CHAPTER XIII. 



CRYSTALLOGRAPHY OF THE HEMOGLOBINS OF 

 THE RODENTIA. 



The blood of 18 species of the rodents was examined, representing 6 

 of the 18 families into which the order is usually divided. Of the Sciuridce 

 3 species of Sciurus, the European red squirrel, the fox-squirrel, and the 

 gray squirrel were examined; also the flying-squirrel, Sciuropterus, and the 

 ground-squirrel, Tamias; as well as the prairie-dog, Cynomys, and the 

 ground-hog, Marmota. Of the Castoridce, the only species examined was 

 the beaver, Castor canadensis. Five members of the Muridce were exam- 

 ined, representing the genera Mus and Fiber; the rats (genus Mus) were the 

 Norway rat, the albino of the same species, the black rat, and the Alexandrine 

 rat; while the muskrat represented the genus Fiber. The Erethizontidce 

 were represented by the porcupine, Erethizon dorsatus; the Caviidce by the 

 guinea-pig, Cavia, and the capybara, Hydrochoerus. All of the above species 

 are members of the group Simplicidentata, while the Duplicidentata were 

 represented by 2 species of the Leporidce, the common domestic rabbit, 

 Lepus cuniculus, and the Belgian hare, Lepus europceus. 



The crystals from the squirrels of the genera Sciurus and Sciuropterus 

 form hexagonal plates, which, in probably all cases, are pseudohexagonal 

 only, and mimetic twins of the /3-oxyhemoglobin, which crystallizes in the 

 orthorhombic system. In these hexagonal crystals no axial ratio was 

 determinable, as the pyramidal planes were never developed. The prism 

 angle of the hexagonal and of the orthorhombic crystals was the same, 

 60, which explains the possibility of the mimetic twinning that appears 

 to be the cause of the more symmetrical development. Similar hexagonal 

 crystals, probably mimetic twins of the y-oxyhemoglobin, which crystallizes 

 in the monoclinic system, with a prism angle of 58, were seen in the case 

 of the ground-hog, Marmota monax. 



The hemoglobins of all species of the Sciuridce were rather insoluble, 

 and crystallized very readily; so that usually crystallization had to be 

 somewhat restrained to produce satisfactory crystals. In some cases, as, 

 for instance, the prairie-dog, Cynomys ludovicianus, the crystals formed so 

 rapidly that it was not possible to determine the crystallographic constants, 

 on account of the hair-like character of the crystals. This blood was exam- 

 ined before we had perfected our methods for restraining the rapid forma- 

 tion of crystals, and no doubt we could now crystallize it satisfactorily. In 

 the ground-hog three kinds of oxyhemoglobin crystals were observed, crys- 

 tallizing in the hexagonal, orthorhombic, and monoclinic systems, and in 

 several other cases two forms of oxyhemoglobin were noted. 



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