538 OXIDATION FERMENTS 



presence of peroxide of hydrogen are, however, just as 

 readily changed into their colored derivatives by minute 

 quantities of blood as by a vegetable peroxidase or bit of liv- 

 ing plant tissue. In view of the great practical difficulty to 

 thoroughly free vertebrate tissue of residual amounts of 

 blood it seems by no means an easy task to differentiate 

 between the influence of blood and the effect of peroxidases. 



Further difficulties are met in the fact that the action of 

 peroxidases is closely connected with the presence of per- 

 oxide of hydrogen ; that the tissues, however, contain at the 

 same time agents, the catalases, to be considered hereafter, 

 which disintegrate hydrogen peroxide and thus antagonize 

 the peroxidases. It is clear, too, that easily oxidizable sub- 

 stances of various kinds may cause disturbance by abstract- 

 ing the activated oxygen, thus diverting it from the reagents. 



Finally, too, much of the confusion attaching to the ques- 

 tion of the oxidases comes from the fact that under certain 

 circumstances when guaiac resin (which since the time of 

 Schonbein has been regarded more or less as a universal re- 

 agent for oxidases) is added to tissue extracts, even in the 

 absence of hydrogen peroxide the characteristic blue reac- 

 tion is observed. This has led to the recognition of ' ' direct ' ' 

 and "indirect" oxidases. According to Bach and Chodat 

 the former are, however, nothing more than mixtures of 

 oxygenases (therefore of peroxides) and peroxidases. It 

 should also be recalled that a solution of guaiac resin is 

 likely to undergo spontaneous change if exposed to the air 

 and can become charged with oxygen combined as in per- 

 oxides. This difficulty may be avoided by employing the 

 active principle, guaiaconic acid, instead of the resin, using 

 the acid in chemically pure state and in freshly prepared 

 solution. Guaiaconic acid is properly employed, as Carlson 

 has recommended, in combination with hydrogen peroxide 

 but not with turpentine resin, as in the well known blood test 

 proposed by the Dutch physician Van Deen in 1861, in which 



