262 INTESTINAL DIGESTION. 



changed and absorbed. The various forms of starchy and saccharine matters, 

 unless they have been taken in excessive quantity, soon disappear from the 

 intestine ; and the glucose, which is the result of their digestion, may be rec- 

 ognized in the portal blood. As a rule, fatty matters are not found in the 

 lower part of the ileum, having passed into the lacteals, in the form of an 

 emulsion. Neither fibrin, albumen nor caseine, can be detected in the ileum ; 

 .and the muscular substance, as recognized by its microscopical characters, 

 becomes gradually disintegrated and is lost except a few isolated fragments 

 deeply colored with bile some time before the indigestible residue passes 

 into the large intestine. 



In the human subject those portions of the food which resist the succes- 

 sive and combined action of the different digestive secretions are derived 

 chiefly from the vegetable kingdom. Hard, vegetable seeds, the cortex of 

 the cereals, spiral vessels, and, indeed, all parts which are composed largely 

 of cellulose, pass through the intestinal canal without much change. These 

 .substances form, in the faeces, the greatest part of what can be recognized as 

 the residue of matters taken as food. It is well known that an exclusively 

 animal diet, particularly if the nutritious matters be taken in a concen- 

 trated and readily assimilable form, leaves very little undigested matter to 

 pass into the large intestine, and gives to the faeces a character quite different 

 from that which is observed in herbivorous animals or in man when subjected 

 to an exclusively vegetable diet. The characters of the residue of the diges- 

 tion of albuminoid substances are not very distinct. As a rule, none of the 

 albuminoids are to be recognized in the healthy fasces by the ordinary tests. 



Absorption of various articles of food in a liquid form may take place 

 with great activity in the large intestine, although it has not been shown that 

 the secretions in this part of the alimentary canal have any distinct digestive 

 properties ; still, as is shown in rectal alimentation, eggs, milk and meat-ex- 

 tracts may be taken up by the mucous membrane, and they enter the circu- 

 lation in such a form that they contribute to the nutrition of the body. 



Processes of Fermentation in the Intestinal Canal. The processes of 

 fermentation in the intestines are not properly digestive and are to a great 

 extent due to the action of micro-organisms, which exist here in great num- 

 bers and variety. It is possible, however, that future researches may show 

 that micro-organisms play an important part in actual digestion, as is fore- 

 shadowed in a recent article by Pasteur (August, 1887). Pasteur has isolated 

 seventeen different micro-organisms of the mouth. Some of these dissolved 

 albumen, gluten and caseine, and some transformed starch into glucose. The 

 micro-organisms described were not destroyed by the action of the gastric 

 juice. These observations are very suggestive, and they seem to open a new 

 field of inquiry as regards certain of the processes of digestion. Most of the 

 fermentations in the small intestine are either putrefactive or of a nature 

 analogous to fermentation, and the processes are continued with increased 

 activity in the large intestine. 



Some of the substances resulting from intestinal fermentations have 

 .already been described. Indol, skatol, phenol etc., seem to be produced by 



