436 THE NERVOUS SYSTEM. 



both excitability and sensibility become manifest, in proportion as the 

 irritation is applied nearer the medulla oblongata and the inferior 

 peduncles. Furthermore, its removal, either in part or in whole, does 

 not essentially diminish either sensation or the power of movement. 

 The senses remain active, and the intelligence is unimpaired, provided 

 the cerebral hemispheres are intact. If injury of other adjacent parts 

 be avoided, the cerebellum may be extensively wounded or even totally 

 removed in many animals without causing death. One-half or two- 

 thirds of its substance have often been taken away in the pigeon ; and 

 in one of the experiments of Flourens, a fowl lived for more than four 

 months after its complete extirpation. 



Aside from these particulars, experiments consisting in mutilation 

 or removal of the cerebellum have yielded very uniform and striking 

 results, quite different from those caused by injury to other parts of the 

 brain. These effects were first described by Flourens,* and notwith- 

 standing the great activity of research since that time, his results have 

 been corroborated in all essential particulars by subsequent observers. 

 They have been witnessed, by different observers, in the pigeon, fowl, 

 duck, turkey, and other birds ; and, among quadrupeds, in the dog, the 

 cat, the mole, the rat, and the guinea-pig. 



The effect produced by partial or complete destruction of the cere- 

 bellum is a peculiar disorder of movement in the body and limbs, from 

 want of harmony in their muscular action. The power of associating 

 different muscles, in such a way as to produce coordinated movements, 

 is impaired in proportion to the extent of injury to the nervous centre. 

 In the pigeon, if a small portion only of the cerebellum be removed, 

 the animal exhibits a peculiar uncertainty in the gait, and in the move- 

 ment of the wings. If the injury be more extensive, the power of 

 flight is lost and the bird can walk, or even stand, only with difficulty. 

 There is no actual paralysis, for the movements of the limbs are often 

 rapid and energetic ; but there is a want of control over the muscular 

 contractions, similar to that shown by a man in a state of intoxication. 

 The movements are confused and blundering ; so that the animal cannot 

 direct his steps to any particular spot, nor support himself in the air by 

 flight, He reels and tumbles, but can neither walk nor fly. 



The senses and the intelligence are at the same time unaffected, and 

 this causes a striking difference between the effects produced by removal 

 of the cerebrum and that of the cerebellum. If these operations be done 

 upon two different pigeons, the animal from which the cerebrum only 

 has been removed will remain standing upon his feet, in a condition of 

 complete repose ; while the other, from which the cerebellum has been 

 taken away, is in a constant state of agitation, frequently endeavoring, 

 with violent and ineffectual struggles, to perform movements which he 

 cannot accomplish. 



*Becherches Exp^riraentales sur les Propri6ts et les Fonctions du Systeme 

 Nerveux. Paris, 1842, pp. 37, 53, 102, 133. 



