T/iroinbosis. 135 



or layered thrombi, usually forminf;' upon a limited area of the vessel 

 wall, Itegin b}' the adhesion of white blood corpuscles and plaques 

 to the altered part of the vessel wall and their accumulation at such 

 site ; upon this basis fibrin is deposited in layers of varying extent 

 and quantity, enclosing the corpuscular elements of the blood in its 

 structure. The arrangement of this coagulum is often such that 

 in microscopic sections the framework of the thrombus may be 

 observed to be formed of wavy trabecula of granular substance 

 made up of blood platelets (Ribbert) ; these bands always sur- 

 rounded by a broad zone of leucocytes and between them the net- 

 work of fibrin fibrils spread out with the red corpuscles included 

 in the reticulum (Ribbert). Corresponding" with the greater or 

 smaller amount of the constituent fibrin and cells and the types of 

 formation described, the general appearance of thrombi and their 

 color and consistence vary. There may be distinguished the follow- 

 ing varieties from this viewpoint: 



I. Red thrombi, showing a homogeneous, blood red, gelatinous 

 mass, similar to the post-mortem clots ["'currant-jelly thrombi"]. 



I. White and grayish-red thrombi, reminding one of bacon-fat 

 or spinal-cord tissue or minced meat, not transparent, but opaque, 

 dull, of the consistence of soft rubber or cooked minced meat. 



3. Mixed and stratified thrombi, made up of alternating layers 

 of red and white coagulum, well seen in cross-section, often arranged 

 concentrically like the tunics of an onion and separable like the 

 leaves of a book from each other. The reason for this lamination 

 and alternating arrangement is to be found in the fact that new 

 layers are not being continuous!}- formed upon the primary clot 

 but are deposited at intervals, the older layers thus attaining a cer- 

 tain degree of firmness, and the new ones not adhering so closely 

 to the previously formed strata and remaining easily separable from 

 them. Where such mode of increment is frequently repeated the 

 thrombus may exhibit quite a number of layers. The surface of 

 these thrombi may be either smooth or uneven, often marked by 

 ridges or ribs ; the latter peculiarity is due to the trabecula of blood 

 platelets and leucocytes extending to the surface and forming ledge- 

 like projections with trough-like depressions between them (similar 

 to the wavy deposit of river sand, and according to Zahn probably 

 produced by the wave-like motion of the blood). [Such appearance 

 may be produced, too, by the uneven contraction of the mass, the 

 shrinkage being most marked in the fibrinous network lying between 

 the coarser plaque-trabecula.] 



