THE ANTIRACHITIC VITAMINE 225 



Considering the manner of preparing commercial cod liver oil, 

 we must marvel, in the light of the above mentioned observations, 

 that the oil still has therapeutic properties. In this connection, it 

 would be interesting to observe the action of oxy-cod liver oil a 

 preparation which, according to Freudenberg and Klocman (602), 

 is made by oxidation of cod liver oil with hydrogen peroxide as well 

 as cod liver oil emulsions prepared by shaking in alkaline medium. 

 The influence of such a procedure on the therapeutic action is dis- 

 cussed by Hess and linger (603). If the vitamine A of cod liver oil 

 really withstands the above mentioned treatment and long storage, 

 then we must assume that the vitamine from this source is exception- 

 ally stable, a characteristic which should bs significant in further 

 studies. According to Zilva and Miura (I.e. 574a), cod liver oil 

 contains 250 times as much vitamine A as butter, and 3 milligrams 

 of this oil per day is sufficient for rats. Drummond, Coward and 

 Watson (603a), found that certain samples of butter contained 

 no more vitamine A than refined vegetable oils. The above data 

 undoubtedly explain the differences observed in the value between 

 cod liver oil and butter in the treatment of rickets. 



DEMONSTRATION OF VITAMINE A 



Till now, the only method used, as we have already seen, is the 

 behavior of the rat. To make the demonstration definite, it is neces- 

 sary, according to Drummond and Coward (604) to provide, above all, 

 that the basal diet is completely free from this substance. The basal 

 diet used for this purpose is composed as follows: 



Purified casein 18 Yeast extract 5 



Purified rice starch 52 Orange juice 5 



Purified reduced vegetable oil. .15 Salt mixture 5 



The casein is heated in open dishes for 24 hours at 105C. Rice 

 starch has been shown to be pure for this purpose and may be used, 

 as such. Completely reduced vegetable oil, usually cotton seed 

 oil, or steam distilled palm-kernel oil (Stammers, 604a) is used as 

 a fat. If one is uncertain as to the freedom of this oil from vitamine 

 A, then the addition of fat should be omitted entirely. Orange 

 juice is free from vitamine Aj while yeast extract has not yet been 

 investigated sufficiently in this respect. Rats weighing 50 to 70 

 grams, and 4 to 5 weeks old should show no growth at all, on this 



