Are the intensity differences of sensation quantitative? (1) / by Charles S. Myers.

  • Charles Samuel Myers
Date:
[1913?]
Catalogue details

Licence: In copyright

Credit: Are the intensity differences of sensation quantitative? (1) / by Charles S. Myers. Source: Wellcome Collection.

    8/24 (page 142)
    supply), Lucas1 has been able to prove that the force with which the muscle contracts as a whole is due simply to the number of the indi¬ vidual muscle fibres involved in the contraction. § 4. Next, as regards nerve fibres (which are of more immediate interest)—thanks mainly to the work of Gotch2 and Adrian3—there can be little doubt that the principle holds good for them as it does for muscle fibres. Gotch found (i) that the rate of propagation of the wave of excitation (as shown by the concomitant electrical changes within the nerve trunk) is the same whether the excitation is strong or weaker; and (ii) that the effects obtained by exciting only a portion of the nerve fibres of a nerve trunk closely resemble those evoked by a weaker stimulus applied to the entire nerve trunk. These results suggest that a stronger stimulus to a nerve does not increase the strength of the impulse passing down any one nerve fibre but merely leads to a greater number of nerve fibres being involved. It is corroborated by Gotch’s observation that the electro-motive force in a stimulated nerve trunk always takes the same time to show itself and to reach its height and to disappear, however it be made to differ in amount by employing different strengths of stimulation. Adrian’s experiments point to the same conclusion. He finds that the time needed to narcotize a nerve trunk by alcohol or by other means, so that the passage of the nervous impulse is blocked, depends not merely on the length of the nerve trunk which is narcotized, but on the disposal of that length. For example, if in one preparation 9 mm. of nerve be narcotized, and if in another two lengths of 4-5 mm. of nerve be narcotized, these shorter lengths being separated by a non-narcotized interval of normal nerve, the times taken to narcotize one and to narcotize both of the 4*5 mm. lengths are the same, while they are considerably longer than that taken to narcotize the 9 mm. length. “ The disturbance [corresponding to the nervous impulse] has much greater difficulty in passing one length of 9 mm. of affected nerve than it has in passing two lengths of 4’5 mm.” We must assume “that the disturbance [correspondirig to the nervous impulse] increases in size in the normal area between the two lengths of 45 mm.” And Adrian brings forward evidence that “ the increase of a subnormal disturbance on entering normal nerve tissue is certainly complete before the disturb¬ ance has travelled 5 mm. in the normal region, and it may be instan¬ taneous ”; and that “ the disturbance increases to a fixed size on entering 1 J. of Physiol. 1908-9, xxxviii. 113-133. 2 Ibid. 1902, xxvii. 395-416. 3 Ibid. 1912, xlv. 389-412.