In consideration of this difficulty it seems easier to assign the rôle of mediator of disintegration not to heat but to electricity. Production of electricity is likewise a property of all living substance. Differences of electrical potential between two points may be equalized in the stretch by conduction through the intervening space. Electricity would then fulfil the important conditions, which must be demanded for the form of energy, acting as mediator for the conduction of disintegration from cross section to cross section. [Illustration: Fig. 25. Model of a “Kernleiter.” A, B--Glass tube, with a number of side tubes filled with saline solution, through which a wire is passed. _c_ and _d_--Side tubes with electrodes for stimulation. _e_ and _f_--Tubes for connection with a galvanometer. (After _Hermann_.) ] Physiologists even at an early date, misled by the apparent likeness in the conduction of excitation, especially in the nerve, to that of electricity in a metal wire, regarded both processes as identical. When, however, _Helmholtz_ first demonstrated experimentally the rapidity of the conduction in the nerve, the thought that electrical conduction was concerned, such as takes place in a metal wire, had to be abandoned, as the velocity shows too great a difference in the two cases. [Illustration: Fig. 26. Scheme of the conduction by local electric currents in a “Kernleiter.” (After _Hermann_.)] The observations, on the other hand, on the conductivity in the so-called “core model,” seemed to offer another possibility of attributing the conduction of excitation in the nerve to electric processes. _Matteucci_, later _Hermann_ and finally _Boruttau_[114] have endeavored to apply the results obtained when electricity is introduced in a wire covered with a moist envelope (saline solution), to the explanation of conductivity in the nerve. (Figure 25.) The fact has been shown, that in such a model the application of electricity to a point, as a result of polarization between the moist envelope and the metal, produces a weak local current, which in turn disturbs the electrical potential in the next cross section and consequently a new local current is produced and so on through the whole length of the wire. (Figure 26.) This fact, in connection with the apparent similarity in the differentiation of the axial fibers and peripheral envelope in the nerve, has led _Boruttau_ to apply the principles of conductivity in the “core model” to that of the nerve. Then, however, _Nernst_ and _Zeyneck_ brought forward their theory, according to which the galvanic current is operative as a stimulus in that it brings about an alteration in the concentration of the ions at the junction of two different electrolites which, in turn, produce local currents. _Boruttau_ then dropped the assumption of the existence of a simple physical polarization between the wire and the envelope and replaced it