THE LYMPHATIC GLANDS 59 



it is known that they receive the plasma which has been 

 passed 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 conne'ctive tissue fibers together with some 

 elastic and non-striated muscle fibers. They are very abun- 

 dantly 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 

 other flexures. The deep glands 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 afferentia. The current must be consid- 

 erably delayed in the glands. They are concerned in the pro- 

 duction of leucocytes, while their retention of toxic materials 

 even to their own hurt is a common pathological occur- 

 rence. 



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 found in lymph except accidentally. The 

 specific gravity is lower than that of the blood. Lymph 



