432 Bayliss an4 Starling, 



wave would be less than the first, whereas it is usually greater (i. e., 

 the curve is anacrotic). In the third place, if these were instrumental 

 vibrations, their period would be Yes of a second, as shown above, 

 where as it is much longer, about Yso of a second, in fact; and the 

 interval between the first and second is moreover considerably less 

 than that between the second and third. This last point is shewn 

 best in Fig. 6, where the drum was moving at a slightly greater speed 

 than in the other figures; unfortunately, the tuning fork was not in 

 position, so that we must give the measurements in distance, the 

 interval between the first and second waves being 3 mm, and that 

 between the second and third being 4 mm. 



In Fig. 4 (vagus excitation) and Fig. 6, there is seen the wave 

 on the descending limb, first noticed by Chauveau and Marey, and not 

 obtained in the dog until recently (by Frédéricq and Hürthle with 

 improved methods of registration). 



When the heart is beating slowly (Figs. 4 and 5), there is a 

 well-marked negative pressure in the ventricle at the commencement 

 of diastole. In amount this is about 23 mm Hg. 



The wave following the negative pressure in Fig. 4 is no doubt 

 an auricular beat, since it bisects the interval between the undoubted 

 auricular beats preceding the two ventricular beats. In this case the 

 ventricle was only beating in sequence to each alternate auricular i 

 contraction, as so often happens in vagus excitation. 



One point remains to be mentioned. Von Frey's explanation of I 

 the origin of the plateau, viz., that the sound was inserted too far 

 into the ventricular cavity and was obstructed by the ventricular walls ; 

 before the systole was completed^), certainly does not hold good for i 

 our experiments, since our catheter tube was only passed just beyond 

 the aortic valves and its withdrawal by only about Y2 ^11 ^^^^^^ ^^^^ 

 sufficient to convert the ventricular curve into an aortic one. 



The Aortic Pressure Curve. ' 



The aortic, like the intraventricular pressure curve, is sometimes 

 anacrotic (Figs. 7—10. Plate XX), but it always shows the three | 



^j Frey und Krehl, Arch, für Auat. und PliysioL, Physiol. Abteilung. 1890. 

 pp. 37—42. I 



