Effects which follow Ligation of the Cerebral Arteries. 



481 



be paralysed for a few minutes, and tumble and walk on the back of 

 the fore-paws, but these symptoms quickly disappear even though the 

 pupils' light reflex may have been abolished for 15' — 20'. 



2. Cortical Excitability after Ligation of Cerebral Arteries. 



The author has produced contra-lateral clonic spasms in himself by 

 sudden compression of one carotid artery. Consciousness of the 

 cortical discharge arises from the sensations received from the parts 

 in movement. The cortical discharge itself is unaccompanied with 

 consciousness. 



The cortex cerebri of dogs remains excitable and even hyper- 

 excitable to electrical excitation after both carotid and vertebral 

 arteries have been tied. The brain under these conditions is supplied 

 with blood by the branches of the superior intercostal artery which 

 enter the anterior spinal artery. 



The brain is, however, rendered profoundly anaemic by the operation, 

 and the animals are in consequence rendered more or less demented, 

 ansesthetic, and paralysed. The paralysis results from a block established 

 by the anaemia in the sensory projection, and association fields of the 

 cortex cerebri for the motor cells are unaffected, in so far as not only 

 purposive movements but typical fits can be excited on stimulating the 

 " motor area." The " motor centres " are clearly not autonomous, and 

 these experiments confirm the previous deductions concerning the origin 

 of the paralysis which was obtained by Mott and Sherrington after divi- 

 sion of the posterior nerve-roots of a limb, and by Exner after circum- 

 vallation of the cortex. Isolation of the cortical motor cells from 

 sensory impulses produces paralysis, although the cells remain directly 

 excitable. 



In many monkeys the two carotids, and even the two carotid and 

 one vertebral artery, can be tied without lessening the cortical excit- 

 ability. The ligation of all four arteries is followed within one minute 

 by loss of cortical excitability. In some monkeys (especially those in 

 bad condition) ligation of both carotids abolishes the excitability. 



3. The Effect of Absinthe cfter Ligation of the Cerebral Arteries. 



The injection of absinthe, after ligation of the four cerebral 

 arteries in cats and of the two carotid arteries in monkeys, produces 

 as a rule only extensor rigidity of the fore limbs and dyspnceic respira- 

 tion. No clonic convulsions occur. On loosening the carotids violent 

 clonic and tonic convulsions ensue, and these can be again cut short by 

 re-clamping the carotids. So soon as the carotids are re-clamped, the 

 extensor rigidity reappears. It is deduced from these experiments 

 that clonus is of cortical, and tonus of sub-cortical, and probably of 

 cerebellar, origin. 



VOL. LXVI. 2 P 



