The processes of excitation of all the effects of stimulation are those which have invariably claimed place in the interest of physiologists. The study of the processes of depression, on the other hand, has remained more or less in the background. This is readily understood when it is considered how much more apparent the processes of excitation are than those of depression. Nevertheless, these latter possess no less importance for the course of vital phenomena than those of excitation. Without depression no excitation can take place in the vital activity of the organism, for, as we have seen, every excitation is secondarily followed by a refractory period. To this must be added the great number of primary depressions, directly brought about by the most varied stimuli, such as cold, want of oxygen, poisons, etc., without the presence of a preceding excitation. Thus it is essential that the processes of depression should be studied with no less interest than those of excitation, and it is much to be desired that the former should receive a more detailed analysis than has up to now been the case. Even as it is, extensive material has been obtained for the analysis of this group of reactions. With the closer study of the process of excitation the facts in connection with the refractory period and fatigue make it necessary that the processes of depression be taken into consideration. Toxicology and pharmacology likewise furnish innumerable effects of depression produced by poisons and drugs. Unfortunately the investigation of these reactions has been in the main purely superficial. This arises from the recency of the development of these sciences. Even later than physiology they are only now beginning to extend their investigations, directed up to the present to the grosser organic reactions, to the cellular analysis of the effects of poisons. How rarely we find instances in which the effect of some drug is studied at the point of attack and systematically followed to the specific cell form, and its primary excitating or depressing effect on this or that constituent process of the metabolic activities ascertained. And how great, on the other hand, is the number of “medicines” making their appearance each year in pharmacology of which nothing further is known than a few secondary effects on the action of the heart, the blood pressure, the secretion and excretion and on some other outwardly perceptible organic actions! This deplorable condition of present-day pharmacology must be ascribed to the regrettable circumstances that pharmacological research is only in a very small degree the result of careful investigations, carried out by biologically and chemically trained pharmacologists, but is for the most part undertaken at the instigation of chemical manufacturers. This eager haste to obtain superficially practical results has lessened in great degree the interest in the close and painstaking theoretical analysis of reaction to poisons. Thus it happens that, in spite of the numberless examples of the depressing effects of poisons discovered by pharmacologists, it is only in rare instances that the physical nature of these processes is more closely studied. Therefore, investigation in pharmacology and toxicology in so far as they are carried out in a purely scientific spirit and not influenced by the desire for merely superficial results, may find here a wide field of research work, rich in future promise. It is from such investigation that we may expect an abundance of material for the closer analysis of the processes of depression. For the present, however, we must restrict ourselves to the consideration of some individual cases which have been studied somewhat more in detail by physiologists.

Simple reflection shows the possibility that depression, that is, the retardation of the normal vital processes, can be brought about in various ways. As on the one hand the normal metabolism of rest is composed of very numerous chemical constituent processes, and on the other hand the closest interdependence exists between these individual constituent processes, it follows that every factor which increases or retards even one of these must secondarily influence the course of the entire activity. Hence a wide range of possibilities exists for the processes of depression. As the complicated works of a clock can, by the stopping of a single moving part, be brought to a standstill, so in like manner the metabolic activity can be depressed by very different constituent members. In spite of this we have every reason to assume that the greater number of all processes of depression result from the primary effect of one or a few constituent members. A primary simultaneous depression of all or at least of numerous constituent processes of the entire metabolism may only be assumed as possible, resulting from decrease of temperature within certain limits. But even in the case of “cold depression” it is not probable, owing to the great effect of every alteration in the relations of masses in the cell, that depression is solely the manifestation of a uniform retardation of all individual constituent metabolic processes. If, therefore, the greater part of the processes of depression are brought about by the primary effects of an individual constituent process, then the possibility must be admitted that any component of the chain can by the means of some specific external influence form the starting point for a depression. The number of the various kinds of processes of depression would be, therefore, enormous. The knowledge obtained up to the present shows, however, that this variety is not quite as great as the above facts might lead one to expect. Even though future investigation will certainly not do away with the assumption of the existence of the most manifold physical types of depression, the analysis of a few processes which have been studied up to now demonstrates the singular fact that a number of these which are brought about by quite different external factors, are based on an absolute uniformity of their mechanism. As we have previously seen, a certain constituent of the metabolic chain can be excitated primarily by very different kinds of stimuli. In like manner there exists in metabolic activity a certain point of predilection for different kinds of stimuli, from which their depressing effects proceed. Here the highly interesting fact is shown that this point of predilection, which represents that of the most frequent attack, is the same for excitating as for depressing stimuli. These are the oxydative processes. As our knowledge of the reactions to stimuli in anaërobic organisms is still almost nil it is not possible at present to ascertain which component in the metabolism of these organisms, adapted to life without oxygen, plays an analogous rôle to that of the oxydative in aërobic systems. Our investigations must, therefore, be restricted to the world of aërobic organisms. Here we have seen that the different stimuli which produce an excitating effect invariably increase the oxydative disintegration of the living system and we now find that these constituent processes of metabolism likewise form a point from which depressing responses to stimuli very readily proceed.

The prototype of this group of processes of depression in which this is manifested in a most striking manner, is that of a simple asphyxiation by the withdrawal of the oxygen supply from the exterior. If the supply of oxygen is withheld from an aërobic organism, oxydative disintegration is gradually found to be more and more decreased and further breaking down takes place anoxydatively, as oxydative decomposition forms the chief source of energy production, and energy production consequently undergoes a gradual decrease. Excitating stimuli, therefore, meet with less response than when a sufficient supply of oxygen is present, that is, irritability is diminished. As a result of this decrease, a corresponding decrement in the extension of excitation takes place, which, in turn, is likewise manifested by the restriction of the perceptible response to stimulation. In the same degree in which oxydative disintegration becomes less, anoxydative breaking down products are accumulated. The accumulation of these products likewise plays a part in the production of depression and increases the decrement in the conduction of excitation. The decrease of energy production by decline of the oxydative decomposition, as well as the accumulation of anoxydative breaking down products, therefore, similarly reduce irritability; that is, their effect is depressing. This whole series of processes, which we have previously considered in detail, takes place on the withdrawal of oxygen and leads to the depression of asphyxiation. It can readily be observed in the most varied kinds of aërobic organisms in rhizopods and infusoria, in plant and ganglion cells, but finds its most complete demonstration in the nerves. Here these processes can be easily produced with any rapidity desired, accordingly as a relative or absolute want of oxygen is brought about. These same typical results are likewise shown in numerous processes in which the external conditions are quite different in nature.

We have previously become acquainted with such a case and studied it in detail. This is the state of fatigue. Fatigue is a typical state of depression, that is, a state in which the vital process is retarded and irritability in response to stimuli correspondingly decreased. Fatigue is, however, as we have found, the result of a relative deficiency of oxygen. The amount of oxygen at disposal is not sufficient to allow of disintegration, increased by constant functional activity oxydatively taking place, to develop to its full extent. In consequence the previously cited sequence of processes takes place. A “depression of activity” is produced. Fatigue is true asphyxiation and it is here evident that depression proceeds from the same constituent processes of metabolism as excitation, brought about by a single stimulus. Excitation produced by constant stimuli gradually merges into depression as the amount of oxygen at disposal, even if augmented in the intact organism by the increased blood supply, for instance, is still insufficient to meet the demand made by the increased oxygen consumption as a result of continuous functional activity.

A further very interesting example of depression produced by oxygen deficiency is furnished by heat depression. It has long been known that with increasing temperature the vital manifestations of all poikilothermic organisms at first undergo a heightening of their intensity. If, however, after a maximum is reached, the temperature is still further increased a sudden depression sets in. The increase in the rapidity of the vital process as a result of increased temperature is readily understood when based on the well-known law discovered by van’t Hoff. Numerous investigations on the rapidity of the course of special vital manifestations, as, for instance the growth of the eggs of the frog and sea urchin, the assimilation of carbon dioxide in green plant cells, the number of vacuole pulsations in the infusoria cells, the frequency of the heart rate of the frog and of the mammal, etc., have shown that their increase does in fact follow the van’t Hoff law, being doubled or tripled in amount with every increase of ten degrees of temperature. The genesis of depression produced by heat, developed in different organisms at various heights of temperature, requires a closer analysis. This depression takes place at temperatures below that in which coagulation of proteins occurs. Therefore, under certain conditions, with which we shall presently become acquainted, it is capable of being recovered from, whereas in higher temperatures, in which albumen coagulates, vital activity is permanently obliterated. Depression produced by heat is, therefore, in itself not a necrobiotic process, which, as such, must necessarily lead to death. But rather like fatigue it must be looked upon as an asphyxiation process. Its relations to oxygen exchange have been chiefly demonstrated by Winterstein202 by his investigations on the central nervous system of frogs and on medusæ. He found that when placed in a heated chamber in a temperature of 32–40° the activity and reflex excitability of the frog are at first augmented. Within the lapse of a short time this increase has become so great that the slightest touch produces tetanic contractions, similar to those characteristic of strychnine poisoning. Very soon, however, this state of high excitation is followed by one of depression, in which no response to stimuli can be obtained. The animal remains entirely motionless in any position in which it is placed, in the same manner as a frog whose nerve centers have been completely exhausted by strenuous activity. On the basis of our knowledge of the rôle played by the deficiency of oxygen in the bringing about of exhaustion the thought arose, if in this heat depression exhaustion might not likewise be the result of oxygen deficiency. This assumption has been most strikingly confirmed by the investigations of Winterstein. It has been demonstrated that recovery of the animal in a state of heat depression cannot be obtained by mere cooling, but is only brought about when at the same time a renewed oxygen supply is provided. For instance, a frog is depressed in the warm chamber and even when a strychnine injection has been introduced, does not show the slightest reaction to stimuli. In the warm water bath artificial circulation is now applied in the previously described manner with an oxygen-free saline solution at 30° C., so that the blood is displaced and thus the renewed oxygen supply to the nervous centers prevented. The animal can now be cooled and the warm saline solution be replaced by a cooled one without the least recovery taking place. If, however, blood of the ox with contained oxygen is substituted for the oxygen-free saline solution, the frog shows signs of recovery within a few minutes and after ten or fifteen minutes responds as a result of the strychnine to the merest touch with tetanic contractions of the whole body. By modifying these methods of investigation to a certain extent Bondy203 has confirmed these results to the fullest extent. Later Winterstein by quantitative determinations of oxygen consumption on medusæ showed that at 30–35° C., at which temperature heat depression sets in, the consumption of oxygen shows an increase of about three and a half times compared to that in a temperature of 11–12° C. These facts show that we have in heat depression a process which, as far as its genesis is concerned, is completely analogous to that of fatigue. In fatigue, a relative want of oxygen is produced by the increased consumption following functional activity, in heat depression by the increase of the entire metabolism producing a corresponding increase of oxygen requirement. In both instances we have an excitation produced by external stimuli which result in an increase in the amount of oxygen required, and in both instances the oxygen at disposal is not sufficient to permanently meet the augmented demand. In both types, therefore, decomposition must become more and more anoxydative and the well-known series of processes is developed, which find their expression in depression.

In another direction likewise heat depression is of special interest, that is, in regard to the theory of nature of the processes in the living substance. According to the van’t Hoff law we may assume that every individual constituent metabolic process, if we imagine it as isolated and taking place in a test tube, undergoes in more or less the same degree as all others an increased rapidity of reaction as a result of increased temperature. At the same time, in living substance we find on the contrary that the van’t Hoff law is only within certain narrow limits more or less applicable to the sum total of all metabolic processes. Beyond certain degrees of temperature no further increase of the vital process takes place, instead a retardation occurs. The analysis of depression produced by heat shows us in the clearest and simplest manner the reason for this apparent deviation from the general law of van’t Hoff. This reasoning is based on the fact that the rapidity of reaction of a chemical process is not merely dependent upon the temperature, but likewise upon the mass relations of the reacting substances. In spite of the effect of the temperature in increasing the rapidity of reactions, the process undergoes retardation which extends to a complete cessation if the supply of material necessary to its existence does not keep pace with the increase produced by temperature. In the present instance the amount of reserve supplies for the building up of the disintegrating molecules exists in abundance, and it is merely the available oxygen which is in relatively a very small quantity. As soon, however, as metabolism in its entirety, or even merely in those parts in which oxygen is directly required, is increased by whatever means, the oxydative processes would be the first to fail and it must be from this point that the disturbance of the harmony in the interacting of the individual metabolic processes proceeds. This principle which we here see manifested in its simplest form in the effect of temperature on oxygen exchange in the form of a disturbance in the correlations of the individual constituent processes based on an alteration of the mass relation and the rapidity of reactions of individual members is, however, not merely restricted to effects of temperature and the results quickly following on a relative oxygen deficiency. It has, indeed, a much more general significance for all manner of constituent metabolic processes, for it is applicable to all nutrition and to all growth, and forms one of the most important factors which influence the process of development, that is, the gradual “metachronic” alterations in metabolism to which all living systems are subjected as long as life endures.

A very extensive group of depression processes is produced by the action of chemical stimuli. Among these the processes to which we apply the collective term of “narcosis” must claim our special interest. As is well known, an enormous number of substances of very different chemical nature, such as carbon dioxide, alcohol, ether, chloroform, chloral hydrate, etc., exist, which, possessing the property of producing cessation of the vital activities in all living systems, after withdrawal of their application, if it has not been too prolonged or intense, permit a complete restoration to normal vitality. These are the general narcotics. Besides these there are a series of substances which have a depressing effect only upon certain forms of living substance, and which we may, therefore, term special narcotics. As, however, the particular nature of depression following the application of chemical substances has hitherto been closely studied only in a very few instances, we are not, at present, in a position to sharply define the limitations of the conception of narcosis, a conception which originally had hardly any further meaning than the production of unconsciousness by chemical means. In the following discussion, therefore, we shall deal merely with narcosis produced by the well-known general narcotics, such as carbon dioxide, alcohol, ether, chloroform, etc. From the time of the introduction of ether narcosis into medical practice by Jackson and Morton in the year 1848 up to the present day, the theory of this process has awakened the liveliest interest. Many attempts have since been made to explain the physical nature of this interesting process without, however, any generally acknowledged theory of narcosis being established. I will refrain from entering into these former theories in detail as they have been exhaustively treated by Overton204 in his studies on narcosis.

In connection with our present observations, however, I will more closely analyze the process itself, following the results of investigations extending over more than ten years carried out by my coworkers and myself. In these investigations it has been found that narcosis belongs to this group of depressing processes. A satisfactory theory of narcosis, however, and this I must explain from the first, can even today not be arrived at. Such a theory would require the ascertainment of all primary and secondary alterations produced by the narcotic in the course of normal vital activity. For this, however, a number of minute details are still lacking. Nevertheless, the careful and detailed investigations during the last ten years have acquainted us with a large number of alterations, which, acting as conditioning factors for the process of narcosis, must be taken into consideration, and which to a certain extent give us an idea of the mechanism of this process. They are equally interesting from a theoretical as well as from a practical point of view. The presentation will become more detailed as more of such conditioning factors are established by the deeper penetrating of future analysis. I will deal here with the facts found up to the present and then proceed to the deductions which these furnish for the theory of narcosis.

In the first place narcosis is stamped as a typical process of depression, being characterized by a decrease of irritability with a corresponding decrement of the extent of excitation. The chief feature of all narcotized systems is, that in slight narcosis excitating stimuli produce a greatly weakened excitation, and that in deep narcosis no perceptible response is obtained. This can readily be ascertained in the various forms of living substance. According to the previous observations on the inseparable relations between conduction of excitation and irritability, it is self-evident that with decrease of irritability there must be a corresponding decrease in the capability of the conduction of excitation from the point of stimulation. This decrease in conductivity must, therefore, be the greater the more irritability is reduced; that is, the deeper the narcosis, the greater must be the decrement undergone by the wave of excitation in its extension from the point of stimulation. These facts can be observed in the highest perfection in the nerve, and have, as we have seen, been demonstrated by the investigations of Werigo, Dendrinos, Noll, Boruttau and Fröhlich.205 Upon deeper analysis of this process of depression, the next task for the investigator must be the ascertainment of the special components of the metabolic activity, which are depressed as a result of the narcotic.

As a consequence of the result of my investigations on fatigue, the idea occurred to me to test if possibly oxygen exchange likewise undergoes depression during narcosis. The spinal cord centers of the frog, which had served me in ascertaining the rôle played by oxygen in the bringing about of the depression of activity, appeared likewise a favorable object for this investigation. Indeed, the question if consumption of oxygen takes place during narcosis, could be experimentally determined in direct connection with the investigations on fatigue. This was based on the following consideration. If an oxygen-free saline solution is introduced into the aorta of a frog and in order to increase the activity of the spinal cord centers to the maximum the animal is poisoned with strychnine, after a very short time complete exhaustion takes place as a result of oxygen deficiency. This exhaustion can only be removed by the introduction of oxygen. In this condition the oxygen requirement of the centers is enormously increased. If the centers are narcotized by adding a narcotic to the oxygen-free circulating fluid in amounts which, as experience has found, would produce complete loss of reaction in the normal animal, for example, about 5 per cent. of alcohol, it can then be tested if, in this state of narcosis, the centers are capable of oxygen consumption. It is merely necessary to replace the oxygen-free saline solution containing alcohol by blood rich in oxygen, containing alcohol in an amount sufficient to continue the narcosis, but supplying an abundance of oxygen. If, after this artificial circulation has lasted for a sufficient period, the blood is then displaced by an oxygen-free saline solution containing alcohol, and then this, in turn, is replaced by an oxygen- and alcohol-free saline solution, so that cessation of the narcosis is now produced, it can be ascertained by the responses of the animal if consumption of the oxygen, when at the disposal of the centers during narcosis, has taken place or not. If the former is the case, then on the cessation of narcosis reflex contraction must occur in the same manner as in every strychninized frog totally exhausted by oxygen deficiency and into which a saline solution containing oxygen is reintroduced. If during narcosis, on the other hand, oxygen has not been consumed by the centers, depression must continue to be present after cessation of narcosis. Testing the recovery of the animal on the introduction of blood, rich in oxygen, serves as an indicator for the vital activity and capability of recovery of the centers. A great number of experiments based on this scheme of investigation were undertaken at my request by Winterstein.206 These were carried out with alcohol, ether, chloroform and also carbon dioxide. His experiments have shown in the most uniform manner that, in spite of the requirement of oxygen by the centers being increased to its highest extent, and notwithstanding the most ample oxygen supply during narcosis, after cessation of the same and the introduction of an oxygen-free saline solution no trace of recovery occurred, whereas after a supply of oxygen was introduced tetanic contractions reappeared at once. During narcosis, therefore, the centers, in spite of their great requirement of oxygen, lose their capability of oxydative splitting up and consumption of oxygen.

After the methods for asphyxiation of the nerve had been worked out and perfected the wish arose likewise to carry out for these structures an analogous series of experiments to that employed for the centers and based on the same chain of reasoning. These investigations have the advantage of essentially simpler conditions. After having convinced myself by experiments, that the results on the nerve were in complete conformity with those on the spinal cord, at my suggestion Fröhlich207 repeated and continued these experiments on a more extended scale. A nerve was asphyxiated by the previously described method. This is accomplished in the simplest manner by the opening or closing of stop cocks in the apparatus I have employed which permit of pure nitrogen, or nitrogen with ether, and finally also oxygen with ether or pure oxygen being conducted at will through the glass chamber. If the nerve was so far depressed in pure nitrogen that conductivity became obliterated for about two cm. of the asphyxiated stretch, it was then narcotized in nitrogen. Following this oxygen with ether was supplied for a time. Then the oxygen-ether mixture was displaced by one of nitrogen and ether and finally by pure nitrogen. Even after a prolonged period, a recovery in pure nitrogen never took place. On the other hand, the nerve recovered at once, as soon as oxygen without ether was introduced. The results of these investigations are, therefore, completely in harmony with those undertaken by Winterstein on the nervous centers. They were later likewise entirely confirmed by similar experiments of Heaton.208 All these investigations furnished the proof that in narcosis, living substance, notwithstanding even the greatest oxygen deficiency, is not capable of producing oxydation, neither can consumption of oxygen take place, with which, after cessation of the narcosis, oxydative splitting up can be carried out.

Recently Warburg209 has likewise found an oxydative depression during narcosis in the eggs of the sea urchin and in the red corpuscles of geese, and the same fact has lately been also demonstrated by Joannovics und Pick210 for the oxydative activity of the liver cells of the dog.

This fundamental establishment of the fact that narcosis prevents oxydations in living substance is at once followed by the further problem, in what manner do the disintegration processes undergo alterations during narcosis? That they must be altered, and this in the form of a reduced energy production, is clearly shown by the decrease of irritability and the increase of the decrement of the conduction of excitation. Both become the greater the deeper the narcosis. The observations just discussed render these facts at once self-evident. They follow as a simple and necessary result of the elimination of the oxydative processes. If these are suppressed further breaking down, if not influenced by addition of other factors, proceeds anoxydatively. The previously observed series of processes is developed, which invariably take place when oxygen deficiency occurs and which produce in the clearest form the results of asphyxiation on the withdrawal of oxygen supply. If, therefore, the disintegration processes are not influenced in some other manner during narcosis, they must then take place in the same way as in the withdrawal of the oxygen supply. The question, if this is actually the case, can be experimentally decided by comparing, on the one hand, the development of the course of asphyxiation during narcosis, and on the other, the withdrawal of the oxygen supply. We have carried out this comparison for the spinal cord centers as well as for the medullated nerve. A prolonged series of experiments have been made by Bondy211 with the apparatus constructed for this purpose by Baglioni.212 Two frogs under uniform conditions of temperature were submitted to artificial circulation, the one merely with an oxygen-free fluid, the other with the same, but with the addition of 5 per cent. of alcohol. In order to render the least trace of irritability perceptible, responsivity was increased in both animals by the employment of strychnine. It then appeared that, on the average, irritability was obliterated in the narcotized frog in about the same time as in the animal simply asphyxiated. These experiments were controlled by introducing at their conclusion a saline solution containing oxygen into both frogs and by ascertaining the degree of recovery. In like manner Fröhlich213 has established the same fact for the nerve. The period of asphyxiation for the nerve in a nitrogen-ether mixture is approximately the same as in pure nitrogen. Analogous experiments have been carried out in amœbæ by Ishikawa.214 Here also it has been shown that living substance becomes asphyxiated in narcosis and can finally recover only when oxygen is supplied. In more than a hundred experiments Ishikawa has, however, obtained the uniform result that amœbæ asphyxiate rather sooner in narcosis than in pure nitrogen. The most striking experiments are those which Heaton215 has carried out on the nerve. Using both sciatic nerves of the same frog, he passed each one through a separate glass chamber, as previously described, and laid the central stumps projecting from the chamber over a pair of platinum electrodes, while the stretch within was likewise placed on platinum electrodes. The muscles served as indicator of the capability of conduction and irritability. The alterations thereof were tested by the ascertainment of the threshold of stimulation. The nerve in the one chamber was then subjected to a pure nitrogen current, that in the other merely to one of pure air with ether. In order to test the degree of asphyxiation the air-ether current in the latter chamber was replaced from time to time by an ether-nitrogen current, and then by one of pure nitrogen, so that the narcosis was interrupted without the entrance of oxygen being possible in the mean time. During this suspension of the narcosis, the nerve recovered each time in nitrogen, its irritability again increasing and its capability of conduction returning with every test. However, recovery showed itself as less and less complete. Finally irritability had sunk so low that the capability of conduction disappeared entirely. At the end of the experiment as control, nitrogen was displaced by air in the two chambers and in both nerves recovery took place.

In both cases recovery could only be brought about by an introduction of oxygen. From the sum of all these experiments it results that during narcosis in air the nerve, even when a sufficiency of oxygen is present, gradually asphyxiates and loses its capability of conduction, and this in about the same length of time as the other nerve in pure nitrogen. These investigations furnish two important facts for the theory of narcosis. First, that in narcosis living substance becomes asphyxiated notwithstanding the presence of an ample oxygen supply, and secondly, that asphyxiation occurs in the same time, or somewhat more rapidly, in pure nitrogen under otherwise similar conditions than without narcosis. In other words, it is shown that the breaking down processes of metabolism continue in narcosis as anoxydative disintegration. In narcosis, therefore, asphyxiation takes place with approximately the same or a somewhat greater rapidity than that in an oxygen-free medium.

The fact here established explains in the simplest manner the often described observation that in the human being and in mammals during prolonged anæsthesia typical products of insufficient combustion, such as fatty acids, lactic acid and above all aceton, in not inconsiderable quantities are eliminated, as the case may be, by the urine or the respiratory air.216 If, as has been shown by the foregoing experiments, the processes of disintegration can continue to anoxydatively take place during narcosis, the problem arises, if this anoxydative breaking down can be further increased by excitating stimuli. This question has been answered likewise by means of experiments on the nerve made by Heaton.217 The two sciatic nerves of the same frog were drawn through a double glass chamber of the form previously described so that each nerve lay on an electrode and with the central stump protruding out of the chamber hanging likewise over an electrode. As in the former instances the muscle contraction of the shank again served as indicator. Both nerves were then subjected to the same current of nitrogen-ether. When, as a result of the narcosis, their irritability has sunk to the level of “stromschleifen” the central stump of the one nerve was continuously stimulated with faradic shocks during a prolonged period, while the other nerve remained at rest. Finally, by displacement of the current of nitrogen-ether with one of pure nitrogen, cessation of narcosis was brought about. It was then seen that the irritability of the continuously stimulated nerve showed a much greater decrease than that of the nonstimulated. The control made by introduction of air demonstrated that both nerves recovered in an oxygen supply. There can, therefore, be no doubt, by comparative experiments we find, that during narcosis anoxydative disintegration can be still further increased by the action of stimuli.

In view of this knowledge of the influence of narcotics on oxygen exchange it may be considered as a firmly established fact, that a process of depression is developed during narcosis, which can be classified with the large group of depressions, resulting from deficiency of oxygen. This is followed by the important problem, is it possible to attribute the whole series of alterations, produced by the narcotic, solely to this one factor? In other words, is narcosis the result of acute suppression of the oxydative processes?

If the individual symptoms which characterize narcosis are investigated from this point of view, one must indeed confess that they are all readily understood when regarded as the results of suppression of the oxydative processes. Indeed, the disappearance of the perceptible vital activities, the decrease of irritability, the restriction of the conduction of excitation, the continuance of an anoxydative breaking down, the recovery on cessation of narcosis, provided oxygen is present, etc., in short, all the characteristics of narcosis so far known must be expected and demanded if a suppression of the oxydative processes exists during narcosis.

There is only one point which at the first glance would not seem to agree entirely with the assumption. This is the fact that depression sets in with a relatively greater rapidity in narcosis than when the supply of oxygen is completely withdrawn. Depression of the centers in the spinal cord, which begins in about five to ten minutes after artificial circulation of an oxygen-free, alcohol-containing, saline solution, is not brought about for more than an hour when the same saline solution but without alcohol is introduced. This difference is still more strikingly apparent in the nerve. The same degree of depression, which is produced in the nerve in a nitrogen-ether mixture within about five minutes, is not reached in pure nitrogen without ether until after the lapse of from two to four hours. In order to investigate this relation somewhat more closely I have questioned if it is possible for a living system, which has been narcotized to a certain extent, to regain its irritability in a completely oxygen-free medium, if cessation of the narcosis takes place after a period essentially shorter than the time of asphyxiation of the system under equal conditions. If the depression of narcosis is founded exclusively on asphyxiation, it would be expected that no recovery could occur. Experiments which I have made on the spinal cord centers as well as on the peripheral nerves have, however, demonstrated exactly the contrary. If a frog is subjected to an artificial circulation of an oxygen-free saline solution containing 5 per cent. of alcohol until reaction is lost, being certain of this by the injection of a weak dose of strychnine, and if now a cessation of the narcosis is brought about by the transfusion of oxygen-free saline solution, the centers of the animal recover completely within ten to fifteen minutes, as shown by typical strychnine tetanus. If a nerve is placed in a gas chamber through which a mixture of nitrogen and ether is allowed to flow until irritability is greatly decreased, and is then displaced by pure nitrogen, irritability increases more or less completely according to the time which has passed from the beginning of asphyxiation. This investigation proves that living substance, even after the deepest narcotic depression, may recover on cessation of the narcosis, although in an entirely oxygen-free medium. Fröhlich, Bondy and Heaton, by the methods of their experiments above described, have proved this fact in a great number of instances. On the other hand, Ishikawa could not observe a pronounced recovery in amœbæ from narcosis in pure nitrogen. But it is possible that here the difference is perhaps merely quantitative.

What position should be taken in the face of these facts? Does recovery of a deeply narcotized tissue in an oxygen-free medium really make it difficult to suppose that narcosis is the result of an acute suppression of the processes of oxydation? On closer view, it will be found that this difficulty is merely apparent. In reality it is quite possible to bring these facts into harmony with the assumption that narcosis consists in a suppression of these processes. If one proceeds from the supposition that living substance possesses a certain, even though merely a small supply of oxygen in its interior, then it is at once evident that a more or less complete recovery of irritability from narcosis depression is possible, even in an oxygen-free medium. It can take place at the cost of the oxygen still present in the living substance and which during the narcosis, on account of the suppression of the oxydation processes, could not be consumed. If the presence of a certain oxygen reserve in living substance is entirely set aside and a different explanation sought for the primary continuance of irritability after a complete withdrawal of the oxygen supply from without, the great difference of time in the setting in of the depression in narcosis and that of the complete elimination of the oxygen supply from without would make it necessary to assume the processes occurring in narcosis are entirely different in nature. The explanation that narcosis is the result of suppression of the oxydative processes would indeed be out of the question in such a view.

The assumption, however, that in a living system at the same moment when oxygen is removed from the neighborhood, let us say by a stream of nitrogen, no oxygen would be present and that in consequence every oxydative process must cease, contains so little probability that I have rejected it on various occasions.218 The way in which irritability is lost in asphyxiation of the nerve likewise very clearly demonstrates the untenability of this view. The recent investigations of Lodholz219 have shown that decrease of irritability takes place after a sudden displacement of all oxygen from the surrounding medium uniformly and gradually in the form of a logarithmic curve. If at the moment of oxygen withdrawal from the outer medium, metabolism became entirely anoxydative, the curve of irritability must under all circumstances show a sudden steep decline at this point, and subsequent to this a further slower decrease. For, as the oxydative processes constitute by far the chief part in the energy production of living substance, the production of energy, and with this irritability, would undergo considerable loss at the same moment in which oxydative was replaced by anoxydative disintegration. The curve of decrease of irritability during the transition period from oxygen supply to oxygen withdrawal shows, on the contrary, a completely uniform course and it is not until later that a very slow decline takes place, which only after a prolonged time assumes increasing rapidity. But the assumption that at the moment when the supply of oxygen ceases, anoxydative breaking down could acquire such enormous dimensions that it furnishes just exactly the same amount of energy as was before supplied oxydatively, is a view which no one will seriously entertain. In connection with this I wish to call attention to the experiments of Fröhlich220 in which he compared the time required for asphyxiation to take place in the nerves, when, on the one hand, the frogs had been kept several days previous to the experiment in temperature of 14–40° C., and on the other, in one merely a few degrees above zero. He found that the nerves of the cooled frogs required on an average twice or three times as long for their irritability to sink to the same degree as those of the heated frog, although during the experiment the same temperature was present in both. It was also shown that the asphyxiation period was prolonged up to a certain limit, depending upon the length of time the animals were kept at a low temperature. It would seem to me that these facts admit of no other explanation than that in a low temperature a greater amount of oxygen is stored in the nerve than in high temperatures. From the standpoint that from the moment of withdrawal of oxygen from without, disintegration likewise takes place exclusively anoxydatively, these facts would be completely incomprehensible. When, however, the assumption is made, and this would appear to me as inevitable, that living substance contains in itself a certain even though a very slight quantity of oxygen, which in low temperature is greater, in a high temperature less, the recovery from narcosis, when oxygen is withheld, is not at all surprising. The comparatively rapid setting in of depression in narcosis finds a simple explanation in the violent manner in which the oxydative breaking down, notwithstanding the presence of oxygen, is suddenly suppressed by the flooding by the narcotic. Finally, this view receives unlooked-for support by a group of facts which at the first glance would appear to bear no relation whatever to the process of narcosis.

In a series of investigations on the mechanism of movement in naked protoplasm,221 I have pointed out the rôle played by oxygen in the genesis of the amœboid protoplasm movement. We can distinguish two antagonistic phases in the movement of amœboid cells, the expansion phase and the contraction phase. The first consists in an increase, the latter in a diminution of the surface, the mass remaining the same. The expansion phase is manifested in the stretching out of the pseudopods by a centrifugal outflowing of the protoplasm into the surrounding medium, the contraction phase by the indrawing of the pseudopods by the centripetal inflowing of the protoplasm to the cell body. In total contraction, such as occurs, for instance, in strong excitation following stimuli, the cell body becomes ball shaped. In local contraction of the long thread or net-shaped outstretched pseudopods of the sea rhizopoda, the protoplasm of the retracting pseudopod forms balls and spindles. Considered from a physical point of view the expansion phase of amœboid movement is an expression of decrease, the contraction phase an increase of the surface tension. I have shown that the factor which under physiological conditions decreases the surface pressure and thereby brings about the expansion phase is the introduction of oxygen into the living substance. With removal of oxygen the stretching out of the pseudopods ceases. The cell gradually draws in all pseudopods and assumes the shape of a ball. On the reintroduction of oxygen the outflow of the pseudopods begins anew. This fact can be observed in all amœboid cells. When, therefore, consumption of oxygen and oxydative changes is suppressed during narcosis it is to be expected that all naked protoplasm masses by being narcotized lose their capability of assuming the expansion phase of movement and contract into the shape of balls. Experimentation confirms this deduction in the most striking manner. When amœbæ are placed in a drop of water under the microscope in a gas cell through which air and a little ether are allowed to flow, the pseudopod formation of the amœbæ ceases within a few minutes and they all assume the shape of a ball. (Figure 62.) In asphyxiation in pure nitrogen, the changes in the amœbæ take place in exactly the same manner with the exception that in this case a longer period ensues according to the size and activity of the animals. About 20 to 60 minutes elapse before depression becomes complete. If larger sea rhizopoda are narcotized in the same manner all pseudopods are more or less retracted and the contained protoplasm flows centripetally and contracts in the characteristic manner into balls and spindles. (Figure 63.) If the narcosis is removed by displacing the ether by pure air, the stretching out of the pseudopods then begins anew, provided the narcosis has not been too deep or too prolonged.