PHYSIOLOGY OF THE CIRCULATION. 65 



the two processes of imbibition and absorption do 

 not proceed simultaneously, and with equal degrees 

 of activity, in all the organs of the body, and in 

 every part of the smaller sanguiferous tubes ; for if 

 an equal amount of interchange took place in the 

 animal body wherever two fluids are separated 

 from each other by a thin membranous septum, we 

 should, in this case, continually incur the danger of 

 being poisoned by the re- absorption of excreted 

 noxious matters. 



Srdly. The same viscidity and cohesiveness, 

 which impede so powerfully the passage of the 

 blood through its smaller vessels, must oppose a still 

 greater amount of resistance to that minute separation 

 of its particles which is necessary for the effusion of 

 albumen through the invisible pores of membrane. 

 And the difficulty of applying this power to the 

 explanation of certain of the functions in question is 

 still further increased by the fact that, in expe- 

 riments with viscid fluids, they are found to imbibe 

 much more than they exhale. 



It is true that the ordinary physical properties of 

 membrane are said to be modified in the living body 

 by peculiar physical causes, such as heat, electricity, 

 &c. But from a consideration of these, and other 

 reasons that might be mentioned, it would appear 

 that this doctrine tends to invest the porosity of 

 membrane, considered as a cause of motion, with 

 much greater and more varied powers than it has 

 been experimentally proved to possess ; at the same 

 time that the functions which are referred to those 

 powers remain as unintelligible as ever. Nor can 



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