CH. XXII.] LYMPHATIC GLANDS 315 



All the lymphatics pass at some point of their course through 

 lymphatic glands, which are the factories of these corpuscles. Lym- 

 phocytes also pass into the lymph stream wherever lymphoid tissue 

 is found, as in the tonsils, thymus, Malpighian bodies of the spleen, 

 Peyer's patches, and the solitary glands of the intestine. The lymph 

 that leaves these tissues is richer in lymph-cells than that which 

 enters them. 



When lymph is collected from the thoracic duct after a meal 

 containing fat, it is found to be milky. This is due to the presence 

 in the lymph of minutely subdivided fat particles absorbed from the 

 interior of the alimentary canal. The lymph is then called chyle. 

 The fat particles constitute what used to be called the molecular basis 

 of chyle. If the abdomen is opened during the process of fat absorp- 

 tion, the lymphatics are seen as white lines, due to their containing 

 this milky fluid. They are consequently called lacteals. 



The structure and arrangement of the lymphatic vessels are given 

 in Chapter XVI 1 1., and we have now to study the structure of 



The Lymphatic Glands. 



Lymphatic glands are round or oval bodies varying in size from 

 a hemp-seed to a bean, interposed in the course of the lymphatic 

 vessels, and through which the lymph passes in its course to be dis- 

 charged into the blood-vessels. They are found in great numbers in 

 the mesentery, and along the great 

 vessels of the abdomen, thorax, and 

 neck; in the axilla and groin; a 

 few in the popliteal space, but not 

 further down the leg, and in the 

 arm as far as the elbow. 



A lymphatic gland is covered 

 externally by a capsule of con- 

 nective-tissue, generally containing 

 some unstriped muscle. At the 

 inner side of the gland, which is 

 somewhat concave (hilus), (fig. 304), 

 the capsule sends inwards processes 

 called trabeculce in which the blood- 

 vessels are contained, and these join with other processes prolonged 

 from the inner surface of the part of the capsule covering the 

 convex or outer part of the gland ; they have a structure similar 

 to that of the capsule, and entering the gland from all sides, and 

 freely communicating, form a fibrous scaffolding. The interior of the 

 gland is seen on section, even when examined with the naked eye, to 

 be made up of two parts, an outer or cortical, which is light coloured, 



the central part of the figure), medullary 



