Effects wliicli folloio Ligation of the Cerebral Arteries. 483 



in blood supply. This substantiates previous work of the author in 

 regard to the slight metabolism of the brain as measured by the 

 exchange in blood gases. At the same time it does not favour the 

 ana3mic theory of sleep. 



3. The electrical excitability of the motor area of the cortex cerebri 

 persists when the sensory side of the brain is to a large extent para- 

 lysed, and the animals rendered more or ' less demented by profound 

 -cerebral ansemia. 



4. The functions of the brain rapidly return so soon as efficient 

 anastomosis is established. The period of partial paralysis and 

 dementia lasts in dogs two or three days. Rabbits recover after the 

 pupil reflex has been abolished for 15" — 20". 



5. The limits between the degree of anaemia required to produce 

 dementia and that which paralyses the respiratory centre are extremely 

 narrow. For example, monkeys recover without symptoms after ligation 

 ■of both carotids, but as a rule die after ligation of both carotids and 

 one vertebral artery. 



6. There is considerable variation in the number of arteries which 

 can be safely tied in various animals, e.g., in man, birds, goats, and 

 horses (Mayer) one carotid ; in monkeys both carotids ; in rabbits and 

 cats both carotids and often both carotids and one vertebral ; in dogs 

 both carotids and both vertebrals. 



7. The four cerebral arteries can be safely tied in monkeys in 

 successive operations. 



8. The cortex cerebri is the place of discharge of clonic convulsions. 

 Tonus is of sub-cortical origin. The clonic stage of an epileptic fit can 

 be cut short by compression of both carotid arteries. 



Dr. Mott, to whom I am greatly indebted for help and advice in 

 this research, has determined by microscopical examination of the 

 anaemic brains by Nissl's method, that — 



1. The cortical cells in the brains of the demented animals are 

 swollen and diflfusely stained. The stichochrome granules are absent. 

 The nuclei are swollen. The veins are congested and there may occur 

 hsemorrhages in the cortex. 



2. The large pyramidal cells are least affected. 



3. The changes occur very rapidly after ligation of the cerebral 

 arteries, and disappear synchronously with the recovery of the animals 

 from the stage of dementia. 



In the case of the monkey, described above, the cerebrum was 

 softened in patches, many of the cortical cells were degenerated, and 

 there were signs of active phagocytosis. No changes in the neurons 

 were displayed by the Golgi method. 



The expenses of this research have beeh met by grants from the 

 Royal Society Government Grant. 



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