264 



DIGESTION. 



and according to Sappey, are most abundant in persons of feeble constitution. The 

 villi are very large and prominent on the mucous membrane covering the first variety 



of Peyer's patches, especially at the summit of the folds. 

 In the second variety, the villi are the same as over other 

 parts of the mucous membrane, except that they are 

 placed more irregularly and are not so numerous. 



The intimate structure of the patches of Peyer has not 

 been definitely settled in all its particulars. It is well deter- 

 mined, however, that the follicles which compose them are 

 completely closed, the openings which have been said to 

 exist being undoubtedly accidental ruptures made in pre- 

 paring specimens for microscopical examination. These 

 follicles are somewhat pear-shaped, with their pointed 

 projections directed toward the cavity of the intestine. 

 Just above .the follicle, there is generally a small opening 

 in the mucous membrane, surrounded by a ring of intes- 

 tinal tubules, and leading to a cavity, the base of which 

 is convex and formed by the conical projection of the 

 follicle. The diameter of the follicles is from T ^ to 

 -fa or even T ^ of an inch. The small-sized follicles are 

 generally covered by mucous membrane and have no 

 opening leading to them. Each follicle consists of a rather 



tary glands upon the valvulse con- 

 niventes. 



FIG. 69. Patch of Peyer. (Sappey.) 



1, 1, 1, patch of Peyer ; 2, 2, folds seen 

 on the surface; 3, 3, grooves be- 

 tween the folds ; 4, 4, fossettes be- 

 tween some of the folds ; 5, 5, 5, 

 5, 5, 5, 5, 5, valvulae conniventes; 



smaller 'son tary 7 fands!' 8, 's,' soli- strong capsule composed of an almost homogeneous or 

 very slightly fibrous membrane, enclosing a semifluid, 

 grayish substance, cells, blood-vessels, and probably lym- 

 phatics. The semifluid matter is of an albuminoid character. The cells are very small, 

 rounded, and mingled with numerous small, free nuclei. The blood-vessels have rather a 

 peculiar arrangement. In the first place they are distributed between the follicles, so as 

 to form a rich net-work surrounding each one. Numerous capillary branches are sent 

 from these vessels into the interior of the follicle, returning in the form of loops. 

 The obscurity in the anatomy of the follicles is chiefly with regard to the arrangement 



of their lymphatic vessels. These have not been dis- 

 tinctly traced within the investing membrane. They 

 have been demonstrated surrounding the follicles, but it 

 is still doubtful whether they exist in their interior. 

 This question is so unsettled that it is impossible to 

 make a definite statement on the subject. All that is 

 known is that, during digestion, the number of lacteals 

 coming from the Peyerian patches is greater than in 

 other parts of the mucous membrane ; but vessels con- 

 taining a milky fluid are never seen within the follicles. 

 The mucous membrane covering the prominent 

 patches is generally so thick and folded that the closed 

 follicles cannot be seen from above and are only dis- 

 cernible from the under surface. In the smooth patch- 

 es, the follicles are generally well brought out by macer- 

 ation in acetic acid. 



The description of the follicles which compose the 



FIG. 10. Patch of Peyer, seen from its 



attached surface,. (Sappey.) 



1,1, serous coat of the intestine; 2, 2,2.2, patches of Peyer answers, in general terms, for the soli- 

 serous coat removed to show the * J 



patch ; 3, s, fibrous coat of the intes- tary glands, except that the latter are iound in botn 



vaTvuli c'onSvenies 5 ' 5 ' & ' 5 ' * 5 ' 5 ' * the small and the large intestine. 



