VITAMIN D 335 



crease in calcifying properties was imparted to the winter-produced milk 

 than there was to the summer-produced milk. 



"These results indicate that both winter- and summer-produced 

 milk may have the same potential capacity for endowment with anti- 

 rachitic and calcifying properties by ultraviolet light. The realization 

 of this potential capacity is not attained in milk produced either in the 

 summer or winter months. However, when the cows are subjected to 

 the greater solar irradiation prevailing in the summer months the em- 

 bodiment of the antirachitic and calcifying properties in the milk is 

 greater than in the winter months when the animals are exposed to 

 the activating rays to a much less degree.- Because of the inherent 

 conditions in the quality of the food consumed by cows in the tem- 

 perate zones during the winter and summer months, the effect of such 

 conditions on the antirachitic properties of the milk is not precluded 

 by the data recorded herein." 



Thus it appears that while both fresh green feed and sunshine im- 

 prove the antirachitic value of the milk, the relative importance of each 

 factor separately depends on the quality of the cow's ration, both from 

 the standpoint of its vitamin and mineral content. 



Apparently vitamin D is not abundantly furnished in most food 

 materials. Fish oils, &gg yolk, butterfat and whole milk are the best 

 natural sources ; green leafy foods contain it in small quantities. Most 

 unrefined foods contain to a greater or less degree the vitamin pre- 

 cursor which can be rendered antirachitic by exposure to light rays 

 of less than 310 fxn in wave length. 



Several of the topics briefly summarized in this chapter are fully 

 and excellently treated by Blunt and Cowan in their Ultraviolet Light 

 and Vitamin D in Nutrition. 



