THE CIRCULATING LIQUIDS OF THE BODY 



45 



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 

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

 tetrahedra belonging to the rhombic system, and in the squirrel 

 six-sided plates of the hexagonal system (Fig. 8). 



Reduced haemoglobin can also be caused to crystallize, though 

 with more difficulty than 

 oxyhaemoglobin, since it is 

 more soluble. Crystals of re- 

 duced haemoglobin were first 

 prepared from human blood 

 by Hiifner, who allowed it 

 to putrefy in sealed tubes 

 for several weeks. 



When a solution of oxy- 

 haemoglobin of moderate 

 strength is examined with 

 the spectroscope, two well- 

 marked absorption bands * 

 are seen, one a little to the 

 right of Fraunhofer's line 

 D, and the other a little to 

 the left of E. A third 

 band exists in the extreme 

 violet between G and H. 

 It cannot be detected with 

 an ordinary spectroscope, 

 but has been studied by the 

 aid of a fluorescent eye- 

 piece, by projecting the 

 spectrum on a fluorescent 

 screen, and by photograph- 

 ing the spectrum. The ad- 

 dition of a reducing agent, a ' b ' / rom n ; c ' f r m cat ; d ' 



' e, from hamster ; /, Irom squirrel (Frey). 



such as ammonium sul- 



phide, causes the bands in the visible spectrum to disappear, 

 and they are replaced by a less sharply-defined band, of which 

 the centre is about equidistant from D and E. This is the 

 characteristic band of reduced haemoglobin. The spectrum of 

 ordinary venous blood shows the bands of oxyhaemoglobin. 



Carbonic oxide hemoglobin is a representative of a class of haemo- 

 globin compounds analogous to oxyhaemoglobin, in which the loosely- 

 combined oxygen has been replaced by other gases (carbon monoxide, 

 nitric oxide) in firmer union. Its spectrum shows two bands very 

 like those of oxyhaemoglobin, but a little nearer the violet end. 

 Carbonic oxide haemoglobin is formed in poisoning with coal-gas. 



FlG - 8. OXYH^MOGLOBIN CRYSTALS. 



