CRYSTALLOGRAPHY OP HEMOGLOBINS OF THE RODENTIA. 



229 



Oxyhemoglobin of Fiber zibethicus. 



Monoclinic: Axial ratio a : b : t =1.6318 : 1 : 6; /? = 68. 



Forms observed: Unit prism (110), base (001). 



Angles: Prism angle 110 A HO =63; prism edge to base, edge 110-lTO A 001 =68 =/?. 



204 



206 



Flos. 203, 204, 205, 206. Fiber zibethicu Oxyhemoglobin. 



Habit thin tabular on the base, the crystal consisting of the base (001) bounded 

 by the prism (110). The first crystals to form are long needles or lath-shaped crystals 

 with oblique ends; among these soon appear blade-like crystals of the same habit, often 

 twinned; and, at about the same time, lozenge-shaped tabular crystals appear all through 

 the slides. These latter (text figures 203 and 204), which are undistorted crystals, are 

 very symmetrical rhombic plates, sometimes untwinned, sometimes twinned repeatedly. 

 They do not seem to form mimetic twins and develop into hexagonal plates, as is so 

 commonly the case with rodents. The twins are of the usual horse-type (text figure 205), 

 on a twin axis normal to a prism-base edge and lying in the base. But in the blade-like 

 crystals these appear as contact twins with the common prism-like edge parallel to the 

 length of the blade-like crystal; the blades being elongated in the direction of two oppo- 

 site prism faces, and consisting, therefore, of the two basal faces and two prism faces 

 and terminated by the prism faces. This elongation produces in the untwinned crystals 

 a triclinic appearance. In these same blade-like crystals another kind of twinning is 

 very commonly seen, on a unit pyramid as the plane of twinning, the twin being inter- 

 penetrant and showing an X-shaped cross-section (text figure 206). These were also 

 observed in the plates. The twins of the plates are, as stated, of the usual horse-type, 

 but the plates being very symmetrical the group formed by the twinning has often the 

 outline of a truncated triangle, and sometimes is nearly triangular. By parallel growth 

 the plates become greatly elongated in the direction of the clino-axis, forming parallel 

 growth groups, and they also grow together on the base in groups, extending in the direc- 

 tion of the same axis. Sometimes the rhombic plates form radiating groups by uniting 

 on the base, the radial character showing when the plates are seen on edge. 



On the base, the color of the crystals is a deep scarlet, owing to the very slight 

 pleochroism on this aspect. Pleochroism is weak on the base, but strong when the edge 

 aspect is presented; a pale reddish-orange, b blood-red; c blood-red, somewhat deeper 

 than 6, but the two practically equal. Double refraction is so weak on the basal aspect 

 that the quartz wedge scarcely shows the difference between 6 and c. On the edge view, 

 looking along c or b, however, the double refraction is quite strong. On the edge view 

 looking along b the extinction is oblique, about 15 in the acute angle. The orientation 

 of the optic axes is a A S=37, in the obtuse angle; b=b; c A a = 15, in the acute 

 angle. The plane of the optic axes is the plane of symmetry (010), and the acute bisec- 

 trix is the axis of least elasticity, J5x = a; the optical character is hence negative. 



