15G DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Admitting the existence of stereoisomeric forms of starch-substance, and that a 

 priori there should be corresj^onding specific stereoisomeric forms of dextrins, we meet 

 with a very obvious difficulty in the study of the specificities of these hypothetical decom- 

 position products in relation to genera, species, etc., in the total lack of exact knowledge 

 of the precise dextrinous products of digestion. It is manifest from the literature quoted 

 in this and other chapters that our information as to the 'precise nature of the dextrins 

 formed is nil; that most if not all experimenters have been working with impure bodies 

 or mixtures; that our metliods of distinguishing tlifTerent erythrodextrins and different 

 achroodextrins obtained from the same preparation, if such really have existence, are by 

 no means certain ; and that it is therefore useless under present conditions to attempt the 

 differentiation of corresponding dextrins from the starches of different species, except in 

 a crude and inconclusive way, as, for instance, as done by Pottevin, Roux, and others, 

 by taking the dextrinous products as a whole. 



THE SYNTHESIS OF STARCH. 



According to the well-known hypothesis of van't Hoff (Zeit. f. anorgan. Chemie, 1898, 

 XVIII, 1) an enzyme gives rise only to such products in the analysis of a given substance 

 as it will under appropriate conditions combine in synthetizing the same substance. In 

 other words, if a given enzyme or mixtm'e of enzymes acts upon starch to decompose it 

 tlarough a series of actions into a series of products such as erythrodextriu, aclu'oodextrin, 

 maltose, and glucose, it or they will under properly modified conditions reverse the opera- 

 tions and thus synthetize starch. The results of modern research lead unquestionably 

 to the belief that the activities of enzymes underlie vital processes. Various plant and 

 animal enzymes ha^'e been used to break down starch into the products mentioned, and 

 these iDroducts correspond with substances found in plants during the formation of 

 starch ; hence they are presumably intermediate bodies between starch and the immediate 

 antecedents of glucose that are synthetized from carbon dioxide and water. Moreover, 

 syntheses representing at least two of these hypothetical steps in starch formation have 

 been carried out in vitro by Croft Hill (Jour. Chem. Soc. Trans., 1903, lxxxiii, 578) and 

 E. F. Armstrong (Proc. Roy. Soc, 1905, lxxvi, B. 592), in which the maltose-glucose reac- 

 tion was reversed, and by the author (Univ. Penna. Medical Bull., 1910, xxiii, 57; Proc. Soc. 

 Exper. Biology and Med., 1910), in which the starch-erythrodextrin reaction was reversed, 

 with slight evidence of an achroodextrin-maltose reversion and also of a maltose-glucose 

 reversion. Luig (page 148) suspected a glucose reversion. 



Until comparatively recent years the energies of the chemist in the study of bodies 

 which occur naturally only in plants and animals have been chiefly in the direction of 

 analysis, so that he has worked essentially in a direction opposite to those in living matter 

 in the syntheses of these substances; but during the last ten or twelve years especially he 

 has come in touch with Nature's processes, owing to the eijochal investigation of Croft Hill, 

 with the result of successes in the syntheses of carbohydi-ates, fats, and proteins which 

 scarcely more than two generations ago would generally have been regarded as being 

 im]irobable or impossible; and he has at the same time thrown extremely important light 

 on the analytic and synthetic processes that take jjlace in living matter. The important 

 discovery of Wohler, in 1828, that he had made urea by the interaction of ammonia and 

 lead acetate, is the first on record of the synthesis in vilro from inorganic substances 

 of an organic substance that is inherently peculiar to hving matter. Wohler evidently 

 appreciated the great fundamental importance of his discovery, but it seems that this was 

 far from being the case with his contemi)oraries, and that, as is often the case, an epochal 

 in\'estigation remains wholly unappreciated for years until new inquiries bring it to the 

 forefront. Even his teacher Berzelius failed to realize its importance. The progress in 

 the synthesis of plant and animal substances from this period up to the present has been 



