DISEASES OF THE ORGANS OF CIRCULATION 67 



quantitatively rather rapidly by the resorption of the lymph con- 

 tained in the tissues and the fluids present in the stomach and 

 intestines. The new-formed blood is at first very rich in water, 

 while the red blood-corpuscles are few in number. The latter are 

 replaced slowly. 



The exact nature of the processes concerned in the formation of 

 the thrombus is not entirely understood. In the spontaneous 

 arrest of hemorrhage a white thrombus is generally present, formed 

 by the aggregation of white blood-corpuscles and blood-platelets, 

 and differing esseAtially from the usual products of coagulation, 

 which consist of fibrin inside or outside of the body. The subse- 

 quent history of the white thrombus varies, depending upon 

 whether infectious materials gain entrance to it or not. If it remains 

 free from infection, organization takes place; i.e., a firm connective 

 tissue develops, which is supplied with nutrient vessels, and which 

 closes the wounded vessel with a solid and permanent cicatrix. 

 The cells of the thrombus do not actively participate in the process; 

 they play only a passive r61e, being gradually repressed by the new- 

 formed tissue. The formation of new connective tissue results 

 from the growth of the vessel endothelium. The endothelial cells 

 of the intima proliferate and are transformed into spindle-shaped 

 and variously formed cells which extend toward the centre of the 

 thrombus, grow into it and around it, and later are changed into 

 fibrillar connective-tissue cells, the thrombus being thus finally 

 compressed and replaced by firm connective tissue. At the same 

 time, as a result of budding of the vasa vasorum, new vessels are 

 formed in the thrombus and it becomes vascularized. About four 

 weeks after the injury, in the smaller vessels, the thrombus is trans- 

 formed into a mass of cicatricial connective tissue permeated with 

 capillaries, which subsequently becomes more solid in consequence 

 of contraction and the atrophy of the newly formed blood-vessels. 

 More rarely, calcification of the thrombus occurs (so-called vein 

 stones or phleboliths). The interruption to the circulation result- 

 ing from the thrombus is overcome by the estabUshment of a col- 

 lateral circulation while the arterial branches situated centrally and 

 peripherally to the thrombus and their vasa vasorum are dilated. 



