134 



PBACTICAL PHYSIOLOGY 



with anything like the velocity of the pulse-wave. In the vascular 

 system the pulse-wave travels in the arteries 8 metres per second, while 

 the blood travels J-metre. 



The resistance to flow is chiefly situated in the arterioles, where the 

 velocity is high. It is due to the friction of the moving concentric layers 

 of blood against one another, and against the stationary layer .which 

 wets the walls of the blood vessels. It is proportional to the surface 

 area, to the viscosity of the blood nearly proportional to the square 



To 

 Manometer 



To 

 Manometer 



=1= 



To 

 Mmometer 



FIG. 133. Artificial schema of the circulation. 



of the velocity of flow, and inversely proportional to the sectional 

 area of the vessel. In the arterioles the velocity is high, the total wall 

 surface wet by the blood great, the sectional area of each arteriole very 

 small. 



In the schema the resistance is increased by diminishing the sectional 

 area of the arterioles and increasing the velocity of flow. Owing to 

 the resistance to the outflow the arteries are expanded by each systolic 

 output, and the elasticity of their walls comes into play, causing the 

 outflow to continue during the succeeding diastole of the heart. The 

 larger part of the kinetic energy of the systolic outflow is stored up as 

 potential energy by the stretched arteries, and converted into kinetic 

 energy during diastole. 



Stop the pump, the pressures in the manometers fall to the same 

 level. Start the pump again. The fluid is taken from the vein and 



