74 THE BLOOD. 



Chemical Composition of Bed Blood-cells. 



It has been before remarked that the red blood-corpuscles 

 are formed of a colourless stroma, infiltrated with a colour- 

 ing matter termed liamoglobin. As they exist in the 

 blood they contain about three-fourths of their weight of 

 water. 



The stroma appears to be composed of a nitrogenous 

 proximate principle termed protagon, combined with albu- 

 minous matter (paraglobulin or fibrinoplastin), fatty mat- 

 ters including cholesterin, and salts, chiefly phosphates, of 

 potash, soda and lime. 



Haemoglobin, which enters far more largely into the com- 

 position of the red corpuscles than any other of their con- 

 stituents, is allied to albumen in some respects, but differs 

 remarkably from it in others. One of its most marked 

 distinctive characters is its tendency under certain arti- 

 ficial conditions to crystallize ; the so-called blood-crys- 

 tals being but the natural crystalline forms assumed by 

 this substance. 



Haemoglobin can be obtained in a crystalline form with 

 various degrees of difficulty from the blood of different 

 animals, that of man holding an intermediate place in this 

 respect. Among the animals whose blood colouring-matter 

 crystallizes most readily, are the guinea-pig and the dog ; 

 and in these cases to obtain crystals it is generally suffi- 

 cient 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 somewhat less simple process must be 

 adopted; as the addition of chloroform or ether, rapid freezing 

 and then thawing, or other means which separate the colour- 

 ing-matter from the other constituents of the corpuscles. 



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

 panying figures. 



Another and most important character of haemoglobin is 

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



