218 DETECTION OF BLOOD STAINS. [BOOK I. 



In recognizing blood by means of the spectroscope the observer endeavours 

 to obtain a succession of characteristic spectra ; even when haemoglobin has 

 been decomposed and the stain contains methaemoglobin or haematin a 

 satisfactory series of spectrum observations may be made 1 . 



If the quantity of red solution be sufficient, a few drops may be 

 treated with solution of ammonia which will induce no change. The 

 greater part of the liquid, or, if its quantity be small, the whole of 

 it, is now heated to boiling; the red colour will disappear and a 

 turbidity or coagulation will be observed to form, the coagulum 

 having a dirty grey colour ; on now adding a drop of a solution of 

 caustic potash to the turbid liquid, this will be instantly cleared and 

 the solution will be observed to be green by transmitted and red by 

 reflected light ; on adding a small drop of nitric acid the precipitate 

 will be reproduced. 



Guaiacum Another test which adds confirmatory evidence to 



that afforded by other means, and which is of extreme 

 delicacy, rests upon the reaction developed by haemoglobin and its 

 derivatives when brought in contact with guaiacum and hydric 

 peroxide. To try this test it is best to moisten the stain with 

 distilled water, and then to press a piece of white filtering paper 

 firmly against it ; a little of the colouring matter will adhere to 

 the filtering paper. Having secured a slight stain on the filtering 

 paper, this is moistened with a drop of tincture of guaiacum, and 

 then with a few drops of an ethereal solution of peroxide of 

 hydrogen. A beautiful blue colour will be developed if the stain 

 is one of blood. It must be borne in memory, however, that 

 this test cannot be relied upon by itself, though the evidence 

 which it affords is valuable when taken in connection with other 

 facts. 



TheHaemin I n the case of very old blood-stains it may not only 



test - be impossible to obtain blood corpuscles for microscopic 



examination, but even to obtain a solution containing the colouring 

 matter and proteids of the blood. In such a case the haemin-test is 

 of special value. This test is based upon the fact that when 

 haemoglobin or haematin are heated with glacial acetic acid and 

 common salt, a hydrochlorate of haematin is formed, which, on 

 evaporation, is deposited in the form of reddish brown prisms, the 

 so-called haemin-crystals. The test is one of great delicacy and the 

 result is remarkably free from fallacy. The blood-stain, having been 

 cut out, is placed with a few drops of glacial acetic acid and a very 

 minute (indeed scarcely perceptible) crystal of common salt, in a 

 watch-glass, which is then heated to boiling over a spirit-lamp 

 flame. The liquid will soon assume a brownish red tint; the little 

 piece of cloth may then be squeezed with a rod against the side 



1 Consult Sorby, " On some improvements in the spectrum method of detecting 

 blood." Monthly Microscopical Journal, Vol. vi. (1871) p. 9. Also MacMunn, The 

 Spectroscope in Medicine. London, Churchill, 1880. 



