Inquiry into the Nature and Properties of the Blood. 187 



and living body * : in fact, no extraneous circumstance whatever 

 can be regarded as a c«?/5«' of this phaenomenon, however greatly 

 its tendency to coagulation may be retarded or influenced by 

 any one extrinsic agent. The fluidity of water and other li- 

 quids is ascribed to the presence of caloric, and these may be 

 rendered volatile by an increase of the heat : not so the blood ; 

 this increase would only tend to destroy it altogether as blood. 



Can we say it is a vital heat or the animal heat which 

 keeps it fluid ? We thinknot; because the cold-blooded animals 

 as they are called, have their blood equally fluid. Is the motion 

 to which it is subjected ; the constant agitation by the heart ; 

 the incessant straining as it were which it undergoes through 

 the minute capilli, — sufficient to preserve it in a fluid state? or 

 more, to cause it to be so ? The action of the heart may be re- 

 ferred to several causes, so may the reaction of the capillary 

 vessels upon the blood, and both ultimately to the presence of 

 life in the body : but blood or living fluids existed before the 

 heart that moves them, as in the first days of conception ; they 

 existed before any vessel was formed for them to circulate 

 through : wherefore the first cause of the blood's fluidity must 

 be sought for independently of the secondary or accessory 

 causes just adverted to. And we may venture to assert, be- 

 cause our assertion is founded in fact, that the essential and 

 primary cause of the blood's fluidity is its vitahty : and this is 

 consonant to that rule in philosophy, which teaches " that the 

 cause of the cause is also the cause of the effect," — causa cau- 

 sans est causa cffectus\. 



The fluidity of the blood must be regarded as a very ex- 

 traordinary property indeed, and one which is eminently cha- 

 racteristic of some more active and energetic agent existing 

 within it, which withholds it from yielding to its own natural 

 tendency to coagulation. This agent some would identify with 

 a vital principle at once, without considering the possibility that 

 material elements may admit of such states or combinations 

 as to render them highly active in their nature, extremely sub- 

 tile in their form, and capable of imparting their own activity 



* If we take a fish out of the sea, the heat of its body perhaps about G0°, 

 and bring it into an atmosphere of 70°, the blood on being let out of the 

 vessels will immediately coagulate. This was ascertained on board of a 

 ship lying oflfHcllisle, in the summer of 17fi' : for immediately upon a fish 

 being caught, I ascertained its heat ; and letting out part of its blood, it 

 immediately coagulated, although the blood discharged was become warmer 

 than that reniaiuing in the vessels of the fish ; which, however, still con- 

 tinued fluid. — Treatise on the Jiluod, by J. Hunter, vol. i. p. ;}5. 



f The blood, says Mr. Hunter, has the power of preserving its fluidity; 

 or in other words, the living principle in the body has the power of pre- 

 serving it in this state. — Treatise on the Blood, vol. i. p. 14H. 



2 13 2 and 



