376 



THE BLOOD AND ITS CIRCULATION 



Diagram showing the exchange between blood 

 and the cells of the body. 



up its food material to the lymph. This it does by passing it 

 through the walls of the capillaries. The food is in turn given up to 



the tissue cells which are 

 bathed by the IjTnph. 



Some of the amoeboid 

 corpuscles from the blood 

 make their way between 

 the cells forming the walls 

 of the capillaries. Lymph, 

 then, is practically blood- 

 plasma plus some colorless 

 corpuscles. It acts as the 

 medium of exchange between 

 the blood proper and the 

 cells in the tissues of the 

 body. By means of the food suppi>' thus brought, the cells of the 

 body are able to grow, the fluid food being changed to the proto- 

 plasm of the cells. By means of the oxygen passed over by the 

 lymph, oxidation may take place within the cells. Lymph not 

 only gives food to the cells of 

 the body, but also takes away 

 carbon dioxide and other waste 

 materials, which are ultimately 

 passed out of the body by 

 means of the lungs, skin, and 

 kidneys. 



^jLymph Vessels. — The lympli 



is collected from the various tissues 

 of the body by means of a number 

 of very thin-walled tubes, which 

 are at first very tiny, but after 

 repeated connection with other 

 tubes ultimately unite to form 

 large ducts. These lymph ducts 

 are provided, like the veins, with 

 valves. The pressure of the blood 

 within the blood vessels forces 

 continually more plasma into the 

 Ij-mph ; thus a slow current is 



The lymph vessels ; the dark spots are 

 lymph glands: iac, lacteals; re, thoracic 

 duct. 



