TO SPECIES, ACCORDING TO PREVIOUS INVESTIGATORS. 139 



Kunde and Lehmann observed "tetrahedra" in the "hemoglobin" of the 

 black rat. These were doubtless the ^-oxyhemoglobin crystals, which are iso- 

 metric, and appear as the three-sided plates that develop from the flattening 

 of the octahedron. Such a crystal seen on edge would be described as a prism. 

 When the different habits that the same crystal combination may 

 assume are considered, the difficulty of interpreting the observations 

 increases enormously. Thus, crystallization may begin with the formation 

 of needle-like or capillary crystals, and these may later become short prisms. 

 Friboes describes these two forms of the same crystal as two kinds of crys- 

 tals in the case of cat hemoglobin; and, as has been stated, by looking at 

 the same crystal in two aspects at 45 to each other, he sees two kinds of 

 prisms, thus making three kinds of crystals of the same identical crystal 

 combination. In certain species of the cats the hemoglobin occurs in all 

 of these variations of the prismatic type of crystal and also in the tabular 

 form, yet the crystal forms shown may be the same in prism and plate. 

 Under less pressure the crystals form as prisms; under greater pressure 

 they form as plates. 



Crystals from the blood of the black rat have been described as tetra- 

 hedra, prisms, elongated plates, and hexagonal plates. The tetrahedra have 

 already been referred to, and they are evidently, as stated, /3-oxyhemoglobin. 

 The prisms, elongated plates, and hexagonal plates are all the same combi- 

 nation of crystal forms, the prism and macrodome, and are our a-oxyhemo- 

 globin. When symmetrically developed the crystal is the squarish prism 

 terminated by the dome. Flattening of the crystal on two opposite prism 

 faces produces the "elongated plates" of Hoppe-Seyler, and shortening of 

 this flattened prism produces the apparently hexagonal plate. Careful 

 focusing would show at once that this plate is not bounded by vertical sides 

 and that the angles are not hexagonal angles. All of these forms we have 

 observed in the crystals from the blood of the common rat. 



The crystals are frequently interfered with by the slide and cover pro- 

 ducing false planes, so that a tabular crystal on edge, thus confined, becomes 

 a "prism." Many examples of crystals with such false planes have been 

 figured, even as late as the work of Moser (1901). 



When it comes to the determination of the crystal system, we find that 

 most of the observers make no attempt at it. Preyer states that in his 

 table (page 103) five of the six crystal systems are recorded, the triclinic 

 being the only one not included. The isometric, he writes, may be ruled out 

 because all hemoglobin crystals are doubly refracting and because isometric 

 crystals can not be doubly refracting. Crystallographers now recognize 

 that the tetartohedral class of the isometric system is doubly refracting, 

 and, as will be shown later, we have found singly refracting isometric crys- 

 tals of hemoglobins. The tetragonal system he eliminates because the 

 statements of Hoppe-Seyler in regard to the tetragonal character of the 

 guinea-pig crystals were disproved by von Lang. Similarly he excludes 

 the monoclinic because he states that Funke, who claims to have observed 

 monoclinic crystals in the case of the cat and man, "supports his state- 

 ment by nothing. " This leaves only the orthorhombic and the hexagonal. 



