54 INFLUENCE OF SALTS AND LIVING WALLS OF VESSELS. [BOOK T. 



in the process (the supposed fibrin-generators) be dissolved in weak solu- 

 tions of sodium hydrate and mixed, no coagulation will occur, unless there 

 be added to the mixture the dialysate from the two operations, reduced by 

 evaporation to a small volume, or unless sodium chloride be added until 

 it amount to 1 per cent, of the mixture; then, however, coagulation does 

 occur. The quantity of salt which is needed to bring about coagulation 

 increases with the volume of the solution of the fibrin-factors, a circum- 

 stance which fully explains why by largely diluting a spontaneously 

 coagulating fluid, a slowing of the process of coagulation, and a diminution 

 in the quantity of fibrin produced, are always brought about. 



Non-coagulation of the blood within living blood-vessels. 



Any theory of the coagulation of the blood which would lay claim 

 to truth or completeness should be adequate to explain the remark- 

 able circumstances that the blood does not coagulate as long as it is 

 contained within the living uninjured vessels, but that it does coagulate 

 when the vessel is injured or dies. 



Let us examine the facts which we at present possess in reference 

 to this matter. 



(1). So long as the vessels are uninjured and alive, the 

 blood which circulates within them does not coagulate. When a 

 foreign- body is however introduced into the vessels, as when a silver 

 needle is made to transfix an artery, a coagulum of fibrin forms 

 around the metal, although it be in the stream of living blood. 



(2) If, however, the coats of an artery be diseased or injured 

 in such a way that the endothelial coat which lines it ceases to be 

 intact, coagulation will occur, giving rise to a solid plug or 'thrombus/ 

 the latter term being applied specifically to the coagulation which 

 occurs in a vessel during life. Perhaps the most common example 

 of a thrombus is that which is occasioned by the application of a 

 ligature to an artery; in this case both the middle and internal coats 

 are usually severely injured, the continuity of the endothelial lining 

 of the internal coat being certainly affected, and, almost immediately, 

 there results coagulation. 



: Another common example of the production of thrombus during 

 life is afforded by the occurrence of the process in aneurisms, in which, 

 amongst other lesions of the arterial walls, a direct breach in the 

 continuity of the endothelium certainly often exists. 



(3) But not only does thrombosis occur where a direct break 

 in the continuity of endothelium can be distinctly proved to exist, 

 but also where an injury of any kind is inflicted upon an artery. 

 The process has been studied with great minuteness by Zahn in the 

 case of the arteries of the frog and deserves particular attention in 

 reference to the doctrines of coagulation. 



Zahn 1 has observed that when a crystal of sodium chloride is 



| : Zahn, Virchow's Arclilv, Vol. LXII. p. 81. See Cohuheim, Vorlcsungen iiber allgemeine 

 Pathologic, 1877, Vol. i. p. 150 et seq. 



