CHAP, ii.] RESPIRATION. 567 



oxide (monoxide) be passed through a solution of haemoglobin, a 

 change of colour takes place, a peculiar bluish tinge making its ap- 

 pearance. At the same time the spectrum is altered ; two bands 

 are still visible, but on accurate measurement it is seen that they 

 are placed more towards the blue end than are the otherwise 

 similar bands of oxyha?moglobin (see Fig. 75, G) ; their centres corre- 

 sponding respectively to about wave-lengths 572 and 533, while 

 those of oxy haemoglobin as we have seen correspond to 578 and 

 539. When a known quantity of carbonic oxide gas is sent through 

 a haemoglobin solution, it will be found on examination that a 

 certain amount of the gas has been retained, an equal volume of 

 oxygen appearing in its place in the gas which issues from the 

 solution. If the solution so treated be crystallized, the crystals 

 will have the same characteristic colour, and give the same 

 absorption spectrum as the solution ; when subjected to the action 

 of the mercurial pump, they will give off a definite quantity of 

 carbonic oxide, 1 grm. of the crystals yielding T59 c.cm. of the gas. 

 In fact, haemoglobin combines loosely with carbonic oxide just as it 

 does with oxygen ; but its affinity with the former is greater than 

 with the latter. While carbonic oxide readily turns out oxygen, 

 oxygen cannot so readily turn out carbonic oxide. Indeed, 

 carbonic oxide has been used as a means of driving out and 

 measuring the quantity of oxygen present in any given blood. 

 This property of carbonic oxide explains its poisonous nature. 

 When the gas is breathed, the reduced and the unreduced haemo- 

 globin of the venous blood unite with the carbonic oxide, and 

 hence the peculiar bright cherry-red colour observable in the blood 

 and tissues in cases of poisoning by this gas. The carbonic oxide 

 ha?moglobin, however, is of no use in respiration; 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 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. 



Products of the decomposition of Htvmoglobin. 



350. 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 substance, which may be separated out from the hasmo- 



