Page:Popular Science Monthly Volume 1.djvu/362

350 was chloroformed; the left side, which was more drawn up, where the muscles experienced a tonic contraction predominating over those of the right side, became then more feeble. This effect became more and more pronounced in proportion as the chloroform took effect, up to the time when the two sides were completely affected; then the frog would no longer rest on his fore-feet, and the hind-feet remained extended and motionless. In proportion as the anæsthesia disappeared, the feet of the healthy side folded themselves and approached the body; those of the opposite side remained still extended. Then these folded themselves similarly. The attitude of the two sides was then identical, but, when the normal state was recovered, the limbs on the side affected by the cerebral lesion again became more drawn up, and the body leaned on that side.

In this frog we have again on one side the influence of the cerebral lobes, but, on the other side, the locomotive centres are completely independent, and they act alone on the movements which take place on the corresponding side of the body. What happens, then, when the animal attempts to move? From the healthy side the movements are made according to the desire and the will, they are limited to the end wished by the animal; but, on the other side, they are made en masse, automatically, invariably; they drag the animal from their side; at the same time, the mathematical regularity of their contractions becomes, so to say, a dynamic centre for the movements of the opposite side, which are less regular. In this way we explain the movement in a circle, the side in relation with the wounded part being in the interior of the circle made by the animal. This also is the reason why such movements, particularly when the circumference is small, occur only when the animal can change his place, and very often commence only after the first moments of locomotion.

In case the cerebral influence is abolished, the locomotive centres become absolutely independent, as is shown by the forced automatic movements. Again these centres may be excited by a tumor, or a prick, and then their dependence upon the cerebral lobes ceases at once, notwithstanding the anatomical communications which still exist. It is in these cases that the compulsion, from the instant of the lesion, becomes invincible, and forces the animal into movement. The locomotive centres become active, and, as long as the excitement lasts, the animal is completely under their influence. Neither the will, nor emotion, nor physical obstacles, can prevent the limbs from moving.

A hunter gave us the following account: From a considerable distance he had shot at some wild-ducks that were on the water; one of these ducks was not able to fly, and remained on the water, turning in a circle. This duck had received a superficial wound from a grain of lead in the side of its head; it had absolutely no other wound on its body. Now, the curious fact, and what astonished the hunter, was, that this duck could not fly, and yet neither the will nor the means