Those who contest the purity of the Jewish race lay great stress upon the Chozars as forming the nucleus of the Russian Polish Jews, who are, as is well known, a predominant majority among present-day Jews, probably ninety per cent of whom either dwell in the Russian dominions or are descended from former inhabitants of old Poland. Yet against this is the absence of any reference to Jews in Poland during the time the Chozars flourished (eighth to eleventh centuries), while the very speech of the Polish Jews--the so-called "Yiddish," really archaic German mixed with Hebrew--indicates their true source, the German kingdoms and principalities. Professor Ripley throws some doubt upon the possibility of such large numbers as those of the Polish Jews having been derived from Germany. Nowadays there are probably five millions of Jews in the regions once possessed by Poland, but the remarkable fertility of Jews is one of the most striking characteristics of their vital statistics, to which, indeed, Professor Ripley has called attention in his remarks upon their vitality. The development of a generation depends, as is well known, upon the relative number of deaths under five years of age, and it is just at this period that Jewish mortality presents so favorable an aspect, owing to the care of Jewish mothers and the absence of alcoholism among the fathers. I have estimated that the Jewish population of the world in 1730 (six generations ago) was only 1,300,000, whereas at the present moment it is at least nine times as much. If one could assume the same rate of progress to have existed through the middle ages the Jewish population in the fourteenth century would have been not much more than 25,000. Such a rate of progress is, however, extremely unlikely, considering the large losses by persecution, which in Poland alone, during the disastrous Cossack inroads between 1648 and 1656, is said to have removed no less than 180,000 Jews. But, making every allowance for this disturbance in the rate of progress, it would have been quite possible for 50,000 Jews who had migrated to Poland in the thirteenth and fourteenth centuries to increase to over half a million at the beginning of the eighteenth. Americans, who have seen nearly half a million Russian Jews land upon their shores within the last twenty years after crossing nearly half the world, need not be incredulous as to the possibility of one tenth of that number passing over the borders between Germany and Poland in a couple of centuries during the middle ages, when, if means of transit were less numerous, intensity of persecution and motives for emigration were ten times as strong as even under the iron rule of the Russian Czar.