284 MEMORANDA. 



takes place more or less readily, according as more or less 

 ozone is present. " Ozonides," or bodies containing ozone, 

 have a similar eifect. Among organic substances, gum, 

 gluten, and unboiled milk render the resin blue. The reac- 

 tion with the pulp of the raw potato is well known. Other 

 bodies, as starch, fibrine, boiled milk, and the red colouring 

 matter of the blood, have no such effect. Boiling prevents 

 the development of this blue colour ; nor do these bodies 

 recover it when cool. But while neither blood nor antozone, 

 when applied separately, have any bluing action on guaiacum, 

 yet, Avhen they are applied together, an intense blue is the 

 result. If a drop of blood be mixed with half an ounce of 

 distilled water, and a drop or two of guaiacum be added, a 

 cloudy precipitate of the resin is thrown down, and the solu- 

 tion has a faint tint, due to the quantity of the tincture used. 

 If now a droj) of an ethereal solution of peroxide of hydrogen 

 be added, a blue tint will aj)pear, which will gradually 

 deepen and spread after a few minutes' exposure to the air. 

 This test acts better when very small quantities of blood are 

 used ; as otherwise, if the blood is in excess, the solution is 

 red, and gives, with antozone, a purplish or dirty green 

 colour. So minute and delicate is the reaction, that in a case 

 where the microscope failed to identify any blood from a stain 

 in a man's trousers Dr. Day succeeded in obtaining sixty 

 impressions. 



Water has the effect of destroying the shape of the blood- 

 corpuscle, and so it cannot sometimes be recognised by the 

 microscope, but it in no "svay interferes with this new 

 chemical test. Its accuracy may be thus sho^^m. A piece of 

 linen was stained with blood in the year 1840 (Guy's 

 ' Forensic Medicine,' 3rd ed., p. 316) ; from this a fibre was 

 taken, containing at its extremity a most minute stain of 

 blood; this was placed on a white slab, and treated first with 

 a dro]3 of tincture of guaiacum, and then with a drop of 

 " ozonized ether ;" and, although the quantity was so 

 small, and no less than twenty-eight years old, the 

 chai'acteristic blue appeared at once. We have found 

 same result in blood obtained from the urine in a case of 

 haematuria, and also in blood drawn from different animals. 

 Dr. Taylor, in ' Guy's Hospital Reports,' has shown that red 

 colouring matters, cochineal, kino, catechu, carmine, &c.j 

 exert no such influence; and, as far as it is at present known, 

 no other red stain will produce this result. 



Black currants will cause a stain resembling that of blood 

 more than any other ; but antozone has no effect upon it. 



Ink-stains will cause a blue with guaiacum ; so will rust- 



