352 THE HUMAN BODY. 



especially in the small intestine, the cells are peculiarly abun- 

 dant, forming local aggregations of about the size of the head 

 of a small pin: these are named dosed or solitary follicles. 

 A minute artery enters each and gives rise to a capillary net- 

 work in it, from which the blood is carried off by a small vein. 

 The follicle lies in, or rather projects into, a lymph-lacunae 

 which closely invests it, and is in direct communication with 

 other lymphatic vessels of the neighborhood. The central 

 leucocytes of the follicle are smaller than the outer, and their 

 nuclei are often found in various stages of karyokinesis. 

 Each follicle must therefore be regarded as a seat of forma- 

 tion of new leucocytes, new-made ones being pushed to the 

 outside, growing, and finally being cast out into the sur- 

 rounding lymph-lacuna, to be carried away in the lymph- 

 current. 



Near the lower part of the ileurn large numbers of solitary 

 follicles are closely collected side by side at intervals along 

 the part of the bowel opposite to that at which the mesentery 

 joins it: these aggregations are known as Peyer's patches; and 

 are easily recognizable by the unaided eye, as villi are absent 

 from the part of the mucous membrane opposite them, and 

 they also cause a bulging, visible on the outside of the intes- 

 tine. They disappear after middle life. 



The Lymphatic Glands are essentially Peyer's patches 

 more complicated in structure by the fact that the constitu- 

 ent follicles are more closely united and are gathered into 

 roundish masses instead of being spread out in a single layer. 

 They are found in various regions on the course of lymphatic 

 vessels; especially in the mesentery, groin and neck. In the 

 latter position they often inflame and give rise to abscesses, 

 especially in tuberculous persons; and still more often enlarge, 

 harden and become more or less tender, so as to attract at- 

 tention to them. In common parlance it is then frequently 

 said that the person's " kernels have come down/' or that he 

 has " waxing kernels." Each lymphatic gland is enveloped 

 in a connective-tissue capsule, partitions of which incomplete- 

 ly divide it into chambers in which the lymphoid tissue lies. 

 The partitions are more complete in the outer parts of the 

 gland (cor.tical portion), which accordingly looks different 

 from the central portion (medulla) in sections. In the lym- 

 phoid tissue are contained many leucocytes in process of 

 division. " Afferent " lymphatic vessels open into the pe- 



