238 



CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



amount of oxalate had been added. This blood was highly charged with 

 ether (from the method of preparation) and this prevented the develop- 

 ment of bacteria, so that the blood kept well. In this series, the first crys- 

 tals to appear were the a-oxyhemoglobin crystals, as before, but of a differ- 

 ent type; and soon after they appeared the /^-crystals began to form, of 

 the same habit as in the first experiment. All the crystals examined were 

 determined to be oxyhemoglobin by the microspectroscope. 



a-Oxyhemoglobin of Erethizon dorsatus. 



Monoclinic: Axial ratio a : b : <!=0.5543 : 1 : 6; /3=56. 



Forms observed: Unit prism (110), orthopinacoid (100), clinopinacoid (010), 

 basal pinacoid (001). 



Angles: Prism angle, traces of the prism on the base, edges 110-001 A lTO-001 = 

 58 (normals); orthopinacoid to base 100 A 001=56=/?. 



232 



\ 



234 



235 



Fios. 232, 233, 234, 235. Erethiton dorsalut a-Oxyhemoglobin. 



Habit tabular on the base; in the untwinned crystals of the first preparation, type 

 (a), the combination was the base cut by one-half of the prism and one face of the ortho- 

 pinacoid, with the two faces of the clinopinacoid (text figures 232, 233), much in the 

 habit of the clinohedrite type of the monoclinic system (domatic class). In the twinned 

 crystals of the second preparation, from blood containing more oxalate, type (b), while 

 the corresponding angles are the same, the crystal is a twin on a normal to the prism-base 

 edge, but so developed that it looks as though the composition plane was the normal 

 to the base that included this common prism-base edge (text figure 234). The obtuse 

 prism angle of 122 (or 58 normals) appears symmetrically four times on these twins, 

 while the double of the acute angle 116 (or 5SX2=64 normals) appears twice in sym- 

 metrical position. In some crystals the development is as usual in this horse-type of 

 twin; the two parts united on the base, elongated on the common prism-base edge, 

 and with the ends overlapping (text figure 235). These twins are evidently repeated 

 in polysynthetic order, and the optical characters for the twin are abnormal, being the 

 summation of the optical characters of its members, which vary in their orientation. 

 Hence the twin has a plane of symmetry for its optical characters as seen on the flat, 

 which is normal to the base, and includes the prism-base edge, the twin plane in short. 



The crystals are rather strong oxyhemoglobin red; the simple crystals, being thin, 

 are paler than the twins. On the base, the simple crystals of type (a) are distinctly 

 pleochroic, but not strongly so; on edge, the pleochroism is quite strong. The pleochroic 

 colors in these thin crystals of type (a) are a pale yellowish-red, b rather pale scarlet, 

 c (on edge) deep red. In the second type of crystals, the pleochroism on the base is very 

 slight, owing to the averaging of the elasticities in the composite crystal; and the apparent 

 a comes much nearer to the apparent b. On edge, these still show considerable pleochro- 

 ism; but the contrast is not so strong as in the untwinned crystals. Extinction in type 



