BLOOD 



491 



(2) Hsematoporphyrin. — If hsemoglobin is broken down 

 and the iron removed from the hiematin by means of 

 sulphuric acid, a purple-coloured substance, iron-free 

 hcematin, hsematoporphyrin, is formed, which has no affinity 

 for oxygen. This pigment occurs in the urine in some 

 pathological conditions (Cheynical Physiology). 



One point of great interest in the chemistry' of hieniatin 

 and its derivatives is that they, like the green chlorophyll of 

 plants, yield upon decomf)osition very similar bodies belong- 

 ing to the pyrrol group (see Appendix). 



(3) Bilirubin and Haematoidin. — In the liver, haemoglobin 

 is broken down to form bilirubin and the other bile pigments 

 (p. 324). These are iron-free, and, like hsematoporphyrin, 

 do not take up and give off oxygen. But not only are these 

 iron-free pigments formed from haemoglobin in the liver, but 

 they are produced in the cells of other parts of the body, and 

 thus in blood-extravasations a yellow pigment haematoidin 

 is formed which is really the same as bilirubin. 



(4) Hsemin — the hydrochloride of haE'matin — is formed 

 when blood is heated with sodium chloride and glacial acetic 

 acid. It crystallises in small steel-black rhombic crystals, 

 and its formation is sometimes used as a test for blood 

 stains {Chemical Physiology). 



The following table shows the relationship of these pig- 

 ents to one another : — 



Relationship of Hb and its Derivatives. 

 _HbO, HI .CO \ 



Methaenio2;iobin 



Hb 



Hcematin 



Acid Haematin 



Alkaline Haematin 



Oxidised 



Iron-free Haematin 

 (Hasmatoporphyrin) 



Globin 



Contain Iron 



Reduced / 



I 

 Haematoidin 



Bilirubin 



Iron-free 



