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 labor 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 successively 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 that
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 qualification as arises 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 predictable 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 color, a comparatively small number of
colorless corpuscles, of somewhat larger size and very irregular shape. If
the drop of blood be kept at the temperature of the body, these colorless
corpuscles will be seen to exhibit a marvelous 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 polyp, 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
colorless 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 favor 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, and 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, or 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 that 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 toward 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 protein 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 effected 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 from 40 to 50 degrees Centigrade, which has been called
"heat-stiffening"; though Kuhne'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, it 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,--
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's 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
handbreadth 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 trivial 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
on 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 crustacea 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.
Therefore, in seeking for the origin of protoplasm, we must eventually
turn to the vegetable world. The fluid containing carbonic acid, water,
and ammonia, which offers such a Barmecide feast to the animal, is a table
richly spread to multitudes of plants; and, with a due supply of only such
materials, many a plant will not only maintain itself in vigor, but grow
and multiply until it has increased a million-fold, or a
million-million-fold, the quantity of protoplasm which it originally
possessed; in this way building up the matter of life, to an indefinite
extent, from the common matter of the universe.
Thus, the animal can only raise the complex substance of dead protoplasm
to the higher power, as one may say, of living protoplasm; while the plant
can raise the less complex substances--carbonic acid, water, and
ammonia--to the same stage of living protoplasm, if not to the same level.
But the plant also has its limitations. Some of the fungi, for example,
appear to need higher compounds to start with; and no known plant can live
upon the uncompounded elements of protoplasm. A plant supplied with pure
carbon, hydrogen, oxygen, and nitrogen, phosphorus, sulphur and the like,
would as infallibly die as the animal in his bath of smelling-salts,
though it would be surrounded by all the constituents of protoplasm. Nor,
indeed, need the process of simplification of vegetable food be carried so
far as this, in order to arrive at the limit of the plant's thaumaturgy.
Let water, carbonic acid, and all the other needful constituents be
supplied with ammonia, and an ordinary plant will still be unable to
manufacture protoplasm.
Thus the matter of life, so far as we know it (and we have no right to
speculate on any other), breaks up, in consequence of that continual death
which is the condition of its manifesting vitality, into carbonic acid,
water, and ammonia, which certainly possess no properties but those of
ordinary matter. And out of these same forms of ordinary matter, and from
none which are simpler, the vegetable world builds up all the protoplasm
that keeps the animal world a-going. Plants are the accumulators of the
power which animals distribute and disperse.
But it will be observed that the existence of the matter of life depends
on the preexistence of certain compounds; namely, carbonic acid, water,
and ammonia. Withdraw any one of these three from the world, and all vital
phenomena come to an end. They are related to the protoplasm of the plant,
as the protoplasm of the plant is to that of the animal. Carbon, hydrogen,
oxygen, and nitrogen are all lifeless bodies. Of these, carbon and oxygen
unite in certain proportions, and under certain conditions, to give rise
to carbonic acid; hydrogen and oxygen produce water; nitrogen and hydrogen
give rise to ammonia. These new compounds, like the elementary bodies of
which they are composed, are lifeless. But when they are brought together,
under certain conditions, they give rise to the still more complex body,
protoplasm, and this protoplasm exhibits the phenomena of life.
I see no break in this series of steps in molecular complication, and I am
unable to understand why the language which is applicable to any one term
of the series may not be used with any of the others. We think fit to call
different kinds of matter carbon, oxygen, hydrogen, and nitrogen, and to
speak of the various powers and activities of these substances as the
properties of the matter of which they are composed.
When hydrogen and oxygen are mixed in a certain proportion, and an
electric spark is passed through them, they disappear, and a quantity of
water, equal in weight to the sum of their weights, appears in their
place. There is not the slightest parity between the passive and active
powers of the water and those of the oxygen and hydrogen which have given
rise to it. At 32 degrees Fahrenheit, and far below that temperature,
oxygen and hydrogen are elastic gaseous bodies, whose particles tend to
rush away from one another with great force. Water, at the same
temperature, is a strong though brittle solid, whose particles tend to
cohere into definite geometrical shapes, and sometimes build up frosty
imitations of the most complex forms of vegetable foliage.
Nevertheless we call these, and many other strange phenomena, the
properties of the water, and we do not hesitate to believe that, in some
way or another, they result from the properties of the component elements
of the water. We do not assume that a something called "aquosity" entered
into and took possession of the oxide of hydrogen as soon as it was
formed, and then guided the aqueous particles to their places in the
facets of the crystal, or among the leaflets of the hoar-frost. On the
contrary, we live in the hope and in the faith that, by the advance of
molecular physics, we shall by-and-by be able to see our way as clearly
from the constituents of water to the properties of water, as we are now
able to deduce the operations of a watch from the form of its parts and
the manner in which they are put together.
Is the case in any way changed when carbonic acid, water, and ammonia
disappear, and in their place, under the influence of preexisting living
protoplasm, an equivalent weight of the matter of life makes its
appearance?
It is true that there is no sort of parity between the properties of the
components and the properties of the resultant; but neither was there in
the case of the water. It is also true that what I have spoken of as the
influence of preexisting living matter is something quite unintelligible;
but does anybody quite comprehend the _modus operandi_ of an electric
spark, which traverses a mixture of oxygen and hydrogen?
What justification is there, then, for the assumption of the existence in
the living matter of a something which has no representative, or
correlative, in the not-living matter which gave rise to it? What better
philosophical status has "vitality" than "aquosity"? And why should
"vitality" hope for a better fate than the other "itys" which have
disappeared since Martinus Scriblerus accounted for the operation of the
meat-jack by its inherent "meat-roasting quality," and scorned the
"materialism" of those who explained the turning of the spit by a certain
mechanism worked by the draught of the chimney?
If scientific language is to possess a definite and constant signification
whenever it is employed, it seems to me that we are logically bound to
apply to the protoplasm, or physical basis of life, the same conceptions
as those which are held to be legitimate elsewhere. If the phenomena
exhibited by water are its properties, so are those presented by
protoplasm, living or dead, its properties.
If the properties of water may be properly said to result from the nature
and disposition of its component molecules, I can find no intelligible
ground for refusing to say that the properties of protoplasm result from
the nature and disposition of its molecules.
But I bid you beware lest, in accepting these conclusions, you are placing
your feet on the first rung of a ladder which, in most people's
estimation, is the reverse of Jacob's, and leads to the antipodes of
heaven. It may seem a small thing to admit that the dull, vital actions of
a fungus are the properties of its protoplasm, and are the direct results
of the nature of the matter of which it is composed. But if, as I have
endeavored to prove to you, its protoplasm is essentially identical with,
and most readily converted into, that of any animal, I can discover no
logical halting-place between the admission that such is the case, and the
further concession that all vital action may, with equal propriety, be
said to be the result of the molecular forces of the protoplasm which
displays it. And if so, it must be true, in the same sense and to the same
extent, that the thoughts to which I am now giving utterance, and your
thoughts regarding them, are the expression of molecular changes in that
matter of life which is the source of our other vital phenomena.