MR. E. C. SNOW, in his paper entitled “The Intensity of Natural Selection in Man” (Drapers' Company Research Memoirs, Studies in National Deterioration, No. vii. London: Dulau and Co., 1911), has set himself to answer the following question: Has heavy infantile mortality any selective value or tendency to eliminate the more sickly and to spare the hardier children? Of the data available for the investigation of this problem, the most satisfactory are derived from the annual volumes of Prussian statistics, and the most definite of the results were obtained from them. In order to indicate the method employed, one example will be described. Thirty rural districts in Prussia were taken, and all the children in them born in the year 1881 were considered. It was ascertained for each district how many of these children died in the first two years of life and how many in the next eight. Now it is obvious that if the infantile mortality tends to weed out the weaker children, then in those districts in which the mortality among the children born in 1881 was highest in the years 1881 and 1882 it should tend to be lowest in, ihe years 1883–90, since stronger children less likely to succumb to the ailments of childhood would have survived their first two years. In other words, there will be a negative correlation between the number of deaths in the first two years of life and the number in the next eight, provided that allowance is made for the total number of births in each district for the year 1881 and for the effects of environment. After making these necessary allowances by means of the formula for partial correlation, a coefficient of –0.93 was obtained in the case of males and of –0.85 in the case of females.