COAGULATION OF THE BLOOD. 229 



mate form which fibrin assumes in coagulating, just as albumen 

 takes the form of granules under the same circumstances. The 

 coagulation of fibrin does not differ in character from that of any 

 other organic substance ; it merely differs in the physical conditions 

 which give rise to it. All the coagulable organic substances are 

 naturally fluid, and coagulate only when they are placed under 

 certain unusual conditions. But the particular conditions neces- 

 sary for coagulation vary with the different organic substances. 

 Thus albumen coagulates by the application of heat. Casein, which 

 is not affected by heat, coagulates by contact with an acid Jaody. 

 Pancreatine, again, is coagulated by contact with sulphate of mag- 

 nesia, which has no effect on albumen. So fibrin, which is naturally 

 fluid, and which remains fluid so long as it is circulating in the 

 vessels, coagulates when it is withdrawn from them and brought in 

 contact with unnatural surfaces. Its coagulation, therefore, is no 

 more "spontaneous," properly speaking, than that of any other 

 organic substance. Still less does it indicate anything like organ- 

 ization, or even a commencement of it. On the contrary, in the 

 natural process of nutrition, fibrin is assimilated by the tissues 

 and takes part in their organization, only when it is absorbed by 

 them from the bloodvessels in a fluid form. As soon as it is once 

 coagulated by any means, it passes into an unnatural condition, and 

 must be again liquefied and absorbed into the blood before it can 

 be assimilated. 



As the fibrin, therefore, is maintained in its natural condition of 

 fluidity by the movement of the circulating blood in the interior of 

 the vessels, anything which interferes with this circulation will in- 

 duce its coagulation. If a ligature be placed upon an artery in the 

 living subject, the blood which stagnates above the ligature coagu- 

 lates, just as it would do if entirely removed from the circulation. 

 If the vessel be ruptured or lacerated, the blood which escapes from 

 it into the areolar tissue coagulates, because here also it is with- 

 drawn from the circulation. It coagulates also in the interior of 

 the vessels after death owing to the same cause, viz : stoppage of 

 the circulation. During the last moments of life, when the flow of 

 blood through the cavities of the heart is impeded, the fibrin often 

 coagulates, in greater or less abundance, upon the moving chordas 

 tendinea? and the edges of the valves, just as it would do if with- 

 drawn from the body and stirred with a bundle of twigs. In every 

 instance, the coagulation of the fibrin is a morbid phenomenon, de- 

 pendent on the cessation or disturbance of the circulation. 



