CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 227 



It would appear very probable that the hexagonal crystals of o-oxyhemoglobin 

 were simply mimetic twins of this 7-oxyhemoglobin ; the twins consisting of a number 

 of individuals twinned on the different prism-base edges, and producing a uniaxial effect 

 as in the artificial twin of mica. Both the monoclinic and the hexagonal plates are nega- 

 tive; the monoclinic have their axis of greatest elasticity within 10 (about) of the normal 

 to the plate, which becomes exactly normal, by averaging, in the multiple twins; while, 

 in the hexagonal, the axis of greatest elasticity is normal to the plate also. The double 

 refraction is not so strong in the hexagonal form as in the monoclinic; and this would 

 have to be the case in such mimetic twins, as the elasticity of a is diminished by its being 

 inclined to the plate at an angle of some 80, which would allow the influence of b and c 

 to be shown in the direction normal to the plate; and, of course, these latter axes would 

 neutralize each other to produce the apparently uniaxial character. If the ^-crystals 

 were orthorhombic this lessening of the strength of the double refraction would not 

 be so noticeable. 



Reduced Hemoglobin and Metoxyhemoglobin of Marmota monax. 



As noted above, the hexagonal plates passed by paramorphous change into reduced 

 hemoglobin and metoxyhemoglobin without any apparent change of form or of optical 

 character. This could readily happen in such mimetic twins, even though the angles of 

 the original rhomboidal plates should be slightly different from those of the 7"-oxyhemo- 

 globin; for the composite hexagonal crystal always changes the angles of the rhomboidal 

 plates a few degrees, if necessary, to be exactly 60. The change seemed to be from 

 a-oxyhemoglobin to reduced hemoglobin, and then from reduced hemoglobin to the 

 metoxyhemoglobin. In the reduced hemoglobin the pleochroism on edge is quite strong; 

 e nearly colorless, usually pale lilac; a> deep rose-pink. The elasticity was e > w, and the 

 optical character was negative. The metoxyhemoglobin showed the mixed spectrum 

 of oxyhemoglobin and methemoglobin that is often described as methemoglobin. It 

 seemed to be the final paramorphous change, following the change to reduced hemo- 

 globin. The metoxyhemoglobin is also quite strongly pleochroic; e is colorless or pale 

 yellow, w is deep reddish-brown. The elasticity and optical character are as in the 

 reduced hemoglobin. 



BEAVER, Castor canadensis. Plate 51. 



The specimen was received from the Philadelphia Zoological Gardens 

 in a putrid condition. The usual method of preparation was employed. 

 Crystals formed readily after the slides were covered, and were at first 

 long needle-like rods; but soon they became lath-shaped, and then plate- 

 like crystals began to appear. They were not very stable, many crystals 

 disintegrated and were dissolved within 24 hours after making the prep- 

 aration. The crystals were oxyhemoglobin. 



Oxyhemoglobin of Castor canadensis. 



Monoclinic: Axial ratio a : 6 : t =1.732 : 1 : 6; /?=78 (about). 



Forms observed: Unit prism (110), base (001), orthopinacoid (100). 



Angles: Prism angle 110 A 1TO=60 (or very nearly); orthopinacoid to base 

 010 A 100=78 (about) =/?; prism edge to base, edge 110-TlO A 001=90. 



Habit tabular on the base, the combination being prism and base with a greater 

 or less development of the orthopinacoid, making generally hexagonal plates or truncated 

 lozenge-shaped plates (text figures 197, 198). The first crystals to appear are needles; 

 when these attain dimensions to show planes they are generally seen to be twinned, and 

 are the twin on a twin axis in the base and normal to a prism-base edge, along which 

 the crystal appears to be elongated (text figure 199). In some cases the twin in these 

 prismatic crystals seems to be on a unit pyramid, interpenetrant and forming an oblique 

 cross-shape in the cross-section (text figure 200). The plates appear when these twins 



