of the frequent stimulus, because each succeeding stimulus occurs in the refractory period of the proceeding. In consequence there is a strong reduction of irritability and reaction is absent. That is, the centers during application of the frequent current are _inhibited_. If cessation of stimulation by frequent shocks takes place, stimulation by slowly succeeding individual shocks becomes effective again in a few seconds. This is the simplest example of the process of inhibition and by it I was led to seek in the refractory period the key of the mechanisms of the process of inhibition. This principle once recognized, further material for the more detailed working out and extension of the theory was gathered from the experiences already gained during the course of the preceding years in the researches on fatigue and the refractory period in the nerve. Here it became apparent that the processes resembling inhibition discovered by _Schiff_ in the nerve preparation and which were studied anew at a later date by _Wedenski_, _F. B. Hofmann_ and _Amaja_ and in part attributed by _Hofmann_ to fatigue of the nerve endings, by _Fröhlich_ to fatigue of the nerve itself, were in principle of the same nature as the central inhibitions themselves. _Fröhlich_,[176] by his analysis of the observations of _Richet_, _Luchsinger_, _Fick_, _Biedermann_ and _Piotrowski_ on inhibition in the claw of the crab, then showed that inhibition can be influenced by the alteration of the intensity of the stimulus as well as its frequency. In a series of experimental researches he could then demonstrate that the widely extended antagonistic inhibitions and other special processes of inhibitions in the centers could on the basis of the same principle be physiologically explained. Here the supposition was confirmed that the development of a relative refractory period plays a very important rôle in the inhibition of the nervous centers. Thus, the relations of the processes of inhibition to the refractory period, once established, their entire field, up to then shrouded in darkness, has gradually in the course of years been completely elucidated. [170] _Gaskell_: “On the innervation of the heart with especial reference to the heart of the tortoise.” Journ. of Physiology, Vol. IV, 1884. [171] _Ewald Hering_: “Zur Theorie der Vorgänge in der lebendigen Substanz.” Lotos IX. Prag 1888. [172] _Meltzer_: “Inhibition.” New York Medical Journal, 1899. [173] _Max Verworn_: “Erregung und Lähmung. Vortrag gehalten in der allgemeinen Sitz. der Gesellsch.” Deutsch. Naturf. u. Aerzte zu Frankfurt a. M. 1896. Verh. d. Ges. Deutsch. Nat. u. Aerzte 1896. [174] _Max Verworn_: “Zur Kenntniss der physiologischen Wirkungen des Strychnins.” Arch. f. Anat. u. Physiol. physiolog. Abth. 1900. The same: “Ermüdung, Erschöpfung and Erbolung.” Ibidem Suppl. 1900.