THE CIRCULATION OF THE BLOOD 



68 1 



ventricular or aortic pressure, Piper's modification of Frank's apparatus, already 

 referred to, is the most accurate. The changes in volume of the heart are followed 



FIG. 230. EFFECT OF VAUUS STIMULATION UPON THE AURICULAR BEATS AND UPON 



HEART BLOCK. 



Upper tracing 1 , ventricle of turtle, at rest owing to presence of clamp on auriculo-ventricular groove. 



Lower tracing, auricular beats. 



The effect of vagiis stimulation at B is to slow the auricular rhythm, and thus the conducting tissue is enabled to 



transmit the wave of excitation to the ventricle. 

 At A, with weaker stimulation, where the rate is unaffected, but the strength diminished, the ventricle remains 



at rest. 



(Garrey, 1912, p. 456.) 



by some form of plethysmograph, such as the glass cardiometer of Jerusalem and 



FIG. 231. EFFECT OF VAGUS ON CONDUCTION. The ventricle, owing to auriculo-ventricular 

 clamp, follows only each alternate beat of the auricle. Stimulation of the vagus causes 

 complete block, together with diminution in size of auricular beats, without change 

 of rate. 



(Garrey, 1912, p. 454.) 



tarling (1910). The output of blood may be recorded by the method described 

 by Ishikawa and Starling (1912). 



THE NERVOUS REGULATION OP THE HEART BEAT 



Inhibition. The discovery by the brothers Weber of the fact that the heart 

 can be stopped by stimulation of the peripheral ends of the vagus nerves was of 

 such fundamental importance that a few words as to its history are required. 

 It was at the meeting of Italian Scientific Investigators at Naples in 1845 



