PHARMACOLOGY 



ments of animals with any degree of confidence. It is not known how 

 much of the biotin produced by the intestinal flora is normally available 

 to the host and whether changes in the diet, which can certainly affect 

 the amount of biotin synthesised by them (page 435), can affect the 

 extent to which biotin can be utilised. 



Bearing in mind the possibility that present-day estimates may 

 have to be revised in the light of future observations, the following 

 values have been recorded for the daily requirements of different 

 animal species : for the rat, 2^ and 0-5 to i-o^ /xg. ; for chicks, i^ 

 and 0-65* [xg. (supplied by a diet containing 7 to 10 /xg. of biotin per 

 100 g.^) ; for turkeys, 40 " rat units "; ® for monkeys, 20 /xg. ; ' and for 

 pigs, 100 fig.^ Chick embryos failed to develop if the yolk contained less 

 than 50 m/xg. of biotin per g., bat 150 m^ug. per g. supported growth.^ 



No precise estimate of the human requirements of biotin appears 

 to be available, but subjects made biotin-deficient quickly became 

 normal when 75 to 300 fig. of biotin were injected per day.^** 



References to Section 13 



1. E. Nielsen and C. A. Elvehjem, Proc. Soc. Exp. Biol. Med., 1941, 



48, 349. 



2. G. A. Emerson and J. C. Keresztesy, ibid., 1942, 51, 358. 



3. L. R. Richardson, A. G. Hogan and O. N. Miller, Univ. Missouri 



Agric. Exp. Stat., Res. Bull., 1942, 343 ; J. H. Shaw and P. H. 

 Phillips, /. Nutrition, 1945, 29, 107. 



4. T. H. Jukes and F. H. Bird, Proc. Soc. Exp. Biol. Med., 1942, 49, 



231. 



5. D. M. Hegsted, R. C. Mills, G. M. Briggs, C. A. Elvehjem and E. B. 



Hart, /. Nutrition, 1942, 23, 175. 



6. H. Patrick, R. V. Boucher, R. A. Dutcher and H. C. Knandel, 



Proc. Soc. Exp. Biol. Med., 1941, 48, 456. 



7. H. A. Waisman, K. B. McCall and C. A. Elvehjem, /. Nutrition, 



1945, 29, I. 



8. T. J. Cunha, D. C. Lindley and M. E. Ensminger, /. Animal Sci., 



1946, 5, 219. 



9. J. R. Couch, W. W. Cravens, C. A. Elvehjem and J. G. Halpin, 



/. Nutrition, 1948, 35, 57. 



10. V. P. Sydenstricker, S. A. Singal, A. P. Briggs, N. M. de Vaughn 



and H. Isbell, Science, 1942," 95, 176 ; /. Amer. Med. Assoc, 

 1942, 118, 1 199. 



14. PHAR2VIACOLOGY OF BIOTIN 



The intravenous injection of 250 /xg. of biotin per kg. of bodyweight 

 into anaesthetised cats had no effect on the blood-pressure, heart rate 

 or respiration.^ No effect was produced on strips of guinea pig uterus, 



437 



