Authoritative data show conclusively that irradiation with ultraviolet light is of definite beneficial effect in preventing and in curing rickets.
The antirachitic range of the solar spectrum, the wave lengths influencing the deposition of calcium in rickets, is from 290 to 313 millimicrons. That the ultraviolet rays of the sun's spectrum cannot be depended on, however, either to cure or to prevent the development of rickets in all latitudes and at all seasons of the year has also been established, as they vary in intensity during the different seasons of the year, the intensity being highest during the summer months and lowest during the winter months. The ultraviolet rays vary in intensity according to the geographic location, being more intense in the torrid zone than in the temperate zone and at high altitudes than at sea level. The intensity of the short rays is to a large extent dependent on