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THE BLOOD AND ITS CIRCULATION 



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CORPUSCLES *; 



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WHITE 



CORPUSCLKm 

 LEUCOCYTE ". 



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 lymph. 



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 



Diagram shoeing the exchange between blood ^ ^^ ^ ^ 



and the cells of the body. 



cells in the tissues of the 



body. By means of the food supply 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. 



Lymph Vessels. The lymph 

 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 The lymph ves sel 8 ; the dark spots are 



continually more plasma into the 

 lymph; thus a slow current is 



lymph glands : lac, Jacteals; re, thoracic 

 duct. 



