FOOD AND DIGESTION. 4Q5 



oi faces. After a sojourn of uncertain duration in the sigmoid flexure 

 of the colon, or in the rectum, they are finally expelled by the act of 

 defsecation. 



The average quantity of solid fascal matter evacuated by the human 

 adult in twenty-four hours is about six or eight ounces. 



COMPOSITION OF FAECES. 



The amount of water varies considerably, from 68 to 82 per cent and 

 upward. The following table is about an average composition: 



Water .'<_'; 733 00 



Solids, comprising : 



a. Insoluble residues of the food, uncooked starch, 



cellulose, woody fibres, cartilage, seldom mus- 

 cular fibres and other proteids, fat, cholesterin, 

 horny matter, and mucin .... 



b. Certain substances resulting from decomposition 



of foods, indol, skatol, fatty and other acids, 

 calcium and magnesium soaps 



c. Special excrementitious constituents : Excretin, 



excretoleic acid (Marcet) , and stercorin (Austin 



Flint) 



d. Salts : Chiefly phosphate of magnesium and phos- 



phate of calcium, with small quantities of iron, 

 soda, lime, and silica 



e. Insoluble substances accidentally introduced with 



the food 



f . Mucus, epithelium, altered coloring matter of bile, 



fatty acids, etc. . 



g. Varying quantities of other constituents of bile, and 



derivatives from them . 



267.00 



1000.00 



The Gases contained in the Stomach and Intestines. Under ordi- 

 nary circumstances, the alimentary canal contains a considerable quan- 

 tity of gaseous matter. Any one who has had occasion, in a post-mortem 

 examination, either to lay open the intestines, or to let out the gas 

 which they contain, must have been struck by the small space afterward 

 occupied by the bowels, and by the large degree, therefore, in which the 

 gas, which naturally distends them, contributes to fill the cavity of the 

 abdomen. Indeed, the presence of air in the intestines is so constant, 

 and, within certain limits, the amount in health so uniform, that there 

 can be no doubt that its existence here is not a mere accident, but in- 

 tended to serve a definite and important purpose, although, probably, a 

 mechanical one. 



Sources. The sources of the gas contained in the stomach and bowels 

 may be thus enumerated: 



1. Air introduced in the act of swallowing either food or saliva; &. 

 Gases developed by the decomposition of alimentary matter, or of the 

 secretions and excretions mingled with it in the stomach and intestines; 

 3. It is probable that a certain mutual interchange occurs between the 



