CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



221 



refraction is very weak. The elasticity for the ordinary ray, oj, is somewhat greater than 

 for the extraordinary ray or > aj in refraction indices, and the optical character is 

 hence weakly positive. 



GRAY SQUIRREL, Sciurus carolinensis. Plates 46 and 47. 



The living animal was obtained from a collector at Newport News, 

 Virginia, and was bled in the laboratory. The oxalated blood was laked 

 with ether and centrifugalized, and the slide preparations made in the 

 usual manner. Crystals formed more slowly than with the other squirrels 

 examined; they were larger and showed more tendency to produce com- 

 posite crystals than in the other species. They showed no tendency to 

 dissolve, however, and are evidently quite difficultly soluble in the plasma. 

 Examination with the microspectroscope shows that these crystals are 

 typical oxy hemoglobin. 



187 

 FIGS. 184, 185. Sciurut rufivcnter neglectut Oxyhemoglobin. FIGS. 186, 187. Sciurut carolinentie Oxyhemoglobin. 



Oxy hemoglobin of Sciurus carolinensis. 



Orthorhombic; pseudohexagonal: Axial ratio a : b : c =0.577 : 1 : 6. 



Forms observed: Unit prism (110), brachypinacoid (010), basal pinacoid (001); 

 or, as pseudohexagonal, prism and base. 



Angles: Prism angle 110 A 110=60 (normals); prism to brachypinacoid 110 A 

 010=60 (normals), the two making a perfect hexagonal plate; prism to base 110 A 

 001=90. 



Habit pseudohexagonal, tabular on the base, and with the prism and brachypina- 

 coid faces in equilibrium, so that the plate is a perfect hexagon; sometimes, however, 

 the plate is elongated on the brachy-axis, producing a distinctly orthorhombic habit 

 (text figures 186, 187). The plates are large and perfect hexagons, but are not often 

 simple; they produce groups by piling up on the base, more or less concentrically, and 

 often with curving of the crystals, producing the form of the "eisen rose" of hematite, 

 (see plate 47, fig. 277). The parallel growths on the base may, however, start from several 

 centers, and it is very common to see a small group of this kind near one side of a large 

 plate, not central, but in perfect orientation with the large plate. Twinning seems to 

 be on a brachydome. In the protein ring the crystals form spherulitic masses of the 

 radiating plates, and when these are seen on edge, or interfered with by the cover-glass, 

 they look like lath-shaped crystals. When the piled-up plates are seen on edge, in section, 

 they present a sheaf-shaped appearance. 



The color varies much with the thickness, but in the thicker crystals it shows the 

 normal oxyhemoglobin red. Pleochroism does not show on the flat aspect, the crystal 



