FUNCTION OF THE VALVES. 



123 



Each half or side of the heart, through the action of its 

 valves, may be 

 compared with a 

 kind of forcing 

 pump, like the 

 common enema- 

 syringe with two 

 valves, of which 

 one admits the 

 fluid on raising 

 the piston, but 

 is closed again 

 when the piston 

 is forced down ; 

 while the other 

 opens for the es- 

 cape of the fluid,' 

 but closes when 

 the piston is 

 raised, so as to 

 prevent the re- 

 gurgitation of the 

 fluid already 

 forced through it. 

 The ventricular 

 dilatation is here 

 represented by 

 the raising-up of 

 the piston ; the 

 valve thus admit- 

 ting fluid repre- 

 sents the auriculo- 

 ventricular valve, 

 which is closed 



* Fig. 36. Diagrams of valves of the heart (after Dalton). 



