ELEMIN AND BLOOD TESTS. 35 



it is placed on a microscope slide, a granule of common salt is added, 

 and the whole dried; the dry stain is treated as in (1.) (Struwe). 



(3.) From Fluid Blood. Dry the blood slowly at a low temperature, 

 and proceed as in (1.) 



(4.) From very Dilute Solutions of Haemoglobin. (a.) Struwe's 

 Method Add to the fluid, ammonia, tannic acid, and afterwards glacial 

 acetic acid, until it is acid ; soon a black precipitate of tannate of 

 haematin is thrown down. This is isolated, washed, dried, and treated 

 as in (1.), but instead of NaCl a granule of ammonium chloride is added. 

 (6.) Guning and van Geuns recommend the addition of zinc acetate, -which gives 

 a reddish precipitate; this precipitate is to be treated as in (1.) 



Hsemin crystals may sometimes be prepared from putrefying or 

 lake-coloured blood, but they are very small, and here the test often 

 fails. When mixed with iron-rust, as on iron-weapons, the blood- 

 crystals are generally not formed. In such cases, scrape off the stains 

 and boil them with dilute caustic potash. If blood be present, the 

 dissolved hsematiu forms a fluid, which in a thin layer is green ; in a 

 thick layer red (H. Rose). 



Chemical Characters. Haemin crystals have been prepared from all classes of 

 vertebrates and from the blood of the earth-worm. 



They are insoluble in water, alcohol, ether, chloroform ; but HgSC^ dissolves 

 them, expelling the HC1, and giving a violet-red colour. Ammonia also dissolves 

 them, and if the resulting solution be evaporated, heated to 130C., and treated 

 with boiling water (which extracts the ammonium chloride), pure hcematin is 

 obtained (Hoppe-Seyler) as a bluish-black substance, which on being pounded forms 

 a brown and amorphous powder. Its solutions in caustic alkalies are dichroic; in 

 reflected light, brownish-red; in transmitted light, in a thick stratum, red in a 

 thin one, olive-green. The acid solutions are monochromatic and brown. 



An alcoholic solution of hsematin, when reduced by tin and hydro- 

 chloric acid, yields uroUlin (Hoppe-Seyler), (compare Bile). 



20. Haematoidin. 



Virchow discovered this important derivative from haemoglobin. It 

 occurs in the body wherever blood stagnates outside the circulation, and 

 becomes decomposed as when blood is extravasated into the tissues 

 e.g., the brain in solidified blood-plugs (thrombus) ; invariably in the 

 Graafian follicles. It contains no iron (0 32 , H 36 , N 4 , O 6 ), and crystallises 

 in clinorhombic prisms (Fig. 14) of a 

 yellowish-brown colour. It is soluble in 

 warm alkalies, carbon disulphide, benzol, and 

 chloroform. Very probably it is identical with 

 one of the bile pigments Uli-ruUn (Valen- 

 teiner). [When acted upon by impure nitric 

 acid (Gmelin's reaction), it gives the same Fi 



play of colours as bile.] Hsematoidin Crystals. 



