THE PLANT OXIDASES 241 



recently Bunzel (1912) has perfected it, and introduced 

 several necessary precautions previously omitted. 



Bunzel, too, finds that the amount of chemical change is 

 directly proportional to the concentration of the oxidase 

 present, and concludes that the typical plant oxidase with 

 which he worked " is not an enzyme in the customary 

 sense of the word, but rather a substance entering directly 

 into the reaction, and being destroyed in the course of 

 the same." It must not, however, be forgotten that 

 Bunzel is only measuring the organic peroxide present, 

 assuming the correctness of this view of the nature of the 

 complete oxidase. 



He proposes as a unit, to express the oxidase content 

 of a plant juice, " a solution of such a strength that 1 litre 

 of it will be capable of bringing about the consumption 

 by pyrogallol of the equivalent of 1 gramme of hydrogen 

 i.e., a unit of 8 grammes of oxygen." Since it seems likely 

 that much valuable knowledge will be gained from the 

 systematic application of Bunzel's method to problems of 

 plant physiology, his apparatus will be described here. 



REQUIREMENTS AND LIMITATIONS OF MANOMETRIC 

 METHODS OF ESTIMATING OXYGEN. 



Since the rate of oxidase action is to be measured by 

 the oxygen absorption, numerous precautions in estimating 

 this gas by pressure changes must be observed. Of these 

 Bunzel mentions the following : 



1. The temperature of the reacting substances must be 

 maintained constant to within 0-1. This limit is fixed, 

 as a variation of Ol corresponds to a pressure alteration 

 of 0-025 centimetre of mercury, which is the limit of 

 accuracy of the manometer readings. In addition, con- 

 stancy of temperature is desirable, on account of the large 

 temperature coefficient of the rate of chemical reactions. 



16 



