ON THE CRYSTALLOGRAPHY OF HEMOGLOBIN. 101 



the cover-glass and the object-glass without being heated. If the blood is 

 too thick some distilled water is added to it. 



In order to produce hemoglobin crystals in a short time from fresh 

 blood chosen for microscopic purposes, the following method is best : Several 

 cubic centimeters of defibrinated blood are mixed with just enough water 

 to yield a clear solution. A drop of the mixture covered with a cover-glass 

 crystallizes on being subjected to cold. If this is not the case, about one- 

 fourth the volume of alcohol is added to the solution and the mixture is 

 placed in a platinum or silver vessel in a cooling mixture. Crystals are 

 always obtained. Almost all kinds of blood yield crystals by merely allow- 

 ing the blood to freeze, even ox blood. 



THE FORMS AND SYSTEMS OF CRYSTALLIZATION OF HEMOGLOBINS. 



Upon this subject Preyer writes: Of the six crystal systems only five 

 are to be taken into consideration in the classification of crystals of hemo- 

 globins, namely, the regular (tesseral), the tetragonal, the rhombic, the 

 monoclinic (clinorhombic, monoclinohedric), and the hexagonal. Crystals 

 belonging to the triclinic system have not been claimed to have been found 

 by anyone. Of the remaining five systems the regular and the tetragonal 

 are to be eliminated the regular because all hemoglobin crystals are doubly 

 refractive, and the tetragonal because the only crystals assigned to this 

 system were those of the guinea-pig by Hoppe-Seyler. Hoppe-Seyler's 

 statement is without facts to justify it, and it has been disproved by the 

 accurate investigations of guinea-pig crystals by Victor von Lang and 

 others. There remain then three systems rhombic, hexagonal, and mono- 

 clinic. The last named is also to be eliminated because Funke is the only 

 scientist who asserts that hemoglobin crystallizes in this system, and he 

 does not support his statement. He only asserts that human and cat hemo- 

 globins crystallize in the monoclinic system, yet in another place he him- 

 self calls human blood crystals rhombic, and as a matter of fact so are 

 those of the cat. Monoclinic crystals have not, then, up to this time been 

 shown to exist. On the other hand, crystals belonging to the rhombic and 

 hexagonal systems have been shown to exist beyond any question. The 

 fact that crystals of different species are assigned to two systems is a matter 

 that is not to be ignored. It is firmly settled that squirrel's blood yields 

 crystals that belong to the hexagonal system, while dog's blood yields 

 crystals that with as little doubt belong to the rhombic system. 



The observations of V. von Lang are: 



Squirrel's, 6-sided plates formed from a 6-sided "prism, showing the basal surface. 

 These crystals belong undoubtedly to the hexagonal system, because when observed 

 through the basal surface between crossed nicols they remained dark in all azimuths. In 

 agreement with this, the crystals when observed through the prism surface showed double 

 refraction. All the rays, then, are not of like intensity. The vibrations parallel to the 

 optical and crystallographic axes are less absorbed than those which are perpendicular. 



Preyer states that he confirms von Lang's observations: Between 

 nicol prisms squirrel's blood crystals only show color when their optic 



