MUCOUS MEMBKANE OF THE SMALL INTESTINE. 321 



and leading to a cavity, the base of which is convex and 

 formed by the conical projection of the wall of the follicle. 

 The diameter of the follicles is from 7 V to ^\ or even T V of 

 an inch. 1 The small-sized follicles are generally covered by 

 mucous membrane and have no opening leading to them. 

 Each follicle consists of a rather strong capsule composed of 

 an almost homogeneous, or very slightly fibrous membrane, 

 enclosing a semi-fluid grayish substance, cells, blood-vessels, 

 and probably lymphatics. The semi-fluid 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 arrange- 

 ment 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 ques- 

 tion 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 at other parts ; but vessels containing 

 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 can- 

 not be seen from above and are only discernible from the 

 under surface. In the smooth patches, the follices are gen- 

 erally well brought out by maceration in acetic acid. 



The description of the follicles which compose the patches 

 of Peyer answers, in general terms, for the solitary glands, 

 except that the latter are found in both the small and large 

 intestine. 



1 KOLLIKER, op. cit., p. 332. 

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