Enzymes 153 



mazan dyes have a tendency to secondary organization into 

 coarse crystalline precipitates. Elementary tellurium is black 

 or brown-black. The sections can be counterstained with 

 hematoxylin or carmine; they should be mounted in glycerol 

 or glycerol-jelly. 



b) Oxidases 



Oxidases are a motley group of enzymes having in com- 

 mon the property of catalyzing the oxidation of various sub- 

 strates, mainly phenols and amines, in the presence of at- 

 mospheric oxygen. Their classification is very unsatisfactory. 

 Substrate specificity is usually only relative; the same en- 

 z}Tne will attack a number of substrates (although some of 

 them more readily than others); and, conversely, the same 

 substrate may be attacked by a number of different enzymes. 

 It is impossible to go into the complicated and controversial 

 details of the problem. The interested reader can seek more 

 information in special textbooks of enzymology. Only a few 

 enzymes of histochemical interest will be dealt with here. 



A) Indophenol oxidase {nodi oxidase; cytochrome oxi- 

 dase ) .— 



A mixture of solutions of a phenol or naphthol and an aro- 

 matic diamine is slowly oxidized on exposure to air, with the 

 formation of intensely colored (usually blue) indophenol 

 dyes, most of which are insoluble in water but very soluble 

 in oils and fats. 



The reaction is immediate in the presence of strong oxi- 

 dants, such as dichromate or hypochlorite. Ehrlich in 1885^^ 

 showed by the injection of a mixture of alpha-naphthol and 

 dimethyl-p-phenylene diamine into animals that the for- 

 mation of indophenol blue is catalyzed by living tissues, in 

 the absence of strong oxidants. Rohmann and Spitzer^^ found 

 that ground-up tissues or even alcohol-ether-dried organ 



29. Ehrlich, P.: Das SauerstoflFbediirfnis des Organismus (Berlin: A. 

 Hirschwald, 1885). 



30. Rohmann, F., and Spitzer, W.: Ber. d. deutsch. chem. Gesellsch., 

 28:567, 1895. 



