778 VIII. TROVITAMINS D AND VITAMINS D 



clusively in the yolk, dissolved in the fatty substances in that portion of the 

 egg. The average content of the yolks of hen eggs has been reported as 300 

 I.U. per 100 grams.^^** Although the values for vitamin D have been 

 shown to remain fairly constant with ordinary diets, increased amounts of 

 vitamin D can be introduced into the egg when the hen is irradiated,^" 

 or when the diet of the hens contains larger amounts of vitamin D.^*^-^^^ 



The type of vitamin D which is excreted in the milk^"^ and in the egg^"^ 

 is the same as that ingested. This was beautifully demonstrated by 

 Bethke and his co-workers, ^°^ who showed that about ten times as much 

 vitamin D given as "metabolized" vitamin D milk was required for the 

 chick as was the case when irradiated milk was used. In the first case the 

 vitamin arising from the irradiated yeast was D2; this is very ineffectively 

 utilized by chickens. ^''^ In the irradiated milk, the product formed was vi- 

 tamin D3, which resulted from the activation of the 7-dehydrocholesterol 

 already present in milk. This form of vitamin D is well utilized by chickens. 



Unfortunately, the records for the distribution of vitamins D do not in- 

 dicate which type of vitamin D is present. Brockmann and Busse were 

 the first to prepare vitamins D3 and D2 from halibut liver and tuna liver 

 oils, respectively.^"'' Although both vitamins D2 and D3 have been iso- 

 lated from fish liver oils, it is knoAvn that vitamin D3 is usually present in a 

 larger proportion. Moreover, Bills and co-workers™-^- have suggested that 

 at least six different vitamins D occur in cod liver oil. The efficacy of dif- 

 ferent fish liver oils in preventing or curing rickets in the rat (vitamin D2 or 

 D3) and the chicken (vitamin D3) offers a clue to the varying proportions of 

 vitamins D in the different oils. These data are summarized in Table 5. 



2. Properties of the Vitamins D 



The known vitamins D have properties which are almost identical. 

 They are white crystalline solids which are soluble in organic (fat) solvents 

 and insoluble in aqueous media. They all have an absorption maximum at 

 265 m/x in hexane or in diethyl ether. 



(1) Vitamin D-i 



Vitamin D2, also referred to as calciferol or activated ergosterol, has a 

 molecular weight of 396. It melts at 115-117°C. and has a specific rota- 

 tion ([a]D) of +103° in absolute alcohol, +82.6° in acetone, +33.3° in 

 petroleum ether, and +91.2° in diethyl ether. ^"^^ 



2" G. H. Maughan and E. Maughan, Brit. J. Phys. Med., 7, 137-138 (1932). 



2" G. H. Maughan and E. Maughan, Science, 77, 198 (1932). 



2« G. M. De Vaney, H. E. Munsell, and H. W. Titus, Poultry Sci., 12, 215-222 (1933). 



»« O. N. Massengale and M. Nussmeier, J. Biol Chem., 87, 423-426 (1930). 



