SINCE PREYER'S INVESTIGATIONS. 115 



states, that there are 2 atoms of sulphur to 1 atom of iron. The mean of 

 his elementary analyses is 



C5i.i5H 6 . 76 



and the molecular formula 



C7i2 



Comparing Zinoffsky's percentages with those of other analysts (see 

 page 71), it seems as though there must be errors in his carbon and hydro- 

 gen estimations. Moreover, his iron and sulphur determinations differ 

 materially from those of others, yet his analyses were conducted in such a 

 way as to warrant confidence in these figures. The low C content is cer- 

 tainly suggestive of imperfect combustion, or, according to Hiifner, of 

 contamination with stromata. Zinoffsky's work has been reviewed and 

 supplemented by Hufner (see later). 



The optical properties of oxyhemoglobin, reduced hemoglobin, met- 

 hemoglobin, hemin, and CO-hemoglobin were studied by Ewald (Zeit. f. 

 Biologie, 1886, xxn, 459). He laked the blood by repeated freezing and 

 thawing, and then spread layers of varying thickness upon microscopic 

 slides. The margins of the preparations soon dry, and then a cover-glass 

 is placed directly on the blood or supported by a wedge of glass. If the 

 preparations are examined immediately, only oxyhemoglobin crystals will 

 be found; but after several days violet-purple spots appear which consist 

 of reduced hemoglobin, but which soon pass into solution. He also obtained 

 crystals of reduced hemoglobin by letting the blood stand in tubes for 

 several days; in the deeper layers the oxygen disappears and crystals of 

 reduced hemoglobin form. He found the crystals of oxyhemoglobin and 

 reduced hemoglobin to be doubly refracting and pleochroic, and that the 

 pleochroism is much more marked in reduced hemoglobin. 



In a research to determine whether or not the 6-sided crystals of 

 certain rodents really belong to the hexagonal system, and to find an 

 explanation of the difference in crystalline form that hemoglobin presents 

 in different animals, Halliburton (Jour, of Physiology, 1886, vn, Proc. 

 Physiol. Soc. No. 1 ; Jour. Microscop. Science, 1887-88, xxvni, 181) carried 

 out a series of observations chiefly with the bloods of the rat, guinea-pig, 

 and squirrel. The rat was taken as a type of animals whose crystals are 

 rhombic; the guinea-pig, of those whose crystals are tetragonal; and the 

 squirrel, of those whose crystals are hexagonal. Halliburton notes that 

 Lehmann states, without giving any reason, that although the crystals of 

 the squirrel are hexagonal in form they do not belong to the hexagonal 

 system, and that von Lang, Kunde, and Preyer state that they do. In 

 examinations of squirrel's crystals by polarized light he found evidence, as 

 he believes, of their being true hexagons instead of their being, according 

 to Lehmann, rhombic plates with an "hexagonal habit." It had already 

 been found by von Lang that the tetrahedra of the guinea-pig belong to 

 the rhombic system. 



In experiments instituted to show whether differences in crystalline 

 form are due to some agency extrinsic to the hemoglobin or to some property 



