212 HUMAN PHYSIOLOGY 



living and dead. They also contain mucus and cast- 

 off cells from the epithelium of the tract. The usual 

 coloring matter is from the bile but modified by de- 

 composition from its original form. The gases of the 

 colon are mainly produced by fermentation processes. 

 The most offensive and doubtless the most poisonous 

 compounds originate from proteins, a fact which sug- 

 gests one reason for temperance in the consumption of 

 nitrogenous foods. 



Absorption. It may have been gathered from what 

 has been said that the valuable part of the food is re- 

 moved to the circulation before the colon is reached. 

 This is normally true though the colon has probably some 

 reserve power to absorb nutriment. The small in- 

 testine occupies the central position in the process; 

 absorption such as takes place in the stomach is pre- 

 liminary and that from the colon supplementary. It 

 used to be customary to say that no important work 

 along this line was done by the stomach but that is too 

 radical a statement. 



Some absorption of sugar and peptones may occur in 

 the stomach. The organ is, singularly, unable to take up 

 much water. Water taken on an empty stomach seems 

 to pass the pylorus freely and is soon distributed along 

 the small intestine. When water is taken with a meal 

 it is said to slip along the lesser curvature and to take a 

 position in the antrum in advance of the more solid 

 contents. Alcohol is absorbed from the stomach with 

 great speed; it is not necessary to wait for a transfer of 

 the beverage to the intestine to obtain the cerebral 

 reaction. 



The small intestine is specialized for the duty of 

 absorption. This is apparent when we notice the ex- 

 tension of its surface. Examination with the naked eye 

 shows that this is increased by the presence of many 

 cross-folds. Under the microscope further evidence of 

 such an extension is gained. The lining is discovered to 

 be thickly studded with eminences, the villi. These are 



