354 TEE POPULAR SCIENCE MONTHLY. 



tonic contraction of the muscular groups corresponding to the wounded 

 side. The nearer the lesion is situated to the bulb, the more pro- 

 nounced are the phenomena, and the more the frog leans to one side. 



In geese and ducks, on pricking or cutting the peduncles of th 

 cerebellum, we can well observe phenomena analogous to these seen in 

 frogs. When we remove the cerebellum of the two sides, there is no 

 movement of rotation, but the animal plunges deeply into the water. 

 In the uninjured duck, for example, the thorax penetrates the water 

 but a little way ; the duck, deprived of its cerebellum, penetrates it 

 twice as far. The duck, represented at Fig. 6, is wounded in the right 

 side of the cerebellum, and the animal has a movement of rotation 

 toward the left. side. 



We think these phenomena are due to an irritation of the locomo- 

 tive centx*es, and, with Brown-Sequard, we believe that the lesions of 

 certain points of the encephalon engender a state of irritation, whence 

 arises, whether directly or by reflex action, a tonic contraction of cer- 

 tain muscular groups, and chiefly of muscles of the thorax. 



It is very easy to account for this influence of the muscles of the 

 thorax in producing the movements of swimming. This easy experi- 

 ment shows us, at the same time, that simple paralysis, or the loss of 

 function of one side, does not occasion the movements of rotation. If 

 we swim with one arm and one leg of the same side, we do not deviate, 

 but advance in a right line ; but, if we contract the muscles of the thorax 

 of one side, at once we lean in the water on that side. If we increase 

 this contraction, we draw over a little more in the same direction, until 

 we come to lie completely on one side, and at this moment there super- 

 venes a movement of rotation, almost instinctive, which makes us spas- 

 modically take the normal position. It is something like this which 

 occurs in animals that have movements of rolling. 



By encephalic lesion, animals are led to lean strongly to one side, 

 an attitude which they take even in repose. At the least movement, 

 they are drawn over upon the back ; at once, spasmodically, all the 

 limbs concur in the effort to regain the former state ; but, as soon as 

 taken, the compulsion of the injured side is reproduced, and, as the ani- 

 mal has already acquired motion, this carries it beyond the normal 

 attitude, and leads it on to its side and back ; immediately it seeks to 

 get on its feet, rises, is again drawn over on one side, and so on. When 

 the cerebral lobes are removed, animals cannot remain lying on the 

 back. They always seek to recover their normal attitude, and, conse- 

 quently, when they have deviated from it, all their efforts go to recover 

 equilibrium. It is at this moment that the four limbs concur to execute 

 the gyratory movement. There are two factors in the motion of rota- 

 tion : the first is the contraction of the muscles of the injured side 

 which makes the animal lean over and bear down on that side ; the 

 second is the cooperation of all the members, as soon as the animal is 

 reversed, to produce a half-revolution and recover the normal forced 



