COAGULATION OF THE BLOOD. 33 



VI. In blood shed from an artery, the degree of alkalinity diminishes from the 

 time of its being shed until coagulation is completed (Pfliiger and Zuntz). This is 

 probably due to a decomposition in the blood, whereby an acid is developed, which 

 diminishes the alkalinity (p. 1). 



VII. During coagulation there is a diminution of the in the blood, although 

 a similar decrease also occurs in non-coagulated blood. Traces of ammonia are also 

 given off, which Richardson erroneously supposed to be the cause of the coagulation 

 of the blood. 



[This is refuted (1) by the fact that blood, when collected under mercury (whereby no escape 

 of ammonia is possible), also coagulates ; and (2) by the following experiment of Lister : He 

 placed two ligatures on a vein containing blood, moistening one-half of the outer surface of the 

 vein with ammonia, leaving the other half intact. The blood coagulated in the first half, and 

 not in the other, owing to the properties of the wall of the vein of the former being altered. 

 Neither the decrease of nor the evolution of ammonia seems to have any causal connection 

 with the formation of fibrin. ] 



Pathological. When the blood coagulates within the vessels during life, the process is called 

 thrombosis, and the coagulum or plug so formed is termed a thrombus. When a clot of blood 

 or other body is carried by the blood-stream to another part of the vascular system where it 

 blocks up a vessel, the plug is called an embolus, and the result embolism. 



29. CAUSE OF THE COAGULATION OF BLOOD. [He wson's Experiments (1772.) Hew- 

 son tied the jugular vein of a horse between two ligatures, removed it, and then suspended it by 

 one end (fig. 21). He found that the blood remained fluid for a long time 

 (48 hours), the red corpuscles sank (RC) and left a clear layer of plasma 

 on the surface (P). On drawing off some of this clear plasma it coagulated, 

 thus proving coagulation to be due to changes in the plasma. Lister 

 repeated this experiment, and found that, even if the upper end of the 

 tube be opened and the blood freely exposed to the air, coagulation is but 

 slightly hastened. He showed that the blood might be poured from one 

 vein into another, just as one might pour fluid from one test-tube into 

 another. In this case there were two test-tubes, i.e., the veins and 

 although the blood, on being poured from the one to the other, came into 

 contact with the air, it did not coagulate. Hewson, however, found that 

 blood poured from the vein into a glass vessel coagulated, so that, in his 

 opinion, the blood-vessels exerted a restraining influence on coagulation. 

 By cooling the blood and preventing it from coagulating, he proved that 

 coagulation was not due to the loss of heat. Nor could it be a vital act, 

 as sodic sulphate or other neutral salt prevented coagulation indefinitely, 

 but coagulation took place when the blood was diluted with water.] Fig. 21. 



[Buchanan's Researches. The serous sacs of the body contain a fluid y e i n of horse tied 

 which in some respects closely resembles lymph. The pericardial fluid of between two liga- 

 some animals coagulates spontaneously {e.g., in the rabbit, ox, horse, and tures. P, plasma ; 

 sheep) if the fluid be removed immediately after death. If this be not WC white and 

 done till several hours after death, the fluid does not coagulate spontane- RC } rec [ cor . 

 ously, The fluid of the tunica vaginalis of the testis sometimes accumu- puscles. 

 lates to a great extent, and constitutes hydrocele, but this fluid shows no 

 tendency to coagulate spontaneously. Andrew Buchanan found, however, that if to the fluid of 

 ascites, pleuritic fluid, or hydrocele fluid, there be added clear blood-serum, then coagulation 

 takes place, i.e., two fluids neither of which shows any tendency by itself to coagulate form a 

 clot when they are mixed (1831). He also found, that if " washed blood-clot" (which consists 

 of a mixture of fibrin and colourless corpuscles) be added to hydrocele fluid, coagulation occurred. 

 He compared the action of washed blood-clot to the action of rennet in coagulating milk, and 

 he imagined the agents which determined the coagulation to be colourless corpuscles. Thus, the 

 buffy coat of horses' blood is a powerful agent, and it contains numerous colourless corpuscles. 

 He finally concluded that some constituent in the plasma, to which he gave the name of a 

 "soluble fibrin," is acted upon by the colourless corpuscles and converted into fibrin. The 

 soluble fibrin of Buchanan is comparable to the fibrinogen in Hammarsten's theory. Buchanan, 

 however, did not separate the substance.] 



[Denis's Plasmine (1859). Denis mixed un coagulated blood with a saturated solution of 

 sodic sulphate, and allowed the corpuscles to subside. The salted plasma thus obtained he pre- 

 cipitated with sodic chloride. The precipitate, when washed with a saturated solution of sodic 

 chloride, he called plasmine. If plasmine be mixed with water, it coagulates spontaneously, 

 resulting in the formation of fibrin, while another proteid remains in solution. According to 

 the view of Denis, fibrin is produced by the splitting up of plasmine into two bodies fibrin 

 and a soluble proteid.] 



