Page:Popular Science Monthly Volume 1.djvu/364

352 were lacking, nor could it even plunge, which wild-ducks usually do when wounded, if they cannot fly. Notwithstanding the approach of the dog, and the evident very energetic action which its brain sought to exert at this moment on its movements, it could only swim on the surface of the water with a forced movement of rotation.

When the lesion is made on the two sides, some of the same phenomena are seen; only, as the stimulus to activity on both sides is the same, the animal moves in a right line. We have injected mercury in an opening made with a trepan into the upper part of the cranium of a young cat. In a little while, the mercury, by its weight, having reached the base of the brain, the animal lifted himself up, and plunged forward against the wall, making vain efforts to go straight on; deviating to one side, he continued his course till he encountered a new obstacle, and so on. He stopped only when exhausted, and yet until his death from compression of the bulb, his limbs moved without interruption.

In a man who had all the symptoms of a cranial tumor, we have observed phenomena almost identical with these presented by this young cat. When he had a crisis, he would raise his haggard eyes, and walk straight in his chamber, being guided only by the reflex action of locomotion and by habit. After his crises, he could not remember having walked.

It is evident that, in these cases, it cannot be a question of paralysis, and that the phenomena are the result of excitation of the locomotive centres. If the influence of the cerebrum, on one side, is obliterated, and the locomotive centres are not irritated, they act only when they are solicited to activity by. movements impressed by the opposite side, and then these movements are forced and automatic, but regular and without exaggeration. The result is, a movement in a circle, which occurs when the animal can change his place. If, on the contrary, the centres are directly excited, the impulse is forced, and the animal is obliged to move in the way impressed by the centres.

Better to comprehend the rolling movements, we must explain some facts which have not been dwelt upon, and which we observe in animals in repose. In lesions of the cranial centres, when we wound the pons Varolii, the animal has no longer the same exterior carriage; he leans to one side or the other, according to the side where the lesion is made. All the muscles of this side are then in a state of permanent contraction. The frog represented in Fig. 2, from which have been removed only the cerebral lobes of the two sides, is remarkable for the regularity and the symmetry of the position of his limbs. Placed in the water, he rests on its surface, and the right side is at the same level as the left side. But, if we wound the cerebellum on one side, whether the cerebral lobes are intact or removed, at once the exterior carriage becomes that which is represented in Fig. 4. In this frog, the cerebellum has been destroyed on the left side, and instantly the entire right