VII. ESTIMATION 593 



than !)>■ mouth. A test i)('ii()(l of 4 weeks is customary, and the results ai'c 

 computed as in other growth assays, (lain in \veiji;lit per week (huin<i the 

 test period is a linear function of the lof>;-dose of hiotin within I he ran^c of 

 0.1 to 1.0 7 per day.'' 



j\Iale rats are nioi'e suceptihle to hiotin deficiency than lemale rats,-"* and 

 all)ino rats more tiian piei)ald or l)lack i-ats.-' ■■■ '^ 



2. Chick Method 



The cliick recjuires mucli larjiiM' amounts of biotin than the rat, and even 

 under normal conditions the intestinal synthesis of biotin in chicks is too 

 limited so that biotin deficiency can ))e produced by a biot in-low diet alone, 

 without the aid of avidiii.^' ** Biotin deficiency in chicks mainfcsts itself 

 as in rats by a declining weight curve and by cutaneous lesions, especially 

 on the bottoms of the feet and around the beak. 



The techni(iue used for the biological assay of biotin in rats may also 

 be applied to chicks, with the difference that a biotin-free purified ration 

 is used.^ Successful assays may also be obtained with a commercial chick 

 ration mixed with egg white (avidin to inactivate its biotin content) . The 

 assa}^ ma^' l)egin witiiout a prolonged depletion period and is usually more 

 of prophylactic nature, lasting 4 weeks. Relative potency is computed from 

 growth response and is supported by evidence of dermatis in the negative 

 controls and its prevention at all dosage levels of biotin, except possibly 

 the lowest. 



B. AIICROBIOLOGICAL ESTIMATION 



ESMOND E. SNELL 



A wide variety of microorganisms require biotin for growth, and many 

 of these have been used for its assay. These include Clostridium butylicum, 

 several lactic acid bacteria and yeasts, Rhizobium trifolii, and Neurospora 

 crassa. Each of the various proposed methods has been summarized else- 

 where in some detail.^ Of these, the most widely used and uniformly suc- 

 cessful has been the method of Wright and Skeggs,i° which employs Lac- 

 tohaciUus arabinosus as the test organism. •'■ "■ '- Growth of L. arabinosus 



^ P. Gyorgy, Vitamin Metliods, Vol. 2, pp. 22Sti'. Academic Press, New York, 1951. 

 ■> H. T. Parsons and E. Kelly, /. Biol. Chem. 100, 645 (1933). 



8 S. Ansbacher and M. Landy, Proc. Soc. Exptl. Biol. Med. 48, 3 (1941 ). 



9 E. E. Snell, in Vitamin Methods, Vol. 1, p. 327. Academic Press, New York, 1950. 

 10 L. D. Wright and H. R. Skeggs, Proc. Soc. Exptl. Biol. Med. 56, 95 (1944). 



" L. D. Wright, in Biological Symposia, XII, Estimation of the N'itamins, p. 290. 



Jaques Cattell Press, Lancaster, Pa., 1947. 

 '2 Association of Vitamin Chemists, Methods of \'itanun .\ssa\-, 2iid cd., p. 245. 



Intenscience Publishers, Xew York, 1951. 



