Prevention of Rickets in Rats by Sunlight. 45 



It contains nearly twice the optimal content of calcium, and is 

 decidedly below the optimum in its content of phosphorus and in 

 fat soluble A. Otherwise, it is well constituted. 



Twelve rats placed upon this diet were sent to New Haven, 

 there to be exposed to sunlight. The remaining six rats were 

 retained in Baltimore to be kept as control animals under ordinary 

 laboratory conditions in a large, well-ventilated room completely 

 screened with windows of ordinary glass. The animals treated 

 with the sunlight were divided into two groups and placed in 

 fairly large wire mesh cages. Each clear day the cages were 

 carried out of doors and placed in the sunlight. At first, the 

 weather being warm, the rats were exposed to the sunlight for two 

 short periods of twenty minutes each. Soon, however, the periods 

 were lengthened to six or even more hours. During the experi- 

 mental period, which covered between sixty- two and sixty-seven 

 days, the rats were exposed to the sunlight on every day except 

 nine. The total exposure to sunlight during the experimental 

 period varied between two hundred and forty-two and two hundred 

 and seventy-three hours. The average daily exposure was four 

 hours. 



When first exposed to sunlight, the albinos developed con- 

 junctivitis; the ears of all, in particular the albinos, began to 

 peel; the skin of the tails became sunburned and rough; the hair 

 of some of the albinos acquired a yellowish tint. Long before the 

 experiments were completed it became evident that the animals 

 treated with sunlight were not developing rickets. Though they 

 did not grow normally, they remained extremely active, climbing 

 and darting about the cages. Toward the end of the experiments 

 the males became sexually active; one of the females became 

 pregnant. 



The control rats, killed at the expiration of two months, showed 

 all the gross and microscopic evidences of rickets, the characteristic 

 deformities of the thorax, enlargement and distortion of the 

 costochondral junctions, fractures of the shafts, enlargements at 

 the wrists, ankles and knees, and the ends of all the long bones. 

 The bones cut with diminished resistance. On section a deep 

 rachitic metaphysis entirely free from calcium was exposed. Into 

 it the proliferative cartilage extended in irregular prolongations. 

 The trabecular were surrounded with broad zones of osteoid. 



