524 THE ABSORPTION OF FOOD [CH. XXXIV. 



the main factor. By removal of the epithelium the normal ratio of peptone to 

 glucose absorption is upset, and the value tends to approach that of diffusion of 

 these substances through parchment paper into serum, 



The faeces are alkaline, and contain the following substances : 



1. Water : in health from 68 to 82 per cent. ; in diarrhoea it is 

 more abundant still. 



2. Undigested food; that is, if food is taken in excess, some 

 escapes the action of the digestive juices. On a moderate diet 

 unaltered proteid is never found. 



3. Indigestible constituents of the food : cellulose, keratin, mucin, 

 chlorophyll, gums, resins, cholesterin. 



4. Constituents digestible with difficulty: uncooked starch, 

 tendons, elastin, various phosphates, and other salts of the alkaline 

 earths. 



5. Products of decomposition of the food : indole, skatole, phenol, 

 acids such as fatty acids, lactic acid, etc. ; haematin from haemoglobin ; 

 insoluble soaps like those of calcium and magnesium. 



6. Bacteria of all sorts, and debris from the intestinal wall ; cells, 

 nuclei, mucus, etc. 



7. Bile residues : mucus, cholesterin, traces of bile acids and their 

 products of decomposition, stercobilin from the bile pigment. 



The average quantity of solid faecal matter passed by the human 

 adult per diem is 6 to 8 ounces. 



Meconium is the name given to the greenish-black contents of 

 the intestine of new-born children. It is chiefly concentrated bile, 

 with dttris from the intestinal wall. The pigment is a mixture of 

 bilirubin and biliverdin, not stercobilin. 



