358 



HUMAN PHYSIOLOGY 



replacing it with oxygen. This is accompanied by a change of color 

 from purple (in blood which is poor in oxygen) to that of bright 

 red (in richly oxygenated blood). Other changes take place in 

 other parts of the body. In the muscles the blood gives up food 

 and oxygen, receiving carbon dioxide in return. In the liver, the 

 blood gives up its sugar. In glands, it gives up materials used by 

 the gland cells in their manufacture of secretions. In the kidneys, 

 it loses water and nitrogenous wastes (urea). In the skin, it also 

 loses some waste materials and water. 



Function of Lymph. — Different tissues and organs of the body 

 are traversed by a network of tubes which carry the blood. Inside 



these tubes is the blood proper, 

 consisting of a fluid plasma, 

 the colorless corpuscles, and 

 the red corpuscles. Outside 

 the blood tubes, in spaces be- 

 tween the cells which form tis- 

 sues, is found another fluid very 

 much like plasma of the blood 

 in chemical composition. This 

 is the lymph. It is, in fact, a 

 fluid food in which some color- 

 less amoeboid corpuscles are 

 found. Blood gives much of 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 the blood proper and the cells 

 in the tissues of the body. It not only gives food to the cells of 

 the body but also takes away vv^aste materials, which are ulti- 

 mately passed out of the body by means of the 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 



Diagram showing how food reaches the cells 

 from the capillaries. 



