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a couple of hours from thermostable zymogens, as has been 

 shown by Woods ' in the case of the oxidase of tobacco leaves. 

 It is remarkable, however, that no other workers have as yet 

 been able to find this zymogen. That they are colloidal and 

 can be precipitated from aqueous solution by the addition of 

 alcohol has also been shown. 



The quantitative estimation of oxidases and of their rate of 

 action presents many difficulties. Among the most successful 

 attempts in this direction may be mentioned those of Chodat 

 and Bach, 2 who examined the action of peroxidase upon a 

 mixture of pyrogallol and hydrogen peroxide by weighing the 

 purpurogallin formed under standard conditions. Their results 

 showed that the peroxidase and peroxide take part in the 

 reaction in a definite ratio, and that the weight of purpurogallin 

 produced is proportional to the peroxidase. The above authors 

 also devised a volumetric method. However, the most funda- 

 mental quantity to measure seems to be the amount of oxygen 

 absorbed, and this Foa 3 and Mathews 4 have done and Bunzel 6 

 more recently with an elaborate apparatus and many necessary 

 precautions previously omitted. Bunzel, too, finds that the 

 amount of chemical change is directly proportional to the con- 

 centration of the oxidase present, and concludes that the typical 

 plant oxidase with which he worked " is not an enzyme in the 

 customary sense of the word, but rather a substance entering 

 directly into the reaction, and being destroyed in the course 

 of the same." He proposes as a unit to express the oxidase 

 content of a plant juice " a solution of such a strength that one 

 litre of it will be capable of bringing about the consumption by 

 pyrogallol of the equivalent of one gram of hydrogen — i.e. a unit 

 of eight grams of oxygen." It seems likely that much valuable 

 knowledge will be gained from Bunzel's systematic quantitative 

 researches at present in progress. 



Before going further a distinction must be drawn between 

 the terms oxidase and peroxidase. Originally those tissues 

 which could bring about oxidations of natural chromogens or 

 of artificial ones such as guaiacum resin, benzidine, a-naphthol 



1 Woods, Bull. No. 18, U.S. Dept. of Agric. 1902. 



3 Chodat and Bach, Chem. Ber. 1904, 37, 1342. 

 5 Foa, Biochem. Zeitschr. 1908, 11, 382. 



4 Mathews, A. Y.,Journ. Biol. Chem. 1909, 6, 3. 



5 Bunzel, H. H., Bull. No. 238, Bureau of Plant Industry, U.S. Dept. of Agric. 



