462 M Wheldale. 



Tests for oxydases and peroxydases. 



The use of freshly prepared^) guaiacum tincture has alreadj- 

 been mentioned. In referring to this test, the blueing- given by an 

 oxydase is termed the direct action, that given by the Peroxydase 

 on addition of hydrogen peroxide, the indirect action. 



Another reaction, which may be used as a control, is the 

 liberation of iodine from a slightly acidified potassium iodide solution, 

 the free iodine being detected by means of starch solution. 



In addition, the indo-phenol test may be emploj-ed, i. e., the 

 formation of a violet colour an addition of an oxydase to solutions of 

 paraphenj^lendiamine and a-napthol. 



I have found all powerful oxydases bring about the above 

 reactions, but there are cases in which the starch iodide test fails 

 though the direct guaiacum action is developed to some degree and 

 the indophenol action after a lapse of time. 



Distribution of Oxydases. 



Among a collection of plants selected more or less at random 

 from various Natural Orders, it will be found that many species, 

 widely distributed among the Orders, give a direct oxydase reaction 

 but at the same time other species quite as frequently give the 

 indirect action onlj^, that is after addition of hydrogen peroxide. 



It cannot by any means be always predicted whether the extract 

 of any plant will show the oxydase capacity; when, however, 

 discolouration arises on injuiy to the tissues, this 

 phenomenon may generally be taken as an indication 

 of the presence of one of these enzymes. 



Though the direct action is more or less restricted to certain 

 species, the indirect action may be said to be almost universally 

 given by extracts of living tissues. Thus, for instance, of the 

 Eanunculaceae, the sap of flowers of Anejnone spp. and TroUius spp. 

 has a direct blueing action on guaiacum; that from Bmiuncidus spp. 

 on the other hand only blues guaiacum on addition of hydrogen 

 peroxide. Not only do genera differ in this respect but also species 



') Guaiacum solution itself is capable of autoxydation to some extent on ex- 

 posure to air. Hence erroneous results may be obtained unless tbe tincture is 

 freshly prepared each time before using. 



