61 
Name of substance. References. 
Thymol 77, 124. 
Ortho-toluidin 74,76. 
Para-toluidin 74,76. 
Meta-toluidin 76. 
Ortho-, meta-, and para-cresols 76. 
Xylidin 76. 
Anilin 74,76. 
Ortho-, meta-, and para-xylenols 77. 
Carvacrol 77. 
Many of these reagents have found special application in the study 
of particular phases of biological oxidations. Thus/ hydroquin one 
and guaiacum have been most extensivelv used in the investigation 
of laccase; tvrosin in the studA^ of tvrosinase; and salicAdic aldehvde 
in the study of aldehydase. So, in the same Avay, guaiacum, aloin, 
benzidin. the leuco-base of malachite green, and phenolphthalin 
have been most extensively used in testing for blood. Avhereas the 
potassium iodide-starch reagent (v. Storch ( 414 )), para-phenylene 
diamin, and guaiacum, haA~e been most extensively employed in 
distinguishing betAveen raAv and boiled milk. 
Various attempts haA^e also been made to determine quantitatively 
the oxidizing power of these various catalysts by means of certain 
of these reagents. Thus, Laborde ( 256 ) has proposed a colorimetric 
method in which tincture of guaiacum is used for this purpose; simi- 
larly SloAvtzofF( 404 ) has employed the indophenol reaction, Kastle( 239> 
24°, 241 ^ oxidation of phenolphthalin, and Czylilarz and von 
Furtli ( 131 ) the oxidation of the leuco-base of malachite green, as the 
basis of colorimetric methods. Bach ( 19 ) has made use of the oxida- 
tion of hydriodic acid (potassium iodide and acetic acid), for quanti- 
tatVe purposes, and later Bach and Chodat ( 30j 31 ) have employed the 
change of pyrogallol to purpurogallin for the quantitative study of 
the peroxidase reaction. Herzog and Meier ( 21 °) haArn measured such 
oxidations quantitatively by means of vanillin, Avhich is converted 
into dehydro vanillin, and Battelli and Stern ( 35 ) have employed the 
oxidation of formic acid. The conversion of tArosin into melanin 
has also been studied quantitatively by von Furtli and Jerusalem ( 178 ), 
and by Bach( 24 ). (See pp. 79-81.) 
LACCASE. 
This oxidase has been so fully considered in the historical deA^elop- 
ment of the subject of the oxidases that but little additional need be 
said concerning it. As already pointed out in the foregoing, it 
mpidly blues guaiacum and oxidizes hydroquinone Avith the absorp- 
tion of oxygen, and its activity is greatly augmented by the presence 
V very small amounts of manganese salts. Like other ferments, its 
