64 THE BIOCHEMISTRY OF B VITAMINS 



Iridium butylicum™ 2 and Neurospora crassa, 1G3 among others, but these 

 have not been used extensively. 



Biological Assay. Biological assays of biotin are relatively of little 

 importance. By introducing raw egg white into the diet of rats they 

 become deficient in biotin (vitamin H) and develop characteristic lesions. 

 The daily dose of biotin required to cure this condition was used as a 

 "unit." 164 Other animals, chicks, guinea pigs, rabbits, monkeys and dogs 

 are capable of developing egg white injury and may therefore be used 

 for assay purposes. Ansbacher and Landy 165 produced biotin deficiency 

 in chicks by feeding a heated diet low in biotin and suggested the use of 

 this procedure as the basis of an assay method. 



Trager 166 has reported the presence in the plasma of various animals, 

 of fat-soluble material — not oleic acid — which replaces biotin in the tests 

 involving lactic acid organisms and which is active for biotin-deficient 

 chicks. Contrary to these findings, however, Axelrod, Mitz and Hof- 

 mann, 1G7 as a result of a thorough study, conclude that the biotin-like 

 activity present in plasma is explicable on the basis of the content of 

 known fat acids. 



Inositol 



For the assay of inositol, chemical and microbiological methods are 

 available. In addition, some use of experimental animals has been made. 



Chemical Method. The only serviceable chemical method for inositol 

 is that of Piatt and Glock, 168 and it is subject to limitations both as to 

 specificity and to convenience and speed. Earlier chemical methods were 

 investigated in the author's laboratory 169 and were judged to be almost 

 valueless. Actual isolation and weighing of the inositol was one of the 

 expedients used, but this obviously has very serious drawbacks. 170 



The method of Piatt and Glock involves very briefly: (1) extraction 

 with water, (2) precipitation of extraneous material with acetone, (3) 

 removal of glucose by fermentation, (4) removal of other extraneous sub- 

 stances with base exchange resins, (5) differential oxidation of the resid- 

 ual glycerol and inositol with periodic acid. The last step takes advan- 

 tage of the fact that glycerol can be oxidized quantitatively without more 

 than a very small fraction of the inositol being attacked. As Woolley m 

 has indicated, however, there are in certain tissues several other sub- 

 stances closely related to inositol including isomers, and these presumably 

 would not be eliminated by any of the treatments. On this basis there is 

 some reason to question the specificity of the method. Furthermore, its 

 application is relatively exacting and time-consuming. 



Microbiological Methods. The microbiological determination of ino- 

 sitol stems from the finding of Eastcott 172 that inositol serves as a growth 



