FUNCTIONS OF THE INTESTINES. 



319 



their lactcals, are thickly distributed throughout the entire 

 length of the small intestine. In the duodenum and jejunum 

 they. doubtless fully satisfy the needs of the organism, both 

 as to absorption and prophylaxis. In the lower part of the 

 intestinal canal, however, more protection is required, owing 

 perhaps to continued exposure of the contents to a relatively 

 high temperature during the time elapsed since this material 

 has been submitted to powerful antiseptic treatment in the 

 stomach: i.e., several hours to a day, according to the meal. 

 A morning movement of the bowels, for instance, includes 

 products of the breakfast of the preceding day, thus repre- 

 senting twenty-four hours of exposure in the intestine to a 

 temperature averaging 39 C. (102.2 F.). This additional 

 precaution is represented by the solitary lymph-follicles and 

 the agminated lymph-follicles, or Peyer's patches. While the 

 solitary lymph-follicles are found throughout the entire canal, 

 small and large, they are by far most numerous in the lower 

 part of the ileum and in the first part of the colon. Peyer's 

 patches, or the agminated follicles, are likewise found in the 

 duodenum and jejunum, though rarely in the former; but their 

 site of predilection is also in the ileum, and, inasmuch as they 

 vary from one-half inch to four inches in length and are oval 

 or round, they cover an extensive area, though only twenty 

 to thirty in number. Especially is this the case since they are 

 practically limited to one side of the intestine: i.e., to the 

 portion facing the latter^s attachment to the mesentery. They 

 also frequently form a continuous layer in the vermiform ap- 

 pendix. 



A single "solitary follicle" is typical of them all, includ- 

 ing those in Peyer's patches. A follicle consists, on the whole, 

 of a rounded mass lodged in the submucous tissue, a small part 

 of its upper portion appearing upon the free surface of the 

 latter, though the epithelium of the intestine also covers it. 

 The overlying layer of epithelium, however, is separated from 

 the follicle by a special delicate membrane perforated with a 

 multitude of holes that .surround its projecting portion and 

 communicate with the organ itself. 



The structure of the body of the follicle will perhaps be 

 best understood if it is divided into three different parts, be- 



