x HEMOGLOBIN-CRYSTALS 477 



others. Gscheidlen recommends to let blood undergo putrefaction, 

 as haemoglobin is not altered thereby, while Giirber removes the sub- 

 stances preventing crystallisation, by means of dialysis. For the 

 crystallisation of reduced haemoglobin the same methods are used 

 as were given above for oxy-haemoglobin. 



Oxyhaemoglobin and haemoglobin crystallise generally in plates, 

 prisms, or needles, belonging to the rhombic system, but those of the 

 squirrel belong to the hexagonal system, and that from other rodents 

 may be prepared as hexagonal plates (Halliburton 1 ). Halliburton 

 and Keichert, 2 by mixing blood of guinea-pigs and of rats in definite 

 proportions, have also prepared derivatives of tetrahedra and spindle- 

 shaped crystals, while the normally occurring haemoglobin crystals of 

 the guinea-pig form true tetrahedra. Uhlik 3 obtained from horse's 

 blood, in addition to the ordinary prismatic, rhombic crystals, even 

 after putrefaction had set in, hexagonal holo-hedric crystals in six-sided 

 plates on employing low temperatures. The different forms of crystals 

 pass into one another on recrystallisation, and therefore no significance 

 is attached to the form of the crystals (Cohnheim). That the author 

 does not share this view has been pointed out on p. 470. The older litera- 

 ture dealing with haemoglobin crystals will be found in the important 

 paper of Rollet. 4 Accurate measurements of the angles have been 

 made by Rollet and v. Lang. 5 Those bloods which do not crystallise 

 readily form as a rule only microscopic crystals, while Hiifner and 

 Biicheler 6 obtained from horse's blood large needles measuring 2 to 3 

 mm. in length and 0'5 mm. in thickness. Gscheidlen once prepared 

 a haemoglobin crystal measuring 3 '5 cm. in length. 



The optical properties of the crystals have been studied by Preyer 

 and more thoroughly by Ewald. 7 They are silky, doubly refractile, 

 and not transparent ; they also possess a very marked pleochroism. 

 This last property is especially well seen in the crystals of reduced 

 haemoglobin, for when viewed with only one Nicol prism they show 

 three distinct axial colours, namely, a bluish purple, a reddish purple, 

 and no colour. The crystals of oxy haemoglobin show the pleochroism 

 less distinctly, but still quite definitely ; according to the position 

 of the Nicol's prism they are either of a dark scarlet tint, or of a 

 bright yellowish red. Pleochroism is also shown by the other haemo- 



1 W. D. Halliburton, Quart. Journal of Micr. Sc. 28. 181 (1888). 



2 Edw. T. Reichert, Amer. Journ. of Physiol. 9. 97 (1903). 



3 M. Uhlik, Pfiugers Arch. 104. 64 (1904). 



4 Rollet, Sitzb. d. kaiserl. Akad. d. Wiss. Wien, math.-natunv. Klasse, 46. 65 (1862). 



5 V. v. Lang, Wiener Akademie, 46. 1862 (according to Preyer). 



6 G. Hiifner and Biicheler, Zeitschr.f. physiol. Ghem. 8. 358 (1884). 



7 A. Ewald, Zeitschr.f. Biol. 22. 459 (1886). 



