THE BLOOD 



Methemoglobin. If an aqueous solution of oxyhemogJobin is ex- 

 posed 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 oxyhemoglobin, 

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

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

 globin is again produced. Methemoglobin is probably a stage in the deoxida- 

 tion of oxyhemoglobin. It appears to contain less oxygen than oxyhemo- 



tio. 122. rleischl's Hemoglobinometer. 



globin, 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 

 Fleischl, of Vienna. In this instrument the amount of hemoglobin 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 Fleischl instrument has been recently 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 plaster mirror below, 

 S, figure 122, which casts light through the opening. Beneath the plate is a 

 metal framework containing a colored glass wedge, and along the side of 



