56 THE HUMAN BODY. 



which it may receive or to which it may give off gaseous 

 bodies. But it is easy to prove that none of these three 

 things is the cause of coagulation. Stirring the drawn 

 blood and so keeping it in movement does not preTent but 

 hastens its coagulation; and blood carefully imprisoned in 

 a living blood-vessel, and so kept at rest, will not clot for a 

 long time: not until the inner coat of the vessel begins to 

 change from the want of fresh blood. Secondly, keeping 

 the blood at the temperature of the Body hastens coagula- 

 tion, and cooling retards it; blood received into an ice-cold 

 vessel and kept surrounded with ice will clot more slowly 

 than blood drawn and left exposed to ordinary tempera- 

 tures. Finally, if the blood be collected over mercury from 

 a blood-vessel, without having been exposed to the air even 

 for an instant, it will still clot perfectly. 



The formation of fibrin is then due to changes taking 

 place in the blood itself when it is removed from the 

 blood-vessels; clotting depends upon some rearrangement 

 of the blood constituents. That the primary change is a 

 breaking-down of the plaques (p. 48) (or, as they are also 

 named, the corpuscles of Hayem or Osier) is probable, be- 

 cause these plaques always do break up when blood clots; 

 and because everything which retards or prevents the 

 coagulation of blood also retards or prevents the breaking- 

 up of the plaques. Moreover, when blood clots, the fibrin 

 threads are seen first near the disintegrating plaques. 

 They probably yield the ferment. 



Relation of the Blood- Vessels to Coagulation. As to 

 the role of the blood-vessels with respect to coagulation, 

 two views are held between which the facts at present 

 known do not permit a decisive judgment to be made. 

 One theory is that the vessels actively prevent coagulation 

 by constantly absorbing from the blood some substance, 

 as, for example, the fibrin ferment and fibrinoplastin, which 

 may be supposed constantly to develop, and the presence 

 of which is a necessary condition for the formation of 

 fibrin. The other view is that the blood-vessels are passive. 

 They simply do not excite those changes in the blood con- 

 stituents which give rise to the formation of fibrinoplas- 



