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On the cauSe of the coagulation of the fibrin 

 out of the body, many experiments have been 

 made. Blood has been carefully kept at the 

 same temperature, and exposed to air containing 

 no oxygen gas, and alsb in an exhausted receiver- 

 Blood has been frozen rapidly, and again thawed, 

 Or mixed with water ; but, in all these expe- 

 riments, it has, sooner or later, coagulated. The 

 cause of this coagulation remains entirely un- 

 known to us; and a conjecture has been made, 

 that it is only its motion in the vessels which pre- 

 vents it. Some Experimenters have ascribed to 

 the fibrin a vital irritability, in consequence of 

 the tremulous motion perceivable in small drops 

 of blood, when exposed to the effect of the elec- 

 tric column ; but this idea was proved by HEID- 

 MAN to be completely erroneous, and he shewed 

 that the motion proceeded from the shrinking of 

 the fibrin itself, when suddenly coagulated. The 

 chemical examination of the fibrin, the colour- 

 ing matter, and the albumen, lias discovered that 

 these three substances very nearly resemb}e one 

 another in chemical properties ; their composition 

 must therefore be nearly similar, and they are 

 capable either of being changed, by means of 

 small alterations within the living animal, the 



<*ne into the other, or of being employed to 



" 



