Catalysts of Organic and Inorganic Origin. 315 



The Oxidase of the Carrot. 



According to Moore and Whitley the " peroxidase " of the carrot is most 

 abundant in the protoxylem. They were either misled by the lignin 

 reaction or mistook the central wood cylinder of the carrot for pith. With 

 both guaiacum and ursol tartrate in the presence of H 2 2 the oxidase reaction 

 is given first in the cambium, cambium segments and phloem. The central 

 wood cylinder is the last part to show any true oxidase reaction. All parts 

 decompose H 2 2) and in ursol tartrate alone a green colour slowly appears 

 along the line of the cambium, while the vessels in the wood within colour 

 reddish-brown. The latter colour appears in a boiled section but not the 

 former. We are evidently dealing with a somewhat weak oxidase, most 

 abundant in the cambium and phloem, next in the outer cortex and least of 

 all in the central wood cylinder. 



According to Moore and Whitley the cut surface of a carrot rapidly 

 develops peroxides and will then give a blue with guaiacum without any 

 addition of H 2 2 . It is difficult to see how this explanation can apply to 

 a tissue like that of a carrot which rapidly decomposes peroxides, or at least 

 peroxide of hydrogen, or to a section of carrot immersed in a large quantity 

 of a watery solution of ursol tartrate, in which the reaction is slowly given 

 by the uncut cells beneath the surface, and where any peroxides formed in 

 the uninjured cells would be washed away. Actual tests failed to detect any 

 peroxide of hydrogen in living or dead carrot tissue. 



The Oxidase of Red Beetroot. 



In spite of its red colour the expressed sap of the beetroot shows a strong 

 reaction with guaiacum, but is difficult to use with other oxidants. Hence the 

 sap was squeezed out, the pulp washed, the excess of water squeezed out, and the 

 residue pounded with glycerine, the first portion of which was thrown away. 

 In this way a pale pink strongly active oxidase was obtained, which closely 

 resembled potato oxidase. It reacted to guaiacum and tyrosin in the absence, 

 but to ursol tartrate only in the presence, of hydrogen peroxide. It has no 

 action on tannic acid by itself and only a feeble one in the presence of sodium 

 phosphate. It has a weaker power of decomposing hydrogen peroxide than 

 potato oxidase and the peroxide appears to inhibit its action on pyrogallol, 

 but acts as a sensitiser in the case of ursol tartrate. 



The pounded pulp reacts strongly and rapidly to ursol tartrate in the 

 presence of hydrogen peroxide but only slowly and faintly or not at all in its 

 absence. Neither the pulp nor the expressed sap appears to contain any 

 perceptible amount of chromogen capable of oxidation. 



vol. lxxxviii. — b. • 2 A 



