CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE UNGULATES. 197 



described is the one that is present. Twinning on a pyramid, making an interpenetrant 

 twin with an X-shaped cross-section, is also seen in some cases (text figure 132). 



Etching figures were observed on the base in many cases when the crystals had 

 begun to dissolve; they consisted of shallow lozenge-shaped pits, with sides parallel to 

 the prism-edge boundaries of the plate; and, even, evidently negative pyramids (see 

 text figure 133). On the clinopinacoid, which was developed as a plane of contact with 

 the cover or slide, etching figures were also observed; triangular, with one side (the 

 short side of the triangle) parallel to the clinopinacoid-base edge. They have a rather 

 hemimorphic aspect (see text figure 133). One side of this triangle, as stated, is parallel 

 to the a-axis; of the others, one is parallel to the 6 axis, but the third is inclined. Hence 

 this is a negative positive hemi-pyramid, base, and probably prism, for the three planes 

 of the triangular depression. 



Pleochroism is strong; a pale yellowish-red, b bright cochineal-red, c deep blood- 

 red. Extinction is symmetrical on the base, and straight, looking along a, but oblique 

 looking along b, about 12 or 13, measured from the trace of the base. The orientation 

 of the elasticity axes is a A a = 12 to 13, in the obtuse angle; b =6; c A k =5 to 6, in the 

 obtuse angle. The plane of the optic axes is the plane of symmetry; and, looking along 

 the normal to the base, one excentric brush of the biaxial figure is seen, but the other is 

 out of the field. The angle 2E is hence probably above 85. The acute bisectrix is, 

 however, c, Bx a = c, and the optical character is positive. 



HIPPOPOTAMUS, Hippopotamus amphibius. Plates 30 and 31. 



The specimen of blood was received from the National Zoological 

 Park at Washington, and was in good condition. The oxalated blood 

 was laked with ether and centrifugalized and the preparations made in the 

 usual manner. Crystals formed readily, soon after covering the slides; 

 at first rather short prisms, later plates or tabular crystals, which showed 

 a great tendency to form aggregates and to twin. While the crystals formed 

 readily, they were rather soluble, and soon began to show signs of corrosion 

 when brought into the room (20 C) . The twinned crystals especially grew 

 to large size, so that over night some of these composite crystals had in- 

 creased to a couple of millimeters long. These large crystals, grown in the 

 cold, dissolved readily upon a slight increase of temperature. The composite 

 crystals and parallel growths formed quite complex groups and the crys- 

 tallography was not very easy to make out. Examination with the spec- 

 troscope showed that the crystals were oxyhemoglobin. 



Oxyhemoglobin of Hippopotamus amphibius. 



Monoclinic: Axial ratio a : b : 6 =1.600 : 1 : A; /? = 66 (about). 



Forms observed: Prism (110), base (001), hemiorthodome (101). 



Angles: Angle of prism, traces on the base, edge 110-001 A 110-001=64, edge 

 110-110 A 001 =66=/?. The angle of the orthodome to base was not accurately 

 determined. 



Habit at first rather short prismatic, the prism being two or three times as long as 

 it is thick (text figure 134); also nearly equidimensional, resembling rhombohedrons, 

 and the prism reduced to such an extent that the crystal becomes tabular on the base 

 (text figure 135). Only occasionally did the hemiorthodome appear; it was in the obtuse 

 angle (text figure 134). Twins form in the plates in the usual way (horse-type), the 

 plane of twinning normal to the base, and parallel to a prism-base edge, which is a com- 

 mon direction for the two members of the twin, or the twin axis is normal to the edge 

 110-001 and lies in the plane of the base. In this twin the two halves continue to grow 



