334 THE VITAMINS 



results showing that the antirachitic value of the milk (vitamin D 

 content) was found to depend principally on the effect of sunlight on 

 the cow. At the same time there was some indication that the diet of 

 the cow, if consisting of fresh green food, was a contributing factor. 

 Their experiments confirmed those of Luce in showing that "pasture- 

 fed" milk possessed the maximum antirachitic value while that yielded 

 by the cow when receiving a diet of cereals and roots appeared, on the 

 whole, inferior in this respect, in spite of exposure to maximum illu- 

 mination out of doors in summer. 



Hart, Steenbock, Scott and Humphrey (1927) reported that ultra- 

 violet light had little if any, direct influence upon the calcium and 

 phosphorus metabolism of dairy cows. It was suggested that this should 

 not be interpreted as indicating that exposure of the dairy cow to sun- 

 light is not beneficial. 



Hart, Steenbock, Teut and Humphrey (1929) reported that the 

 feeding of cod-liver oil to dairy cows for more than a year had little 

 influence on calcium assimilation. By feeding the ether extracts of the 

 feces of these animals, they found that there was poor assimilation of 

 vitamin D from the intestinal tract. Hart, Steenbock, Kline and Hum- 

 phrey (1930) next fed irradiated yeast at the level of 200 grams 

 per cow per day and found that the absorption of calcium was not 

 increased and that there was vitamin D in the feces. Some vitamin D 

 was absorbed, however, for the amount in the milk was increased. 

 Since calcium retention was secured with an intake of green plant 

 tissue and high calcium, they conclude that something in green plant 

 tissue other than vitamin D is effective in calcium retention. 



Golding, Soames and Zilva (1926) have shown that the antirachitic 

 potency of milk fat can be considerably increased by feeding the cows 

 cod-liver oil up to 8 ounces daily in addition to straw, roots and 

 meal mixture ; on the other hand, the addition of kale (40 pounds 

 daily) to the cow's diet (straw, mangolds and meal mixture) did 

 not measurably improve the antirachitic potency of milk fat in these 

 experiments. 



Supplee and Dow (1927) presented data which "appear to confirm 

 the existence of a significant interdependence between antirachitic 

 properties and the degree of ultra-violet light to which the product 

 itself, or its synthesizing agent the body of the cow has been exposed." 

 . . . "Summer-produced milk possessed greater antirachitic and calci- 

 fying properties than winter-produced milk. Irradiation of the summer- 

 and winter-produced dry milk imparted measurably greater antirachitic 

 and calcifying properties to both products. A greater increment of in- 



