274 DIGESTION. 



Composition of Fences. 



Water, 733 00 



Solids, 267.00 



Special excreientitious constituents : Excretin, 

 excretoleic acid (Marcet), and steroorin 

 (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 coloring matter of bile, 

 fatty acids, &c. j 



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 intestine, and twenty- 

 four to thirty-six hours by the passage through the large 

 bowel. 



On the Gases contained in the Stomach and Intestines. 



It need scarcely be remarked that, under ordinary circum- 

 stances, the alimentary canal contains a considerable quantity 

 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 afterwards occupied by the bowels, and by the 

 large degree, therefore, in which the gas, which naturally dis- 

 tends them, contributes to fill the cavity of the abdomen. In- 

 deed, 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 ac- 

 cident, but intended to serve a definite and important purpose, 

 although, probably, a mechanical one. 



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. 



2. Gases developed by the decomposition of alimentary 



