CHAP, ii.] RESPIRATIOX. 341 



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. As 

 Bernard phrased it, the corpuscles are paralysed. 



Haemoglobin similarly forms a compound, having a character- 

 istic 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 inconclusive. 



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, associated with a coloured 

 compound named hcematin. All the iron belonging to the haemo- 

 globin 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. 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 

 haemoglobin), but though belonging to the globulin family, has 

 characters of its own; it is possibly a mixture of two or more 

 distinct proteids. It has been provisionally named globin and is 

 said to be free from ash. Haematin when separated from its 

 proteid fellow, and purified, appears as a dark-brown amorphous 

 powder, or as a scaly mass with a metallic lustre, having the 

 probable composition of C S2 , H^, N 4 , Fe, 6 . It is fairly soluble 

 in dilute acid or alkaline solutions, and then gives characteristic 

 spectra. 



An interesting feature in haematin is that its alkaline solution 

 is capable of being reduced by reducing agents, the spectrum 

 changing at the same time, and that the reduced solution will, like 

 the haemoglobin, take up oxygen again on being brought into 



