. Electro-physiology. Electrophysiology. VIM CONDUCTIVITY AND EXCITABILITY OF NERVE 93 excitable near the point where they leave the spinal cord than lower down, and at this last point again than at a still lower place, ; He concluded that "greater force must be employed to evoke a twitch, in proportion as the seat of excitation is further from the spinal origin of the nerve, or (which is the same thing) nearer to its insertion in the ; He found, moreover, in the course of his experiments that certain points in the nerve " are much more excitable than others lyin
. Electro-physiology. Electrophysiology. VIM CONDUCTIVITY AND EXCITABILITY OF NERVE 93 excitable near the point where they leave the spinal cord than lower down, and at this last point again than at a still lower place, ; He concluded that "greater force must be employed to evoke a twitch, in proportion as the seat of excitation is further from the spinal origin of the nerve, or (which is the same thing) nearer to its insertion in the ; He found, moreover, in the course of his experiments that certain points in the nerve " are much more excitable than others lying both above and below them, while others again are characterised by great ; These last he termed " nodal ; The excitation of one point of a nerve at a given strength of current will often discharge a perceptible twitch, while a point 1 mm. off, with the same strength of current, gives no sign of contraction. One point especially. FIG. 163. noticeable in this connection lies in the middle third of the thigh, where the nerve gives off a large branch. Another such is commonly found near the starting-point of the motor roots. Pf!tiger (43) subsequently summed up all these facts in the dictum that " the same stimulus, applied in succession to two different points of the nerve, does not excite the muscle in the same degree ; that excitation is the more effective which is applied at the point most distal to the ; The highest tract alone, next to the section, was relatively less excitable. According to Pfliiger, the curve of excitability drawn from the nerve as abscissa would, therefore, resemble Tig. 163. There is a depression at the point where the branch is given off to the thigh. It is questionable whether the ordiuates of this curve can really be regarded as a direct measure of excitability. It is evident that they express only relative magnitudes of stimulation-effects at the different points of the nerve, two explanations of
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