[Footnote 62: E. Mach: Sitzungsberichte der K. Akademie der Wissenschaften, vol. 47 (2), p. 43, 1863; and in the tables, figs. 48-53.] [Footnote 63: L. Hill, in Schaefer's Text-book of Physiology, vol. 2, p. 111, 1902. The same opinion maybe found in Hermann's Lehrbuch der Physiologie (12th ed.), p. 79, 1900. "Ihre (der dicrotischen Wellen) Erklärung ist noch nicht widerspruchsfrei gestellt." In the previous editions different views were given, and this critical doubt may be regarded as the final outcome of the investigations of almost half a century.] [Footnote 64: Sudden compression is the most convenient way of producing a wave in a liquid which is enclosed in an elastic tube. It was used already in the first experiments on the propagation of these waves. (E. H. Weber: Anwendung der Wellenlehre auf die Lehre vom Kreislaufe des Blutes und insbesondere auf die Pulslehre, Berichte d. Kgl. Sächsischen Ges. d. Wissenschaften, Math.-Phys. Cl., p. 177, 1850.)] [Footnote 65: Bayliss and Starling: On the form of the intraventricular and aortic pressure curves obtained by a new method, Intern. Monatsschrift f. Anatomie u. Physiologie, vol. 11, pp. 426-435, 1894.] [Footnote 66: W. T. Porter: A new method for the study of the intraventricular pressure curve, Journal of Experimental Medicine, vol. 1, pp. 296-303, 1896. A similar method was used by O. Frank: Ein experimentelles Hülfsmittel für die Kritik der Kammerdruckkurven, Zeitschrift f. Biologie, vol. 35, pp. 478-480, 1897.] [Footnote 67: O. Frank, _loc. cit._, p. 480.] [Footnote 68: Huerthle: Beiträge zur Hämodynamik, VIII, Zur Kritik des Lufttransmissionsverfahrens, Arch. f. d. ges. Physiologie, vol 53, pp. 281-331, 1892.] [Footnote 69: The special assumption on the rate of outflow is by no means essential for the following theory. Two other possible assumptions are mentioned in the author's "L'Analyse des Sphygmogrammes," and others may be found easily. Every one of these theories is equally probable as long as no experimental evidence can be brought forward. The assumption that the rate of outflow through the arterioles is uniform has the merit that it is the simplest and that it can be deduced from considerations of the average directions of tubes which split up in "every" direction.] [Footnote 70: A detailed discussion shows that four different cases are possible, but this distinction is of minor importance for the purpose of this paper. The distinction holds that the movement is either periodic or aperiodic.] [Footnote 71: Edgren: Kardiographische und sphygmographische Untersuchungen, Skandinavisches Archiv f. Physiologie, vol. 1, pp. 88-91, 1889; Fredericq: Vergleich der Stoss und Druckcurven der rechten Herzkammer des Hundes, Centralblatt f. Physiologie, vol. 7, p. 770, 1893; Einthoven und Geluk: Die Registrierung der Herztöne, Archiv f. d. Ges. Physiologie, vol. 57, p. 631, 1894.]