342 



DIGESTION. 



of feeces. 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 

 defeecation is accomplished, see p. 223. 



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 Faces. 



Water . 

 Solids 



733-00 

 267-00 



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, 

 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 

 different opinions have been expressed in regard to the 

 subject. Dr. Brinton supposes twelve hours to be occupied 

 by the journey of an ordinary meal through the small intes- 



