CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



241 



Oxyhemoglobin of Domesticated Variety of Cavia cutleri. 



Orthorhombic sphenoidal: * Axial ratio a : b : (5=0.9428 : 1 : 0.8875. 



Forms observed: Right sphenoid (111), left sphenoid (111), base (001). 



Angles: The three plane angles on the triangular face of the sphenoid were meas- 

 ured as 57, 60, 63, and from these angles the axial ratio was calculated. 



Habit sphenoidal, the angles being such that the sphenoids can not, without meas- 

 urement, be distinguished from isometric tetrahedra. Ordinarily the simple sphenoid 

 alone (111) (text figure 239) is the only form shown except in twins, but in some prepara- 

 tions, and especially when considerable amounts of salts have been added, the left- 

 handed sphenoid appears, truncating the corners of the right-handed sphenoid, but 

 rarely forming a large plane (text figure 240) ; they are not seen in equilibrium. The 

 crystals occur singly or uniting in irregular groups; or more often, when composite, 

 uniting as twins. The two common types of twins seen in tetrahedrite occur most com- 

 monly: (a) The right-handed and left-handed sphenoids interpenetrant, with their edges 

 crossing in the polar axis, analogous to the twins in the isometric mineral eulytite (text 

 figure 241, also plate 57, fig. 340). (b) The two interpenetrant sphenoids having a common 

 plane as the base of the tetrahedron, and also a common apex to the tetrahedron (text 

 figures 242 and 243). In these the base forms a six-pointed star, and the edges from the 

 points of the star all meet in one point (see plate 58, fig. 343). (c) The interpenetrant 

 sphenoids uniting point to point with their bases in the same orientation; in these the 



240 



242 



243 



FIGS. 239. 240, 241, 242, 243, 244. Cavia cutleri (domesticated variety) Oxyhemoglobin. 



apex of each sphenoid appears through the base of the other, and the bases may be 

 quite near together (text figure 244, also plate 57, fig. 341). In the composite crystals that 

 appear to be simply irregular aggregates, it can often be seen that two of these kinds of twin- 

 ning are present and the parts are really in twin position. Only interpenetrant twins were 

 observed. Parallel growths also occur, but much more rarely. The crystals were generally 

 the sphenoids only, but in a few preparations the basal pinacoid occurs (text figure 240). 

 Pleochroism is not very strong, the shade of the red changing from paler red for 

 light vibrating parallel to a to deeper red for light vibrating parallel to c. The orientation 



* The orthorhombic character of the tetrahedra of the guinea-pig oxyhemoglobin crystals was first 

 determined by von Lang (Sitzungsb. d. Math.-nat. Klasse d. Kais. Akad. d. Wiss., Wien, 1862-63, XLI, 

 Heft ii, p. 85), who showed that they were orthorhombic sphenoidal. More recently, Donog&ny (Mathe- 

 matikai 6s terme'szettudomanyi ertesito, xi, 262; Zeit. f. Kryst., 1894, xxm, 499) confirmed von Lang's 

 determination, and published measurements of the three plane angles of the triangular face of the sphenoid 

 as 64 11', 60 50', and 55 45'; but without giving any axial ratio. It will be observed that these three 

 angles given by Donogany add up to 180 46', or 46' above two right angles. 



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