CRYSTALLOGRAPHY OP HEMOGLOBINS OF THE RODENTIA. 233 



flattened on two opposite prism faces (text figure 214), have a decidedly monoclinic 

 aspect. Nothing that was observed of the optical characters could determine that these 

 crystals were not orthorhombic ; but no end views, looking along the length of the crystal, 

 could be obtained, and hence they may be really monoclinic. Twins on the brachy and 

 unit pyramids formed as has been described for the white rat; on the flat aspect, twinned 

 on the brachypyramid, they make pseudo-hexagonal groups; and twinned on the unit 

 pyramid, with the edge of the flattened prism presented, they make six-pointed star- 

 shaped groups (text figures 210, 211). What appears to be a twin on the prism also 

 occurs, in some cases producing the effect of a carpenter's miterbox, where the two crystals 

 on edge appear on either side of one presenting the flat aspect (text figure 215). As the 

 crystals continue to develop, short prismatic crystals, flattened on two prism faces, 

 appear, and they produce hexagonal plates, owing to the angle of 120 of the dome 

 profile, which is of course the same as the profile of dome to prism outline (text figure 

 216). These crystals show much less double refraction than the elongated crystals and 

 are sometimes practically isotropic. When the prism is symmetrically developed and 

 in equilibrium with the dome (text figure 217) the crystals resemble octahedra, and 

 they appear to pass into isometric octahedra, the /3-oxyhemoglobin crystal. 



Pleochroism is marked in the elongated prismatic crystals, but wanting in the hexag- 

 onal plates and in the equidimensional, octahedral-looking, prism-dome combinations. 

 The colors are a = 6 (about), pale yellowish-red to pale red; c deeper red. No end views 

 were seen, so that the pleochroism of a and 6 could not be differentiated. Double refrac- 

 tion is strong in the long crystals, but very weak or entirely wanting in the equidimen- 

 sional crystals and in the hexagonal plates. The symmetrical crystals in convergent 

 polarized light showed traces of the brushes of an interference figure, looking along the 

 macro-axis, the brushes passing out of the field upon rotation of the stage, showing that 

 the observation was being made on the obtuse bisectrix of the optic axes. The orienta- 

 tion of the elasticity axes is a =6; 6=a; c = i. No observation of the interference figure, 

 looking along the acute bisectrix was possible, but the acute bisectrix is the axis of least 

 elasticity, Bx a =c, and the optical character is positive. 



p-Oxyhemoglobin of Mus norvegicus. 



Isometric or pseudo-isometric. 



Forms observed: Octahedron (111). 



Angles: The angle over the pole of the octahedron 111 A III 71 (about). 



218 22 



FIGS. 218,219,220. M us nortitgicut ,8-Oxyhemoglobin. 



Habit octahedral; symmetrical isometric octahedra, or distorted octahedra formed 

 by the crystal lying on one face and hence developing into forms with a nearly triangular 

 to almost hexagonal profile (text figures 218, 219, 220). These hexagonal sections of the 

 octahedron closely resemble the hexagonal-looking tabular crystals of the a-oxyhemo- 

 globin, but may be distinguished from them by careful examination. 



The crystals show the oxyhemoglobin red of the white and Norway rats, rather 

 a pale brownish or yellowish-red. There is no pleochroism nor double refraction; the 

 crystals appear to be absolutely isotropic. 



