COAGULATION OF THE BLOOD. 



very solicitous about the structure of his cask, 

 and neglect the consideration of the wine con- 

 tained in it." (Essay on Human Blood.) 



One of the most important facts connected with 

 the vital properties of the blood, is the process of 

 coagulation by which its fibrin becomes solid, 

 when removed from the vessels, and unites the 

 red particles into a mass of greater or less den- 

 sity. But the cause of this change remains an 

 unresolved problem. As it must always have 

 been known that inorganic fluids become solid 

 under the influence of cold, it was maintained by 

 Hippocrates and Aristotle, whose opinion was 

 adopted by Harvey and Sydenham, that the co- 

 agulation of blood is owing to the loss of animal 

 heat. For the first time in the history of science, 

 this error was refuted by Hewson, who found that 

 the process was always retarded by cold, and 

 hastened by increase of temperature. He there- 

 fore concluded, that it was owing to the influence 

 of atmospheric air. But as it was observed by 

 Spallanzani to take place within the cellular 

 tissue when extravasated, removed from the cir- 

 culation, and not exposed to the air, he inferred 

 that it was owing to the cessation of its motion. 

 This opinion has also been refuted by the fact, 

 that coagulation cannot be wholly prevented by 

 agitation of blood out of the body. Yet it would 

 appear from the experiments of Magendie, that 

 it is greatly retarded by the natural movements 



