1903.] on Becent Advances in Slereochemistry. . 313 



chemical action induced by some non-living substance contained in 

 the expressed juice of the yeast cells. This substance — zymase — has 

 been isolated in the solid state and belongs to the class of substances 

 known as unorganised ferments or enzymes. Although many enzymes 

 are known, each active in inducing the occurrence of some particular 

 chemical change or changes, nothing is as yet known as to their 

 molecular constitutions; ages of evolution have given such complexity 

 to these substances that a century or less of chemical investigation 

 has contributed practically nothing towards elucidating their nature. 

 During the investigation of great numbers of cases of animal and 

 vegetable vital activity, instances of the action of enzymes have been 

 found, the function of the euzyme being to bring about the molecular 

 degradation and, in certain cases, the molecular complication, of more 

 or less complex materials used or produced in the organism. As an 

 example of molecular degradation due primarily to enzymic action, 

 the action of zymase on grape sugar — d-glucose — may be quoted. In 

 aqueous solution, one molecule of grape sugar becomes directly 

 converted into two molecules of alcohol and two molecules of carbon 

 dioxide, in accordance with the equation — 



CeHi.Os = 2C,1SL,0 + 2C0,, 



by the enzyme zymase. The enzyme itself suffers no permanent 

 change as a result of exercising the power of causing this chemical 

 reaction to take place, so that a comparatively minute quantity of the 

 enzyme, acting for a more or less prolonged period, is able to convert 

 an unlimited quantity of grape sugar into alcohol and carbon dioxide. 

 The power which the enzyme possesses of inducing the occurrence 

 of some chemical reaction which otherwise does not take place is not 

 peculiar to enzymes ; many substances, which are all classed together 

 as the so-called catalytic agents, are known to exercise the same sort 

 of influence in assisting a chemical reaction to occur. Thus the 

 action of finely divided platinum in causing certain inflammable gases 

 to ignite in air at the ordinary temperature is a catalytic action. The 

 particular function exercised by enzjmes in animal or vegetable life 

 consists in bringing about chemical change quietly and continuously 

 without necessitating the application of any violent chemical effects 

 such as we are in the habit of using in the laboratory. Although 

 they proceed so quietly, the chemical changes thus effected are, in 

 many cases, changes which we have not yet succeeded in carrying 

 out without the assistance of an enzyme ; in the conversion of sugar 

 into alcoliol and carbon dioxide, zymase is performing a reaction 

 which has never yet been brought about by the use of the ordinary 

 laboratory methods. 



Without quoting more specific instances, it may be generally 

 stated that most of the cases of enzymic action hitherto investigated 

 are cases in vp-hich a large molecular complex is degraded or broken 

 down into substances of lower molecular weight. But it is important 

 to note that the organism is also the seat of processes which result 



Y 2 



