COMPOSITION OF FJ2CES. 347 



By these means the contents of the large intestine, as 

 they proceed towards the rectum, become more and more 

 solid, and losing their more liquid and nutrient parts, 

 gradually acquire the odour and consistence characteristic 

 of faeces. After a sojourn of uncertain duration in the 

 rectum, they are finally expelled by the contraction of its 

 muscular coat, aided, under ordinary circumstances, by the 

 contraction of the abdominal muscles. 



For a description of the mechanism by which the act of 

 defaecation is accomplished, see p. 234. 



The average quantity of solid faecal matter evacuated by 

 the human adult in twenty-four hours is about five ounces ; 

 an uncertain proportion of which consists simply of the 

 undigested or chemically modified residue of the food 

 and the remainder of certain matters, which are excreted 

 in the intestinal canal. 



Composition of 

 Water .......... 733' 



Solids . . ........ 267-00 



Special excrementitious constituents: Excretin, 



excretoleic acid (Marcet), and stercorin 



(Austin Flint). 

 . Salts : Chiefly phosphate of magnesia and phos- 



phate of lime, with small quantities of iron, 



soda, lime, and silica. 

 Insoluble residue of the food (chiefly starch, ) 267.00 



grains, woody tissue, particles of cartilage, 



and fibrous tissue, undigested muscular fibres 



or fat, and the like, with insoluble substances 



accidentally introduced with the food. 

 Mucus, epithelium, altered colouring matter of 



bile, fatty acids, etc. / 



The time occupied by the journey of a given portion of 

 food from the stomach to the anus, varies considerably even 

 in health, and on this account, probably, it is that such 



