File:General physiology of muscles and nerves (1881) (14591176327).jpg

Identifier: generalphysiolo00rose (find matches)
Title: General physiology of muscles and nerves
Year: 1881 (1880s)
Authors: Rosenthal, I. (Isidor), 1836-1915
Subjects: Physiology Muscles Nerves
Publisher: New York, D. Appleton and company
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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are of a certain medium strength,the neutral point is exactly midway between the twoelectrodes. This electrotonic condition of the nerve may be ex-hibited as in fig. 31. In this n n indicates the nerve,a and h the electrodes, a signifying the anode, h thekathode. The direction of the current within the nerveis, therefore, that indicated by the arrow. In order to7 130 PHYSIOLOGY OF MUSCLES AND NERVES. indicate the change which the excitability undergoes atany definite point in the nerve, let us suppose a straightline drawn at this point at right angles to the longitu-dinal direction of the nerve, and let this line be madelonger in proportion as the change is greater. In order,moreover, to show that the changes which occur towardthe anode are of an opposite tendency to those towardthe kathode, let the line on the anode side be drawndownward, that on the kathode upward. By connectingtogether the heads of these lines a curve is obtainedwhich diagrammatically represents the changes at each
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Fig. 31. Electrotonts under the influence ok currents ofvarying strexgth. point. Of the three curves, the middle represents thecondition under the influence of a current of mediumstrength; the other two curves, indicated, the one byshort lines, the other by a dotted line, represent theconditions under the influence of a strong and of aweak current respectively. These curves show that thechanges are more marked in proportion as the cur-rent is stronger ; that they are most strongly developedexactly at the electrode points; and, finally, that theneutral point, under the influence of currents of dif-ferent degrees of strength, assumes a variable positionbetween the electrodes. MODIFICATION OF THE EXCITABILITY. 131 2. Apart from these clianges in the excitabilitywhich are thus observable while a continuous currentpasses through the nerve, others can also be shown tooccur immediately after the opening of the current.Indeed, the excitability altered in electrotonus does notimmediately rever

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