FORENSIC MICROSCOPY. 127 



size and sometimes of considerable age. Two problems 

 are involved — first, as to the presence or absence of blood 

 in the specimen presented, and second, as to its nature, 

 whether human or animal. The presence of blood in 

 general may be settled pretty easily by four methods — ■ 

 one chemical, one microchemical, one microspectro- 

 scopical, and one purely microscopical. The chemical 

 test consists in the application to the stain of an alcoholic 

 solution of gum guaiacum, which yields a blue color 

 reaction on the further fddition of aerated turpentine. 

 The microchemical test depends on the fact that haemo- 

 globin, the complex albuminoid substance characteristic 

 of the red blood-corpuscles, yields on treatment with 

 acetic acid a crystalline iron salt, haematin, whose triple 

 chloride is known as hsemin. In making this test the 

 blood, if in a dry condition, is placed on a slide and gently 

 warmed in glacial acetic acid. This is allowed to evapo- 

 rate and replaced by a 0.07% solution of sodium chloride, 

 which in its turn is carefully evaporated without heating 

 the slide above 60° C. Another drop of acetic acid is 

 added and the slide is this time heated so that the liquid 

 boils. After evaporation it is examined under the ^-in. 

 objective; if blood be present, crystals of haemin (or 

 haematin trichloride) will appear as minute flat rhom- 

 boids often superposed in the form of a cross. They 

 vary from yellow to reddish brown in color and from 

 0.005-0.02 mm. in size. This test is a delicate one, serv- 

 ing to detect from 0.05-0.15 mg. of dried blood, and even 

 very old material gives satisfactory results, as in the classic 

 case of the blood of the murdered Kotzebue, detected 



