292 DIGESTION. 



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 successive and com- 

 bined action of the different digestive 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 with- 

 out 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 fseces a character quite different from that which is observed in herbiv- 

 orous animals or in man when subjected to an exclusively vegetable diet. The charac- 

 ters 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 faeces by the ordinary 

 tests. 



Many insoluble inorganic substances are taken with the food and appear unchanged 

 in the fasces. The fseces of dogs fed exclusively on bones, which were formerly adminis- 

 tered internally as a remedy for epilepsy, under the name of album Grcecum, are composed 

 almost entirely of calcareous matter. "With regard to the ordinary inorganic constituents 

 of the faaces, however, it is difficult to say how much is derived from the ingesta and 

 how much from the different intestinal secretions. 



Contents of the Large Intestine. 



"When the contents of the small intestine have passed the ileo-caecal valve, they be- 

 come changed in their general character, partly from admixture with the secretions of 

 this portion of the canal, and are then known as the faeces. The most palpable of these 

 changes relate to consistence, color, and odor. 



Faecal matter has a much firmer consistence than the contents of the ileum, which is 

 due to a constant absorption of the liquid portions. As a rule, the consistence is great in 

 proportion to the length of time that the fseces remain in the large intestine ; and this is 

 variable in different persons and in the same person, in health, depending somewhat upon 

 the character of the food. The color changes from the yellow, more or less bright, 

 which is observed in the ileum, to the dark yellowigh-brown, characteristic of the faeces. 

 Although the bile-pigment cannot usually be recognized by the ordinary tests, it is this 

 which gives to the contents of the large intestine their peculiar color, which is lost when 

 the bile is not discharged into the duodenum. In a specimen of healthy human fasces, 

 which had been dried, extracted with alcohol, the alcoholic solution precipitated with 

 ether, and the precipitate dissolved in distilled water, we failed to detect the slightest 

 trace of the biliary salts by Pettenkofer's test. In a watery extract of the same faeces, 

 the addition of nitric acid also failed to show the reaction of the coloring matter of the 

 bile. The color of the faeces, however, has been found to vary considerably with the diet. 



The odor of the fseces, which is characteristic and quite different from that of the 

 contents of the ileum, is somewhat variable and is due in part to the peculiar decompo- 

 sition of the residue of the food, in part to the decomposition of the bile, and in part to 

 matters secreted by the mucous membrane of the colon and of the glands near the anus. 



The entire quantity of fasces in the twenty-four hours was found by Wehsarg to be 

 about 4'6 ounces. This was the mean of seventeen observations ; the largest quantity 

 being 10'8 ounces, and the smallest, 2*4 ounces. 



The reaction of the faeces is undoubtedly very variable, depending chiefly upon the 

 character of the food. Marcet found the human excrements always alkaline. "Wehsarg, 

 on the other hand, found the reaction generally acid, but very frequently, alkaline or 

 neutral. 



