01 



38 



THE BEGINNINGS OF LIFE. 



temporarily-abolished functions. Non-sensitive parts 

 again become sensitive^ and the paralysis of motor power 

 disappears. Even when the posterior part of the body 

 of such an animal has been completely severed from the 

 anterior^ and when all signs of reflex excitabihty have 

 disappeared^ M. Brown-Sequard has, nevertheless^ found 

 that the injection for a time of oxygenated and defibri- 

 nated blood seems to restore to the spinal cord all its 

 properties — so that irritation of the skin again gives 

 rise to reflex movements. The functions of the brain 

 are similarly dependent upon, and modifiable by, the 

 nature of the blood supply. Sir Astley Cooper having 

 tied the two carotid arteries of a 



rabbit, completely 



cut off the afflux of blood to the brain by compressing 

 the two vertebral arteries j when the animal very 

 shortly lapsed into a state of complete stupor or comaj 

 which continued until the compression was removed 

 from the two latter vessels. As soon as this was done^ 

 however, the animal again exhibited signs of hfe. The 

 experiments of M. Vulpian upon frogs have yielded even 

 still more striking results. He stopped the circulation 

 of blood throughout the body generally, by tying the 

 heart at the origin of the great vessels. This occasioned 

 a gradual cessation of all vital manifestations. In 

 such animals, however, these manifestations are slow 

 to disappear, so that it was not till after the expi- 

 ration of two or three hours that all signs of life had 

 gone. After this period no trace of any excitability 



could be detected in. the spinal cord, and the ani 



imal 



lished. The othe 



After 



move 



slowly. 



respiratory 

 irregular and disi 

 their accustomed 

 two hours more 

 ;ained its excita 

 producible by ii 

 power of volunta 

 viously dead ani 

 vital powers I 



1 



The animal, as 

 ^'ilin itself the pot 

 tissues and organs , 

 othenvise. 



' .^'« We seen, ; 

 '^!% remain i^ 

 ^-H in the Aa 



"''' ^- capable 



eth 



Spinal 



centres. 



Surie 





Ptesci 



^"Wer au 



lence. 



Le 



ccsur p, 



i 



