130 



NUTRITION OF FARM ANIMALS 



culatory apparatus is a closed system. Even the very thin 

 delicate walls of the capillaries are continuous and the blood 

 does not come into direct contact with the living cells, except, 

 of course, those lining the blood vessels. The accompanying 

 diagram (Fig. 19) illustrates schematically the anatomical re- 

 lations of the cells, intercellular spaces, capillaries and lym- 

 phatics, A representing a minute artery, or arteriole, subdi- 

 viding into capillaries which are reunited to form the small 

 vein V. Through the capillary walls the nutritive substances 

 contained in the blood pass, partly by osmosis and partly by 



FIG. 19. Relation of cells to blood vessels and lymphatics. (Hough and 

 Sedgwick, The Human Mechanism.) 



filtration, into the lymph to maintain its stock, while the waste 

 products of cell action pass in the opposite direction into the 

 blood and are carried off. 



186. Lymphatics. In the intercellular spaces there orig- 

 inates another set of minute vessels, the lymphatics, which 

 unite like the capillaries to form larger ones (L in Fig. 19) and 

 finally form two main lymphatic trunks, the thoracic duct 

 and the small lymphatic trunk, which empty into the great veins 

 near the heart. The lacteals of the intestinal villi, through which 

 the fats are chiefly resorbed, belong to the lymphatic system. 



