The Dynamics of Living Matter

Acids as well as alkalis act as poisons in comparatively low concen- trations. The toxic concentration for acids is generally much smaller than for bases; the toxic effects are not altogether in proportion to the concentration of the H- or HO- ions. Organic acids as a rule are more toxic than should be expected from their degree of dissociation. A very weak base like NH4OH is for Gammarus (possibly for many organisms) more toxic than NaHO, while tetramethylammonium hydroxide is less toxic.f This indicates that in the case of ammonia the NH3 is responsible for the toxic effects, and not the HO- ion. This is supported by the fact that NH4C1 is more toxic for animals than NaCl, and almost as, if not slightly more toxic than KC1. By way of digression I may remark that, contrary to a possibility I had considered for some time, I have reached the conclusion that the toxic effects of electrolytes are determined by chemical reactions and equilibrium conditions, and not by the electric charges of the ions.

In plants, electrical stimulation plays no r61e, and the same may be said to be true for those phenomena in the life of animals which they share with plants, e.g. cell division. From all we know cell division cannot be called forth or controlled by the galvanic current; but the galvanic current is an excellent stimulant for the functions of those tissues which may be considered characteristic of animals alone; namely, muscles and nerves. It is perhaps more than a mere acci- dent that in this respect the efficiency of Na- or K- and Ca-salts and the electrical current coincide.

We have seen in the third lecture that the solid parts of living tissue consist of colloids which are nonconductors, while the liquids are col- loidal solutions which contain also salts. It is obvious that such a system can act only as a liquid conductor in which the current is carried by the dissociated ions or such colloidal particles as possess an electric charge. The concentration of the colloidal particles is very small compared with that of the electrolytes in solution, so that for the con- duction the latter are mainly or practically exclusively responsible.

When a constant current is sent through a nerve-muscle prepara- tion or through a muscle, two kinds of effects are to be considered: the one effect shows itself only at a rapid change in the intensity of the current, and consists in a twitching of the muscle. The second effect shows itself throughout the whole duration of the current, and consists in an increase of irritability at the cathode and a decrease at the anode. It can be shown that the twitching originates on the making of the cur- rent at the cathode and on the breaking at the anode. The two effects of a current are therefore different at the two poles.

When a current goes through a liquid conductor its work consists, first, in the pulling of the ions through the liquid to the electrodes, and second, in the withdrawal of the charges from the ions and the trans- formation of the latter into uncharged atoms at the electrodes. The question arises as to which of the two effects of the current the physio- logical actions are due: to the increase of the concentrations of ions at the electrodes, or to the withdrawal of their charges. I believe that this question can be decided for the twitchings in favor of the idea that the twitchings are due solely to the increase in the concentration of the ions at one pole, and not to the loss of the charge of the ions.

It had been known for a long time that the galvanic current can only cause a twitching in the muscle, when it goes lengthwise through its nerve; while its effect diminishes or becomes zero when it travels crosswise through the nerve. I true when the nerves are stimu- lated by induction.* Let a and b (Fig. 16) be the elec- trodes of a Toepler-Holtz ma- chine, and cd the nerve of a nerve-muscle preparation of a frog; the preparation is placed on an insulated glass plate. If cd is parallel to the spark discharge and at not too great a distance from it, the muscle twitches every time a spark passes between a and b. If, however, this nerve is put at right angles to the spark discharge and symmetrical to the two electrodes, but equally near or even a little nearer to it than before (Fig. 17), no twitch-

ing or a much weaker one occurs when a spark is produced. The same effect can be produced when a Rumkorff induction apparatus is used in place of a Toepler-Holtz machine. The explanation of the experiment is as follows: let us assume that at a given moment the electrode a (Fig. 16) be charged positively d a positive charge. As soon as the spark passes, the charges in the nerve will disappear also; a current will go lengthwise through the nerve, and a twitching will result. If, however, the nerve is placed at right angles to the spark discharge and symmetrical in regard to the two electrodes (Fig. 17), the current must go crosswise through

the nerve, and no effect or only a minimal effect ensues. In this experi- ment no electrical charges are withdrawn from the ions, and the only effect of the current exists in a change in the concentration of the ions at various places in the nerve. Since, however, in this case of stimula- tion of the nerve by induction, the effect is the same as in the case of a direct application of the electrodes to the nerve, we must draw the con- clusion that in the latter case also the change of concentration is suffi- cient for the physiological effect, and that the withdrawal of the charge from the ion cannot be the cause.

Nernst has tested the idea that the electrical current only stimu- lates the nerve by bringing about changes in the concentration of ions at various places in the nerves.* It had been known for some time that the interrupted current is an excellent medium for stimulating nerves or muscles, and it was also generally known or accepted that alternating currents produce only weak effects when the number of alternations becomes very high. Quantitive determinations had also shown that the minimum intensity of an alternating current which is required to bring about tetanus, increases with the number of alterna- tions. These facts Nernst used as a starting point to test the idea that the current acts only by changing the concentration of ions at the place of stimulation. "According to our present knowledge, the galvanic current cannot produce in a tissue, i.e. a purely electrolytic conductor, any other effects than displacements of ions, i.e. changes of concen- tration; we therefore conclude that the latter must be the cause of the physiological effects. In the case of an alternating current, changes

* Nernst, Nachrichten der Gesellschaft dcr Wissenschaften zu Gottingcn, p. 104, 1899. of concentration occur whose sense changes with the direction of the current. When their average reaches a definite value, the physiological effect becomes noticeable and the threshold is reached. " It is possible to calculate the average changes of concentration without making excessively specific assumptions. We know that in tissues the composition of the watery solution which acts as the elec- trolytic conductor is not everywhere the same, and especially that it is different inside and outside the cells. Semipermeable membranes prevent the equalization by diffusion and only at such membranes can changes in the concentration be produced by the current. In the in- terior of a homogenous solution, the current cannot produce such an effect, as in each instance just as many ions migrate into such an ele- ment of volume as leave it. At the semipermeable walls, changes of concentration must occur, inasmuch as the current carries salts to such a membrane which blocks their further motion. Such salts as are able to pass through the membrane undertake the conduction of the current through the membrane. The seat of the electrical stimulation must therefore be at the latter.

" If a current of the density i carries the quantity v of salt to the membrane, a migration of the salt away from the membrane must occur through diffusion. The average change of concentration at the mem- brane depends therefore upon the antagonistic effects of the current and diffusion."* Nernst developed the equations for this process (ac- cording to a method by Warburg), which show that the intensity of an alternating current, which is just sufficient to produce a stimulating effect, must increase in proportion to the square root of the number of alternations in the second. Nernst tested this theory experimen- tally in cooperation with Von Zeynek and Barratt, and found it true for alternations from 100 to 2000. This proves that the experimental data agree with the assumption that the electrical stimulation is due to a change in the concentration of ions in the living tissues. Such changes occur wherever the progress of ions is blocked, and this may be at the limit of each individual surface film of protoplasm. In some cases it may be at the surface of the protoplasmic layer of a cell, in other cases, such blocks may occur inside a single cell.

Nernst's experiments were concerned only with the physiological effects of alternating currents, and he does not discuss the effects of con- stant currents. While a constant current is passing through a nerve or muscle, the latter generally remains at rest. As long as the current continues to pass through, new ions must be carried to the poles. It is difficult to understand why this should not result in any motor effect ; here is a gap which needs to be filled.

It is of the greatest importance that the stimulation at the making of a current occurs at the cathode, as this indicates that an increase in the concentration of the cations is responsible for this result. On account of the fact that the migration ' velocity of the potassium ions is greater than that of the other cations in the muscle, it might appear as though the latter were responsible for the stimulating effect at the cathode at the making of the current.* If the current is broken, the stimulation occurs at the anode. It has been suggested by Griitzner that the effect of the breaking of a current is in reality due to a current of polarization which, of course, has the opposite direction from the polarizing current. In this case, too, the stimulating effect at the anode at the breaking of a current is due to an increase in the concen- tration of the cations.

While a constant current is passing through a nerve, a region of increased irritability exists around the cathode. I pointed out four years ago that such a condition can be produced in the nerve by treat- ing it with a salt which precipitates or diminishes the concentration of the calcium ions, e.g. sodium-oxalate, -citrate, -fluoride, -carbonate, etc. It is not impossible that a substitution of K for Ca, or vice versa, in ion-colloids actually occurs at the cathode, while a constant current flows through the nerve. At the anode we must expect, and we find, a de- creased irritability. Until quite recently the phenomena of catelectrotonus and anelectrotonus, and perhaps the effects of the current in general, were explained on the basis of antagonistic physiological processes being aroused by the current, one being called assimilation, the other dissimilation. As it is impossible to connect an adequately definite chemical idea with these terms, it is useless to discuss this view. It is obvious that those who used these terms did so under the impression of the since refuted notion that a metallic conduction occurs in living tissues, and that therefore a current can directly break up chemical compounds in the nerve or muscle ; while we now know that the disso- ciation exists before the current starts. Moreover, the above-mentioned experiments on the effects of induction on the nerve show that even without any charges being withdrawn from the nerve, and without any secondary chemical effects, the stimulation occurs. This shows that the secondary chemical reactions at the poles, due to the trans- formation of the ions into atoms, have nothing to do with the stimu- lating effects of the current. I believe that for these reasons it is advisable to discontinue the assertion that the current causes dissimi- lation at the one and assimilation at the opposite pole of a cell.

It seems to be a general law that wherever the constant current * I expressed this possibility in my lectures five years ago. has any effect whatever, the stimulation occurs at the cathode. As far as Infusorians are concerned, it is generally stated that the stimu- lation occurs at the anode; but this statement is nevertheless wrong, as Dr. Bancroft has recently shown.* If a constant current goes through a Paramtzcium, the effect is that the position of the cilia on the side of the cathode is altered, while on the side of the anode the cilia retain their normal position, provided the current is not too strong. The abnormal position of the cilia on the side of the cathode consists in their free end pointing toward the oral end of the Paramcecium. It can be shown that this is the position of the cilia which is produced by any kind of stimulus, mechanical or chemical. Budgett and I have

shown that if a ParamcBcium be put into — solution of NaCl (or any salt), the Infusorian moves backward. This is due to the fact that the salt causes a change in the position of the cilia, the latter pointing with their free end forward instead of backward. If a constant current is sent through a Paramacium, this change in the position of the cilia occurs at the cathode end, while at the anode end no such change occurs. It is therefore obvious that if we speak of the stimulating effect of a constant current upon an Infusorian, we should state that this stimulation occurs at the cathode side of the Infusorian. The opposite statement is due to an observation made by Kiihne; namely, that Acti- nosphcerium, a Rhizopod, when subjected for some time to a constant current, begins to disintegrate on the anode side.f This effect he called a stimulation, or even tetanus. Maxwell and I, however, pointed out long ago that this is merely a play on words, inasmuch as these phe- nomena of disintegration (cytolysis ?) observed by Kiihne are caused by electrolysis and are not necessarily connected with the stimulating effect of the current. This is corroborated by observations made by Budgett and myself.J

Not only muscular contractions but phenomena of secretion can also be produced by a current. When a current is sent through a trough filled with water which contains an Amblystoma, a secretion of whitish mucus appears on the skin wherever the outside of the latter is struck by the current curves emanating from the anode (Figs. 18 and 19). § Here we have also apparently an anode effect of the current. This effect depends partly, at least, upon a stimulation of the central nervous system, and we do not know whether the stimulation is anodic or cathodic. It may be that the influence of the central

t Kiihne, Untersuchungen uber das Protoplasma und die Contractilitat, Leipzig, 1864. nervous system consists only in causing a contraction of muscular or FIG. 18. — The secretion of mucus on the skin of Amblystoma under the influence of a constant current. The animals were kept in a trough of water through which a current passed. The current lines were straight and parallel with the longitudinal axis of the animal. The black dots indicate the spots where the secretion of mucus appeared. The drawing shows that the glands secrete at the anode side of the animal where the current lines cut its surface.

contractile elements which result in the contents of the mucous glands being squeezed out. The secretion is partly, however, a direct effect of the current on the skin, and results finally in the disintegration of the latter. In this case we may be dealing with an electrolytic effect due to secondary chemical reactions. Budgett and I found that these anodic effects of the current on Infusorians and Amblystoma can be imitated by applying NaHO to these organisms. Whatever the cause of the secretion may be, we are not justified in identifying the disintegration of an Infusorian or the skin of an Amblystoma with the tetanus of a muscle.

It is not our intention to give more than the general idea of irritability and stimulation. Besides chemical and electrical stimulation, mechanical stimu- lation plays an important role. When a nerve has been put into a decalcifying solution for some time, or has lost water, it becomes extremely sensitive to slight mechanical agitation. When a nerve reaches the climax of its sensitiveness, it suffices to knock on the table that FIG. 19. — The same experiment as in Fig. 18 carried out with pieces of Amblystoma.

supports the stand with the nerve to bring about a twitching of the muscle. If we may be guided by physical analogies, — which however, are not absolutely reliable, - - this mechanical stimulation might be compared with the effect which a mechanical agitation has, under certain conditions, upon an oil drop on the surface of a Na2CO3 solution. In this case it may lead to a dissolution of a solid soap film on the surface, or to an alteration of the surface, by bringing new particles of both liquid media in contact. Thus phenomena of spread- ing may be provoked by a slight mechanical agitation. Mechanical stimulation is much more effective in nerves than in muscles.

As a rule, heat is also mentioned as a stimulant though nobody uses this form of energy for this purpose. The term " stimulation by heat " is a misleading phrase, as we shall see presently. It appears from the foregoing that by the word " stimulation " we mean a process which is unknown to us, which, however, seems to con- sist after the data given in this lecture in the substitution of Na- or K- ions for Ca, or "vice versa, in some colloidal (proteid or lipoid) compound of the muscle or nerve, whereby some physical qualities of the colloidal substances are changed.

IN discussing the effects of heat or temperature upon life phenom- ena, we meet with the difficulty that heat influences living matter in two ways; namely, chemically and physically. In chemical re- gard the temperature influences the reaction velocity most powerfully, and in physical regard it influences the viscosity of the liquids of the cell (colloidal solutions) and their state of matter (coagulation, gela- tion). In studying the influence of temperature upon life phenomena we must keep these two effects apart.

There is an upper temperature limit at which all organisms can be killed; it is generally assumed that in this case death is due to the fact that certain proteids are coagulated by heat, and this process is not reversible. Setchell has ascertained that in hot springs whose tem- perature is 43° C., or above, no animals or green algae are found.* In hot springs whose temperature is above 43° he found only the Cyanophycea, whose structure is more closely related to that of the bacteria than to that of the algae, inasmuch as they have neither definitely differentiated nuclei nor chromophores. The highest temperature at which Cyanophycece occurred was 63° C. Not all the Cyanophycece. were able to stand temperatures above 43° C., but only a few species. The other Cyanophycece. are found at a temperature below 40° C., and were no more able to stand higher temperatures than the real algae or animals. The Cyanophycea of the hot springs were as a rule killed by a temperature of 73°. From this we must con- clude that they contain proteids whose coagulation temperature lies above that of animals and green plants, and may be as high as 73°. Among the fungi many forms can resist a temperature above 43° or 45°; the spores can generally stand a higher temperature than the vegetative organs. Duclaux found that certain bacilli (Tyrothrix)

found in cheese are killed in one minute at a temperature of from 80° to 90°; while for the spores of the same bacillus a temperature of from 105° to 120° was required.* Duclaux has called attention to a fact which is of importance for the investigation of the upper temperature limit for the life of organ- isms. According to this author it is erroneous to speak of a definite temperature as a fatal one, instead we must speak of a deadly tem- perature zone. This is due to the fact that the length of time which an organism is exposed to a higher temperature is of importance. Du- claux quotes as an example a series of experiments by Christen on the spores of the bacilli of the soil and of hay. The spores were exposed to a stream of steam and the time determined which was required at the various temperatures to kill the spores.

In warm-blooded animals 45° is generally considered a temperature at which death occurs in a few minutes; but a temperature of 44°, 43°, or 42° is also to be considered fatal with this difference only, that it takes a longer time to bring about death. This fact is to be con- sidered in the treatment of fever. It is generally held that death in these cases is due to an irreversible heat coagulation of proteids. According to Duclaux, it can be directly observed in microorganisms that in the fatal temperature zone the normally homogeneous, or finely granulated, protoplasm is filled with thick, irregularly arranged bodies, and this is the optical expression of coagulation. The fact that the upper temperature limit differs so widely in different forms is explained by Duclaux through differences in the coagulation temperature of the various proteids. It is, e.g. known that the coagulation temperature varies with the amount of water of the colloid. According to Cramer, the mycelium of Peni- cillium contains 87.6 water to 12.4 dry matter, while the spores have 38.9 water and 61.1 dry substance. This may explain why the myce- lium is killed at a lower temperature than the spores. According to Chevreul, with an increase in the amount of water, the coagulation temperature of albuminoids decreases. The reaction of the proto--

plasm influences the temperature of coagulation, inasmuch as it is lower when the reaction is acid, higher when the reaction is alkaline. The experiments of Pauli show also a marked influence of salts upon the temperature of coagulation of colloids. The process of heat coagulation of colloids is also a function of time. If the exposure to high temperature is not sufficiently long, only part of the colloid coagulates; in this case an organism may again recover. We gain from these experiments a further confirmation of the idea expressed in an earlier lecture, that the process of coagulation or gelation may not be a purely physical process, but the outcome of a chemical reaction.

When we analyze the effects of heat upon life below the upper fatal temperature zone, we must first realize that the velocity of chemical reactions is raised to two or more times its original amount, whenever the temperature advances 10° C. (van't Hoff and Arrhenius). This holds good for the reactions in living organisms as well as for non- living, as may be seen from the following table concerning the influence of temperature upon the CO2 production by seeds of lupines: 100 gr. of seeds produced in one hour according to Clausen,* the following number of milligrams of CO2 : —

We see that below the temperature of 40° the amount of CO2 is approxi- mately doubled for every rise of 10° in temperature. Above this temperature, however, the amount of CO2 diminishes rapidly with any further increase of the temperature. This is very generally observed in enzymatic processes, and may be due to the fact that the enzyme itself undergoes hydrolysis, which of course follows the temperature law of van't Hoff and Arrhenius ; t or it may be that the enzyme undergoes heat coagulation (or a process of clumping), by which

* Quoted after Cohen, Lectures on Physical Chemistry for Physicians and Biologists, New York, 1902. the reaction area between enzyme and fermentable substance is diminished. The question arises, Can we show that certain life phe- nomena are a direct function of a reaction velocity? In my book on the Comparative Physiology of the Brain, I expressed the idea that the rhythmical contractions of the jellyfish, of the heart, and perhaps in general, are a function of enzymatic processes. It seemed to me that this idea could be put to a test, since in case it were true, the rate of heartbeats should vary with the temperature, according to the figures found by Arrhenius for the influence of temperature, upon re- action velocity, i.e. we should find that with a rise of temperature of 10° C. the rate of heartbeats should at least double. At my request Mr. Snyder undertook experiments in this direction on strips of the ventricle of the tortoise heart. He found, indeed, that inside the tem- perature range of from 5° to 30° C., the number of heartbeats is about doubled for every rise of temperature of 10° C. The strips of the ven- tricle were kept in a moist chamber, which was submerged in a water bath of constant temperature. The contractions of the strips were recorded in the usual way. I will give as an example the records of six experiments.* The hearts of six terrapins were put into moist chambers, and the latter were kept at a constant temperature for two hours and forty minutes. Two strips were kept at a temperature of 10° C., two at 20° and two at 30°. The average number of heartbeats was determined for every five or ten minutes. The left vertical column of the following table gives the time in minutes, the other vertical columns gives the average number of heartbeats for each heart at that time.