OTHER ELEMENTS OF THE BLOOD 



83 



they possess the familiar crimson tint of freshly drawn blood. In 

 thin layers solutions of hemoglobin are quite transparent, in 

 thicker layers they become more and more opaque. 



Various crystalline and amorphous substances may be obtained 

 by decomposition of hemoglobin. The iron of the coloring matter 

 may be thus obtained in the form of hematin, a soluble amorphous 

 compound of a brownish-red color. If hematin is combined with 

 hydrochloric acid the chlorid of hematin, hemin, is produced. 

 Hemin occurs in deep brownish-red crystals which differ some- 

 what according to the animal species from which they are ob- 

 tained ; those of human blood take the form of triclinic plates. 



Hemin crystals derive a 

 certain importance as a 

 forensic test for the pres- 

 ence of blood, and they 

 may be obtained from old 

 and dried-up specimens as 

 readily as from fresh blood. 

 The hemin crystals ob- 

 tained from human blood, 

 however, are identical with 

 those from the blood of 

 other mammals. 



> 



m w 



FIG. 84. HEMOGLOBIN CRYSTALS. 

 a and 6, from human blood ; c, from the cat ; 

 d, from the guinea-pig ; e, from the hamster ; /, 

 from the squirrel. (After Ranvier.) 



FIG. 85. CRYSTALS OF CHLORID OF 

 HEMATIN OR HEMIN. 



(After Kanvier.) 



When extravasations of blood occur within the tissues of the 

 body the coloring matter is frequently deposited as hematoidin, 

 an iron-free derivative of hemoglobin which forms stellate groups 

 of yellowish needle-like crystals. 



