COAGULATION OF THE BLOOD. 27 



the contractions of the heart force out the coagulated blood which has closed 

 the opening. 



From the foregoing considerations, it is evident that coagulation of the 

 blood has for its chief office the arrest of haemorrhage. Coagulation never 

 takes place in the organism unless the blood be in an abnormal condition 

 with respect to circulation. Here its operations are mainly conservative ; 

 but as almost all conservative processes are sometimes perverted, clots in the 

 body may be productive of injury, as in the instances of cerebral apoplexy, 

 clots in the heart occurring before death, the detachment of emboli etc. 



Cause of the Coagulation of the Blood. Alex. Schmidt, in 1861, proposed 

 a theory of coagulation, which involves the coming together of certain mat- 

 ters called fibrin-factors. This theory, which had been indicated by Buch- 

 anan, in 1845, has been adopted and more or less modified by Kiihne, Virchow 

 and others. If blood-plasma, rendered neutral with acetic acid, be diluted 

 with ten times its volume of water at 32 Fahr. (zero C.), and then be treated 

 with a current of carbon dioxide, a flocculent precipitate is formed, which 

 has been called paraglobuline, or fibrinoplastic matter. This substance may 

 be dissolved in water containing air or oxygen in solution. After this pre- 

 cipitate has been separated, if the clear liquid be diluted with about twice its 

 volume of ice-cold water and be treated for two or three hours with a current 

 of carbon dioxide, a viscid scum is produced, which has been called fibrino- 

 gen. More recently, a third principle, a ferment, has been described by 

 Schmidt, which he considers necessary to the formation of fibrin. This 

 ferment is produced in some way by the leucocytes of the blood, probably 

 by partial decomposition of these bodies. 



In view of the results of recent investigations with regard to the cause of 

 the coagulation of the blood, which, unfortunately, are not as positive and 

 definite as could be desired, some physiologists have adopted the following as 

 a provisional theory of the mechanism of this process : 



There exists, probably in small quantity in the circulating blood and in 

 considerable quantity in blood drawn from the vessels or arrested in its cir- 

 culation, a peculiar ferment which is produced in some way by changes in 

 the leucocytes. This ferment may be concerned in the decomposition of 

 plasmine. It is certainly thrown down with plasmine when plasmine is pre- 

 cipitated by the . action of reagents. The action of this ferment either in- 

 duces or hastens the separation of plasmine into the so-called fibrin-factors, 

 paraglobuline and fibrinogen. Of these two substances, fibrinogen is the 

 more important in the formation of fibrin, a small quantity of fibrin, only 

 about three parts per thousand of blood, being formed. A large quantity of 

 paraglobuline is not used in the formation of fibrin and remains in the serum. 

 It is possible, indeed, that no part of the paraglobuline is concerned in coagu- 

 lation. If the latter be true, paraglobuline may be regarded as identical with 

 metalbumen, a view which was advanced by Eobin many years ago and is 

 now adopted by some physiologists. 



Adopting these views, the mechanism of coagulation may be succinctly 

 described as follows : 



