84 HANDBOOK OF PHYSIOLOGY. 



C. 53.85; H. 7.32; K 16.17; 0. 21.84; S. .63; Fe. .42; and if the 

 molecule be supposed to contain one atom of iron the formula would be 

 C 60f , H 960 , N 154 , FeS 3 ]79 . The most interesting of the properties of 

 haemoglobin are its powers of crystallizing and its attraction for oxygen 

 and other gases. 



Crystals. The haemoglobin of the blood of various animals pos- 

 sesses the power of crystallizing to very different extents (blood- 

 crystals). In some animals the formation of crystals is almost spon- 

 taneous, 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 expose it for a few minutes to the 

 air. Light seems to favor the formation of the crystals. In many in- 



Fia. 78. Crystals of oxy-haemoglobin prismatic from human blood. 



stances other means must be adopted, e. g., the addition of alcohol, 

 ether, or chloroform, rapid freezing, and then thawing, an electric cur- 

 rent, a temperature of 140 F. (60 C.), or the addition of sodium 

 sulphate. 



The haemoglobin of human blood crystallizes with difficulty, as does 

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



The forms of haemoglobin crystals, as will be seen from the appended 

 figures, differ greatly. 



Haemoglobin crystals are soluble in water. Both the crystals them- 

 selves and also their solutions have the characteristic color of arterial 

 blood. 



A dilute solution of haemoglobin 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 plate), one in 

 the yellow, with its middle line some little way to the right of D, is very 



