102 NUTKlYIOfrAV PHYSIOLOGY 



The action of the skeletal muscles at this time resembles 

 that in vomiting, but is, of course, much more largely 

 voluntary and more sustained in character. 



The Feces. Two classes of material may be mingled in 

 the contents of the colon: the residues of the diet and the 

 excretions of the alimentary tract including its glands. 

 The proportion existing between these two is a variable 

 one. Physiologists have lately come to regard the food 

 residues in the feces, under average conditions, as forming 

 a less prominent element than was formerly supposed. 

 A correspondingly increased importance is assumed by the 

 excretions. The feces passed during long fasting are evi- 

 dently made up exclusively of bodies of the second class. 

 Such feces, while small in amount, may have practically 

 the same composition as those formed upon a moderate 

 and digestible diet. This suggests that the increased 

 quantity which results from eating does not imply a greater 

 residue so much as a greater production of secretions along 

 the active canal. A mass very much like normal feces 

 may gather in an isolated loop of the intestine to which no 

 food is admitted. Among the substances originating from 

 the tract rather than from the food are the modified bile- 

 pigments, cholesterin or its derivatives, mucus, and de- 

 tached cells. 



Bacteria, living and dead, intimately mixed with the 

 numerous products of their own life activity, are promi- 

 nent in the bowel discharges. These organisms can in one 

 sense be said to have their origin in the diet, since that was 

 the source of the primary seeding or infection. From 

 another point of view they are largely developed at the 

 expense of the body itself, for they have multiplied in the 

 intestine and may have lived in part upon its secretions as 

 well as upon the food. The gases of the colon are due to 

 them. 



True food residues include the indigestible matter of the 

 diet and some undigested food normally but little of the 

 latter. Absorption is strikingly efficient with most sub- 

 jects and reasonable diets. Not more than 5 per cent, of 



