432 PHYSIOLOGY CHAP. 



which consists in abnormal movements directed to meeting and 

 partially compensating the effects of deficiency. 



(e) The phenomena of cerebellar deficiency, in association with 

 the processes of functional compensation, make up a syndrome or 

 characteristic complex of phenomena, which has long been known 

 by the generic name of cerebellar ataxy. It is the task of 

 physiology to make as exact an analysis as possible of the 

 individual elements that go to form this ataxy, with the object of 

 distinguishing the phenomena due to loss of cerebellar innervation 

 from those due to the instinctive or voluntary compensatory acts, 

 which are directed to nullifying the effects of the former. 



(/) As each lateral half of the cerebellum is connected mainly 

 with the corresponding half of the body, it is obvious that the 

 symptoms of unilateral cerebellar extirpation must be greater on 

 the side of the operation than on the opposite side. Hence, 

 comparison of the two halves of the body in an animal from 

 which one-half of the cerebellum was removed is equivalent to 

 comparing two animals of the same species, age, and constitution, 

 one of which is in full enjoyment of its cerebellar innervation, the 

 other almost entirely deprived of it. 



III. If not too deeply anaesthetised or enfeebled by bleeding 

 during the operation, dogs show signs of distress and agitation 

 immediately after complete removal of one-half of the cerebellum. 

 The animal also presents pleurothotonus or curvature of the 

 vertebral axis to the side operated on, tonic extension of the 

 anterior limb on the same side, with clonic movements of 

 the three other limbs ; rotation of the neck and head towards the 

 healthy side, slight nystagmus and squint with inward and down- 

 ward deviation of the eye on the side operated on, and downward 

 and upward of the eye on the healthy side ; and rotation round 

 the long axis of the body in the same direction as that of the 

 neck and head (i.e. from the side operated on to the healthy side 

 if the animal is looked at in front, from the healthy side to the 

 operated side if it is viewed from behind). 



The immediate dynamic phenomena after total removal of the 

 cerebellum are agitation, unrest, and cries from the animal ; 

 opisthotonus, or backward curving of the vertebral axis, par- 

 ticularly of the neck and head ; tonic extension of both fore-limbs, 

 with .alternating clonic movements of hind-limbs ; bilateral con- 

 vergence of the eyes ; and tendency to stagger and fall backwards. 



These symptoms may seem more simple than those which follow 

 unilateral destruction, but they are really the same dynamic 

 disturbances spread over both sides. Opisthotonus is substituted 

 for pleurothotonus ; tonic extension of both limbs for tonic 

 extension of one limb, regression and falling backward for rotation 

 on the long axis. 



After destruction of the vermis and, generally speaking, after 



