THE ENZYMES AND TRAUBE'S THEORY. 21 



fermenting material (e.g. sugar) and discharged the fermentation 

 products as waste matter. 



According to another, the decomposing force simply emanated 

 from the cells and became the direct cause of the decomposition 

 of the fermentable matter around them. 



The physico-molecular theory, proposed by NAGELI (II.), ex- 

 presses this view in the following words : " Fermentation is, 

 therefore, the transference of conditions of movement in the 

 molecules, atomic groups, and atoms of the various compounds 

 constituting the living plasma (which compounds remain chemi- 

 cally unchanged) to the fermentative material, whereby the 

 equilibrium of its molecules is destroyed and their dissociation 

 induced." The radius of the sphere of influence of the individual 

 yeast cells is estimated by Nageli as from 20 to 50 p. 



This definition differs from that formerly given by Liebig 

 merely in a single, though important, consideration, viz., it regards 

 the living cell as the source of action, whereas the other definition 

 speaks of inanimate albuminoid substances. Nageli was, how- 

 ever, unable to prove the correctness of his theory, and the calcula- 

 tions, deduced from other observations, which he brought forward 

 in support thereof have in course of time proved inapplicable. 



18. The Enzymes and M. Traube's Ferment Theory. 



There is still another possible explanation of the power of 

 living cells to act at a distance. This regards the cells, not as 

 centres of radiating molecular movements, but as forming centres 

 of production of metabolic products which penetrate through the 

 cell membrane into the surrounding liquid. There they become 

 widely distributed by diffusion, and by their influence bring about 

 the decomposition of certain constituents of the solution, but do 

 not undergo any chemical change themselves. These active bodies 

 are called enzymes, and their behaviour is, as will be observed, 

 different from that of ordinary chemical agents, since the latter 

 effect alterations in other groups of atoms by their chemical affinity, 

 whereby the old combination is broken up, and the separated 

 portion enters into a new atomic grouping with a part of the 

 active agent. Accordingly, a definite weight of the agent can 

 only displace a definite quantity (known as the "equivalent 

 weight ") of other compounds ; whereas the enzymes behave 

 differently, their activity being practically illimitable. They do 

 not combine with the products of the reaction, but continue to act 

 on the residual undecomposed substance. 



The first enzyme was discovered by PAYBX and PERSOZ (I.) 

 in 1833, who detected in malt extract a substance which they 

 termed diastase capable of converting starch into sugar. They 

 were, however, unable to isolate it in a pure condition. Three 

 years later THEODOR SCHWANN (III.) discovered in gastric juice 



