THE FACTORS CONCERNED IN THE BUILDING OF THE LIVING
MACHINE.
History of the living machine--Evidence for this
history--Historical--Embryological--Anatomical--Significance
of these sources of history--Forces at work in the building of
the living machine--Reproduction--Heredity--Variation--Inheritance
of variations--Method of machine building--Migration and
isolation--Direct influence of environment--Consciousness--Summary
of Nature's power of building machines--The origin of the cell
machine--General summary 131
LIST OF ILLUSTRATIONS.
FIGURE PAGE
_Amoeba Polypodia_ in six successive stages of division _Frontispiece_
1. Figure illustrating osmosis 30
2. Figure illustrating osmosis 31
3. Diagram of the intestinal walls 32
4. Diagram of a single villus 33
5. Enlarged figure of four cells in the villus membrane 33
6. A bit of muscle showing blood-vessels 36
7. A bit of bark showing cellular structure 61
8. Successive stages in the division of the developing
egg 63
9. A typical cell 65
10. Cells at a root tip 66
11. Section of a leaf showing cells of different shapes 66
12. Plant cells with thick walls, from a fern 67
13. Section of potato 67
14. Various shaped wood cells from plant tissue 68
15. A bit of cartilage 68
16. Frogs' blood 69
17. A bit of bone 69
18. Connective tissue 70
19. A piece of nerve fibre 70
20. A muscle fibre 71
21. A complex cell, vorticella 71
22. An amoeba 73
23. A cell as it appears to the modern microscope 86
24. A cell cut into pieces, each containing a bit of
nucleus 89
25. A cell cut in pieces, only one of which contains any
nucleus 90
26. Different forms of nucleii 93
27 and 28. Two stages in cell division 96
29 and 30. Stages in cell division 98
31 and 32. Latest stages in cell division 100
33. An egg 103
34 and 35. Stages in the process of fertilization of the
egg 104
36 and 37. Stages in the process of fertilization of the
egg 105
38, 39, and 40. Stages in fertilization of the egg 106
41 and 42. Latest stages in the fertilization of the egg 109
43 and 44. Two stages in the division of the egg 111
45. A group of cells resulting from division, the first step
in machine building 135
46. A later step in machine building, the gastrula 135
47. The arm of a monkey 144
48. The arm of a bird 144
49. The arm of an ancient half-bird, half-reptile animal 144
50. Diagram to illustrate the principle of heredity 156
THE STORY OF THE LIVING MACHINE.
INTRODUCTION.
==Biology a New Science==.--In recent years biology has been spoken of as
a new science. Thirty years ago departments of biology were practically
unknown in educational institutions. To-day none of our higher
institutions of learning considers itself equipped without such a
department. This seems to be somewhat strange. Biology is simply the
study of living things; and living nature has been studied as long as
mankind has studied anything. Even Aristotle, four hundred years before
Christ, classified living things. From this foundation down through the
centuries living phenomena have received constant attention. Recent
centuries have paid more attention to living things than to any other
objects in nature. Linnæus erected his systems of classification before
modern chemistry came into existence; the systematic study of zoology
antedated that of physics; and long before geology had been conceived in
its modern form, the animal and vegetable kingdoms had been comprehended
in a scientific system. How, then, can biology be called a new science
When it is older than all the others?
There must be some reason why this, the oldest of all, has been recently
called a _new_ science, and some explanation of the fact that it has
only recently advanced to form a distinct department in our educational
system. The reason is not difficult to find. Biology is a new science,
not because the objects it studies are new, but because it has adopted a
new relation to those objects and is studying them from a new
standpoint. Animals and plants have been studied long enough, but not as
we now study them. Perhaps the new attitude adopted toward living nature
may be tersely expressed by saying that in the past it has been studied
as _at rest_, while to-day it is studied as _in motion_. The older
zoologists and botanists confined themselves largely to the study of
animals and plants simply as so many museum specimens to be arranged on
shelves with appropriate names. The modern biologist is studying these
same objects as intensely active beings and as parts of an ever-changing
history. To the student of natural history fifty years ago, animals and
plants were objects to be _classified_; to the biologist of to-day, they
are objects to be _explained_.
To understand this new attitude, a brief review of the history of the
fundamental features of philosophical thought will be necessary. When,
long ago, man began to think upon the phenomena of nature, he was able
to understand almost nothing. In his inability to comprehend the
activities going on around him he came to regard the forces of nature as
manifestations of some supernatural beings. This was eminently natural.
He had a direct consciousness of his own power to act, and it was
natural for him to assume that the activities going on around him were
caused by similar powers on the part of some being like himself, only
superior to him. Thus he came to fill the unseen universe with gods
controlling the forces of nature. The wind was the breath of one god,
and the lightning a bolt thrown from the hands of another.
With advancing thought the ideas of polytheism later gave place to the
nobler conception of monotheism. But for a long time yet the same ideas
of the supernatural, as related to the natural, retained their place in
man's philosophy. Those phenomena which he thought he could understand
were looked upon as natural, while those which he could not understand
were looked upon as supernatural, and as produced by the direct personal
activity of some divine agency. As the centuries passed, and man's power
of observation became keener and his thinking more logical, many of the
hitherto mysterious phenomena became intelligible and subject to simple
explanations. As fast as this occurred these phenomena were
unconsciously taken from the realm of the supernatural and placed among
natural phenomena which could be explained by natural laws. Among the
first mysteries to be thus comprehended by natural law were those of
astronomy. The complicated and yet harmonious motions of the heavenly
bodies had hitherto been inexplicable. To explain them many a sublime
conception of almighty power had arisen, and the study of the heavenly
bodies ever gave rise to the highest thoughts of Deity. But Newton's law
of gravitation reduced the whole to the greatest simplicity. Through the
law and force of gravitation these mysteries were brought within the
grasp of human understanding. They ceased to be looked upon as
supernatural, and became natural phenomena as soon as the force of
gravitation was accepted as a part of nature.
In other branches of natural phenomena the same history followed. The
forces and laws of chemical affinity were formulated and studied, and
physical laws and forces were comprehended. As these natural forces were
grasped it became, little by little, evident that the various phenomena
of nature were simply the result of nature's forces acting in accordance
with nature's laws. Phenomena hitherto mysterious were one after another
brought within the realm of law, and as this occurred a smaller and
smaller portion of them were left within the realm of the so-called
supernatural. By the middle of this century this advance had reached a
point where scientists, at least, were ready to believe that nature's
forces were all-powerful to account for nature's phenomena. Science had
passed from the reign of mysticism to the reign of law.
But after chemistry and physics, with all the forces that they could
muster, had exhausted their powers in explaining natural phenomena,
there apparently remained one class of facts which was still left in the
realm of the supernatural and the unexplained. The phenomena associated
with living things remained nearly as mysterious as ever. Life appeared
to be the most inexplicable phenomena of nature, and none of the forces
and laws which had been found sufficient to account for other
departments of nature appeared to have much influence in rendering
intelligible the phenomena of life. Living organisms appeared to be
actuated by an entirely unique force. Their shapes and structure showed
so many marvellous adaptations to their surroundings as to render it
apparently certain that their adjustment must have been the result of
some intelligent planning, and not the outcome of blind force. Who
could look upon the adaptation of the eye to light without seeing in It
the result of intelligent design? Adaptation to conditions is seen in
all animals and plants. These organisms are evidently complicated
machines with their parts intricately adapted to each other and to
surrounding conditions. Apart from animals and plants the only other
similarly adjusted machines are those which have been made by human
intelligence; and the inference seemed to be clear that a similar
intelligence was needed to account for the _living machine_. The blind
action of physical forces seemed inadequate. Thus the phenomena of life,
which had been studied longer than any other phase of nature, continued
to stand aloof from the rest and refused to fall into line with the
general drift of thought. The living world seemed to give no promise of
being included among natural phenomena, but still persisted in retaining
its supernatural aspect.
It is the attempt to explain the phenomena of the living world by the
same kind of natural forces that have been adequate to account for other
phenomena, that has created modern Biology. So long as students simply
studied animals and plants as objects for classification, as museum
objects, or as objects which had been stationary in the history of
nature, so long were they simply following along the same lines in which
their predecessors had been travelling. But when once they began to ask
if living nature were not perhaps subject to an intelligent explanation,
to study living things as part of a general history and to look upon
them as active moving objects whose motion and whose history might
perhaps be accounted for, then at once was created a new department of
thought and a new science inaugurated.
==Historical Geology==.--Preparation had been made for this new method of
studying life by the formulation of a number of important scientific
discoveries. Prominent among these stood historical geology. That the
earth had left a record of her history in the rocks in language plain
enough to be read appears to have been impressed upon scientists in the
last of the century. That the earth has had a history and that man could
read it became more and more thoroughly understood as the first decades
of this century passed. The reading of that history proved a somewhat
difficult task. It was written in a strange language, and it required
many years to discover the key to the record. But under the influence of
the writings of Lyell, just before the middle of the century, it began
to appear that the key to this language is to be found by simply opening
the eyes and observing what is going on around us to-day. A more
extraordinary and more important discovery has hardly ever been made,
for it contained the foundation of nearly all scientific discoveries
which have been made since. This discovery proclaimed that an
application of the forces still at work to-day on the earth's surface,
but continued throughout long ages, will furnish the interpretation of
the history written in the rocks, and thus an explanation of the history
of the earth itself. The slow elevation of the earth's crust, such as is
still going on to-day, would, if continued, produce mountains; and the
washing away of the land by rains and floods, such as we see all around
us, would, if continued through the long centuries, produce the valleys
and gorges which so astound us. The explanation of the past is to be
found in the present. But this geological history told of a history of
life as well as a history of rocks. The history of the rocks has indeed
been bound up in the history of life, and no sooner did it appear that
the earth's crust has had a readable history than it appeared that
living nature had a parallel history. If the present is a key to the
past in interpreting geological history, should not the same be true of
this history of life? It was inevitable that problems of life should
come to the front, and that the study of life from the dynamical
standpoint, rather than a statical, should ensue. Modern biology was the
child of historical geology.
But historical geology alone could never have led to the dynamical phase
of modern biology. Three other conceptions have contributed in an even
greater degree to the development of this science.
==Conservation of Energy==.--The first of these was the doctrine of
conservation of energy and the correlation of forces. This doctrine is
really quite simple, and may be outlined as follows: In the universe, as
we know it, there exists a certain amount of energy or power of doing
work. This amount of energy can neither be increased nor decreased;
energy can no more be created or destroyed than matter. It exists,
however, in a variety of forms, which may be either active or passive.
In the active state it takes some form of motion. The various forces
which we recognize in nature--heat, light, electricity, chemism,
etc.--are simply forms of motion, and thus forms of this energy. These
various types of energy, being only expressions of the universal energy,
are convertible into each other in such a way that when one disappears
another appears. A cannon ball flying through the air exhibits energy of
motion; but it strikes an obstacle and stops. The motion has apparently
stopped, but an examination shows that this is not the case. The cannon
ball and the object it strikes have been heated, and thus the motion of
the ball has simply been transformed into a different form of motion,
which we call heat. Or, again, the heat set free under the locomotive
boiler is converted by machinery into the motion of the locomotive. By
still different mechanism it may be converted into electric force. All
forms of motion are readily convertible into each other, and each form
in which energy appears is only a phase of the total energy of nature.
A second condition of energy is energy at rest, or potential energy. A
stone on the roof of a house is at rest, but by virtue of its position
it has a certain amount of potential energy, since, if dislodged, it
will fall to the ground, and thus develop energy of motion. Moreover, it
required to raise the stone to the roof the expenditure of an amount of
energy exactly equal to that which will reappear if the stone is allowed
to fall to the ground. So in a chemical molecule, like fat, there is a
store of potential energy which may be made active by simply breaking
the molecule to pieces and setting it free. This occurs when the fat
burns and the energy is liberated as heat. But it required at some time
the expenditure of an equal amount of energy to make the molecule. When
the molecule of fat was built in the plant which produced it, there was
used in its construction an amount of solar energy exactly equivalent to
the energy which may be liberated by breaking the molecule to pieces.
The total sum of the active and potential energy in the universe is thus
at all times the same.
This magnificent conception has become the cornerstone of modern
science. As soon as conceived it brought at once within its grasp all
forms of energy in nature. It is primarily a physical doctrine, and has
been developed chiefly in connection with the physical sciences. But it
shows at once a possible connection between living and non-living
nature. The living organism also exhibits motion and heat, and, if the
doctrine of the conservation of energy be true, this energy must be
correlated with other forms of energy. Here is a suggestion that the
same laws control the living and the non-living world; and a suspicion
that if we can find a natural explanation of the burning of a piece of
coal and the motion of a locomotive, so, too, we may find a natural
explanation of the motion of a living machine.
==Evolution==--A second conception, whose influence upon-the development
of biology was even greater, was the doctrine of evolution. It is true
that the doctrine of evolution was no new doctrine with the middle of
this century, for it had been conceived somewhat vaguely before. But
until historical geology had been formulated, and until the idea of the
unity of nature had dawned upon the minds of scientists, the doctrine of
evolution had little significance. It made little difference in our
philosophy whether the living organisms were regarded as independent
creations or as descended from each other, so long as they were looked
upon as a distinct realm of nature without connection with the rest of
nature's activity. If they are distinct from the rest of nature, and
therefore require a distinct origin, it makes little difference whether
we looked upon that origin as a single originating point or as thousands
of independent creations. But so soon as it appeared that the present
condition of the earth's crust was formed by the action of forces still
in existence, and so soon as it appeared that the forces outside of
living forces, including astronomical, physical and chemical forces, are
all correlated with each other as parts of the same store of energy,
then the problem of the origin of living things assumed a new meaning.
Living things became then a part of nature, and demanded to be included
in the same general category. The reign of law, which was claiming that
all nature's phenomena are the result of natural rather than
supernatural powers, demanded some explanation of the origin of living
things. Consequently, when Darwin pointed out a possible way in which
living phenomena could thus be included in the realm of natural law,
science was ready and anxious to receive his explanation.
==Cytology.==--A third conception which contributed to the formulation of
modern biology was derived from the facts discovered in connection with
the organic cell and protoplasm. The significance of these facts we
shall notice later, but here we may simply state that these discoveries
offered to students simplicity in the place of complexity. The doctrine
of cells and protoplasm appeared to offer to biologists no longer the
complicated problems which were associated with animals and plants, but
the same problems stripped of all side issues and reduced to their
lowest terms. This simplifying of the problems proved to be an
extraordinary stimulus to the students who were trying to find some way
of understanding life.
==New Aspects of Biology==.--These three conceptions seized hold of the
scientific world at periods not very distant from each other, and their
influence upon the study of living nature was immediate and
extraordinary. Living things now came to be looked upon not simply as
objects to be catalogued, but as objects which had a history, and a
history which was of interest not merely in itself, but as a part of a
general plan. They were no longer studied as stationary, but as moving
phases of nature. Animals were no longer looked upon simply as beings
now existing, but as the results of the action of past forces and as the
foundation of a different series of beings in the future. The present
existing animals and plants came to be regarded simply as a step in the
long history of the universe. It appeared at once that the study of the
present forms of life would offer us a means of interpreting the past
and perhaps predicting the future.
In a short time the entire attitude which the student assumed toward
living phenomena had changed. Biological science assumed new guises and
adopted new methods. Even the problems which it tried to solve were
radically changed. Hitherto the attempt had been made to find instances
of _purpose_ in nature. The marvellous adaptations of living beings to
their conditions had long been felt, and the study of the purposes of
these adaptations had inspired many a magnificent conception. But now
the scientist lost sight of the purpose in hunting for the _cause._
Natural law is blind and can have no purpose. To the scientist, filled
with the thought of the reign of law, purpose could not exist in
nature. Only cause and effect appeal to him. The present phenomena are
the result of forces acting in the past, and the scientist's search
should be not for the purpose of an adaptation, but for the action of
the forces which produced it. To discover the forces and laws which led
to the development of the present forms of animals and plants, to
explain the method by which these forces of nature have acted to bring
about present results, these became the objects of scientific research.
It no longer had any meaning to find that a special organ was adapted to
its conditions; but it was necessary to find out how it became adapted.
The difference in the attitude of these two points of view is
world-wide. The former fixes the attention upon the end, the latter upon
the means by which the end was attained; the former is what we sometimes
call _teleological_, the latter _scientific;_ the former was the
attitude of the study of animals and plants before the middle of this
century, the latter the spirit which actuates modern biology.
==The Mechanical Nature of Living Organisms.==--This new attitude forced
many new problems to the front. Foremost among them and fundamental to
them all were the questions as to the mechanical nature of living
organisms. The law of the correlation of force told that the various
forms of energy which appear around us--light, heat, electricity,
etc.--are all parts of one common store of energy and convertible into
each other. The question whether vital energy is in like manner
correlated with other forms of energy was now extremely significant.
Living forces had been considered as standing apart from the rest of
nature. _Vital force_, or _vitality_, had been thought of as something
distinct in itself; and that there was any measurable relation between
the powers of the living organism and the forces of heat and chemical
affinity was of course unthinkable before the formulation of the
doctrine of the correlation of forces. But as soon as that doctrine was
understood it began to appear at once that, to a certain extent at
least, the living body might be compared to a machine whose function is
simply to convert one kind of energy into another. A steam engine is fed
with fuel. In that fuel is a store of energy deposited there perhaps
centuries ago. The rays of the sun, shining on the world in earlier
ages, were seized upon by the growing plants and stored away in a
potential form in the wood which later became coal. This coal is placed
in the furnace of the steam engine and is broken to pieces so that it
can no longer hold its store of energy, which is at once liberated in
its active form as heat. The engine then takes the energy thus
liberated, and as a result of its peculiar mechanism converts it into
the motion of its great fly-wheel. With this notion clearly in mind the
question forces itself to the front whether the same facts are not true
of the living animal organism. It, too, is fed with food containing a
store of energy; and should we not regard it, like the steam engine,
simply a machine for converting this potential energy into motion, heat,
or some other active form? This problem of the correlation of vital and
physical forces is inevitably forced upon us with the doctrine of the
correlation of forces. Plainly, however, such questions were
inconceivable before about the middle of the nineteenth century.
This mechanical conception of living activity was carried even farther.
Under the lead of Huxley there arose in the seventh decade of the
century a view of life which reduced it to a pure mechanism. The
microscope had, at that time, just disclosed the universal presence in
living things of that wonderful substance, _protoplasm._ This material
appeared to be a homogeneous substance, and a chemical study showed it
to be made of chemical elements united in such a way as to show close
relation to albumens. It appeared to be somewhat more complex than
ordinary albumen, but it was looked upon as a definite chemical
compound, or, perhaps, as a simple mixture of compounds. Chemists had
shown that the properties of compounds vary with their composition, and
that the more complex the compound the more varied its properties. It
was a natural conception, therefore, that protoplasm was a complex
chemical compound, and that its vital properties were simply the
chemical properties resulting from its composition. Just as water
possesses the power of becoming solid at certain temperatures, so
protoplasm possesses the power of assimilating food and growing; and,
since we do not doubt that the properties of water are the result of its
chemical composition, so we may also assume that the vital properties of
protoplasm are the result of its chemical composition. It followed from
this conclusion that if chemists ever succeeded in manufacturing the
chemical compound, protoplasm, it would be alive. Vital phenomena were
thus reduced to chemical and mechanical problems.
These ideas arose shortly after the middle of the century, and have
dominated the development of biological science up to the present time.
It is evident that the aim of biological study must be to test these
conceptions and carry them out into details. The chemical and mechanical
laws of nature must be applied to vital phenomena in order to see
whether they can furnish a satisfactory explanation of life. Are the
laws and forces of chemistry sufficient to explain digestion? Are the
laws of electricity applicable to an understanding of nervous phenomena?
Are physical and chemical forces together sufficient to explain life?
Can the animal body be properly regarded as a machine controlled by
mechanical laws? Or, on the other hand, are there some phases of life
which the forces of chemistry and physics cannot account for? Are there
limits to the application of natural law to explain life? Can there be
found something connected with living beings which is force but not
correlated with the ordinary forms of energy? Is there such a thing as
_vital energy_, or is the so-called vital force simply a name which we
have given to the peculiar manifestations of ordinary energy as shown in
the substance protoplasm? These are some of the questions that modern
biology is trying to answer, and it is the existence of such questions
which has made modern biology a new science. Such questions not only did
not, but could not, have arisen before the doctrines of the conservation
of energy and evolution had made their impression upon the thought of
the world.
==Significance of the New Biological Problems==--It is further evident
that the answers to these questions will have a significance reaching
beyond the domain of biology proper and affecting the fundamental
philosophy of nature. The answer will determine whether or not we can
accept in entirety the doctrines of the conservation of energy and
evolution. Plainly if it should be found that the energy of animate
nature was not correlated with other forms of energy, this would demand
either a rejection or a complete modification of our doctrine of the
conservation of energy. If an animal can create any energy within
itself, or can destroy any energy, we can no longer regard the amount of
energy of the universe as constant. Even if that subtile form of force
which we call nervous energy should prove to be uncorrelated with other
forms of energy, the idea of the conservation of energy must be changed.
It is even possible that we must insist that the still more subtile form
of force, mental force, must be brought within the scope of this great
law in order that it be implicitly accepted. This law has proved itself
strictly applicable to the inanimate world, and has then thrust upon us
the various questions in regard to vital force, and we must recognize
that the real significance of this great law must rest upon the
possibility of its application to vital phenomena.
No less intimate is the relation of these problems to the doctrine of
evolution. Evolution tries to account for each moment in the history of
the world as the result of the conditions of the moment before. Such a
theory loses its meaning unless it can be shown that natural forces are
sufficient to account for living phenomena. If the supernatural must be
brought in here and there to account for living phenomena, then
evolution ceases to have much meaning. It is undoubtedly a fact that the
rapidly developing ideas along the above mentioned lines of dynamical
biology have, been potent factors in bringing about the adoption of
evolution. Certain it is that, had it been found that no correlation
could be traced between vital and non-vital forces, the doctrine of
evolution could not have stood, and even now the special significance
which we shall in the end give to evolution will depend upon how we
succeed in answering the questions above outlined. The fact is that this
problem of the mechanical explanation of vital phenomena forms the
capstone of the arch, the sides of which are built of the doctrines of
the conservation of energy and the theory of evolution. To the
presentation of these problems the following pages will be devoted. The
fact that both the doctrine of the conservation of energy and that of
evolution are practically everywhere accepted indicates that the
mechanical nature of vital forces is regarded as proved. But there are
still many questions which are not so easily answered. It will be our
purpose in the following discussion to ascertain just what are these
problems in dynamical biology and how far they have been answered. Our
object will be then in brief to discover to what extent the conception
of the living organism as a machine is borne out by the facts which have
been collected in the last quarter century, and to learn where, if
anywhere, limits have been found to our possibility of applying the
forces of chemistry and physics to an explanation of life. In other
words, we shall try to see how far we have been able to understand
living phenomena in terms of natural force.
==Outline of the Subject==.--The subject, as thus presented, resolves
itself at once into two parts. That the living organism is a machine is
everywhere recognized, although some may still doubt as to the
completeness of the comparison. In the attempt to explain the phenomena
of life we have two entirely different problems. The first is manifestly
to account for the existence of this machine, for such a completed piece
of mechanism as a man or a tree cannot be explained as a result of
simple accident, as the existence of a rough piece of rock might be
explained. Its intricacy of parts and their purposeful interrelation
demands explanation, and therefore the fundamental problem is to explain
how this machine came into existence. The second problem is simpler, for
it is simply to explain the running of the machine after it is made. If
the organism is really a machine, we ought to be able to find some way
of explaining its actions as we can those of a steam engine.
Of these two problems the first is the more fundamental, for if we fail
to find an explanation for the existence of the machine, our explanation
of its method of action is only partly satisfactory. But the second
question is the simpler, and must be answered first. We cannot hope to
explain the more puzzling matter of the origin of the machine unless we
can first understand how it acts. In our treatment of the subject,
therefore, we shall divide it into two parts:
I. _The Running of the Living Machine_.
II. _The Origin of the Living Machine_.