ASSAY METHODS 65 



substance for yeast. Woolley 173 and Williams and co-workers m inde- 

 pendently developed assay methods based upon this observation. The 

 work of the latter group was in part an outgrowth of earlier work 169 in 

 the author's laboratory. 



The two methods are essentially alike, the main difference being in 

 some of the constituents of the basal medium. In order to take care of 

 unknown yeast nutrilites, 155 Williams and co-workers introduced into the 

 basal medium a liver autolyzate which was rich in unknown nutrilites 

 but relatively poor in inositol. This small amount of inositol caused the 

 growth in the basal medium to be heavier than would otherwise be the 

 case; but adequate responses were obtained by the addition of 0.1 /*g to 

 0.8 fig inositol, and the method was applied extensively 96 - 101 with success. 

 Woolley used a dialyzed rice bran extract (which was lacking in free 

 inositol) as an ingredient of his basal medium because it contained un- 

 known yeast-stimulating material; he obtained satisfactory results. 



It appears that, provided the problem of extraction is cared for (p. 38) , 

 either of the yeast methods yields satisfactory results. It is also probable 

 that either method could be improved if it were reinvestigated in the 

 light of present knowledge. The extensive application of one of the yeast 

 methods to the study of the contents of tissues yielded results which in 

 one case apply to the amount freed by autolysis and in a later study to 

 the amount freed by enzymatic digestion. 96 " 101 The total inositol values 

 were generally materially higher than those obtained by autolysis or 

 enzymatic digestion. 85 From the nutritional standpoint the total inositol 

 values may well be the most important, because bound forms of inositol 

 are utilizable by mice. On the other hand, the general nutritional impor- 

 tance of inositol is problematical and the availability of different forms 

 of inositol to different animals is largely unknown. The fact that phytic 

 acid interferes with the assimilation of calcium in diets 175 suggests that 

 inositol is not always freed by digestion and hence is not uniformly avail- 

 able in this form. 



Woolley 176 has made a careful study of the specificity of the yeast test 

 for inositol, and has found that only meso-inositol is effective. Other 

 naturally occurring polyalcohols including isomers are inactive, as are 

 also inositol esters, including phytic acid and soybean lipositol. The bound 

 inositol in amylase is freed by enzymatic action, since about the same 

 values were obtained whether enzymatic digestion or acid digestion was 

 used. 177 



Another microbiological method for the determination of inositol in- 

 volves the use of a mutant strain of Neurospora. 178 This appears to yield 

 satisfactory results but has not been extensively applied. The dosage 



