268 



CRYSTALLOGRAPHY OP THE HEMOGLOBINS 



twin plane (text figure 297) . In such twins, the extinction angle is, of course, less than 

 that recorded above, about 7 or 8. 



CHOW DOG, Cam's familiaris var. Plate 73 . 



The specimen of blood was received from the Philadelphia Zoological 

 Gardens, and was in a clotted and rather putrid condition. The specimen 

 was ground in sand and etherized and then centrifugalized for several hours; 

 and from the clear solution thus obtained the slide preparations were made 

 as usual. Crystals form rapidly and readily at room temperature, and 

 show no sign of dissolving. Within 3 hours after the slide preparations 

 were made, satisfactory photographs were procured. The crystals were 

 oxyhemoglobin, and resemble those of the common domestic dogs very 

 closely; appearing, however, to differ slightly in angles. 



Oxyhemoglobin of Cam's familiaris var. 



Orthorhombic : Axial ratio a : b : <J =0.6696 : 1 : 0.2878; 

 a : <5 =1 : 0.4348. 



Forms observed : Unit prism (110), macrodome (101), base (001). 

 Angles: Prism angle 110 A 110=67; macrodome angle 101 A 

 T01=47. 



Habit long prismatic on the vertical axis, the crystals consist- 

 ing of the unit prism terminated by the macrodome and sometimes 

 also by the base (text figures 298 and 299). The first crystals to 

 form are long and hair-like or needle-like; but, as they grow, they 

 develop greater thickness; so that the normal and fully developed 

 crystal has a ratio of length to thickness of about 25 : 1 to 15 : 1, 

 and sometimes somewhat less, down to 10 : 1. Doubly terminated 

 crystals of measurable quality are comparatively common and the 

 crystals are well developed and sharp in outline. Cross-sections of 

 the crystals are, however, difficult to find, owing to the great length 

 of the crystals in proportion to their thickness. Parallel growth is 

 normal on the prism faces and on the brachypinacoid, and the crystals flatten in this way 

 in the macropinacoid direction. A very common feature is the development of double 

 crystals in this way, two growing side by side in parallel orientation and united on the 

 brachypinacoid. The hair-like crystals which have a ratio of length to thickness of 

 100 : 1, or even 200 : 1, do not show this tendency to parallel growth until they have 

 considerably increased in thickness; the most perfect crystals are generally found in the 

 ratio of about 20 : 1. The crystals grow singly through the slide, or in irregular groups, 

 and often in radiating clusters; small thin rods, attached in such radiating groups to 

 larger composite crystals, being particularly common. In the protein ring, and along the 

 cover edge, they grow usually more or less normal to the surface from which they spring; 

 but radiating tufts are common here also. Twinning was not definitely observed; but 

 indications of twinning upon the brachydome and upon the pyramid were seen; and 

 twinning on the prism appeared to be present in many of the composite groups. These 

 last could hardly be made out with certainty without observations of cross-sections, and 

 these were impossible to find. 



Pleochroism is marked and is as follows: a yellowish-red, b pale red (medium oxy- 

 hemoglobin red), c deep red. Double refraction is strong, and extinction is parallel to 

 the vertical axis in all side views; on cross-sections extinction is symmetrical, and parallel 

 to the crystal axes. Looking along the brachy-axis in convergent light, the interference 

 figure is seen, with widely separated brushes, the plane of the axes being the brachypina- 

 coid. The orientation of the elasticity axes isa = a; b = 6; c=i. The acute bisectrix 

 of the optic axes is the axis of greatest elasticity, Bx a = a, and the optical character is 

 hence negative. 



299 



FIGS. 298, 299. Oxyhemo- 

 globin of "Chow Dog." 



