154 CRYSTALLOGRAPHY OF THE HEMOGLOBINS 



The axial plane lies in the plane of symmetry, and the orientation of the optic axes 

 is as follows: b=b, a A a = 10 in the obtuse angle, c A 6 = 10 in the obtuse angle; the 

 extinction angle, looking at the crystals in edge view along the ortho-axis b, is 10 from 

 the trace of (001) or from the edge of (110). On the flat view, the basal pinacoid (001), 

 the crystal examined in convergent light shows one brush of the interference figure, 

 with the other appearing on rotation of the crystal, the plane of the optic axes being 

 the plane of symmetry, and their position indicates an angle between the optic axes, 

 2^ = 100 or more. Seen in this aspect, the extinction is, of course, symmetrical with 

 the rhombic section of the crystal. The optical character is positive, Bx a =c. 



When crystals of this material are allowed to dry on the slide, shearing cracks 

 develop that are normal to the plane of symmetry, as was also noted in the case of the 

 reduced hemoglobin crystals. 



The shad from whose blood these crystals were prepared was taken alive from the 

 seine and immediately bled into a tube; the blood was not oxalated, but allowed to clot. 

 It was hence not exposed to the oxidation that occurs in fish that die in the air, 

 when the blood becomes fully oxygenated, as with a fish that was purchased in the 

 market. This freshly drawn, clotted blood was then ground in sand, ether-laked, and 

 centrifugalized; and after it became clear it was oxalated. Slides were prepared in 

 the usual way, and crystals formed very soon after the preparations were covered. 

 The negatives from which the photographic illustrations were taken were made on the 

 following day. 



(3) Reduced Hemoglobin of Alosa sapidissima. 



Monoclinic: Axial ratio, a : b : 6 = 1.786 : 1 : <f; /? = 70 as in metoxyhemoglobin, 

 but the ratio in some crystals becomes a : 6 = 1.732 : 1. 



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



Angles: On the base (001) edges 110 A 110 = 58 30' for the smaller and more per- 

 fect crystals, but in reduced hemoglobin, recrystallized from solution of the metoxy- 

 hemoglobin after reduction of the solution by a reducing agent, the crystals had angles 

 of 60 almost exactly. The angle of 60 was seen in crystals that were evidently twinned, 

 as is the case in the metoxyhemoglobin. In fact, the form is so nearly the same in the 

 two that the hemoglobin might be a paramorph of the metoxyhemoglobin. In some 

 of the preparations, however, the habit in the reduced hemoglobin is quite different 

 from that in the metoxyhemoglobin. The angle [I was 70 or a little over. 



Habit of the crystals usually tabular, flattened on the base (001) (text figures 10 

 and 11), or short prismatic, the prism length usually falling between the longer and 

 shorter diagonals of its section. In crystals of this latter habit (text figure 12), the 

 side view is commonly seen, and in some aspects the crystal looks like a rhombohedron. 

 Twins are very common, the forms being the same as those described under oxyherno- 

 globin, especially the "horse-type" this twin, having the parts grown together on the 

 base and two prism-base edges matched, is the normal form. Three crystals growing 

 together in this way, interpenetrating with the composition face normal to the base, 

 and including the prism-base edge, produce a six-pointed star, which has the orientation 

 of the opposite points the same. Text figure 15 shows an optical section of the homo- 

 geneous regular growth, the first kind, the orientation being such that for two parts 

 of the twin the extinction is straight, looking nearly along a; while for the other parts 

 the extinction is about 14, indicating that the crystal is being examined along 6. The 

 cleavage is perfect, parallel to the prism, and was readily obtained by crushing the 

 crystals. It develops also from the pressure of the cover upon the crystals, due to evapo- 

 ration. On allowing the crystals to dry, they develop cracks normal to the plane of 

 symmetry, as in the case of the metoxyhemoglobin crystals. These cracks are due to 

 tension, and are at 60 to the cleavage. 



Pleochroism strong; a nearly colorless, b rose-pink, c deep red, as is usual in 

 reduced hemoglobin. The spectrum is the normal reduced hemoglobin spectrum, with 

 a strong absorption band between D and E and the blue end absorbed up to near 450 fi/i. 



