Abstract
In the present work, stimuli, were given to the vagal nerve of Buf o vulgaris, and thus the inotrophic and chronotrophic effects of the stimuli were investigated under heart irrigation.
If the frequency and duration of the repetitive stimulation were fixed, and when the strength of stimulus approached the threshold, an acceleratory effect, though slight, appeared. Further, even if the strength was set at the maximum, an acceleratory effect appeared when the frequency was extremely lowered. Even under the conditions inducing the above acceleratory effect when right and left vagal nerves are separately stimulated, supressive effect instead of acceleratory effect appeared when stimulus was given to both vagal nerves simultaneously. When acetylcholine was added to the irrigating solution, acceleratory effect appeared if the concentration was low. However, when its concentration became higher, supressive effect appeared. Similar acceleratory effect was recognized when the heart was irrigated with the mixture of atropine and acetylcholine. From the above facts, the authors insist that the vagal nerve contains fibres which act supressively or acceleratory as according to the concentration of acetylcholine, contrary to the theory claimed by various workers that acceleratory fibres are contained in the vagal nerve.
