THROMBOSIS. 221 



organ ; the larger ones are arrested in transitu. The vessels give 

 way behind the point of obstruction ; hemorrhage, inflammation 

 and softening ensue ; in short we get a sum of anatomical dis- 

 turbances associated with most severe clinical symptoms. The 

 vetia mirabilia of the kidneys are likewise unfavourable to the 

 free transit of the pigmentary particles; at least these organs 

 stand next to the brain in the frequency with which they exhibit 

 melanasmic j^igmentation, in the form of black dots and strisB 

 in their cortical substance, corresponding in position to the Mai- 

 pighian bodies and their afferent vessels. 



h. Coagulation of Blood in the Vessels (Thrombosis). 



§ 185. One of the most important chapters of general patho- 

 logy is taken up with the causes and consequences of the coagu- 

 lation of blood in the interior of the vessels. We shall content 

 ourselves with so much of it as is needful to understand the 

 histology of the process. 



Coagulation is determined by two conditions ; retardation of 

 the blood-current, and irregularities on the inner wall of the 

 vessel which increase the friction between it and the passing- 

 blood. Thrombosis often complicates many of those diseases of 

 the vessels to which the ensuing section Avill be devoted. But 

 coagulation from increased friction may indeed be often if not 

 always referred to coagulation from stagnation ; and that 

 wherever the irregularities in question afford even the smallest 

 recesses in which the blood may pause. We shall return to this 

 subject when we speak of endocarditis. 



§ 186. The proximate cause of coagulation is in every case a 

 precipitation of fibrin from the blood. The fibrin is not con- 

 tained in the blood as such ; it is produced during the act of 

 coaoculation itself. A. Schmidt has established the interesting: 

 fact that the blood-corpuscles contain an albuminoid substance 

 (globulin, fibrinoplastic matter) Avhicli forms an insoluble com- 

 pound with a similar body (fibrinogen) contained in the liquor 

 sanguinis, whenever the obstacles to coagulation are removed, or 

 conditions favourable to coagulation are present. This insoluble 

 compound is what we call "fibrin." 



Recently precipitated fibrin is a colourless substance mucli 

 swollen by imbibition. Two parts of fibrin in a thousand are 



