Post-natal Loss of Weight in Infants. 



67 



normal curve of extra-uterine growth. It represents the continu- 

 ation of this latter curve backwards from the time of birth. In 

 the same way, plotting the weights of children born somewhat 

 later than the average term, we obtain a curve which is identical 

 with and overlies the normal curve of extra-uterine growth for the 

 period which it covers. By combining these various data a con- 

 tinuous curve of intra- and extra-uterine growth is obtained 

 without any interruption due to the post-natal loss of weight which 

 normally occurs during the first week after birth. From this we 

 can readily estimate what would be the average rate of growth in 

 an infant during its first two weeks of extra-uterine life were it not 

 for the shock due to birth. For South Australian male infants I 

 find that the gain during the first week following birth should be six 

 ounces, during the second seven ounces. But the average male 

 infant in South Australia actually weighs 6.2 ounces less at one 

 week than it did at birth. Since it should have weighed 6 ounces 

 more than it did at birth the true loss of weight due to birth is 

 12.2 ounces which is 9 per cent, of its weight at birth. At the 

 end of the second week of extrauterine growth the average South 

 Australian male infant weighs 3.4 oz. more than it did at birth, 

 but since it should have gained 13 oz. since birth the loss of weight 

 due to birth is now 9.6 oz. Part of the effect of the shock of birth 

 is therefore overcome during the second week of post-natal life by 

 compensatory overgrowth, for whereas the deficit in weight due to 

 birth at the end of the first week is 12.2 oz., at the end of the 

 second it is only 9.6 oz., i. e., 2.6 oz. of compensatory overgrowth 

 have occurred. Corresponding figures were obtained for females. 

 Hence it appears probable that the average weight of an infant at 

 any given age represents a true dynamic equilibrium, any disturb- 

 ance of which tends to be rectified by compensatory gains or 

 losses. 



The post-natal loss of weight is greater the greater the weight, 

 and, consequently, the size of the infant at birth. It appears 

 probable therefore that the post-natal loss of weight is primarily 

 due to mechanical shock; although defective nutrition and func- 

 tional shock doubtless contribute to it. 



