498 POPULAR SCIENCE MONTHLY. 



never been isolated in a pure condition, and hence no definite knowl- 

 edge of their chemical composition and constitution has yet been 

 secured. In general, enzymes are precipitated by alcohol from the 

 watery extract of plant or animal tissue, but such a precipitate con- 

 tains the enzyme inextricably mingled with other chemical compounds, 

 and all attempts to separate out a pure enzyme have thus far signally 

 failed. The whole field of enzyme study is therefore at present beset 

 with the same sort of difficulties that the science of bacteriology en- 

 countered before the days of 'pure cultures,' and it is doubtless true that 

 effects that are at the present time ascribed to individual enzymes are 

 in reality caused by mixtures of distinct varieties. 



The different kinds of enzymes are at present chiefly distinguished 

 through the differences in the changes that they produce in other sub- 

 stances. The enzymes that act upon starchy substances, for instance, 

 may be conveniently grouped together; those that disintegrate 

 albuminous compounds may be similarly treated, and so on. 



Enzymes converting starchy substances into sugar. The longest 

 known and perhaps most thoroughly studied enzyme is a representative 

 of the group that transforms insoluble carbohydrate substances into 

 soluble ones. Amylase, or diastase, is the well-known enzyme that 

 accomplishes the conversion of the starch of the barley-grain into 

 sugar in the process of malting. The action of the enzyme in 

 this process appears to be quite elaborate since the complex 

 starch molecule passes through several stages during its conver- 

 sion into sugar, the hardly less complex substances known as 

 'erythrodextrins' and 'achroodextrins' being formed on the way. 

 The theory has been advanced that the starch molecule breaks down by 

 the taking on of successive molecules of water and by subsequent de- 

 compositions, sugar (maltose) being formed at each splitting, together 

 with a dextrin of lower molecular weight. Duclaux, however, main- 

 tains the existence of two enzymes in malt, one, a liquefying or de- 

 coagulating enzyme to which he would restrict the name amylase, and 

 which converts the insoluble starch into the soluble dextrins, and a 

 second (dextrinase), which has a saccharifying power and converts the 

 dextrins into sugar. Other enzymes that may be placed in the same 

 group with amylase are inulase and cytase. Inulase converts into fruit 

 sugar a reserve food-substance found in many plants and known as 

 inulin. Inulin is allied to starch in its chemical composition, and 

 probably breaks down by successive stages under the action of inulase 

 just as starch does under the influence of amylase. Another form of 

 reserve food-substance stored up by many plants is the familiar sub- 

 stance comprising the cell-wall of most plants and known as cellulose. 

 This substance, like inulin and starch, can be changed into a more 

 directly utilizable substance by the action of cytase, an enzyme found 



