838 PHYSIOLOGY 



20 C. All the various fixing fluids which have been recommended for the 

 display of blood-platelets may owe their virtues, not to the fact that they 

 preserve, but to the fact that they produce platelets. These may therefore 

 be regarded as precipitates produced in the plasma directly it undergoes 

 alterations, their appearance being the first sign of changes in this fluid. 

 They consist of some substance probably belonging to the class of nucleo- 

 proteins, and like these yield a precipitate on gastric digestion, and have 

 a. specific affinity for basic dyes. Even after their first appearance they 

 are unstable, tending to undergo further alteration and to give off sub- 

 stances to the surrounding plasma which play an important part in the 

 formation of fibrin-ferment and in the coagulation of the blood. 



