168 CRYSTALLOGRAPHY OF THE HEMOGLOBINS OF AVES. 



(a) a-Oxyhemoglobin of Columba livia var. 



Orthorhombic: Axial ratio a : b : t= 0.9856 : I : t; and by twinning this becomes 

 pseudo-tetragonal. 



Forms observed: Prism (110) and base (001). 



Angles: 110 A 110 = 90 50'; 110 A 001=90. The angle of the prism of 90 50' 

 (89 10' normals) becomes by twinning exactly 90. 



Ib 



FIGS. 47, 48, 49, 50. Columba livia o-Oxyhemoglobin. 



Habit tabular, in square plates (text figures 47 and 48) , which pile on one another 

 by twinning; also growing into somewhat arborescent groups by parallel growth in the 

 direction of a crystal axis. Twins on an axis normal to the prism-base edge, with the 

 base as the composition face (text figure 49) ; this being repeated produces, by mimetic 

 twinning, a composite crystal that is practically tetragonal, being isotropic on the flat 

 and nearly so on the edge view (text figure 50). 



Pleochroism is rather marked; a pale yellowish-red, b deeper yellowish-red, c deep 

 red. In the twinned crystals, that show little double refraction on the edge view, the 

 absorption c > b or a is still noticeable. Extinction is straight on all edge views and 

 symmetrical on the base. The orientation of the elasticity axes is a =b, b=a, (=6. The 

 axis of least elasticity c appears to be the acute bisectrix; Bx a =t, hence the optical 

 character is positive. 



These crystals were gradually converted by paramorphous change into pure methe- 

 moglobin, giving the absorption band 630 pp to 605 pp and extending to 680 pp in the 

 red; this change to pure methemoglobin appeared first in these crystals, although pure 

 methemoglobin was later seen in the form of 6-crystals also. 



(b) Metoxy hemoglobin of Columba livia. 



Orthorhombic: Axial ratio a : 6 : 6 =0.4615 : I : 6. 



Forms observed: Prism (110), base (001). 



Angles: 110 A 1TO=49 33'; 110 A 001=90. 



Habit tabular, in rather acute rhomboidal plates (text figures 51 and 52), usually 

 occurring singly, elongating on the macrodiagonal by parallel growth or sometimes on the 

 brachydiagonal; but not twinning in the way commonly seen in these tabular crystals, on 

 an axis normal to the prism-base edge. After the crystals of this metoxyhemoglobin 6-type 

 had passed into the pure methemoglobin, they formed a sort of regular growth with the 

 tufts of needles of the reduced hemoglobin, the needles being arranged in tufts growing 

 nearly normal to the prism-base edge of the crystals (see plate 13, fig. 77). These crystals 

 showed a laminated structure parallel to the plane of symmetry, perhaps indicating a 

 cleavage in that direction (see plate 13, fig. 76). 



The color of these crystals is reddish-brown, rather dark, and the spectrum showed 

 absorption bands at 640 pp to 615 pp, rather faint (the methemoglobin red band); and 

 stronger bands at 580 pp to 565 pp and 550 pp to 530 pp, the oxyhemoglobin bands. 

 When they finally became converted to methemoglobin, the oxyhemoglobin absorption 

 bands disappeared entirely. 



