THE PLANT OXIDASES 245 



that no pyrogallol enters it. For, as is well known, 

 alkaline solutions of pyrogallol rapidly absorb oxygen. 

 The apparatus is completed by the manometer O, which 

 may be disconnected by the stopcock N. 



For titrating the contents of the basket H at the end of 

 each experiment, the whole piece GH is removed, and the 

 ground-glass joint K inserted into a large-bore rubber 

 stopper, R, after pulling out a rubber bung. The stopper 

 R serves to close a flask, S, shown in Fig. 25. In the 

 bottom of this are sticks of sodium hydroxide to remove 

 all carbon dioxide from the air in it. A burette, T, filled 

 with dilute acid is inserted into the flask by a ground-glass 

 aperture, V, in which it can rotate, so as to be placed above 

 H. The upper end of V is kept dust-free by a plug of 

 cotton in W. 



MATERIALS USED IN BUNZEL'S OXIDASE ESTIMATIONS. 

 As a source of oxidase, Bunzel employed the juice 

 pressed from potatoes through a piece of silk cloth. Fresh 

 juice only was used, and previous to pressing the tubers 

 were peeled and passed through a meat-chopper. In 

 experiments upon beets the leaves and roots were similarly 

 treated. In no case was the sap further cleared by filtra- 

 tion through paper. It may be remarked that such treat- 

 ment would yield sap of a truly comparable nature from 

 each source, but that the values obtained would in no 

 case be absolute, nor would the results from different 

 tissues have any accurate comparative value. Preparation 

 of the sap after treatment with liquid air would entirely 

 do away with this source of error. 



Pyrogallol was used as the substance to be oxidized, for 

 several reasons. It is obtainable in a high degree of 

 purity, is very soluble in water, and its solutions are very 

 nearly neutral. Again, the best of the known existing 



