THE BLOOD AND LYMPH. 127 



fibrils may be aggregated into larger threads variously interwoven, 

 or they may be still further condensed to form masses of a hyaline 

 character. The fibres may undergo a disintegration into granules, 

 Avhen their fibrinous nature is not readily revealed. Fibrin is not 

 found in the body under normal conditions, but separates from the 

 blood if the circulation be arrested for any considerable length of 

 time. It appears to be the result of the interaction of four sub- 

 stances : fibrinogen, fibrinoplastin, fibrin-ferment, and salts of lime. 

 The latter are always present in the tissues; fibrinogen exists in 

 the plasma of the blood and lymph, and is, therefore, very widely 

 distributed. The fibrinoplastin is believed to be derived from the 

 bodies of cells that have undergone some destructive change ; and 

 the ferment may be derived from the same source. These four 

 substances are present when the flow of blood through the ves- 

 sels has been seriously checked for a considerable period ; fibrin is 

 then formed, causing a coagulation of the blood. Such a clot, 

 within a vessel during life, is called a " thrombus." Coagulation 

 takes place more rapidly if there be a destruction of tissue ; e. g., 

 a break in the wall of the vessel. It may also be occasioned by a 

 roughness on the internal surface of the vessel, if the flow of blood 

 over that obstruction is seriously retarded. In such a case the 

 fibrin-forming elements may be liberated from the bodies of leuco- 

 cytes that find lodgement behind the obstruction and suffer injury, 

 or they may be derived from blood-plates that have been arrested 

 and undergone similar changes. In a like manner, fibrin may be 

 formed in the lymphatic vessels or the interstices of the tissues. 1 



1 An explanation of fibrin-formation, offered by Lilienfeld, would serve to 

 elucidate many cases of coagulation under morbid circumstances. According to 

 this observer, fibrin is formed by the union of " thrombosin " with calcium, and is, 

 therefore, a calcium-thrombosin compound. The thrombosin is produced from 

 fibrinogen by the action of nuclein, which in turn is formed from the nucleohiston 

 contained in the nuclei of cells. Coagulation, then, would be the result of the 

 following process : the nucleohiston in the nuclei, during "karyolysis" or disintegra- 

 tion of the nucleus, is decomposed into " histon " and nuclein. The latter, acting 

 ,on fibrinogen, produces thrombosin, which unites with calcium to produce fibrin. 



