As to the population problem, Raymond Pearl has studied the ratio between births and deaths in France, Prussia, Bavaria, and England and Wales from 1913 to 1920[130] and finds that, in general, the birth ratios rose during the war--in England to the 100 per cent mark--and that immediately after the war was over the death-birth ratio began to drop rapidly in all countries. Vienna suffered perhaps more than any other city but made the best recovery, showing how promptly the growth of population tends to regulate itself back toward the normal after even so great a disturbance. Thus the war, which was the greatest depopulator since the epidemic of the Middle Ages, caused “only a momentary hesitation in the steady onward march of population growth.” If we take any given land area of fixed limits, there must necessarily be an upper limit to the number of people it can support, but this limit will be approached asymtotically and the most rapid rise will be midway between the upper and lower limit, namely, at that point where half the possible resources of subsistence have been drawn upon and utilized. The statistician must approach this problem as the astronomer does in calculating the complete orbit of a comet, that is, he must construct his curve from a limited number of specific data. If we study the curve of growth of population in this country, we find that we have long since passed the most rapid rate of increase. If we compare this with that of France, which is an old country and much nearer the upper limit than ours, which started near the lower asymtote only a century and a half ago; or compare it with that of Serbia, which is intermediate, all the statistics available conform with singular accuracy to the theoretic curve.