58 CARBON IS ACCUMULATED 



In a word, the heart is a forcing pump, which 

 sends arterial blood into all parts of the body ; and 

 also a suction pump, by means of which all fluids 

 of whatever 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 transforma- 

 tions of organised parts, must be compelled to move 

 towards the heart. 



These compounds cannot be employed for the 

 reproduction of those tissues from which they are 

 derived. They pass through the absorbent and 

 lymphatic vessels into the veins, where their accu- 

 mulation would speedily put a stop to the nutritive 

 process, were it not that this accumulation is pre- 

 vented 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 separate from both all substances in- 

 capable of contributing to nutrition. 



Those new compounds which contain the nitrogen 



