POLARITY IN LIFE.
Contrast of living and dead—Eating and
being eaten—Trace matter upwards and life
downwards—Colloids—Cells—Protoplasm—Monera—Composition
of protoplasm—Essential qualities of life—Nutrition and
sensation—Motion—Reproduction—Spontaneous generation—Organic
compounds—Polar conditions of life.
Polarity having been established as the universal law of the inorganic
world, we have now to pass to the organic, or world of life. At first
sight there seems to be a great gulf fixed between the living and the
dead which no bridge can span. But first impressions are very apt to
deceive us, and when things are traced up to their origins we often
find them getting nearer and nearer until it is difficult to say where
one begins and the other ends. Take for instance such an antithesis as
‘eating or being eaten.’ If a hunter meets a grizzly bear in the Rocky
Mountains, one would say that no distinction can be sharper than whether
the bear eats the man, or the man the bear. In the one case there is
a man, and in the other a bear, less in the world. But look through a
microscope at a glass of water, and you may see two specks of jelly-like
substance swimming in it. They are living creatures, for they eat and
grow, and thrust out and retract processes of their formless mass, which
serve as temporary legs and arms for seizing food and for voluntary
motion. In short, they are each what may be called strictly individual
amœbæ, forming separate units of the animated creation as much as the man
and the bear. But if the two happen to come in contact, what happens?
The two slimy masses involve one another and coalesce, and the resulting
amœba swims away merrily as two gentlemen rolled into one.
Now in his case what became of their individualities: did amœba A eat
amœba B, or _vice versâ_, and is the resulting amœba a survival of A or
of B, or of both or neither of them? And what becomes of the antithesis
of ‘eating or being eaten’ which was so clear and distinct in the highly
specialised forms of life, and is so evanescent in the simpler forms?
This illustration may serve to teach us how necessary it is to trace
things up to their origins, before expressing too trenchant and confident
opinions as to their nature and relations.
In the case of the organic and inorganic worlds the proper course
obviously is, not to draw conclusions from extreme and highly specialised
instances, but to follow life downwards to its simplest and most
primitive form, and matter upwards to the form which approaches most
nearly to this form of life. Following matter upwards, we find a regular
progression from the simple to the complex. Take the diamond, which is
one of the simplest of substances, being merely the crystallised form of
a single ultimate element, carbon. It is extremely hard and extremely
stable. Ascending to compounds of two, three, or more elements, we
get substances which are more complex and less stable; and at last we
arrive at combinations which involve many elements and are extremely
complex. Among these latter substances are some, called colloids, which
are neither solid, like crystals, nor fluid, like liquids, but in an
intermediate state, like jelly or the white of an egg, in which the
molecules have great mobility and are at a considerable distance apart,
so that water can penetrate their mass. These colloids are for the most
part very complicated compounds of various elements based on a nucleus
of carbon, which, from its atom having four poles with strong mutual
attractions, is eminently qualified for forming what may be called
the inner skeleton of these complex combinations. Colloids of this
description form the last stage of the ascending line from inorganic
matter to organic life.
Next let us trace life downwards towards matter. There is a constant
succession from the more to the less complex and differentiated: from
man, through mammals, reptiles, fishes, and a long chain of more simple
forms, until at its end we come to the two last links, which are the same
for all animals, all plants, and all forms of animated existence. The
last link but one is the cell, the last of all is protoplasm.
Protoplasm, or, as Huxley calls it, ‘the physical basis of life,’ is a
colourless jelly-like substance, absolutely homogeneous, without parts or
structure, in fact a mere microscopic speck of jelly.
The cell is the first step in the specialisation of protoplasm, the
outer layer of which, in contact with the surrounding environment,
becoming hardened so as to form an enclosing cell-wall, while a portion
of the enclosed protoplasm condenses into a nucleus, in which a further
condensation makes what is called the nucleolus or second smaller
nucleus. This constitutes the nucleated cell, whose repeated subdivision
into other similar cells in geometrical progression furnishes the raw
material out of which all the varied structures of the world of life
are built up. Plants and animals, bones, muscles, and organs of sense,
are all composed of modified cells, hardened, flattened, or otherwise
altered, as the case may require. If we trace life up to its origin in
the individual instead of in the species, we arrive at the same result.
All plants and animals, whether of the lowest or highest forms, fish,
reptile, bird, mammal, man, begin their individual existence as a speck
of protoplasm, passing into a nucleated cell, which contains in it the
whole principle of its subsequent evolution into the mature and completed
form.
Protoplasm is, therefore, evidently the nearest approach of life
to matter; and if life ever originated from atomic and molecular
combinations, it was in this form. To suppose that any more complex form
of life, however humble, could originate from chemical combinations,
would be a violation of the law of evolution, which shows a uniform
development from the simple to the complex, and never a sudden jump
passing at a bound over intermediate grades. To understand life,
therefore, we must understand protoplasm; for protoplasm, closely as it
approximates to colloid matter, is thoroughly alive. A whole family,
the Monera, consist simply of a living globule of jelly, which has not
even begun to be differentiated. Every molecule, as in a crystal, is
of homogeneous chemical composition and an epitome of the whole mass.
There are no special parts, no organs told off for particular functions,
and yet all life-functions—nutrition, reproduction, sensation, and
movement—are performed, but each by the whole body. The jelly-speck
becomes a mouth to swallow, and turning inside out, a stomach to digest.
It shoots out tongues of jelly to move and feel with, and presently
withdraws them.
With these attributes it is impossible to deny to protoplasm the full
attributes of life, or to doubt that, like the atom in the material
world, it is the primary element of organic or living existence. Given
the atom, we can trace up, step by step, the whole evolution of matter;
so given the protoplasm, we can trace up the evolution of life by
progressive stages to its highest development—man. To understand life,
therefore, we must begin by trying to understand protoplasm.
What is protoplasm? In its substance it is a nitrogenous carbon compound,
differing only from other similar compounds of the albuminous family of
colloid by the extremely complex composition of its atoms. It consists
of five elements, and its average composition is said by chemists to be
52·55 per cent. carbon, 21·23 oxygen, 15·17 nitrogen, 6·7 hydrogen, 1·2
sulphur. Its peculiar qualities, therefore, including life, are not the
result of any new and peculiar atom added to the known chemical compounds
of the same family, but of the manner of grouping and motions of these
well-known material elements. It has in a remarkable degree the faculty
of absorbing water, so that its molecules seem to float in it in a
condition of semi-fluid aggregation, which seems to be necessary for the
complex molecular movements which are the cause or accompaniment of life.
Thus, many seeds and animalculæ, if perfectly dry, may remain apparently
as dead and as unchanging as crystals, for years, or even, as in the case
of the mummy wheat, for centuries, to revive into life when moistened.
But in addition to those material qualities in which protoplasm seems
to differ only from a whole group of similar compounds of the type of
glycerine, by the greater complexity and mobility of its molecules, it
has developed the new and peculiar element which is called life. Life
in its essence is manifested by the faculties of nutrition, sensation,
movement, and reproduction.
As regards nutrition there is this essential difference between living
and non-living matter. The latter, if it feeds and grows at all, does
so only by taking on fresh molecules of its own substance on its outer
surface, as in the case of a small nucleus-crystal of ice in freezing
water. If it feeds on foreign matter and throughout its mass, it does
so only in the way of chemical combination, forming a new product.
Living matter, on the other hand, feeds internally, and works up
foreign substances, by the process we call digestion, into molecules
like its own, which it assimilates, rejecting as waste any surplus or
foreign matter which it cannot incorporate. It thus grows and decays
as assimilation or waste preponderates, remaining always itself. The
distinction will be clear if we consider what happens when water rusts
iron. In a certain sense the iron may be said to eat the oxygen, reject
the hydrogen, and grow, or increase in weight by what it feeds on; but
the result is not a bigger piece of iron, but a new substance, rust,
or oxide of iron. That living matter should feed internally is not
so wonderful, for its semi-fluid condition may well enable foreign
molecules to penetrate its mass and come in contact with its own interior
molecules; but it is an experience different from anything known in
the inorganic world that it should be able to manufacture molecules
of protoplasm like its own out of these foreign molecules, and thus
grow by assimilation. For instance, when amœbæ, bacteria, and other
low organisms live and multiply in chemical solutions which contain no
protoplasm, but only inorganic compounds containing the requisite atoms
for making protoplasm, or when a plant not only chemically decomposes
carbonic dioxide, exhaling the oxygen and depositing the carbon in its
stem and leaves, but also from this and other elements drawn from the
soil or air manufactures the living protoplasm which courses through its
channels, the result is that life has manufactured life out of non-living
materials.
If we take sensation, this, in its last analysis, is change, or molecular
motion, induced in a body by the action of its environment. Here there
is a certain analogy between living and non-living matter, for the
latter does respond to changes in the surrounding environment, as in
the case of heat, electricity, and otherwise; but living matter is far
more sensitive, the changes are far more frequent and complex, and in
certain cases they are accompanied by a sensation of what is called
consciousness, which in the higher organisms rises into a perception
of voluntary effort or free-will as a factor in the transformation of
energies. Thus it happens that in the case of dead matter the changes
produced by a change of conditions follow fixed laws and can be predicted
and calculated, while those of living matter are apparently uncertain
and capricious. We can tell how much an iron bar will expand with heat;
but we cannot say whether, if a particle of food is brought within reach
of an amœba, it will or will not shoot out a finger to seize it. If the
amœba is hungry it probably will; if it is enjoying a siesta after a full
meal, it probably will not.
The case of sensation includes that of motion, which is after all only
sensation applied in the liberation of energy of position which has by
some chemical process become stored up, either in the living mass, or
in some special organ of it, such as muscle. Iron, for instance, moves
when it expands by heat or is attracted by a magnet; but it moves, like
the planets, by fixed and calculable laws: while living matter moves,
as might be expected from the variable character of its sensation, in
a manner which often cannot be calculated. There are cases, however,
of reflex or involuntary motion, where, even in the highest living
organisms, sensation and motion seem to follow change of environment, in
a fixed and invariable sequence, as in shrinking from pain, touching or
galvanising a nerve; and it may be that the apparent spontaneousness and
variability of living motion is only the result of the almost infinitely
greater complexity and mobility of the elements of living matter.
Reproduction remains, which is the faculty most characteristic of life,
and which distinguishes most sharply the organic from the inorganic
world. In the inorganic there is no known process by which dead matter
reproduces itself, as the cell does when it contracts in the middle
and splits up into two cells, which in their turn propagate an endless
number of similar cells, increasing in geometrical progression until
they supply the raw material from which all the countless varieties of
living organisms are built up, which, in their turn, repeat the process
and reproduce themselves in offspring. This is the real mystery of life;
we can partly see or suspect how its other faculties might arise from an
extension of the known qualities and laws of matter and of energy; but
we can discern no analogy between the non-reproductive nitrogenous carbon
compound, which makes so near an approach to protoplasm in its chemical
composition, and the reproductive protoplasm, which is fertile, increases
and multiplies, and replenishes the earth. Can the gap be bridged over:
can protoplasm be manufactured out of chemical elements? It is done every
day by plants which make protoplasm out of inorganic elements, and by
the lowest forms of life which live and multiply in chemical solutions.
It is done also in the life-history of all individuals whose primitive
cell or ovum makes thousands or millions of other cells, each containing
within its enclosing membrane as much protoplasm as there was in the unit
from which they started. But in all these instances there was the living
principle to start with, existing in the primitive speck of protoplasm,
from which the rest were developed. Can this primitive speck be created;
or, in other words, can protoplasm be artificially manufactured by
chemical processes?
The answer must be, No; not by any process now known. The similarity of
chemical composition, and the increasing conviction of the universality
of natural law and of evolution, have led to a very general belief that
such a spontaneous generation of life must be possible, and numerous
experiments have been made to produce it. For a time the balance
seemed to be very evenly held between the supporters and opponents of
spontaneous generation. In fact, starting from the assumption, which at
first was common to both sides, that heat equal to the boiling point
of water destroyed all life organisms, spontaneous generation had the
best of it: for it was clearly proved that living organisms did appear
in infusions contained in vessels which had been hermetically sealed,
after being subjected to this, or even a higher degree of heat. But
subsequent and more careful experiments have shown that the germs or
spores of bacteria and other animalculæ, which are generally floating
in the air, can, when dry, withstand a greater degree of heat, and that
when the experiments are made in optically pure air no life ever appears
and the infusions never putrefy. On questions of this sort all who are
not themselves expert experimentalists must be guided by authority, and
we may be content to accept the dictum of Huxley that biogenesis, or all
life from previous life, was ‘victorious along the whole line.’ But in
doing so we must accept Huxley’s caution, ‘that with organic chemistry,
molecular physics, and physiology yet in their infancy, and every day
making prodigious strides, it would be the height of presumption for any
man to say that the conditions under which matter assumes the qualities
called vital, may not some day be artificially brought together.’
And further, ‘that as a matter not of proof but of probability, if it
were given me to look beyond the abyss of geologically recorded time, to
the still more remote period when the earth was passing through chemical
and physical conditions which it can never see again, I should expect
to be a witness of the evolution of living protoplasms from non-living
matter.’ Such is the cautious candour with which scientific men approach
problems upon which theologians dogmatise with the unerring intrepidity
of ignorance.
In the meantime what may be said as to Huxley’s reservations is this:
A considerable step has been made in the direction indicated, by the
success of recent chemistry in forming artificially what are called
organic compounds, that is, substances which were previously known only
as products of animal or vegetable secretions. Urea, for instance, the
base of uric acid, with which so many are unfortunately familiar in the
form of gout; indigotine, the principle of the blue colouring matter of
the indigo plant; and alizarine, that of madder; are all now produced
artificially, and have even become important articles of commerce. If
chemists can make the indigotine, which the growing plant elaborates at
the same time as it elaborates protoplasm, may we not hope some day to
make the latter as well as the former product? Now organic compounds
of this class are being formed artificially every day, and it is said
that chemists have already succeeded in producing several hundreds.
But even if this expectation is never fulfilled, we may fall back on
Huxley’s second reservation of the enormous difference of chemical and
physical conditions in the early stages of the earth’s life from anything
now known. It has been calculated that the earth’s temperature when
it first started on its career as an independent planet was something
like 3,000,000° Fahrenheit. At this heat probably all atoms would be
dissociated; but as the temperature diminished they would come closer
together, but still with a great deal of motion, and making wide
excursions, which might bring many different atoms together in complex
though unstable combinations. Moreover, carbon, which is the basis of all
such combinations of the class of protoplasm, was far more abundant in
those early days in the form of carbonic dioxide gas, before the enormous
amount of vegetable matter in the form of coal and otherwise, had been
subtracted from it. In any case the first protoplasm must be extremely
ancient, for the remains of sea-weeds are found in the oldest strata,
and vegetation of any sort implies the manufacture of protoplasm from
inorganic matter.
The passage from the organic into the inorganic world is best traced by
following the line of Pasteur’s researches on ferments. How does the
world escape being choked up by the accumulation of dead organic matter
throughout innumerable ages? By what are called ferments, inducing
processes of fermentation and putrefaction, by which the course of life
is reversed, and the organic elements are taken to pieces and restored
to the inorganic world. Pasteur proved, in opposition to the theories
of Liebig and other older chemists, that this was not done directly by
the oxygen of the air, but through the intermediate agency of living
microbes, whose spores, floating in the air, took up their abode and
multiplied wherever they found an appropriate habitation. Given an air
purified from germs, or a temperature low enough to prevent them from
germinating, and putrescible substances would keep sweet for ever. The
practical realisation of this is seen in the enormous commerce in canned
meats and fruits, and in the imports of frozen beef and mutton, causing a
fall of rents and much lamentation among British landlords and farmers.
But then the question was asked, How are your microscopic organisms
disposed of? What are the ferments of your ferments? For even microscopic
bacteria and vibrios would, in time, choke up the world by their residue
if not got rid of. Pasteur answered that the ferments are destroyed by
a new series of organisms—aerobes—living in the air, and these by other
aerobes in succession until the ultimate products are oxidised. ‘Thus,
in the destruction of what has lived, all is reduced to the simultaneous
action of the three great natural phenomena—fermentation, putrefaction,
and slow combustion. A living being, animal or vegetable, or the _débris_
of either, having just died, is exposed to the air. The life that has
abandoned it is succeeded by life under other forms. In the superficial
parts, accessible to the air, the germs of the infinitely little aerobes
flourish and multiply. The carbon, hydrogen, and nitrogen of the organic
matter are transformed by the oxygen of the air, and under the vital
activity of the aerobes, into carbonic acid, the vapour of water, and
ammonia. The combustion continues as long as organic matter and air are
present together. At the same time the superficial combustion is going
on, fermentation and putrefaction are performing their work in the midst
of the mass by means of the developed germs of the original microbes,
which, note, do not need oxygen to live, but which oxygen causes to
perish. Gradually the phenomena of destruction are at last accomplished
through the work of latent fermentation and slow combustion.’
This seems a complete demonstration of the passage of the organic into
the inorganic world in the way of analysis, or taking the puzzle to
pieces. In the opposite way of synthesis, or putting it together, the
nearest approach yet made has been in the manufacture of those organic
compounds already referred to, such as urea, alizarine, indigotine and
other products which had hitherto only been known as products of animal
or vegetable life. Of these a vast number have been already formed from
inorganic elements by chemical processes, and almost every day announces
some fresh discovery.
Under these circumstances it is unsafe to affirm either, on the one
hand, that the problem has been solved and that life has ever been made
in a laboratory; or, on the other hand, that there is any such great gulf
fixed between the organic and the inorganic, that we can assume a break
requiring secondary supernatural interference to surmount it, and ignore
the good old maxim that ‘Natura nihil facit per saltum.’ Positive proof
is wanting, but the probabilities point here, as they do everywhere else
throughout the universe, to the truth of the theory of ‘original impress’
as opposed to that of ‘secondary interference.’
It remains to show how the fundamental law of polarity affects the more
complex relations of life and of its various combinations. And here
it is important to bear in mind that as the factors of the problem
become more intricate and complex, so also do the laws which regulate
their existence and action. Polarity is no longer a simple question of
attraction and repulsion at the two ends of a magnet or at the opposite
poles of an atom. It appears rather as a general law under which as the
simple and absolute becomes differentiated by evolution into the complex
and manifold, it does so under the condition of developing contrasts.
For every _plus_ there is a _minus_, for every like an unlike; one
cannot exist without the other; and, although apparently antagonistic,
harmonious order is only possible by their co-existence and mutual
balance.
This is so important that it may be well to make the idea clearer by an
illustration. The earth revolves round the sun in its annual orbit under
the influence of two forces: the centripetal, or force of gravity tending
to draw it towards the sun; and the centrifugal, tending to make it dart
away into infinite space. During half the orbit the centripetal seems to
be gaining ground on the centrifugal, and the earth is approaching nearer
to the sun. If this continued it would revolve ever nearer and soon fall
into it; but the centrifugal force is gradually recruiting its strength
from the increased velocity of the earth, until it first equals the
centripetal, and finally outstrips it, and for the remaining half of the
orbit it is constantly gaining ground. If this went on, the earth would
fly off into the chilly regions of outer space; but the centripetal force
in its turn regains the ascendency; and thus by the balance of the two
forces our planet describes the beautiful ellipse, its harmonious orbit
as a habitable globe; while comets in which one or the other force unduly
preponderates for long periods are alternately drawn into fiery proximity
to the sun, and sent careering through regions void of heat.
Compare this passage from Herbert Spencer: ‘As from antagonist physical
forces, as from antagonist emotions in each man, so from the antagonist
social tendencies man’s emotions create, there always results not a
medium state, but a rhythm between opposite states. The one force or
tendency is not continuously counterbalanced by the other force or
tendency; but now the one greatly preponderates, and presently by
reaction there comes a preponderance of the other.’
And again: ‘There is nowhere a balanced judgment and a balanced action,
but always a cancelling of one another by opposite errors. Men pair off
in insane parties, as Emerson puts it.’
The reader will now begin to understand the sense in which polarity
applies to these complex conditions of an advanced evolution.
To return, however, from this digression to the point at which it began,
viz. the origin of life, we have to show how the law of polarity prevails
in the organic as well as in the inorganic world. In the first place the
material to which all life is attached, from the speck of protoplasm to
the brain of man, is strictly a chemical product of atoms and molecules
bound together by the same polar laws as those of inorganic matter.
In like manner all the essential processes by which life lives, moves,
and has its being, are equally mechanical and chemical. If the brain,
receiving a telegram from without through the optic nerve, sends a reply
along another nerve which liberates energy stored up in a muscle and
produces motion, the messages are received and transmitted like those
sent by a voltaic battery along the wires of a telegraph, and the energy
is stored up by the slow combustion of food in oxygen, just as that of
the steam-engine is produced by the combustion of coal. All this is
mechanical, inorganic, and therefore polar.
But when we come to the conditions of life proper, we find the influence
of polarity mainly in this: that as it develops from simpler into more
complex forms, it does so under the law of developing contrasts or
opposite polarities, which are necessary complements of each other’s
existence. Thus, as we ascend in the scale of life, we find two primitive
polarities developed: that of plant and animal, and that of male and
female.