4J6 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



viz. to 0.256 of a second, the diastole was reduced to 0.213 of a second an 

 enormous decline. 



These results upon the human subject have been confirmed upon animals 

 by experiments in which were registered the movements of a lever laid across 

 the exposed heart ; l or the fluctuations of the pressures within the ventricles. 2 



By whatever means investigated, the ventricular systole is found to be 

 shortened with the cycle, and to be lengthened with it ; the diastole is short- 

 ened or lengthened much more, however. In fact, if the pulse become very 

 frequent, the diastole may be so shortened that the "pause" nearly disap- 

 pears, and the systole of the auricles follows speedily after the opening of 

 the cuspid valves. This signifies that, for a time, the cardiac muscle can do 

 with very little rest, and that effective means exist for a very rapid " charg- 

 ing " of the ventricular cavity when necessary. For the working period of 

 the ventricle, however, a more uniform time is required. For the average 

 human pulse-rate this time of work is decidedly shorter than the time of 

 rest viz. about 0.3 of a second for the former as against about 0.5 for the 

 latter. 



Lengths of Auricular Events and of the Pause. The systole of the 

 auricles is very brief, being commonly reckoned at about 0.1 of a second, as 

 the result of various observations. 3 At the average pulse-rate, therefore, the 

 auricular systole is only about one-third as long as the ventricular, and the 

 length of the auricular diastole is to that of the ventricular as seven to five. 

 Consequently, a cardiac cycle of 0.8 of a second would comprise an auricular 

 systole of 0.1 of a second ; a ventricular systole of 0.3 of a second ; and a 

 pause, or repose of the whole heart, of 0.4 of a second one-half of the cycle. 



Practical Application. The observations above described upon the inter- 

 val between the beginnings of the sounds have a practical bearing upon physical 

 diagnosis ; for they show how faulty are the statements often made which 

 assign regular proportions to the lengths of the sounds and the silences of the 

 heart. The length of the " second silence " must be very fluctuating, as it 

 comprises the longer part of the fluctuating ventricular diastole. The length 

 of the first sound and of the very brief first silence together must be very con- 

 stant, as they nearly coincide with the ventricular systole. 



M. THE PRESSURES WITHIN THE VENTRICLES/ 



We must now approach the study of further details of the working of the 

 ventricular pumps, which details depend for their elucidation upon the measur- 

 ing and recording of the pressures within the ventricles. 



1 N. Baxt : " Die Verkiirzung der Systolenzeit durch den Nervus accelerans cordis," Archiv 

 fur Anatomic und Physiologic, Physiologische Abtheilung, 1878, p. 122. 



J M. von Frey und L. Krehl: " Untersuchungen iiber den Puls," Archiv fur Anatomie und 

 Physiologic, Physiologische Abtheihmg, 1890, p. 31. W. T. Porter: "Researches on the Filling 

 of the Heart," Journal of Physiology, 1892, vol. xiii. p. 531. 



3 H. Vierordt: Daten und Tabellen zum Gebrauchefur Mediciner, 1888, p. 105. 



4 The matters connected with the ventricular pressure-curve may best be studied in the fol- 

 lowing writings, in which citations of other papers may be found : K. Hiirthle, in Pfliiger's 



