92 INTRODUCTION. 



the other principles in the fact that it is not dissolved, but 

 decomposed by potash, giving off ammoniacal vapor. 



Coloring Matters. 



These substances have been classed with the organic 

 nitrogenized principles, from the fact that they contain ni- 

 trogen ; but they do not seem to be endowed with the vital 

 properties which characterize this class, with the exception 

 perhaps of hematine and melanine. As a peculiarity of 

 chemical constitution, they all contain iron, which is molec- 

 ularly united with their other elements. The following are 

 the principles of this group : 



Hematine^ 

 Melanine, 

 Biliverdine, 

 Urrosacine. 



Hematine. This is the red coloring matter of the blood, 

 and exists, intimately united with globulin e, in the blood 

 corpuscles. The iron which it contains can be readily dem- 

 onstrated, even in a single drop of blood, by the following 

 process : To a small quantity of blood in a watch-glass we 

 add a drop of nitric acid, then evaporate slowly over a lamp, 

 when fumes of nitrous acid are driven off, the iron takes 

 oxygen and is converted into a per-oxide. If we then add a 

 drop of the sulpho-cyanide of potassium, we produce the 

 characteristic red color of the sulpho-cyanide of iron. Sep- 

 arated from the blood, hematine is soluble in ether and boil- 

 ing alcohol, but insoluble in water and in acids. 



"We do not exactly understand the mode of formation of 

 hematine, but pathology teaches us that it is an essential 

 principle of the blood. In certain cases of anemia, when 

 there is extreme pallor and consequently deficiency of hema- 

 tine, the administration of iron in any form induces the for- 

 mation of this substance, restores the normal constitution of 



