Form and Function

E >> E. S. (Edward Stuart) Russell >> Form and Function

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He begins by contrasting the teleological with the materialistic
conception of living things. In the teleological view, a special force
works in the living organism, guiding and directing its activities
towards a purposeful end. According to the materialistic view there are
no other forces at work in the living organism than those which act in
the inorganic realm, or at least there are none but forces at one with
these in their blindness and necessity. True, the purposiveness of
living processes cannot be denied; but its ground lies, according to
this view, not in a vital force which guides and rules the individual
life, but in the original creation and collocation of matter according
to a rational plan. The purposiveness of life is part of the
purposiveness of the universe; just as the stars circle for ever in
harmoniously adjusted paths, so do the processes of life work together
towards a common end. Both are the inevitable result of the original
distribution of matter in the primitive chaos, a distribution fixed by a
rational and foreknowing Being (p. 222).

Which of the two conceptions is to be adopted in biology? Teleological
explanations have long been banished from the physical sciences, and in
biology they are only a last resort when physical explanations have
proved incomplete (p. 223). And if the ground of the purposiveness of
living Nature is the same as the ground of the purposiveness of the
universe, is it not reasonable to suppose that explanations which have
proved satisfactory for inorganic things will in time with sufficient
knowledge prove adequate also for organic things?

The teleological conception, again, leads to difficulties particularly
when it is applied to the facts of reproduction. If we suppose that a
vital force unifies and coordinates the organism and is its very
essence, we must also suppose that this force is divisible and that a
part of it--separated in reproduction--can bring about the same results
as the whole. If on the contrary the forces having play in the organism
are the mere result of the particular combination of the matter
composing it, the reconstruction of a particular combination of
molecules in the ovum is all that is necessary to set development
a-going along exactly the course taken by the ovum of the parent.
Another argument against the teleological view is derived from the facts
of the cell-theory. The cell-theory tells us that the molecules of the
living body are not immediately built up in manifold combinations to
form the organism, but are formed first into unit-constructions or
cells, and that these units of composition are invariably formed in all
development, of plants and animals alike, however diverse the goal of
development may be. If there were a vital principle would we not expect
to find that, scorning this roundabout way of reaching its goal, it went
straight to the mark, taking a different and distinctive course for each
individual development, building up the organism direct without the
intermediary of cells? But since there is a universal principle of
development, namely, the formation of cells, does it not seem that the
cells must be the true organisms, that the whole "individual" organism
must be an aggregate of cells, and that the concept of individuality
applied to the organism is accordingly a logical fiction? And it is just
upon this notion of the individuality of the organism that the
teleological concept is based. The teleological view can perhaps not be
completely refuted until the adequacy of materialistic explanations has
been finally shown; but it is certain that the most promising method for
research is the materialistic (p. 226).

"We start out then from the assumption that the basis of the organism is
not a force acting according to a definite plan; on the contrary, the
organism arises through the action of blind and necessary laws, of
forces which are as much implicit in matter as those of the inorganic
world. Since the chemical elements in organic Nature differ in no way
from those of inorganic Nature, the ground or cause of organic phenomena
can consist only in a different mode of combination of matter, either in
a peculiar mode of combination of the elementary atoms to form atoms of
the second order, or in the particular arrangement of these compound
molecules to form the separate morphological units of the organism or
the whole organism itself" (p. 226). Accepting then the materialistic
conception of the organism, we have to consider this further problem.
Does the ground of organic processes lie in the whole organism or in its
elementary parts? Translated into terms of metabolism--note the
physiological point of view--the question runs, are metabolic processes
the result of the molecular construction of the organism as a whole, or
does the centre of metabolic activity lie in the cell? Is it the cell
rather than the organism that is the immediate agent of assimilatory
processes? In the first alternative the cause of the growth of the
constituent parts lies in the totality of the organism; in the other
alternative:--"Growth is not the result of a force having its ground in
the organism as a whole, but each of the elementary parts possesses a
force of its own, a life of its own, if you will; that is to say, in
each elementary part the molecules are so combined as to set free a
force whereby the cell is enabled to attract new molecules and so to
grow, and the whole organism exists only through the reciprocal action
of the single elementary parts.... In this eventuality it is the
elementary parts that form the active element in nutrition, and the
totality of the organism can be indeed a condition, but on this view it
cannot be a cause" (p. 227).

To help in the decision of this question, appeal must be made to the
facts established as to the cellular nature of the organism and of its
reproductive elements. We know that every organism is composed of cells,
which are formed and grow according to the same laws wherever they are
found, whose formation therefore is everywhere due to the same forces.
If we find that certain of these cells--all of which we know to be
essentially identical one with another--have the power when separated
from the others of growing and developing into new organisms, we can
infer that not only such cells but also all other cells have this
assimilatory power. The ova of animals, the spores of plants, the
isolated cells of lower organisms in general, all show the power of
separate assimilation and development. "We must therefore, in general,
ascribe to the cell an individual life, that is to say, the combination
of the molecules in the single cell does suffice to produce the force
whereby the cell is enabled to draw to itself new molecules. The ground
of nutrition and growth lies not in the organism as a whole, but in the
separate elementary parts, the cells. The fact that it is not every cell
that can continue to grow when separated from the organism is not in
itself an objection to this theory, any more than it is an objection to
the individual life of a bee that it cannot continue to exist apart from
the swarm. The activation of the forces existing within the cell depends
on conditions which the cell encounters only in connection with the
whole" (pp. 228-9).

Schwann's next step is to discover what are the essential forces active
in the cell, and here he enters the realm of hypothesis. He finds they
can be reduced to two--an attractive force and a metabolic force. The
attractive force is seen in the process of cell-formation, where first
of all the nucleolus is formed by a concentration and precipitation of
substances found free in the cytoblastem, and in the same way the
nucleus and later the cell are laid down as concentric precipitates from
the cytoblastem. Cell-formation also involves the second or metabolic
force, by means of which the cell alters the chemical composition of the
medium surrounding it so as to prepare it for assimilation. Schwann's
attractive force brings about the actual taking up of the prepared
substance; his metabolic force is the cause of the digestion of food
substances, and is nearly identical with enzyme action. With what
inorganic process, he now asks (p. 239), can the process of
cell-formation be most nearly compared, and the answer obviously is,
with the process of crystallisation. Cells are, it is true, quite
different in shape and consistency from crystals, and they grow by
intussusception, not by apposition--their plastic or attractive forces
seem therefore to be different. A still more important difference is
that the metabolic force is peculiar to the cell. Yet there are
important analogies between crystals and cells. They agree in the
important respect that they both grow in solutions at the cost of the
dissolved substance, according to definite laws, and develop a definite
and characteristic shape. It might even be maintained, Schwann thinks,
that the attractive force of crystals is really identical with that of
cells, and that the difference in result is due merely to the difference
between the substance of the cell and the substance of the crystal. He
points out how organic bodies are remarkable for their powers of
imbibition, and he seeks to show that the cell is the form under which a
body capable of imbibition must necessarily crystallise, and that the
organism is an aggregate of such imbibition-crystals. The analogy
between crystallisation and cell-formation he works out in the following
manner:--"The substance of which cells are composed possesses the power
of chemically transforming the substance with which it is in immediate
contact, in somewhat the same way as the well-known preparation of
platinum changes alcohol into acetic acid. Each part of the cell
possesses this property. If now the cytoblastem is altered by an already
formed cell in such a way that a substance is formed that cannot become
part of the cell, it crystallises out first as the nucleolus of a new
cell. This in its turn alters the composition of the cytoblastem. A part
of the transfomed substance may remain in solution in the cytoblastem or
may crystallise out as the beginning of a new cell; another part, the
cell-substance, crystallises round the nucleolus. The cell-substance is
either soluble in the cytoblastem and crystallises out only when the
latter is saturated with it, or it is insoluble and crystallises as soon
as it is formed, according to the aforementioned laws of the
crystallisation of imbibition-bodies; it forms thus one or more layers
round the nucleolus, etc. If one imagines cell-formation to take place
in this way, one is led to think of the plastic force of the cell as
identical with the force by means of which a crystal grows" (pp.
249-50).

Two difficulties have to be faced by this theory--(1) the origin of the
metabolic power of the cells, (2) the reason why the cells arrange
themselves so as to form an organism of complex and definite structure.
Schwann tries to explain the origin of the "metabolic" action, the
analogy of which with the contact-action of colloidal platinum he
recognises, by attributing it to the peculiar structural arrangements of
molecules. In attempting to account for the harmonious structure of the
organism he points to the analogy of ordinary crystals, which often form
complex and regular tree-like arrangements; plants in particular
resemble these regularly shaped crystal-aggregates.

The whole ingenious theory is offered merely as an hypothesis and a
guide to research. It is interesting as one of the most carefully
thought-out attempts ever made to give a thorough-going materialistic
account of the origin and development of organic form, and it arose
directly out of the cell-theory.

Schleiden and Schwann started out from an erroneous theory of the origin
and development of cells, which impaired to some extent the value of
their results. It was not long, however, before their theory of the
origin of cells by "crystallisation" from an intra- or extra-cellular
cytoblastem was challenged and overthrown, and the generalisation that
cells originate by division from pre-existing cells put in its place.

This was established for plant cells by Meyen, Unger, von Mohl, Naegeli
and Hofmeister in or about the forties.[261] Criticism of the
Schwann-Schleiden theory from the zoological side was suggested by the
study of the segmentation of the ovum--the developmental process in
which the multiplication of cells is most easily observed. The
segmentation of the ovum was well known to Schwann, for the process had
been described in the frog by Prevost and Dumas in 1824,[262] in the frog
and newt by Rusconi,[263] and an elaborate study of the process in the
frog had been made by von Baer.[264] Schwann indeed suspected that there
must be some connection between the segmentation of the ovum and the
formation of cells, but he did not realise that the cellular blastoderm
of the chick was formed by the division or segmentation of the egg-cell.

Segmentation was soon found to be of widespread occurrence. Von Siebold
in 1837 described the process in Entozoa,[265] and in the same year Loven
saw segmentation in _Campanularia_,[266] and Sars in the starfish and in
Nudibranchs.[267]

In 1838 Bischoff[268] observed segmentation in the mammalian ovum, and the
whole course of segmentation in the ovum of the rabbit from the 2-celled
to the morula stage was carefully described and figured by Barry[269] in
1839. C. Vogt[270] in 1842 described segmentation in _Coregonus_ and
_Alytes_. The discovery of segmentation in the ovum of birds was not
made until 1847, by Bergmann,[271] confirmed independently by Coste[272]
in 1850. By 1848 segmentation had been noted in _Hydra_ and various
hydroids, in acalephs, in starfish, polyzoa, nematodes, rotifers,
leeches, oligochaetes, polychaetes, in most groups of molluscs and
arthropods, and in all the vertebrate classes.[273]

The process was at first held to be merely one of yolk-division, or
_Dotterfurchung_, and its details were by most interpreted in the light
of the Schleiden-Schwann theory of cell-formation.

The first steps towards a truer conception of the process seem to have
been taken by Bergmann, who in 1841[274] called attention to the presence
of nuclei in the segmentation-spheres of the frog's egg, and by Bagge in
the same year, who observed that division of the nuclei preceded the
multiplication of the segmentation spheres.[275] He considered the nuclei
to be anucleate cells, and the same view was taken by Koelliker in
1843.[276] Next year, however, in his classical paper on Cephalopod
development[277] Koelliker came to the opinion that they were really
nuclei. He showed that segmentation was brought about by cell-division,
that between "total" and "partial" segmentation there was a difference
of degree and not of kind, and that the cells of the body were formed by
division of the segmentation spheres. He held, however, that the nuclei
multiplied endogenously and not by division. The division of nuclei was
observed by Coste in 1846.[278] Leydig in 1848[279] took the necessary step
in advance and maintained that the nuclei as well as the cells increased
always by division. He was supported by Remak, who in a paper of
1852,[280] and more fully in his monumental _Untersuchungen ueber die
Entwickelung der Wirbelthiere_ (Berlin, 1850-55), proved that in the
frog's egg at least segmentation was a simple process of cell-division,
initiated always by division of the nucleus.[281]

One point Remak left undecided--the fate of the _Keimblaeschen_ or
egg-nucleus. It was generally held, even so late as the 'fifties, that
the egg-nucleus disappeared just before segmentation began--Bischoff
clung to this belief even in 1877.[282] Though Barry had held in 1839 that
the egg-nucleus does not disappear in segmentation, J. Mueller seems to
have been the first actually to prove that it forms by division the
nuclei of the first two segmentation spheres. He furnished the
demonstration in the egg of _Entoconcha mirabilis_,[283] and his paper was
known to Remak, who could not, however, observe a similar division of
the egg-nucleus in the frog. Mueller's discovery was confirmed for
_Oceania armata_ by Gegenbaur,[284] and for _Notommata sieboldii_ by
Leydig.[285]

In 1854 Virchow,[286] previously a supporter of Schwann, crystallised the
new views in the famous phrase--_Omnis cellula e cellula_--and gave wide
publicity to them in his classical lectures on Cellular Pathology,
delivered in 1858.[287] The new doctrine of cell-formation was also taught
by Leydig[7] in his text-book of histology, published in 1857.

The Schleiden-Schwann theory of the origin of cells by generation in a
cytoblastem was now definitely overthrown.

The importance of the protoplasmic content of the cell was brought into
prominence through the work of Dujardin,[289] Purkinje,[290] Cohen[291] and
Max Schultze.[292] The last-named in 1861 proposed a definition of the
cell which might be accepted at the present day. "A cell," he wrote, "is
a little blob of protoplasm containing a nucleus" (p. 11).

[238] _Theoria generationis_, Halae, 1759.

[239] See J. v. Sachs, _Geschichte der Botanik_, book ii.,
Eng. Trans., 2nd impr., 1906.

[240] Mueller's _Archiv_, pp. 137-76, 1838.

[241] _Trans. Linnean Soc._, xvi., p. 710, 1833.

[242] _Myxinoiden_, i. Theil., p. 89, 1835.

[243] _Ann. Sci. nat._ (2) (_Zool._) ii., pp. 107-18, pl.
11, 1834.

[244] _Proc. Phil. Soc. Glasgow_, xix., pp. 71-125,
1887-8.

[245] _Traite sur le venin de la vipere_, 1781.

[246] Mueller's _Archiv_, 1836.

[247] J. Mueller, _Jahresbericht ue. d. Fortschritte der
anat.-physiol. Wissenschaften im Jahre_ 1838. Mueller's
_Archiv_, 1838.

[248] _Symbolae ad anatomiam villorum imprimis eorum
epithelii_, Berlin, 1837.

[249] _U. d. Ausbreitung des Epitheliums im menschlichen
Koerper_. Mueller's _Archiv_, 1838.

[250] See Schwann's _Bemerkungen_ at the end of his
_Mikroskopische Untersuchungen_.

[251] Republished in Ostwald's _Klassiker der exakten
Wissenschaften_, No. 176, Leipzig, 1910. References in
the text are to the original pagination.

[252] _Symbolae ad ovi avium historiam_.

[253] _De ovi mammalium et hominis genesi_.

[254] _De mulierum organis_, 1672.

[255] _Ann. Sci. nat._, iii., p. 135, 1842.

[256] _Recherches sur la generation des Mammiferes_.
Report by Academy Committee. _Ann. Sci. nat._ (2)
(_Zool._) ii., pp. 1-18, 1834; also _Embryogenie
comparee_, 1837.

[257] _Lond. and Edin. Phil. Mag._ (3) vii., 1835; _Phil.
Trans._ 1837.

[258] _Handbuch der Enfwickelungsgeschichte_, 1835, and
Mueller's _Archiv_, 1836.

[259] _Prodromus historiae generationis hominis atque
animalium_, Lipsiae, 1836.

[260] Mueller's _Archiv_, 1837.

[261] Sachs, _History of Botany_, Book ii.

[262] _Ann. Sci. nat._, i., pp. 110-14, 1824. Swammerdam
is said to have observed the 2-celled stage in the egg
of the frog (_Bibl. Nat._, 1752), and Roesel v. Rosenhof
the same stage in the tree-frog (_Hist. nat. ranarum
nostratium_, 1758).

[263] _Developpement de la grenouille commune_, Milan,
1826. _Biblioteca italiana_, lxxix., 1836, and Mueller's
_Archiv_, 1836. Agassiz is said by Vogt (1842) to have
seen segmentation in the Perch as early as 1831.

[264] Mueller's _Archiv_, 1836.

[265] In Burdach, _Die Physiologie als
Erfahrungswissenschaft_, 2nd Ed., vol. ii.

[266] Wiegmann's _Archiv_, 1837.

[267] _Bericht Versamml. deutsch. Naturf. in Prag_, 1837.

[268] _Bericht Versamm. deutsch. Naturf. in Freiburg_,
1838. Later in his _Entw. d. Wirbelth_., and in his
papers on the development of the rabbit.

[269] _Phil. Trans._, 1839. See particularly Pl. vi.,
figs. 105-12.

[270] _Embryologie des Salmones_ 1842.

[271] Mueller's _Archiv_, 1847.

[272] _C.R. Acad. Sci._, xxx., p. 638.

[273] See review by Leydig in _Isis_, 1848, pp. 161-193.

[274] Mueller's _Archiv_, pp. 89-102, 1841.

[275] _De evolution Stronzyli auric. el Ascaridis acum._,
Erlangen, 1841.

[276] Mueller's _Archiv_, pp. 66-141, 1843.

[277] _Entwickelungsgeschichte der Cephalopoden_, Zurich,
1844.

[278] _Froriep's Notizen_, No. 800, 1846.

[279] _Isis_, 1848.

[280] Mueller's _Archiv_, p. 47, 1852, also 1854 and 1858.

[281] See particularly Plate IX., figs. 3-7.

[282] _Hist.-krit. Bemerkungen zu den neuesten
Mittheilungen ue. d. erste Entwickelung d.
Saeugethiereier_, Muenchen, 1877.

[283] _Monatsber. Akad. Wiss. Berlin_, 1851.

[284] _Zur Lehre von Generationswechsel u. d. Fortpflanzen
d. Medusen u. Polypen_.

[285] _U. d. Bau u. d. system. Stellung d. Raederthiere_,
1854.

[286] _Arch f. path. Anat. Phys._, vii., pp. 1-39, 1854.
Also in his _Beitraege z. spec. Path. u. Therapie_.

[287] _Die Cellularpathologie_, Berlin, 1858.

[288] _Lehrbuch der Histologie_, 1857.

[289] _Ann, Sci. nat._ (2) iii., pp. 108-9 and pp. 312-4,
1835. Also iv, pp. 343-77.

[290] 1839 or 1840.

[2913] _Nova Acta Acad. Leop._, xxii., 1850. Trans. in 1853
for Ray Society.

[292] _Arch. f. Anat. u. Physiol._, pp. 1-27, 1861.

CHAPTER XII

THE CLOSE OF THE PRE-EVOLUTIONARY PERIOD

The influence of the cell-theory on morphology was not altogether happy.
The cell-theory was from the first physiological; cells were looked upon
as centres of force rather than elements of form, and the explanation of
all the activities of the organism was sought in the action of these
separate dynamic centres. There resulted a certain loss of feeling for
the problems of form. The organism was seen no longer as a cunningly
constructed complex of organs, tissues and cells; it had become a mere
cell-aggregate; the higher elements of form were disregarded and
ignored.

We have seen this physiological attitude expressed with the utmost
clearness by the founder of the cell-theory himself; we shall see the
same attitude taken up by most of his successors. Thus Vogt, who was
later to become one of the protagonists of materialism in Germany,
developed in his memoir on the embryology of _Coregonus_[293] the theory
of the independent or individual life of the cell. "Each cell," he
wrote, "represents in some measure a separate organism, and while their
development necessarily conforms to the general plan and the particular
tendencies of the parent organism, they nevertheless each follow their
own particular tendency and do not lose their independence until, by
reason of the metamorphoses which they undergo, they lose their cellular
nature" (p. 275).

And again, "... we are obliged to admit the existence in the cell of an
independent life, which makes its development self-sufficient.... Each
cell consequently represents a little independent organism, which
assimilates foreign substances, builds them up, and rejects those that
are useless; from this point of view the embryo can be compared up to a
certain point with a zoophyte stock, of which each polyp, while living
its own independent life, is yet incorporated in the common corm, which
impresses its distinctive character upon every polyp" (p. 293).

Classical expression was given to the "colonial theory" of the organism
by Virchow in his lectures on "Cellular Pathology."[294] For Virchow the
organism resolves itself into an assemblage of living centres, the
cells; the organism has no real existence as a unity, for there is no
one single centre from which its activities are ruled. Even the nervous
system, which appears to act as a co-ordinating centre, is itself an
aggregate of discrete cells. "A tree is a body of definite and orderly
composition, the ultimate elements of which, in every part of it, in
leaf and root, in stem and flower, are cellular elements--so also are
animal forms. _Every animal is a sum of vital units_, each of which
possesses the full characteristics of life. The character and the unity
of life cannot be found in one definite point of a higher organisation,
for example in the brain of man, but only in the definite, constantly
recurring disposition shown individually by each single element. It
follows that the composition of the major organism, the so-called
individual, must be likened to a kind of social arrangement or society,
in which a number of separate existences are dependent upon one another,
in such a way, however, that each element possesses its own particular
activity, and, although receiving the stimulus to activity from the
other elements, carries out its own task by its own powers" (2nd ed.,
pp. 12-13).

Analysis, decomposition, or disintegration of the organism is here
pushed to its extreme point, and the problem of recomposition, synthesis
and co-ordination shirked or forgotten.

The harmful influence of the cell-theory upon morphology did not pass
unnoticed by the broader-minded zoologists of the day. Virchow's earlier
paper[295] on the application of the cell-theory to physiology and
pathology called forth a vigorous protest from Reichert,[296] who
discussed in a very instructive way the contrast between the older
"systematic" and the newer "atomistic" attitude to living Nature.

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