242 CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



of the elasticity axes appears to be a=c, b=6, c=a; and the plane of the optic axes is 

 therefore the brachypinacoid. As the sphenoids lie on their faces, a single brush of a 

 biaxial figure is frequently seen; and, when looking along the elasticity axis c, the sym- 

 metrical figure can be made out, with the axes moderately separated, the angle 2Z?=35 

 to 40. The acute bisectrix is c, which can be determined upon the interference figure by 

 means of the quartz wedge, etc. As the acute bisectrix Bx a =c, the optical character 

 is positive. 



CAPYBARA, Hydrochoerus capyvara. Plates 58 and 59. 



The specimen of blood was obtained from the National Zoological 

 Park at Washington, District of Columbia, and was very thick, containing 

 soft clots. The oxalated blood was diluted with an equal volume of water 

 and laked with ether, and then centrifugalized for 3 hours. The slide 

 preparations were made in the usual manner. Crystals formed readily at 

 room temperature, but less readily than with normal blood of the guinea- 

 pig. The first crystals to form were prisms; later pyramidal crystals ap- 

 peared. Crystallization proceeded readily at room temperature, and the 

 crystals showed no tendency to dissolve on slight increase of temperature. 

 Inside of 3 hours after the slides were prepared, the crystals were large 

 enough to give good photomicrographs. After a day, most of the prismatic 

 crystals had lost their terminal planes through solution. The P5 r ramidal 

 crystals kept very well, and increased in size to many times the dimensions 

 of the original first crystals; they were sharp and perfect after several days. 

 All of the crystals examined were oxyhemoglobin. The normal and per- 

 manent crystal is evidently the pyramidal type; the prismatic crystal is 

 not so insoluble and more unstable. The pyramidal crystal is distinguished 

 as a-oxyhemoglobin ; the prismatic crystal is called /3-oxyhemoglobin. 

 They evidently crystallize in different systems. 



a-Oxyhemoglobin of Hydrochoerus capyvara. 



Tetragonal: Axial ratio a : 6 = 1 : 1.8184. 



Forms observed: Unit pyramid (111), second- 

 order pyramid (201). 



Angles : On the unit pyramid over the pole, 1 1 1 A 

 TTl =42 30' ; angles of the pole edges of the unit pyra- 

 mid, over the pole, edges 111-lTl A Tll-TTl =57 30' 

 (calculated 57 36'). The pyramid edges in the hori- 

 zontal plane make an angle of 90 with each other. 



245 \y Habit pyramidal; consisting of the unit pyramid 



alone in very symmetrical development (text figure 245), 



Floe. 245, 246. Hydroehoems capyvara , i i ii_ 



o-oxyhemogiobin. except when the crystals become large, when the cover 



and slide distort them. Crystals generally occur singly or 



more rarely in groups, interpenetrating each other, but not twinned apparently. Very rarely 

 on some of the larger crystals the second-order pyramid was observed (text figure 246). 

 The crystals generally lie on one pyramid face and present a lozenge-shaped profile; more 

 rarely they are found in such a position that the angle of the pole edges can be measured. 

 The color is a bright oxyhemoglobin red, and pleochroism is readily observed, as 

 the vertical axis is nearly normal to the line of sight in the usual aspect. The pleochroism 

 is s colorless, a> deep red. The vertical axis (=) is the direction of greatest elasticity; 

 all directions normal to this (o) are of equal and less elasticity. Double refraction is 

 strong; extinction is parallel to the vertical axis, or symmetrical in all of the usual 

 aspects. Looking along the vertical axis, in convergent polarized light, the uniaxial 

 cross is seen. The refractive indices are w > E and hence the optical character is negative. 



