The observation of Tisdall and Brown1 that in Toronto a sharp increase occurs in the antirachitic effect of sunshine about the first of March aroused our interest in the question as to whether or not a similar condition exists in Colorado. The general impression which one may draw from the relatively large percentage of sunshine throughout the year, as well as from the low incidence of rickets in Colorado, suggests that there is no such marked difference in the antirachitic effect of winter and summer sunshine in Colorado as occurs in Toronto.
Forbes and Green2 reported that from the point of view of clinical data there is a relatively low incidence of rickets in Colorado. In a continuation of this work, Forbes, Green and Stephenson,3 by use of the x-ray method of diagnosis, confirmed this conclusion. In their reports, they gave consideration to climatologic conditions in Colorado