The suggested relation between cystine and vitamin B(2).

IT has been suspected that some of the diets used in vitamin work, which contain protein in the form of purified caseinogen, may be deficient in cystine. This is particularly the case with diets used in experiments with the B-vitamins, since those used in the study of the fat-soluble vitamins usually contain the B-vitamins in the form of yeast or yeast extracts, which are rich in cystine. The realisation of this fact has led some workers to guard against the possibility of a deficiency by adding cystine to the diet [Jansen, personal communication; Block and Farquar, 1933] and has led others to consider whether the syndrome of growth failure and dermatitis, hitherto considered to be due to a deficiency of vitamin B2, may not in reality be due, in part, to a deficiency of cystine. This view has recently been put forward by Itter et al. [1935]. In 1932, with the idea of investigating this question, we studied the effect of variations in the cystine content of the diet on the growth of rats receiving different amounts of vitamin B2 and on the dermatitis developing in rats deprived of this vitamin. Although it was found that one of the samples of purified caseinogen used had a low content of cystine, the deficiency of cystine in the diet was found to be slight, and no interrelation between cystine and vitamin B2 could be found. The work was therefore not published. The results we obtained, however, partly confirm and partly extend the recently published work of Itter et al., and as they lead us to different conclusions, it is now thought desirable that they should be published.