120 THE SO-CALLED INORGANIC ENZYMES 



particular enzyme or group of enzymes, or is a general property 

 attaching to all enzymes. The action, as has been stated, is stopped 

 by a trace of hydrocyanic acid without interfering with the specific 

 action of the enzyme accompanying the " peroxidase," it is also 

 stopped by the action of heat similarly to that of an enzyme, 

 but it has not clearly been shown that the substance causing the 

 oxidation is not altered in the process, nor that there is no stochio- 

 metric relationship between the quantity of " peroxydase " and 

 the amount of hydrogen-peroxide changed. In fact, it appears that 

 the " peroxydases " are very sensitive, and that after conversion 

 of a certain amount of peroxide the action ceases. 



Whether the " peroxidases " be specific enzymes or not, the 

 action of hydrocyanic acid in stopping or " poisoning," both in 

 their case and that of colloidal platinum, is confined to one re- 

 action, that of the conversion of hydrogen-peroxide into water 

 and oxygen, and it appears to the writer that this is a narrow 

 basis on which to lay any weight as a proof of identity in mode 

 of action between enzymes and colloidal platinum. It has not 

 even been proved, for example, that hydrocyanic acid does not act 

 directly as a negative catalyst to the reaction concerned. 



While it cannot be admitted, therefore, that the terms " in- 

 organic enzyme " and " poisoning " can be legitimately employed 

 in connection with these metallic catalysts, the effects obtained 

 with them are of high interest in regard to- the manner in which 

 a colloid in solution can act as a catalyst. 



It was already known to Faraday that all porous bodies, and 

 especially certain metals, such as platinum, possessed the pro- 

 perty of absorbing large amounts of gases. The velocity with 

 which the gases are absorbed increases with the state of sub- 

 division of the metal, and is best seen in the case of platinum 

 when this is used in the finely divided form of platinum black. 

 Faraday pointed out also that this sub-division favoured the 

 action of^the platinum black as a catalyst by increasing the local 

 concentration of the substances to be catalysed, and even showed 

 that the action of catalysis by platinum black of an explosive 

 mixture of hydrogen and oxygen was stopped by the presence 

 of traces of carbon bisulphide or sulphuretted hydrogen. It is 

 wonderful how closely this view of Faraday comes to the modern 

 view with regard to the mode of action of a colloidal catalyst 

 or enzyme. 



