33% INTESTINAL MUCOUS MEMBRANE. [sect. 1 5 7. 



(muscles, bones, nerves, heart), also furnishes the muscular coat of 

 the intestine, as well as the vessels, nerves and investments of the 

 intestinal glands. 



At the commencement, and for some time after, the inner layer, or the epi- 

 thelial tube, consists merely of cells ; and, by their continued multiplication 

 both in the area and thickness of the membrane — and effected, accord- 

 ing to Remak, by division, — it becomes converted, first, into the subsequent 

 epithelium, and, secondly, into the [/lands of the intestine. Of the latter, 

 the LieberkUhnian glands of the small intestine are, from the commence- 

 ment, hollow recesses of the epithelium ; whilst the salivary and the 

 Brunnerian glands, like the sudoriparous glands, are solid processes of the 

 epithelium, and acquire their cavities when they become further ramified. 



The glands of the stomach and large intestine also certainly arise from the 

 primitive epithelial tube, whether as inversions or solid growths is still undeter- 

 mined, and form, at first, a layer which is completely separated from the 

 fibrous layer of the intestine, and, consequently, the epithelium, upon these 

 places, appears much thicker than subsequently. Afterwards, delicate vas- 

 cular processes grow inwards from the fibrous layer between the glands, till at 

 length both layers, becoming intimately connected, represent the proper 

 mucous membrane. Similar and still more considerable outgrowths of the 

 fibrous layer form the villi, whilst from its outer parts the muscular and serous 

 coats are developed. 



The investigation of the intestinal mucous membrane presents greater 

 obstacles than that of other parts. The epithelium is generally found well 

 preserved only in perfectly fresh specimens, and, for the most part, readily dis- 

 integrates into its elements. The villi are best seen in thin perpendicular 

 sections made with fine scissors, and examined with low magnifying powers 

 by reflected light. During the process of absorption, they are mostly found 

 filled with fat and nuclei, so that their several parts are imperceptible, with 

 the exception of the chyle-vessels, which become distinct by the addition 

 of acetic acid, or still better of diluted caustic soda. At other times, the 

 muscles of the villi are easily recognised by their nuclei when acetic acid 

 is added. To study the blood-vessels, injections must be employed, especially 

 usch as have been made contemporaneously from the arteries and veins, and 

 are preserved in moist condition (still, the vessels of the villi are readily 

 seen, even in perfectly fresh objects). The same applies to the other parts 

 of the intestine, in which perpendicular sections are especially instructive. 

 For the glands, I employ fresh pieces of intestine, although the preparation of 

 such is frequently, as in the stomach, extremely difficult ; also, such as have 

 been hardened in absolute alcohol, wood-vinegar, or chromic acid ;■ further, 

 mucous membrane boiled with acetic acid of 80 per cent, and dried {Purhinjc 

 and Middeldorpf), or saturated with gum and dried ( Wasmann), of which thin 

 perpendicular and transverse sections are to be made with a sharp knife, 

 and which, if requisite, may be rendered clear by the addition of a little 

 caustic soda. The separation of the mucous membrane into its ele- 

 ments is most difficult, especially when it is thick, as in the horse and pig. 

 This is easier in the dog, cat, and rabbit, and in the ruminants, in which, 

 when the back of the knife is carried over the mucous membrane at the same 



