VII. KS'I'IM ATIOX 589 



mainly on its hioloj^iical crtcct in hii^licr animals or mici'»i(ii'^;anisms. Xo 

 c'liemi(."il aiul physical mclhods arc axailahlc at the ])rcsciit time lor the 

 determination of hiotin. 



The microl)ioloj>;ical methods hax'c the achanta^e of heinji technically 

 simple and short-term procetlure.s. However, they have also seriinis limi- 

 tations. Most of the microorganisms used for assay of l)iotin will respond 

 only to fit'c and not to hound biotin. Thus, concentrates must be prepared 

 throuuh enzNinatic licalmeiit or acid hydrolysis in order to free bound 

 biotin and bi-inu; it into a(|ueous solution (.see p. 529). Furthermore, micro- 

 organisms ma>' also I'espond to clo.se homologs, analogs, breakdown pi'od- 

 ucts, or piecursors, .such as pimelic acid, and to other seemingly uiu'elated 

 chemicals, such as oleic acid (see p. 558) in a much more unspecific maimer 

 than higiier animals do. 



A. HIO.VSS.VV rSIXG HIGHER ANIMALS 



PAIL GVORGV 



The biological estimation of biotin may be cai'ried out with rats and 

 chicks made deficient in biotin by the use of special rations. 



1. IiAT Method 



Under ordinary dietary conthtions the l)iotin re(iuirement of the growing 

 or adult rat appears to be fully co\'ered by the amount of biotin produced 

 by the intestinal flora.' Incorporation of raw egg white (fresh or dried) or 

 avidin in a .synthetic experimental ration results in biotin deficiency by 

 preventing the intestinal absorption of biotin which forms with avidin a 

 stable unabsorbable complex (see p. 555). The gross manifestations of this 

 egg white injury, .synonymous with biotin deficiency, are characterized l)y 

 cessation of growth and by a variety of symptoms involving fur and skin, 

 such as "spectacled eyes," seborrheic dermatitis, alopecia, and other less 

 specific oi- le.ss regularly occurring manifestations.-"^ \'arying degrec^s of 

 deficiency may be identified in the experimental ainmals. Rats showing 

 cessation of giowth, "spectacled eyes," or beginning alopecia are "incip- 

 iently deficient." Any coml)iiiati()ii of these symptoms coupled with more 

 marked alopecia, closure of the eyes by exudate, and red, inflamed nose 

 and snout characterizes a slightly to moderately deficient rat. Advanced 

 lo.ss of hair, spastic gait, beginning or advanced development of cracks and 

 sores along with encrustation in the skin, scab formation, and seborrlieic 

 deposits classify the rat as moderately to severely deficient (Figs. 5 and 6). 



'V. flu \'iKno:iU(l and K. A. Kvans, Jr.. 'tlic iiioio^iical Action of tlic \"it;iniin.s, 

 pp. t44IT. Uiiivor.sity of C'liicafio Press, C'hicat;o 1942. 



2 M. A. Boas, Riochem. .1 . 21, 712 (1927). 



3 P. Gyorsy, Z. arztl. Forlbild. 28, 377, 417 (1931). 

 ' P. Gyorgy, J. Biol. Chem. 131, 733 (1939). 



