ESTIMATION OF HEMOGLOBIN 139 



Nitric oxide produces a similar compound to the carbonic-oxide hemo- 

 globin, which is even less easily reduced. 



Nitrous oxide reduces oxyhemoglobin, and therefore leaves the reduced 

 hemoglobin in a condition actively to take up oxygen. 



Sulphuretted hydrogen, if passed through a solution of oxyhemoglobin, 

 reduces it and an additional band appears in the red. If the solution be 

 then shaken with air, the two bands of oxyhemoglobin replace that of reduced 

 hemoglobin, but the band in the red persists. 



Methemoglobin. If an aqueous solution of oxyhemoglobin is exposed 

 to the air for some time, its spectrum undergoes a change; the two d and 



FIG. 122. Fleischl's Hemoglobinometer. 



e bands become faint and a new line in the red at C is developed. The 

 solution, too, becomes brown and acid in reaction, and is precipitable by 

 basic lead acetate. This change is due to the decomposition of oxyhemo- 

 globin, and to the production of methemoglobin. On adding ammonium 

 sulphide, reduced hemoglobin is produced, and on shaking this up with air, 

 oxyhemoglobin is again produced. Methemoglobin is probably a stage in 

 the deoxidation of oxyhemoglobin. It appears to contain less oxygen than 

 oxyhemoglobin, but more than reduced hemoglobin. Its oxygen is in more 

 stable combination, however, than is the case with the former compound. 

 Estimation of Hemoglobin. The most exact method is by the esti- 

 mation of the amount of iron (dry hemoglobin containing 0.42 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. Of the several varieties of hemoglobinom- 

 eter, one of the best adapted to its purpose is that invented by Professor 



