The purpose of a recently reported study by Pearl1 was to determine the proportion of women potentially capable physiologically of reproducing in 1930 who actually did so in that year. In the birth registration area of the United States, which in 1930 included all the states except Texas and South Dakota, there were 30,871,292 living females between the ages of 15 and 50. Approximately 63 per cent were married, while 37 per cent were either single, widowed or divorced. Nevertheless, as Pearl points out, the vast majority of them were potentially capable physiologically of reproduction. Theoretically, therefore, there might conceivably have been an equal number of births, or at least some kind of product of conception during that year. Actually, in 1930 there were officially recorded as occurring in the same area to mothers aged 15 to 49 inclusive a total of 2,256,913 living and stillbirths, including the illegitimate