128 



HUMAN PHYSIOLOGY 



CHAP. 



the fact that very dark red blood is seen through the 

 yellowish skin. The blood escaping from a cut vein 

 looks bright red because the moment it comes in con- 

 tact with air it takes up oxygen which changes its 

 color at once. 



97. Lymphatics. Some of the blood that exudes 

 from the capillaries and forms part of the lymph around 

 the cells does not again enter the capil- 

 laries but is returned to the blood by 

 means of the lymphatics. We studied 

 lacteals and lymphatics in connection 

 with absorption of fats from the small 

 intestine. The spaces between the cells 

 in all parts of the body are filled with 

 lymph from which the cells get their 

 foods and to which they give off their 

 wastes. In these lymph spaces the 

 lymphatic capillaries have their begin- 

 ning. They serve to return most of the 

 cell wastes into the blood, carbon dioxid 

 being the only waste that enters the capil- 

 laries and is returned through, the veins. 

 The lymphatics resemble the veins in 

 their structure, but they are much 

 smaller, have thinner walls, and have 

 valves closer together. 

 The lymphatics may be said to begin in lymph spaces 

 in all parts of the body. Uniting, they gradually grow 

 larger until they form two main ducts which empty 

 into the veins at the base of the neck. The left thoracic 



F [G. 68. Lymphat- 

 ics of the right 

 arm. G, lymph 

 glands (Huxley). 



