CIRCULATORY SYSTEM. 107 



Other circumstances and agents also affect the coagulation. 

 It will congeal sooner when drawn from a small orifice, or al- 

 lowed to trickle down the side of the vessel or the animal's neck, 

 than under opposite circumstances. Various chemical agents 

 thrown into the vessel will effect its coagulation at once : such 

 are certain of the neutral salts, acids, alcohol, and alum. 



Of the various conjectures and opinions that have been framed 

 to account for this miraculous change in the blood, none seems 

 so well worthy our attention as that left us by the famed John 

 Hunter. He ascribed the coagulation to the presence of a vital 

 principle in the fluid. To use his own words: "To conceive 

 that blood is endowed with life while it is circulating, is, perhaps, 

 carrying the imagination as far as it can go; but the (iifficulty 

 arises merely from its being a fluid, the mind not being accus- 

 tomed to the idea of a livingy/z/iVZ." He next proceeds to shew, 

 " that organization and life do not depend in the least on each 

 other ; that organization may arise out of living parts and produce 

 action, but that life can never rise out of, or depend on, organ- 

 ization." And, in the third place, he evinces, by many ingenious 

 facts and experiments, a striking analogy between the coagula- 

 tion of the blood and the contraction of muscular fibre. Animals 

 killed by lightning or electricity have not their blood coagulated, 

 nor their muscles contracted. Those that are hunted to death, 

 or, in fact, in any way suddenly extinguished, exhibit the same 

 coincident phenomena ; also their bodies are more disposed to 

 run into putrefaction. From all which evidence, Mr. Hunter 

 concluded that blood in a living body, was possessed of what 

 he termed a materia vit<s diffiiscB. 



Dr. Bostock objects to the Hunterian doctrine on the score 

 that, even were " the life of the blood fully established, it would 

 not orter any explanation of the cause of its coagulation ; for the 

 same difficulty (adds he) still remains, in what manner the pre- 

 sence of life operates, so as to produce either the coagulation of 

 the blood or the contraction of the muscles." But this remark is 

 one that would equally apply to all vital phenomena. The Doc- 

 tor gives it as his opinion that, " perhaps, the most obvious and 

 consistent view of the subject is, that thejibrin has a natural dis- 

 position to assume the solid form, when no circumstance (either 

 chemical or mechanical) prevents it from exercising this inherent 

 tendency." 



RED PARTICLES. 



It has been observed that, by repeated ablution, the crassamen- 

 tum may be deprived of its red colour, and thereby converted 

 into fibrin alone : the water that has been employed for this pur- 



