374 VETERINARY PHYSIOLOGY 



fate of the cholalic acid is not known, but it is supposed to 

 be excreted in the faeces. 2. The pigments undergo a change 

 and lose their power of giving Gmelin's reaction. They appear 

 in the faeces as what may be called stercobilin. It is probably 

 formed by reduction of bilirubin in the intestines as the result 

 of the action of micro-organisms. 3. The cholesterin is passed 

 out in the faeces. 



Faeces 



The materials not absorbed from the intestine, whether these 

 are derived from the food or from the alimentary canal, are 

 thrown off from the rectum as the faeces. In fasting animals 

 these are passed at long intervals, and consist of mucin, shed 

 epithelium, the various products of the bile constituents, and 

 inorganic salts. In feeding animals the amount and character 

 of the faeces depends largely upon the amount and character 

 of the food, and upon the bacteria which are growing in the 

 large intestine. The unabsorbed material, as it passes down 

 the large intestine, becomes inspissated from the absorption of 

 water, but, if much undigested matter is present, water may 

 also be added, and the consistence of the faeces may thus be 

 varied. The colour is normally brown, from the haematin 

 of the flesh eaten, while the sulphide of iron formed by the 

 splitting of the haematin compounds in the intestine may 

 make them darker in colour. On a milk diet they are 

 light yellow in colour, and if a large excess of fatty food is 

 taken, or if fat is not absorbed, as in jaundice, they become 

 clay coloured. The derivatives of the bile pigments play but 

 a small, part in colouring the faeces. 



The reaction of the faeces varies. Usually the outside of the 

 mass is alkaline from the alkaline secretion of the intestine, 

 while the inside is acid from the free fatty acids and other 

 acids formed by the action of such acid-forming bacteria as the 

 bacillus coli communis. The amount of solid faeces depends on 

 the amount of food, and on a vegetable diet, from the presence 

 of undigested cellulose, the amount is very much greater. 



The solids of the faaces of a feeding animal consist of 

 the same constituents as the faeces in a fasting animal, with 

 the addition of all the undigested constituents of the food 

 elastic and white fibrous tissue, remains of muscle fibres, often 



