206 



A TEXTBOOK OF PHYSIOLOGY 



upon the energy of the heart and upon the peripheral resistance. In 

 the living animal these factors are varying constantly. 



1. With the energy of the heart constant, (a) the peripheral re- 

 sistance may increase, so that the pressure in the aorta becomes greater 



if iy /v /y ii' /; tf if 

 FIG. 110. VELOCITY OF FLOW BY PLETHYSMOGRAPHIC METHOD. (Hewlett.) 



Observations on a single individual : a, Passing from comfort to marked chilli- 

 ness; 6, comfort; c, passing from coolness to beginning perspiration. 



FIG. 111. DIAGRAM SHOWING GENERAL KELATIONS OF THE VELOCITY o F THE BLOOD 

 IN THE ARTERIES, CAPILLARIES, AND VEINS. (Fredericq.) ^__ 



and the velocity less; (6) the peripheral resistance may decrease, the 

 velocity becoming greater and the pressure less. 



2. With the resistance constant, the energy of the heart may 

 increase or decrease, thereby increasing or decreasing both velocity 

 and pressure. 



