The Mechanism of Life

One of the great laws of the universe is the law of continuity in time and space. We must not lose sight of this law when we attempt to follow the metamorphoses of matter, of energy and of form in living beings. Evolution is but the expression of this law of continuity, this succession of phenomena following one another like the links of a chain, without discontinuity through the vast extent of time and space. The other great universal law, that of conservation, applies with equal force to living and to inanimate things. This law asserts the uncreateability and the indestructibility of matter and of energy. A given quantity of matter and of energy remains absolutely invariable through all the transformations through which it may pass.

We need not here discuss the question of the possible trans- formation of matter into ether, or of ether into ponderable matter. Such a transformation, if it exists, would have but little bearing on the phenomena of life. Moreover, it also will probably be found to conform to the law of conservation of energy. In marked contrast to the permanence of matter and of energy is the ephemeral nature of form, as exhibited by living beings. Function, since it is but the resultant of form, is also ephemeral. All the faculties of life are bound up with its form, a living being is born, exists, and dies with its form.

The phenomena of life may in certain cases slow down from their normal rapidity and intensity, as in hibernating animals, or be entirely suspended, as in seeds. This state of suspension of life, of latent life as it were, reminds us of a machine that has been stopped, but which retains its form and substance unaltered, and may be started again whenever the obstacle to its progress is removed. During the whole course of its life a living being is intimately dependent on its entourage. For example, the phenomena of life are circumscribed within very narrow limits of temperature. A living organism, consisting as it does essentially of liquid solutions, can only exist at temperatures at which such solutions remain liquid, i.e. between C. and 100 C. Certain organisms, it is true, may be frozen, but their life remains in a state of suspension so long as their substance remains solid. Since the albuminoid substances which are a necessary component of the living organism become coagulated at 44 C., the manifestations of life diminish rapidly above this temperature. The intensity of life may be said to augment gradually as the temperature rises from to 40, and then to diminish rapidly as the temperature rises above that point, becoming nearly extinct at 60 C.

Another condition indispensable to life is the presence of oxygen. Life, compared by Heraclitus to a flame, is a com- bustion, an oxydation, for which the presence of oxygen at a certain pressure is indispensable. There are, it is true, certain anaerobic micro-organisms which apparently exist without oxygen,, but these in reality obtain their oxygen from the medium in which they grow. Life is also influenced by light, by mechanical pressure, by the chemical composition of its entourage, and by other conditions which we do not as yet understand. In each case the conditions which are favourable or noxious vary with the nature of the organism, some living in air, some in fresh water, and others in the sea.

Formerly it was supposed that the substance of a living being was essentially different from that of the mineral world, so much so that two distinct chemistries were in existence organic chemistry, the study of substances derived from bodies which had once possessed life, and inorganic chemistry, dealing with minerals, metalloids, and metals. We now know that a living organism is composed of exactly the same elements as those which constitute the mineral world. These are carbon, oxygen, hydrogen, nitrogen, phosphorus, calcium, iron, sulphur, chlorine, sodium, potassium, and one or two other elements in smaller quantity. It was formerly supposed that the organic combinations of these elements were found only in living organisms and could be fashioned only by vital forces. In more recent times, however, an ever increasing number of organic substances have been produced in the laboratory.

(1) Carbohydrates, including the sugars and the starches, all of which may be considered as formed of carbon and water. (2) FatSj which may be considered chemically as the ethers of glycerine, combinations of one molecule of glycerine and three molecules of a fatty acid, with elimination of water. (3) Albuminoids, substances whose molecules are complex, con- taining nitrogen and sulphur in addition to carbon, oxygen, and hydrogen. The albuminoid of the cell nucleus also contains phosphorus, and the haemoglobin of the blood contains iron. (4) Minerals or inorganic elements, such as chloride of sodium, phosphate of calcium, and carbonic acid. This group also includes water, which is the most important constituent, since it forms more than a moiety of the sub- stance of all living creatures.

Wohler in 1828 accomplished the first synthesis of an organic substance, urea, one of the products of the decom- position of albumin. Since then a large number of organic substances have been prepared by the synthesis of their inorganic elements. The most recent advance in this direction is that of fimile Fischer, who has produced polypeptides having the same reactions as the peptones, by combining a number of molecules of the amides of the fatty acids.

In the further synthesis of organic compounds the problems we have before us are of the same order as those already solved. There is no essential difference between organic and inorganic chemistry; living organisms are formed of the same elements as the mineral world, and the organic com- binations of these elements may be realized in our laboratories, just as in the laboratory of the living organism. Not only so, but a living being only borrows for a short time those mineral elements which, after having passed through the living organism, are returned once again to the mineral kingdom from which they came.

All matter has life in itself or, at any rate, all matter susceptible of incorporation in a living cell. This life is potential while the element is in the mineral state, and actual while the element is passing through a living organism. Mineral matter is changed into organic matter in its passage through a vegetable organism. The carbonic acid produced by combustion and respiration is absorbed by the chlorophyll of the leaves under the stimulus of light the oxygen of the carbonic acid being returned to the air, while the carbon is utilized by the plant for the formation of sugar, starch, cellulose, and fats.

Thus plants are fed in great part by their leaves, taking an important part of their nourishment from the air, while by their roots they draw from the earth the water, the phosphates, the mineral salts, and the nitrates required for the formation of their albuminoid constituents. A vegetable is a laboratory in which is carried out the process of organic synthesis by which mineral materials are changed into organic matter. The first synthetic reaction is the formation of a molecule of formic aldehyde, CH 2 O, by the combination of a molecule of water with an atom of carbon.

From this formic aldehyde, or formol, we may obtain all the various carbohydrates by simple polymerization, i.e. by the association of several molecules, with or without elimi- nation of water. Thus two molecules of formol form one molecule of acetic acid, 2CH 2 O C 2 H 4 O 2 . Three molecules of formol form a molecule of lactic acid, 3CH 2 O = C 3 H 6 O S . Six molecules of formol represent glucose and levulose, 6CII 2 O = C 6 H 12 O 6 . Twelve molecules of formol minus one molecule of water form saccharose, lactose, cane sugar, and sugar of milk, l#CH 2 = C 12 II 22 O n + II 2 O 5 n times six mole-

i cules of forinol minus one molecule of water, ??(C 6 H 10 O 6 ), Animals derive their nourishment from vegetables either directly, or indirectly through the flesh of herbivorous animals. The mineral matter, rendered organic in its passage through a vegetable growth, is finally returned by the agency of animal organisms to the mineral world again, in the form of carbonic acid, water, urea, and nitrates. Thus vegetables may be regarded as synthetic agents, and animals and microbes as _?L_ d^ony^itimi. Here also the difference is only

relative, for in certain cases vegetables produce carbonic acid, while some animal organisms effect synthetic combinations. Moreover, there are intermediary forms, such as fungi, which possessing no chlorophyll are nourished like animals by organic matter, and yet like vegetables are able to manu- facture organic matter from mineral salts. The work of combustion begun by the animal organism is finished by the action of micro-organisms, who complete the oxydation the rc-mincralizatioii of the chemical substances drawn originally from the inorganic world by the agency of plant life.

To sum up. Vegetables ^>btai n^ Jjiej r^ jiourisl imgnt. from mineral substances, which they reduce^ dc-oxydi/c 2 and ^charge with_ so^r_energy. Anin^j3iga^sms oij_the contrary oxydi/e, and micro-organisms complete the oxydation of these sub- stances, returning _them to the mineral world as watej, carbonates, .nitrate^ and sulphates. Thus matter circulates eternally from the mineral to the vegetable, fiom the vegetable to the animal world, and back again. The matter which forms our structure, which is to-day part and parcel of ourselves, has formed the structure of an infinite number of living beings, and will continue to pursue its endless reincarnation after our decease.

Tll!?-S!^^ ss c y c k f Hfkjs ^k? an endless cycle of energy. The combination of carbon with water carried out by the agency of chlorophyll can only take place with absorption of energy. This energy comes directly from the sun, the red and orange light radiations b^HlJ-LJ 1 ^ The arrest of vegetation during the winter months is due not so much to the lowering of temperature as to the diminution of the radiant energy received from the sun. In the same way shade is harmful to vegetation, since the radiant energy required for growth is prevented from reaching the plant.

The energy radiated by the sun is accumulated and stored in the plant tissues. Later on, animals feed on the plants and utilize this energy, excreting the products of decomposition, i.e. the constituents of their food minus the energy contained in it. Thus the_ whole of the energy which animates living from the sun. To the sun also we owe all artificial heat, the energy stored up in wood and coal. We are all of us children of the sun. The radiant energy of the sun is transformed by plants into chemical energy. It is this chemical energy which feeds the vital activity of animals, who return it to the external world under the form of heat, mechanical work, and muscular contraction, light in the glow-worm, electricity in the electric eel.

There is a marked difference between the forms affected by organic and inorganic substances. The forms of the mineral world are those of crystals geometrical forms, bounded by straight lines, planes, and regular angles. Livmg organisms, on the contrary, affect forms which are less regular curve( l surfaces and rounded aiigles. The physical reason for this difference in form lies in a difference of consistency, crystals being solid, whereas living organisms are liquids or semi - liquids. The liquids of nature, streams and clouds and dewdrops, affect the same rounded forms as those of living organisms.

Living beings for the most part present a remarkable degree of symmetry. Some, like radiolarians and star-fish, have a stellate form. In plants the various organs often radiate from an axis, in such a manner that on turning the plant about this axis the various forms are superposed thrice, four, or more often five times in one complete revolution. It is remarkable how often this number five recurs in the divisions and parts of a living organism. In other cases the similar parts are disposed symmetrically on either side of a median line or plane, giving a series of homologous parts which are not superposable.

The most important characteristic of a living being is its form. This is implicitly admitted by naturalists, who classify animals and plants in genera and species according to the differences and analogies of their form. All living beings are composed of elementary organizations called cells. In its complete state, a cell consists of a membrane or envelope containing a mass of protoplasm, in the centre of which is a nucleus of differentiated protoplasm. This nucleus may in its turn contain a nucleolus. In some cases the cell is merely a protoplasmic mass without a visible envelope, so that a cell may be defined as essentially a mass of protoplasm provided with a nucleus.

A living organism may consist merely of a single cell, which is able alone to accomplish all the functions of life. Most living beings, however, consist of a collection of in- numerable cells forming a cellular association or community. When a number of cells are thus united to constitute a single living being, the various functions of life are divided among different cellular groups. Certain cells become specialized for the accomplishment of a single function, and to each function corresponds a different form of cell. It is thus easy to recognize by their form the nerve cells, the muscle cells which perform the function of movement, and the glandular cells which perform the function of secretion. The cells of a living being arc microscopic in size, and it is remarkable that they never attain to any considerable dimensions.

In order that life may be maintained in a living organism, it is necessary that a continual supply of aliment should be brought to it, and that certain other substances, the waste- products of combustion, should be eliminated. In order to be absorbed and assimilated, the alimentary substances must be presented to the living organism in a liquid or gaseous state. Thus the essential condition necessary for the life _is the coiitact_ of t\vo different liquids. This is the necessary condition which renders possible the chemical ex- changes and the transformations of energy which constitute life. It is in the study of the phenomena of liquid contact and diffusion that we may best hope to pierce the secrets of life. The physics of vital action are the physics of the phenomena which occur in liquids, and the study of the physics of a liquid must be the preface and the basis of all inquiry into the nature and origin of life.

WK have seen that living beings are transformers of energy and of matter, evolutionary in form and liquid in consistency ; that they are solutions of colloids and crystalloids separated by osmotic membranes to form microscopic cells, or consisting merely of a gelatinous mass of protoplasm, Avith a nucleus of slightly differentiated material. The elementary pheno- menon of life is the contact of two different solutions. This is the initial physical phenomenon from which proceed all the other phenomena of life in accordance with the ordinary chemical and physical laws. Thus the basis of biological science is the study of solution and of the phenomena which occur between two different solutions, either in immediate contact or when separated by a membrane.

A solution is a homogeneous mixture of one or more solutes in a liquid solvent. Before solution the solute or dissolved substance may be solid, liquid, or gaseous. Soliites ? or substances capable of solution, may^ be divided into t wo jjjissfis substances which are cjy^ble^jof crystal- . r 5II^U?J4s au d those which are incapable^ of n^ the jcpllqids. Crystalloids may be divided again into two classes, those whose solutions arc ioni/ablc and therefore conduct electricity, chJefly jj^ and those whose solutions are non-ioni/able and are there- fore non-conductors. These latter are for the most part crystalli/able substances of organic origin, such as sugars, urea, etc.

Avogadro's law asserts that under similar conditions of temperature and pressure, equal volumes of various gases contain an equal number of molecules. Under similar conditions, the molecular weights of different substances have therefore the same ratio as the weights of equal volumes of their vapours. Hence if we fix arbitrarily the molecular weight of any one substance, the molecular weight of all other substances is thereby determined. The molecular weight of hydrogen has been arbitrarily fixed as two, and hence the molecular weight of any substance will be double its gaseous density when compared with that of hydrogen.

Gramme- Molecule. A gramme-molecule is the molecular weight of a body expressed in grammes. Occasionally for brevity a gramme-molecule is spoken of as a " molecule. 1 ' Thus we may say that the molecular weight of oxygen is 16 grammes, meaning thereby that there are the same number of molecules in 16 grammes of oxygen as there are atoms in 1 gramme of hydrogen. Concentration-. The concentration of a solution is the ratio between the quantity of the solute and the quantity of the solvent. The concentration of a solution is expressed in various ways. (a) The weight of solute dissolved in 100 grammes of the solvent, (b) The weight of solute present in 100 grammes of the solution. (c) The weight of solute dissolved in a litre of the solvent, (d) The weight of solute in a litre of the solution. The most usual method is to give the concentration as the weight of solute dissolved in 100 grammes or in one litre of the solvent.

Molecular Concentration. Many of the physical and biological properties of a solution are proportional, not to its mass or weight concentration, but to its molecular con- centration, i. e. to the number of gramme-molecules of tlie. S( Zk l J*L Contained in a litre of the solution. Many physical properties are quite independent of the nature of the solute, depending only on its degree of molecular concentration. Normal Solution. A iigi;imxl_solutioii is one which contains

solution contains one-tenth of a gramme-molecule of the solute per litre, and a centi normal solution one-hundredth of a gramme -molecule. A normal solution of urea, for example, contains 60 grammes of urea per litre, while a normal solution of sugar contains 34 grammes of sugar per litre. The Dissolved Substance is a Gas. Van t' HofF, using the data obtained by the botanist Pfeffer, showed that the dissolved matter in a solution behaved ^exactly as if it were a gas. The analogy is complete in every respect. Like the gaseous molecules, the molecules of a solute are mobile with respect to one another. Like those of a gas, the molecules of a solute tend to spread themselves equally, and to fill the whole space at their disposal, i.e. the whole volume of the solution. The. 1 surface of the solution represents the vessel containing the gas, which confines it within definite limits and prevents further expansion.

Osmotic Pressure. Like the molecules of a gas, the mole- cules of a solute exercise pressure on the boundaries of the space containing it. This osmotic pressure follows exactly the same laws jas jjaseous pressure. It has the same constants, and all the notions acquired by the study of gaseous pressure are applicable to osmotic pressure. Osmotic pressure is in fact the jgascous pressure of the molecules of the solute. When a gas dilates and increases in volume, its temperature falls, and cold is produced. Similarly, when a soluble substance is dissolved, it increases in volume, and the temperature of the liquid falls. This phenomenon is well known as a means of producing cold by a refrigerating mixture.

The i_ phenomena of 'life are governed by the laws of gaseous pressure, since all these _pjienpnieii_a take place in solutions. The fLmdamental laws of biology are those of the distribution of subsj:ances_in solution, which is regulated by the laws of gaseous pressure, since all these laws are applicable also to osmotic pressure. Boyle's Law. When a gas is compressed its volume is diminished. If the pressure is doubled, the volume is reduced to one-half. The quantity V X P, that is the volume multiplied by the pressure, is constant.

Gay-Lussac's Law. For a difference of temperature of a degree Centigrade all gases dilate or contract by ^f 3 of their volume at Centigrade. Daltoii's Law. In a gaseous mixture, the total pressure is equal to the sum of the pressures which each gas would exert if it alone filled the whole of the receptacle. Pressure proportional to Molecular Concentration. The above laws are completely independent of the chemical nature of the gas, they depend only on the number of gaseous molecules in a given space, i.e. on the molecular concentration. If we double the mass of the gas in a given space, we double the number of molecules, and we also double the pressure, whatever the nature of the molecules. We may also double the pressure by compressing the molecules of a gas, or of several gases, into a space half the original size. The molecular concentration of a gas, or of a mixture of gases, is the ratio of the number of molecules to the volume they occupy. The pressure of a gas or of a mixture of gases is proportional to its molecular concentration. This is a better and a shorter way of expressing both Boyle^s law and Daltoifs law.