[135] _Langendorff u. Winterstein_: “Beiträge zur Reflexlehre.” Pflüger’s Arch. Bd. 127, 1909. [136] _Fr. W. Fröhlich_: “Beiträge zur Analyse der Reflexfunction des Rückenmarks mit besonderer Berücksichtigung von Tonus, Bahnung und Hemmung.” Zeitschrift f. allgem. Physiologie Bd. IX, 1909. [137] _Julius Vészi_: “Der einfachste Reflexbogen im Rückenmark.” Zeitschr. f. allgem. Physiologie Bd. XI, 1910. If the existence of the refractory period is based on the fact that during the time of and subsequent to an excitation the quantity of substances necessary for disintegration is decreased and that of the breaking down products increased, and if it is limited by the restitution of the substances required for decomposition and the elimination of the disintegration products, its duration must be dependent upon the length of these processes. All factors which lessen the decomposition and hasten the metabolic self-regulation must, therefore, shorten its duration. This is completely confirmed by experimental investigations. As can be understood, the factors of special interest for us are those which influence the duration of the refractory period in the physiological occurrences of the organism. One of these factors is temperature. As we know, the rapidity of chemical reactions increases with ascending and decreases with falling temperature. As in the disintegration as well as in the restitution, processes are chemical in nature, it is to be expected that the duration of the refractory period is influenced in like manner by temperature. Indeed, _Kronecker_[138] found some time ago that in the isolated frog’s heart a much more frequent rhythm of stimulation is effective at a higher than at a lower temperature. When the heart is stimulated at a temperature of 11–12° C. with twelve rhythmical induction shocks in the second, every stimulus is operative and produces a systole. If a stimulus of the same frequency is used at a temperature of 5° C., the heart responds merely to every second stimulus. This shows that the refractory period is of longer duration at a lower than at a higher temperature. [138] _H. Kronecker_: “Das charakteristische Merkmal der Herzmuskelbewegung.” Beiträge zur Anatomie and Physiologie als Festgabe Carl Ludwig zum 15 October 1874 gewidmet. Leipzig 1874.