CIRCUMSTANCES WHICH MODIFY COAGULATION. 149 



which are near the surface from escaping from the clot during 

 its contraction. 



Circumstances which modify Coagulation -out of the Body. 



The conditions which modify coagulation of the blood 

 have been closely studied by Ilewson, Davy, Thackrah, Robin 

 and Yerdeil, and others. They are, in brief, the following : 



Blood flowing slowly from a small orifice is more rapidly 

 coagulated than when it flows in a full stream from a large 

 orifice. If it be received into a shallow vessel, it coagulates 

 much more rapidly than when received into a deep vessel. 

 If the vessel be rough, coagulation is more rapid than if it 

 be smooth and polished. If the blood, as it flows, be received 

 on a cloth or a bundle of twigs, it coagulates almost instan- 

 taneously. In short, it appears that all circumstances which 

 favor exposure of the blood to the air, hasten its coagulation. 

 The blood will coagulate more rapidly in a vacuum than in 

 the air. 



Coagulation of the blood is prevented by rapid freezing, 

 but afterwards takes place when the fluid is carefully thaw- 

 ed. Between 32 and 140 Fahr., elevation of temperature 

 increases the rapidity of coagulation. 1 Experiments are 

 impracticable above 140, as we , are then likely to have 

 coagulation of the albumen. According to Richardson, agi- 

 tation of the blood in closed vessels retards, and in open 

 vessels hastens coagulation. 2 



Various chemical substances retard or prevent coagula- 

 tion. Among them we may mention : solutions of potash 

 and of soda; carbonate of soda; carbonate of ammonia; 

 carbonate of potash; ammonia; sulphate of soda. In the 

 menstrual flow the blood is kept fluid by mixture with the 

 abundant secretions of the vaginal mucous membrane. 



1 RICHARDSON, The Cause of the Coagulation of the Blood. Astley Cooper 

 Prize Essay for 1856, p. 140 et seq. 



2 Ibid., p. 228. 



