36 A Manual of Veterinary Physiology. 



If blood be drawn from the body and left at rest, it will 

 be found within a few minutes to have undergone the pro- 

 cess of clotting, the fluid first becomes a jelly, and then 

 a firm clot or crassamentum, taking a complete cast of the 

 vessel in which it is placed, and so firm in consistence that 

 the vessel may be inverted without any blood being lost. 

 In a short time on the surface of the clot fluid may be seen 

 which has been produced by the process of contraction, and 

 in the course of a few hours the clot commences to sink in 

 the now abundant blood-coloured serum which has collected 

 as the result of this process. The blood of the horse is 

 remarkable for the slow rate at which coagulation occurs, 

 and the red cells being specifically heavier than the plasma 

 have time to fall in the fluid before the process is com- 

 pleted, the result being that the upper solid la} 7 er is con- 

 siderably decolourized, forming the so-called Bufiy coat, 

 which though natural to the horse, is indicative in other 

 animals of the presence of an inflammatory process in the 

 system. 



I have here closely followed the account given by human 

 physiologists of the coagulation of the blood in the horse, 

 but the appearance described is by no means invariable ; 

 coagulation of the blood in this animal is often complete in 

 less than five minutes, when, of course, no buft'y coat forms, 

 and I am inclined to believe that when life is instantaneously 

 destroyed, and blood at once drawn, that rapid coagulation 

 and non-bufty coat is the rule rather than the exception. 

 The fluid drawn during life in many cases also clots with 

 extreme rapidity. 



The time occupied in coagulation varies in man from two 

 to six minutes; in the horse Colin puts it at from fifteen to 

 twenty-five or even thirty minutes, the same observer putting 

 the sheep and dog at four to five minutes, and the <>x at 

 eight minutes. In my experience the time mentioned for 

 the horse is exceptionally long. 



If we examine the clot microscopically, it is found to 

 consist of fine fibrils entangled in which are the blood 

 corpuscles ; if the fibrin produced be washed completely 



