IN THE BILE. 57 



kind, as soon as they enter the absorbent vessels which 

 communicate with the veins, are drawn towards the 

 heart. This suction, arising from the vacuum caused 

 by the expansion of the heart, is a purely mechanical 

 act, which extends, as above stated, to fluids of every 

 kind, to saline solutions, poisons, &c. It is obvious, 

 therefore, that by the forcible entrance of arterial blood 

 into the capillary vessels, the fluids contained in these, 

 in other words, the soluble compounds formed by the 

 transformations of organized parts, must be compelled 

 to move towards the heart. 



These compounds cannot be employed for the re- 

 production of those tissues from which they are derived. 

 They pass through the absorbent and lymphatic vessels 

 into the veins, where their accumulation would speedily 

 put a stop to the nutritive process, were it not that this 

 accumulation is prevented by two contrivances adapted 

 expressly to this purpose, and which may be compared 

 to filtering machines. 



The venous blood, before reaching the heart, is made 

 to pass through the liver ; the arterial blood, on the other 

 hand, passes through the kidneys ; and these organs sep- 

 arate from both all substances incapable of contributing 

 to nutrition. 



Those new compounds which contain the nitrogen of 

 the transformed organs are collected in the urinary blad- 

 der, and being utterly incapable of any further applica- 

 tion in the system, are expelled from the body. 



Those, again, which contain the carbon of the trans- 

 formed tissues, are collected in the gall-bladder in the 

 form of a compound of soda, the bile, which is miscible 



