1911.] Direct Guaiacum Reaction given by Plant Extracts. 123 



These conclusions are based upon three observations : — 



(1) Pyrocatechin can be detected by the green reaction with ferric 

 chloride (subsequently purple and red on addition of dilute sodium carbonate) 

 in extracts from plants giving both the direct action and a brown pigment 

 on exposure to chloroform vapour. The alcoholic extract of the plants is 

 evaporated to dryness, and the pyrocatechin extracted with ether or acetone 

 after the removal of chlorophyll and other substances soluble in chloroform. 

 Pyrocatechin was not detected in any appreciable quantity in plants giving 

 the indirect action only. 



(2) After evaporation, the ether extract containing pyrocatechin will 

 bring about in many cases a direct blueing of guaiacum when added to a 

 solution containing peroxidase only.* Care must be taken to neutralise the 

 residue (if acid) after evaporation of the ether and before addition of the 

 peroxidase and guaiacum. 



(3) When a slightly alkaline solution of commercial pyrocatechin is allowed 

 to stand in air, oxidation takes place and a brown colour is developed. Such 

 a solution added to a peroxidase solution and guaiacum tincture brings 

 about a blueing of the guaiacum. Similar experiments were made with 

 phenol, resorcinol, hydroquinone, pyrogallol, and phloroglucin ; also with 

 benzoic, salicylic, m-oxybenzoic, ^-oxybenzoic, protocatechuic, gallic, and 

 tannic acids, and quercetin. 



A positive result was obtained with protocatechuic acid only. There is 

 therefore probably a connection between the ortho-position of the hydroxyl 

 groups and the specific capacity of these substances as regards their power to 

 activate the peroxidase. According to Czapek,f protocatechuic acid rarely 

 occurs free in the plant, but further experimental investigation would be 

 necessary to establish this point. 



Hence we may conclude that the direct action of certain plant extracts is 

 due to the post-mortem oxidation of a definite metabolic product, and the 

 action as such has probably no significance in the metabolism of the living plant. 



There is some evidence in favour of the supposition that the pyrocatechin 

 exists as a glucoside, and that the hydrolysis of this compound into sugar and 

 phenol is accelerated by injury or chloroform vapour. In many cases very 

 little oxidation takes place in the alcoholic residue obtained by plunging the 

 leaves of a pyrocatechin-containing plant into boiling alcohol and thereby 

 preventing decomposition of the glucoside. If, however, such a residue is 



* Extract of white Brompton Stock was used for this purpose. The guaiacum 

 tincture was always boiled with animal charcoal before using, as recommended by 

 Moore and Whitley, loc. cit. 



t Czapek, ' Biochemie der Pflanzen.' 



