VITAMIN D 327 



be incorporated into the basal diet. It does not seem to have proved 

 generally satisfactory. 



Grayzell and Miller (1928) found that normally the reaction of 

 the intestinal contents of dogs is acid practically throughout the entire 

 length of the tract ; on a rickets-producing diet, the reaction tends to 

 become alkaline, but administration of cod-liver oil or ultra-violet 

 irradiation under such conditions changes the reaction back to normal 

 values. 



The alteration of the reaction of the intestinal tract may be but 

 one mode of action of the antirachitic vitamin. It explains the dis- 

 covery of Zucker, Johnson and Barnett (1922) that rickets could be 

 prevented by substituting calcium chloride for calcium lactate in a 

 rachitic ration and the ability of Jones (1924) to cure rickets in chil- 

 dren by the addition of hydrochloric acid to their diet. 



Spectroscopic Tests. — The recently established facts that the provi- 

 tamin shoves w^ell-defined absorption bands with maxima at 293 /z/i, 

 280 fiju and 269////, enabled Rosenheim and Webster (1927c) to rely 

 to a large extent on the spectroscopic test in place of animal experi- 

 mentation in their investigations on the parent-substance of vitamin 

 D. They say, "Although such a test had already been tentatively sug- 

 gested by Schlutz and Morse (1925), a firm basis for its application 

 was only established when we showed by animal experiments that the 

 absence of absorption bands in the ultra-violet coincided with the loss by 

 cholesterol of its property of becoming antirachitic on irradiation. It 

 is evident that the destruction or absence of provitamin can be rapidly 

 proved by a negative spectroscopic test, whilst the animal experiment 

 remains indispensable in confirmation of positive spectroscopic evi- 

 dence." 



Under the auspices of the Committee on Accessory Food Factors 

 of the Medical Research Council, Great Britain, a standard solution 

 of irradiated ergosterol similar to that in use at the Pharmaceutical 

 Societies laboratories (cf. Coward, 1928) has been prepared and tested 

 for stability after prolonged storage. The Medical Research Council in 

 a recent announcement in Lancet has described the preparation of this 

 standard as follows : 



"A quantity of ergosterol from yeast, purified and dried by methods carefully 

 recorded, was subjected, in an accurately made alcoholic solution, to irradiation 

 with the rays from a mercury arc, the physical details of the procedure being 

 measured and recorded with the greatest practicable accuracy. All conditions 

 known to influence the amount of vitamin D formed should, therefore, be repro- 

 ducible at any future date, or in any other laboratory, leaving only the final adjust- 

 ment of a new standard to equivalence with this original one to be made on the 

 basis of comparative biological assay. The irradiation products were carefully 



