BLOOD-CRYSTALS. 



99 



They are very common in the coagula within aneurismal 

 sacs, in apoplectic clots, and in other masses of extrava- 

 sated blood. Such crystals may also often be formed 

 artificially, by ex- 

 posing a drop of re^ 

 cently drawn blood, 

 diluted with water, 

 to the air for a few 

 minutes, and then 

 breathing upon it. 

 The addition of alco- 

 hol, ether, and espe* 

 cially chloroform, is 

 said to facilitate the 

 process. In some 

 cases, however, the 

 blood crystallizes at 

 once,, on simple ex- 

 posure to the air : 

 in others, more com- 

 plex processes have 

 to be resorted to 

 for their production, 

 such as rapid freez- 

 ing and then thaw- 

 ing, electricity, and 

 exhaustion in the air- 

 pump (Eollet). Whe- 

 ther formed natural- 

 ly or artificially, the 

 blood crystals (figs. 



* Figs. 27, 28. and 29, illustrate some of the principal forms of blood- 

 crystals : 



Fig. 27, Prismatic, from human blood. 



f Fig. 28, Tetrahedral, from blood of the guinea-pig. 



