The experimental rations used in the study of the vitamin B~ complex, espedally of vitamin B6 and its related factors, are, as a rule, low in content of choline. This is also true of the basal diet deficient in vitamin Be which one of us (1) has employed during the last seven years in the production of rat acrodynla. It consists of 18 parts of casein, 68 of sucrose or rice starch, 8 of melted butter fat, 4 of salt mixture, 2 of cod liver oil, and is supplemented with thiamine and riboflavin. This diet is deficient in choline, but, until recently, no pathological changes attributable to this defect have been recognized in animals fed this mixture. On the whole, the ration appeared to serve its purpose without any visible interference due to the absence of choline.Oleson, Bird, Elvehjem and Hart (2) have lately reported the results of experiments in which choline (300 to 500 mg. per kilo) was added to the basal diet used for the studies of the vitamin B2 complex, but these authors did not mention the reason for this precautionary measure.The experimental data presented here not only substantiate the need for the incorporation of choline in a synthetic ration for rats used in the study of the vitamin B~ complex, but they also support the important interrelationship between content of choline and the ratio cystine/methionine in the diet. Du Vigneaud, Chandler, Moyer and Keppel (3) have called attention to the close relationship of choline and methionine metabolism. At about the same time and independently, Griffith and Wade (4) have pointed out the importance of the ratio cystine/methionine together with a low choline content in the diet.
EXPERIMENTSOur first observations pertaining to the recognition of choline as a member of the vitamin B2 complex were purely accidental. With the isolation and, later, with the synthesis of vitamin B6 it became possible to go one step 1 on