J. Gordon Wilson

The effects of stimulation of the labyrinth of the ear in the living animal. (With demonstration.)

It may be shown that if one sits in a moving railway train and observes objects out of the window, they may seem to be moving in a direction opposite to that of the train. If one notices the movements of ones eyes in observing these objects, it will be seen that the eyes move slowly backward, opposite to the direction in which the train is going, and more quickly return to the median position, the quick movement of the eye being in the same direction as the movement of the train. We may express this relation between eye-movements and apparent movement of external objects or real passive movement of the ones own body by the statement that the apparent movement of external objects is in the direction of the slow deviation of the eyes, and the real passive movement of ones body is in the direction of the quick movement of the eyes. The otic labyrinth is not involved in these reactions. We may extend this relationship still further and say that under whatever conditions of this kind, with one possible exception, 1 one may be placed the movement, either real or apparent, of external objects is in the direction of the slow deviation of the eyes, and passive movement, either real or apparent, of ones own body is in the direction of the quick movement of the eyes. While many of the facts have long been known, we have not seen any general expression of the relationships in terms of the slow and quick eye movements. Stimulation of the otic labyrinth in a number of different ways, including rotation about a particular axis of the head, evokes movements of the eyes, and sensations of apparent movement of external objects or of ones own body, or both.

A demonstration of the effects of some lesions of the nervous system

The effects of the lesions were shown in cinematograph films of three different animals. A rabbit which was brought into the laboratory some months ago presented constant marked torsion of the head to the left. There was no nystagmus, but merely a constant deviation of the eyes. The animal could move about on rough surfaces if it went slowly and carefully, or if its left side was supported by the side of the cage. If put on a smooth surface with the left side unsupported, any attempt on the part of the animal to move was followed by rolling movements to the left, about the long axis of the body. If no obstacle was placed in its way, the animal might roll for several yards before regaining its upright position. The animal was said to be about eight months old at the time it was brought into the laboratory, and to have been in the same condition from birth. The only gross changes visible at autopsy were in the left otic labyrinth. The nature of these changes was not determined by inspection. The histological report will be presented later. One interesting point in the deportment of the rabbit was its lack of compensation for the loss of the labyrinth, as compared with the deportment of cats or dogs after loss of one labyrinth. Two cats were subjected to experimental ablation of the vermis and left lateral lobe of the cerebellum. The eye movements were different from those following labyrinthine lesions. One marked motor defect was the trembling and uncertainty of movement of the head when attempting to take food. Two different stages in recovery from the effects of the cerebellar lesion were shown, in one of the cats, with the gradual amelioration of the symptoms in the second stage taken at an interval of about one month after the first.

A comparison of the effects of labyrinthine and cerebellar lesions in the turtle

It is of some interest, in view of the tendency in some quarters to insist upon the essential similarity of the effects of lesions of the labyrinth and of the cerebellum, to ascertain whether this supposed constancy of relationship obtains in animals with a relatively small cerebellum. It may be mentioned that, anatomically, the floor of the mid brain (the pons) and that portion of the roof represented by the vermis cerebelli are phylogenetically old. The lateral lobes of the cerebellum are new developments. The cerebellum of turtles is represented by the vermis. The cerebellum in the genera of turtles used for experiment—–Nanemys and Chrysemys—–is smaller than in the sea turtles. We have already pointed out the fact that there is a great uniformity in the effects of labyrinthine lesions in all animals so far studied 1 and that the effects in the turtle are much the same as in other animals. 2 Ablation of the cerebellum in the turtle does not give rise to the same train of symptoms that is observed after labyrinthine extirpation. We find, in agreement with Fano, 3 that the righting reaction is not abolished by ablation of the cerebellum. There was a small, scarcely noticeable, disturbance of coördination in swimming, manifested most clearly in a slight awkardness in approaching the side of the tank. Occasionally, lack of precision of limb movements on the injured side was observed after unilateral operations. One other symptom was that the animal was rarely or never seen to swim deep in the water after cerebellar removal. Our observations substantiate those of Fano, Bickel 4 and Sergi, 5 whose experiments were done on different genera of turtles. The results on turtles are in substantial agreement also with those of Steiner, 6 Loeb, 7 Bethe 8 and Corso, 9 who report no noticeable motor disturbances in sharks (Scyllium) after cerebellar ablation.

The function of the otic labyrinth in turtles

The peculiar method of progression in serpents 1 and the widely different modes of progression in lizards, snakes and turtles 2 have attracted attention to the relation of the semi-circular canals to the processes of progression and maintenance of equilibrium in these forms. The general results of labyrinthine extirpation in all these forms are similar to the results observed in other vertebrate types. There is, in the turtle, torsion of the head to the injured side, permanent deviation of the eyes and a tendency to crawl or swim toward the injured side, when the lesion is unilateral. The body on the uninjured side may be raised higher than on the injured side. After bilateral operation, there are coarse wide tremors of the head which seriously interfere with grasping food. The gait on land is not markedly affected permanently, and there is no permanent torsion of the head to either side. The head may, however, be displaced directly upward and backwards in the first few days following extirpation. Swimming is a matter of great difficulty. When the turtle moves slowly, progress is fairly good, but agitation or hurry upset coördination and extreme disorientation results. The animals reactions are not biologically adequate (Edinger). It may be shown in turtles and snakes particularly that the otic labyrinth is a great proprioceptive organ for the head segment (Sherrington). The rô1e of the labyrinth in the maintenance of equilibrium rests primarily upon its relation to the head, and only secondarily upon its relation to the body. It may be shown that under certain conditions, the head is the only part affected.

A note on the relation of the semi-circular canals of the ear to the motor system

The work on the semi-circular canals was undertaken with the object of studying: (1) The results of stimulation of the end organ of the vestibular nerve; (2) the immediate and remote results of destruction of the labyrinth or of the eighth nerve on one or both sides; (3) the effect of removal of various parts of the brain on phenomena which have been observed to follow stimulation or destruction of the labyrinth, and (4) the paths of nervous connection between the labyrinth and the eye muscles — the optico-acoustic path. Later it is the intention to study anatomically the degenerative processes occurring in various parts of the central nervous system after destruction of the labyrinth or eighth nerve. Method.—The mastoid bone is exposed by a skin incision and the separation of the muscles from their attachment at the linea nuchæ superioris and the anterior inferior border of the pars mastoidea. A trephine opening is made through the outer table and diploe of the mastoid bone. The hard portion of the otic bone, in which the semi-circular canals are imbedded, can be removed with a mastoid gouge and the labyrinth destroyed without direct anatomical injury to the cochlea. Dogs, cats and tortoises were used. The results here given apply to dogs, unless otherwise stated. Results.-Immediately following recovery from the anesthetic after removal of one labyrinth, there is marked torsion, particularly of the anterior part of the body, of the animal toward the injured side. The animal is unable to walk and falls over toward the injured side on attempting to stand. It may roll completely over on the floor. There is a quick movement of the eyes toward the sound side and a slow return to the injured side.