CRYSTALLOGRAPHY OF HEMOGLOBINS OF THE RODENTIA. 235 



figure 223). By shortening of the prism the tabular crystal becomes hexagonal in outline 

 (text figure 224) ; the crystals do not elongate into the long tabular crystals so common 

 in the Norway and albino rats. Twinning on the flat and on edge, as seen in the white 

 rat, was observed, but it did not occur so frequently as in the case of that species. The 

 twinning is upon a pyramid in each case, as is common in the rats. The twins on edge 

 were of two individuals only, as a rule, and did not form the six-pointed star like Norway 

 and white rat twins (text figure 225). On the flat, the twin consists of two individuals 

 also (text figure 226), and does not result in the formation of a hexagonal plate, as in 

 the case of the Norway and white rat crystals. The difference in the twins is no doubt 

 due to the fact that in the twin on the brachypyramid the prism edge of one individual 

 is parallel to the prism-dome trace of the other; but in the corresponding twins of the 

 white rat and the Norway rat crystals the angle of the twin of the prism edges in the 

 three members is 120, while in the black rat (and Alexandrine rat) the angle of the 

 prism edges in the two members of the twin is about 130 25', being for the Alexandrine 

 rat 130 19' and for the black rat 130 26'. Three crystals of the Norway or white rat 

 could twin at the angle of 120 to make a regular hexagonal plate; but three crystals 

 of the black or Alexandrine rat so twinned could not produce a regular hexagonal plate. 



224 



FIGS. 221. 222, 223, 224, 225, 226. M u ratlut Oxyhemoglobin. 



Pleochroism is fairly strong, but from the positions of the crystals presented a and 

 b can not be directly observed. The colors of a and b are evidently close together, rang- 

 ing from pale yellowish-red to deeper red, according to the thickness of the crystal. The 

 color of c is always much deeper; even in the thinner plates it is a deep red. Double 

 refraction is strong, extinction is straight in all aspects presented. The orientation of 

 a and b could not be observed; it is probably the same as in the Norway rat, a =b, b =a; 

 the axis of least elasticity c =<!. From the fact that the elasticities of a and b are nearly 

 the same, it is probable that the axis of least elasticity c is the acute bisectrix, Bx a =c; 

 this makes the optical character positive. No interference figure could be observed. 



ALEXANDRINE RAT, Mus alexandrinus. Plate 55. 



Specimens of the blood of the Alexandrine rat were obtained from the 

 Wistar Institute of Anatomy, of Philadelphia. The blood was collected 

 in oxalate and was used immediately. The corpuscles were separated by 

 centrifugalization, laked with ether, additional oxalate added, and the 

 solution centrifugalized. The slide preparations were made as usual. 

 Crystallization proceeded rapidly before and after covering the slides; 



