THE CHEMISTRY OF DIGESTION 



421 



finally prepared for absorption. By the cnzyms thus far de- 

 scribed none of the carbohydrate digestion is carried to comple- 

 tion, and only part of the proteins are made ready for use, for 

 proteose and peptone are not end products, but only intenncdiate 

 .products of digestion. Fats are the only foods which do not re- 

 quire the aid of the succus entericus for their complete digestion. 



The digestive enzyms of the succus entericus are four; one pro- 

 teolytic, erepsin, which acts particularly on proteoses and pep- 

 tones, thus completing the work of the gastric pepsin; and three 

 so-called inverting enzyms, which change double sugars to single 

 sugars. These enzyms are specific in their action, each affecting 

 only its particular sugar. Maltase inverts maltose, thus com- 

 pleting the starch digestion begun by ptyalin and amylopsin; 

 invertaSe splits cane-sugar, and lactase converts milk-sugar, lac- 

 tose, to- single sugar. The result of the action of these three en- 

 zyms is to bring all the carbohydrates of the food, except cellu- 

 lose, into the condition of single sugars, in which form they are 

 ready for the use of the Body. 



Summary of the Digestive Process. The chemical reactions by 

 which the various food-stuffs are made ready for absorption and 

 use by the Body can be conveniently summarized in tabular form : 



1 Intermediate products. 



2 Final products. 



Bacterial Digestion. The human intestines normally contain 

 enormous numbers of bacteria. In the small intrstim- these an- 

 for the most part fermentative bacteria; organisms having the 



