when passing through intervening ganglion stations so that it has undergone a strong decrement before reaching the responding structure, where an inhibitory effect may be manifested. In this connection it is of interest that the reciprocal “antagonistic reflexes” discovered by _Sherrington_,[197] who recognized their importance in the functional processes of the nervous system, can be explained, as _Fröhlich_ showed, upon this principle of inhibition resulting from weakened excitation. On the basis of numerous investigations in the Göttingen laboratory as well as that of Bonn[198] we have come to look upon the reflex arc in the spinal cord as consisting of the following elements: a neurone in the spinal ganglion, a neurone in the posterior horn and a motor neurone in the anterior horn. This is the most direct route between the point of stimulation and that of the responding organ of a unilateral reflex. (Figure 60.) It is known that the excitation becomes weaker in passing from the entrance of the excitation into the spinal cord to the motor elements of a lower level on the same side or to those on the opposite side. In order to obtain a response a stronger stimulus is necessary. Here the weakening of the excitation as well as the prolongation of the reaction time is brought about by the introduction of intercalated neurones. The reflex arc contains more stations. (Figure 61.) If we accept the most plausible assumption that the central connection of antagonistic muscles possesses like relations, then the effects discovered by _Sherrington_ are self-explanatory. In this case stimulation of the sensory path, which brings about a strong reflex excitation of the motor neurons of the anterior horns controlling a muscle, at the same time stimulates the antagonistic muscle with sub-threshold stimuli. The result of this as shown by the experiments of _Vészi_ is not a motor response of the antagonists, but an inhibition if the motor neurons of the antagonists are at the time in a state of excitation. It is, therefore, understandable that reflex excitation of a muscle under normal conditions of irritability has an inhibitory effect on its antagonist. [197] _Sherrington_: “Experimental note on two movements of the eye.” Journ. of Physiology XVII, 1895. The same: “On the reciprocal Innervation of antagonistic muscles.” Proceed. of the Royal Soc., 1897. [198] _Max Verworn_: “Die einfachsten Reflexwege im Rückenmark.” Zentralblatt f. Physiologie Bd. XXIII. _Tiedemann_: “Untersuchungen über das absolute Refractärstadium und die Hemmungsvorgänge im Rückenmark des Strychninfrosches.” Zeitschr. f. allgem. Physiologie Bd. X, 1910. _Julius Vészi_: “Der einfachste Reflexbogen im Rückenmark.” Zeitschr. f. allgem. Physiologie Bd. XI, 1910. _Oinuma_: “Ueber die asphyktische Lähmung des Rückenmarks strychninisierter Frösche.” Zeitschr. f. allgem. Physiol. Bd. XII, 1911. _Satake_: Not yet published. [Illustration: Fig. 60.