142 THE BLOOD 



Action of Gases on Hemoglobin. Carbon monoxide gas passed through 

 a solution of hemoglobin causes it to assume a cherry-red color and to 

 present a slightly altered spectrum; two bands are still visible but are 

 slightly nearer the blue end than those of oxyhemoglobin, see Plate I. 

 The amount of carbon monoxide taken up is equal to the amount of the 

 oxygen displaced. Carbon monoxide gas readily displaces oxygen under 

 the ordinary respiratory conditions. It is less readily displaced by excess 

 of oxygen and by carbon dioxide, hence the poisonous effects of coal gas 

 which contains much carbon monoxide. Carbon monoxide hemoglobin 

 is not 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 carbon monoxide hemoglobin closely resemble in form those 

 of oxyhemoglobin. 



Nitric oxide produces a similar compound to the carbon monoxide 

 hemoglobin, which is even less easily reduced. 



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 

 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 hemo- 

 globinometer, one of the oldest adapted to its purpose is that invented by 

 professor Fleischl, of Vienna. In this instrument the amount of hemo- 

 globin in a solution of blood is estimated by comparing a stratum of 

 diluted blood with a standard solid substance of uniform tint similar 

 spectroscopically to diluted blood. The instrument has been modified 

 and made more accurate by Miescher. The Fleischl-Miescher apparatus 

 consists of a stand with a metal plate having a circular opening and a 



