394: DIGESTION. 



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 absorp- 

 tion of the liquid portions. As a rule, the consistence is 

 great in proportion to the length of time that the faeces re- 

 main in the large intestine; and this is variable in different 

 persons and in the same -person, in health, depending some- 

 what 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 yellowish-brown, 

 characteristic of the faeces. Though 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 faeces which 

 had been dried, extracted with alcohol, the alcoholic solution 

 precipitated with ether, and the precipitate dissolved in dis- 

 tilled 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. 1 The color, 

 however, has been found to vary considerably with the diet. 

 Wehsarg has shown that with a mixed diet, the color is yel- 

 lowish-brown ; with an exclusively flesh-diet, it is much 

 darker ; and witli a milk-diet, it is more yellow. 8 



The odor of the faeces, 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 decomposition 

 of the residue of the food, in part to the decomposition of 



1 Prof. Dalton, in comparative analyses of the contents of the small and the 

 large intestine in dogs, in which the matters were first evaporated to dryness, the 

 residue extracted with absolute alcohol and then precipitated with ether, always 

 detected biliary matters by Pettenkofer's test in the contents of the small intes- 

 tine, while they were invariably absent in the contents of the large intestine. 

 (Treatise on Human Physiology, Philadelphia, 1864, p. 193.) 



2 Op., cit. 



