The action of aconitine on the circulation is due to an initial stimulation of the cardio-inhibitory centre in the medulla oblongata (at the root of the vagus nerves), and later to a directly toxic influence on the nerve-ganglia and muscular fibres of the heart itself.
The initial action of digitalis is a stimulation of the cardiac terminals of the vagus nerves, so that the heart's action is slowed.
The initial hastening is due to a stimulation of the vagus terminals in the lung, as it does not occur if these nerves are previously divided.
The nature of this is not very easy to analyse, but as mental depression is closely associated with irritation of the vagus nerve and weakening of the circulation, it seems not at all unlikely that mountain air acts by accelerating the pulse and quickening the circulation, and thus creating a sense of well-being.
Professor Schafer recommended the use of atropine prior to the administration of a general anaesthetic, in cases where the action of the vagus nerve upon the heart is to be dreaded; and there is little doubt of the value of this precaution, which has no attendant disadvantages, in all such cases.