fixing and staining
•with iodine - alcohol, 90, 91 ; of
staining and investigating proto-
plasm, 124 footnote ; of fixing the
pseudopodia of Miliolidce, etc.,
100 footnote; of fixing plasmodia,
112 ; optical, of investigating
protoplasm, 86

Micrococci, their resemblance to proto-
plasmic granules, 193

Microscopic foam, appearance of, 23 ;
false network in, 213-216 ; granu-
lar appearance in, 27, 30 ; nodal
points of, 26 - 30 ; properties of,
23-25 ; theoretical explanation of
their fluid nature, 34 and footnote
investigation of protoplasm, 86

Microsomes of Hanstein, 192, 223

Miliolidce, protoplasm of, 95, 96 ;
pseudopodia of, 97-101

Molecules of protoplasm and imbibi-
tion, 271-278

Montgomery, hypothesis of protoplasmic
movement, 287, 288

Movements caused by surface tension
in oil -drops, 62-67; of foam-
drops, 47 - 54 ; continuance of,
52, 53 ; under action of electric
current, 58 ; influence of tempera-
ture upon, 53, 54 ; influence of
gravity, 54 ; of light, ib. ; inde-
pendent, of granules, 319 - 323 ;
of protoplasm, see Protoplasmic
Movement

Muscle fibril, structure of, 325-327 ;
thread in stalk of Zoothamnium,
90

Muscular contraction, explanation of,
325-327

Myxomycetes, protoplasm of, Pfeffer's
views, 226 footnote; see also

NAGELI, on independent movement of
granules, 321 ; and Schwendener
on contractility, 271 ; on dif-
fraction arese, 210 ; optical ap-
pearances in air-bubbles, 29 ; on
streaming in plant cells, 291 ;
on the viscid nature of proto-
plasm, 222

Nansen's views upon nerve structure,
146-148, 154, 155

Nassula, two radiate layers in, 241

Negative streamings in foam - drops
caused by electrolysis, 54-57

Nematode eggs, cell plate in, 239
(see also Ascaris)

" Nematodes " of Altmann, 196

Nerves, Remak's observations on, 158 ;
structure of, 148-156 ; in Annelids
(Eohde), 285-287

Network, appearance of, in microscopic
foam, 23, 25 ; elongation of
meshes of, causing fibrous ap-
pearances in oil -foams, 45 ; (op-
tical) seen between suspended
granules or droplets and in foams
and protoplasm, 209-216; false,
in plasmodia of ^Ethalium, 113

Noctiluca, structure of, 174

Nodal points of oil-foams, 26-30

Nodes of Ranvier, 150

Non-polarisable brush electrodes, use
of, 55

Nuclear division of Euglypha, 253
spindles, 246 - 251 ; in ovum of
Sphcer echinus, 126, 127

Nucleus, Altmann's views upon, 200 ;
of Bacteria and Cyanophycece, 117-
122 ; of blood corpuscles of frog,
129 ; radiate layer of alveoli
round, 243, 244 ; Frommann's
views upon, 170 ; Heitzmann's
views upon, 163

Nuclei of capillaries, 143, 144 ; of
connective tissue cells, 145 ; of
epithelial cells ofLumbricus, 135 ;
giving rise to radiate appearances
in the protoplasm, 253 ; of sheath
of Schwann, 152

OIL, diffusion of, through watery
lamellae, experiments to prove,
41

Oil-drops, minute, apparent network
between, 212, 213 ; extension-
currents and movements in, 61-
74 ;" rotational currents in, 74

Oil-foams, alterations in volume of,
under the influence of the sur-
rounding fluid, 38-41 ; alveolar
layer of, 32-36 ; apparent homo-
geneous border in, 37 ; appear-
ance of, 20 ; arrangement of
alveoli in, 31 ; durability of,
46, 47 ; fibrous structures in drops
of, 44-46 ; fluid nature of, 31,
32 ; fluid nature of alveolar layer,
35, 36 ; Frommann's experiments
upon, 82-84 ; granular appear-
ances in, 27-30 ; influence of in-
duction shocks upon, 60, 61 ;
influence of temperature upon

INDEX

375

streaming movements of, 53, 54 ;
influence of gravity, 54 ; of light,
ib. ; movements in drops of, under
action of electric current, 58 ;
nodal points of, 27-30 ; opacity
of, 21 ; pellicle-like layer round,
36 ; position of granules in, 244-
246 ; preparation of, 8, 18, 19 ;
produced by the electric current,
56 ; produced by potassium car-
bonate solution, 21 ; produced
again in reduced drops, 31 ;
radiate appearances in drops of,
41-44 ; drops of, reaction to
electricity, 54-61 ; reduction of,
by evaporation, 30 ; resemblance
to protoplasm, 85 ; streaming
movements of, 47-52 ; streaming
movements of drops of, in cells,
80, 81 ; explanation of streaming
movements in drops of, 74-80 ;
structure of, 22-38 ; made from
viscid oil, nature of, 44 ; fibrous
structures in, 44-46

Oil membrane of protoplasm, 309,
318, 319 ; Quiucke's views on,
306, 307

Oils suitable for oil-foams, experiments
on, 18

Olive oil, for producing foams, 8, 11 ;
method of preparing, for produc-
ing oil-foams, 16, 17

Ophidomonas jenensis, structure of,
118

Optical apparatus used for investigat-
ing protoplasm, 86
appearance of a network between
suspended granules, etc., and
in foams and protoplasm, 209-
216 ; in plasmodia of jEthalium,
113
properties of microscopic foam, 23

Organisation of protoplasm (Briicke),
220, 221

Oscillarice, structure of, 118, 120,
121

Osmosis producing radiate appearances
in protoplasm, 252, 253

Ova, radiate appearances in, 251-253 ;
structure of, 124-127 ; Schneider's
observations on, 182

PARAFFIN OIL, for producing oil-foams,
11 ; extension- currents in drops
of, 63, 64

Paramcecium, trichocyst layer, 241 ;
caiidatum and putrinum, structure
of endoplasm, 89 ; macro-nucleus,
90, 91 ; bursaria, reticular struc-
ture of protoplasm, 89

Pellicle in drops of oil-foam, 32, 36 ;
on Surface of protoplasm, 236 ;
in Acineta, 87 ; in Amcebce, 107,
312; in Flagellata (Chilomonas),
91 ; in red blood corpuscles of
frog, 128 ; in pseudopodia of
Gromia, 104 ; in ova of Hyda-
tina, 125 : in liver cells (frog),
141 ; in protoplasm of Miliolidce,
etc., 95 ; round vacuoles, 233 ;
in Vorticella, 88

Pelomyxa, currents in water surround-
ing, 317-319 ; movement of, 308
footnote; non-adherent, 295 foot-
note; protoplasm of, 116, 117;
viridis, structure of (Bourne), 311
footnote

Peripatus, structure of egg, 176

Periplaneta orientalis, Bacteroids in
fat body, 201 ; salivary glands of,
105

Peritoneal cells of BranchioMetta, 136,
137

Pfeffer, artificial production of vacuoles,

232 ; on the nature of protoplasm
in plasmodia, 226 footnote; on
the "protoplasmic membrane,"

233 footnote, 235

Pfitzuer, alveolar layer observed by,
239 ; on blood corpuscles of frog,
130 ; on reticular structures in
protoplasm, 173; on protoplasmic
structures, 193, 194

Pfliiger, criticism of Leydig on nerve
structure, 281, 282 ; on the
nature of protoplasm, 224 ; ob-
servations on epithelial cells,
axis-cylinders, and liver cells,
161 ; views on protoplasmic
structure, 181

Phanerogams, radiate appearances in
embryo sac of, 253

Phascolosoma elongatum, cuticle of,
138, 241

Pigment cells of Aulastomum, 143

Pilidium, epidermic cells of, 162

Plant cells, movements of granules in,
320 ; protoplasm of, 122 - 124 ;
rotational currents in, 327-330 ;
streamings in : Berthold's views,
290 - 305 ; Engelmann's views,
277, 278; Nageli and Schwen-
dener, 291 ; Quincke, 305-307 ;
Schmitz's observations on, 169 ;
Strassburger's observations on,
167 ; Velten, 291 ; Wakker, ib. ;
structure of, Fayod's observations
on, 184 ; Quincke, 306 ; Velten's
observations on, 165

Plasmodia of jEtluilium septicum, 111

376

PROTOPLASM

116 ; de Bary and Cienkowsky
upon, 221 ; movements of, Ber-
thold, 293 ; Pfeffer's views on,

226 footnote

Plasmolysis, analogous process to, in
oil-foam, 22, 41 ; of Bacteria, etc.,
118-122

Plastin in protoplasmic framework,
309

Plateau, experiments on tension in
fluid films, 323, 324 ; on the
lamellae of foams, 264, 265 ; laws
of foam, 6 ; observations on
foams, 245 footnote; properties
of microscopic foams, 23

Polar suns, 126, 246-251

Posterior end of Amcebce, pseudopodia
at, 312-314

Potash, action of, on Amcebce, 314

Potassium carbonate, employed for pro-
ducing oil-foams, 16 ; solution of,
action on oil-drops, 21
nitrate, for producing foams, 8

Precipitation a cause of reticular struc-
tures, 201-217

Preparation of oil-foams, 8, 18

Properties of microscopic foams, 23-25

Protoplasm of Acineta, 87, 88 ; of
jftthaliuin septicum, 111 - 116 ;
condition of, in the aggregate,[220-

227 ; alveolar layer of, 236-240 ;
of Amcebce, 106-111; of epithelium
of small intestine, 142, 143 ; of
pigment cells of Aulastomum, 143 ;
of Bacteria and Cyanophycece,
117-122; of capillaries, 143,144;
of Ciliata, 88-91 ; of connective
tissue cells of frog, 144, 145 ; of
epithelial cells, 131-136 ; external
surface of, 234 - 236 ; fibrillar
theory of, 177-184 ; fibrous, 255-
257 ; of Flagellate, 91, 92 ; the
foam -like nature of, 219 et seq. ;
of frog's blood corpuscles, 127-131 ;
of ganglion cells, 145-148 ; granu-
lar theory of, 191-201 ; of Gromia
Dujardini, 101-106 ; of Heliozoa,
93, 94 ; homogeneous, 262-266 ;
independent movements of granules
in, 319 - 323 ; internal displace-
ments in, 323-325 ; of intestinal
epithelium of Branchiobdella, 137 ;
liver cells, 140-142 ; movement of,
see Protoplasmic Movement ; of
nerve fibres, 148-156 ; oil mem-
brane on, 318, 319 ; optical appa-
ratus used for investigating, 86 ; of
ova,124-127 ; of ova,radiate appear-
ances in,251 -253 ; ofPelomyxa, 116,
117 ; of peritoneal cells of Branchi-

obdella, 136, 137 ; position of
granules in, 244 - 246 ; radiate
appearances in, 246 - 253 ; of
Radiolaria (Thalassicolla), 92, 93 ;
resembled by oil-foam, 85 ; theory
of reticular structure of, 158-176 ;
of marine Rhizopoda, 94 - 101 ;
spherular theory of, 184-191 ;
(striated) in epithelial cells, 254,
255 ; structure and chemical
nature of, 309, 310 ; structures
of, due to coagulation, 201-219 ;
theories concerning radiate appear-
ances in, 257-262 ; of vegetable
cells, 122-124 ; of Vorticella, 88,
89

Protoplasmic movement, 267 et seq. ;
contractility as a cause of, 267-
271 ; effects of granules on, 323-
325 ; and electricity, 279, 280 ;
imbibition theories of, 271-279 ;
and Leydig's hyaloplasm, 280 -
287 ; Montgomery's hypothesis,
287, 288 ; and surface tension,
theories of, 289-307

Protoplastin, 223

Pseudopodia of Actinosphcerium, 93 ;
hyaline, of Gromia, 103 - 106 ;
(reticulate) of Miliolidce, etc.,
97-101 ; cause of, 307 - 317 ;
fibrous structure of, 255 ; Ber-
thold's explanation of, 290-305 ;
formation of, Engelmann's views
on, 276, 277

QUINCKE'S explanation of amoeboid
movement, 315-317 ; of granular
movement, 322 ; of protoplasmic
movement, 305 - 307 ; investiga-
tions on protoplasm, 7, 8 ; oil
membrane in Amcebce, 318, 319 ;
on spreading of fluids upon solid
bodies, 293, 294; theory as to
the cause of the movements in
oil-drops, 66

RABBIT, epithelium of small intestine
of 142, 143 ; liver cells of, 142

Rabl, on fibrillse in the aster and
radiate appearances in protoplasm,
261

Radiate appearances in drops of oil-
foam, 41 - 44 ; in protoplasm,
246 - 253 ; theories concerning,
257-262; in ova, 251-253
protoplasm in ovum of Sphoerechinus

and Barbus fluviatilis, 126, 127
layer of alveoli round nucleus, 243,
244 ; in cells from Gammarus,

INDEX

377

131 ; of ganglion cells, 146 ; of
liver cells, 142 ; round vacuoles
in oil-foams, 36, in protoplasm,
230, in coagulated colloids, 216

Eadiolaria (Tkalassicolla), structure of,
92, 93

Rana esculenta, see Frog

Red blood corpuscles of the frog,
127-131

Reduction of oil-foams by evaporation,
30

Reinke, electrical experiments on plant

cells, 279

and Rodewald, observations upon
protoplasm of ^Ethalium, 170,
171

Remak, observations on nerve structure,
159

Resemblance of oil-foam to protoplasm,
85

Reticular structures due to coagulation,

201-219
theory of protoplasm, 159-176

Reticulose pseudopodia, 315 ; otMilio-
lidce, etc., 97-101

Reticulum, false optical, seen between
suspended granules or droplets,
and in foams and protoplasm,
209-216 ; Altmann's views upon,
196-198 ; Pfitzner's views upon,
193, 194 ; Vejdowsky's views
upon, 194, 195

Retraction of pseudopodia in Gromia,
105

Retreating movements of drops of water
before ether or alcohol, 296-305

Rhizopoda, marine, with reticulate
pseudopodia, 94-101

Rhynchelmis, structure of ova of, Vej-
dowsky's observations on, 194,
195, 218 footnote, 253 footnote

Rindfleisch on adhesion as cause of
movement in protoplasm, 290

Rohde on nerve structures in Annelids,
285-287 ; on structure of ganglion
cells, 147

Rotational currents produced in oil-
drops, 74 ; in plant cells, 327-330 ;
Berthold's views, 291 - 293 ; En-
gelmaun's explanation of, 277,
278

Rotifers, ova of, 124, 125

SACHS, alveolar layer in zoospores, 238 ;
hypotheses of "imbibition" and
protoplasmic movement, 272-274

Salamandra maculosa, blood corpuscles
of, 129

Sarcoplasm of muscle cells, 325-327

Schafer on hyaloplasm, 282-284

Schewiakoff, observations on nuclear
division of Euglypha, 253

Schleicher on structure of cartilage
cells, 177

Schmitz, on limiting surface of proto-
plasm, 235 ; on limiting membrane
of vacuoles, 228 ; observations
upon reticular structures in vege-
table protoplasm, 169

Schneider, Anton, views upon radiate
appearances in protoplasm, 258 ;
Schneider, C. C., on fi brill ar struc-
ture of protoplasm, 182, 183 ; on
limiting surface of protoplasm,
235, 236 ; on limiting membrane
of vacuoles, 229

Schultze, Max, upon axial thread in
pseudopodia of Miliolidce, 100 ;
on the fluid nature of protoplasm,
220

Schwalbe, observations on blood cor-
puscles and ganglion cells, 166

Schwarz on granules suspended in a
viscid fluid, 266 ; on the nature
of protoplasm, 224 ; processes of
desolution, 15, 16 ; on protoplasm,
204-208

Schwendener, see Na'geli and Schwen-
dener

Secretion, cell membranes formed by,
242

Secretions, structure of, 175, 176

Sedgwick, reticulum in egg of Peri-
patus, 176

Sepia granules, false network between,
209-211

Sheath of Schwann, 152

Shells possessing structure of alveolar
layer, 241 ; of Gromia, 101

Sliding movements of granules (Na'geli),
321

Soap-bubbles, currents in, 319

Soap, influence of, in producing foam
in oil, 13, 31 ; influence of, in
streaming of plant cells (Quincke),
306 ; solution for producing ex-
tension-currents, 62

Sphcerechinus, ova of, 125-127

Sphere of attraction in ovum of Sphcere-
chinus, 126

Spherular theory of protoplasm (Ku'nst-
ler), 184-191

Spirema stage of Euglypha, 253

Spirofibrillse and spirospartse of Fayod,
184

Spirogyra, de Vries's experiments on,
232

Spongioplasma of Leydig, 172 ; and
hyaloplasm, 280-287 ; in ganglion
cells, 147

378

PROTOPLASM

Spreading of fluids on solid bodies,
293-296

Staining, methods of, 124 footnote

Stalk muscle of Zoothamnium, 90

Strassburger, alveolar layer in zoospores,
238 ; on limiting surface of proto-
plasm, 235 ; on the nature of
protoplasm, 224 ; observations on
radiate appearances in embryo sac
of Phanerogams, 253 ; protoplasm
of vegetable cells, 167 ; on reticu-
lar structure of protoplasm, 171 ;
on radiate appearances in proto-
plasm, 258

Streaming movements causing fibrous
appearances in drops of oil-foam,
44 ; circulatory, produced in oil-
drops, 74 ; during conversion of
oil-paste into foam, 9, 10, 14, 19 ;
in foam-drops, 47-52 ; explana-
tion of, 74-80 ; continuance of,
52, 53 ; increased by warming,
79 ; influence of temperature
upon, 53, 54 ; influence of gravity,
54 ; of light, ib. ; in cells, 80, 81 ;
in foam- drops, under action of
electric current, 55-60 ; in endo-
plasm of Ciliata, 306, 307, 324, 325 ;
in Pdomyxa and Amcebce, 308,
317-319 ; in plant cells, 122-124,
327-330 ; in soap-bubbles, 319

Striated border of oil-foams, 32 ; round

vacuoles in oil-foams, 36
protoplasm in Amoeba actinophora,
110 ; in central capsule of Thalas-
sicolla, 93 ; in ciliated cells of
Hydatina, 133 ; of ova, 251-253 ;
of epithelial cells, 254, 255 ; in
cells from gill lamellae of Gam-
marus, 131 ; of epithelial cells of
Lumbricus, 135 ; in epithelial
cells, observations of Friedrich,
160 ; of Eberth, Marchi, Leydig,
Henle, Pfliiger, and Heidenhain, 161

Strongylocentrotus, ova of, 182

Structure of Bacteria and Cyanophycece,
1 17-122 ; of blood corpuscles of
frog, 127-131 ; of ganglion cells,
145-148 ; of nerve fibres, 148-156;
of hyaline pseudopodia in Gromia,
103-106 ; of muscle fibrils, 325-
327 ; of oil-foams, 22-38 ; of plant
cell (Quincke), 306 ; of proto-
plasm due to coagulation, 201-21 9 ;
of thread-like pseudopodia, 98-
101

" Struggle for existence " in currents of
plant cells (Berthold), 292

Suns of nuclear spindle, 246-251 ; in
egg of Sphcerechinus, 126

Superficial extension - currents, 61-80

(see Extension-Currents)
Surface of protoplasm, 234-236

tension, experiments on, 61-80 ; and

granular movement, 322, 323 ; and

protoplasmic movement, theories

of, 289-307
Surirella, granules in protoplasm, 92 ;

movements of granules in, 320

TEMPERATURE, influence of, upon
streaming movements in foam-
drops, 53, 54

Tension causing fibrous structures in
foam, 45, 46 ; in protoplasm,
255

Tentacles of Tokophrya, 88

Thalassicolla, structure of, 92, 93

Theories as to radiate appearances in
the protoplasm, 257-262; of proto-
plasmic movement, 267 et seq.

Theory of the alveolar nature of proto-
plasm, 219 et seq.

Tokophrya, tentacles, 88

Tonoplast theory, 230-233

Trachelomonas, granules in endoplasm,
91

Tradescantia, protoplasm of, 122 et
seq.', movements of granules in
cells of, 320

Trinchese, observations on reticular
structures in protoplasm, 166, 167

Triton, blood corpuscles of, 129

Tubules in nerves, 146-148

UROCENTRUM, trichocyst layer, 241
Urtica, protoplasm of, 122 et seq.
Utricle, protoplasmic, in plant cells
(Quincke), 306

VACUOLE of Amoeba terricola, radiate
appearances round, 246, 247

Vacuoles in oil - foams, 22 ; striated
border round, 36 ; in protoplasm,
227-233 ; in ganglion cells, 147

Van Beneden, alveolar layer in cells of
Ascaris observed by, 238 ; ob-
servations on sexual elements of
Ascaris, 173, 252 ; on limiting
membrane of vacuoles, 228 ; on
radiate appearances in protoplasm,
260

Vaucheria, alveolar layer in zoospores
of, 238

Vegetable cells, protoplasm of, see
Plant Cells

Vejdowsky on structure of protoplasm,
194, 195 ; observations on egg of
Rhynchelmis, 248 footnote, 253
footnote

INDEX

379

Velten's electrical hypothesis of proto-
plasmic movement, 279, 280 ; on
movements of granules, 322 ; on
the nature of protoplasm, 222,
223 ; observations on protoplasmic
structure, 165 ; on streaming in
plant cells, 291

Venetian soap for assisting the forma-
tion of foam in oil, 13

Viscid external layer of Amcebse, 314
nature of protoplasm, 225, 226
oil, how to correct, 18 ; foam pro-
duced from, 20, 44 ; transparency
of, 21

Vorticella, structure of, 88, 89

WAKKER on streaming in plant cells,

291
Wallich on the currents in Amoebae

and on contractility, 270

Water-drops retreating from ether or
alcohol, 296-305

Weber on streaming in plant cells,
291

Went on vacuoles, 231

White of egg, its influence on forma-
tion of foam in oil, 14

XYLOL and soap solution, foam pro-
duced from, 6

Z AC H ARIAS. E., on structure of Bac-
teria, etc., 120, 121

Zoochlorellse in Pelomyxa viridis, 311
footnote

Zoospores of Vaucheria, alveolar layer
in, 238

Zoothamnium, endoplasm of, 89 ; stalk
muscle, 90

Zooxanthellse in Foraminifera, 191

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