INTRODUCTION It is generally recognized today that the penetrating power of the chemical rays (i.e., the ultraviolet) of the solar spectrum is very slight, and that the heat rays (i.e., the red and yellow) penetrate much more deeply. Current opinion, for this and other reasons, tends more and more to emphasize the deleterious effects of heat and to minimize those of the chemical rays. The irregular distribution of heat cases in different tropical countries and also in the temperate zone is a curious anomaly which invites investigation. In order to promote understanding of this matter, it seems eminently desirable to gather from various parts of the world a larger body of statistical data upon heat cases than has yet been brought together. A first step in this direction has been taken by analyzing the officially reported deaths from heat effects in the United States Registration Area during the years 1900–1928.