264 MANUAL, OF PHYSIOLOGY. 



communicated to levers brought into contact with their surface, 

 or by recording graphically the pressure changes which occur 

 within the cavities by introducing into them little elastic sacks 

 filled with air, whence the pressure changes are communicated to 

 an ordinary "tambour." and registered on a smoked surface. 



Of the whole period of the cycle the passive interval or pause 

 is the longest and the most variable, for in ordinary changes in 



FIG. 119. 



Curves drawn on a moving surface by three levers, which are connected 

 with the interior of the heart, viz. : Upper line shows the changes of pres- 

 sure occurring in the right auricle ; centre line shows the pressure changes 

 within the right ventricle ; lower line shows the changes of pressure oc- 

 curring in the left ventricle. (The smoked surface is moved from right to 

 left.) (After Chauvian.) 



the heart's rhythm it is the pause that varies. Next in duration 

 is the ventricular systole, while the shortest is the auricular systole. 

 The following figures give approximately the proportion of time 

 occupied by each part of the cycle in the case of a horse, whose 

 intra-cardiac tension was registered in the manner just referred 

 to, while his heart beat about fifty times in the minute \ 



