284 DIGESTION 



increases with age. In the very young the stomach 

 is simply a reservoir for the food, when it is passed 

 into the small intestine. Pepsin has been found in 

 the infant's stomach, and some hydrochloric acid, 

 which accounts for its acidity. And in early life some 

 lactic acid. 



Rennin plays an important part in infant digestion. 

 It is the ferment which coagulates mothers' and cows' 

 milk, splitting the casein into a solid mass (clot), 

 and whey (the liquid portion). Intestinal digestion is 

 not very active in infancy, the ferment from the 

 pancreas acting more like ptyalin in the saliva of 

 the adult. Absorption of nourishment takes place 

 from the mucous membrane of the intestines. In 

 breast-fed infants 2 to 5 per cent, of the fat and 

 protein pass directly through the intestines; in bottle- 

 fed ones, 1 to 3 per cent, more for the fats, and a 

 still greater increase for the proteins (Appelmann) . 

 Numerous bacteria are present in the intestinal canal 

 of infants. They may play some part in digestion; 

 however, it is one on which neither life nor health 

 depends. 



QUESTIONS 



1. What organs constitute the digestive apparatus? 



2. Describe mastication; insalivation. 



3. Name the glands which secrete saliva. 



4. Is the reaction of saliva acid or alkaline? 



5. Describe the physiologic (physical) action of saliva; chemical. 



6. What change takes place in the bloodvessels of the mucous 

 membrane of the stomach during digestion? 



7. What part do the muscular coats of the stomach play during 

 digestion? 



8. How is the food held within the stomach while the walls 

 contract upon it? 



9. What do you understand by the term chyme? 



10. How long does digestion last in the stomach? 



11. What juice is secreted from the glands of the mucous mem- 

 brane of the stomach during digestion? 



12. Do the blood or lymph vessels absorb any nourishment from 

 the stomach? 



13. Is gastric juice acid or alkaline in reaction during digestion? 



