OCCURRENCE 



7. L. D. Wright and H. R. Skeggs, Proc. Soc. Exp. Biol. Med., 1944, 



56, 95- 



8. G. M. Shull and W. H. Peterson, /. Biol. Chem., 1943, 151, 201 ; 



F. F. Tomlinson and W. H. Peterson, Arch. Biochem., 1944, 

 5, 221. 



9. M. Landy and D. M. Dicken, /. Lab. Clin. Med., 1942, 27, 



1086. 



10. E. C. Barton-Wright, Analyst, 1945, 70, 283. 



11. V. R. WilHams and E. A. Fieger, Ind. Eng. Chem., Anal. Ed., 1945, 



17, 127 ; V. R. Williams, /. Biol. Chem., 1945, 159, 237. 



12. A. Z. Hodson, ibid., 1945, 157, 383. 



13. W. B. Emery, N. McLeod and F. A. Robinson, Biochem. J., 1946, 



40, 426. 

 13a. A. Z. Hodson, /. Biol. Chem., 1949, 179, 49. 



14. N. G. Heatley, ibid., 1944, 38, 61. 



15. T. I. Williams, Nature, 1948, 161, 19. 



i^a. D. S. Genghof, C. W. H. Partridge and F. H. Carpenter, Arch. 

 Biochem., 1948, 17, 413. 



16. F. Kogl and W. van Hasselt, Z. physiol. Chem., 1936, 243, 



189. 



17. R. C. Thompson, R. E. Eakin and R. J. Williams, Science, 1941, 



94, 589. 



8. OCCURRENCE OF BIOTIN IN FOODSTUFFS 



The materials richest in biotin are probably egg-yolk, liver and 

 yeast, all of which have been used as sources for its isolation. It is 

 also present in kidney and cow's milk but not in rice polishings, beef 

 muscle or human milk.^ Cow's milk contained 11 to 37 /xg. of biotin 

 per litre, the value rising to a maximum after the first few days and 

 then falling.2 It occurs in a large variety of seeds. ^ Oat seedlings 

 contained somewhat larger amounts in the root and coleoptile tips 

 than in other parts. Biotin was also found in the aqueous extracts 

 of many tissues of dogs, cows, calves and hens.* The tissues of dogs 

 contained on the average 0-004 /^§- P^^ g-^ ^^^ tissues of cows 0-007 A^g- 

 per g. and of the hen 0-02 /itg. per g. The liver and kidney of all species 

 of animals examined were particularly rich in biotin.^ A high propor- 

 tion of the biotin originally present remained in meat after cooking. ^ 



Fresh cheese contained from o-oii to 0-076 /xg. per g. of biotin, 

 and the amount increased 2- or 3-fold on ripening.^ 



In yeast and animal products, biotin appeared to exist mainly in a 

 combined water-insoluble form, whereas in vegetable material and 

 plants it existed predominantly as a water-soluble form. In cereals 

 and nuts, however, a considerable proportion was present in combina- 

 tion with protein. To obtain satisfactory analyses of yeast and meat, 



423 



