I9I9] 



ROSE— BLISTER CANKER 



125 



A unimolecular reaction is one in which the concentration of 

 only one substance is changed. If oxidation of pyrogallol by plant 

 material in the oxidase apparatus be such a reaction, the substance 

 whose concentration is changed is pyrogallol. The "oxidase'' then 

 appears as the catalyst, its concentration remaining unchanged 

 during the course of the reaction. Even at that it is not neces- 

 sarily proved to be an enzyme, since the linear relationship between 

 time and amount of change is also shown in the oxidation of pyro- 

 gallol by potassium carbonate. 



Effect of adding protective colloids. — Bayliss (6) and 

 Perrin (26) have suggested that the oxidizing enzyme is an active 

 form of the colloidal hydroxide of manganese, iron, or copper, 

 kept in this active state by an emulsion colloid such as gum or 

 albumin, acting as a protective colloid. Tables XV and XVI 

 show the effects of additions of gelatine and gum arabic. Table XV 

 shows that o . 2 per cent gelatine increases considerably the oxida- 

 tion by healthy bark and only sHghtly that by diseased bark. 

 Three other experiments with pyrogallol and 2 with pyrocatechin 

 with o . 2 per cent gelatine added showed similar results. The use 

 of o . 8 per cent gelatine with pyrogallol also showed a similar effect. 

 Both 0.2 and 0.8 per cent gum arabic had little or no effect on 

 healthy bark and a slight accelerating effect on diseased bark. 



TABLE XV ' 



Effect of o . 2 per cent gelatine on oxid.ation of pyrogallol by healthy 

 and diseased b.ark; temperature 22-24° c. 



Since gelatine is amphoteric, one might infer that it or its 

 splitting products act as buffers, thus reducing the rate of increase 

 of the hydrogen ion concentration with progress of the oxidation 



