236 MANUAL OF PHYSIOLOGY. 



can only be obtained in an atmosphere of hydrogen or nitrogen, 

 as it immediately takes up oxygen to form haematin. The form- 

 ula CegH^NgFejOj,, has been given for haematin. It dissolves in 

 weak alkaline and acid solutions, but not in water or in alcohol. 

 Hsematin is readily prepared by mixing acetic acid with a strong 

 solution of haemoglobin, which becomes a dark brown color. The 

 dark haematin can be removed by ether. But if the acid used be 

 strong, the solution of haematin is found to be free from iron. 

 This iron-free haematin Preyer calls hcematoin. If now the acid 

 haematin solution be saturated with ammonia, the iron again be- 

 comes united with the haematoin, forming alkali-haematin. 



HJEMIN. 



Haematin unites with hydrochloric acid to form a crystallizable 

 body called hcemin or hydrochlorate of haematin (Teichmann's 

 crystals). 



If blood or dry haematin be mixed with a small quantity of 

 common salt, a drop of glacial acetic acid added, and the mixture 



FIG. 108. 



1 1.rmi n Crystals. 



boiled, small characteristic crystals appear which have been 

 found to be produced by the union of two atoms of hydrochloric 

 acid with the haematin. 



The formation of these crystals is very easily accomplished with 

 a small quantity of old dried blood ; therefore this substance 

 becomes, in medico-legal inquiries, an important test for blood 

 stains. 



Crystals of a substance called Haematoidin are formed in old 

 blood-clots retained in the body. It does not contain any iron, 

 and has the chemical formula C 32 H 36 N 4 O 6 . It is probably iden- 

 tical with bilirubin, one of the coloring matters found in bile. 



