350 THE BLOOD. 



observers. Nencki has shown that this is owing to the fact that 

 hsemin contains two hydroxyl groups, and that the substance not 

 only forms ethers with acid and alkyl radicles with great readiness, 

 but also addition-products with indifferent compounds. Its prep- 

 aration lias been described above. 



Isolation of Oxyhaemoglobin. Oxyhsemoglobin in crystalline form 

 is best obtained from the red corpuscles of the horse or dog, 

 according to the following method : the blood is first rendered 

 uncoagulable by treating with ammonium oxalate (0.06-0.1 per 

 cent.), and is then centrifugalized to effect the separation of the cor- 

 puscles. This mass, when freed from plasma by siphonage, is treated 

 with twice its volume of water and placed on ice. The resulting 

 fluid is now mixed with an equal volume of a saturated solution of 

 ammonium sulphate that has likewise been cooled to a low tempera- 

 ture. This mixture is also placed on ice until the precipitate of 

 globulins, which is referable to remaining plasma, has settled. On 

 filtering in the refrigerator a perfectly clear dark-red filtrate is 

 obtained, which contains the greater portion of the coloring-matter. 

 If now the solution is brought to the temperature of the room, 

 the separation of crystalline oxy hemoglobin begins, and may be 

 hastened, if necessary, by the further addition of a small amount 

 of the ammonium sulphate solution. After a few days the process 

 is completed, when the crystals are filtered off through a Buchner 

 filter by the aid of a suction pump, and are partially freed from the 

 mother-liquor by pressing between filter-paper. The substance is 

 then purified by recrystallization. To this end, the crystalline 

 mass is dissolved in water, reprecipitated by the addition of an equal 

 volume of the ammonium sulphate solution, and so on, until the 

 required degree of purity has been attained. Adhering ammonium 

 sulphate is finally removed mechanically. To preserve the sub- 

 stance, it is dried in a vacuum or at a low temperature over sulphuric 

 acid, and is then quite stable. 



The ease with which oxyhsemoglobin can be brought to crystal- 

 lization differs with different animals. In guinea-pigs, squirrels, and 

 rats it is most pronounced ; and it is here only necessary to mix a 

 few drops of the blood with an equal amount of water, when the 

 process may be directly observed with the microscope. Human 

 blood, as also that of the pig and the ox, is much more refractory, 

 and is not well adapted for the preparation of the pigment in its 

 crystalline state. 



The form of the crystals varies in different animals. We thus 

 find hexagonal platelets in the squirrel, rhombic tetrahedra in 

 the guinea-pig and various birds, rhombic needles in man, etc. 



In its chemical behavior oxyhsemoglobin manifests its albuminous 

 nature. It is thus coagulated on boiling, and on treating with 

 absolute alcohol and most of the salts of the heavy metals. It is to 

 be noted, however, that the process of coagulation is associated with 

 the decomposition of the compound into hsematin and globin, which 



