286 PHYSIOLOGY. 



elasticity of the arteries. The ventricle is able to send out a quantity 

 of blood with much less expenditure of force. 



The circulation in the arteries is under the dependence of two 

 very important properties of these vessels : elasticity and contrac- 

 tility. The nature of the movement of the blood, has, therefore, been 

 transformed in its course from the heart to the extremities. It is 

 now known that this transformation is due in the main to the elas- 

 ticity of the arteries. 



Each new entrance of the blood into the arterial system must 

 necessarily be accompanied with a dilatation of the whole vascular 

 tree. As soon as the three ounces of blood ejected from the left 

 ventricle has penetrated into the aorta, as it flows through the capillary 



Fig. 91. Marey's Intermittent Afflux Apparatus. (LAHOUSSE.) 

 A, Force-pump. B, Tube with rigid walls. C, Tube with elastic walls. 



system, there results a contraction of the whole arterial system until 

 the moment when a new output of blood arrives. 



It has been ascertained experimentally that the arterial vessels 

 are much more elastic in the direction of their axis than in their 

 transverse diameter. It is in the former direction then that increased 

 capacity of the arteries will especially occur. When the trunks of 

 the arteries are of considerable extent the elongation may become 

 apparent to the naked eye, as in the temporal artery, while there does 

 not seem to exist any increase in the transverse direction of the same 

 vessel. 



According to Weber, the principal role of arterial elasticity is to 

 establish, between the arterial and venous tensions, a difference which 

 is indispensable to the movement of the liquid within the circulatory 

 apparatus. In addition, the uses of vascular elasticity may be said to 



