CH. XXVI.] CARBONIC OXIDE HEMOGLOBIN 437 



oxygen combined as oxyhaemoglobin is discharged, and this may be collected and 

 measured ; the addition of a small amount of sodium carbonate or ammonia to the 

 blood is necessary to prevent the evolution of any carbonic acid. This discharge of 

 oxygen from oxyhaemoglobin is at first sight puzzling, because, as just stated, 

 methaemoglobin contains the same amount of oxygen that is present in oxyhaemo- 

 globin. What occurs is that after the oxygen is discharged from oxyhaemoglobin, 

 an equal quantity of oxygen, due to the oxidising action of the reagents added, 

 takes its place ; this new oxygen, however, is combined in some way different from 



that which was previously united to the haemoglobin. (Haldane.) 



+ 



Carbonic oxide haemoglobin may be readily prepared by passing 

 a stream of carbonic oxide or coal gas through blood or through a 

 solution of oxyhaemoglobin. It has a peculiar cherry-red colour. Its 

 absorption spectrum is very like that of oxyhaemoglobin, but the two 

 bands are slightly nearer the violet end of the spectrum (spectrum 4 

 in coloured plate). Eeducing agents, like ammonium sulphide, do 

 not change it ; the gas is more firmly combined than the oxygen in 

 haemoglobin. CO-haemoglobin forms crystals like those of oxyhaemo- 

 globin. It resists putrefaction for a very long time. 



Carbonic oxide is given off during the imperfect combustion of 

 carbon such as occurs in charcoal stoves or during the explosions that 

 occur in coal-mines ; it acts as a powerful poison, by combining with 

 the haemoglobin of the blood, and thus interferes with normal respira- 

 tory processes. The bright colour of the blood in both arteries and 

 veins, and its resistance to reducing-agents, are in such cases 

 characteristic. 



Nitric Oxide Haemoglobin. When ammonia is added to blood, 

 and then a stream of nitric oxide passed through it, this compound 

 is formed. It may be obtained in crystals isomorphous with oxy- 

 and CO-haemoglobin. It also has a similar spectrum. It is even 

 more stable than CO-haemoglobin ; it has no practical interest, but is 

 of theoretical importance as completing the series. 



Bohr has advanced a theory that haemoglobin forms a compound with carbonic 

 acid, and that there are numerous oxyhaemoglobins containing different amounts of 

 oxygen, but his views have not been accepted. 



Estimation of Haemoglobin. The most exact method is by the estimation of 

 the amount of iron (dry haemoglobin containing '42 per cent, of iron) in the ash of a 

 given specimen of blood, but as this is a somewhat complicated process, various 

 colorimetric methods have been proposed which, though not so exact, have the 

 advantage of simplicity. 



Growers' Haemoglobinometer. The apparatus (fig. 371) consists of two glass 

 tubes of the same size. One contains glycerin jelly tinted with carmine to a 

 standard colour viz., that of normal blood diluted 100 times with distilled water. 

 The finger is pricked and 20 cubic millimetres of blood are measured out by the 

 capillary pipette, B. This is blown out into the other tube and diluted with distilled 

 water, added drop by drop from the pipette stopper of the bottle, A, until the tint 

 of the diluted blood reaches the standard colour. This tube is graduated into 100 

 parts. If the tint of the diluted blood is the same as the standard when the tube is 

 filled up to the graduation 100, the quantity of oxyhaemoglobin in the blood is 

 normal. If it has to be diluted more largely, the oxyhaemoglobin is in excess ; if to 

 a smaller extent, it is less than normal. If the blood has, for instance, to be diluted 



