The Prevention of Rickets in Rats. 9 



infantile rickets can be cured by means of the rays produced by 

 the mercury- vapor lamp. In 191 8 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 ex- 

 perience 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. 



In carrying out experiments on rats our practice has been to 

 keep the colony in a semi-dark room, the yellow shades being 

 drawn at all times. In testing the effect of sunlight, the rats 

 (weighing at the outset about 40 grams) were kept in absolute 

 darkness, one series being taken out of the room and exposed to 

 the direct sunlight for a period of 15 or 30 minutes. There was no 

 difference whatsoever in the diets of these two groups. After 

 a period of about three weeks the animals were x-rayed in order 

 to observe early lesions of the epiphyses, and after thirty to forty 

 days were killed and autopsied. These experiments were begun 

 in April when the weather permitted four to five exposures a 

 week. 



It was found for the first time in our experience that diet No. 

 84, the "rachitic dietary," did not lead to rickets — that the rats 

 which received sun treatment did not show signs of rickets either 

 by x-ray or by histological examination of the bones. It is un- 

 necessary to discuss in detail the histological criteria which we 

 consider characteristic of rickets, as this question has been fully 

 considered in a previous paper. 6 It may be stated briefly that 

 they consist of increased width and irregularity of the prolifera- 

 tive cartilage, absence of calcium deposition and great excess of 



6 Sherman, H. C, and Pappenheimer, A. M., /. Exper. Med., 1921, xxxiv, 189. 

 6 Hess, A. F., McCann, G. F., and Pappenheimer, A. M., /. Biol. Chem., 1921, 

 xlvii, 395. 



