106 PHYSIOLOGICAL CHEMISTRY 



brown. On dilution and observation with the spectroscope, a 

 dark absorption band between the C and D lines is observed. Two 

 fainter bands in the position of the oxyhemoglobin bands are 

 considered by some investigators to be due to the presence of a 

 small amount of this latter pigment. On adding Stokes' reagent 

 to a methemoglobin solution, the substance is changed first into 

 oxyhemoglobin, and this into hemoglobin, with corresponding 

 changes in the spectrum. 



On adding an alkali to a methemoglobin solution, alkaline 

 methemoglobin is formed, which gives a characteristic spectrum 

 of its own. 



Acid Hematin. Hematin is the compound into which oxy- 

 hemoglobin may be split by the action of acids or other agents. 

 It contains the iron of the hemoglobin molecule, and is com- 

 paratively simple in structure. It has been shown to contain 

 four pyrrol rings. 



HC CH 



II II 

 HC CH 



\/ 



N 



H 



Pyrrol 



Hematin is formed from oxyhemoglobin by the action of gas- 

 tric and pancreatic juices. It is found thus in the feces after 

 gastric or intestinal hemorrhage, but also, of course, after a 

 meal of bloody meat. Hematin gives the brown color to cooked 

 meat. It may be prepared by adding blood to glacial acetic acid 

 and ether. The absorption spectrum of acid hematin is variable 

 with the kind of acid used in its preparation and other condi- 

 tions. If prepared as above, however, it shows a sharp dark band 

 between the C and D lines and a fainter broad band between the 

 D and F lines. Alkaline hematin shows characteristic bands. 



HemocJiromogen. Hemochromogen, or reduced alkaline hem- 

 atin is obtained by splitting off the globin from hemoglobin by 

 the action of acids or alkalies, or by the reduction of alkaline 

 hematin with Stokes' reagent. Like hematin, it also contains 



