228 ON THE NATURE AND PRINCIPLES OF 



dial agent, we must possess a clear and definite 

 knowledge of the seat, the active cause, and the 

 mechanism of absorption. And on these point - 

 there exists among physiologists some difference of 

 opinion. 



The doctrine now generally received, both in this 

 country and on the continent, is that advanced by 

 Magendie and others, who refer the act of absorption 

 to an affinity of the vascular walls for the matters 

 absorbed ; the absorbing power of the capillary 

 membrane being, in their opinion, assisted by the 

 unequal density and viscidity of the fluids situated 

 on either surface. Against this doctrine I have, on 

 a former occasion, advanced various objections : 

 amongst others 



1. That the laws of endosmosis and exosmosis 

 apply only to stagnant fluids, and not to rapidly- 

 moving streams, like those traversing the capillaries. 



2. That it does not explain how, in certain parts 

 of the body, one or other action, namely, either 

 effusion or absorption, wholly preponderates. 



3. That the force which it supposes to operate is 

 not sufficiently active to cause that rapid absorption 

 which we so often witness. 



4. That it leaves us as ignorant as before of the 

 immediate cause of absorption, and is therefore prac- 

 tically useless in guiding our employment of that 

 process as a remedial agent. 



Conceiving, therefore, that neither the porosity 

 of the capillary walls nor the difference in the phy- 

 sical properties of the fluids situated on either surface 

 of that membrane, constituted a satisfactory expla- 



