98 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



believed that dextrin existed in the starch-grain and that it is converted into sugar. This 

 view was accepted until Musculus (1860), as before noted, stated the existence of a definite 

 ratio between the quantities of dextrin and sugar formed, and formulated the theory of 

 the hydrolysis of starch directly into conjoint molecules of dextrin and sugar. This theory 

 was opposed by a number of contemporaneous workers, but the later work of Musculus 

 and his co-workers, and of Brown and Heron (Ann. d. Chem. u. Phar., 1879, cxcix, 241), 

 and of a number of subsequent experimenters, set the seal of approval, so that it seems 

 to have been accepted without much question, even up to the present, although the inves- 

 tigations of Lintner and Diill (Ber. d. d. chem. Gesellsch., 1893, xxvi, 2533) and others 

 pointed strongly to the contrary, as will be referred to later. That dextrin may be formed 

 without an attendant production of sugar has been shown by subjecting starch to torre- 

 faction, to modified enzymes, and to the restricted actions of high moist heat, glycerine, 

 sulphurous anhydride, etc. Such being the case, the assumption that it is a conjoint 

 product with sugar by a process of hydrolysis is needless and untenable. 



The conception of the disaggregation of starch into sugar by consecutive stages of 

 hydi'olysis had its origin, as stated, in misconceptions of Musculus, and it received support 

 in the fact that in a related reaction the conversion of dextrin into sugar is owing to hych-ol- 

 ysis, and in the assumption that existed up to a very recent period that diastase, for 

 instance, is an individual or unit substance having properties which are manifested seri- 

 ally in the liquefaction of starch, in the conversion of starch into dextrin, in the conversion 

 of dextrin into maltose, and in the conversion of maltose into glucose, respectively, and, 

 as a consequence, that if one of the processes is hydrolytic, the natural inference is that 

 all must be. It has, however, been clearly demonstrated by the investigations of recent 

 years that enzymes as ordinarily prepared are very commonly composites, each com- 

 ponent enzyme exercising its own special properties, so that a product of one enzyme 

 wliich may not be further altered by that enzyme may become an initial substance in 

 relation to another.* 



The properties of diastase were shown by Bourquelot (Compt. rend., 1887, civ, 71, 

 177, 576) to be capable of modification in such a manner by the action of moist heat as 

 to materially alter the character of the products of digestion, from which he was led to 

 assume that diastase contains several enzymes which present unequal resistance to the 

 injurious influence to heat. When saliva was heated to 70° its power of forming sugar 

 fell about 90 per cent, and when heated to 71° dextrinization continued, but no sugar 

 was formed. Experiments of later investigators also show that even though sugar forma- 

 tion ceases at the above temperature, dextrin formation continues. Emulsin after being 

 heated, was shown by Jacobsen (Zeit. f. physiolog. Chem., 1892, xvi, 340) to be active in 

 relation to amygdaline, but no longer in relation to hydrogen peroxide. 



Duclaux (Traits de microbiologie generale, ii. Diastases, Toxines et Venins, 1899), 

 from the results of his experiments, concluded that diastase consists of two enzymes, 

 one of which (amylase) converts starch into dextrin, and the other (dextrinase) con^ferts 

 dextrin into sugar. Since that time much evidence has accumulated to show not only that 

 enzymes as ordinarily prepared are generally composed of two or more distinct enzjanes, 



* Fischer and Lindner (Ber. d. d. chem. Gesellsch., 1895, xxviii, 984) showed that three enzymes are consecutively 

 active in the conversion of raffinose (a trihexose) into glucose, fructose, and galactose. Buclmcr and Meisenhoimer 

 (Ber. d. d. chem. Gesellsch., 1904, xxxvii, 417) found that two enzymes are active in the alcoholic fermentation of 

 sugar, one (zymase) converting sugar into lactic acid, and the other (lactacidase) converting lactic acid into alcohol 

 and carbon dioxide. Bourquelet (Compt. rend., soc, biol., 1902, liv, 1140) and Bourquelot and Hdrrisey (Compt. 

 rend., 1902, liv, 399) in experiments with gentianose (a trihexose wliich consists of two molecules of glucose and one 

 of levulose) found that two enzymes, invertase and emulsin, which exist in the juice of Aspergillus, split it into simple 

 hexoses, one splitting off levulose and the other splitting the glucose. Armstrong and Ilorton (Proc. Roy. Soc, 1908, 

 Lxxx, 312) proved that emulsin of almond contains three enzymes: lactase, ;8-glucase, and a third enzyme. The 

 enzymic conversion of maltose into glucose has been shown to be due to a special enzyme (glucase) found in variable 

 quantities in the preparations of diastase, ptyalin, amylopsin, etc. (For the sources, actions, etc., of glucase, and for 

 other references, see page 141.) 



