164 THE VITAMINES 



We come now to the discussion of the difficulties involved in the 

 field of vitamine fractionation. Starting from any crude material 

 and subjecting it to a variety of chemical and physical manipulations, 

 we usually find that the vitamines are quite resistant. If now a 

 chemical fractionation is undertaken, we note that some procedures 

 cause either a partial or total disappearance of vitamine activity. 

 What then is there in the natural combination which protects the 

 vitamines against destruction? It has long been thought that it 

 was an acid which served to protect these substances, but this is 

 apparently only partially the case. A second possibility is that the 

 natural combination is protective against oxidation; this may be 

 tested experimentally and will be spoken of later. 



The main difficulty of isolation, in our opinion, is that in most of 

 the starting material used till now, the vitamines are associated with 

 large amounts of inactive substances. When we mix a small quantity 

 of a known substance with a large quantity of another known sub- 

 tance, we find it hard to effect a separation. Here, too, we are 

 dealing with the law of mass action, and only those substances which 

 occur in large amounts in the mixture may be easily separated. Now, 

 if we recall that we are dealing with cellular constituents, the chemical 

 nature of which is still insufficiently known, then it is clear that our 

 problem becomes much more complicated. Just how little the con- 

 stituents of the cells are known becomes more evident when we 

 attempt a fractionation of the vitamines; we immediately encounter 

 cell components totally unknown to us. It is sought to avoid these 

 difficulties by the choice of starting material which, in addition to a 

 definite vitamine content, has less inactive substances. Even this 

 procedure is uncertain, since upon concentration of the vitamines, 

 there is a corresponding concentration of the impurities. There is 

 no method whereby we may, in one operation, remove the vitamines 

 from the bulk of its associated impurities, and which would be 

 applicable to a large quantity of crude material. Besides, it is not 

 impossible that the delay attending the usul chemical procedures 

 may have some destructive influence on the vitamines. For example, 

 if it should be necessary to exclude air, it is not very difficult to 

 provide for this for a few days, but it is another matter when the 

 procedures employed involve weeks instead of days. It is necessary, 

 therefore, that we should try to develop some color reaction or 

 pharmacological test for the demonstration of the vitamines, which 



