CHAP, i.] BLOOD. 21 



or slightly altered living blood-vessels; the following shew that 

 coagulation may take place even in the living vessels. 



4. If a needle or piece of wire or thread be introduced into f VA> 'w 

 the living blood-vessel of an animal, either during life or imme-; , !,"7', 

 diately after death, the piece will be found encrusted with fibrin. 



5. If in a living animal a blood-vessel be ligatured, the 

 ligature being of such a kind as to injure the inner coat, coagu- 

 lation takes place at the ligature and extends for some distance 

 from it. Thus if the jugular vein of a rabbit be ligatured roughly 

 in two places, clots will in a few hours be found in the ligatured 

 portion, reaching upwards and downwards from the ligatures, the 

 middle portion being the least coagulated. Clots will also be 

 found on the far side of each ligature. The clots will still appear 

 if the ligature be removed immediately after being applied, 

 provided that in the process the inner coat has been wounded. 

 If the ligatures be applied in such a way as not to injure the 

 inner coat, coagulation will not take place, though the blood may 

 remain for many hours perfectly at rest between the ligatures. 



So also when an artery is ligatured a conspicuous clot is formed 

 on the cardiac side of the ligature. The clot is largest and firmest 

 in the immediate neighbourhood of the ligature, gradually thinning 

 away from thence and reaching usually as far as where a branch J" 

 is given off. Between this branch and the ligature there is stasis ; 

 the walls of the artery suffer from the want of renewal of blood, 

 and thus favour the propagation of the coagulation. On the distal 

 side of the ligature where the artery is much shrunken, the clot 

 which is formed, though naturally small and inconspicuous, is 

 similar. 



6. Any injury of the inner coat of a blood-vessel causes a 

 coagulation at the spot of injury. Any treatment of a blood-vessel 

 tending to injure its normal condition causes local coagulation. 



7. Disease involving the inner coat of a blood-vessel causes a 

 coagulation at the part diseased. Thus inflammation of the lining 

 membrane of the valves of the heart in endocarditis is frequently 

 accompanied by the deposit of fibrin. In aneurism the inner coat 

 is diseased, and layers of fibrin are commonly deposited. So also 

 in fatty and calcareous degeneration without any aneurismal 

 dilation there is a tendency to the formation of clots. 



Similar phenomena are seen in the case of serous fluids which 

 coagulate spontaneously. If, as soon after death as the body is 

 cold and the fat is solidified, the pericardium be carefully removed 

 from a sheep by an incision round the base of the heart, 

 the pericardial fluid may be kept in the pericardial bag as in 

 a living cup for many hours without clotting, and yet a small 

 portion removed with a pipette clots at once, and a thread left 

 hanging into the fluid soon becomes covered with fibrin. 



The only interpretation which embraces these facts is that 1 

 so long as a certain normal relation between the lining surfaces ofjj 



