[145] _Bowditch_: “Ueber die Eigenthümlichkeiten der Reizbarkeit, welche die Muskelfasern des Herzens zeigen.” Arbeiten aus der physiologischen Anstalt zu Leipzig VI Jahrgang 1871, Leipzig 1872. [146] _Tiegel_: “Ueber den Einfluss einiger willkürlichen Veränderungen auf die Zuckungshöhe des untermaximal gereizten Muskels.” Arbeiten aus der physiol. Anst. zu Leipzig X Jahrgang 1875, Leipzig 1876. [147] Minot: “Experiments on tetanus.” Journ. of Anat. and Physiol. Vol. XII. [148] _Fr. W. Fröhlich_: “Ueber die scheinbare Steigerung der Leistungsfähigkeit des quergestreiften Muskels im Beginn der Ermüdung. (Muskel Treppe), der Kohlensäurewirkung und der Wirkung anderer Narcotica (Aether, Alkohol).” Zeitschr. f. allgem. Physiologie Bd. V, 1905. [149] _Frederic S. Lee_: “The cause of the Treppe.” Americ. Journ. of Physiol. Vol. XVIII, 1907. [150] _Alexander Rollet_: “Ueber die Veränderlichkeit des Zuckungsverlaufs quergestreifter Muskeln bei fortgesetzter periodischer Erregung und bei der Erholung nach derselben.” Pflügers Arch. Bd. 64, 1896. [Illustration: Fig. 34. Series of muscle curves graphically recorded one over the other, showing the retardation in the course of contraction with increasing fatigue. (After _Rollet_.) ] Exactly similar conditions as those of the muscle are seen in the central nervous system. The reflex contraction of the triceps of the frog produced by stimulation of the central end of the sciatic nerve with single induction shocks demonstrates clearly as _Ishikawa_[151] has proved in certain stages of fatigue, an increase in height and a strong relaxation which does not depend upon the fatigue of the muscle but on that of the centers. If the fatigue is greater, the height of the contraction then decreases, whereas the extension of the course of relaxation increases further. The possibility of fatigue of the muscle during these experiments was, of course, precluded by proper precautionary measures. Irritability and the course of excitation in fatigue of the centers show exactly the same alterations as developed in fatigue of the muscle. The processes of oxydative breaking down are retarded more and more with increasing fatigue, that is, fatigue is characterized by exactly the same processes as is the prolongation of the refractory period by the deficiency of oxygen, and likewise in fatigue this retardation of the oxydative disintegration processes is conditioned by the relative deficiency of oxygen. This is shown by the rôle played by oxygen in recovery after fatigue. [151] _Hidetsurumaru Ishikawa_: “Ueber die scheinbare Bahnung.” Zeitschr. f. allgem. Physiologie Bd. XI, 1910.