8 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



These astonishing manifestations of selectivity, which of course mean important 

 differences in the configurations of the molecules and specific relationshii)s of these differ- 

 ences to the protoplasmic structures and nutritive mechanisms of the organism, must 

 be of the deepest fundamental significance. Not only do these organisms thus distinguish, 

 as it were, between the dextro and Ltvo isomers, but also between different dextro forms. 

 Thus, while 07ily the dextro varieties of hexoses are fermentable, 7iot all of them are 

 fermentable; and those which are exhibit different degrees of fermentability that vary in 

 specific relationship to their molecular configurations. As has been shown, dextro-glucose, 

 dextro-mannose, and dextro-fructose are closely alike in their configurations, and all 

 three are attacked with readiness; dextro-galactose and dextro-talose are likewise closely 

 related, but the former is fermentable by means only of a specially prepared yeast-juice, 

 while the latter is, so far as known, unfermentable. All of these differences are readily 

 explainable upon the basis of the existence of slight differences in the relative positions 

 of OH groups. The enzyme emulsin is without action on both a-methyl dextro-glucoside 

 and a-methyl dextro-galactoside, but it breaks down /3-methyl dextro-glucoside and 

 (3-methyl dextro-galactoside; whereas, the destruction by yeast is the reverse, the former 

 substance being metabolized but not the latter. 



Studies of the properties of stereoisomers from the aspects of toxicity and general 

 physiological actions have afforded interesting and even startling examples of the as yet 

 little appreciated importance of molecular configuration of substances in their relations 

 to protoplasmic processes. A few instances hastily gathered from the researches of various 

 investigators are all that are required at this junctm-e. Brion, in experiments on dogs with 

 the dextro-, laivo-, meso-, and racemic tartaric acids, found marked differences in the extent 

 to wliich they were oxidized. He recorded that the lajvo and meso forms are destroyed 

 in equal degree, the dextro form to a less degree, and the racemic form to a very slight 

 degree. Pohl, two years before, had also found, in experiments on rabbits and dogs, that 

 tartaric acid (dextro form) is only to a slight extent destroyed in the system. Neuberg and 

 Wohlgemuth, in investigations on rabbits with dextro-, laevo-, and racemic arabinose, re- 

 corded that when these substances were given by the mouth the percentages which disap- 

 peared were in order, Isevo-, racemic, and dextro-arabinose ; and they also noted that only 

 the Isevo form gave rise to glycogen formation. Beyerinck recorded that the nutritive 

 values of the stereoisomeric tartaric, fumaric, and maleic acids may be markedly different. 

 Nagano noted differences in the absorbability of certain kinds of sugars: Thus, a 2.5 

 per cent solution of dextro-mannose was distinctly less absorbable than the same concen- 

 tration of dextro-galactose, dextro-glucose, and dextro-fructose, while Isevo-xylose was 

 decidedly more absorbable than Isevo-arabinose. With stronger solutions differences were 

 noted in the first three. Mayer found that dextro-mannose is more readily oxidized than 

 Isevo-mannose, but that, unlike the difference noted in the enantiomorphous forms of 

 arabinose, both (instead of only one) led to the formation of glycogen. Neuberg and 

 Mayer, in experiments on rabbits with the three mannose stereoisomers, recorded not 

 only that the dextro form is the best in respect to nutritive value, but also that both the 

 dextro and racenoic forms are glycogen-builders, the latter being partially split, and all 

 three yielding a derivative of the glucose series. McKenzie found that the dextro-^- 

 oxybutyric acid is more reacUly broken down than the lajvo form, and that after giving 

 racemic salts, racemic and lievo acids were excreted in the urine, the dextro acid disap- 

 pearing in tlie body. 



Instances to show that the configuration of molecules is of great importance in rela- 

 tion to the degree of toxicity and general physiological actions are numerous. Maleic 

 and fiunaric acids are stereoisomers, and in the exijeriments of Isliizuka on dogs it was 

 found that tlie former is distinctly the more toxic, and confirmatory results are recorded 

 by Kahlenberg and True in experiments with Penicillium glaucum and Lupinus albus. 



