140 



THE BLOOD 



tents. In some the formation of crystals is almost spontaneous, whereas 

 in others it takes place either with great difficulty or not at all. Among 

 the animals whose blood coloring-matter crystallizes most readily are the 

 guinea-pig, rat, squirrel, and dog; and in these cases to obtain crystals it 

 is generally sufficient to dilute a drop of recently drawn blood with water 

 and to expose it for a few minutes to the air. In many instances other means 

 must be adopted; e.g., the addition of alcohol, ether, or chloroform, rapid 

 freezing and then thawing, the application of an electric current, a tempera- 



4\ 



FIG. 119. Crystals of Oxyhemoglobin 

 Prismatic, from Human Blood. 





FIG. 1 20. Oxyhemoglobin Crystals 

 Tetrahedral, from Blood of the Guinea-pig. 



ture of 60 C., the addition of sodium sulphate, or the addition of decom- 

 posing serum of another animal. 



The hemoglobin of human blood crystallizes with difficulty, as does also 

 that of the ox, the pig, the sheep, and the rabbit. 



The forms of hemoglobin crystals, as will be seen from figures 119 and 

 1 20, differ greatly. Hemoglobin crystals are soluble in water. Both the 

 crystals themselves and also their solutions have the characteristic color of 

 arterial blood. 



A dilute solution of Oxyhemoglobin gives a characteristic appearance 

 with the spectroscope. Two absorption bands are seen between the solar 

 lines D, which is the sodium band in the yellow, and E, see the frontispiece,, 

 one in the yellow, with its middle line some little way to the right of D. This 

 band is very intense, but narrower than the other, which lies in the green 

 near to the left of E. Each band is darkest in the middle and fades away 

 at the sides. As the strength of the solution increases, the bands become 

 broader and deeper. Both the red and the blue ends of the spectrum become 

 encroached upon until the bands coalesce to form one very broad band when 

 only a slight amount of the green and part of the red remain unabsorbed. 

 Any further increase of strength leads to complete absorption of the spectrum. 



If crystals of hemoglobin are exposed to an atmosphere of oxygen they 

 take up oxgyen and form Oxyhemoglobin, each gram of the pigment fixing 



