478 ORGANIC SENSATIONS 



but more directly with those of the opposite side and in particular with those 

 which move the head and vertebral column. Accordingly the muscles of either 

 side would be roused to activity in any given case chiefly by the opposite 

 labyrinth. In agreement with this is the fact that if one labyrinth be left 

 intact and the other be suppressed, rigor appears sooner after the death of the 

 animal on the side opposite the normal labyrinth. 



In other species of animals extirpation of one labyrinth produces somewhat 

 different results. In the rabbit rolling of the entire body around its longitudinal 

 axis sets in soon after the operation. This is caused by extension of the legs on 

 the opposite side, and by the consequent rotation of the animal toward the 

 operated side until it comes to lie on its back. The animal tries to regain its 

 feet, but as soon as it succeeds, begins once more to roll over. The legs of the 

 operated side are entirely passive all the while. After bilateral extirpation in 

 the dog, the animal exhibits a certain unsteadiness in his gait. When he jumps 

 down from a table, he falls sprawling on the floor. Some difficulty in chewing 

 and in swallowing may also be observed. All of which symptoms point to a 

 reduction of muscular strength and of the ability to properly control the muscles. 



The disturbances arising from bilateral extirpation of the labyrinths grad- 

 ually disappear again. This occurs in all likelihood mainly because the animal 

 gradually becomes accustomed to regulating his movements without the help 

 of the afferent impulses from the semicircular canals. 



The cerebrum appears to play the most important part in this regulation. 

 With pigeons from which the cerebrum was removed, unilateral extirpation 

 evoked the usual complex of symptoms, but some of them, especially the rota- 

 tion of the head, were no longer compensated. After the symptoms accompany- 

 ing bilateral extirpation in the dog had been improved as much as possible, 

 J. R. Ewald removed the surface of the cortex from the motor zone of both sides. 

 The dog exhibited disturbances of coordination of the profoundest kind. He 

 could no longer jump or run or walk or even stand ; in fact he could not lie on 

 his belly. He lay rather on one side or the other, and despite his most vigorous 

 efforts was unable to raise himself with his legs. The head, however, was used 

 to more purpose. Gradually these disorders improved, but they immediately 

 returned and in exactly the same fashion, as directly after the operation, 

 when the animal was taken into a room which was suddenly darkened. The dog 

 showed therefore that after exclusion of the impulses mediated through the laby- 

 rinths and through the so-called motor zone of the cortex, he had been thrown 

 back upon his eyes for the regulation of his movements. Since now no such 

 disturbances result from destruction of the cortex alone, even when the visual 

 sensations also are excluded, it follows that after extirpation of the labyrinth 

 the cerebral cortex takes upon itself the business of replacing the missing afferent 

 impulses as far as possible. Then when the cerebral cortex also is destroyed, a 

 compensation can once more be effected through the eyes, but this fails on exclu- 

 sion of the visual sensations. 



The disturbances which appear on suppression of the labyrinth are there- 

 fore, (1) a reduction of muscular strength, and (2) derangements in the 

 coordination of movements, which to all appearances are due to the loss of 

 afferent impulses. 



