94 INVESTIGATIONS OF PREYER 



hemoglobins crystallize in the monoclinic system has long been refuted. 

 Accordingly, as Preyer writes, all the hemoglobins accurately investigated 

 crystallographically up to the present time are rhombic, with the single 

 exception of that of the squirrel. 



The remaining portion of Preyer's article, which is very largely a record 

 of his own researches on the physical, chemical, and optical properties of 

 hemoglobin and methemoglobin, is included practically in full in his mono- 

 graph, which was published three years later. Owing to the authoritative 

 character of this publication, its indispensable value to the physiological 

 chemist, the practical impossibility of obtaining copies, and the rareness 

 of the work in the libraries of this country, we have deemed it advisable 

 to embody in this memoir a rather full and free translation of his chapters 

 on the methods of preparation and on the descriptions of the crystals. 

 This extract constitutes the remainder of this chapter. 



PROCESSES USED BY PREYER FOR OBTAINING CRYSTALS IN 

 LARGE QUANTITIES. 



(I) Lehmann's process has the advantage over the others which fol- 

 low in that a very low temperature is not necessary. The solvent of the 

 coloring matter of the corpuscles is water. The fresh blood is allowed to 

 coagulate and the coagulum to shrink, the serum is drawn off, and the 

 coagulum is ground up. The fluid is separated from the clot by straining 

 through linen, and to this fluid are added from 1 to 1.5 volumes of water. 

 O is then passed through this diluted extract of the clot for about half an 

 hour, and then CO 2 for 10 or 15 minutes. The formation of crystals begins 

 within a few minutes and a rich mass of crystals has separated after 2 hours. 

 By this method crystals were obtained only from the blood of the guinea- 

 pig, rat, and mouse. In order to prepare crystals from dog's blood, and 

 from other blood that is not readily crystallizable, small quantities of 

 alcohol are added to the blood before and during the passage of the gases. 

 The solution very quickly becomes cloudy with crystals and congeals to a 

 crystal pulp. Instead of alcohol, ether can be used in part, but it does not 

 suffice alone. The crystals obtained in this way are, however, not pure. 

 Since recrystallization is necessary in order to obtain pure crystals, and 

 as this can not be done except at low temperatures, there is no advantage 

 in this method if it is necessary to secure a pure product. Preyer found, 

 moreover, that it is only necessary to pass for many hours diy or moist 

 atmospheric air free from carbonic acid through the defibrinated blood of 

 the dog in order to cause crystallization, which occurred abundantly at 

 room temperature, or at about 35 to 38 ('. 



(II) As a solvent for the coloring matter of the corpuscles Rollett 

 made use of freezing. He placed a platinum vessel containing defibrinated 

 blood in a freezing mixture, and after about half an hour the blood was 

 allowed to thaw slowly. It was then poured into shallow vessels to a depth 

 of about 15 mm. These vessels were placed in the cold at even temperature 

 to crystallize. Within an hour or so a deposit of crystals had formed. 

 In this way guinea-pig and squirrel blood quickly yielded well-formed 



