CHEMISTRY OF HEMOGLOBIN 351 



in the ultraviolet spectrum is, however, not characteristic of hemo- 

 globin. It is also shown by solutions of its protein component, Globin, 

 and more or less distinctly by solutions of many other proteins. It is 

 distinctly visible in the light transmitted through solutions of Tyrosine, 

 Phenylalanine and other aromatic ammo-acids, to which radicals its 

 presence in the protein absorption-spectrum is due. 



It was first shown by the English physicist, Stokes, that if blood be 

 placed under a vacuum, or acted upon with a reducing-agent such as 

 an alkaline solution of ferrous sulphate or ferrous tartrate (known 

 as Stokes' Reagent), or warm solutions of the alkaline sulphides, the 

 absorption-spectrum of the solution changes. Only one band is now to 

 be seen in the visible spectrum, where formerly there were two. This lies 

 between D and E, nearer to D than to E. The same spectrum is sup- 

 plied by the blood of asphyxiated animals. This absorption-spectrum 

 is due to hemoglobin as distinguished from the Oxyhemoglobin which 

 is formed when hemoglobin solutions are aerated. The center of the 

 band lies at wave-length X = 559. The band in the photographic 

 spectrum is at the same time shifted, as Gamgee has shown, the center 

 of this band in solutions of Reduced Hemoglobin lying nearer the visible 

 spectrum than it does in solutions of oxyhemoglobin. The color of 

 solutions of oxyhemoglobin is the typical scarlet of arterial blood; 

 solutions of reduced hemoglobin are darker, with a slightly purple 

 hue and they also exhibit the phenomenon of Dichroism, the color of 

 light reflected from the surface of the solution being green, while 

 transmitted light, as we have stated is red, with a slightly purple tinge. 



By the action of oxidiz ing-agents reduced hemoglobin is rapidly 

 converted into oxyhemoglobin, but the further action of many oxidiz- 

 ing-agents such as ozone, potassium permanganate, potassium ferri- 

 cyanide and chlorates results in the formation of a modification of 

 oxyhemoglobin which is designated Methemoglobin. The absorption 

 spectrum of methemoglobin resembles that of oxyhemoglobin, except- 

 ing that the /3 band is more intense than the a band and a third band is 

 present between C and D. The color of methemoglobin solutions 

 is chocolate-brown, changing to red when the solution is rendered acid, 

 the absorption-spectrum changing at the same time and showing only 

 one absorption-band between C and D. The oxygen-content of met- 

 hemoglobin appears to be identical with that of oxyhemoglobin, but 

 it is much more firmly combined and is not given up under a vacuum, 

 nor is it displaced by a stream of Carbon Monoxide. When, however, 

 methemoglobin is treated with Stokes' reagent reduced hemoglobin 

 is reformed and this in turn forms oxyhemoglobin on shaking the 

 solution up with air. Methemoglobin is often spontaneously formed 

 when arterial blood is allowed to stand in sealed tubes and it may 

 be found in transudates and cystic fluids stained with blood, or in old 

 extravasations of blood following upon injuries. 



The blood of animals which have been asphyxiated by illuminating 

 gas is of a peculiar florid cherry-red color, which does not change when 



