BLOOD-CRYSTALS. 69 



imate principle termed protagon, combined with albuminous 

 matter (paraglobulin or fibrinoplastin), fatty matters includ- 

 ing cholesterin, and salts, chiefly phosphates, of potash, soda, 

 and lime. 



Haemoglobin, which enters far more largely into the compo- 

 sition of the red corpuscles than any other of their constituents, 

 is allied to albumen in some respects, but differs remarkably 

 from it in others. One of its most marked distinctive charac- 

 ters is its tendency under certain artificial conditions to crys- 

 tallize ; the so-called blood-crystals being but the natural crys- 

 talline forms assumed by this substance. 



Haemoglobin can be obtained in a crystalline form, with 

 various degrees of difficulty, from the blood of different ani- 

 mals, that of man holding an intermediate place in this re- 

 spect. Among the animals whose blood-coloring matter crys- 

 tallizes most readily are the guinea-pig and the dog ; and in 

 these cases, to obtain crystals, it is generally sufficient to dilute 

 a drop of recently drawn blood with water, and expose it for a 

 few minutes to the air. In many instances, however, a some- 

 what less simple process must be adopted ; as the addition of 

 chloroform or ether, rapid freezing and then thawing, or other 

 means which separate the coloring matter from the other con- 

 stituents of the corpuscles. 



Different forms of blood-crystals are shown in the accom- 

 panying figures. 



Prismatic, from human blood. 



Another and most important character of haemoglobin is 

 its attraction for oxygen, and some other gases, as carbonic and 



1 Figs. 26, 27, and 28, illustrate some of the principal forms of 

 blood-crj'stals. 



