BLOOD AND LYMPH 213 



haemoglobin, the bodies of those poisoned with the gas main- 

 tain the florid colour of life. Its spectrum is very like that 

 of oxyhaemoglobin, the bands being slightly more to the blue 

 end of the spectrum (fig. 103). 



It may be at once distinguished by the fact that when 

 gently warmed with ammonium sulphide it does not yield 

 reduced haemoglobin. (Chemical Physiology.} 



Decomposition of Haemoglobin. Haemoglobin is a somewhat 

 unstable body, and, in the presence of acids and alkalies, splits 

 up into about 96 per cent, of a colourless protein globin 

 belonging to the globulin group, and about 4 per cent, of a 

 substance of a brownish colour called hsematin. 



The spectrum and properties of this substance are different in 

 acid and alkaline media. In acid media it has a spectrum 

 closely resembling methaemoglobin, but it can at once be dis- 

 tinguished by the fact that it is not changed by reducing agents. 

 In medicine it is sometimes important to distinguish between 

 these pigments since both may appear in the urine. Heematin 

 in alkaline solution can take up and give off oxygen in the 

 same way as haemoglobin does. Eeduced alkaline haematin or 

 haemoehromogen has a very definite spectrum (fig. 103), and its 

 preparation affords a ready means of detecting old blood stains. 

 Haematin contains the iron of the haemoglobin, and it is this 

 pigmented iron-containing part of the molecule which has the 

 affinity for oxygen. Apparently it is the presence of iron which 

 gives it this property, because, if the iron be removed 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 con- 

 ditions. (Chemical Physiology.) 



One point of great interest in the chemistry of haematin 

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

 plants, yield upon decomposition bodies belonging to the 

 pyrrhol group (see p. 9). 



In the liver haemoglobin is broken down to form bilirubin 

 and the other bile pigments. These are iron-free, and, like 

 iron-free haematin, do not take up and give off oxygen. But not 

 only is this iron-free pigment formed from haemoglobin in the 

 liver, but the cells of any part of the body have the faculty 

 of changing haemoglobin in blood extravasations into a pig- 



