particle, which finds space and duration enough to multiply into
countless millions in the body of a living fly; and then of the wealth
of foliage, the luxuriance of flower and fruit, which lies between this
bald sketch of a plant and the giant pine of California, towering to the
dimensions of a cathedral spire, or the Indian fig, which covers acres
with its profound shadow, and endures while nations and empires come and
go around its vast circumference. Or, turning to the other half of the
world of life, picture to yourselves the great Finner whale, hugest of
beasts that live, or have lived, disporting his eighty or ninety feet of
bone, muscle, and blubber, with easy roll, among waves in which the
stoutest ship that ever left dockyard would flounder hopelessly; and
contrast him with the invisible animalcules--mere gelatinous specks,
multitudes of which could, in fact, dance upon the point of a needle
with the same ease as the angels of the Schoolmen could, in imagination.
With these images before your minds, you may well ask, what community of
form, or structure, is there between the animalcule and the whale; or
between the fungus and the fig-tree? And, _à fortiori_[49], between all
four?
Finally, if we regard substance, or material composition, what hidden
bond can connect the flower which a girl wears in her hair and the blood
which courses through her youthful veins; or, what is there in common
between the dense and resisting mass of the oak, or the strong fabric of
the tortoise, and those broad disks of glassy jelly which may be seen
pulsating through the waters of a calm sea, but which drain away to mere
films in the hand which raises them out of their element?
Such objections as these must, I think, arise in the mind of every one
who ponders, for the first time, upon the conception of a single
physical basis of life underlying all the diversities of vital
existence; but I propose to demonstrate to you that, notwithstanding
these apparent difficulties, a threefold unity--namely, a unity of
power or faculty, a unity of form, and a unity of substantial
composition--does pervade the whole living world.
No very abstruse argumentation is needed, in the first place, to prove
that the powers, or faculties, of all kinds of living matter, diverse as
they may be in degree, are substantially similar in kind.
Goethe has condensed a survey of all powers of mankind into the
well-known epigram:--
"Warum treibt sich das Volk so und schreit? Es will sich ernähren,
Kinder zeugen, und die nähren so gut es vermag.
* * * * *
Weiter bringt es kein Mensch, stell' er sich wie er auch will."[50]
In physiological language this means, that all the multifarious and
complicated activities of man are comprehensible under three categories.
Either they are immediately directed towards the maintenance and
development of the body, or they effect transitory changes in the
relative positions of parts of the body, or they tend towards the
continuance of the species. Even those manifestions of intellect, of
feeling, and of will, which we rightly name the higher faculties, are
not excluded from this classification, inasmuch as to every one but the
subject of them, they are known only as transitory changes in the
relative positions of parts of the body. Speech, gesture, and every
other form of human action are, in the long run, resolvable into
muscular contraction, and muscular contraction is but a transitory
change in the relative positions of the parts of a muscle. But the
scheme which is large enough to embrace the activities of the highest
form of life, covers all those of the lower creatures. The lowest plant,
or animalcule, feeds, grows, and reproduces its kind. In addition, all
animals manifest those transitory changes of form which we class under
irritability and contractility; and it is more than probable that when
the vegetable world is thoroughly explored, we shall find all plants in
possession of the same powers, at one time or other of their existence.
I am not now alluding to such phenomena, at once rare and conspicuous,
as those exhibited by the leaflets of the sensitive plants, or the
stamens of the barberry, but to much more widely spread, and at the same
time, more subtle and hidden, manifestions of vegetable contractility.
You are doubtless aware that the common nettle owes its stinging
property to the innumerable stiff and needle-like, though exquisitely
delicate, hairs which cover its surface. Each stinging-needle tapers
from a broad base to a slender summit, which, though rounded at the end,
is of such microscopic fineness that it readily penetrates, and breaks
off in, the skin. The whole hair consists of a very delicate outer case
of wood, closely applied to the inner surface of which is a layer of
semi-fluid matter, full of innumerable granules of extreme minuteness.
This semi-fluid lining is protoplasm, which thus constitutes a kind of
bag, full of a limpid liquid, and roughly corresponding in form with the
interior of the hair which it fills. When viewed with a sufficiently
high magnifying power, the protoplasmic layer of the nettle hair is seen
to be in a condition of unceasing activity. Local contractions of the
whole thickness of its substance pass slowly and gradually from point to
point, and give rise to the appearance of progressive waves, just as the
bending of successive stalks of corn by a breeze produces the apparent
billows of a corn-field.
But, in addition to these movements, and independently of them, the
granules are driven, in relatively rapid streams, through channels in
the protoplasm which seem to have a considerable amount of persistence.
Most commonly, the currents in adjacent parts of the protoplasm take
similar directions; and, thus, there is a general stream up one side of
the hair and down the other. But this does not prevent the existence of
partial currents which take different routes; and sometimes trains of
granules may be seen coursing swiftly in opposite directions within a
twenty-thousandth of an inch of one another; while, occasionally,
opposite streams come into direct collision, and, after a longer or
shorter struggle, one predominates. The cause of these currents seems to
lie in contractions of the protoplasm which bounds the channels in which
they flow, but which are so minute that the best microscopes show only
their effects, and not themselves.
The spectacle afforded by the wonderful energies prisoned within the
compass of the microscopic hair of a plant, which we commonly regard as
a merely passive organism, is not easily forgotten by one who has
watched its display, continued hour after hour, without pause or sign of
weakening. The possible complexity of many other organic forms,
seemingly as simple as the protoplasm of the nettle, dawns upon one; and
the comparison of such a protoplasm to a body with an internal
circulation, which has been put forward by an eminent physiologist,
loses much of its startling character. Currents similar to those of the
hairs of the nettle have been observed in a great multitude of very
different plants, and weighty authorities have suggested that they
probably occur, in more or less perfection, in all young vegetable
cells. If such be the case, the wonderful noonday silence of a tropical
forest is, after all, due only to the dullness of our hearing; and could
our ears catch the murmur of these tiny Maelstroms, as they whirl in the
innumerable myriads of living cells which constitute each tree, we
should be stunned, as with the roar of a great city.
Among the lower plants, it is the rule rather than the exception, that
contractility should be still more openly manifested at some periods of
their existence. The protoplasm of _Algae_ and _Fungi_ becomes, under
many circumstances, partially, or completely, freed from its woody case,
and exhibits movements of its whole mass, or is propelled by the
contractility of one, or more, hair-like prolongations of its body,
which are called vibratile cilia. And, so far as the conditions of the
manifestation of the phenomena of contractility have yet been studied,
they are the same for the plant as for the animal. Heat and electric
shocks influence both, and in the same way, though it may be in
different degrees. It is by no means my intention to suggest that there
is no difference in faculty between the lowest plant and the highest, or
between plants and animals. But the difference between the powers of the
lowest plant, or animal, and those of the highest, is one of degree, not
of kind, and depends, as Milne-Edwards long ago so well pointed out,
upon the extent to which the principle of the division of labour is
carried out in the living economy. In the lowest organism all parts are
competent to perform all functions, and one and the same portion of
protoplasm may successfully take on the function of feeding, moving, or
reproducing apparatus. In the highest, on the contrary, a great number
of parts combine to perform each function, each part doing its allotted
share of the work with great accuracy and efficiency, but being useless
for any other purpose.
On the other hand, notwithstanding all the fundamental resemblances
which exist between the powers of the protoplasm in plants and in
animals, they present a striking difference (to which I shall advert
more at length presently), in the fact that plants can manufacture fresh
protoplasm out of mineral compounds, whereas animals are obliged to
procure it ready made, and hence, in the long run, depend upon plants.
Upon what condition this difference in the powers of the two great
divisions of the world of life depends, nothing is at present known.
With such qualifications as arise out of the last-mentioned fact, it may
be truly said that the acts of all living things are fundamentally one.
Is any such unity predicable of their forms? Let us seek in easily
verified facts for a reply to this question. If a drop of blood be drawn
by pricking one's finger, and viewed with proper precautions, and under
a sufficiently high microscopic power, there will be seen, among the
innumerable multitude of little, circular, discoidal bodies, or
corpuscles, which float in it and give it its colour, a comparatively
small number of colourless corpuscles, of somewhat larger size and very
irregular shape. If the drop of blood be kept at the temperature of the
body, these colourless corpuscles will be seen to exhibit a marvellous
activity, changing their forms with great rapidity, drawing in and
thrusting out prolongations of their substance, and creeping about as if
they were independent organisms.
The substance which is thus active is a mass of protoplasm, and its
activity differs in detail, rather than in principle, from that of the
protoplasm of the nettle. Under sundry circumstances the corpuscle dies
and becomes distended into a round mass, in the midst of which is seen a
smaller spherical body, which existed, but was more or less hidden, in
the living corpuscle, and is called its _nucleus_. Corpuscles of
essentially similar structure are to be found in the skin, in the lining
of the mouth, and scattered through the whole framework of the body.
Nay, more: in the earliest condition of the human organism, in that
state in which it has but just become distinguishable from the egg in
which it arises, it is nothing but an aggregation of such corpuscles,
and every organ of the body was, once, no more than such an aggregation.
Thus a nucleated mass of protoplasm turns out to be what may be termed
the structural unit of the human body. As a matter of fact, the body, in
its earliest state, is a mere multiple of such units; and in its perfect
condition, it is a multiple of such units, variously modified.
But does the formula which expresses the essential structural character
of the highest animal cover all the rest, as the statement of its powers
and faculties covered that of all others? Very nearly. Beast and fowl,
reptile and fish, mollusk, worm, and polype, are all composed of
structural units of the same character, namely, masses of protoplasm
with a nucleus. There are sundry very low animals, each of which,
structurally, is a mere colourless blood-corpuscle, leading an
independent life. But, at the very bottom of the animal scale, even this
simplicity becomes simplified, and all the phenomena of life are
manifested by a particle of protoplasm without a nucleus. Nor are such
organisms insignificant by reason of their want of complexity. It is a
fair question whether the protoplasm of those simplest forms of life,
which people an immense extent of the bottom of the sea, would not
outweigh that of all the higher living beings which inhabit the land put
together. And in ancient times, no less than at the present day, such
living beings as these have been the greatest of rock builders.
What has been said of the animal world is no less true of plants.
Imbedded in the protoplasm at the broad, or attached, end of the nettle
hair, there lies a spheroidal nucleus. Careful examination further
proves that the whole substance of the nettle is made up of a repetition
of such masses of nucleated protoplasm, each contained in a wooden case,
which is modified in form, sometimes into a woody fibre, sometimes into
a duct or spiral vessel, sometimes into a pollen grain, or an ovule.
Traced back to its earliest state, the nettle arises as the man does, in
a particle of nucleated protoplasm. And in the lowest plants, as in the
lowest animals, a single mass of such protoplasm may constitute the
whole plant, or the protoplasm may exist without a nucleus.
Under these circumstances it may well be asked, how is one mass of
non-nucleated protoplasm to be distinguished from another? why call one
"plant" and the other "animal"?
The only reply is that, so far as form is concerned, plants and animals
are not separable, and that, in many cases, it is a mere matter of
convention whether we call a given organism an animal or a plant. There
is a living body called _Aethalium septicum_, which appears upon
decaying vegetable substances, and, in one of its forms, is common upon
the surfaces of tan-pits. In this condition it is, to all intents and
purposes, a fungus, and formerly was always regarded as such; but the
remarkable investigations of De Bary have shown that, in another
condition, the _Aethalium_ is an actively locomotive creature, and takes
in solid matters, upon which, apparently, it feeds, thus exhibiting the
most characteristic feature of animality. Is this a plant; or is it an
animal? Is it both; or is it neither? Some decide in favour of the last
supposition, and establish an intermediate kingdom, a sort of biological
No Man's Land for all these questionable forms. But, as it is admittedly
impossible to draw any distinct boundary line between this no man's land
and the vegetable world on the one hand, or the animal on the other, it
appears to me that this proceeding merely doubles the difficulty which,
before, was single.
Protoplasm, simple or nucleated, is the formal basis of all life. It is
the clay of the potter: which, bake it and paint it as he will, remains
clay, separated by artifice, and not by nature, from the commonest brick
or sun-dried clod.
Thus it becomes clear that all living powers are cognate, and that all
living forms are fundamentally of one character. The researches of the
chemist have revealed a no less striking uniformity of material
composition in living matter.
In perfect strictness, it is true that chemical investigation can tell
us little or nothing, directly, of the composition of living matter,
inasmuch as such matter must needs die in the act of analysis,--and upon
this very obvious ground, objections, which I confess seem to me to be
somewhat frivolous, have been raised to the drawing of any conclusions
whatever respecting the composition of actually living matter, from that
of the dead matter of life, which alone is accessible to us. But
objectors of this class do not seem to reflect that it is also, in
strictness, true that we know nothing about the composition of any body
whatever, as it is. The statement that a crystal of calc-spar consists
of carbonate of lime, is quite true, if we only mean that, by
appropriate processes, it may be resolved into carbonic acid and
quicklime. If you pass the same carbonic acid over the very quicklime
thus obtained, you will obtain carbonate of lime again; but it will not
be calc-spar, nor anything like it. Can it, therefore, be said that
chemical analysis teaches nothing about the chemical composition of
calc-spar? Such a statement would be absurd; but it is hardly more so
than the talk one occasionally hears about the uselessness of applying
the results of chemical analysis to the living bodies which have yielded
them.
One fact, at any rate, is out of reach of such refinements, and this is,
that all the forms of protoplasm which have yet been examined contain
the four elements, carbon, hydrogen, oxygen, and nitrogen, in very
complex union, and that they behave similarly towards several reagents.
To this complex combination, the nature of which has never been
determined with exactness, the name of Protein has been applied. And if
we use this term with such caution as may properly arise out of our
comparative ignorance of the things for which it stands, it may be truly
said that all protoplasm is proteinaceous, or, as the white, or albumen,
of an egg is one of the commonest examples of a nearly pure proteine
matter, we may say that all living matter is more or less albuminoid.
Perhaps it would not yet be safe to say that all forms of protoplasm are
affected by the direct action of electric shocks; and yet the number of
cases in which the contraction of protoplasm is shown to be affected by
this agency increases every day.
Nor can it be affirmed with perfect confidence, that all forms of
protoplasm are liable to undergo that peculiar coagulation at a
temperature of 40°-50° Centigrade, which has been called
"heat-stiffening," though Kühne's beautiful researches have proved this
occurrence to take place in so many and such diverse living beings, that
it is hardly rash to expect that the law holds good for all.
Enough has, perhaps, been said, to prove the existence of a general
uniformity in the character of the protoplasm, or physical basis, of
life, in whatever group of living beings it may be studied. But it will
be understood that this general uniformity by no means excludes any
amount of special modifications of the fundamental substance. The
mineral, carbonate of lime, assumes an immense diversity of characters,
though no one doubts that, under all these Protean changes, is one and
the same thing.
And now, what is the ultimate fate, and what the origin, of the matter
of life?
Is it, as some of the older naturalists supposed, diffused throughout
the universe in molecules, which are indestructible and unchangeable in
themselves; but, in endless transmigration, unite in innumerable
permutations, into the diversified forms of life we know? Or, is the
matter of life composed of ordinary matter, differing from it only in
the manner in which its atoms are aggregated? Is it built up of ordinary
matter, and again resolved into ordinary matter when its work is done?
Modern science does not hesitate a moment between these alternatives.
Physiology writes over the portals of life--
"Debemur morti nos nostraque,"[51]
with a profounder meaning than the Roman poet attached to that
melancholy line. Under whatever disguise it takes refuge, whether fungus
or oak, worm or man, the living protoplasm not only ultimately dies and
is resolved into its mineral and lifeless constituents, but is always
dying, and, strange as the paradox may sound, could not live unless it
died.
In the wonderful story of the _Peau de Chagrin_, the hero becomes
possessed of a magical wild ass' skin, which yields him the means of
gratifying all his wishes. But its surface represents the duration of
the proprietor's life; and for every satisfied desire the skin shrinks
in proportion to the intensity of fruition, until at length life and the
last handbreath of the _peau de chagrin_, disappear with the
gratification of a last wish.
Balzac's studies had led him over a wide range of thought and
speculation, and his shadowing forth of physiological truth in this
strange story may have been intentional. At any rate, the matter of life
is a veritable _peau de chagrin_, and for every vital act it is somewhat
the smaller. All work implies waste, and the work of life results,
directly or indirectly, in the waste of protoplasm.
Every word uttered by a speaker costs him some physical loss; and, in
the strictest sense, he burns that others may have light--so much
eloquence, so much of his body resolved into carbonic acid, water, and
urea. It is clear that this process of expenditure cannot go on forever.
But, happily, the protoplasmic _peau de chagrin_ differs from Balzac's
in its capacity of being repaired, and brought back to its full size,
after every exertion.
For example, this present lecture, whatever its intellectual worth to
you, has a certain physical value to me, which is, conceivably,
expressible by the number of grains of protoplasm and other bodily
substance wasted in maintaining my vital processes during its delivery.
My _peau de chagrin_ will be distinctly smaller at the end of the
discourse than it was at the beginning. By and by, I shall probably have
recourse to the substance commonly called mutton, for the purpose of
stretching it back to its original size. Now this mutton was once the
living protoplasm, more or less modified, of another animal--a sheep. As
I shall eat it, it is the same matter altered, not only by death, but by
exposure to sundry artificial operations in the process of cooking.
But these changes, whatever be their extent, have not rendered it
incompetent to resume its old functions as matter of life. A singular
inward laboratory, which I possess, will dissolve a certain portion of
the modified protoplasm; the solution so formed will pass into my
veins; and the subtle influences to which it will then be subjected will
convert the dead protoplasm into living protoplasm, and transubstantiate
sheep into man.
Nor is this all. If digestion were a thing to be trifled with, I might
sup upon lobster, and the matter of life of the crustacean would undergo
the same wonderful metamorphosis into humanity. And were I to return to
my own place by sea, and undergo shipwreck, the crustacean might, and
probably would, return the compliment, and demonstrate our common nature
by turning my protoplasm into living lobster. Or, if nothing better were
to be had, I might supply my wants with mere bread, and I should find
the protoplasm of the wheat-plant to be convertible into man with no
more trouble than that of the sheep, and with far less, I fancy, than
that of the lobster.
Hence it appears to be a matter of no great moment what animal, or what
plant, I lay under contribution for protoplasm, and the fact speaks
volumes for the general identity of that substance in all living beings.
I share this catholicity of assimilation with other animals, all of
which, so far as we know, could thrive equally well on the protoplasm of
any of their fellows, or of any plant; but here the assimilative powers
of the animal world cease. A solution of smelling-salts in water, with
an infinitesimal proportion of some other saline matters, contains all
the elementary bodies which enter into the composition of protoplasm;
but, as I need hardly say, a hogshead of that fluid would not keep a
hungry man from starving, nor would it save any animal whatever from a
like fate. An animal cannot make protoplasm, but must take it ready-made
from some other animal, or some plant--the animal's highest feat of
constructive chemistry being to convert dead protoplasm into that living
matter of life which is appropriate to itself.