The proletariat constitutes a large majority of the inhabitants of the urban districts; the proportion of artificially reared children is greater than in the country, the housing conditions are less favourable, there is less opportunity for open-air life, venereal diseases are more prevalent, and fertility is lower. But against these considerations we must set the fact that the urban population is more intelligent, and for this reason better understands the various methods of artificial feeding of infants; the fact that charitable institutions are more effective in the towns, and the fact that in the towns better hygienic conditions prevail. The sanitary improvement of the towns by better cleansing of the streets, an improved water supply, better methods of disposing of sewage and refuse, &c., has led to a reduction not merely of the general urban death-rate, but also of the infantile urban death-rate; whereas in the country districts these rates have remained stationary, or have even undergone an increase. In wealthy towns the death-rate is lower than in poor towns; like differences are observed as between the rich and the poor quarters of one and the same town. Wealth has so marked an influence in lowering infant mortality that in the wealthy villa quarters of large towns the infantile death-rate may be as low as from 10 to 20 per mille. _The Effect of Housing Conditions._--The infantile death-rate is very closely connected with the character of the housing conditions. The rate of infant mortality in any particular dwelling varies directly with the number of inhabitants, and varies inversely with the number of rooms available per family. Those living in the upper stories of tenement houses have a higher death-rate than infants living in lower stories and basements. This influence of bad housing conditions in producing a rise in the infantile death-rate is only to be expected. The habitation exercises its influence upon the infant by day and by night, and through every detail of the infant’s life. To give one instance, there is an intimate connection between the quality of the dwelling and the quality of the infant’s food; in a suitable dwelling milk may be more readily kept cool, preserved from contamination, sterilised, &c. _The Effect of Age._--The degree to which bad conditions of life endanger health varies inversely with the age. The maximum danger to health from such conditions is incurred by infants. The younger the infant the greater the danger that bad conditions will prove fatal; and most of the environmental factors unfavourable to the maintenance of infant life come into operation immediately after birth. The younger the infant, the less resistant it is to external influences. Therefore the younger the infant, the more carefully does it need to be watched and safeguarded. Physicians and statisticians lay great stress upon the degree to which the infant’s chances of life depend upon its age in days and months.