330 THE VITAMINS 



Supplee and Dow (1927) found that upon feeding reconstituted 

 dried milk to rats on the Sherman-Pappenheimer diet No. 84, pro- 

 gressive increases in the ash content of the humeri could be obtained. 

 Fed at 15 cubic centimeter levels, little difference could be seen between 

 non-irradiated summer milk, irradiated summer milk and irradiated 

 winter milk. At lower levels of feeding, higher antirachitic potency 

 could be observed in summer milk than in winter milk, and in irradiated 

 milks than in non-irradiated milks. 



Sherman and Stiebeling (1929) added further to the evidence that 

 milk as ordinarily produced (at least under conditions prevailing in 

 this country) contains significant amounts of vitamin D. This evidence 

 remains valid even though rickets occasionally occurs in children re- 

 ceiving fairly liberal amounts of milk; among children less adequately 

 fed the incidence of severe rickets is much greater. 



Bills summarized in 1927 an extensive study of the distribution of 

 vitamin D in various fats and oils. Of all the oils which he examined 

 only the fish oils and the oil of the adult seal were active. He found 

 a great diflference in activity between the oils of different species of 

 fish, and even within one species. Puffer fish liver oil (2 samples) was 

 about 1,500 times as potent as cod-liver oil (average of 300 samples) ; 

 goose fish liver (1 sample), herring (4 samples), sardine oil (4 

 samples), and cod-liver oil had about the same potency and the oils of 

 several other species ranged in potency from 3 to 40 per cent of the 

 value of the cod-liver oil. Body oil as well as liver oil may contain 

 vitamin D. 



Schmidt-Nielsen (1930) reports that the liver oils of cartilaginous 

 fish contain very little vitamin D in comparison with those of bony fish 

 and suggests selective absorption in the latter to meet the needs of bone 

 formation. 



As previously noted in the discussion of rickets-producing diets, 

 some of these are of such drastic character that when employed as a 

 means of testing for vitamin D they have resulted in reports that this 

 vitamin is absent from various natural foods in which it more probably 

 occurs in small or moderate amounts. 



Origin of Vitamin D in Nature. — Green leaves have been reported 

 by many investigators to be poor sources of vitamin D. On the other 

 hand, experiments by Hess and Weinstock and others have demon- 

 strated that irradiation with ultra-violet light can confer marked anti- 

 rachitic potency upon leafy foods, thus showing that they are at least 

 potentially antirachitic to an important degree. Chick and Roscoe (1926) 

 suggested that the explanation of this apparent discrepancy might lie 



