THE SEMI-CIRCULAR CANALS OF THE EAR,
By Mr. FLOURENS
Being read to the royal Academy of the Sciences, on October 13, 1828.
1.In my previous Report, I made known the singular effects which follow the section of the semi-circular canals of the ear, among birds. It was important to see up to which extent these effects are reproduced or modified in the other classes, and especially among mammals.
2. But, in mammals, semi-circular canals are so wrapped by the hard and compact substance of the pars petrosa that to reach them, it is absolutely necessary to begin by freeing and loosing them of this substance.
3. Now, that is the first operation which, on living animal, cannot be made without a great difficulty; difficulty which would be insuperable maybe if there were not any species where the pars petrosa is much less thick and less dense than it is generally, and, besides, if one could not even in these species, go back up to an age where it did not yet acquire all the hardness and the consistency which it should have later.
4. According to these two points, age and species, young rabbits appeared to me the most appropriate animals for my new experiments: at first, in rabbits as in all rodents, the pars petrosa remains much less thick and less dense than in most of the other families of mammals at any age; and, secondly, rabbits, as all the rodents, begin to walk, to run, to jump, to stand plumb, finally to move with a certain energy, at a still very young age, and consistently before the ossification of the pars petrosa is complete. So, in these animals, there is a moment when the ossification of the pars petrosa is not too much advanced, and where the movements are nevertheless rather energetic; and it is this moment which must be chosen for the experiment being made.
5. In the carnivorous animals, on the contrary, as in the cat, the dog, for example; the locomotion develops too late, on one hand; on the other hand, ossification of the pars petrosa advances too fast: from which it follows that, when the pars petrosa would be soft enough for the experiment, the movements of the animal are too weak, and that, when the movements would be rather strong, the pars petrosa is no longer soft enough.
6. For rabbits, the age I found the most favourable for the experiment being made is that, about, from one and a half month to two months; it is on rabbits about this age that the experiments were made.
1. On an rabbit, about two months old, I began with loosening and getting visible the horizontal canal on each side; after, I cut the horizontal canal of the left-hand side.
At once, the animal was taken by a movement of the head from left to right and from right to left; this movement, as in the pigeons first operated, stopped during the rest; It began again as soon as the animal moved; it became always all the more hard as the animal tried to move faster; maybe it had not as much speed as in pigeons, but it had more constancy. One remembers that, in pigeons, the movement of the head which follows the section of the horizontal canal of a single side lasts only one moment; in the rabbit, on the contrary, several hours after the operation, this movement, although weakened, persisted still.
Besides, I notice that at the time of the section of the canal, the anima1 gave signs of pains; remark which applies to all the experiments which follow.
The movement of the head always came along with a very lively excitement of eyes and eyelids; but as soon as the head was at rest, eyes and eyelids did the same.
In the state of rest, the head was almost always worn on the left-hand side, rarely in its natural position, ever on the right. Finally, the animal often turned on itself and always on its left-hand side.
2. I cut the horizontal canal on the other side: immediately the horizontal movement became more violent; sometimes it was so violent that it took, from right to left and from left to right not only the head, but also the forelimbs and, with them, the forequarters of the animal.
This movement disturbed and disorganised all other movements, especially all the fast one; so, when the animal wanted to run, it fell and rolled on the ground.
At rest, head movement stopped; but as soon as the animal, or only its head, moved, head movement began again and always with all the more force as the movement about which it began again was faster.
Constantly head horizontal oscillations, having suddenly, on the occasion of some excitement, acquired a certain magnitude and a certain speed, decreased progressively then, in speed as in magnitude, then, did not constitute more than a light shiver, and then eventually disappeared.
The eyes globes and the eyelids, as in the previous case of the only left-hand side canal cut, were in a perpetual excitement as long as the head moved; this excitement was all the more lively as the head moved faster; and when the head stopped moving, the excitement of eyes and eyelids stopped also.
But what is to be noticed, it is that the head which, after the section of the only left-hand side canal, was almost always turned to the left, had, since the section of the second canal, resumed its natural position on the median line; and that the animal which, in the first case, always turned of its left-hand side, turned now sometimes on one side and sometimes on the other one.
I kept this rabbit; it was able to ate by itself, and, as weak it was because of its young age, nevertheless it survived for more than a month. The sway of its head and the rotation of the animal around itself, sometimes on one side, sometimes the other one, always remained; but the sway of the head became less lively, and as a consequence all other movements of the animal less disturbed and less muddled.
3. On a rabbit of the same age as the precedent, having freed also the horizontal canals from the substance of the pars petrosa, which surrounds them, I cut at first the horizontal canal of the right-hand side.
The movement of the head, and all the effects of this movement on the other movements of the body, reappeared immediately, as in the previous rabbit, but with this difference that, this time, the head was almost always turned to the right, and it was always on its right-hand side that the animal turned.
4. I cut the horizontal canal of the left-hand side: immediately the head resumed its position on the median line, and the animal turned sometimes on one side, sometimes on the other one.
5. Both posterior vertical canals having been exposed on a third rabbit, I cut the canal of the left-hand side. These canals are the same as inferior or external canals of birds; but, in mammals, they do not any more cross the horizontal canals.
The section was just operated that began a movement of the head from bottom to top and from top to bottom. This movement stops at the rest; the slightest movement renewed it, and it always increases especially since the other movements are faster.
In their bigger violence, the oscillations of the head are very vast; these oscillations weaken then progressively: a moment before stopping there is not more than a light shiver exactly the same which is observed among some old mans.
Sometimes the head, in its movement from bottom to top and from top to bottom, makes like a right or left about-turn: very often also the movement from bottom to top takes all the body of the animal behind and almost brings it down on its back.
This beginning of behind tumble, joined to the movement of the head of which it is only a stronger degree, disturbs standing upright, walking, and especially running.
Eyes and eyelids are in an excitement, which lasts as long as the movement of the head lasts; and which, as in the previous cases, stops as soon as this movement stops.
Furthermore, this movement of the head, movement that faints almost immediately in pigeons, in case of a single canal cut, persisted still several hours after the operation in this rabbit.
6. I cut the right posterior vertical canal: immediately the vertical movement of the head became more violent; the movements of behind tumble more frequent and stronger, and as a consequence all other movements of the animal, walking, running, jumping, were more disturbed and more muddled.
Finally, as usually, the movement of the head stops at the rest, and is reborn by a movement: it's the same for the rotation of the eyes globe; it is reborn by the movement of the head and disappears with it.
This rabbit, although still very young and consistently very weak, especially for such experiment, nevertheless survived during seven/eight days. It ate by itself; and, as long as it was alive, the movement of its head remained.
7. It remained to tempt the section of the third and last canal, or the anterior vertical canal (it is the superior or internal in birds). But in rabbits, animal well fitted to my experiments, the cerebellum presents, on the side of each hemispherium, a small lobus, which passes under this canal. The area where this small lobus adheres to the hemispherium narrows in a pedicle that the canal surrounds as a ring: out of this ring the 1obus of the cerebellum blooms and develops, so that the canal is hidden in a profound furrow between the blooming of the lobus and the hemispherium. It was completely impossible for me, any precautions that I took, to cut this canal without hurting this lobus, more or less, and without complicating the effects, more or less.
8. Fortunately in fact what mattered was to see if the singular phenomenon which follows the section of semi-circular canals in birds, reproduced in mammals, that is to say if, at first, the section of a some canal was followed by some movement; and if, then, the direction of the cut canal always determined the direction of the produced movement.
9. Now, as for the first point, it had been enough to reach only one of the three canals; and, as for the second, it was enough to be able to reach the horizontal canal and a vertical canal, whatever it was, because it was from the main opposition between the direction of these two canals that the main contrast of the phenomena should be born.
10. Nevertheless, I wanted to see if, on rabbits of an age less advanced than those I had operated up to now, finally I could not manage to reach the anterior vertical canal remotely. Indeed, as one goes back up towards the time of the birth, the cerebellum and the lobus of the cerebellum, less developed, exceed less and less the canal, and so oppose fewer and fewer to reaching the canal.
11. After several attempts, I succeeded, on rabbits about twelve or fifteen days old, in cutting sometimes the anterior vertical canal without hurting the cerebellum; but even at this age, most of the time, I was not able to cut this canal without hurting the cerebellum, more or less.
12. In cases of this complication, the effects of hurting the cerebellum masked more or less the specific effects of canal lesion; I was able to obtain only a vague result.
On the contrary, when the section of the canal was simple, and loosened of any complication of hurting the cerebellum, I saw constantly, the movement of the head from top to bottom and from bottom to top, and the trend to tumble forward which accompany the section of this canal in birds.
13. Besides, in rabbits, to the vertical movement of the head, which is the only one observed in birds, was joined an horizontal movement of this part, sometimes, and sometimes also the animal turned on itself.
I repeated these experiments, either on the horizontal canal, or on the posterior vertical canal, or on the anterior vertical canal, on several rabbits: the result was always the same. So:
1 ° In rabbits, as in the pigeons, the section of the horizontal canals is followed by a horizontal movement; and the section of the vertical canals, by a vertical movement of the head.
Furthermore, the section of the horizontal canal is followed by a whirling of the animal on itself; that of the posterior vertical canal, by a behind tumbling; and that of the anterior vertical canal, by a forward tumbling.
2 ° All these movements, either sway of the head, or whirling, or tumbling, are less violent in rabbits than in pigeons.
That is to say the swaying of the head is less vigorous: the animal turns on itself with less speed: it begins tumbling, but the tumbling is not complete; and, evidently, there is no series of continuous tumbling, as in pigeons.
3 ° In rabbits as in pigeons, the movement of the head stops at rest; it is reborn by movement, and it always increases all the faster are the other movements.
4 ° The movements brought about by the section of semi-circular canals are always the same for the same canals, always different for different canals, in rabbits, as in pigeons; and doubtless it deserves being noted that there are exactly so many different directions for these movements that there are many cardinal directions of any movement: backwards, forwards, from top to bottom and from bottom to top; from right to left and from left to right.
5 ° The movement of the head (and all the effects of this movement) which follows the section of a vertical or horizontal canal, appeared to me to have more constancy in rabbits than in pigeons.
6 ° Finally, the movement of the head, after the cutting of both canals, vertical or horizontal, always persists in rabbits as in pigeons, although less energetically in the first ones than in the second; and in any of them, although it persists, it does not prevent the animal from living and from keeping all its senses and all its intelligence.
2. The singular movements brought about by the cutting of semi-circular canals are the same in mammals, as in birds. These movements constitute a phenomenon which till now appears as general as surprising.
3.The only thing we have to do is to look at the semi-circular canals of reptiles and fishes, especially the cartilaginous ones, where these canals are so developed, and where moreover the tenderness of the cartilage should set fewer difficulties to the experiment.
4. The research I am now being engaged on these two classes will be the subject of a new report.
( Thanks to Madam Florence GREFFE, librarian of the Academy of the Sciences, for her collaboration to the publication of this text on Web)