Direct Guaiacum Reaction given by Plant Extracts. 121 



whether a small movement of the slit caused a greater difference in hue, with 

 or without white, the above results were confirmed, i.e., in the case of yellow 

 and red, no increase due to the white was observable, and in the case of the 

 green a small addition of white seemed to make the difference in hue very 

 slightly more pronounced. 



The above observations seem to indicate that difference in our power of 

 appreciating differences in hue, according as we are comparing two mono- 

 chromatic patches, or a single patch in which the hue changes gradually from 

 one side to the other, is not due to admixture of white light. 



On the Direct Guaiacum Reaction given by Plant Extracts. 

 By Miss M. Wheldalb, Fellow of Newnham College, Cambridge. 



(Communicated by W. Bateson, F.R.S. Received April 25,— Bead 

 May 18, 1911.) 



In the literature dealing with oxidising enzymes considerable attention 

 has been drawn to the fact that the juices of some plants blue guaiacum 

 tincture directly (direct action), whereas the juices of other plants only 

 bring about the blueing on addition of hydrogen peroxide (indirect action). 



As an explanation of this phenomenon Chodat and Bach formulated a 

 hypothesis which has, in part, been generally accepted. These authors 

 maintain that direct blueing of guaiacum is brought about through the 

 activity of a system consisting of oxygenase, peroxide, and peroxidase. 

 The peroxidase is an enzyme capable only of transferring oxygen from the 

 peroxide to the guaiacum. The peroxide, after reduction, is again 

 re-oxidised by a second enzyme, the oxygenase. The juices of such plants 

 as give a direct action contain, according to Chodat and Bach, all three 

 components of the system. In others, the peroxidase alone is present, and 

 hence the guaiacum cannot be oxidised until a peroxide, such as hydrogen 

 peroxide, is artificially supplied. 



In a recent paper Moore and Whitley* have cast considerable doubt 

 upon the existence of any such enzyme as an oxygenase and give experi- 

 mental evidence as proof of the view that all plants contain a peroxidase, 



* Moore and Whitley, " The Properties and Classification of the Oxidising Enzymes/' 

 'JBiochem. Journ.,' vol. 4, 1909. 



