HEMOGLOBIN 



213 



species from which they are obtained; those of human blood take the 

 form of triclinic plates (Fig. 228). Hemin crystals derive a certain 

 importance as a forensic test for the presence of blood, and they may 

 be obtained from old and dried-up specimens as readily as from fresh 

 blood. The procedure for testing a suspected stain consists in heating 



to the boiling point in a drop 

 of acetic acid, a drop of a nor- 

 mal salt solution of the speci- 

 men. From fresh blood the 

 crystals may be produced by 

 heating together on a slide a 

 drop of blood, a grain of so- 

 dium chlorid, and a drop of 

 acetic acid. Hemin crystals 

 prove only that hemoglobin is 

 present, but give no precise in- 



FIG. 227. HEMOGLOBIN CRYSTALS. 



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

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

 from the squirrel. (After Ranvier.) 



FIG. 228. CRYSTALS OF 

 CHLORID OF HEMATIN OR 

 HEMIN. 



(After Ranvier.) 



formation as to the species from which the blood in question came, for 

 the crystals obtained from many mammals are apparently identical. 



Hematin may decompose also into hemosiderin,, an iron-containing 

 hemoglobin derivative, in the form of light-brown granules, frequently 

 found in phagocytic leukocytes as the product of cellular digestion of 

 effete erythroplastids. Hemosiderin granules thus appear in the spleen 

 and bone-marrow. Iron in the tissues, and ferruginous pigments gen- 

 erally, can be recognized by application of the ferrocyanid test, which 

 stains the iron blue. 



