The metabolism of the breast-fed infant in the first week of life has to be considered briefly. This has been and still is a subject which brought forth many erroneous explanations and conceptions. During the very first days of life the infants suffer from the pressure on the head and brain experienced during birth; they sleep a great deal and do not require much food, wherefore they do not drink much even from the breast of a wet-nurse with abundant milk supply. An infant can only with great effort obtain a small amount of colostrum from the mother's breast. The metabolism is connected with a considerable loss of body weight (about 200 Gm.) (7 ounces) up to the end of the third day, after which the infants arc several days in a state of convalescence.
The occurrences in these first three days may be illustrated by the following observation of Camerer (the elder) which is the most complete that has been made up to the present time. It was made on a girl with a birth weight of 3370 Gm., who was the fifth child, and who was nursed b? her mother.
During the first twelve hours of the second day there was no secre tion of urine at all. The urine of the first and second days is concen trated and particularly rich in uric acid (see p. 392): from the third day on, it becomes more dilute and similar to the urine of later infancy. The insensible perspiration may be estimated to consist of about 15 per cent. carbon and 85 per cent. water vapor. On the first, second, and third days we would have an excretion of carbon amounting to 15 Gm., 12 Gm., and 13 Gin., respectively, while 0.6 Gin., 6 Gm., and 1S Gm. carbon were introduced. In the first days about 20 Gin. of carbon (C of urine and feces included) arc lost, which would mean the decomposi tion of nimut 2.5 (lilt. fat The on Na containing body substance is much less, since the colostrum is very rich in proteids. It may be c:LIculated that nearly 1 Gm. proteid is introduced on the first day and G to 7 Cm. on the second and third day. On the second day, therefore,
a gain of body substance is to he expected, while there !nay be some loss on the first day. The loss of body weight on this first day of about 100 Gm. is composed of 00 Gm. meconin In alld urine and about 100 Gm. insensible perspiration, against winch there is an introduction of 10 Cm. milk. Some decomposed body substance has been passed with the urine, but this cannot be calculated, since at birth a certain amount of preformed urea, etc., is found in the tissue juices and in most cases al ready in the bladder. but these figures show that even on the first duty of life—a veritable day of starvation—the loss On the said body sub stance cannot be more than a few grains of fat: the main constituents of the loss are meconium and body water (see Table 1, p. 367).
The infant sustains the weight on the third day with about 200 Gm. milk: on the fourth, fifth, and sixth the weight increases markedly on an average of 350 Gm. milk. This and the erroneous opinion that every increase of the infant's weight means growth. led to the con clusion that a sufficient growth could be obtained later on with some such "minimal quantity of food"; this would correspond to an introduction of 30 to 50 calories per kilo body weight.
Such ideas, which are justified to a certain degree under patholog ical conditions, are absolutely out of place in regard to the healthy in fant. We have seen that an infant may increase in body weight for a short time, even if moderately underfed, but this entails a loss of body fat, and a normal fat content (about 12 per cent. of the body weight) is necessary to sustain health. The gain of the infant front the fourth to the eleventh day is mostly composed of water and a little fat, as in all cases of convalescence. On the eleventh day it may have reached the birth weight on water and fat, and beside it may have used up about 4 Gni. X, which is equal to 30 Gm. body substance. Front now on, the gain and fat will be smaller.