12S VETERINARY PHYSIOLOGY 



which the cerebrum above the tectum has been removed. 

 Decerebration rigidity in the position of extension manifests 

 itself. This rigidity is removed on one side, if that side of 

 the spinal cord in the neck be divided, showing that it is a 

 cerebellar action. The hypertonus is not removed on slicing 

 away the cerebellum until the basal nuclei and nucleus of 

 Deiters are destroyed. Apparently the cerebellum is con- 

 trolled by the cerebrum, and acts to excess after its removal, 

 either (a) directly upon the spinal arcs, or (6) indirectly 

 through its superior peduncles and the red nucleus. 



While absinthe leads to clonic spasms in the intact 

 animal, when one cerebral hemisphere is removed the clonus 

 is replaced by tonus on the opposite side, the absinthe now 

 stimulating the cerebellum alone. 



2. Removal of the Cerebellum. — This operation is easily 

 performed in the pigeon (fig. 34, p. 80), and the animal, 

 for a time at least, loses the power of balancing itself, and, 

 when disturbed, makes violent movements to recover its 

 equilibrium. 



In the dog three stages are seen — 



(1) Irritative Stage. — Immediately after removal, there 

 is marked extension of the spine — ojnsthotonus — extension 

 of the fore limbs, and alternating clonus of the hind limbs. 

 In the monkey the same symptoms appear, but there is tonic 

 flexion at the elbows. 



(2) Stiige of Inadequacy. — These symptoms gradually 

 pass off, and the animal then shows general muscular 

 weakness. 



(3) Stage of Compensation. — Later still, this condition may 



in large measure be recovered from. 



o 



8. Partial Removal. — If one side of the cerebellum be 

 removed the symptoms are — (1) At once a tonic contraction 

 of the muscles of the limbs of the same side by which the 

 fore limb in the dog may be powerfully extended. The head 

 is twisted with the ear to the shoulder of the side of the 

 removal, and the chin to the opposite shoulder, and the 

 animal may be driven round its long axis to the opposite 

 side. The eyes show a coarse lateral nystagmus — a jerking 



