COAGULATION OP THE BLOOD. 73 



under different appearances. In the first place let us 

 examine the properties of the blood, and then we will look 

 at the heart and vessels by which it is circulated. 



The most remarkable property of the blood, is that 

 of its coagulating when drawn from the vessels. This 

 process seems to be independent of external causes, and 

 has never been satisfactorily accounted for by physiolo- 

 gists. 



Emily. May it not be because it is at rest, instead 

 of being in a state of constant motion as it is in the body ? 

 Or perhaps it is a kind of freezing process, produced by 

 its exposure to a less degree of warmth than the tem- 

 perature of the body. 



Dr. B. By exercising your ingenuity in this way, 

 you might fabricate many other theories, all which have 

 been already anticipated, and all equally incapable of 

 explaining the effect in question. The coagulation of 

 the blood is not prevented by keeping it constantly agi- 

 tated after it is drawn, and is rather hastened than re- 

 tarded, by exposing it to a degree of heat less than that 

 of the body. The celebrated John Hunter thought he 

 explained it, by saying that the blood possessed life, and 

 that coagulation was- a vital process. As it is a process 

 of a very peculiar nature and one of great use in the 

 animal economy, it may not be improper to give it that 

 name ; but it is very probable that the causes on which 

 it depends are of a physical nature. It is a little re- 

 markable that in animals which have been run to death, 

 or killed by lightning, the blood loses entirely its power 

 of coagulaticn. 



Emily. These are the same conditions under which 

 the muscles lose their contractilility after death. May 

 not the cause be the same in both ? The coincidence is 

 too singular to be accidental. 



Dr. B. It is very probably as you suggest, but the 



cause whatever it may be, is thereby no better made 



known. If you have ever observed a quantity of blood, 



an hour or two after it has been drawn, and suffered to 



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