456 PHYSIOLOGY CHAP. 



(c) When the unilateral atrophy involves the cortex of the 

 involuted folia, but not the deeper parts, slight and not very 

 characteristic motor disturbances result ; there is merely slow 

 progression and a tendency to make backward steps. 



(d) Only when the atrophy involves the whole of one-half of 

 the cerebellum is the characteristic drunken gait and manifest 

 asthenia of the muscles on the affected side to be seen. 



(e) Incomplete bilateral agenesia of the cerebellum seldom 

 runs its course without symptoms. This, however, occurred in a 

 case described by Ingels, in which the weight of the cerebellum 

 was reduced to ^V of the normal. But in the majority of cases 

 there is ataxia with a greater degree of astasia, or pronounced 

 ataxia particularly in the lower limbs with general asthenia 

 and astasia, which may appear in the hands and arms in the 

 form of tremor. 



(/) In bilateral sclerotic atrophy the main symptoms of 

 cerebellar deficiency are seldom absent. The most constant are : 

 swaying in the upright position (astasia), which compels the 

 patient to widen his base of support to avoid falling ; a zigzag 

 gait like that of a drunken man, which is sometimes accompanied 

 by marked diminution of power (asthenia) in the lower limbs 

 rarely in the upper so that the patient is obliged to support 

 himself by the walls, seats, or a friendly arm to avoid falling. 



These facts, derived from a critical examination of this group 

 of clinical cases which is certainly the most important from the 

 physiological point of view not only agree with those obtained 

 experimentally by ourselves in dogs and monkeys, but are a 

 useful complement to them. 



The cases of agenesia that run a latent course seem to us of 

 the highest value, because they show that if a partial arrest of 

 development takes place in the cerebellum, such organic adaptations 

 may come about in the cerebral system as a whole as can wholly 

 or partially compensate the cerebellar deficiency. 



The cases of atrophy which present no symptoms during life, or 

 only such as are slight and not characteristic, agree perfectly with 

 the experimental fact that more or less complete organic com- 

 pensations may occur with surprising rapidity after incomplete 

 mutilations, symmetrical or asymmetrical, of the cerebellum in 

 dogs and monkeys. 



Evidently when cerebellar disease develops very slowly, it may 

 attain a considerable severity without any visible symptoms, since 

 the effects of deficiency are obscured or repaired by simultaneous 

 organic compensation in proportion as they make their appearance. 



It is also plain that the process of organic compensation by the 

 intact parts of the cerebellum can only take place imperfectly in 

 cases of bilateral agenesia or atrophy, when the healthy and func- 

 tioning part of the organ is reduced to a minimum. 



