Many investigators have noted that the inclusion of large amounts of egg white in special experimental diets causes a definite nutritional disease in animals. This disorder, commonly called egg white injury, has for its chief symptom an "eczematous dermatitis" which can be prevented or cured by a protective substance formerly called vitamin H which is present in certain foodstuffs. There appears frequently in rats, in addition to the severe general eczematous dermatitis involving the eyelids and lips, an ischemic gangrene of the tip of the tail, presumably due to local vasoconstriction. Recent reports1 have indicated that vitamin H is identical with biotin, a yeast growth factor, and also with coenzyme R, a growth and respiration factor for many strains of the legume nodule organism Rizobium. Williams and his co-workers2 have demonstrated that the so-called egg white injury is due to an induced biotin deficiency caused by the binding