98 INVESTIGATIONS OF PREYER 



hours, so that a large amount of nearly pure crystals can be obtained 

 by decantation with a mixture of 4 volumes of water and 1 volume of 

 absolute alcohol. Nevertheless, this method does not always give such 

 favorable results. 



PROCESSES GIVEN BY PREYER FOR OBTAINING CRYSTALS IN 

 SMALL QUANTITIES. 



One of the simplest processes for obtaining crystals from the blood of 

 several animals is by heating. Max Schultze (Archiv f. mikrosk. Anat., 

 1865, 1, 31) found that the corpuscles were dissolved at a temperature of 

 about 60, forming a lake-colored blood solution. Every drop then evapo- 

 rated yields crystals, Preyer observed this also in guinea-pig's blood when 

 he gradually heated a drop on a slide to about 60, and then allowed it to 

 cool and to evaporate slowly ; and also when a large quantity of blood was 

 warmed in a water-bath to at least 60. With squirrel's, calf's, and human 

 blood crystallization did not succeed. On the other hand, Preyer writes, 

 by no other method could there be obtained from horse's blood such well- 

 formed and large crystals. The temperature must be at least 60, but it 

 should not go beyond 64. Preyer proceeded in the following way : Horse's 

 blood was collected in a vessel, defibrinated by agitation, and decanted. 

 The defibrinated blood was separated after several minutes into two por- 

 tions an upper layer of serum and a lower dark-red layer of corpuscles. 

 The serum was pipetted off and the corpuscles heated in a water-bath at 

 60. This produced a lake-colored solution, of which every drop, upon 

 being cooled and evaporated, yielded extraordinarily beautiful crystals. 



This crystallization, which is brought about by warmth causing a 

 separation of the coloring matter from the corpuscles, is not to be con- 

 founded with one earlier reported by Bojanowski (Zeit. f. wissensch. Zool- 

 ogie, 1863, xn, 323), who evaporated the diluted extract of the coagulum 

 of rabbit's blood at 50, and who noticed in so doing that the upper surface 

 of the blood was covered with a delicate crust composed of prismatic crys- 

 tals. In this process the coloring matter had been extracted by water, so 

 that the effect of warmth can only be looked upon as an aid to rapid evapo- 

 ration. The favorable influence of slight warmth as a means of hastening 

 evaporation has been repeatedly misunderstood and denied, and generally 

 it has been regarded as a hindrance to crystallization. 



If an extract of the coagulum of dog's blood prepared with cold dis- 

 tilled water is shaken with sufficient ether so that it smells of it, and then 

 a little alcohol added, and then very gradually heated in a very shallow 

 vessel until the margin of the fluid or the drop on the object-glass begins 

 to dry, evaporation proceeds quickly and regularly, and crystals form as 

 the blood cools. In this way a most beautiful preparation can be obtained 

 in a short time. However, without artificial heating as many hours are 

 necessary to obtain crystals as minutes are required with it. 



Electric shocks have a similar effect in causing a solution of the hemo- 

 globin from the corpuscles, as was found by Rollett. A. Schmidt had 

 already noted that a like effect is caused by the galvanic current. By both 



