136 C. J. T. DORYLAND 



It is clear from the results of numerous investigators that 

 microorganisms can utilize various carbohydrates, alcohols and 

 salts of fatty acids as sources of carbons, both for energy ma- 

 terial and cell construction. It has, also, long been known that 

 the optical isomers of a substance containing an asymmetrical 

 carbon atom behave very differently toward biological agents, 

 such as yeast, molds, and bacteria. The classical researches 

 of Pasteur showed that Penicillium glaucum, assimilated only 

 d-tartaric acid and not the 1-tartaric acid. Recent investi- 

 gations have shown, however, that this organism will also de- 

 compose the 1-tartaric but less rapidly than the d-tartaric form. 

 Likewise there are other organisms, bacteria, yeast and molds, 

 some of which prefer a d-form of an isomeric compound while 

 others prefer the 1-form of the isomer. Investigations of the 

 action of yeast on all the known hexoses has shown that only 

 four are fermented, viz., the d-forms of glucose, mannose, galac- 

 tose and fructose. Wlien the behavior of different species of 

 yeast toward these hexoses is studied, it is found without a 

 single exception that any species of yeast which ferments any 

 one of the three hexoses, glucose, mannose or fructose, likewise 

 ferments all three of them. We know, too, from the work 

 of E. Fischer and his associates that certain enzymes which 

 are able to decompose certain organic compounds cannot attack 

 their opposite isomers. Thus, for example, a-methyl glucoside 

 is hydrolyzed by the maltase (a-glucosidase) of yeast, while 

 j8-methyl glucoside is hydrolyzed by emulsin (j8-glucosidase) . 

 Emulsin does not act on the a-glucoside and maltase has no 

 effect on the /3-glucoside. So fundamental is this action that 

 the composition of an organic compound may often be deter- 

 mined by its behavior in the presence of an enzyme. While 

 lack of knowledge concerning the behavior of optically inactive 

 compounds toward enzymes does not permit us to speak as 

 definitely as we may concerning the optically active, neverthe- 

 less it is probable that an enyzme is capable of attacking only 

 a certain group, or formation. Such, for example, is the action 

 of myrosin upon sinigrin and other sulphur containing glucosides, 

 where the change is confined to the sulphur linkage. This 



