This information can no longer be doubted in the presence of such evidence as was presented above. This indeed is a fact of far-reaching importance in the understanding of the functional activity of our nervous system, for it is evident that the difference of intensity in the conduction of excitation is not, as has been assumed until now, the result of the conduction of varying strengths of a single excitation in the same elementary fibers, but rather the involvement of a various number of fibers, and that a series of processes which we have to the present attributed to the varying intensities are now to be explained by difference in the duration and form of excitation. This gives us an entirely different but nevertheless a more definite picture of the physiological character of the processes in the nervous system. Still, this question belongs to another chapter of physiology. Here we are interested in the fact that we have in the nerve a form of living substance, in which irritability has reached a high degree, and every stimulus which is at all operative brings about disintegration of all the material involved in excitation, and consequently the property of conductivity in the nerve reaches the state of highest development of all living structures, in that the medullated nerve conducts with the greatest rapidity on the one hand, and on the other, there is no decrement of the velocity and intensity of excitation. All these characteristics: the existence of the “all or none law,” the rapidity of the conduction of excitation, the absence of a decrement in the velocity, the absence of a decrement of the intensity of the excitation wave, the want of the capability of summation of excitation, are all dependent upon one another, for they are the combined expression of one and the same factor, that of the high state of irritability. When the irritability is artificially reduced, then the nerve approaches more and more, depending upon the amount of reduction, to the series of living substances in which we found the protoplasm of the rhizopoda to occupy the other extreme. Between the normal medullary nerve with its maximal, and the pseudopods of the rhizopods with their minimal capability of reaction, we find innumerable gradations in groups of living substances. Whether or not other forms of living substances follow the type of the nerve, whether for example the “all or none law” can be applied to the skeletal muscle as the investigations of _Keith Lucas_[112] seem to show, requires further investigation. [112] _Keith Lucas_: “On the gradation of activity in a skeletal muscle fiber.” Journal of Physiology, Vol. IX, 1888. The same: The “all or none” contractions of the amphibian skeletal muscle-fiber. Journ. of Physiology, Vol. XXXVIII, 1909.