Prevention of Rickets by Light Rays. 



239 



efficacy. Rickets can be prevented in rats by daily exposures of 

 about 2 minutes to the rays of the mercury vapor quartz lamp, or 

 by 4 minutes or less exposure, at a distance of three feet, to the 

 rays from a carbon arc lamp. X-rays were found ineffective. 



In order to test the effect of the pigment of the skin on the 

 protective action of light, a group of white and another group of 

 black rats (the melanic form of the Norway rat) were exposed to 

 the radiation from the mercury lamp. In the first experiment 

 both sets of animals were protected as the dosage was excessive. 

 In the second experiment, when one and one-and-one-half minute 

 exposures were employed, all the white but none of the black rats 

 were protected. The black rats showed rickets by x-ray and by 



Ultra-violet Radiation — White and Black Rats. 

















Inorg. P. 





Wgt. 



U.-V. Ray 



Diet 



X-Ray 



Path. 





Mg. 

 per cent. 



White... . 



70-70 

 58-60 

 60-70 

 60-70 

 60-80 

 64-70 



1 min. 



g ;; 



8 4 3 



Neg. 



Neg. 





5-45 

 4.44 



Black.'". 



50-60 

 50-60 

 60-58 

 50-50 

 48-54 

 60-60 



1 " 

 ti ;; 





R. 



R. 



::} 





2.92 

 3-oo 



pathological examination, and their blood contained a less per- 

 centage of inorganic phosphate. This experiment shows that 

 pigment retards the rays which are effective in rickets, and indi- 

 cates one factor in the exceptional susceptibility of negro infants 

 to this disorder. 



Prolonged exposure to direct sunlight failed to prevent or to 

 delay the onset of scurvy in giunea-pigs. 



