66 DIGESTION 



bodies giving odor to the feces. The color is due to hydro- 

 bilirubin. 



Summary of Digestion. Protein food is but slightly 'altered 

 in the mouth, and only in a mechanical way. The muscle 

 fibers of meat, for instance, are crushed, and their connective- 

 tissue sheaths broken by the action of the teeth, thus becoming 

 somewhat lighter in appearance. Mixed with saliva, which 

 has no digestive action on these foodstuffs, they are passed 

 into the stomach and brought under the influence of the gastric 

 juice. By the combined action of the hydrochloric acid and 

 the ferment pepsin proteins pass through a series of steps 

 which consist essentially of a taking up of water and a break- 

 ing into simpler bodies. Syntonin, the first product formed, 

 becomes converted into proto- and deuteroproteoses, and peptones. 

 But the food does not remain in the stomach long enough 

 for all the proteins to be changed to peptones. Some pass 

 through entirely unchanged, while others have reached various 

 stages of digestion. 



In the intestine the energetic action of the trypsin changes 

 those proteins that reach it to peptones more quickly than 

 does the gastric juice, the intermediate stage of the primary 

 proteoses being omitted. The peptones are still further changed 

 to comparatively simple amino bodies and nitrogenous bases. 

 The most important of these are leucin and tyrosin. Finally, 

 in the large intestine proteins that still remain are attacked 

 and decomposed by bacteria, but some escape and are ejected 

 in the feces. 



Albuminoids. These bodies undergo changes analogous to 

 those of proteins; the conversion in the stomach reaches chiefly 

 only the gelatose stage, but the pancreatic juice produces 

 gelatin peptones. 



Carbohydrates. The time that starches remain in the mouth 

 is too short for the ptyalin of the saliva to produce any very 

 great changes, but the digestion may continue for some time 

 within the stomach. The acidity of the gastric juice later 

 stops all carbohydrate digestion, and it is not until the food 

 reaches the intestine that the arnylopsin of the pancreatic 

 juice actively begins the conversion of starches. The action 

 of ptyalin and amylopsin is identical. Starch is modified into 

 soluble starch, and then begin a series of hydration changes 



