Quetelet weighed ten individuals of male and female sex of all periods of age during the total time of growth. Naturally, these obser vations are insufficient in many regards, and it is surprising that even to-day they are used exclusively in many statistics. Quetelet had many followers, among whom, Bowditch for instance, made a very careful statistical study of growth; his observations were made on several hundred individuals classified according to age. Very few continuous observations of the growth of individual children were at our disposal until about 25 years ago. Since then Camerer (the elder) has collected and worked out a rich material of very carefully observed individual cases, and at present several hundred cases of the first years of life are at our service. The figures given in the following are chiefly based on these observations.
The birth weight of normal healthy German boys of the middle classes is about 3-100 Gm., that of girls 3200 Gm. The sex of the infants, the social condition and race of the parents, the term of birth. the num ber of previous births, and other factors, exercise a considerable influ ence on the birth weight and are not taken sufficiently into considera tion. For instance, the average birth weight is often given as 3000 Gin. The reason for this is that the first and most frequent investigations with regard to the birth weight were conducted in maternity hospitals. Nearly all the mothers admitted to such institutions live in poor circum stances and frequently do hard physical work until a short time before parturition. According to the data of Fehling, the birth weight of children of W0111C11 working in factories is the lowest, then follow those of servant girls, seamstresses. and shop girls. The birth weight of such infants is relatively low on account of peculiar conditions, and cannot be taken as normal.
The injuries sustained by the infants during parturition cause a loss of weight of about 200 Gm. during the first days of life. The first (lay participates in this loss with about two-thirds, the second \•ith one third. But even from the first day on, a small gain of weight is noted in most cases, and the infants regain their birth weight on the eighth to the tenth day. From then on the gain in weight proceeds The daily gain of breast-fed infants is about 30 Gin. to the fourth week; 26 to 2S Gm. from the fifth to the twelfth week; 20 to 24 Gm. from the 13th to the 20th week; HI to 1ti Gm. from the 21st to the 36th week; 10 to 15 Gm. from the 37th to the 52nd week. Accordingly, the weight of breast-fed infants is about 4000 Gin, at the end of the first month: at the beginning of the fifth month the weight is about double the birth weight, and at the end of the first year it is about three times the birth weight. The difference in the weight of boys and girls increases
gradually more and more in favor of the boys and at the end of the first year it amounts to about 500 Gm., so that at this time the boys weigh about 10.2 kilos, the girls 9.7 kilos.
The course of the growth during the first year can best he shown graphically. The curve of growth shows in the case of breast-fed in fants (see Fig. 63, and the explanation. on p. 420) an uninterrupted rise with gradually increasing acceleration. except for the fall in the first days of life, the reasons for which have been discussed. In the third quartet' a second insignificant inhibition of growth occurs, with a conse quent transitory acceleration; this inhibition is due to the weaning and to the development of the teeth. Artificially fed infants remain consid erably behind the breast-fed in the first quarter. In this period their daily growth is only about 22 Gm.. but until about the sixth month it keeps itself rather constantly on this level. while the daily growth of the breast-fed infants increases from the fourth week on, as previously pointed out. Irrational and disorders of nutrition are responsible for the small gain of the artificially fed infants during the first quarter. The constancy of the gain in the second quarter is to he regarded as a manifestation of convalescence. At the end of the first year the artifi cially fed infants reach about the same weight as the breast-fed ones, provided the feeding has been rational. Therefore, the weight at the end of the first year is not dependent on the kind of food but on the birth weight. This becomes particularly clear in the case of infants with an abnormally small birth weight. Such children may stay behind in fants with normal birth weight at the end of the first year and remain considerably behind for many years to come (see Fig. 62); as to whether they were breast-fed or raised artificially makes no difference.
The cause of the gain in weight during the first year of life under the different conditions is best illustrated in Fig. 63. The uppermost, red curve indicates the gain in weight of fifty-seven healthy breast-fed boys under continuous observation; the second, yellow curve, the gain of 114 breast-fed boys and girls; the third, green curve, the gain of S5 artificially fed boys and girls, all of these infants weighing at birth be tween 3 and 4 kilos; the fourth, black curve, the gain of 24 boys and girls with an average birth weight of 2400 Gm.; the fifth, dotted curve, the gain of fourteen boys and girls with a birth weight below 2 kilos. Furthermore, these observations show that the frequently constructed "normal curve for the growth in the first year of has only a very limited value.