346 PHYSIOLOGY CHAP. 



is partly due to biliverdin and bilirubin (Lesage), which are 

 normally reduced in adults. 



The obnoxious odour of the faeces increases with the putrefac- 

 tive processes of the intestine, and depends principally on the 

 development of scatole (Brieger). With a flesh diet the faecal 

 odour is more pronounced than with a vegetable diet. 



The chemical and morphological composition of the faeces are 

 so variable that it would be tedious to quote the analysis given for 

 individual cases. Halliburton distinguishes the following groups 

 of materials : 



(a) Undigested Food-stuffs. Neutral fats, carbohydrates, and 

 also proteins with a superabundant protein diet. It should be 

 noted that unaltered protein is never found in the faeces with a 

 moderate diet (Hoppe-Seyler). 



(b) Indigestible Food-stuffs. Cellulose, keratin, mucin, nuclein, 

 chlorophyll, gum, resin, cholesterol, phosphates and other bases, 

 particularly calcium. 



(c) Food-stuffs difficult of Digestion. Granules of raw starch, 

 fragments of elastic tissue, tendon, cartilage and (especially with a 

 superabundant flesh diet) more or less unaltered muscle fibres. 



(d) Waste Products of Food-stuffs. Groups of aromatic sub- 

 stances (scatole, indole, phenol, etc.) formed by putrefactive pro- 

 cesses and probably tending, when formed, to check or arrest these 

 processes ; groups of fatty acids, (formic, acetic, butyric, isobutyric, 

 yalerianic, capronic acid, with others such as lactic, malic, succinic, 

 etc., in a free state or combined with ammonia and other bases) ; 

 haematin from decomposition of haemoglobin ; insoluble and non- 

 absorbable soaps of calcium and magnesium ; stercorin, which 

 according to Flint, is a decomposition product of cholesterol ; 

 excretin, as described by Marcet for human faeces, the composition 

 of which is wholly unknown. All these products originate not in 

 the activity of the digestive enzymes, but in the fermentative and 

 putrefactive processes effected by the intestinal bacteria. 



(e) Substances converted and not reabsorbed, of the Bile and 

 other Intestinal Secretions. Mucin, cholalic acid, cholesterol, 

 lecithin, which partly come from the foods, hydrobilirubin and 

 stercobilin, which are reduction products of the bile pigments, and 

 no longer give Gmelin's reaction. The co-operation of the pancre- 

 atic juice seems necessary in the formation of these pigments, since 

 in two cases of obstruction of Wirsung's Duct, Walker found no 

 stercobilin in the excreta, which had the clay colour characteristic 

 of the faeces in jaundice, although the liver was healthy and the 

 bile flowed freely into the intestine. 



(/) Bacteria of different Kinds, Epithelial Cells and Detritus. 

 Great quantities of bacteria are present, Bacterium coli commune 

 (as we have seen) largely predominating. The epithelial cells 

 shed by the mucous membrane are sometimes almost intact, the 



