While morbid excitement thus pervades generally or partially the sanguiferous system, depression and debility are increased in the alimentary canal, and in the nervous and muscular systems. In the stomach, bowels, and muscles, this debility is occasioned by their excitement being abstracted, and translated to the blood-vessels. I shall now endeavour to illustrate the propositions which have been delivered, by taking notice of the manner in which fevers are produced by some of its most obvious and common causes. Has the body been debilitated by exposure to the cold air? its excitability is thereby increased, and heat acts upon it with an accumulated force: hence the frequency of catarrhs, pleurisies, and other inflammatory fevers in the spring, after a cold winter; and of bilious remittents in the autumn, when warm days succeed to cold and damp nights. These diseases are seldom felt for the first time in the open air, but generally after the body has been exposed to cold, and afterwards to the heat of a warm room or a warm bed. Mild intermittents have frequently been observed to acquire an inflammatory type in the Pennsylvania hospital, in the months of November and December, from the heat of the stove rooms acting upon bodies previously debilitated and rendered excitable by cold and disease. Has there been an abstraction of heat by a sudden shifting of the wind from the south-west to the north-west or north-east points of the compass, or by a cold night succeeding to a warm day? a fever is thereby frequently excited. These sources of fever occur every autumn in Philadelphia. The miasmata which exist in the body at that time in a harmless state, are excited into action, in a manner to be mentioned presently, by the debility from cold, aided in the latter case by the inaction of sleep, suddenly induced upon the system. Again: has the body been _suddenly_ debilitated by labour or exercise? its excitement is thereby diminished, but its excitability is increased in such a manner that a full meal, or an intemperate glass of wine, if taken _immediately_ after the fatigue is induced upon the body, excites a fever: hence the frequency of fevers in persons upon their return from hunting, surveying, long rides, or from a camp life.