CONTENTS OF THE LARGE INTESTINE. 263 



the action of micro-organisms ; but the effect of these products is to kill the 

 micro-organisms and thus to limit the putrefactive processes. The produc- 

 tion of indol, skatol and phenol is arrested by the action of certain drugs, 

 ;such as calomel, salicylic acid and other so-called antiseptics. The fermenta- 

 tive changes in the intestines involve the production of certain gases, which 

 will be described at the close of this chapter. 



CONTENTS OF THE LARGE INTESTINE. 



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

 they become 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 notable changes relate to consistence, color and odor. The odor, 

 especially, of normal faecal matter is characteristic. 



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 

 faeces 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 yellowish-brown characteristic of the 

 faeces. Although the bile-pigment can not usually be recognized by the ordi- 

 nary 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 duode- 

 num. In a specimen of healthy human faeces, which had been dried, ex- 

 tracted with alcohol, the alcoholic extract precipitated with ether and the 

 precipitate dissolved in distilled water, it was impossible to detect the biliary 

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

 tion of nitric acid failed to show the reaction of the coloring matter of the 

 bile (Flint, 1862). The color of the faeces, however, varies considerably 

 under different forms of diet. With a mixed diet the color is yellowish- 

 brown ; with an exclusively flesh-diet it is much darker ; and with a milk- 

 diet it is more yellow (Wehsarg). 



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

 that of the contents of the ileum, is variable and is due in part to the pecul- 

 iar decomposition 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 faeces in the twenty-four hours, according to Weh- 

 sarg, is about 4*6 ounces (128 grammes). This was the mean of seventeen 

 observations ; the largest quantity being 1O8 ounces (306 grammes), and the 

 smallest, 2-4 ounces (68 grammes). 



The reaction of the faeces is variable, depending chiefly upon the char- 

 acter of the food. Marcet found the human excrements always alkaline. 

 Wehsarg, on the other hand, found the reaction generally acid, but very fre- 

 quently it was alkaline or neutral. 



The proportions of water and solid matter in the faeces are variable. Ber- 



