322 PHYSIOLOGY OF ALIMENTATION 



of the digestive ferments found here, it reduces still more 

 markedly that of the ferments found in the bacteria,- for the 

 growth of these is decidedly kept in check throughout this 

 hollow viscus, and their putrefactive action upon the food 

 (which, under pathological conditions, may become of a 

 serious character) prevented to a large extent. 



The amount of faeces cast off by an animal is depend- 

 ent upon the amount and character of the food consumed. 

 Other things being equal, a large amount of food will yield a 

 greater amount of excrementitious material than a smaller one. 

 The extent to which a food can be absorbed is however of 

 great importance. Fine white-flour breads are, for example, 

 absorbed more perfectly than rye or whole-wheat breads, 

 because they represent more nearly pure starch,in a form that 

 can be acted upon by the digestive ferments. Mashed potatoes 

 yield less faecal matter than boiled potatoes, for in the former 

 the cellulose membranes surrounding the cells are more per- 

 fectly broken than in the latter, and the starch absorption is 

 in consequence more perfect. Because of the large amount 

 of cellulose they contain, the vegetable diets in general yield 

 a larger amount of faecal matter than meat diets. The faeces 

 do not, however, represent only remnants of food that can- 

 not be digested, but also a certain amount that can be, but, 

 for various reasons, has not been digested. In addition it 

 must not be forgotten that the secretions of the gastro- 

 intestinal tract itself and of the glands connected with it 

 contribute largely toward making up the body of the faeces. 



The color of the faeces is variable. A meat diet yields 

 dark, one of bread, lighter faeces. The color is determined in 

 large part by the bile, being gray in its absence, yellowish or 

 yellowish brown in its presence. For the most part, it is not 

 the bile pigments themselves that give this color, but certain 

 of their derivatives formed after the bile has escaped into the 

 intestine. 



