[Examination of vagus nerve tonus in various animal species]

Experiments on pigeons, guinea pigs, rats, cats, rabbits, and dogs showed that tachycardia occurring after ligation of vagus nerves was caused by dissection of their inhibitory tone. They failed to confirm the hypothesis of the sympathetic origin of vagotomic tachycardia. The vagus nerve through the cholinergic neurons may exert heterodirectional (inhibitory and stimulating) effects on the performance of the heart only in animals with its tone. In the absence of tone, there may be only inhibition and stimulation was only short-term as a result of cessation of the inhibitory effect--postvagal tachycardia. The earlier established idea of the inhibitory tone of the vagus nerve remains valid.