THE INTESTINES. 109 



appears much thicker than it subsequently is. At a later period, 

 delicate vascular processes grow from the fibrous layer between 

 the glands, until at length both layers, intimately united, con- 

 stitute the proper mucous membrane. Similar and more con- 

 siderable processes of the fibrous layer form the villi, whilst the 

 muscular and serous tissues are developed from its external 

 portion. 



[The examination of the intestinal mucous membrane pre- 

 sents greater difficulties than that of other parts. The 

 epithelium is usually in a good state of preservation only in 

 quite fresh subjects, and generally breaks up into its elements 

 with extreme ease. The villi are best seen in thin perpen- 

 dicular sections, made with fine scissors, viewed with a low 

 power, and illuminated from above. During absorption, they 

 are usually found full of fat and nuclei, so that their separate 

 portions are not perceived, with the exception of the lacteals, 

 which become distinct by the use of acetic acid and still better 

 by that of dilute caustic soda. At other times, the muscles 

 of the villi are easily recognised by their nuclei, on the 

 addition of acetic acid. Injections are required for the blood- 

 vessels : the best are made by injecting from both arteries and 

 veins at the same time, and should be preserved in fluid. The 

 same holds good of the other parts of the intestine, for which per- 

 pendicular sections are especially instructive. For the glands, 

 recent pieces of intestine are particularly required, although 

 it is often, as in the stomach, exceedingly difficult to prepare them. 

 Mucous membrane, hardened in alcohol, pyroligneous acid, or 

 chromic acid, or boiled in acetic acid of 80 per cent, and dried, 

 according to the method of Purkinje and Middeldorpf, or satu- 

 rated with gum and dried, thin transverse and longitudinal sec- 

 tions being made with a sharp knife, according to Wasmann's 

 method, may be used, being first rendered clear by a little soda. 

 The analysis of the gastric mucous membrane into its elements, 

 presents the greatest difficulties, especially when it is as thick, 

 as in the Horse and Pig. In the Dog, Cat, Rabbit, and in 

 Ruminants, the process is easier, since, frequently, by merely 

 scraping the mucous membrane with the back of a knife, the 

 epithelium of the glands may be drawn out in a connected 

 state and affords all the information required as to their form 

 and lining. Simple teasing out is also frequently sufficient to 



