CHAP, iv.] THE VASCULAR MECHANISM. 



209 



contents may be discharged before the actual systole ends ; but 

 the observations and arguments which we have just related, 

 shew that such an event must be regarded as of exceptional, and 

 not, as has been contended, of normal occurrence. 



Of the smaller secondary variations visible on the systolic 

 plateau, conspicuous in some curves (4, 5, 6, 7 in Fig. 46), various 

 explanations have been given. Into the discussion of these we 

 c-aiinot enter here ; we may however say that in many observations, 

 which we may probably regard as correct, these secondary markings 

 arc identical in the curves of ventricular pressure, of aortic pressure 

 and of the cardiac impulse, or of the change in the outward form 

 of the heart ; the events which cause them tell in the same way 

 on all three. 



Systole 



Diastole 



FIG 54. DIAGRAM OK VENTRICULAR AND AORTIC PRESSURE AND OF THE 

 CARDIAC IMPULSE. HURTIILK. 



We give in Fig. 54 a diagram of the cardiac events according 

 to the exposition which we have just made. The curves previously 

 given were copies of actual curves obtained by experiment ; this 

 is a constructed diagram. The upper curve is the curve of thf 

 cardiac impulse. The middle curve is the curve of pressure in the 



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