222 MORBID STATES OF THE BLOOD, ETC. 



enoua*l"i to give the coagulum a jelly-like consistency. Recent 

 fibrin is invisible under the microscope owing to its great homo- 

 geneity and transparenc}'. These properties begin however to 

 he modified from the moment that coagulation has occurred. 

 The molecules of fibrin possess so high a degree of mutual attrac- 

 tion, that the mass continues to shrink, squeezing out more and 

 more of the fluid contained in its meshes. A highly character- 

 istic change in the microscopical appearances is associated with 

 this separation of the solid and liquid constituents of the clot ; in 

 the homogeneous mass above alluded to, a number of little gaps 

 and fissures make their appearance, between which the solidify- 

 ing fibrin remains as a more or less delicate network composed 

 of round threads. 



§ 187. The above change maybe observed wherever the field 

 is not obscured by too great an abundance of corpuscular ele- 

 ments. But this is almost invariably the case when blood 

 coao-ulates in the vessels. Red and white blood-corpuscles in 

 vast numbers are entangled in the coagulated fibrin and mask 

 the microscopic details of coagulation so completely, that we are 

 unable to make out anything even in the finest sections through 

 a hardened thrombus. We may consider it as settled that a pre- 

 cipitation of fibrin underlies thrombosis ; that the subsequent 

 contraction and the peculiar desiccation which the thrombus 

 undercroes are certainlv due to the above-described chancres in 

 the fibrin ; but the microscope fails to demonstrate the presence 

 of fibrin among the innumerable cells of the intravascular 

 thrombus ; and I may add that this fibrin never subsequently 

 reappears. 



§ 188. The recent thrombus is always of a dark red coloiu' 

 and a jelly-like consistency, like any other blood-clot. Its shape 

 depends on that of the cavity in which coagulation has occurred. 

 Cylindrical plugs are very common, occupying the entire hnnen 

 of a small vessel or one of medium size, and terminating in a 

 conical point at the end turned towards the still pervious part of 

 the channel (obstructing thrombi). Other clots do not block the 

 vessel completely, but adhere to one side of its wall, exhibiting 

 more of a ribbon-like aspect with a tongue-shaped end (lateral 

 thrombi). Farther modifications are brought about by the 

 secondary precipitation of fibrin which is everywhere caused by 

 existing coagula when these are immersed in the blood-current. 



