Page:The Harveian Oration,1902.djvu/22

 The most epoch-making discovery in reference to the innervation of the heart was the observation of the brothers Ernst and Edward Weber in 1845, that electrical irritation of the vagus caused the heart to beat more slowly or to stop altogether for a time in the state of diastole. This fact was an altogether new one in neurology and has been far-reaching in its consequences and application. Through the vagi the cardiac centres exercise a more or less constant restraining influence, so that when they are cut the heart beats more quickly. This effect was observed both by Willis and Richard Lower, but both regarded it as essentially of a paretic nature due to cutting off the main stream of animal spirits. Willis says:—

"And here it may be rightly inquired into whether the pulse of the heart so necessarily depends on the influence of the animal spirits through the nerves, that it being hindered, the action of the heart should wholly cease? For the decision of this we once made a trial of the following experiment on a living dog. The skin about the throat being cut longways, and the trunk of both the wandering pair being separ-