The Blood, 39 



It is a matter of common observation, that after death 

 the coagulation of blood in the vessels is a slow process, 

 though by exposure to the air clotting is almost at once 

 produced ; it was supposed that the air in some way 

 influenced this, but it has been shown that the action 

 is rather due to the influence on the blood exerted by 

 the wall of the vessel. The jugular vein of a horse has 

 been included between ligatures and excised, nevertheless 

 the blood has remained fluid in it for one or two days, 

 though suspended in such a way as to be left freely exposed 

 to the air, yet on removal from the vein clotting will at once 

 occur; while suspended the corpuscles sink, and it is found 

 that the serum in the upper layer has considerably lost its 

 power of coagulation, though the blood drawn from the 

 lower stratum clots readily ; evidently the corpuscles take 

 an active part in the production of clotting. This was the 

 view held by Schmidt, who maintained that the white cor- 

 puscles were rapidly dissolved in the plasma, in the horse 

 to the extent of 71 7 per cent., and that the result of this 

 dissolution was serum globulin and the fibrin ferment. 



When blood-vessels are injured during life, or when 

 pathological changes occur in the blood, coagulation in the 

 vessels will occur. 



Clotting in dead blood may be retarded or hastened 

 by certain conditions. Blood of a horse received into a 

 vessel so constructed as to expose it to a freezing tempera- 

 ture may be kept fluid for an indefinite period, though 

 coagulation will at once occur when the temperature is 

 allowed to rise. 



The addition to the blood in certain proportions of the 

 neutral salts of the alkalies and earths, ammonia, and 

 sulphate of magnesia delay clotting ; the addition of acetic 

 acid and a current of C0 2 by precipitating the fibrinogen 

 entirely prevent it, (venous blood which is rich in CO., is 

 slow in clotting). By rapidly heating blood to 133° F. 

 clotting is prevented, owing to the precipitation of the 

 fibrin-forming substances ; the addition of oil also retards 

 clotting. The shape of the vessel in which the coagulating 



