640 Professor W. M. Bayliss [March 24, 



Xow it is evident that something of tlie kind contemplated by 

 these two latter possibilities is at the bottom of the process called 

 *' catalysis " by Berzelius. This chemist directed attention to the 

 numerous cases known, even at his time, where the presence of a 

 third substance brings about an enormous acceleration of a reaction, 

 without itself taking part in it, so far as appears at first sight ; at all 

 events, this third substance reappears at the end unchanged. An 

 example is the effect of finely divided platinum on hydrogen peroxide. 

 Similar phenomena were known to Faraday, and described by him 

 about the same time, but without giving them a special name. 



Agents of this kind were soon discovered to be present in living 

 cells. Such catalysts are called, for convenience, " enzymes," as sug- 

 gested by Klihne, although there is no real scientific necessity for the 

 name. That of " ferments " is still sometimes used, and is not now 

 liable, as it was in Kiihne's time, to cause confusion by application to 

 living microbes. 



Since catalysts are, as a rule, found unchanged at the end of their 

 work, it is clear that they do not themselves afford energy for the 

 purpose. Indeed, the energy change of a catalysed homogeneous 

 system is the same as that of the reaction when proceeding at its 

 ordinary slow rate. How, then, do they act ? 



The first thing to note with respect to enzymes is that they are 

 capable of activity in media in which they are insoluble. Whatever 

 may be the nature of this activity, therefore, it is exerted by the 

 surface of the catalyst. We may then reasonably ask, as the most 

 obvious hypothesis, is there ground for holding that the increased 

 rate of reactions brought about by enzymes is effected by increase of 

 concentration of the reagents at the surface and consequent accelera- 

 tion of the reaction by mass action ? We know that substances 

 which lower surface energy of any form are concentrated at such 

 boundary surfaces. The process is well known as " adsorption," and 

 is a consequence of the operation of the principle of Carnot and 

 Clausius, which states that decrease of free energy always occurs, if 

 it is possible for it to do so. In fact, such an explanation was given 

 by Faraday of the effect of metallic platinum in causing combination 

 of oxygen and hydrogen gases. Although the name " adsorption " 

 was not used in this description, Faraday had very clear ideas of the 

 process, and gives several interesting cases. He showed that the 

 necessary condition for the activity of platinum in the case referred 

 to is a chemically clean surface, in order that the gases may condense 

 on it. It matters not whether the removal of deposit is effected by 

 mechanical poHshing ; by the action of acid or of alkali ; by oxida- 

 tion or reduction — making it either anode or kathode in an electro- 

 lytic cell will serve. It should be mentioned that this ^-iew did not 

 receive universal acceptance, but the fact that it recommended itself 

 to the keen insight of Faraday is powerful evidence in its favour. 



I would not venture to state that this hypothesis is yet in a 



