THE PLANT OXIDASES 223 



treatment was prolonged for four days. Again, contrary 

 to the experience of Keeble and Armstrong, with other 

 flowers, in two cases only was organic peroxide formed in 

 darkness. 



Thus, since the occurrence of the peroxide constituent 

 of the oxidizing system is so variable, being influenced by 

 external conditions, Keeble and Armstrong regard it of 

 relative unimportance so far as the distribution of oxidases 

 is concerned, whether a tissue is or is not found to contain 

 the complete peroxidase system. This opinion seems to 

 the writer to be fully justified. 



For a discussion of Traube's (1882) theory of oxidation 

 by means of peroxides, and its modifications by Bach 

 (1897), Engler (1904), and others, reference should be made 

 to the monographs and textbook previously named. The 

 very interesting monograph by Dakin on " Oxidations 

 and Reductions in the Animal Body " should also be 

 consulted. 



CHEMICAL COMPOSITION OF LACCASE. 

 The chemical constitution of laccase is not known, for, 

 as is the case with many enzymes, its purification is very 

 difficult. A pure specimen prepared by Slowtzoff (1900) 

 gave all the reactions for protein, and contained 12*8 per 

 cent, nitrogen, 0-53 per cent, sulphur, and but little ash. 

 Neither manganese nor phosphorus could be detected in 

 it. Slowtzoff considers it to belong to the group of albu- 

 mins. Its activity is greatest in faintly alkaline solutions, 

 but is not destroyed by weak acids or by peptic or pancreatic 

 digestion. It must be pointed out, however, that it is 

 only to the negative results of such analyses that much 

 attention should be given; thus, for instance, manganese 

 was not found in the ash, therefore this metal cannot be 

 an essential constituent of the enzyme. Again, it cannot 



