THE CIRCULATION OF THE BLOOD. 



237 



Fia. 203.— Diagram showing the relative height of the blood-pressnre in different parts 

 of the vascular system (after Yeo). A, heart; o, arterioles ; v, small veins; A, 

 arteries ; C, capillaries ; V, large veins; H, V, representing the zero-line, i. e., at- 

 mospheric pressure ; the blood-pressure is indicated by the height of the curve. 

 The nnmbers on the left give the pressnre approximately, in mm. of mercury. , 



Belative Time occupied by the Various Phases of the Cardiac 

 Cycle.— The old and valuable diagram reproduced below is 

 meant to convey through the eye the relations of the main 

 events in a complete 

 beat of the heart or 

 cardiac cycle. The 

 relative length of the 

 sounds; the long peri- 

 od occupied by the 

 pause ; the duration of 

 the ventricular sys- 

 tole, which it is to be 

 observed is in excess 

 of that of the first 

 sound, are among the 

 chief facts to be noted. 



The tracings of 

 Chauveau and Marey, 

 obtained from the 



heart of the horse, Fio. 204.— Diagram representmg the movements and 

 .... . sounds of the heart durmg a cardiac cycle (after 



which has a very slow sharpey). 



