Abstract
Vagus and sympathetic trunk are said to have two kinds of cholinergic and adrenergic fiber. Employing rabbits, both nerves were exposed and stimulated with varying intensity by use of a Poter type inductorium for the investigation of the cardiac intervals of ECG.
When a weak stimulation was given on the vagus, the interval was shortened while it was prolonged when it was given on the sympathetic trunk. Whereas, when a strong stimulation was placed on the vagus the interval was prolonged, while it was shortened when it was placed on the sympathetic trunk. The reason for this phenomenon is considered to be due to the difference in the threshold of the electric stimulation between the two nerves which contain both kinds of adrenergic and cholinergic fiber. Under the influence of stimulation, moreover, fractional narcosis of vagus and sympathetic trunk was undertaken by the use of 2.0% urethan-Ringer solution. In the case of vagus, the cardiac intervals diminished following the advance in the time of narcosis reaching its minimum 4 to 6 minutes after starting. Thereafter, however, the intervals began to be increased being restored to their normal value by the end of 10 to 12 minutes. The findings of the narcosis of sympathetic trunk were practically the same. When the same expriments . were repeated by use of 1.6% urethan-Ringer solution, the cardiac intervals became minimum 6 minutes after starting narcosis but showed no change thereafter for a considerable period of time. This suggests the intrruption of the cholinergic fiber conduction and the presence of adrenergic one which is considered to be due to the higher susceptibility of cholinergic fiber to the influence of narcotics than adrenergic one.
