5. Certain causes which act by over-stretching a part, or the whole of the body, such as lifting heavy weights, external violence acting mechanically in wounding, bruising, or compressing particular parts, extraneous substances acting by their bulk or gravity, burning, and the like[1]. The influence of debility in predisposing to fevers is further evident from their attacking so often in the night, a time when the system is more weak than at any other, in the four and twenty hours. [1] Cullen's First Lines. II. Debility being thus formed in the system, by the causes which have been enumerated, a _sudden_ accumulation of excitability takes place, whereby a predisposition is created to fever. The French writers have lately called this predisposition "vibratility," by which they mean a liableness in it to be thrown into vibrations or motions, from pre-existing debility. It is not always necessary that a fever should follow this state of predisposition. Many people pass days and weeks under it, without being attacked by a fever, by carefully or accidentally avoiding the application of additional stimuli or irritants to their bodies: but the space between this state of predisposition, when it is recent, and a fever, is a very small one; for, independently of additional stimuli, the common impressions which support life sometimes become irritants, and readily add another link to the chain of causes which induce fever, and that is, III. Depression of the whole system, or what Dr. Brown calls indirect debility. It manifests itself in weakness of the limbs, inability to stand or walk without pain, or a sense of fatigue, a dry, cool, or cold skin, chilliness, a shrinking of the hands and face, and a weak or quick pulse. These symptoms characterize what I have called in my lectures the forming state of fever. It is not necessary that a paroxysm of fever should follow this depressed state of the system, any more than the debility that has been described. Many people, by rest, or by means of gentle remedies, prevent its formation; but where these are neglected, and the action of stimuli, whether morbid or natural, are continued, IV. Re-action is induced, and in this re-action, according to its greater or less force and extent, consist the different degrees of fever. It is of an irregular or a _convulsive_ nature. In common cases, it is seated primarily in the blood-vessels, and particularly in the arteries. These pervade every part of the body. They terminate upon its whole surface, in which I include the lungs and alimentary canal, as well as the skin. They are the outposts of the system, in consequence of which they are most exposed to cold, heat, intemperance, and all the other external and internal, remote and exciting causes of fever, and are first roused into resistance by them.