234 CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 



The passage of the orthorhombic crystal of a-oxyhemoglobin into the isometric 

 or pseudo-isometric crystal of /3-oxyhemoglobin, that was described above, depends 

 upon the pseudo-isometric character of the a-oxyhemoglobin (its angles being near the 

 angle of the octahedron), if no change in substance occurs in the change from the dis- 

 tinctly orthorhombic crystal to the pseudo-isometric crystal of the hexagonal or equi- 

 dimensional type. More probably there is a change of substance and an isomer or polymer 

 is formed (or may already exist in the solution) and then the hexagonal or the equidimen- 

 sional form is a mixed crystal containing both a-oxyhemoglobin and /3-oxyhemoglobin. 

 The influence of the /3-oxyhemoglobin on the a-oxyhemoglobin, or the concentration of 

 the solution, determines the conversion of the a-oxyhemoglobin into the other isomer 

 (or polymer) /3-oxyhemoglobin. 



BLACK RAT, M us rattus. Plates 54 and 55. 



Specimens of the blood of the black rat were obtained from the Wistar 

 Institute of Anatomy, of Philadelphia. The animal was bled into oxalate 

 and the blood used immediately. The corpuscles, separated by centrif- 

 ugalizing, were laked with ether, oxalated, and the solution again centrif- 

 ugalized. From the clear solution thus obtained the slides were prepared. 

 The blood crystallized very readily; in fact, it is probable that better prep- 

 arations would have been obtained if the whole blood had been used. The 

 crystals do not form so readily as those of the white rat or the Norway rat, 

 but they are quite permanent, show no signs of dissolving on slight increase 

 of temperature, and they keep for weeks in the slides. They are not nearly 

 so insoluble as the crystals of the white or Norway rats, however, and 

 upon an increase of temperature, up to a temperature of 25 C., they begin 

 to dissolve, so that they can not be satisfactorily studied in warm weather. 

 This character is in sharp distinction from the insolubility of the oxyhem- 

 oglobin crystals of the white and Norway rats, which are permanent at 

 temperatures up to 35 C. The crystallization is not so complete as in the 

 case of the other rats mentioned, so that the fluid remains of a strong red 

 color, showing much oxyhemoglobin still in solution. 



Oxyhemoglobin of Mus rattus. 



Orthorhombic: Axial ratio 0:6: 6=0.7829 : 1 : 0.5864. 



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



Angles: No cross-sections of the prism could be observed. The only angle that 

 can be determined is the plane angle of the brachydome on the prism face, edges 110- 

 011 A 1 10-01 1 =130 26', average of nine measurements. Assuming the same prism 

 for this rat that was determined for the Norway rat from the true dome angle and the 

 plane angle of the dome on the prism, the axial ratio was calculated. This makes the 

 macrodome of the black rat (101), the macrodome (405) on the axial ratio of the 

 Norway rat, the average measured angle for the edges, 130 26', agreeing exactly with 

 the calculated value. 



Habit tabular on two faces of the prism, the crystal consisting of the prism (110) 

 and the brachydome (Oil). The prism is flattened on two opposite faces, as is common 

 in the rats (text figure 221), and the dome termination may be of four equally developed 

 dome faces, or two large and two small dome faces, or even of two equally developed 

 faces on one end and one large and one small face on the other end. In some crystals 

 two dome faces appear at one end of the prism and only one at the other end, making 

 a five-sided plate (text figure 222). When two dome faces on the same side of the crystal 

 are developed (one at each end), the plate becomes unsymmetrically four-sided (text 



