230 ON THE NATURE AND PRINCIPLES OF 



4. The tenuity and porosity of the capillary walls 

 being also demonstrable, it must be admitted as per- 

 fectly possible for the freely-moving streams tra- 

 versing those minute vessels to exercise, through the 

 intervening pores, their power of lateral draught 

 upon any external stagnant fluid. 



As this doctrine refers absorption to the motion 

 of the blood, as its direct and active cause, we are by 

 it at once enabled to understand why absorption in- 

 variably ceases as soon as the circulation through a 

 part is arrested, a fact established by numerous 

 experiments. And, as the absorbing power of the 

 minute blood-streams operates by diminishing the 

 pressure acting on the internal surface of the capil- 

 laries, it is moreover in perfect harmony with those 

 observations of Magendie, in which he found the 

 rapidity of the absorbing process to be increased 

 by vascular depletion. The mode of operation of 

 this important law is indeed rendered more intel- 

 ligible by it than by the general doctrine of absorp- 

 tion propounded by that illustrious physiologist 

 himself. 



It will be seen that the essential difference be- 

 tween the opinion of Magendie on the mechanism of 

 absorption, and that which I have ventured to ad- 

 vance, consists in this circumstance that, whereas 

 he considers the active power employed in this 

 process to reside in the capillary membrane, and that 

 the streams of blood merely carry away the fluids 

 which that membrane has absorbed, I claim for the 

 rapidly moving blood-columns the chief, the prime, 

 the active share in the operation, and regard th 



