of the narcotized stretch of the nerve plays an important rôle in the obliteration of conductivity. It has been found by the application of a stimulus above the narcotized stretch of nerve, that the longer this stretch is, the less is the reduction of irritability which obliterates the excitation wave reaching this area. Further: The shorter the stretch, the greater must be the reduction in irritability before this result is brought about. (Figure 22.) In other words, the conductivity in the narcotized nerve is dependent upon the length and the irritability of the narcotized stretch. From this observation the important fact is evolved, that the wave of excitation meets with a decrement of its intensity in the narcotized area. This decrement becomes larger as the wave progresses through the involved stretch. Further it is progressively increased as the amount of the irritability is reduced. Finally, when the stretch is long enough, the wave of excitation is obliterated. This important fact has been further established by the experiments of _Boruttau_ and _Fröhlich_,[107] in which they studied the intensity of the current of action, produced by a wave of excitation, from two points in the narcotized stretch. The wave of negative variation, brought about by the excitation, gradually decreases in the narcotized stretch as the electrode is further removed from the point of entrance. Beside a decrement of _intensity_, as the investigations of _Fröhlich_[108] prove, the wave of excitation shows a decrement of the velocity in the narcotized stretch. And it is probable that the wave of excitation extends with _progressive_ reduction in the velocity, corresponding to the decrement of intensity. The work of _Koike_[109] under the direction of _Garten_, in which the conclusion arrived at is that the reduction in the velocity is the same throughout the narcotized area, should not be accepted as conclusive in spite of the delicate method employed. These investigations are extremely difficult, being in the field of the most delicate of present-day methods. The decrement, which the wave of excitation meets with in its progress in the narcotized stretch, makes the conflicting testimony concerning the apparent separation of irritability and conductivity intelligible. It depends entirely upon the length of the narcotized area, and the amount of reduction in irritability on the one hand, and the strength of the stimulus used for testing the irritability on the other, whether the conductivity will disappear _before_ the irritability or _vice versa_. If I test the irritability in the narcotized stretch with a weak stimulus, just slightly _above_ the threshold, then by slight reduction in the irritability complete absence of response occurs, when the same stimulus is applied. This occurs at a time when excitation reaches the narcotized area from above and meets with a decrement so slight that it can pass through