FUNCTIONS OF THE CEREBELLOI. 3S7 



direct ratio to the amount of cerebellar substance involved 

 in the disease or injury. We do not make the reservation, 

 that more than half of the cerebellum must be destroyed in 

 order necessarily to produce difficulty in muscular coordina- 

 tion, on purely theoretical grounds, but regard this point as 

 positively demonstrated by experiments on animals. These 

 experiments show that one-half of the organ is capable of 

 performing the function of the whole. AVe have an analogy 

 to this in the action of the kidneys, one of which is sufficient 

 for the elimination of the effete constituents of the urine, 

 after the other has been removed. 



Notwithstanding the contrary views of many physiologi- 

 cal writers, we are firmly convinced, from experiments and 

 a careful study of pathological facts, that there is no one 

 point in the physiology of the nerve-centres more definitely 

 settled than that the cerebellum presides over equilibration 

 and the coordination of the muscular movements, particu- 

 larly those of progression. In this statement, we make ex- 

 ceptions in favor of the movements of respiration, degluti- 

 tion, of the face, and of those concerned in speech, as well as 

 the involuntary movements generally. As another example 

 of a nerve-centre presiding over muscular coordination, we 

 have the instance of the portion of the left anterior lobe of 

 the cerebrum, which coordinates the action of the muscles 

 concerned in speech. 



The theory that the disordered movements which follow 

 injury of the cerebellum are due simply to vertigo is not 

 tenable. In only three of the cases cited, is vertigo men- 

 tioned; and in two, the word vertigo seems to be used 

 rather as an explanation of the phenomena observed, than 

 in their simple description. There is a disease involving the 

 semicircular canals and other parts of the internal ear, 

 called Meniere's disease, in which there is marked want of 

 equilibration and muscular coordination, attended with, and 

 probably dependent upon vertigo. The vertigo is always 

 very distinct, and is mentioned in all of these cases ; and 



