246 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



methods for the measurement of peroxidases was also based 

 upon the oxidation of pyrogallol in presence of hydrogen 

 peroxide. 



The most important reason of all is considered by 

 Bunzel to be that the action of the oxidase upon pyro- 

 gallol can be assumed, on the analogy of the behaviour of 

 other enzymes, to be purely catalytic; for pyrogallol is 

 slowly oxidized in presence of atmospheric oxygen, with 

 the production of colours passing from yellow through 

 orange to deep red. Thus, the action is not initiated by 

 the enzyme,' but merely accelerated. 



THE METHOD OF CARRYING OUT ESTIMATIONS WITH 

 BUNZEL'S APPARATUS. 



The oxidase apparatus (Fig. 24) is placed in the ther- 

 mostat, being clamped to the shaking machine. At this 

 stage 8 c.c. of 1 per cent, pyrogallol and 2 c.c. of plant- 

 juice have been run out from the pipettes into the com- 

 partments C and A respectively, while H contains 1 c.c. 

 normal sodium hydroxide solution. Of the stopcocks, M 

 is closed, but N and I remain open. The heating current 

 is then switched on, and about half an hour suffices to 

 reach the constant temperature and to allow the air in the 

 apparatus to become nearly saturated at that temperature. 

 The thermostat is now opened sufficiently to permit of 

 the stopcock I being closed. When this is done, shaking 

 is begun at the rate of five complete excursions in 3' 3 

 seconds. Readings are taken at intervals of ten or twenty 

 minutes, the shaking being interrupted for the purpose. 

 After about two hours no further oxygen absorption takes 

 place. 



As a check on the quantity of oxygen used up, the 

 carbon dioxide produced is estimated by removing the 

 piece GH, and placing it in position in the carbon dioxide- 



