Haematin unites with hydrochloric acid to form a crystallizable body called haemin 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 boiled, small characteristic crystals appear, which have been found to be produced by the union of two molecules 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 hce7?iatoidin are formed in old blood clots retained in the body. It does not contain any iron, and has the chemical formula C32 H:36 N4 06. It is probably identical with bilirubin, one of the coloring matters found in bile.

Haemin Crystals.

Fig. 108. Haemin Crystals.