1. Anatomy

The alimentary tract of the newborn infant differs in many details from that of the adult. The mouth is free from teeth until the sixth or eighth month. This naturally restricts the food to liquids for the greater part of the first year. The stomach at birth has a vertical position, extending from the tenth dorsal vertebra to a point midway between the lower end of the sternum and the umbilicus, the pylorus lying usually in the midline, less often to the right or to the left. This position, together with an imperfect development of the fundus, probably favors the regurgitation and vomiting that is so frequent during the earlier months. The pylorus is relatively wide in infancy and especially at birth. The capacity of the stomach has been carefully studied on both the living child and the cadaver, and has been placed at about one to two ounces at birth; two to three ounces at the end of the first month; six ounces at the sixth month; and from nine to ten ounces at the end of the first year. Too much importance has probably been given to these figures as measures of the size of single feedings in artificially fed infants, because different stomachs vary considerably in size, and in larger feedings some of the food has passed beyond the pylorus before the last of it has been taken.

The intestine is relatively larger than in the adult. This is especially true of the sigmoid flexure, which varies widely in different individuals, and is situated wholly extrapelvically. The musculature of the intestine is relatively thin, and this is probably related to the frequency of colic in infancy. Histologically, both stomach and intestine differ only in unimportant details from that of the adult.

The liver is relatively very large at birth, two and one half times that of the adult.

2. Physiology

Practically all functions are present at birth, but most of them are still in a developmental and comparatively imperfect state. The digestive ferments, salivary, gastric, pancreatic, hepatic, and enteric, are all found, but many are very weak at first. The ptyalin of the salivary secretions, for example, is present at birth, but is not very active till after the fourth or fifth month. The liver secretes bile from the middle of embryonic life. The normal acid of the stomach is hydrochloric acid, as in the adult; and other acids, such as lactic acid, that have been considered normal by some, are probably always pathological. Hydrochloric acid not only aids in digestion, and in the coagulation of casein by rennin, but has probably a decided germicidal action.

3. Bacteriology

Bacteria are found in the previously sterile alimentary tract of the newborn infant within four to ten hours after birth. As soon as the child gets milk from the breast, the intestinal flora begins to assume a definite form that is present in every infant that is properly digesting human milk. The prevailing bacterium of its so-called "physiological fecal flora" (Moro) is a "gram-positive," long, slender rod, pointed at both ends, often branching, especially in culture, giving it the name of Bacillus biftdis communis (Tissier). Many other varieties of bacteria occur in lesser numbers. This definite flora accounts for the uniform condition of the bowels in breast-fed infants. The predominant action is fermentative, forming gases and acids that favor peristalsis and looseness of the bowels. When any other food is given, such as cow's milk, the bacterial flora changes and becomes

> polymorphous and varying. The importance of this will be seen later.