34 HUMAN PHYSIOLOGY 



globin, but ammonium sulphide does not change its two absorp- 

 tion bands to the single absorption band of reduced haemoglobin. 

 CO-haemoglobin gives a bright-red precipitate with sodium hydrate 

 or with potassium ferrocyanide and acetic acid. 



By acids and alkalies, haemoglobin is broken up into its 

 components, globin (96$) and hsematin (4$). 



Globin is a globulin-like proteid, showing all the charac- 

 teristics of a proteid, but containing no sulphur which is 

 easily split off. 



Hczrnatin, C 32 H 32 N 4 O 4 Fe, is insoluble in water, but soluble 

 in dilute acids and alkalies and in alcohol containing am- 

 monia or sulphuric acid. The brownish-red acid haematin 

 solution has four absorption bands (like the methsemo- 

 globins) ; the carmin-red alkaline solution has but one absorp- 

 tion band, located in the orange. By ammonium sulphide, 

 haematin is reduced to hsemochromogen, which has two 

 absorption bands in the green. Haematin therefore corre- 

 sponds to oxyhaemoglobin ; haemochromogen, to reduced 

 haemoglobin. 



If haematin is boiled with a little NaCl and acetic acid and the 

 mixture is allowed to cool and evaporate, brown crystals, the 

 so-called Teichmanri 's hcemin crystals, are produced. Hcumin is 

 haematin hydrochloride. This reaction can be used in the detec- 

 tion of blood. The reaction succeeds still better if potassium 

 iodide is used instead of NaCl; in this case the crystals are 

 haematin hydroiodide. 



By the action of strong sulphuric acid, haematin loses its iron 

 and haematoporphyrin is formed. This is a red pigment and has 

 a narrow absorption band in the orange and a broad band in the 

 yellow-green. For the physiological importance of haemoglobin, 

 see Chapters II and III. 



Hcematoidin is an orange-colored pigment crystallizing in rhombic 

 tables. It is formed from the blood pigment of old extravascular 

 blood-clots. It is supposed to be identical with the bile pigment, 

 bilirubin. 



Melanine, a black pigment found in the body, is also supposed 

 to be derived from the haemoglobin. 



(2) Compounds of simple protcids and carbohydrates. 

 Glyco-proteids. In this class are the mucins and mucous 

 substances, found in the secretions of the mucous glands and 



