212 



BLOOD 



then prone to crystallize on evaporation in. the form of minute brownish- 

 yellow prisms. The crystals of the various species of any genus belong 

 to a crystallographic group (Reichert) but generic differences are fre- 

 quently striking; thus, in human blood they are long rhombohedra (Fig. 

 227), in guinea pig, tetrahedra, in squirrel, hexagonal plates, in rat, 



FIG. 226. SECTION OP BONE MARROW FROM SKULL OF 25 MM. TURTLE EMBRYO 

 (CHELYDRA SERPENTINA), SHOWING THREE MAIN STAGES IN THE HEMOPOIESIS. 



L, hemoblast (lymphocyte), differentiating in the mesenchyma and passing into 

 a blood-vessel; Me, blood mother cell (hemoblast); Mg, megaloblast; Eb, erythro- 

 blast; EC, erythrocyte; E, endothelial cell; Mes, mesenchymal cell; PC, pigmented 

 cell. Helly fixation; Giemsa stain. X 700. 



elongated six-sided plates, in hamster (a rodent), rhombohedra, and in 

 dog they appear as rhombic prisms which are diamond shaped in cross- 

 section. 



Various other crystalline, and also amorphous hemoglobin derivatives 

 may occur as decomposition products. The iron of the coloring matter 

 of the hemoglobin may be thus obtained in the form of hematin, a 

 soluble, amorphous protein compound of a brownish-red color. If he- 

 matin is combined with hydrochloric acid the chlorid of hematin, hemin, 

 is produced. Hemin occurs in deep brownish-red crystals, known also as 

 Teichmann's crystals, which differ somewhat according to the animal 



