CHAPTER VI

Experiments on Frogs

IT is probably best to begin with the facts and give their interpretation afterwards. It seems advisable to give the reader a clear and full account of my work as a whole, to avoid being entangled in a mesh of unnecessary details. While I experimented on a great number of frogs I present here but a few typical experiments. The reader will thus be in a far better position to get a fair view of the work and be more enabled to judge critically the conclusions drawn from the experiments.

            When the frog is put on its back, its lower lid (its only eyelid) is drawn up. If kept in the same position for a few minutes, the frog ceases to struggle and becomes quiet. The lower lid is kept shut, but when the lid is drawn down the frog becomes lively. If the frog is put on its back and stroked gently, the eyes close, the lower lid being pulled up. The frog becomes very quiet, but soon becomes again lively.

            The frog was kept on its back for a few minutes; it was held down and its voluntary movements were restricted; it soon became cataleptic. There was a change in the respiration as shown by pneumographic tracings.

            A cloth was wrapped round the frog’s head. The frog remained very quiet apparently in a very deep “sleep.” The eyelids were found drawn up. The same experiments were repeated on other frogs, small and large, and the same results were obtained.

            When a cloth is put on the eyes of the frog so as to exclude all light, the frog sinks into a state of rest. It is cataleptic and can then be put in any unnatural position; it does not make any attempt to change its position. The frog reacts but feebly to sensory stimuli; the eyelids are found to be drawn up.

            The experiments were then somewhat modified, the eyelids of the frog were held together with collodion painted over them. At first the frog struggled, and was very restless, but soon it became very quiet, apparently sunk into deep “sleep.”

            The more often the frog is put in that apparent “sleep” or rest-state the easier it is afterwards to induce the same condition.

            A big lively frog was blinded. It was easily put in any position, though it would not have retained such awkward postures in its normal healthy state, before it was deprived of sight. It may be well to add that the experiments were performed after the frog recovered from the shock of the operation. The blinded frog could be manipulated far more easily than any other specimen of its kind. It could be placed in any awkward position and would remain so indefinitely until disturbed. No frog with its eyesight unimpaired would have remained for a moment in such awkward uncomfortable positions. The frog, for instance, was hung up by its front limbs on a board, it remained in the same position until disturbed. The frog was put over the edge of a jar where it hung with the front limbs, the body and hind legs relaxed in the jar. It remained in this uncomfortable position until disturbed.

            The blinded frog was left in the jar for a few days and then the same experiments were repeated with the same results. The frog was turned on its back, it remained in the same position, as if frozen and turned to stone. The flame of a match was applied to him and he responded to the pain stimuli very sluggishly, but did not turn over. The respiratory and swallowing movements were reduced from 60 to 48 per minute. If left undisturbed, he would remain in the same position indefinitely.

            The frog was put in a jar; he tried to jump out of it,—body and forelimbs were outside the jar, but the hind legs remained in the jar dangling. He remained in this position without any change. It seemed as if he fell “asleep” and “forgot” about the jumping out; it reminded one of the story of the sleeping kingdom.

            To control the experiments on the blinded frog I took a healthy frog which was not operated and closed its eyes firmly. It was put in a very awkward position. It remained hanging over the board without any movement for a period of 5 minutes Respirations became very slow. In this position I could carry it round the laboratory without disturbing it in the least. After 5 minutes it opened its eyes slowly and changed its position.

            The blinded frog was put in an upward sitting posture. Its back was supported by a board so that it should not tumble over. In this attitude it remained without change for a long time.

            A healthy, not blinded frog, was then taken and after having closed its eyes firmly with my fingers for a period of a few minutes it was put in a sitting posture similar to the one given to the blinded frog. The healthy frog remained, as if stiffened in the same position. Respiration fell to 48 per minute. During the whole period of the experiment the respiration and heart beats were greatly reduced. Response to sensory stimuli was very sluggish; the limbs were in a state of relaxation.

            After a few weeks the blind frog was still alive and kicking. It kept very quiet and could easily be put into a cataleptic state.

            The blind frog remained in the same position, when left to itself. It remained in any posture given to it. When put over the edge of the jar, it remained in the same position without changing a single muscle. During this time it reacted very sluggishly to external stimulations. Respiration and heart beats were very much retarded.

            Similar experiments were carried out by me on a number of frogs with the same results.  In some cases interesting effects of inhibition could be observed. Thus in one of the actively respiring frogs with pronounced swallowing movements the latter ceased, when the muscles of the hind legs were seized and sharply and violently pressed or pinched.

            Frogs were placed on their backs and then a heavy weight was put on them to hold them for a few minutes in the same position. The frogs soon fell into a cataleptic state and remained in that state even when the pressure was removed. The lower eyelids were found drawn up, the eyes were partly closed. Some of the frogs when released from the pressure, relaxed their extremities and remained in a quiet state.

            Similar experiments I carried out on a number of frogs; the results were of the same character. It is interesting to observe that when the frogs open the eyes and turn to their usual position they remain for some time very quiet.

            There is one point to which I want to draw special attention and that is the significant fact that when the frogs are put in the cataleptic condition, and are from time to time restrained from righting themselves to their normal position, they finally fall into a very quiet state,—the limbs are relaxed and remain in a relaxed condition, the respiration and heart beat are greatly reduced and there is little response to external stimulations to which, though of slight intensity, they would have responded in their normal “waking” state by jumping away. In this respect I can fully confirm Huebel who pointed out this fact in his excellent work on the frog.

            When I carried out the above experiments on the frog, I was unacquainted with Huebel’s remarkable work. I was glad on reading that observer's experiments to find that the work done by me did not stand by itself, but that I had struck a path which had been trodden by a previous explorer having a similar goal in view. Now when I began my experiments on frogs I hesitated to speak of “sleep” in frogs. When however I continued my experiments, I could not help coming to the conclusion that there are such states as sleep in frogs and that those states can be induced under conditions very similar to those we had found in human beings. Still I greatly hesitated to term the states induced in frogs “sleep;” I termed them "rest-states." I had however a lurking suspicion that they might really be of the nature of sleep-states found in human subjects. I was therefore glad to find that Huebel had fearlessly and unhesitatingly described those rest-states by the term we describe similar states in human beings,—namely, sleep. I then took courage and walked with less hesitation and with more confidence on a path that had been unfortunately left untrodden and neglected by the foot of the scientific explorer.

            I must, however, add that I am not quite so sure as Huebel is that the “rest-states,” induced in the frog and described in my experiments, are sleep-states, but I do think that they are closely analogous to what we regard as sleep-states in the higher animals.

            Without knowing of Huebel’s work I came pretty nearly to the same results. I observed as Huebel had before me that frogs after they had been put in the characteristic cataleptic condition described by investigators, such as Czermak, Preyer, Danilewsky and others, that the frog passed into a quiet state, the limbs, though keeping apparently the same position, really not being any longer cataleptic, but rather relaxed, that the respiration and heart beats were greatly lowered and that if the frog could be left in this state without any disturbance, it would remain in that quiet condition for a very long time.

            I did not observe as Huebel did that the frogs put in such states remained in it for over five hours, but I did observe that if the environment and external stimulations could be kept quiet, the frogs would remain in their passive states for a very long time. Unfortunately, the place where I worked was rather noisy; in fact unusually so, for the successful carrying out of such delicate experiments. I should not wonder then that I could not fully get all the results that Heubel got who was working under more favorable conditions. I am not quite ready to claim that the passive states in which the frogs fall are really sleep-states, a claim defended very strongly by Heubel, but I do favor Heubel’s statement and think that the states of the frog, after the cataleptic state has passed, is very much like what is usually regarded in the higher animals as sleep.

            Now if we scrutinize more closely the series of experiments carried out on the frogs, we find present the conditions of monotony and of limitation of voluntary movements as well as of limitation of what may be regarded in the frog as consciousness, or of the limitation of the activity of the sensorium by cutting off the regularly incoming sensory stimulations. As a result we find something analogous to what we should have expected in the human subject under like conditions, namely, the presence of peculiar passive states,—that is all that we are thus far justified to say of them, observed and described as they are by experimenters who do not have the possibility of getting the subjective experience of the animal under observation.

            What we find in the state of the frog is a condition somewhat analogous to what we have found in our experiments in human subjects, namely the presence of intermediary states of the subwaking or hypnoidal type. The symptoms observed differ somewhat, but in general they may be [regarded] as alike. We find a passive state with cataleptic manifestations. The state varies from catalepsy to relaxation or what may be regarded as lethargy, and again from passivity to activity, from sluggish to very lively reactions in response to external stimulations. We have therefore here, manifestations which remind one of like manifestations, in the human subject, namely subwaking, hypnoidal states which are on the borderland of waking, hypnosis and sleep. Of course, we should not expect to find that frogs which stand so low in the scale of vertebrates would manifest phenomena of the same character as the higher vertebrates, but we should expect that some similar phenomena, though otherwise widely different, would be present. This is precisely what we find in the frog. We find the general characteristics, though rather vague, of what is afterwards fully developed in man as the subwaking, hypnoidal state.

            We must remember besides that the hypnoidal state is very unstable and its manifestations, having the characteristics of waking-state, sleep and hypnosis, greatly vary in different individuals and at different times in the same individual. We should therefore expect that the hypnoidal state would show still more radical differences from the typical in the various species of animals, especially in those that stand so far apart from each other as frog and man. What is surprising to me is not the fact of the variation and great difference of the hypnoidal state in the frog as contrasted with man, but that the difference is really not far greater, considering the gap that exists between the two organisms. In fact, the similarity is far more striking than is the difference between the hypnoidal states of the two contrasted organizations so widely apart in the scale of evolution.

            My view then is that the phenomena observed in the frog are hypnoidal in character. The phenomena themselves as well as the conditions under which they are induced warrant my view of the hypnoidal nature of the states.

            In this respect we can well understand the apparent disagreement of the early observers on the subject. Czermak and Danilewsky regard the phenomena as being of the hypnotic order, Heubel regards them as being more of sleep-states, while Preyer views them as being the results of fright which give in the waking-state cataleptic manifestations closely similar to those observed in hypnosis. Verworn who regards the phenomena as “Lagecorrectionen” due to central inhibitions really does not conflict with any of the views. It is simply a general physiological hypothesis which may be in accord with any view, a physiological hypothesis which may or may not be true; it is a hypothesis far removed from the special facts and should be tested on its own merits. My point of view is not a matter of hypothesis, but describes and explains the phenomena in terms of states having similar manifestations and produced under the same conditions, states which are more developed and stand out more pronounced in higher animals. These states possess many of the characteristics of the waking state, sleep and hypnosis. Hence the reason why the early observers regarded the phenomena as waking states, as Preyer did; others regarded them as hypnosis, a view maintained by Czermak, Heidenhein, Danilewsky; while other investigators regarded the phenomena as sleep-states. As a matter of fact the phenomena and the conditions under which they are induced make the view highly probable that the different investigators are not far away from the truth, but not being acquainted with the peculiar hypnoidal states described, they observed the phenomena in too one sided terms, in terms of sleep, or hypnosis, or of waking-states. In reality the phenomena and the conditions under which they are induced point strongly to the fact that the states are hypnoidal in character, states which partake at once of all the three apparently contradictory manifestations,—waking, sleep and hypnosis. Now the manifestations of the waking-state, and now the symptoms of sleep, and now again of hypnosis predominate. In short, the state induced in the frog under the conditions of monotony, limitation and inhibition is a variety of the subwaking, hypnoidal states. This induced hypnoidal state being intermediary in character may either partake of the catalepsy of hypnosis strongly modified and manifesting itself differently in the frog than in the human subject, or may again go over into the passive state of “sleep” or some state analogous to it.

            It is perhaps of importance to call attention to the significant fact that the first stages induced in the frog ate rather of an unstable character,—the frog when put on its back and kept down for but a short time falls into an apparently cataleptic state of short duration. The animal soon rights itself and is fully awake as before. This instability is very characteristic. Now the hypnoidal states are just characterized by this fundamental trait of instability. It is only when the condition of monotony, limitations of voluntary movements and inhibition are sufficiently prolonged that the catalepsy becomes more or less fixed for some period of time, and when this passes off, and the conditions, under which the frog is kept are continued still further, it is only then that the frog sinks into a passive state which may last indefinitely, unless brought out of it by some strong, stimulation. It seems to me then, that if we take all this into consideration, we cannot possibly describe the state in which the frog is put in other terms than what we have on other occasions discovered to be the intermediary, subwaking, hypnoidal state.

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