The alimentary tract of the new-born infant differs in many ways from that of the adult.
As compared with other mammals, the human infant is the most helpless and undeveloped and therefore the most delicate and easily affected. It is practically dependent on its mother for nourishment which will completely supply its needs.
The capacity of the stomach, after careful study, has been placed at from 1 to 2 ounces at birth, 2 to 3 ounces at the end of the first month, 6 ounces at the 6th month, and from 9 to 10 ounces at the end of the first year. This is simply an average guide, as stomachs vary somewhat in size. Quantities somewhat larger than the foregoing are sometimes fed, but some of the food has passed beyond the pylorus before the last of it is taken. Digestion begins as soon as the food enters the stomach.
The secretion of bile begins within 12 hours after birth, increases rapidly, and is fully established within a week or ten days.
The pancreatic ferments which digest starches and sugar are present in the new-born, although scanty; the sucking movements of the child when nursing exercise the salivary glands so that saliva is secreted; but starch digestion is not completed in the mouth, hence starch and a greater proportion of sugar than is in the mother’s milk are difficult for the infant to digest.
The intestines, when compared with the length of the body, are relatively long in infants, but the muscular coat is comparatively weak; digestion is therefore relatively slow and more subject to derangement by substances that influence peristalsis.
The fact that infants vomit with comparatively little effort, the food overflowing from an overloaded stomach, is due to the relatively feeble closure of the cardiac orifice.
The stomach contents are kept germ-free by the secretion of hydrochloric acid and the upper intestine is nearly free from bacteria in breast-fed infants, because of the antibacterial nature of the intestinal secretion. In some digestive disturbances this safeguard fails and bacteria develop rapidly.
Intestinal Disturbances
Intestinal disturbance in the breast-fed infant is most often caused by overfeeding, the infant often nursing too frequently, thereby emptying the breasts and securing a high fat ratio. Frequent nursing does not give the stomach time to empty and thus digestive disturbances are apt to occur. Therefore, as a means of relieving intestinal trouble in the infant, nursing at regular intervals and not too frequently, is of much importance.