THE PHENOMENA OF LIFE AND OSMOTIC PRODUCTIONS--A STUDY IN PHYSIOGENESIS
It is impossible to define life, not only because it is complex, but
because it varies in different living beings. The phenomena which
constitute the life of a man are far other than those which make up the
life of a polyp or a plant; and in the more simple forms life is so greatly
reduced that it is often a matter of difficulty to decide whether a given
form belongs to the animal, vegetable, or mineral kingdom. Considering the
impossibility of defining the exact line of demarcation between animate and
inanimate matter, it is astonishing to find so much stress laid on the
supposed fundamental difference between vital and non-vital phenomena.
There is in fact no sharp division, no precise limit where inanimate nature
ends and life begins; the transition is gradual and insensible, for just as
a living organism is made of the same substances as the mineral world, so
life is a composite of the same physical and chemical phenomena that we
find in the rest of nature. All the supposed attributes of life are found
also outside living organisms. Life is constituted by the association of
physico-chemical phenomena, their harmonious grouping and succession.
Harmony is a condition of life.
We are quite unable to separate living beings from the other productions of
nature by their composition, since they are formed of the same mineral
elements. All the aliments of plants--water, carbon, nitrogen, phosphorus,
sulphur--before their absorption and assimilation belonged to the mineral
kingdom. The carbon and the water are transformed into {148} sugar and fat,
the nitrogen and the sulphur into albumen, and the compounds so formed are
then said to belong to the organic world. These organic bodies are returned
once again to the mineral world by the action of animals and microbes,
which transform the carbon into carbonates, and the nitrogen, sulphur, and
phosphorus into nitrates, sulphates, and phosphates. Hence life is but a
phase in the animation of mineral matter; all matter may be said to have
within itself the essence of life, potential in the mineral, actual in the
animal and the vegetable. The flux and reflux of matter is alternate and
incessant, from the mineral world to the living, and back again from the
living to the mineral world.
At the same time there is a continuous flux of energy. Organic matter
contains potential energy, the energy of chemical combination; and during
its passage through the living being it is gradually stripped of this
energy and returned to the mineral world. The first step in synthetic
biology is the addition of potential energy to matter, the reduction of an
oxide, the separation of a salt into its radicals, the production of some
endothermic chemical combination. The energy stored up by such processes
can be again liberated as heat, that fire which the ancients with wonderful
prescience long ago recognized as the symbol of life.
Attempts have been made to differentiate a living being by the nature of
its chemical combinations, the so-called organic compounds. It was supposed
that life alone could realize these and cause the production of the various
substances which form the structure of living beings. Of late years,
however, a large number of these organic substances have been artificially
produced in the laboratory, and the synthetic problems which remain are of
the same order as those which have been already solved.
As one learns to know the mineral kingdom and the living world more
intimately the differences between them disappear. Thus a living being was
supposed to be characterized by its sensibility, _i.e._ its faculty of
reaction against external impressions. But this reaction is a general
phenomenon of nature; there is no action without reaction. Neither can the
{149} reaction to internal impressions, immediate or deferred, be
considered as the characteristic of life, since osmotic growths exhibit a
most exquisite sensibility in this direction. Since, then, the faculty of
reaction is a general property of matter, the characteristics of life in
the lower organisms are only three in number, viz. nutrition, growth, and
reproduction by fission or budding. But crystals are also nourished and
grow in the water of crystallization. They have moreover a specific form,
and every biologist who wishes to establish a parallel between the
phenomena of the living and the mineral world is wont to compare living
beings with crystals. Crystals, it is said, affect regular geometric forms,
salient angles, and rectilinear edges, while living beings have rounded
forms without any geometric regularity. Another supposed distinction is
that living beings are nourished by intussusception, whereas crystals
increase by apposition. Again, living beings are said to assimilate and
transform the aliment they absorb, whereas crystals do not transform the
matter which is added externally to their structure. Another supposed
difference is that living things eliminate and discharge their products of
combustion, while the evolution of a crystal is accompanied by no such
elimination. Finally, the phenomenon of reproduction is said to be the
exclusive characteristic of a living being; but crystals may also be
reproduced and multiplied by the introduction of fragments of crystalline
matter into a supersaturated solution.
The resemblance between an osmotic growth and a living organism is much
closer than that between a living being and a crystal, there being not only
an analogy of form, but also of structure and of function. In order to find
the physical parallel to life, we must turn to osmosis and osmotic growth
rather than to crystals and crystallization.
The first and most striking analogy between living beings and osmotic
growths is that of form. The morphogenic power of osmosis gives rise to an
infinite variety of forms. An osmotic growth, even at the first sight,
suggests the idea of a living thing. One need only glance at the
photographs of osmotic productions to recognize the forms of madrepore,
fungus, alga, and shell. It is wonderful that a force capable {150} of such
marvellous results should have hitherto been almost entirely neglected.
A second analogy between vital and osmotic growths is to be found in their
structure, both being formed by groups of cells or vesicles separated by
osmotic membranes. An osmotic stem, formed by a row of cellular cavities
separated by osmotic membranes, has a great structural resemblance to the
knotted stems of bamboos, reeds, and the like. The foliaceous expansions of
osmotic growths are formed by colonies of cells or vesicles disposed in
regular lines, which may present various patterns of innervation, parallel,
palmate, or pennate. Many of the lamellar osmotic growths are striped in
parallel lines alternately opaque and transparent. The terminal organs have
also their enveloping membranes, their pulp and nucleus, just like
vegetable forms.
The analogies of function are no less remarkable than those of form and
structure. Nutrition is perhaps the most elementary and essential vital
phenomenon, since without nutrition life cannot exist. Nutrition consists
in the absorption of alimentary substances from the surrounding medium, the
chemical transformation of such substances, their fixation by
intussusception in every part of the organism, and the ejection of the
products of combustion into the surrounding medium. Osmotic growths absorb
material from the medium in which they grow, submit it to chemical
metamorphosis, and eject the waste products of the reaction into the
surrounding medium. An osmotic growth moreover exercises choice in the
selection of the substances which are offered for its consumption,
absorbing some greedily and entirely rejecting others. Thus osmotic growths
present all the phenomena of nutrition, the fundamental characteristic of
life.
In the living organism nutrition results in growth, development, and
evolution. Growth and development also follow the absorption and fixation
of aliment by an osmotic production. An osmotic production grows, its form
develops and becomes more complicated, and its weight increases. An osmotic
growth may weigh many hundred times as much as the mineral sown in the
solution, the mother liquor losing a {151} corresponding weight. Thus
growth, which has hitherto been considered an essential phenomenon of life,
is also a phenomenon common to all osmotic productions.
Osmotic growths like living things may be said to have an evolutionary
existence, the analogy holding good down to the smallest detail. In their
early youth, at the beginning of life, the phenomena of exchange, of
growth, and of organization are very intense. As they grow older, these
exchanges gradually slow down, and growth is arrested. With age the
exchanges still continue, but more slowly, and these then gradually fail
and are finally completely arrested. The osmotic growth is dead, and little
by little it decays, losing its structure and its form.
The membranes of an osmotic growth thicken with age, and thus oppose to the
osmotic exchanges a steadily increasing resistance. Young osmotic cells
appear swollen and turgescent, whereas old ones become flaccid, relaxed,
and wrinkled. Analogous phenomena are met with in living organisms, the
calcareous infiltration of the vessels representing the thickening and
hardening of the osmotic membranes. The plumpness of a child and the
turgescence of young cells are but the expression of high osmotic tension,
while relaxation and flaccidity of the tissues in old age betrays the fall
of osmotic pressure in the intracellular tissues.
Circulation of the nutrient fluid may also be observed in an osmotic growth
as in a living organism. If we take a calcareous growth with long ramified
stems and dilute the mother liquor considerably, we may see currents of
liquid issuing from the summit of the growth--currents which are made
visible by the cloudy precipitates which they cause. The same current is
also rendered visible in the stems themselves by the motion of the
granulations and gas bubbles in the interior of the osmotic cells. It is
plain that some such circulation must exist, for how could a membrane be
formed 30 centimetres from the seed if the membranogenous substance did not
circulate through the stem? A moment's consideration will show that the
propulsion is due to osmotic pressure and not to mere differences of
density, for the liquid {152} which rises in the stem is a concentrated
solution of calcium salt much denser than the mother liquor, and the
current of liquid after rising in the stem may be seen to fall back again
through the liquid.
[Illustration: FIG. 61.--A group of osmotic forms.]
Organization has long been considered as one of the principal
characteristics of life, _i.e._ the arrangement of matter so as to produce
an animated and evolutionary form accompanied by transformation of energy.
But osmotic growths are also organizations endowed with the same faculties,
and the physical mechanism which is at the basis of their formation is the
same as that which determines the organization of living matter.
The phenomena of osmotic growth show how ordinary mineral matter,
carbonates, phosphates, silicates, nitrates, and chlorides, may imitate the
forms of animated nature without {153} the intervention of any living
organism. Ordinary physical forces are quite sufficient to produce forms
like those of living beings, closed cavities containing liquids separated
by osmotic membranes, with tissues similar to those of the vital organs in
form, colour, evolution, and function.
It is only necessary to glance at the photographs of these osmotic growths
to appreciate the wonderful variety of form. The variety of function is not
less evident, and in many instances, especially with manganese salts, the
difference of function of various regions is marked by differences of
colour. When a large osmotic cell projects beyond the mother liquor and
grows up into the air, it is evident that the function of liquid absorption
must be localized in the submerged part. In other cases we have a local
evolution of gas, which may be demonstrated by growing a fragment of
calcium chloride in a mother liquor composed of the following saturated
solutions:--
Potassium carbonate 76 parts.
Potassium sulphate 16 "
Tribasic potassium phosphate 46 "
During the whole period of growth there is an abundant liberation of
bubbles of gas, which is accurately limited to a belt around the base of
the growth, and sometimes also to a cap at the summit.
Since morphological differentiations of different parts is but the result
of differences of evolution, _i.e._ of functional differences of the
various parts, we may consider that osmotic growths possess the faculty of
organization like living beings.
An osmotic growth may be wounded, and a wound delays its growth and
development like a disease or an accident in a living being. A wound in an
osmotic production may also become cicatrized and covered with a membrane,
when the growth will recommence exactly as in a living being.
An osmotic growth is a transformer of energy. It increases in bulk, pushing
aside the mother liquor, and thus doing external work. An osmotic growth
has a temperature above its medium, since the chemical reaction of which it
is the seat is accompanied by the production of heat. We know {154} but
little of the transformation of energy which takes place in an osmotic
production, but we may say with certainty that it is capable of
transforming both chemical energy and osmotic energy into heat and
mechanical motion.
An osmotic production is the arena of complicated chemical phenomena which
produce a veritable metabolism. It has long been known that diffusion and
osmosis may determine various chemical transformations. H. St. Clair
Deville has demonstrated that certain unstable salts are partially
decomposed by diffusion. Thus during the diffusion of alum, the sulphate of
potash is separated from the sulphate of aluminium. Similarly, when the
chloride or acetate of aluminium is caused to diffuse, the acids become
separated from the aluminia. This decomposition is the result of the
different resistance which the medium offers to the diffusion of different
ions. This difference of resistance may even cause a difference of
potential between two media, similar to the differences of potential in
living organisms. Frequently also a difference of hydration in the chemical
substances on either side of an osmotic membrane will determine a chemical
reaction, which like all other chemical reactions is accompanied by a
corresponding transformation of energy. The study of these chemical
metamorphoses and the transformations of energy in osmotic growths has
opened up a new subject for experimental investigation in the field of
organic chemistry.
_Coagulation._--There is a most remarkable analogy between the phenomena of
coagulation as seen in living beings and the phenomena which occur when the
liquid in the interior of an osmotic growth comes into contact with the
mother liquor. When the sap of a plant or the blood of an animal escapes
into the air or water of the surrounding medium, it coagulates, _i.e._ it
changes from a liquid to a gelatinous consistency. In the same way, when
the liquid in the interior of an osmotic growth leaks out into the mother
liquor it forms a gelatinous precipitate. This gelatinous precipitation is
a physico-chemical phenomenon of the same nature as coagulation. It is by
the study of coagulation in liquids less complex than blood that we may
hope to elucidate the mechanism of the process, {155} which is simply a
physico-chemical phenomenon exactly analogous to gelatinous precipitation.
Calcium phosphate is always prone to coagulate; it has been called the
gelatinous phosphate of lime, and we have already seen how readily tribasic
calcium phosphate takes the form of beautiful transparent colloidal
membranes which are gelatinous in texture.
We may obtain colloidal precipitates exactly analogous to coagulated
albumin by mixing a weak solution of chloride of calcium with potassium
carbonate or tribasic phosphate. Like albumin this precipitate forms
flakes, and is deposited slowly as a gelatinous colloidal mass. Like
albumin also this calcic solution is coagulated by heat; a solution of a
calcic salt of a volatile acid on heating forms a precipitate which has all
the appearance of albumin coagulated by heat.
Finally, Arthus and Pages have shown that blood does not coagulate when
deprived of its calcium salts by the addition of alkaline oxalates,
fluorides, or citrates, and that the blood thus treated recovers its
coagulability on the addition of a soluble salt of calcium. The coagulation
of milk is also a calcium salt precipitation. Coagulation therefore would
seem to be merely the colloidal precipitation of a salt of calcium.
Diffusion and osmosis are the elementary phenomena of life. All vital
phenomena result from the contact of two colloidal solutions, or of two
liquids separated by an osmotic membrane. Hence the study of the physics of
diffusion and osmosis is the very basis of synthetic biology.
A living being exhibits two sorts of movements, those which are the result
of stimulus from without, and those which are determined by an excitation
arising from within. In the higher animals the stimulus or exciting energy
coming from the entourage may be infinitely small when compared with the
amount of energy transformed. Moreover, the response to an identical
excitation may so vary as to give to these different responses an
appearance of spontaneity. There is in reality no spontaneity, since the
difference in response is governed by previous external impressions which
have left their record on the machinery. There is in fact no such thing as
a spontaneous action, since every action of a living {156} being has as its
ultimate cause a stimulus or excitation coming from without.
The movements of the second category are also conditioned by an excitation,
but the stimulus comes from within the organism. These movements consist
principally of changes of nutrition, or movements of the circulation and
respiration; they are rhythmic in character and are probably produced by
the same chemico-physical causes which determine rhythmic movements outside
the living body.
Just in the same way osmotic growths present two sorts of movements,
external movements and those which are connected with their nutrition. A
free osmotic growth swimming in the mother liquor will alter its position
and form under the influence of the slightest exterior excitation or
vibration. It responds to every variation of temperature, or to a slight
difference of concentration produced by adding a single drop of water, and
reacts to every exterior influence by displacement or deformation.
An osmotic growth also shows indications of movements which are connected
with its nutrition, and these movements are rhythmic, like those of
respiration or circulation in a living organism. The growth of an osmotic
production shows itself not as a continuous process but periodically. The
water traverses the membrane, raises the pressure, and distends the cell;
at first the cell wall resists by reason of its elasticity, it then
suddenly relaxes, yielding to the osmotic pressure and bulging out at a
thinner spot on the surface; the internal pressure falls suddenly, and
there is a pause in the growth.
This rhythmic growth may be best observed by sowing in a solution of a
tribasic alkaline phosphate, pellets composed of powdered calcium chloride
moistened with glycerine, to which has been added 1 per cent. of monobasic
calcium phosphate. The experiment is so arranged as to bend or incline the
growing stems which shoot out from these grains. This may be done by
carefully pouring above the mother liquor a layer of water, or a less
concentrated solution. As the internal osmotic pressure rises, the drooping
extremity of the twig will become turgescent and gradually lift itself
{157} up, and then suddenly fall again for several millimetres. We have
frequently watched this rhythmic movement for an hour or more--a slow
gradual elevation of the extremity of the twig and a rapid fall recurring
every four seconds or so.
It may be objected that the substance of an osmotic growth is continually
undergoing change, whereas a living organism transforms into its own
substance the extraneous matter which it borrows from its environment. The
distinction, however, is only an apparent one. The substance of a living
being is also continually undergoing chemical change; it does not remain
the same for a single instant. We see an evidence of this change in the
evolution of age; the substance of the adult is not that of the infant. In
some living organisms such as insects, especially the ephemeridae who have
but a brief existence, this change of substance is even more rapid than
that in an osmotic growth.
It has been objected that osmotic productions cannot be compared with
living organisms since they contain no albuminoid matter. This is to
consider life as a substance, and to confound the synthesis of life with
that of albumin. If albumin is ever produced by synthesis in the laboratory
it will probably be dead albumin. All living organisms contain albumin;
this is probably due to the fact that albuminoid matter is particularly
adapted for the formation of osmotic membranes. Our osmotic productions are
composed of the same elements as those which constitute living beings; an
osmotic growth obtained by sowing calcium nitrate in a solution of
potassium carbonate with sodium phosphate and sulphate contains all the
principal elements of a living organism, viz. carbon, oxygen, hydrogen,
nitrogen, sulphur, and phosphorus.
The whole of the vegetable world is produced by the osmotic growth of
mineral substances, if we except the small amount of organic matter
contained in the seeds.
The most important problem of synthetic biology is not so much the
synthesis of the albuminoids as the reduction of carbonic acid. In nature
this reduction is accomplished by the radiant energy of the sun, by the
agency of the catalytic action of chlorophyll. {158}
The physico-chemical study of osmotic growth is as yet hardly begun; we
have but indicated the method, the way is open, and the problems awaiting
solution are legion. Only work and ever more work and workers are required.
Experiments should be made with substances which are chemically unstable
like the albuminoids, substances which readily combine and dissociate
again, alternately absorbing and giving up the potential energy which is
the essence of life. Experiments should also be made with substances which
readily unite or decompose under the influence of water, since hydration
and hydrolysis appear to be the dominant mechanism in all vital reaction,
as they undoubtedly are in osmotic growth, which consists of an increase of
hydration on one side of an osmotic membrane and a diminution on the other
side.
Life is not a substance but a mechanical phenomenon; it is a dynamic and
kinetic transference of energy determined by physico-chemical reactions;
and the whole trend of modern research leads to the belief that these
reactions are of the same nature as those met with in the organic world. It
is the grouping of physical reactions and their mode of association and
succession, their harmony in fact, which constitutes life. The problem we
have to solve in the synthesis of life is the proper attuning and
harmonizing of these physical phenomena, as they exist in living beings,
and there should be no absolute impossibility in our some day realizing
this harmony in whole or in part.
Albert Gaudry says: "I cannot conceive why in determining the connecting
links of the animal world the fact that an organic body is formed of such
and such elements should be of greater importance than the manner in which
these elements are grouped. Descartes regarded extension as the essential
property of an organized being; he supposed it to be inert of itself, and
that it had the Deity for its motive force. To-day the hypothesis of
Descartes has given way to that of Leibnitz, who regards force as the
essential property of the living being, the visible and tangible matter
being only of secondary importance. If we regard the living being as a
force, this force is able to aggregate matter under such and such a form,
{159} with such or such a structure, and such or such a chemical essence.
It does not seem that the classification depending on differences of
substance are any more important than those which depend on differences of
form."
The biological interest of osmotic productions is quite independent of the
chemical nature of the substances which enter into their growth. All
substances which produce osmotic membranes by the contact of their
solutions exhibit phenomena analogous to those of nutrition. Osmotic
morphogenesis is a physical phenomenon resulting from the contact of the
most diverse substances. It has given us our first glimpse of the manner in
which a living being may be supposed to have been formed according to the
ordinary physical laws of nature. We cannot at present produce osmotic
growths with all the combinations found in living beings, but that is only
because chemistry still lags far behind physics in the synthesis of organic
forms.
We are often told "not to force the analogy." But error is equally produced
by the exaggeration of unimportant differences. We have already seen that
nutrition, absorption, transformation, and excitation are not the
characteristics of living organisms alone; nor is reaction to external
impressions the appanage only of animate beings. To insist on the
resemblance between an osmotic production and a living being is not to
force an analogy but to demonstrate a fact.
Let us briefly recapitulate. An osmotic growth has an evolutionary
existence; it is nourished by osmosis and intussusception; it exercises a
selective choice on the substances offered to it; it changes the chemical
constitution of its nutriment before assimilating it. Like a living thing
it ejects into its environment the waste products of its function.
Moreover, it grows and develops structures like those of living organisms,
and it is sensitive to many exterior changes, which influence its form and
development. But these very phenomena--nutrition, assimilation,
sensibility, growth, and organization--are generally asserted to be the
sole characteristics of life.
* * * * *
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