118 AGE-INCIDENCE OF CAUSES OF INFANT MORTALITY 



greater errors must arise with respect to mortality in those parts 

 of life where the incidence of mortality is relatively high, as in 

 infancy. 



The Registration Cities contributed 448,113 deaths to the total 

 mortality, and to the mortality under one year 92,314 deaths. 

 The rural parts of the Registration States contributed 243,461 

 deaths, of which number 4,418 occurred under one year of age. 

 The ratio of infant mortality to total mortality was therefore, for 

 the cities, 20.51 per cent., and for the rural parts of the same States 

 18.13 per cent. For the whole Registration Area we find the first 

 quartile of mortality to end at the age of 2.68 years; for the 

 cities at the age of 1.8 years; for the rural parts of these States 

 at the age of 5.5 years. 



In Maryland, outside of Baltimore, that is to say, under rural 

 conditions, Dr. Price has found that the average age of those 

 who die in January, February and March is a little less than 41, 

 while the average age of those who die in July, August and 

 September is a little less than 32. The summer mortality of 

 infants probably causes the difference. Whether the average 

 age at death, stated in the same way, for cities would show like 

 distinctions, I do not know; neither do I doubt that they would. 



These observations confirm our long-standing belief that 

 urban mortality, especially in infancy, is heavier, but they do not 

 justify reference to the rural mortality in the way of contrast. 

 When numbers are subtracted from the young adult rural popu- 

 lation and added to urban populations, it might be expected that 

 the rural population would appear relatively stronger in the age 

 periods which are not diminished by migration ; and so per- 

 haps it is in general. We are not informed about the 

 age distribution of the rural population of the Registration 

 Area in 1908. The rural population under five years, in the 

 whole area is said to have been 9.75 per cent of the whole. The 

 percentage in some of the Registration Cities exceeds this figure, 

 and it therefore appears that the movement city-ward sometimes 

 carries along enough reproductive energy to more than offset 

 the superior fertility commonly attributed to rural population. 

 The infants at risk, in 1908, under rural conditions, were not 

 more numerous proportionately than those at risk in the cities, 

 but above middle age more lives were at risk under rural con- 

 ditions. One must take this into account when interpreting the 

 percentages, quartiles, and average ages. With respect to the 

 average age, one individual aged 60 is equivalent to 60 indi- 

 viduals aged one year. All individuals count alike in the per- 

 centages and quartiles. But there is a wide interval between 

 quartiles of the living and quartiles of the dead ; for old age and 

 infancy, the first and fourth quarters of vitality count faster in 



