But, putting aside this broad and philosophic view of the importance of mortuary statistics, it is evident that the application of their deductions must be of great benefit to the physician as a practitioner alone. This was perceived even as far back as the time of Sydenham, who inculcated the doctrine that the treatment of all disease should have a reference not only to the immediate symptoms and to the season, but also to the epidemic constitution of the year and the locality. It has been remarked by a distinguished author that "man is not born, does not live, does not suffer, does not die, in the same manner on all points of the earth. Birth, life, disease, and death, all change with the climate and soil—all are modified by race and nationality." Medicine, with the other natural sciences, has now been obliged to abandon vague hypotheses for truths determined by observation. Numerical expressions are substituted for uncertain and conjectural assertions. Only a limited number of facts are, however, contained within the horizon of a few observers. The determination of the laws of mortality requires a very wide range of observation, and a considerable space of time, in order to eliminate accidental perturbations.
The next important element of vital statistics is that of birth. Man is ushered into existence under natural circumstances almost as impressive as those which circumscribe his duration of life, and which attend its surrender. While tens of thousands are divesting their being of earthly garb, and entering upon their eternal inheritance, still greater numbers are assuming the heritage of life in forms moulded by antecedent events, and stamped with ancestral peculiarities. If, therefore, it be profoundly interesting to contemplate, arrange, and study the multitude of agencies which impel this innumerable caravan of pilgrims toward their destination, it is almost equally instructive to analyze the manifold causes which have contributed to their assembling together. Such particulars, when massed into statistics, become of acknowledged importance to medical and social science. The disparity in the sexes born at different periods, the average number of women bearing twins, triplets, etc., the proportion of offspring from native or foreign progenitors, the ages and occupations of parents, the average number of children produced at different periods of female life and in different seasons, the influence upon reproduction of the relative ages of parents, the reciprocal relations between illegitimacy and modes of living—these and other kindred questions are of deep concern to the human race, and the source of their solution lies in the largest accumulation of facts.
Moreover, the actual number of births occurring in any community each year is indispensable, in conjunction with other factors, for computing the increment of population during years intervening between those of official enumerations, and consequently for the determination of the true death-rate. The remarkable precision with which this