DIGESTION AND NUTRITION 333 



are acted upon by the pepsin ferment which is present in 

 the stomach of animals. Peptones are produced by this 

 action. Proteids which escape the action of the peptic 

 ferment are later brought into contact with the tryptic 

 ferment which is present in the pancreas and lower parts 

 of the digestive tract. This ferment acts in an alkaline 

 solution while pepsin requires a slightly acid condition. 

 The proteids which fail to be digested by either the 

 peptic or tryptic ferments are usually expelled as indi- 

 gestible proteids. In normal digestion, the fluids of the 

 stomach are slightly acid while those of the pancreas and 

 intestines are alkaline. For the formation of acids and 

 alkalies, sodium chlorid is essential. From this com- 

 pound, hydrochloric acid, present in the gastric juice, is 

 formed , also the alkaline products in the biliary and other 

 fluids. Sodium chlorid is a normal constituent of the 

 blood and of many of the vital fluids of the body. 



After serving the various purposes in the body, as noted 

 in Section 305, the proteids are expelled as amides in 

 either the solid or liquid excrements, the larger portion 

 being in the form of urea. From the time the proteids 

 are acted upon by the soluble ferments in the digestive 

 tract until their products are expelled from the body as 

 amides, a large number of intermediate substances are 

 formed. Should the proteids fail to undergo normal 

 digestion, poisonous products called ptomaines are pro- 

 duced. 



455- Digestion of the Carbohydrates. Digestion of 

 the carbohydrates begins with the ptyalin ferment of 

 the saliva. Carbohydrate digestion takes place mainly 



