III. Experimental rickets The prevention of rickets in rats by exposure to sunlight. 1

Abstract

In recent papers it was shown by Hess and Unger that rickets in infants could be cured by frequent short exposures to the sun's rays. 1 , 2 By this means and without any alteration whatsoever of the dietary, the characteristic signs of this disorder begin to disappear in three to four weeks as noted by clinical examination and by the x-ray. As a result of favorable experiences of this nature, it was concluded in a study of the seasonal incidence of rickets 3 that “hygienic factors, especially sunlight, and not dietetic factors play the dominant rôle in the marked seasonal variations of this disorder.” It seems probable that the ultra-violet rays play a large part in this curative power of the sun, judging from the work of Huldschinsky 4 and others who recently have shown that infantile rickets can be cured by means of the rays produced by the mercury-vapor lamp. In 1918 we tried the curative effect of rays from this source, but, lacking the aid of x-ray examinations, could not convince ourselves of their efficacy; since then we have succeeded in curing rickets by this means.

Having found sunlight efficacious in the rickets of infants, we proceeded to test its value in the prevention of rickets in rats. To this end a series of white rats were placed on the diet (No. 84) described by Sherman and Pappenheimer, 5 consisting of patent flour 95.0 per cent., calcium lactate 2.97 per cent., sodium chloride 2.0 per cent. and ferric citrate 0.1 per cent. It has been the experience of the investigators in this laboratory that such a diet invariably leads to the development in rats of lesions which are anatomically identical with those of infantile rickets.