We ascertain whether a drug has a stimulating action on the accelerating nerves of the heart by cutting both vagi and then injecting the drug. If it quickens the heart still further, we assume that it does so by stimulation of the accelerating nerves. This experiment, however, does not enable us to decide whether the stimulation has affected the accelerating nerves passing to the cardiac ganglia from the central nervous system or those passing from the endocardium.