CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



239 



(a) is symmetrical on the base and straight looking along the a-axis; but is 19 to 20 

 (perhaps higher) on the edge view, looking along b. In the twins of the second type of 

 crystal, the extinction is symmetrical with the outline and parallel to the twin axis. In 

 the untwinned crystals the interference may be easily seen in traces when the crystal 

 does not lie flat; but is not readily observed when the crystal is flat, only traces of it 

 showing. This is due to the orientation of the elasticity axes, which is a =6; b A a =20, 

 in the acute angle; c A 6=54, in the obtuse angle. The plane of the optic axes is 

 normal to the plane of symmetry and inclined to the orthopinacoid at an angle of 54, 

 in the obtuse angle; it is hence inclined 34 to the normal to the base. The acute bisec- 

 trix is the axis of least elasticity, Bx a =c, and the optical character is positive. 



fl-Oxyhemoglobin of Erethizon dorsatus. 



Orthorhombic : Axial ratio a : b : <! = O.S170 :!:<}. 



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



Angles: Prism angle 110 A 110=78 30' (normals); prism to base 110 A 001 =90. 



FIGS. 236, 237, 238. Erethizon dortalus /3-Oxyhemoglobin. 



Habit tabular on the base; consisting of the short prism (110) cut by the basal 

 pinacoid (001) (text figures 236 and 237) ; the ratio of length to breadth of the prism 

 being generally about 1 : 3, but the tabular crystals thicken and become equidimensional 

 in some cases. The crystals are generally more or less hopper-shaped on the base and evi- 

 dently grow more actively on the prism faces and edges and less so on the base ; the result 

 is often the appearance of a skeleton crystal, looking down upon (001), with the crystal 

 axes marked out in more solid substance. On edge views and sections, the solid central 

 part is seen to run out from the center to the four coigns of the basal face; the interven- 

 ing parts, between these four directions and the outer surfaces of the prism, having a 

 porous aspect. These crystals are relatively large, much larger than the crystals of the 

 a-oxyhemoglobin that have been described. The crystals showed parallel growth; and 

 a twin, of the interpenetrant type, on a brachydorne (text figure 238), was seen, the 

 two parts crossing at an angle of nearly 90. 



The crystals are a rather bright scarlet color, and on the flat as well as on edge 

 they are quite pleochroic. The pleochroism is a nearly colorless to yellowish-red, depend- 

 ing on the thickness; b deep scarlet to blood-red; c deep blood-red. On the base, the 

 extinction is symmetrical; and on edge views it is straight in all aspects, when the section 

 is normal to the base. On the base, in convergent light, a biaxial figure is seen, symmet- 

 rically placed, with the separation of the brushes wide; 2E is above 75, but was not 

 exactly measured. The orientation of the elasticity axes is: a = 6; b=a; c = c. The 

 plane of the optic axes is the macropinacoid and the acute bisectrix Bx a = c. The optical 

 character is hence positive. 



Comparing the two crystals, a-oxyhemoglobin and /?-oxyhemoglobin, it is inter- 

 esting to note that the true prism angle is nearly the same in each, 78 30' for the 

 /?-oxy hemoglobin against 79 20' in the a-oxyhemoglobin; it is quite possible that the 

 orthorhombic form is some sort of a mimetic twin of the monoclinic form. The skeleton 

 character of the crystal is an indication pointing in the same direction. 



