COAGULATION OF THE BLOOD. 263 



than if received into a hemispherical bowl, in which the extent of sur- 

 face is less, in proportion to the quantity of blood which it contains. 

 For the same reason, coagulation takes place more rapidly in a vessel 

 with a roughened internal surface than in one which is smooth ; and 

 blood coagulates most rapidly when spread out in thin layers, or entan- 

 gled among the fibres of cloth or sponges. Hemorrhage, accordingly, 

 continues longer from an incised wound than from a lacerated one ; be- 

 cause the blood, in flowing over the ragged edges of lacerated tissues, 

 solidifies upon them, and thus blocks up the wound. 



In all cases there is an inverse relation between the rapidity of coagu- 

 lation and the firmness of the clot. When coagulation takes place slowly, 

 the clot afterward becomes small and dense, and the serum is abundant- 

 When it is rapid, there is but little contraction of the coagulum, an im- 

 perfect separation of the serum, and the clot remains large, soft, and 

 gelatinous. 



The blood coagulates also in the interior of the vessels after stoppage 

 of the circulation. Under these circumstances coagulation takes place 

 less rapidly than if the blood were wholly withdrawn from the body. 

 In man, as a general rule, the blood is found coagulated in the cavities 

 of the heart and large vessels in from twelve to twenty -four hours after 

 death. In the lower animals, coagulation occurs earlier than this, 

 namely, from four to ten hours after death. 



Coagulation of the blood takes place also in the interior of the body, 

 during life, from local arrest or impediment of the circulation. Thus, if 

 blood be accidentally extravasated into the connective tissue, the sub- 

 stance of the brain or spinal cord, or a serous cavity, it coagulates after 

 a short time, and forms a clot which takes the shape of the cavity occu- 

 pied by it. If a ligature be placed upon an artery in the living subject, 

 the blood which stagnates above the ligatured spot coagulates as it 

 would do if removed from the circulation. The clot extends from the 

 ligature backward to the situation of the next collateral branch, that is, 

 to the point at which the movement of the circulation still continues. 

 In an Arterial aneurism, during life, the blood in the dilated portion of 

 the artery, which is sufficiently removed from the centre of the current, 

 gradually coagulates upon the inner surface of the sac. In these cases, 

 as well within as outside the body, and during life as well as after 

 death, the stoppage or retardation of the circulatory movement induces, 

 after a time, the coagulation of the blood. 



It is asserted, however, by some observers, that simple stoppage of 

 the circulation during life will not induce coagulation, unless the inner 

 membrane of the bloodvessels be wounded or irritated. According to 

 Burdon Sanderson, if blood be imprisoned in the jugular vein of the 

 living rabbit by carefully compressing the vessel at two points between 

 transverse needles, so arranged as not to wound or bruise the vascular 

 coats, it will remain fluid in this situation for two clays ; while if ordi- 

 nary ligatures be placed immediately around the vessel, a coagulum is 

 formed in the isolated portion of the vein. 



