A reversed action of the vagus on the mammalian heart / by H.H. Dale, P.P. Laidlaw, and C.T. Symons.

  • Dale, Henry Hallett, 1875-1968.
Date:
1910
Catalogue details

Licence: Attribution 4.0 International (CC BY 4.0)

Credit: A reversed action of the vagus on the mammalian heart / by H.H. Dale, P.P. Laidlaw, and C.T. Symons. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    action of which, as shown by one of us, is in most respects closely similar to that of nicotine, may be substituted in doses of 10—20 rngm., but the effect is more evanescent. Curare will also produce the phenomenon, though in less striking form. We will for convenience take as a type for description an experiment in which nicotine is used. After the preliminary stimulation, for observation of the normal action of the unpoisoned vagus, 1 mgm. of nicotine is injected intravenously. The rise of blood-pressure resulting is allowed to pass off, when it will be found that the heart-beat is somewhat slower than before the nicotine was given. The vagus is again stimulated. If no inhibition is produced during stimulation the secondary coil is moved about 2 cm. nearer to the primary and the stimulus repeated. If inhibition now occurs during the stimulus another dose of 1 mgm. of nicotine is injected. Stimulation of the vagus will now produce either no inhibition during the stimulus, or a mere preliminary slowing for one or two beats, succeeded by a return to the original rate or, in some cases, a slight acceleration beyond it. When the stimulus ceases the rate gradually becomes slower. If no further stimulus is given this after-slowing, or delayed inhibition, gradually passes off and the original rate is regained. If, however, the stimulus be renewed, during the period of slow beating succeeding the first stimulus, the beat, with scarcely noticeable latent period, is rapidly accelerated up to or beyond the initial rate. The faster rate is maintained as long as stimulation is continued, and a further period of more marked slowing appears when the stimulation again ceases. If this process be repeated, the stimulation being in each case renewed before the slowing succeeding the previous Fig. 1. [In this and other reproductions of kymographic tracings the lines of tracing, from above downwards, unless otherwise mentioned, are carotid blood-pressure (mercury manometer), signal key, and clock marking intervals of 2 seconds.] Cat. Paraldehyde. Effect of four successive stimulations of the vagus after 1 mgm. of nicotine. At A and 13 coil at 20 cm.; at C and D coil at 18 cm. 1—2