392 DIGESTION. 



atic fluid. In passing along the canal, the consistence of 

 the mass gradually diminishes, from the absorption of its li- 

 quid portions, and the color becomes darker ; and by the time 

 that the contents of the ileum are ready to pass into the 

 csecum, the greatest part of those substances which, we have 

 recognized as alimentary principles have become changed and 

 absorbed. The various forms of starchy and saccharine prin- 

 ciples, unless they have been taken in excessive quantity, soon 

 disappear from the intestine ; and the glucose, which is the re- 

 sult of their digestion, may be recognized in the blood of the 

 portal system. 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, as we have seen, 

 the muscular substance, as recognized by its microscopic 

 characters, becomes gradually disintegrated and is lost ex- 

 cept a few isolated fragments deeply colored with bile some 

 time before the undigested residue passes into the large in- 

 testine. 



In the human subject, those portions of the food which re- 

 sist the successive and combined action of the different diges- 

 tive secretions, are derived chiefly from the vegetable kingdom. 

 Hard vegetable seeds, the cortex of the cereals, spiral vessels, 

 and, in fine, 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 principles be taken in a concentrated and read- 

 ily assimilable form, leaves very little undigested matter to 

 pass into the large intestine, and gives to the faeces a charac- 

 ter quite different from that which is observed in herbivorous 

 animals, or in man, when subjected to an exclusively vege- 

 table diet. The characters of the residue of the digestion of 

 albuminoid substances are not very distinct. As a rule, 

 none of the albuminoids are to be recognized in the healthy 



