THE LYMPHATIC GLANDS 59 



out of the vascular capillaries and thus collect fluid from well- 

 nigh every tissue in the body. 



The structure of the lymph-vessels is quite similar to that of 

 the veins, though they are more delicate. The lymph capillaries 

 probably contain only a single coat like the venous capillaries. 

 In the large vessels this thin endothelial coat is supplemented by 

 connective tissue fibers together with some elastic and non- 

 striated muscle fibers. They are very abundantly supplied 

 with valves which operate in the same way as the venous valves: 

 The vessel wall is quite elastic and has some contractile power. 



Lymphatic Glands. All the lymphatics pass through one or 

 more lymphatic glands on their way to the larger trunks. These 

 bodies are not true glands. Their structure is adenoid. There 

 are some six or seven hundred in the body, varying in size from 

 a pinhead to a large bean. The superficial glands are especially 

 abundant about the groin, axilla, neck and the other flexures. 

 The deep ones are most numerous about the great vessels. The 

 mesenteric glands are found between the folds of the mesentery. 



The lymphatic glands are of irregular shape and contain 

 within their substance large numbers of lymph spaces or canals 

 through which the incoming lymph must pass. The vasa 

 efferentia are usually fewer in number and larger in size than the 

 vasa qfferentia. The current must be considerably delayed in 

 the glands. They are probably concerned in the elaboration of 

 leucocytes of the lymphatic circulation, while their retention of 

 toxic materials even to their own hurt is a common patho- 

 logical occurrence. 



Properties and Composition of Lymph. Lymph is a com- 

 paratively clear liquid containing leucocytes. After meals the 

 color becomes whitish from the admixture of chyle, and numerous 

 fat droplets are present. Neither red corpuscles nor platelets 

 are thought to be found in lymph except accidentally. The 

 specific gravity is lower than that of the blood. Lymph coagu- 

 lates when drawn, since the fibrin factors are present; but the 



