2. It is induced by such an abstraction of natural stimuli as to reduce the system below its healthy grade of excitement, and thereby to induce what Dr. Brown calls direct debility, but what I shall call debility from abstraction. This general debility is the same, whether brought on by the former or the latter causes. When induced by the latter, the system becomes more excitable than when induced by the former causes, and hence an attack of fever is more frequently invited by it, than by that state of debility which succeeds the application of an undue portion of stimulating powers. To this there is an exception, and that is, when the remote causes of fever act with so much force and rapidity as suddenly to depress the system, without an intermediate elevation of it, and before sufficient time is given to expend any part of its strength or excitability, or to produce the debility of action. The system in this state, is exactly similar to that which arises from a sudden reduction of its healthy excitement, by the abstraction of stimuli. This debility from abstraction, moreover, is upon a footing with the debility from action, when it is of a chronic nature. They both alike expend so much of the quality or substance of excitability, as to leave the system in a state in which irritants are seldom able to excite the commotions of fever, and when they do, it is of a feeble nature, and hence we observe persons who have been long exposed to debilitating causes of both kinds, often escape fevers, while those who are recently debilitated, are affected by them, under the same circumstances of exposure to those causes.
That fevers are preceded by general debility I infer from their causes, all of which act by reducing the excitement of the system, by the abstraction of stimuli, or by their excessive or unusual application. The causes which operate in the former way are,
1. Cold. This is universally acknowledged to be a predisposing cause of fever. That it debilitates, I infer, 1. From the languor which is observed in the inhabitants of cold countries, and from the weakness which is felt in labour or exercise in cold weather. 2. From the effects of experiments, which prove, that cold air and cold water lessen the force and frequency of the pulse.
2. The debilitating passions of fear, grief, and despair.
3. All excessive evacuations, whether by the bowels, blood-vessels, pores, or urinary passages.
4. Famine, or the abstraction of the usual quantity of nourishing food.
The causes which predispose to fever by the excessive or unusual application of stimuli are,
1. Heat. Hence the greater frequency of fevers in warm climates, and in warm weather.
2. Intemperance in eating and drinking.