THE BLOOD. 4S9 



was thought to depend ; but Dr Graham and others demon- 

 strated this to be an error. 



Various organic principles are found in blood, which I 

 need not enter upon at length here, such as kreatin, kreati- 

 nine, hippuric acid, &c. The table will indicate the salts of 



QUANTITY OF BLOOD IN ANIMALS. It is extremely diffi- 

 cult to estimate this, as the body cannot be deprived of all 

 ts blood. According to Colin, blood to the amount of the 

 L8th part of the weight of a horse can be obtained; in the ox 

 md sheep the 23rd part, and in the dog the 12th part may 

 )e abstracted, but the total amount of blood in the body is 

 rery much greater. 



It is important to know, that if blood is drawn from the 

 >ody in considerable quantities, it reproduces itself rapidly, 

 nd the facilities for its reproduction seem to increase by 

 uch periodical abstractions as are not too large to endanger 

 he animal's life at the time. It is in this way that periodic 

 >leeding tends rather to induce than to prevent plethora, 



CHEMICAL CHANGES IN RESPIEATION. 



The respiratory act, as we have already said, consists in a 

 hange induced in blood by contact with atmospheric air. 

 ?he air loses in one way, and gains in another, and the same 

 aay be said regarding the blood. Atmospheric air consists of 



Oxygen, . . . .21 parts 

 Nitrogen, . . . . 79 



;t always contains a certain quantity of water, varying 

 rom a minimum of 4 to a maximum of ] 6 grains in 1000, 

 md respiration goes on more equally and thoroughly when 



