188 THE BLOOD 



and in the presence of this gas to hematin. Quite similarly, hematin 

 may be reduced to hemochromogen, while the latter substance may be 

 oxidized to hematin. 



Hemochromogen is responsible for the color of hemoglobin and, therefore, of the 

 blood. Solutions of this substance exhibit a cherry-red color. It may be prepared 

 in crystalline form by mixing a drop of defibrinated blood with a drop of pyridin 

 to which a small quantity of ammonium sulphid is then added. These crystals 

 possess a stellate shape. ^ 



Hematin is an amorphous substance which may also appear as rhombic needles 

 and platelets. 2 It possesses a dark-brown color, and while insoluble in water, 

 alcohol and ether, is readily soluble in dilute alkalies and acids. It has lost 

 the properties generally assigned to a proteid body and contains all the iron of the 

 hemoglobin molecule. Its formula is given as C32H32N4Fe04. It is found in the 



Fig. 104. — Hemin Cbystals. 



feces after the ingestion of meats and food rich in blood, as well as after hemor- 

 rhages into the stomach or intestinal canal. The reduction of the hemoglobin 

 is accomplished in this case by the gastric and pancreatic juices. 



A very important derivative of hematin is hemin or chlorhematin, the formula 

 for which is given by Kiister^ as: C34H3304N4FeCl. One hydroxyl group of the 

 hematin has been displaced by chlorin. This body is obtained in the form of 

 crystals, the so-called Teichmann's hemincrystals. As these possess a very charac- 

 teristic shape and color and may be derived from very small quantities of blood, 

 the hemin reaction constitutes a most important test for blood. It is possible to 

 prepare them in large numbers by carefully heating a droplet of blood which has 

 been placed upon a glass slide. When dry, a drop or two of glacial acetic acid and a 

 small crystal of sodium chlorid are added, after which a cover-slip is applied and 

 the acid slowly evaporated by drawing the slide repeatedly through a flame. 

 For purposes of examination, any dry stain which is suspected of being caused by 

 blood, must first be thoroughly washed with small amounts of water and the water 

 evaporated to dryness, while solid particles of blood should first be powdered 

 with a few crystals of sodium chlorid. 



1 Donogamy, Jahresber. fur Tierchemie, xxiii, 1894, 126. 



2 Piettra and Vila, Compt. rend., cxli, 1906. 



» Zeitschr. fur physiol. Chemie, xl, 1904, 423. 



