VITAMIN D 333 



"By exposure to the radiations of a quartz-mercury vapor lamp, the 

 antirachitic properties of cow's milk were increased eight or more 

 times. Under the same conditions a sample of goat's milk increased 

 (in potency) about 24 times. The increase in activity can be induced 

 rather promptly though to a lesser degree by direct irradiation of the 

 animal." 



Steenbock and Daniels (1925) conferred antirachitic potency by 

 irradiation upon millet, lard, olive oil, wheat, Indian corn, yeast, cream 

 of wheat, crude casein, hominy, rolled oats, shredded wheat biscuit, 

 milk, tgg yolk, butter, liver, the unsaponifiable fraction of olive oil, 

 cholesterol, and phytosterol (except when prepared from old oil). 



Dutcher and Kruger (1926) found that their irradiated corn oil 

 had at least 38 times the antirachitic potency of irradiated dextrin. 



Hart, Steenbock and their collaborators (1925) found that the 

 antirachitic potency of tgg yolks from irradiated hens was approxi- 

 mately ten times that of egg yolks from non-irradiated hens. 



As yet the experimental evidence is not clear on the relative effect 

 of diet and ultra-violet irradiation of the cow upon the antirachitic 

 value of her milk. 



Boas and Chick (1924) reported that rats fed milk from a cow 

 on dry or fresh food, but kept in the dark, showed less calcium reten- 

 tion than rats fed milk from a cow after 2 months on pasture. 



Luce (1924) later concluded that "the antirachitic value depends 

 on the diet of the cow and possibly also on the degree of illumination 

 to which she is exposed. Milk from a pasture- fed cow has a definite 

 and high antirachitic value ; the same animal when stall-fed in the dark 

 yielded a milk much inferior in antirachitic properties." The part of 

 her study on the effect of light alone was made in November when 

 the average amount of sunshine daily was 3.4 hours and in December 

 when it was but 1.4 hours. This work was later repeated after the 

 cow had been kept for 3 months on a very drastic diet free from fat- 

 soluble vitamins. Under such conditions, exposure to summer sunlight 

 (6.4 hours daily) for 77 days appeared to raise the antirachitic value 

 of her milk sHghtly but not materially. 



In commenting on this work, Steenbock and his collaborators (1925) 

 said that they had come to realize that food may or may not be more 

 important than sunlight — depending upon whether or not the feeds 

 had been exposed to ultra-violet light. "It does, however, appear to be 

 true that sunlight acting upon the animal (cow) itself is not such an 

 extremely active agent as one might be led to assume." 



Chick and Roscoe (1926a) in continuing the work of Luce obtained 



