APPLIED PHYSIOLOGY 



that the results of such study will add much to our 

 knowledge both of physiology and pathology. Mean- 

 while an attempt will be made here to indicate the 

 applications of the chief facts about the circulation on 

 which physiologists are generally agreed. 



The Arterial Circulation. 



The arteries are both propulsive and conducting tubes. 

 Their function in the circulation is to assist the heart 

 in driving the blood into the capillaries, to induce a 

 continuous flow in the latter, and to maintain a ' head 

 of pressure ' sufficient to allow any part of the body 

 to become flushed with blood when its arterioles are 

 dilated. 



The driving power of the arteries is due to their 

 elasticity, and the elastic element in the arterial coat 

 is most abundantly present and most widely diffused 

 throughout the wall in the large arteries? The blood 

 which is expelled from the heart at each systole of the 

 left ventricle distends the aorta and stretches to some 

 extent its elastic wall ; part of the force of the ventricle 

 is thus converted from an actual into a potential form, 

 and is again liberated in the recoil of the arterial wall 

 during disastole, thus maintaining a continuous ' squeeze ' 

 on the contained blood, and causing the flow of the latter 

 to be constant instead of intermittent, whilst distributing 

 the work of the heart over more than twice the time 

 occupied in its contraction. If the elasticity of the 

 arteries be impaired through disease of their walls, the 

 work of the heart is increased, and enlargement of it 

 follows ; at the same time the flow of blood approximates 



