[Illustration: DIAGRAM SHOWING RELATIVE DEATH-RATES PER 100,000 PERSONS IN DIFFERENT CLASSES. ] This difference in the death-rates of the various social classes is even more strongly marked in the case of infants. Mortality in the first year of life differs enormously according to the circumstances of the parents and the amount of intelligent care bestowed upon the infants. In Boston’s “Back Bay” district the death-rate at all ages last year was 13.45 per thousand as compared with 18.45 in the Thirteenth Ward, which is a typical working-class district, and of the total number of deaths the percentage under one year was 9.44 in the former as against 25.21 in the latter. Wolf, in his classic studies based upon the vital statistics of Erfurt for a period of twenty years, found that for every 1000 children born in working-class families 505 died in the first year; among the middle classes 173, and among the higher classes only 89. Of every 1000 illegitimate children registered—almost entirely of the poorer classes—352 died before the end of the first year.[6] Dr. Charles R. Drysdale, Senior Physician of the Metropolitan Free Hospital, London, declared some years ago that the death-rate of infants among the rich was not more than 8 per cent, while among the very poor it was often as high as 40 per cent.[7] Dr. Playfair says that 18 per cent of the children of the upper classes, 36 per cent of the tradesman class, and 55 per cent of those of the working-class die under the age of five years.[8]