ROBBINS: VITAMINS 121 



that bios I was mesoinositol, a substance which more than ten years later was 

 found to be necessary in the diet of chicks and of rats as well as in that of 

 yeasts. R. J. Williams and associates separated a bios fraction which was dem- 

 onstrated to be thiamine and later a fraction which proved to be a new vitamin, 

 pantothenic acid ; but a portion of bios still remained unidentified. 



Kogl in Utrecht began his work in 1932 and devoted his attention to that 

 part of the bios complex which was adsorbed on charcoal and which he called 

 biotin. Four years later he announced the isolation of crystalline biotin. He had 

 obtained 1.1 milligrams of the crystalline material from 250 kilograms of 

 dried egg yolk and estimated that this amount of material originally contained 

 a total of 80 milligrams. On this basis it would take more than 125,000 tons 

 of dry egg yolk to yield 1 pound of biotin or, to put it another way, about 

 1,500,000 hens would have to work for a full year to produce the eggs neces- 

 sary to yield 1 pound of pure biotin. 



But this does not end the story of biotin. About 1933 it was reported that 

 rats fed a diet high in raw egg white developed a peculiar and impressive skin 

 injury which was accompanied by emaciation and eventually terminated 

 fatally. This was called egg white injury. Cooked egg white did not have this 

 effect. It was found further that egg white injury could be cured by injections 

 of liver extract, and it was suggested that this was because of the presence in 

 the liver extract of a new vitamin which was labelled, vitamin H. In the mean- 

 time a group of investigators in the United States Department of Agriculture 

 had become interested in a factor which caused increased growth of the bac- 

 teria which produce nitrogen-fixing nodules on legumes. They named this 

 factor coenzyme R. In 1940 Gyorgy, Melville, Burk and du Vigneaud proved 

 that biotin, coenzyme R and vitamin H were identical. 



In the same year R. J. Williams and his associates isolated from uncooked 

 egg white a peculiar protein, which they named avidin. Avidin it was found 

 combines with biotin so strongly that it renders the vitamin unavailable to 

 the organism. Egg white injury is, therefore, the result of a vitamin deficiency, 

 a deficiency of biotin and now — biotin is suspected of having an intimate rela- 

 tion to cancer. 



Effective quantities of the vitamins. I have spoken from time to time of 

 effective quantities of thiamine, pyridoxine or biotin in terms of 0.01, 0.001 or 

 even 0.0001 of a microgram, and a microgram is one millionth of a gram. This 

 quantity of material cannot be seen, even with the most powerful microscope, 

 and it cannot be weighed, even on the most sensitive balance. It is invisible and 

 imponderable. If I had two dishes before me, one containing 0.001 microgram 

 of biotin, and the other empty you could see nothing in either dish. Yet a little 

 water rinsed in one dish and added to the proper medium would enable the 



