48 A MANUAL OF PHYSIOLOGY 



but not in the same degree in all, a tendency to crystallization ; and 

 the ease with which crystallization can be induced is in inverse pro- 

 portion to the solubility of the haemoglobin. Thus, it is far more 

 difficult to obtain crystals of oxyhaemoglobin from human blood than 

 from the blood of the rat, guinea-pig, or dog, whose blood-pigment 

 is less soluble than that of man, and for a like reason the oxyhaemo- 

 globin of the bird, the rabbit, or the frog crystallizes still less readily 

 than that of human blood. 



As to the form of the crystals, in the vast majority of animals they 



B C 



Oxyhaemoglobin 



Reduced haemoglobin 



Carbonic oxide 

 haemoglobin 



Methaemoglobin (in 

 acid solution) 



Acid-haematin (in 

 ethereal solution). 



Alkaline-haematin 



Haemochromogen 



Hsematoporphyrin 

 (in acid solution) 



Haematoporphyrin 

 (in alka.ine solu- 

 tion) 



B .C D E * F~ 



FIG. 8. TABLE OF SPECTRA OF HEMOGLOBIN AND ITS DERIVATIVES. 

 B, oxygen line; D, sodium line; C and F, hydrogen lines; b, magnesium line. 



are rhombic prisms or needles, but in the guinea-pig they are tetra- 

 hedra belonging to the rhombic system, and in the squirrel six-sided 

 plates of the hexagonal system. 



Reduced haemoglobin can also be caused to crystallize, though 

 with more difficulty than oxyhaemoglobin, since it is more soluble. 

 Crystals of reduced haemoglobin were first prepared from human 

 blood by Hiifner, who allowed it to putrefy in sealed tubes for 

 several weeks. 



