IX. occrHUKNCK I\ I'ooi) 595 



such procedures, a constant, known amount ot liiotin is adilctl lo (•a<'li of 

 sev(M"al tubes, and the amount < 1 protein I'eciuii'ed to render a <i;i\-en i)ro- 

 portioii of it inia\ailal)le to the test organism is deteiinined."' 



VIII. Standardization of Activity 



Hiolin is a\ailal)le in pure syntlietic form. This r//-l)i()tin represents tlie 

 l)est standard for reference pui'poses, if the fact is considered that foi' ani- 

 mals the acti\ity of the syntlietic product is only 50% that of the natural 

 ^/-l)iotin. 



In microliiological tests the hiotin effect is less specific and may be ex- 

 erted by a large number of chemically closely related, but also chemically 

 different, compounds such as oleic acid and pimelic acid. All these effects 

 may i)e expi'es.sed in biotin e([ui\alents. 



IX. Occurrence in Food 



I'ALL (;^()U(;\ 



Biotin is widely i"epresented in various food products. Its estimation in 

 microbiological tests has great limitations, owing mainl>' to two interfering 

 factoi's: (a) the occurrence of chemical comi)ounds with unspecific l)iotin 

 activity; (b) the difHcuity of complete extraction of the l)ound biotin frac- 

 tion (see p. 52V)). 



In animal assay the.se complications are niore or less eliminated, biotin 

 activity being exerted mainly by its true chemical ecjunalent and l)y the 

 liljeration of biotin in the digeHti\e tract followed by its absorption and 

 utilization. 



I'sing rats fed an egg white diet, (lyc'irgy' found li\'ei', kidney, yeast, and. 

 to a much lesser extent, cow's milk and bananas to be good sources of biotin. 

 In contrast, brain, spleen, thymus, blood, heart, peripheral muscle (beef), 

 and rice polish have shown, at least in the doses used, no biological biotin 

 activity. For instanc<', l)eef li\-er (fresh) was therapeutically acti\-e in daily 

 doses of 0.5 g., kidney in 1.0 g., yeast (dry) in 0.8 g., cow's milk in 10 ml., 

 and bananas in 5 g. Heart was gi\-en in dail\' do.ses of up to .S.O g.. nniscle 



'« K. K. Kakiii. K. K. Siicll, and H. .J. William.s. ./. Hiol. ('han. 140. ra") (1!I41 I. 

 ' P. Gyorgy, ./. Hiiil. Chrm. 131. 7:« (laiO). 



