iqiq] rose— blister canker 107 



that the oxidizing power of a tissue bears some relation to its acidity, 

 a relation which was rendered more probable by the fact that, 

 according to titration and indicator tests, the acidity rises in the 

 Bunzell apparatus during the course of an experiment at the same 

 time that oxidation gradually decreases and finally ceases. The 

 suggestion was made, therefore, that ''the gradual slowing down 

 of oxidation in the Bunzell apparatus is brought about in part by 

 the accumulation of oxidation products, probably acetic and oxalic 

 acids in the case of pyrogallol, and not by a using up of the oxidase 

 through chemical combination between oxidase and oxidizable 

 substance.'' The validity of this theory in the light of later investi- 

 gation will be discussed in the experimental part of this paper. 



Experimental 



OXIDASE ACTIVITY 



Extracts of fresh bark. — An account will first be given of 

 that part of the work done at the Missouri State Fruit Experiment 

 Station. Extracts of fresh Ben Davis bark were used, prepared as 

 follows: limbs were brought in from the orchard, the bark quickly 

 ground in a meat grinder, and water and toluol added in the propor- 

 tion of 4.25 cc. of toluol for each 100 cc. of water. The mixture 

 was then allowed to extract at 28-30° C. for i hour, with frequent 

 stirring, and filtered through filter paper. The proportions of 

 water and toluol used, assuming that the fresh bark contained 

 50 per cent water, were such as to make the extracts very nearly 

 equivalent to those prepared for the earlier work (30) with dried 

 bark. All data were corrected to the basis of dry weight deter- 

 mined by weighing and drying samples of the ground bark in 

 triplicate to constant weight in a bath at 95-99° C. 



Measurement of the amount of oxidation was made by means 

 of the simplified Bunzell apparatus, using i cc. of the extract pre- 

 pared as just described, and either 4 cc. of a i per cent solution of 

 pyrogallol, 0.04 gm. of benzidine, or 2 drops (0.025 gm.) of 

 guaiacol; water was added to make the final volume 6 cc. The 

 various combinations of bark, oxidase reagent, and water were 

 run in duplicate. 



