

CHAP. XXV.] THE FAECES. 267 



The ordinary expulsive actions of the rectum are due simply to 

 the stimulus of distension acting upon the circular muscular fibres. 

 When the mucous membrane is irritated, as under the influence of 

 a purgative, or in diseased states, the action of the rectum takes 

 on the character of a reflex act, excited by the contact of the faeces 

 with the irritable mucous membrane. 



The quantity of the faeces is determined partly by the quantity 

 and quality of the food, partly by the quantity of the secretions 

 poured into the canal. If the food exceed much what the alimen- 

 tary canal can reduce and absorb, the quantity of faeces will be 

 considerable. Vegetable food produces a greater amount of faeces 

 than animal, because the former is eaten in greater quantity than 

 the latter, and because it contains much that is incapable of reduc- 

 tion in the stomach or bowels. The faeces of carnivora are always 

 absolutely and relatively smaller in quantity than those of herbivora. 

 And those tribes of mankind who feed chiefly on vegetable food 

 make large quantities of faeces. 



The ordinary quantity of faeces passed daily by men in health 

 is about five or six ounces ; so that if we assume thirty-five ounces 

 as about the average quantity of food taken in twenty-four hours, 

 it may be inferred that at least thirty ounces are appropriated to 

 the various purposes of the oeeonomy. 



Berzelius's analysis of faeces gives the following result : 



Water 73'3 



Matters soluble in water : Bile . . . . 0-9 j 



Albumen . . . 0'9 f 

 Extractive . . 27 f 5 ' 7 

 Salts . . . 1-2 ) 



Insoluble residue of the food 7'0 



Insoluble matters derived from the intestinal canal, as 

 mucus, biliary resin, fat, and a peculiar animal matter 14-0 



100-0 



The ashes of human faeces yield, according to Berzelius and 

 Enderlin, chloride of sodium, sulphate of soda, tribasic phosphate 

 of soda, phosphate and sulphate of lime, phosphate of magnesia, 

 phosphate of iron, and silica. The nature and quantity of these 

 salts, however, vary with the quality of the food. 



A remarkable property of the faeces is their peculiar odour. Upon 

 what this depends has not yet been satisfactorily ascertained. It 

 seems very doubtful that it can depend on any decomposition of 

 the bile; for under certain circumstances, when bile is deficient 



T 2 



