276 CRYSTALLOGRAPHY OF THE HEMOGLOBINS 



both were then centrifugalized, and from the clear solution the slides were 

 prepared. The blood crystallized very rapidly in all cases, and the slides 

 soon became filled with crystals. These were seen to vary in habit some- 

 what according to the method of preparation, but not more than the crys- 

 tals varied in the same slide, according as to how long after covering they 

 appeared. In other words, the habit of the crystals was conditioned by the 

 strength of solution, rather than by its composition. The first crystals 

 to form are capillary, as a rule ; later these grow thicker, or stouter crystals 

 appear; but in the first preparation some well-formed tabular crystals 

 finally made their appearance, which at first sight seemed to be different 

 from the prisms. After a study of their angles and optical characters they 

 were finally determined to be identical with the prisms. All of the crystals 

 observed were oxyhernoglobin. 



Oxyhemoglobin of Vulpes fuhus. 



Orthorhombic : Axial ratio a : b : c= 0.6494 : 1 : 0.2824; a : 6 = 1 : 0.4348. 



Forms observed: Unit prism (110), macrodome (101), brachypinacoid (010). 



Angles: Prism angle 110AlTO=66; macrodome 101 A 101=47. 



Habit prismatic, elongated on the vertical axis (text figure 311), and the prism 

 striated in the same direction, due to parallel growth; or tabular on the brachypinacoid, 

 the crystal in the prismatic habit consisting of the unit prism with the macrodome, and, 

 in the tabular habit, the same faces with the brachypinacoid (text figures 312, 313); 

 but in some cases one pair of opposite dome faces much developed while the alternate 

 pair are much reduced in size or even wanting, giving the crystal a monoclinic aspect 

 (text figure 314). 



The first crystals to form are generally capillary; and in some of the preparations, 

 especially in those that were diluted with plasma, nearly all of the crystals retained the 

 relative dimensions of the capillary crystals, until they attained a length of more than 

 3 mm. As the crystals continue to deposit from the solution, stouter crystals appear, 

 and these resemble more closely the usual crystals seen in the blood of the species of this 

 genus. The thin prisms are usually single crystals until they attain large size; they 

 grow in slightly divergent tufts or more rarely form groups radiating in all directions 

 from a center; in very many cases the groups are so slightly divergent that the individual 

 crystals appear parallel, and the group looks like a parallel growth. Single crystals 

 become covered by smaller ones that are actually arranged in parallel growth; but 

 they do not seem to grow together on the brachypinacoid and hence flatten on the macro- 

 pinacoid; in some cases the groups may contain individuals in twin position on the 

 prism. It is this tendency to form composite groups, with the vertical axes parallel, 

 that produces the characteristic striation in this direction. 



Pleochroism is moderately strong when observed along b with fl and c in the field; 

 but when looking along a it is rather weak. The colors are a pale reddish, somewhat 

 yellowish-red; 6 and c nearly equal and deeper red. The crystals are not highly colored, 

 as they are slender. Double refraction is not very strong except when a and c are in the 

 field; the extinction is straight in all aspects. Traces of a biaxial interference figure 

 were observed. The orientation of the elasticity axes is a = a, b = b, c = ; and the axis 

 of greatest elasticity appears to be the acute bisectrix, Bx a = a; the optical character is 

 hence negative. 



BLUE OR ARCTIC Fox, Vulpes lagopus. Plate 78. 



Two specimens of the blood of this species were received from the 

 National Zoological Park at Washington, District of Columbia, one during 

 warm weather and the other during the winter. The former was kept 



