1. Data are presented which show that in the vitamin B₂ deficiency the groups of rats receiving feces, voided by the animals fed on lactose and dextrinized corn-starch diets, showed a much more favourable growth response than comparable groups of animals receiving sucrose, glucose, and corn-starch.
2. The peculiar properties of the lactose and dextrinized starch are attributed to the formation of vitamin B₂ factors by microorganisms in the intestine of the rats.
3. Flavin is isolated from the feces of such rats.
4. Evidence indicates that the increased level (35%) of either fish protein or egg albumin more greatly inhibits the cataractous change in the lens than 18% level of protein.
I wish to thank Prof. U. Suzuki and Prof. B. Suzuki for their advice and encouragement during the progress of this work, and to Dr. M. Sumi for his helpful suggestions. I am also very grateail to Dr. S. Kato for the spectroscopic assay, to Miss T. Akaho for the lumiflavin determinations, and to Dr. Y. Akutagawa, of Medical Department of Jikei University, for the ophthalmoscopic study on the lens change of the animals. I am indebted to Misses M. Takahashi and H. Sasaki for their willing help in feeding the animals and preparing the materials.

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