DIGESTION IN INFANTS 283 



into the rectum. This gives rise to the sensation 

 felt prior to defecation, then the longitudinal and 

 circular fibers of the rectum contract, and pressing 

 downward on the mass, force it through the relaxed 

 sphincter ani muscles. The wall, contraction of the 

 diaphragm, the muscles of the abdomen levator ani 

 and coccygeus, sphincter ani muscles all aid in the 

 expulsion of the feces. 



Digestion in Infants. The Saliva. This is very 

 scanty at birth, but gradually increases. At the 

 fourth month it is of sufficient quantity and of such 

 strength as to be capable of digestion. When the 

 teeth are erupted there is a marked increase in saliva, 

 and from the eighth to tenth month it will digest a 

 small amount of starch. 



The Capacity of the Stomach. It is essential for the 

 nurse to acquire a knowledge of the capacity of the 

 infant's stomach from birth to the fourteenth month. 

 The following capacities may vary somewhat, and the 

 nurse's judgment must influence her in certain cases 

 if called upon to prepare a bottle for the baby, in 

 regard to the quantity of modified milk to be used in 

 each feeding (according to Holt) : 



Age. Average capacity. 



Birth 1 . 20 ounces 



Two weeks 1 . 50 ounces 



Four weeks 2 . 00 ounces 



Six weeks 2.27 ounces 



Eight weeks 3 . 37 ounces 



Ten weeks . . . - 4 . 25 ounces 



Twelve weeks 4.50 ounces 



Fourteen to eighteen weeks . . . . . 5 . 00 ounces 



Five to six months 5 . 75 ounces 



Seven to eight months 6 . 88 ounces 



Ten to eleven months . 8 . 14 ounces 



Twelve to fourteen months 8 . 90 ounces 



Gastric Digestion. Breast-fed babies retain the milk 

 in the stomach for about an hour after nursing, 

 bottle-fed babies about one hour and a half; this 



