iQig] 



ROSE— BLISTER CANKER 



109 



although the ratio between the two is greater where benzidine or 

 guaiacol was used as oxidase reagent than where pyrogallol was 

 used. The writer prefers to follow Bunzell in using the term 

 oxidase activity or oxidizing power rather than ''oxidase." Where 

 the latter term occurs in this paper, it is used only for the sake of 

 brevity, with no intent to imply any fixed notion as to the nature of 

 the agent which brings about the oxidation. 



Titration and indicator tests on extracts of fresh bark showed 

 the healthy bark to be more acid than the diseased, exactly as 

 had been shown previously in the work with dried bark. No data 



J) 



D-- - ../J-- ^_ -'C^ 



Fig. I. — Oxidation of pyrogallol, guaiacol, and benzidine by extract of fresh 

 bark, healthy and diseased, and extract of dried bark, healthy and diseased: A, 

 pyrogallol and fresh health)^ bark; B, pyrogallol and fresh diseased bark; C, ben- 

 zidine and fresh healthy bark; D, benzidine and fresh diseased bark; E, guaiacol 

 and fresh healthy bark; F, guaiacol and fresh diseased bark; G, pyrogallol and dried 

 healthy bark; H, pyrogallol and dried diseased bark; // = healthy, Z) = diseased. 



are given, since the true condition, at least for dried bark, was 

 determined more accurately by means of a potentiometer. 



Extracts of dried bark. — For the work at the University 

 of Chicago bark was used which had been dried at 35-40° C. for 

 2-3 hours, ground fine enough to go through a 40-mesh sieve, and 

 stored air dry in zinc-capped Mason jars. A few of the experiments 

 were run with oxidases precipitated from an extract of this bark 

 powder, but in most of them the powder itself was used, o.io gm. 

 in each apparatus. The reagents tested were pyrogallol and pyro- 

 catechin, 4 cc. of a i per cent solution; benzidine 0.05 gm.; 



