160 HANDBOOK OF PHYSIOLOGY. 



and to present a slightly altered spectrum ; two bands are still visible, 

 but are slightly nearer the blue end than those of oxj -haemoglobin (see 

 plate). The amount of carbonic oxide taken up is equal to the amount 

 of the oxygen displaced. Although the carbonic oxide gas readily dis- 

 places oxygen, the reverse is not the case, and upon this property de- 

 pends the dangerous effect of coal-gas poisoning. Coal gas contains 

 much carbonic oxide, and when breathed, the gas combines with the 

 haemoglobin of the blood, and produces a compound which cannot easily 

 be reduced. This compound (carb-oxy-haemoglobin) is by no means an 

 oxygen carrier, and death may result from suffocation due to the want 

 of oxygen notwithstanding the free entry of pure air into the lungs. 

 Crystals of carbonic-oxide haemoglobin closely resemble those of oxy- 

 haemoglobin. 



Nitric oxide produces a similar compound to the carbonic-oxide 

 haemoglobin, which is even less easily reduced. 



Nitrous oxide reduces oxy-haemoglobin, and therefore leaves the re- 

 duced haemoglobin in a condition to actively take up oxygen. 



Sulphuretted Hydrogen. If this gas be passed through a solution of 

 oxy-haemoglobin, the haemoglobin is reduced and an additional band 

 appears in the red. If the solution be then shaken with air, the two 

 bands of oxy-haemoglobin replace that of reduced haemoglobin, but the 

 band in the red persists, 



Methaemoglobin. If an aqueous solution of oxy-haemoglobin is 

 exposed to the air for some time, its spectrum undergoes a change; the 

 two D and E bands become faint, and a new line in the red at c is devel- 

 oped. The solution, too, becomes brown and acid in reaction, and is pre- 

 cipitable by basic lead acetate. This change is due to the decomposition 

 of oxy-haemoglobin, and to the production of metlicemogloUn. On add- 

 ing ammonium sulphide, reduced haemoglobin is produced, and on shak- 

 ing this up with air, oxy-haemoglobin is reproduced. Methaemoglobin 

 is probably a stage in the deoxidation of oxy-haemoglobin. It appears 

 to contain less oxygen than oxy-haemoglobin, but more than reduced 

 haemoglobin. Its oxygen is in more stable combination, however, than 

 is the case with the former compound. 



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 a given specimen of blood, but as this is a somewhat 

 complicated process, various methods have been proposed which, though 

 not so exact, have the advantage of simplicity. In Gower's haemoglobin- 

 ometer, this consists in comparing the color of a given small amount 

 of diluted blood with glycerine jelly tinted with carmine and picro-car- 

 mine to represent a standard solution of blood diluted one hundred 

 times. The amount of dilution which the given blood requires will 

 thus approximately represent the quantity of haemoglobin it contains. 



