[3] Perhaps there is no greater enemy to the life of man than cold. Dr. Sydenham ascribes nearly all fevers to it, particularly to leaving off winter clothes too soon, and to exposing the body to cold after it has been heated. These sources of fever, he adds, destroy more than the plague, sword, or famine.--_Wallis's edition, vol. I. p. 357._ To this proposition there is a seeming objection. Cold, sleep, immoderate evacuations, and the debilitating passions of grief and fear (all of which abstract excitement) appear to induce fever without the interposition of a stimulus. In all these cases, the _sudden_ abstraction of excitement destroys the equilibrium of the system, by which means the blood is diverted from its natural channels, and by acting with preternatural force in its new directions, becomes an irritant to the blood-vessels, and thus a stimulating and exciting cause of fever. When it is induced by cold alone, it is probable so much of the perspirable matter may be retained as to co-operate, by its irritating qualities, in exciting the fever. VI. There is but one fever. However different the predisposing, remote, or exciting causes of fever may be, whether debility from abstraction or action, whether heat or cold succeeding to each other, whether marsh or human miasmata, whether intemperance, a fright, or a fall, still I repeat, there can be but one fever. I found this proposition upon all the supposed variety of fevers having but one proximate cause. Thus fire is a unit, whether it be produced by friction, percussion, electricity, fermentation, or by a piece of wood or coal in a state of inflammation. VII. All ordinary fever being seated in the blood-vessels, it follows, of course, that all those local affections we call pleurisy, angina, phrenitis, internal dropsy of the brain, pulmonary consumption, and inflammation of the liver, stomach, bowels, and limbs, are symptoms only of an original and primary disease in the sanguiferous system. The truth of this proposition is obvious from the above local affections succeeding primary fever, and from their alternating so frequently with each other. I except from this remark those cases of primary affections of the viscera which are produced by local injuries, and which, after a while, bring the whole sanguiferous system into sympathy. These cases are uncommon, amounting, probably, to not more than one in a hundred of all the cases of local affection which occur in general fever. In my 4th proposition I have called the action of the arteries _irregular_ in fever, to distinguish it from that excess of action which takes place after violent exercise, and from that quickness which accompanies fear or any other directly debilitating cause. The action of the arteries here is _regular_, and, when felt in the pulse, affords a very different sensation from that _jerking_ which we feel in the pulse of a patient labouring under a fever.