MECHANISM OP ABSORPTION. 55 



circulation, in favouring absorption, is to be ex- 

 plained. 



According to the laws regulating the transmission 

 of stagnant fluids through membranes, exosmosis 

 and endosmosis should be continually occurring 

 through the coats of the vessels of the living body ; 

 and there undoubtedly analogous processes do take 

 place. But it appears to me highly important that 

 we should ascertain how far those laws are modified 

 when one or both fluids are in a state of motion. 

 However, Magendie, and all succeeding physiologists 

 who have adopted his opinion, suppose that the ex- 

 ternal fluid permeating the membranous coats makes 

 its way to the internal surface of the blood-vessel, 

 and is then swept on by the current of the blood. 



According to this hypothesis the chief part of the 

 process of absorption is made to reside in some pe- 

 culiar power possessed by the membranous coats of 

 the vessels, the circulating fluid itself being quite 

 a secondary agent, though, as above stated, its mo- 

 tion is necessary for the action of any poison on the 

 system at large. 



To prove the truth of his opinion, Magendie per- 

 formed an experiment. He passed a stream of water 

 through a portion of carotid artery and jugular vein, 

 having previously applied strychnine to the exterior 

 of the vessels. In a few minutes the water dis- 

 charged had acquired the bitter taste of the poison. 



Now this experiment, considered by itself, throws 

 little light on the mechanism of absorption ; it 

 merely proves that while a stream traverses a mem- 

 branous tube any soluble matters placed on the 



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