34 H^lMIN AND BLOOD TESTS. 



19. Haemin and Blood Tests. 



In 1853 Teichmann prepared crystals from blood, which Hoppe- 

 Seyler showed to be chloride of hcematin or hydrochlorate of haematin. 

 The presence of these crystals is used as a test for blood-stains or 

 blood in solution. These crystals of hsemin (Fig. 12) are prepared by 

 adding a small crystal of common salt to dry blood on a glass slide, 

 and then an excess of glacial acetic acid ; the whole is gently heated 

 until bubbles of gas are given off. On allowing the preparation to 

 cool, the characteristic hsemin crystals are obtained (Hsematin, -f- 2HC1). 



Characters. When well-formed, the crystals are small microscopic 

 rhombic plates, or rhombic rods; sometimes they are single at other times 

 they are aggregated in groups, often crossing each other. Some kinds 

 of blood (ox and pig) yield very irregular, scarcely crystalline, masses. 

 The crystalline forms of haemin are identical in all the different kinds 

 of blood that have been examined (Jahnke, Hogyes). They are doubly 

 refractive and pleo-chromat'ic ; by transmitted light they are mahogany- 

 brown, and by reflected light bluish-black, glancing like steel. They 

 give a brown streak on porcelain. 



(1.) Preparation from Dry Blood-Stains. Place a few particles 

 of the blood-stain on a glass slide, add 2 to 3 drops of glacial acetic 

 acid and a small crystal of common salt; cover with a cover-glass, 

 and heat gently over the flame of a spirit-lamp until bubbles of gas 

 are given off. On cooling, the crystals appear in the preparation 

 (Fig. 13). 



*.U 



VS 



Fig. 12. Fig. 13. 



Haemin Crystals of various forms. Haemin Crystals prepared from 



traces of blood. 



(2.) From Stains on Porous Bodies. The stained object (cloth, 

 wood, blotting-paper, earth) is extracted with a small quantity of dilute 

 caustic potash, and afterwards with water in a watch-glass. Both 

 solutions are carefully filtered, and tannic acid and glacial acetic acid 

 are added until an acid reaction is obtained. The dark precipitate 

 which is formed is collected on a filter and washed. A small part of 



