McWioENEY— Value of Benzidine for Minute Traces of Blood. 221 



mapped out as blue dots or streaks according as tliey are out crosswise or in 

 their length. The subcortical layer is in most cases stained, tliough more 

 slowly, an intense blue. After a few moments the colour spreads to the 

 whole of the cut surface and the pattern is obliterated. 



Subjoined is a list of the vegetables and fruits which I have so far tested, 

 with the results obtained :— 



Potato : diffuse deep blue at once. 



White Turnip : beautifully distinct patterns of the fibro-vascular bundles 

 picked out in deep blue on a white ground. 



Tomato : irregularly distributed f.-v. bundles clearly picked out, sub-cortical 

 and pericarpal tissues deep blue. 



Onion : remarkably distinct pattern of concentric circles and dots corre- 

 sponding with the unopened leaves and f.-v. bundles of the bulb. 



Carrot : very slight reaction. 



Pea : beautifully distinct mapping-out of the in-folded cotyledons and 

 f.-v. bundles of the embryo. 



Radish : distinct pattern. 



Apple : reaction slow to come on ; violet tinge. 



Banana : distinct though slow mapping out of tlie fibro-vascular tissues. 



Strawberry : Isolated f.-v. bundles picked out. 



Orange : very little change. 



Cherry : change also slight. 



This effect is evidently due to powerful oxydases present in the fibro- 

 vascular bundles. The layer of test-fluid covering the cut surface is at first 

 locally tinged, corresponding to the bundles, and then diffusely, whereupon 

 the whole cut surface becomes uniformly stained. 



Such fresh vegetable matters do not occur iu medico-legal practice, and 

 are not, I think, liable to cause error. Still the question must be solved 

 whether and to what extent the reaction would be yielded by fragments of 

 such vegetable parenchyma when dried. The only experiment I have 

 hitherto made was with a slice of potato dried at 37° in the incubator and 

 tested next day. The scrapings struck a faint greenish blue with the 

 benzidine reagent — quite unlike the colour given by blood. 



I have found that boiling the vegetables in water for a few minutes 

 destroys their power of affecting the change of colour, owing, no doubt, to 

 the destruction of the oxydase. Even weak solutions of blood (1 : 1000), 

 however, yield the reaction after boiling for ten minutes quite as well as 

 before. 



The proposal has been made by Einhorn of New York (6) to employ 



