CHEMICAL BASIS OF THE ANIMAL BODY.. 237 



as possible with a minute quantity (trace) of sodium chloride. A little 

 of the powder is then placed on a slide and covered with a slip under 

 which some glacial acetic acid is now run in. It is then warmed 

 carefully to a temperature just short of that which would cause the 

 acid to boil. If the operation has been successful, on cooling crystals 

 of hsemin will be seen under a microscope mixed in either case as in 

 Fig. 38 with a granular debris. If they are absent, warm again, 

 adding more acid if necessary. The crystals are dark brown, fre- 

 quently almost black, elongated rhombic plates and prisms belonging 



FIG. 39. ILEMIN CRYSTALS. (After Preyer.) 



to the triclinic system l . In a purified specimen they are arranged singly 

 or in groups as shown in Fig. 39, and apart from their form are charac- 

 terised by being strongly doubly-refracting : when examined under the 

 microscope between crossed Nicol prisms those crystals whose axes are 

 suitably inclined to the incident light stand out bright yellow or orange 

 on the dark field 2 . They are quite insoluble in either water, alcohol, 

 ether, chloroform or dilute acids : they may however be dissolved to some 

 extent in glacial acetic or hydrochloric acids, especially if warmed, and 

 are readily soluble in alkaline carbonates or dilute caustic alkalis, 

 being at the same time decomposed by the latter solvent into hsematin 

 and a chloride of the alkali. This fact provides the best means for 

 obtaining pure haematin (see above). 



Although it is quite easy to obtain typical crystals under the 

 microscope from minute amounts of haemoglobin or hsematin, their 

 preparation on a large scale is somewhat tedious ; several methods have 



1 Lahorio. Quoted by Schalfejew, Jn. d. russ. phys.-chem. GeselL 1885, S. 30. 

 See Abstr. in Ber. d. d. chem. GeselL Bd. xvm. Kef., S. 232. Cf. Hogges, Centralb. 

 f. d. med. Wiss. 1880, No. 16. 



2 A. Ewald, Zt.f. Biol. Bd. xxn. (1886), S. 474. 



