General Physiology: An Outline of the Science of Life

The simplest method of obtaining a galvanic current, as is well known, is that of soldering together at one end two strips of different metals, e.g., copper and zinc, and bringing their free ends into contact with a moist conductor, e.g., a moist thread (Fig. 118, A). At the moment when the free ends of the metals are joined by the conductor, an electric current begins to flow in the closed circuit, passing from the zinc through the conductor to the copper and from the copper through the

soldered place back to the zinc and circulating as long as the circuit is closed. This arrangement corresponds to Galvani's original experiment in which the nerve represented the moist conductor between the two metals, copper and iron. This principle for the production of a galvanic current has been employed in somewhat more perfect form in galvanic elements (Fig. 118, B}, in which a liquid is employed as the moist conductor, while the two metals, the lower ends of which dip into the vessel containing the liquid, are in contact with one another at their upper ends by a copper wire in place of the soldering ; this has the advantage of allowing the current to be conducted by means of the flexible wire wherever it is needed.

Following the views of Clausius upon the phenomena of electricity in liquids, Sohncke ('88) has presented a very clear idea of the origin of the galvanic current. According to Clausius ('57) the molecules in a liquid are in constant motion and constantly crowd upon one another, the result being that some split into their constituent atoms while other atoms unite into molecules. Hence simultaneously and at all times free atoms and whole molecules are present in the liquid. But while the closed molecule as a whole is electrically indifferent (e.g., water, H2O), its various kinds of constituent atoms, when free, have different kinds of electricity (e.g., hydrogen, H, positive, oxygen, 0, negative). Within the liquid the free atoms retain their charge of electricity. If they come in contact with atoms charged similarly they break away from them ; if they meet those charged dissimilarly, they remain no longer free but unite with the latter chemically into a molecule which is electrically indifferent. But the situation is changed when there is introduced into the liquid a metal plate that exercises upon one kind of the free atoms a chemical attraction. These atoms then accumulate on the surface of the metal, which is non-electric and a conductor, and give off their electric tension to it by conduction.

If, therefore, into a vessel containing acidified water a zinc plate be dipped, free atoms of oxygen accumulate upon its surface and give off their negative electricity to it ; in other words, it becomes negatively charged. If at the same time a copper plate be dipped into the liquid, atoms of hydrogen collect upon it and give to it their positive charge. There arises, therefore, an electric tension between the two metals ; if now the free ends of the copper and the zinc plates be joined by a metallic conductor, this tension is able to equalise itself. During this process, however, new atoms become attracted to the place of contact of the metals with the liquid and become chemically united ; thus the tension becomes continually re-established, and in this way a continual galvanic current is produced.

As is known from the researches of electro-chemistry, especially since the brilliant work of Arrhenius led to the great development of this science, in all chemical processes a disturbance of electric equilibrium takes place. In every chemical decomposition positively and negatively electric atoms or groups of atoms appear. If similar chemical processes take place at all points of a physical system and to the same extent, no current can be led off' from it, for no tension exists between the leadingoff points, because both positive and negative groups of atoms arise in equal quantity (Fig. 119, I). But if in the system, such as a liquid mass, different kinds of chemical transformations, spatially separated, go on, so that there appear at one point a larger number of groups of atoms positively charged, and at another point a larger number negatively charged, an electric tension develops between these two points ; and, so long as the processes continue, a galvanic current can be led off from the

PIG. 119. — Schematic. /. A drop of liquid in which the chemical processes are alike at all points is without a current. //. A drop of liquid in which at two different points chemical processes of different kinds occur gives a current. The large circle is the drop of liquid, the small one the multiplier with the magnetic needle ; the two are united by wires. points to the outside (Fig. 119, //). The conditions under which a galvanic current can appear may be expressed, therefore, as follows : A current can be led off to the outside from a physical system when chemical processes take place in it that produce differences in the electric charge at the two leading-off points.

This proposition is valid for living as well as for lifeless substance. The living substance of a cell is a drop of liquid in which complex chemical transformations continually take place. If these be alike at all points of the cell, no current can be led off (Fig. 120, /); if, however, they be qualitatively or quantitatively different at two different poles, so that differences in the electric charge appear, a tension between the two poles results : and if these could be joined together by a conductor, a current would be obtained in the closed circuit. Naturally, this experiment cannot be performed upon a single cell on account of the

minuteness of the latter, but the rule must hold good as well for the cell-complex, the tissue. As a matter of fact it may be demonstrated in the latter, and Herman's " differential theory " ('67 — '68), according to which a current may be led off from a tissue (muscle, nerve, mucous membrane, etc.) only when different processes are taking place at the leading-off points, is merely the expression of the actual relations. In a resting uninjured muscle, e.g., the sartorms of the frog, which is the best object for demonstrating the truth of this, no current is present, because the same internal processes are taking place at every point (Fig. 121). If, however, at two points in the muscle a difference be produced artificially by warming one point, by cutting the muscle across, which is associated with a local decomposition of living substance, or by making a contractionwave pass over the muscle, an electric current is obtained; the warmed, dying or contracting part becomes negative to all other parts. Tissues

FIG. 120.— Schematic. /. A cell in which at all points of the living substance similar chemical processes are taking place is without a current. //. Polarised cells (e.g., cells of mucous membrane) in which at one pole chemical processes are present that differ from those at the other give a current. whose cells do not possess polar differentiation never show a current in the undisturbed condition, but relatively strong currents can be led off always from glands and mucous membranes, even when undisturbed ; here the cells are polarised in such a manner that the lower part of the cylindrical cell-body contains different substances and transformations of substances from the upper part (Fig. 120, II). The fact discovered by Mendelssohn is interesting, that an excised nerve, when led off from both crosssections, shows an axial current which runs in a direction contrary to the nerve-conduction, i.e., in motor nerves centripetally, in sensory nerves centrifugally.

All such currents may be demonstrated, like those arising thermometrically, by means of the multiplier or the galvanometer (Figs. 115 and 116, p. 259). But a special arrangement of the leading-off electrodes is necessary to avoid false results. If a current be allowed to pass for a time through a wire, the ends of which dip into a moist conductor, electrolytic decompositionproducts of the moist conductor appear at the two ends of the wire, the electrodes, and accumulate there. The precipitation of these products at the two poles produces an electric tension that leads to a current, the so-called polarisation-current, flowing in a direction contrary to the original one. It is evident that the stronger the polarisation-current becomes, the more must the intensity of the original current be thereby diminished. If, therefore, a current be led off from a living tissue by means of metallic electrodes, after a short time a polarisation-current •appears that completely obliterates the tissue-current. In order

to avoid this inconvenience, so-called non-polarisalle electrodes have been constructed, which consist of non-metallic conductors. The most convenient of these non-polarisable electrodes are the brush electrodes suggested by Fleischl, which consist of a glass tube closed at one end by a stopper of plastic clay, and filled with a concentrated solution of sulphate of zinc. A short, soft, pointed camel's-hair brush is stuck into the stopper, and into the solution of zinc sulphate there is dipped an amal- 111 gamated zinc rod, to which the wire is fastened (Fig. 122). The brushes of two such electrodes, each of which is attached to a movable stand, are laid upon the

?^f Aj^iJd^St^ that In this manner *he disturbing phenois without a current. //. when mena of polarisation are avoided. current the injured place being In the electrical phenomena ot most SSon ^KJSSS^ animal- and a11 Plant-tissues the currents the right through the muscle), it are alwavs so feeble that especially sensimonstration ; but in the interesting electrical fishes there are currents of extraordinary strength, although the well-known tale of Alexander von Humboldt, that the South American electric eel is able to stun horses by its shocks must rest upon an error. In contrast to the currents of other tissues, those of the electric fishes are characterised chiefly by their short duration and great intensity ; they appear as brief, strong electric shocks, which can be given off by the animal several times in succession, either spontaneously or upon stimulation. This is comprehensible when it is considered that the production of electricity in these animals serves as a means of defence, which has become differentiated to this great efficiency during the evolution of the race. In accordance with this fact special

organs are developed in the electric fishes for the production of electricity alone. It is most interesting that these electric FIG. 122. — Non-polarisable electrodes. 1. Two non-polarisable electrodes laid upon an excised gastrocnemius muscle of the frog. //. A non-polarisable electrode in its stand. organs have the same embryonic origin as cross-striated muscles, to which also in their adult state they possess great similarity. FIG. 123. — /. Torpedo marmoratus ; the skin is partially cut away so that the electric organ, a, is visible ; it consists of numerous polygonal columns, which are here seen in cross-section. (After Ranvier.) //. Two electric columns from the torpedo seen en face with the electric nerves branching over them. (After R. Wagner.)

The electric organ of the torpedo is composed of numerous long columns, hexagonal in cross-section, which correspond tomuscle-fibres (Fig. 123). Each of these columns is composed of transverse discs lying symmetrically upon one another (Fig. 124, A) ; these are exactly homologous with the cross-striation of the musclefibre, but do not possess doubly refracting elements, and do not undergo changes of form during activity. Still greater is the correspondence in structure of the electric columns and crossstriated muscle in the half-electric or pseudoelectric fishes, e.g., Raja clavata (Fig. 124, B). A very interesting and obvious change

FIG. 124. — A. Two electric columns of Gymnotus electricus. (After Schultze.) B. I. Columns from the pseudo-electric organs of Raja clavata. II. a and b. Single segments of I, more strongly magnified ; the left half in ordinary light, the right half in polarised light. (After Engelmann.) of function is here presented, for the electric organs develop out of genuine, contractile, cross-striated muscle-fibres ; and, as contractility is lost, the electric properties come into greater prominence. The similarity with the muscle is also evident during the activity of the completely-developed organ; for just as the muscle in a single twitch gives only a brief current, so in the electric organ the current is momentary, although of incomparably greater strength.

The above picture of the transformation of energy in living substance is as incomplete as was that of metabolism. As in the latter, so in the former, only the beginning- and the endcomponents of the series are known. Energy enters the living body as chemical energy, light and heat. Light and heat are consumed in providing more chemical energy — light in splitting up in plants carbonic acid, which has in itself very slight value in respect to energy, into atoms of carbon and oxygen possessing free affinities, heat in causing a re-arrangement in the labile compounds of living substance by an increase in intensity of the intramolecular vibrations. Chemical energy is, therefore, the source of all other forms of energy in the organism ; by its transformation there are derived mechanical energy, light, heat, and electricity. In the same proportion in which these are given out by the organism, chemical energy disappears. Hence the end-products of life, carbonic acid, water, ammonia, etc., possess extremely little chemical energy ; into such the introduction of new energy from the outside, in both light and chemical substances, is necessary, in order to make available in the plant new potential energy in the form of free affinities. These are the beginning and the end •of the series. But what in detail are the complex transformations in the living body, what forms of energy in each special case proceed directly from the introduced energy, what intermediate .and retrograde changes the chemical energy passes through, until it leaves the body again in the form of mechanical movement, light, heat and electricity — these are subjects that in great part .are still obscure. More light may be expected here with the advance of knowledge regarding the more special metabolic processes, for the transformation of energy cannot be separated from metabolism.

For convenience, in this chapter, the phenomena of changes of substance, of form, and of energy have been considered separately. In reality, these three groups cannot be separated from one another, for the possession of form and energy belongs to the essence of •substance. Every change of substance is at the same time a change of form and energy. This is inherent in the nature of our conception of matter, and applies to living as well as lifeless matter. What has been treated separately under these three heads is one and the same event merely looked at from different points of view. In brief: All vital phenomena of a body are the expression of a .continual change of the substance of which it consists.

THE living substance of organisms forms a part of the mass of matter that composes the earth. As has been seen, the differences between it and lifeless substances are not fundamental in nature, for the elements that constitute the former constitute also the latter. The differences between organic and inorganic substance are no greater than the differences between many inorganic substances, and consist merely in the mode of union of the elements. It is important to familiarise ourselves with the thought of living substance, not as something mystical, which has no connection with and stands in contrast to all other substance, but as a part of the matter that constitutes the earth's crust. It is evident that life is conditioned wholly by the character of the environment, that the evolution of living substance must be inseparably connected with the evolution of the earth. Accordingly, the composition and the form of the living substance that now covers the earth's surface are to be considered from exactly the same point of view as, for example, the composition of the present sea, i.e., as something that has gradually become, and exists in its present state only because the conditions are such as they are at the moment. Just as the sea with its salt could not have existed as it does now before the water had appeared upon the earth in a liquid state, so also living substance could not then exist with its present composition, for it contains upon an average more than fifty per cent, of water. But just as water was obliged to assume its present form when certain conditions in the earth's evolution were fulfilled, so living substance was obliged gradually to take on its present character to the extent to which the present conditions of the earth's surface were perfected.

The separation of living substance out of the mixture of materials of the earth's crust is only one result of the earth's evolution, like the separation of rocks, salts, or water. The same idea is arrived at from another starting-point, when, not the elementary composition, but the, vital phenomena of living substance are considered. It is an error easily conceived and due to superficial impressions to consider the organism as a closed system, independent of its environment. The fact of metabolism shows this at once ; for, if the organism lives only so long as it takes in matter from the outside and gives off matter to the outside, it stands in the closest dependence upon the external world ; the latter conditions its life.

Thus arises the conception of conditions of life, i.e., conditions that must be fulfilled in order that the life of the organism can exist. It is evident that every change of such conditions must exercise an influence upon the life of the organism. Hence, in order to complete a picture of the mutual relations of the organic world and its conditions, it is necessary not only to investigate the latter as they are now, but, so far as possible, as they were in the earlier periods of the earth's evolution. A few fixed points may thus be obtained for the consideration of the question of the origin, the descent and the evolution of life upon the earth.

All the conditions of life are not equally necessary for all organisms living at the present time. What is absolutely necessary for the existence of one organism may even endanger the life of another. Marine animals when brought into fresh water soon die, and fresh -water animals placed in seawater experience the same fate. This principle holds good not only for large groups of organisms but for every individual form as well. Every individual organism requires for its existence definite special conditions, without the fulfilment of which it cannot continue to live. These special conditions of life are as manifold as the innumerable forms of organisms themselves. -To describe them is to describe the natural history of every organism, and their investigation belongs to the field of special physiology. But in contrast to them there are other requirements that must be fulfilled for all organisms if the latter are to live, and these must, therefore, be termed general conditions of life. General physiology deals with the latter. In the following pages we shall be able to glance at the special conditions only momentarily, when they are of particular interest and present peculiar adaptations of living substance to peculiar circumstances.

It is usual to consider under conditions of life only external factors, such as food, water, oxygen, temperature, etc. But in contrast to these external conditions there are internal conditions, which are inherent in the composition of the organism, and the absence of which, like that of the external factors, is followed by death. The presence of food is required by the fact of metabolism. If living substance is continually undergoing spontaneous destruction, then, in order that it may continue to live, a stream of substances must come into it from the outside, which comprise all those chemical elements that are necessary to its construction. Such chemical substances constitute food. Accordingly, water and oxygen belong to the general conception of food ; it is not customary, however, to include them therein. Following the usage, we shall consider them separately, and shall take up, first, food in the more special sense.

The twelve organic elements of which all living substance is composed (p. 100) must come into the body of the organism in some form as food. In this lies the general significance of food. But the chemical compounds in which these elements are introduced into the body are as manifold for the various forms of organisms as the organisms themselves. A general food for all organisms does not exist; and it has already been seen1 that according to the kind of food-stuffs and the manner in which living substance is constructed from them, organisms may be divided into several large groups, such as green plants, fungi and animals. While the green plants are able to construct their living substance out of inorganic material only, carbonic acid and solutions of various salts, animals without exception require organic food, and cannot live without complex organic^ compounds, such as proteid, carbohydrate, fat, etc. The fungi stand in a certain measure between these two groups, since they can supply their need of nitrogen from inorganic salts, although they require organic compounds for their carbon. An exception to this condition is shown by the interesting nitrogen-bacteria only, which derive both their nitrogen and carbon from ammonium carbonate, and thus like the green plants live exclusively upon inorganic food-stuffs. But, however in individual cases food may be procured, without food of some kind no living body can continue to live.

Regarding quantitative conditions of food, the maximum and the minimum of food that the living body requires, which is different for every form of organism, only a few special cases have been investigated thus far, and these are among the higher vertebrates exclusively. These are questions that still require detailed answer, and, if treated from the cell-physiological standpoint, are capable of yielding results equally important theoretically and practically. Thus far individual values for the whole

organism have been obtained in the case of men only. Voit ('81) has shown that an adult man performing active work can subsist upon a daily food comprising 118 grs. of proteid, 56 grs. of fat and 500 grs. of carbohydrate. With such a diet the man is in metabolic equilibrium, i.e., the quantities of elements excreted in the urine, the sweat, the expiredair, and the faeces are equal to those that are introduced with the food. But, more specifically, these values for the individual elements, such as nitrogen, carbon, etc., introduced with the food must be determined separately, since the body when, e.g., in carbon equilibrium is not necessarily always in nitrogen eqidlibrium. It is thus found that nitrogen equilibrium can be obtained with a quantity of proteid of only 50 grs. (which corresponds to 7*5 grs. of nitrogen), provided only that the quantity of the non-nitrogenous food-stuffs, carbohydrates and fats, is correspondingly increased. 7 '5 grs., therefore, would correspond to the daily minimum of nitrogen with which a man can continue to exist.

The minimum of food necessary to the maintenance of metabolic equilibrium and life is of great importance. If the income of food rises above the minimum, metabolic equilibrium is disturbed only in a very slight degree, slightly smaller quantities of elements appearing in the excreta than are taken in with the food. These very small quantities remain in the body and serve for the increase of living substance and the storing up of reserve - substances, a phenomenon that in husbandry is termed fattening. But this depends upon many factors, which are as yet known exactly only in part. If, on the other hand, the quantity of food falls below the minimum or becomes zero, the condition of hunger or inanition appears, in which the metabolic equilibrium becomes more and more disturbed. This condition has been investigated more fully.

It is worth while to follow somewhat fully the changes experienced by the living organism in the condition of inanition. Every living cell under normal conditions possesses within itself in greater or less quantity substances at whose expense the vital process continues for a time if the food-supply be cut off. These are its reserve-substances. It is a general fact that during inanition the reserve-substances disappear first. Plant-cells that are filled with starch grains consume these when they are brought into the dark, i.e., when they are forced to hunger, for in the dark no assimilation of starch from carbonic acid and water, in other words, no nutrition, takes place. Infusoria, whose cell-bodies in their infusions, where they revel in a superfluity of food, contain all sorts of particles, and hence appear opaque and granular, become clear, transparent and free from granules, when placed in water containing little food-stuff; their cell-bodies become gradually smaller (Fig. 125). The cell, therefore, does not die immediately

at the moment of the withdrawal of food, but lives for some time at the expense of the materials of its own cell-body. If these be consumed, it gradually perishes, just as a clock that is not wound up gradually runs down and then stops. The phenomena of inanition have been studied most carefully in compound multicellular organisms, especially vertebrates, and an important task in this field is left for cell-physiological investigation. Since it is a characteristic peculiarity of living substance that it is continually undergoing spontaneous decomposition, it is clear that in fasting animals metabolic equilibrium must be disturbed. In the decomposition-products of living substance, nitrogen, carbon, hydrogen, oxygen, etc., are continually being excreted, while there is no new

income. The result is that, as in the the multicellular organism, the livingsubstance is gradually consumed and the organism decreases in weight. The animal lives for some time upon its own tissues. It is, therefore, conceivable that as regards their excreta fasting herbivora are like carnivora. The urine of herbivora, which during normal nutrition is alkaline and . turbid, becomes during inanition acid and clear like that of carnivora ; for during inanition herbivora live upon their own, that is, upon animal tissue, and hence in a certain degree become carnivorous. The living substance gradually consumes itself, until the bodyweight has undergone so great a loss that the animal dies. By many experiments Chossat ('43) established this limit of decrease of weight, and found

that with widely different animals death appears when the loss of weight has reached approximately O4 of the whole body-weight. This limit is reached by different animals at very different times. Frogs live longer than a year, and Proteus anguineus, a peculiar amphibian of the Adelsberg grotto, lives several years without food. Man dies in a relatively short time. In earlier times opportunities for investigating human beings who were fasting for a long time were rare, and the early results are to be accepted with caution. Thus, in the year 1831 in Toulouse a convict, who would take only water, is said to have died only after sixty-three days. In later times, with the appearance of the professional faster physiologists have had more frequent opportunity for making exact investigations on fasting men. Luciani ('90) has produced a striking monograph upon fasting, based upon investigations of the well-known Succi, who undertook a thirty