There existed many natural checks to the increase of population among primitive peoples. Droughts and the ravages of diseases played no small part in keeping down numbers. These same natural forces in perhaps fewer forms are still effective in all countries of the world, producing an infant mortality of an alarming proportion. Unsanitary conditions, bad housing, impure milk and water, and the heat of summer are among the checks to the more rapid increase of population. Mr. Phelps says in his statistical study of infant mortality, “In view of the many material changes in the living habits and industrial conditions of the world’s population in the last generation, the great advance in medical knowledge and the marked decrease in the general death-rate, the practical uniformity of the infantile death-rate the world around is simply astounding.”[88] The problem of how to decrease infant mortality has received considerable attention from municipal and philanthropic associations. The results obtained are far from satisfactory, so great and far reaching are its causes. The fall of the birth-rate is generally attributed to psychological rather than to physiological causes. Statistical reports do not show the same decline in the birth-rate among the inhabitants of poor districts of a city as among the well-to-do. A large number of the unskilled workers are foreigners, or people ignorant in respect to medical and physiological knowledge, and likewise unconscious of the prevalence of the practice of the restriction of the birth-rate. But the rapid diffusion of knowledge of all kinds in a democratic country will soon change this state of affairs. Mrs. Commander’s study of the birth-rate led her to believe that the birth-rate among immigrants who come to the United States of America “falls decidedly below European standards, and that the majority of immigrants when only a short time in this country imbibe the idea of limiting family. The small family appears to be an American ideal which immigrants accept as they do other American ideals.”[89]