iqiq] 



ROSE— BLISTER CANKER 



129 



Further study is necessary to show the facts. A test of these pre- 

 cipitates with pyrocatechin showed that while the 2 fractions from 

 healthy bark are about equal in oxidizing power the first fraction 

 from diseased bark is 11 times as active as the second (fig. 7). 



Fig. 7. — Oxidation of pyrocatechin by precipitated oxidases from healthy bark, 

 without gelatine: A, fraction i; B, fraction 2; C, fractions i and 2 tested together; 

 D, sum of fractions i and 2 tested separately. 



Other precipitates were prepared using 25 cc. of alcohol for the 

 first fraction and 100 cc. more for the second. The oxidase activity 

 of these, tested separately and combined, with and without gelatine, 

 is shown in table XIX. 



TABLE XIX 



0XID.\SE ACTIVITY OF FIRST AND SECOND FRACTIONS FROM B-^RK EXTRACT 

 TESTED SEPARATELY AND COMBINED; TEMPERATURE 29.5-30.0° C. 



The mechanism by which gelatine increases the oxidase activity 

 is not clear. It is evidently not through buffer action, as shown by 

 its lack of effect on the hydrogen ion concentration (table XVII, 

 figs. 8, 9, 10). Special tests showed that there was no hydrolysis 

 of the gelatine to amino acids, in either healthy or diseased bark, 

 which would increase its buffer effect. If gelatine is effective 

 through its action as a protective colloid, its effect in this direction 

 must be very complex, as shown by its difference in effect on bark 

 mixtures and precipitated oxidases. 



