172 PHYSIOLOGICAL CHEMISTRY 



averages 15-25 grams. This amount may vary much with the 

 nature of the food. The feces are colored chiefly by derivatives 

 of the bile pigments, but these substances themselves do not 

 occur here ordinarily. If the flow of bile into the intestine is 

 inhibited, the feces are gray, due to the presence of fat and the 

 absence of pigments. Many drugs color the feces black, green, 

 yellow, etc. 



