CAUSE OF COAGULATION OF THE BLOOD. 165 



bottles, I immediately stirred one of them with a clean ivory 

 rod for ten seconds very gently, so as to avoid the introduc- 

 tion of any air, and then left both undisturbed. At the end 

 of a certain number of minutes, I found that, while the blood 

 which had not been disturbed could be poured out as a fluid, 

 with the exception of a thin layer of clot on the surface and 

 an incrustation on the interior of the vessel, the blood in the 

 other vessel, which had been stirred for so brief a period, was 

 already a solid mass." 1 



Other experiments are brought forward, modifications of 

 the one already mentioned as performed by Simon, showing 

 that incrustations will form on the surface of foreign sub- 

 stances introduced into the vessels ; and that after death their 

 introduction will induce coagulation in the entire vessel much 

 sooner than it would otherwise have taken place. 



The idea of simple contact with living tissues preventing 

 coagulation hardly merits discussion. It is well known that 

 coagulation frequently takes place during life, almost always 

 following arrest of the circulation. After division of the ves- 

 sels, the blood, in contact with living parts, performs its con- 

 servative function in the arrest of hemorrhage. There is cer- 

 tainly something very curious in the effect of the contact of 

 foreign substances, and the experiments on this point are very 

 striking. Why is it that a coagulum forms upon a fine thread 

 or a needle passed through a vessel ; or on the wire with which 

 the blood in Mr. Lister's apparatus was stirred, though there 

 was no exposure to the air ? And why did the blood, which 

 was only gently stirred for a few seconds with a smooth ivory 

 rod, coagulate so much more rapidly than that which was 

 undisturbed ? 



These are questions which we must acknowledge our 

 inability to answer. The phenomena cannot be satisfactorily 

 explained by the supposition that ammonia is evolved ; but 

 on the other hand, this is not a sufficient reason for rejecting 

 the fact, experimentally demonstrated, that, out of the or- 



1 Op. tit., p. 83. 



