24 THE ACTIVE FORCES OF LIVING ORGANISMS 

 The cere- jf ^g take the brain as a whole, one of the most 



oral circu- 

 lation, remarkable points in connection with it is the small 



amount of the blood-supply. The actual amount of 

 blood in the brain of a rabbit is hardly more than 

 1 per cent, of that in the whole body.* It is but 

 one-half of that which might be extracted from the 

 kidneys, whilst in the liver there is more than twice 

 as much again, t The cortical supply is, however, 

 probably more abundant than that to the white 

 matter, and since the cortex in the rabbit is but ill 

 developed, the low percentage above-mentioned may 

 to some extent be accounted for in this way. In man 

 we may suppose that the quantity of blood flowing to 

 the gray matter bears a slightly higher proportion to 

 the rest, but at the same time it is none the less true 

 that the quantity of oxygen absorbed and of carbonic 

 acid formed — or, in other words, the intensity of oxida- 

 tion under normal conditions of activity — is governed 

 by the chemical composition of the substance of the 

 brain. When allowance, therefore, has been made 

 for the difference in the development of the cortex in 

 the rabbit and in man, there are still reasons for 

 regarding the nervous system as a whole as an area 

 of relatively limited oxidation. Cerebral circulation 

 is, indeed, slackened and restricted at the very outset 

 by the extreme sinuosity of the arteries. It is said 

 that this is in order to prevent any too sudden or 

 violent flow of blood to the cerebral centres, the con- 

 sequence of which might be dangerous. But this is 

 * Foster, he. eii., p. 1239. f Tbid., p. 1239. 



