by the assumption of an alteration in the concentration of the ions at this position. Thereby the “core model explanation” was already altered in principle, in that only the differentiation of a central fibrilla and a peripheral enveloping substance was appropriated. It seems to me that this factor can likewise be considered as completely dispensable and may, therefore, be omitted; thus nothing remains of the “core model explanation” of the conduction of excitation in the nerve. [114] The enormously extensive literature on this subject up to the most recent date is quoted in _Cremer_: “Die allgemeine Physiologie der Nerven.” In _Nagels_ Handbuch der Physiologie des Menschen, Bd. IV, 1909. Braunschweig. The results of continually increasing numbers of investigation in recent times make it appear almost as a certainty that the elementary fibrillæ in the axis cylinder are nothing else but skeletal substances. _Wolff_,[115] _Verworn_[116] and others have first expressed the view that the neurofibrillæ must be looked upon as skeletal fibers for the soft neuroplasm, and more recently _Lenhossek_[117] and especially _Goldschmidt_[118] have confirmed this assumption in detail. _Goldschmidt_ has shown by extensive comparative studies of cell mechanism the rôle played by the neurofibrillæ in a physical connection as internal skeletal formations, and has proved at the same time, in complete unanimity with other investigators, their continuity with other undoubted skeletal fibrillæ. By this the numerous combinations and speculations of _Apathy_ and _Bethe_ concerning the part taken by the neurofibrillæ have been rendered untenable. In no case is there the slightest justification to regard the apparent “Kernleiterstructur” of the nerve as the principal condition for the process of conductivity, for should we dispense completely with this point for the theory of the conduction of the nerve, we can obtain, solely by the aid of the facts known today in physical chemistry, the foundations for a theory of the conductions of excitation which not merely renders the specific case of the conduction of the nerve intelligible, but contains at the same time the principles of the process of the conduction of excitation for all living substance. [115] _M. Wolff_: “Ueber die fibrillaren Structuren in der Leber des Frosches.” Anatom. Anzeiger Bd. 26, 1905. [116] _Max Verworn_: “Bemerkungen zum heutigen Stand der Neuronlehre.” Medicin. Klinik, Jahrg. IV, 1908. [117] _M. v. Lenhossek_: “Ueber die physiologische Bedeutung der Neurofibrillen.” Anatom. Anzeiger Bd. 36, 1910. [118] _Richard Goldschmidt_: “Das Nervensystem von Ascaris lumbricoides und megalocephala. Ein Versuch in den Aufbau eines einfachen Nervensystems einzudringen.” III Teil. Festschrift zum 60 Geburtstage Richard Hertwigs Bd. II, 1910, Jena. [Illustration: Fig. 27.