THE BLOOD Ais'D ITS CIRCULATION. 337 



blood varies in different animals ; in man it is 90*^, but in 

 the sheep nearly 100°. It is rather warmer in the arteries 

 than in the veins, and is liable to variation from disease, it 

 having been found in severe inflammations to be raised 

 7*^ in man, and in the cold fit of agues 4° lower than in a 

 state of health. It is, however, but slightly raised or de- 

 pressed by external temperature. It was not till compara- 

 tively a recent date that the blood has been considered to 

 possess vitality, which, however, is now generally acknow- 

 ledged. The vitality and fluidity of the blood are intimately 

 associated ; in fact, its coagulation, when removed from the 

 body, constitutes its death. The time in which this is ta- 

 king place is different in different animals, and is influenced 

 by various circumstances. In strong animals, such as the 

 horse, it is longer than in such weak animals as the sheep : 

 in the former it is often as long as fifteen minutes ; and if 

 the body be in a state of plethora, the vital power being too 

 highly developed, the death of the blood is much longer re- 

 sisted. In these cases coagulation is delayed, and, in con- 

 sequence, the red portion of the blood, being the heaviest, 

 falls to the bottom of the vessel, and the fibrine remains at 

 the top, constituting the huffy coat of inflammation. This 

 separation, when arising from the above cause, takes place 

 long before the serum is developed. The coagulation of the 

 blood has been endeavored to be accounted for without suc- 

 cess ; it was held by some that it was produced by the ces- 

 sation of its motion ; but it has been found that if stirred in 

 a vessel it will coagulate quicker than before. It was 

 thought that exposure to the atmosphere was the cause ; but 

 it has been known to coagulate in a vacuum, and likewise 

 in the body when a vein has been tied. It was next con- 

 ceived that it was caused by the low temperature to which 

 it is exposed ; but it has been ascertained that it will coag- 

 ulate quicker if the temperature is either higher or lower 

 than natural ; but if so low as to freeze the blood, it will not 

 coagulate when afterwards thawed. These experiments 

 show that the blood is analogous to no other fluid, and that 

 coagulation cannot be owing to physical causes, but can be 

 explained only by reference to its vitality. 



Although the blood will coagulate in the body if obstructed, 

 yet there is a considerable difference between this state and 

 its coagulation out of the body. In the former instance co 

 agulation is longer occurring, new vessels are thrown into 



29 



