228 



CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



are visible; some are rhomboidal plates, apparently untwinned, but most of them seem 

 to be twinned and in the twins the orthopinacoid planes seem to be more developed 

 (text figure 201). By this twinning being several times repeated the crystals become 

 nearly symmetrically hexagonal in outline, and perfect hexagonal plates appear sparingly 

 (along with the obviously twinned crystals) that are apparently mimetic twins and 

 really hexagonal in symmetry (text figure 202). The rhomboidal plates tend to grow 

 into groups, by piling up of the plates (plate 51, fig. 303), and, as these are nearly all 

 hexagonal in outline, due to development of (100), these groups closely resemble the 

 similar forms seen in the hexagonal plates of other rodents, as the squirrels for example. 



199 

 FIGS. 197, 198. 199, 200, 201, 202. Castor canadenrit Oxyhemoglobin. 



The color of the crystals is a bright scarlet or blood-red. Pleochroism on the basal 

 aspect is hardly noticeable, but probably most of the crystals examined were twinned. 

 The colors were: a yellowish, b yellowish-red, rather a strong color; c deep blood-red. 

 On the basal aspect the double refraction is very weak, and extinction is very hard to 

 observe; it is, however, symmetrical. On the edge view, the double refraction is stronger, 

 and looking along a the extinction is straight; along 6 it is 8 from the trace of the base 

 or from the clino-axis, a. On the base in convergent light the interference figure is readily 

 seen a nearly uniaxial cross, which opens and closes as the crystal is revolved, showing 

 the crystal to be biaxial. The angle of the optic axes, 27? is not above 7 or 8. 



The orientation of the elasticity axes is a A a =8, the extinction angle; b=6, 

 c A 6=4 (about). The plane of the optic axes is the plane of symmetry, and the acute 

 bisectrix is the axis of least elasticity, Bx a =c. The optical character is hence positive. 



As nearly all of the crystals examined were twinned, and as these mimetic twins 

 tend to become uniaxial, it is possible that the above-described interference figure is 

 due to twinning; but if so, the orientation of the optic axes is not altered nor is the 

 optical character. 



MUSKRAT, Fiber zibethicus. Plates 51 and 52. 



The living animal was procured from a collector and bled in the lab- 

 oratory. The blood was oxalated, laked with ether and centrifugalized ; 

 from the clear solution slide preparations were made in the usual manner. 

 The crystals formed readily soon after covering the slides; at first, the 

 crystals were fine needles, but afterwards these became lath-shaped, or flat 

 prismatic crystals appeared amongst the needles; and, at the same time, 

 tabular crystals began to appear. They kept well, showing no sign of dis- 

 solving. Crystallization continued after sealing the slides, until practically 

 the entire slide was filled with crystals. The crystals are oxyhemoglobin. 



