39$ FOOD AND DIGESTION 



hours for the first appearance of the food remnants at the end of the pelvic 

 colon where it is retained until the bowels are opened. Of course, assuming 

 an empty canal ahead of the moving material, the undigested and waste 

 products of the food require on an average from eighteen to twenty-two 

 hours for the passage of the entire alimentary tract. The earliest possible 

 moment at which food remnants can appear in the feces will be when de- 

 fecation occurs just after those remnants which passed immediately through 

 the stomach have reached the ascending colon, say five hours. On the other 

 hand, assuming that a meal is taken on an entirely empty canal, the food 

 remnants will not produce the reflex for opening the bowels until they reach 

 the pelvic colon. Hence if the bowels are open only once in twenty-four 

 hours, it is obvious that the remnants of a meal may not be passed before 

 thirty-six to thirty-eight hours. 



