Ventricular Systole. 



95 



vagi and the accelerator nerves. The only hopeful method of 

 determining which mechanism is at least predominantly concerned 

 is suggested by the observations of Baxt, Pavlow, Frank and Reid 

 Hunt and others 1 that the accelerator nerves exert a predominant 

 effect on the length of systole, whereas the vagi nerves affect 

 chiefly diastole. This, on superficial examination, of course ap- 

 pears contrary to any mechanical conception of the cardiac 

 regulation, such, for example, as the "law of Uniformity of Be- 

 havior" advanced by Henderson and his coworkers. 2 



It is quite obvious that, if, as appears from volume curves re- 

 corded by many different investigators, the rate of ejection dimin- 

 ishes late in systole, then, on the basis of the uniformity law enunci- 

 ated by Henderson, the length of systole will be only slightly 

 altered during the longer cycles but will be progressively more and 

 more abbreviated in a mechanical way as the heart cycles become 

 shorter and shorter. Inasmuch as vagus section and vagus stimu- 

 lation ordinarily do not alter the heart rate beyond the range 

 where slight variations might be expected, whereas accelerator 

 stimulation quickens the beat so that pronounced shortening of 

 systole might be anticipated, the mere demonstration that acce- 

 lerator stimulation shortens the systole is proof neither of any specific 

 influence of these nerves over ventricular contraction, nor does it prove 

 that the heart deviates in its beat from a mechanical scheme. Only if it 

 can be shown that the periods of systole during accelerator nerve 

 stimulation vary materially from those which may be accounted for 

 on the basis of volume curves, can any inference be drawn as to a 

 selective action of the accelerator nerves on the ventricle. Such proof 

 has, however, not been presented by previous investigators, 

 hence a reconsideration of the subject seemed desirable. 



Methods. — As a criterion of the length of systole, we used the 

 interval elapsing between the first and second heart sounds re- 

 corded from animals by the direct method described by Wiggers 

 and Dean. 3 Sounds were recorded consecutively during the 



1 For literature see Hofmann in Nagel's "Handbuch der Physiologie des Men- 

 schen," 1905, I, 269. 



1 Henderson, Amer. Jour. Physiol., 1909, XXIII, 351. 



'Wiggers and Dean, Amer. Jour. Med. Sciences, 1917, CLIII, 666; Amer. Jour, 

 Physiol., 1917, XLII, 476 also Wiggers, Arch. Int. Med., 1918, XXII, 28. 



