90 PHYSIOLOGY OP THE CIRCULATION. 



the relative facilities afforded to the entrance of blood 

 into, and its discharge from, that system of vessels. 



5. That the lateral pressure of the blood contained 

 within the arteries is probably equal to its onward 

 pi ( >-ure, so that the arterial blood will press equally 

 in all directions. 



G. That this lateral pressure of the arterial blood 

 is the force which maintains the large arteries in a 

 state of distension, and thus enables their elastic 

 walls so to re-act upon their contents as to be the 

 means of accomplishing various useful purposes in 

 the animal economy. 



7. That the same force acting on the interior of 

 the minute porous arteries causes that slight but 

 constant exudation of certain portions of the blood 

 which is indispensable to the performance of the 

 important functions of secretion and nutrition. 



8. That the blood contained in the commencement 

 of the capillaries being subservient to the same uses, 

 is also made to exercise some lateral pressure, the 

 degree of which varies in different structures, but is 

 probably never quite equal to that of the onward 

 impulse of the same column of blood. 



In conclusion, it may be remarked that as those 

 impediments which limit the rate of the discharge of 

 blood from the arterial system constitute the first and 

 essential cause of all the subsequent phenomena, so 

 the uses served in the body by the existence of these 

 peculiar physical effects arc, with them, clearly re- 

 ferrible to the same apparent imperfection in the 

 mechanism of the circulation. 



