100 INVESTIGATIONS OF PREYER 



The crystals thus obtained can be recrystallized 5 or 6 times, or as long 

 as the hemoglobin remains undecomposed. This plan, nevertheless, has 

 reference only to the kinds of blood which crystallize easily. These crystals, 

 even after several recrystallizations, show the bright-red color of arterial 

 blood. 



Another means by which the blood can be crystallized is by extracting 

 the gases. In dog's blood from which the gases had been extracted, Rollett 

 found that the blood was lake-colored, very dark, and that it produced 

 hemoglobin crystals immediately. Preyer states that he found that dog's 

 blood and sheep's blood freed from gases crystallize by evaporating a drop 

 on an object-glass, the colorless stromata of the corpuscles still being 

 visible. The addition of a little dilute solution of oxalic acid aided crys- 

 tallization. 



Preyer then tried to decide experimentally if all of the three blood- 

 gases (carbonic acid, oxygen, and nitrogen) were necessary for the preser- 

 vation of the normal condition of the blood corpuscles in the circulating 

 blood. He investigated the blood of asphyxiated animals and found micro- 

 scopically that there was some disintegration of the corpuscles. Previous 

 to this experiment he had found that blood made rich in carbonic acid and 

 freed of oxygen by a continuous stream of carbonic acid crystallized very 

 slightly, and that therefore the absence of oxygen alone (without taking 

 into account the nitrogen) is sufficient to cause a partial decomposition of 

 the blood corpuscles into colorless stromata and hemoglobin. He then 

 made the following experiment: The A. carotis dextra, the V. jugularis 

 externa sinistra, and the trachea of a little dog were laid bare, and into the 

 vessels glass cannulse were tied. The trachea was then clamped so as to 

 prevent the entrance of air to the lungs. The moment the conjunctiva 

 became insensible to the touch the ligatures on the vessels were loosened 

 and the blood drawn into separate receptacles. The blood was dark red, 

 and that of the artery could not be distinguished from that of the vein. 

 A drop of each kind of blood showed under the microscope a rich crystal 

 formation within the first minute after it was caught. Under the eye of 

 the observer the crystals increased in thickness, length, and number as long 

 as the evaporation of the drop on the object-glass lasted, but more slowly 

 if the drop had been covered with a cover-glass. By gently shaking in the 

 air the blood became bright red again. All the manipulations mentioned 

 here by which crystals can be obtained are somewhat troublesome, and are 

 not used for purposes of microscopic preparations. 



C. Bojanowski placed a drop of blood on an object-glass, exposed it to 

 the air several minutes, breathed upon the preparation several times, then 

 covered it with a cover-glass, and allowed it to evaporate slowly. He 

 found that a small addition of alcohol or ether is occasionally necessary. 

 Bojanowski obtained microscopic crystals without adding anything to the 

 blood by merely allowing it (as it comes from the veins, or, better yet, as 

 it is found in them after death) to stand in a vessel 2 to 4 days in a cool 

 place. The blood coagulum partly dissolves and the blood becomes thick 

 and dark red. A drop of the same is allowed to stand several hours between 



