458 HAEMATIN. [Book ii. 



nature. When the gas is breathed, the reduced and the unre- 

 duced haemoglobin of the venous blood unite with the carbonic 

 oxide, and hence the peculiar bright cherry-red colour observ- 

 able in the blood and tissues in cases of poisoning by this gas. 

 The carbonic oxide haemoglobin, however, is of no use in res- 

 piration ; it is not an oxygen-carrier, nay more, it will not 

 readily, though it does so slowly and eventually, give up its 

 carbonic oxide for oxygen, when the poisonous gas ceases to 

 enter the chest and is replaced by pure air. The organism is 

 killed by suffocation, by want of oxygen, in spite of the blood 

 not assuming any dark venous colour ; to adopt a phrase which 

 has been used, the corpuscles are paralyzed. 



Haemoglobin similarly forms a compound, having a charac- 

 teristic spectrum, with nitric oxide, more stable even than that 

 with carbonic oxide. 



It has been supposed by some that the oxygen thus associated 

 with haemoglobin is in the condition known as ozone ; but the 

 arguments urged in support of this view are not as yet con- 

 clusive. 



Products of the decomposition of Hcemoglobin. 



§ 281. Although a crystalline body, haemoglobin diffuses 

 with great difficulty. This arises from the fact that it is in 

 part a proteid body ; it consists of a colourless proteid, associ- 

 ated with a coloured substance, which may be separated out 

 from the haemoglobin, though not in the exact condition in 

 which it naturally exists in the compound ; this substance when 

 separated out appears as a brownish-red body known as hcema- 

 tin. All the iron belonging to the haemoglobin is in reality 

 attached to the haematin. A solution of haemoglobin, when 

 heated, coagulates, the exact degree at which the coagulation 

 takes place depending on the amount of dilution ; at the same 

 time it turns brown from the setting free of the haematin. If 

 a strong solution of haemoglobin be treated with acetic (or 

 other) acid, the same brown colour, from the appearance of 

 haematin, is observed. The proteid constituent however is not 

 coagulated, but by the action of the acid passes into the state 

 of acid-albumin. On adding ether to the mixture, and shaking, 

 the haematin is dissolved in the supernatant acid ether, which it 

 colours a dark red, and which, examined with the spectroscope, 

 is found to possess a well-marked spectrum, the spectrum of the 

 so-called acid haematin of Stokes (Fig. 90, 6). The proteid in 

 the water below the ether appears in a coagulated form owing to 

 the action of the ether. In a somewhat similar manner alkalis 

 split up haemoglobin into a proteid constituent and haematin. 



The exact nature of the proteid constituent of haemoglobin 

 has not as yet been clearly determined. It was supposed to 

 be globulin (hence the name haematoglobulin, contracted into 



