. Electro-physiology. Electrophysiology. 168 ELECTRO-PHYSIOLOGY , HAP. of nerve, the breadth of the glass tube, is covered by it. It is advisable to bring the whole preparation, with the electrodes, into a moist chamber, to preserve the free end of the nerve from drying in prolonged experiments. The muscle is connected with a writing-point outside the chamber by means of a thread wound round a cylinder, by which the changes of form are recorded on the cylinder of a kymograph rotating at varying rapidity. On exciting with weak currents a plain increase of effect from closure will be observed af
. Electro-physiology. Electrophysiology. 168 ELECTRO-PHYSIOLOGY , HAP. of nerve, the breadth of the glass tube, is covered by it. It is advisable to bring the whole preparation, with the electrodes, into a moist chamber, to preserve the free end of the nerve from drying in prolonged experiments. The muscle is connected with a writing-point outside the chamber by means of a thread wound round a cylinder, by which the changes of form are recorded on the cylinder of a kymograph rotating at varying rapidity. On exciting with weak currents a plain increase of effect from closure will be observed after a few minutes, if the current leaves at a part of the nerve treated with NaCl. The twitches, how- ever, soon become tetanic, and after a short time there is a marked. FIG. 188.—Effect upon excitability, of local treatment with salt at the kathode. Transition from descending closure twitch to closure tetanus. tetanus (Fig. 188) at every closure of the current in the direc- tion indicated, which at first disappears again completely on opening the circuit, but is persistent at later stages of the NaCl effect, when of course further observations are impossible. At a time when, after application of NaCl to the electrode proximal to the muscle, a weak descending current already discharges a vigorous closure tetanus, the closure of the same current in the opposite direction yields, as a rule, only a simple twitch, which cannot in time-relations or magnitude be distinguished from the closure twitches discharged under the same experimental con- ditions by local application of NaCl. This fact is by no means without interest, since it shows that, as regards the magnitude of final result from the excitation of any point of the nerve, it is a matter of indifference whether the " excitatory wave " discharged passes through a tract of nerve already in a condition of heightened excitability, or no. The opening of weak ascending currents has, as a rule, no effect after local app
Size: 2542px × 983px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bo, bookcentury1800, bookdecade1890, bookpublisherlondonmacmillan
