870 THE CENTRAL NERVOUS SYSTEM 



tion on account of the fact that the sthenic, tonic and static impulses re- 

 quired for muscular harmony are not properly elaborated. 



After some time, as in the case of complete cerebellar extirpation, the 

 symptoms gradually disappear, but they can be obtained more or less char- 

 acteristically in practically all animals, at least in all those that have been 

 investigated, including dogs and monkeys. 



It will be of interest to consider for a moment the possible causes for the 

 ultimate disappearance of the symptoms of cerebellar extirpation. These 

 are either : (1) an organic compensation by the uninjured parts of the cere- 

 bellum, or (2) a functional compensation by the voluntary centers of the 

 cerebrum. Although the former of these methods of compensation may 

 sometimes develop after partial destruction of the cerebellar cortex, it can 

 not of course explain the recovery which we have seen to occur after the 

 entire cerebellum has been removed. The most important compensation no 

 doubt is effected by the cerebrum, as the following observation clearly in- 

 dicates. If half of the cerebellum of a dog is destroyed, and the animal 

 kept alive until the symptoms of cerebellar extirpation have entirely dis- 

 appeared, it will then be found, if the cerebral center on the opposite side 

 is removed, that the symptoms return in their original severity. After this 

 second operation the powers of standing in the erect position and of 

 walking are permanently lost. 



CLINICAL OBSERVATIONS 



Application of these laboratory results has been recently made in the 

 clinic, the most important contribution having come from the clinic of 

 Barany, who for his work was awarded the Nobel prize. In cases of abscess, 

 cysts, or regional agenesia, it is now possible to determine the exact site of the 

 lesion in the cerebellum. To effect this localization, it has been necessary to 

 work out certain clinical tests. The most important of these is called the 

 index test. This is described by Davidson Black as follows : ' ' The patient 's 

 eyes being closed, he is asked to execute a simple movement in a given 

 direction with one of his extremities. For example, the forearm being 

 firmly supported, the patient's index finger is extended and brought into 

 contact with that of the observer; the patient is then required to move his 

 finger vertically downward and then to return it to its previous position. 

 The test is repeated a number of times, both in the vertical and in the 

 horizonal direction, and if any tendency toward deviation from the plane of 

 movement be present, its direction is noted. By slight modification of the 

 foregoing procedure it is possible to test each of the limb segments in all 

 positions of rotation, pronation or supination." 



The index test is applied (1) without previously producing nystagmus 



