490 VETERINARY PHYSIOLOGY 



characters to the last. Some of it is generally found, along 

 with methsemoglobin, after poisoning with nitrites. 



(4) Carbon dioxide Haemoglobin. — By bubbling CO2 through 

 a solution of haemoglobin, in the absence of oxygen, a two- 

 banded spectrum resembling methsemoglobin has been 

 produced, and on evacuating the gas in an air-pump the 

 single band of haemoglobin has been found to appear. This, 

 again, gives place to the two bands when COo is passed through 

 the solution. It appears from this that heemoglobin can carry 

 CO2 as a definite compound. Probably it is the globin part 

 of the molecule which acts in this way, while the ha^matin 

 part carries the oxygen. 



Decomposition of Haemoglobin. — Haemoglobin is a somewhat 

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

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

 belonginor to the group of histones (Appendix II.), and 

 about 4 per cent, of a substance of a brownish colour called 

 haematin (Chemical Physiology). 



(1) Haematin. — The spectrum and properties of ha3matin 

 are different in acid and alkaline media, (a) In acid media 

 it has a spectrum closely resembling methjemoglobin, but it 

 can at once be distinguished by the fact that it is not 

 chansfed bv such reducino^ ao-ents as ferrous salts. It is 

 sometimes important to distinguish between these pigments, 

 since both may appear in the urine, methaemoglobin occurring 

 in paroxysmal methtemoglobinuria and acid hiEinatin as the 

 result of the action of the acid salts of the urine upon 

 haemoglobin present as the result of kidney disease. (6) 

 Haematin, in alkaline solution, can take up and give off 

 oxygen in the same way as haemoglobin does. Reduced 

 alkaline baematin has a very definite spectrum (fig. 198), 

 and its preparation affords a ready means of detecting old 

 blood stains {Chemical Physiology). 



Hffimatin contains the iron of the haemoglobin, and it is 

 this pigmented iron-containing part of the molecule which 

 has the affinity for oxygen. It is the presence of iron which 

 gives it this property, 1 grm. of iron being able to carry 

 400 c.cm. of oxygen. 



