The probable future population of this and other countries is, as has been pointed out editorially in The Journal,1 important for long-range planning in health matters as well as in other economic subjects. Recognition has been accorded this fact by the federal government in a lengthy report to the National Resources Committee on the problems of a changing population.2 According to the estimates of Warren S. Thompson and P. K. Whelpton, based on medium fertility and mortality rates, the population in the United States will continue to grow for fifty years but at a constantly decreasing rate, reaching 152,000,000 in 1980. Even with the highest rate that might reasonably be assumed, there would be a natural increase of less than 50,000,000 from 1935 to 1980. The minimum estimate on the other extreme would give a peak population of 138,000,000 in 1955 with a decrease of 10,000,000 during the