142 THE BLOOD 



and a second all but midway between D and E. It may be precipitated from 

 its acid solution by adding water or by neutralization, and when redissolved 

 in alkalies presents four bands, a pale band between C and D, a second 

 between D and E, nearer D, another nearer E, and a fourth occupying the 

 chief part of the space between b and F. 



Hematin in Acid Solution. If an excess of acetic acid is added to blood, 

 and the solution boiled, the color alters to brown from decomposition of 

 hemoglobin and the setting free of hematin; by shaking this solution with 

 ether, a solution of hematin in acid solution is obtained. The spectrum of 

 the ethereal solution shows no less than four absorption bands, viz., one in 

 the red between C and D, one faint and narrow close to D, and then two 

 broader bands, one between D and E, and another nearly midway between 

 b and F. The first band is by far the most distinct, and the acid aqueous 

 solution of hematin shows it plainly. 



Hematin in Alkaline Solution. If a caustic alkali is added to blood and 

 the solution is boiled, alkaline hematin is produced, and the solution becomes 

 olive-green in color. The absorption band of the new compound is in the 

 red, near to D, and the blue end of the spectrum is absorbed to a considerable 



ife*. 



FIG. 123. Hematoidin Crystals. (Frey.) Fig. i23a. Hemin Crystals. (Frey.) 



extent. If a reducing agent be added, two bands resembling those of oxy- 

 hemoglobin, but nearer to the blue, appear; this is the spectrum of reduced 

 hematin, or hemochromogen. On violently shaking the reduced hematin 

 with air or oxygen the two bands are replaced by the single band of alkaline 

 hematin. 



Hematoidin. This substance is found in the form of yellowish crystals, 

 figure 123, in old blood extravasations and is derived from the hemoglobin. 

 Their crystalline form and the reaction they give with fuming nitric acid 

 seem to show them to be closely allied to bilirubin, the chief coloring matter 

 of the bile, and in composition they are probably either identical or isomeric 

 with it. 



Hemin. One of the most important derivatives of hematin is hemin. 

 It is usually called hydrochloride of hematin, but its exact chemical com- 

 position is uncertain. Its formula is said to be C 32 H 30 N 4 FeO 3 HCl, and it 

 contains 5.18 per cent, of chlorine, but by some it is looked upon as simply 



