Bloodletting, it must be observed, is not the sole means of accomplishing such a change in the constitution of the blood. We can duce a similar effect by exciting one or all of the secretions which are thrown off by the body. Secretion is performed at the cost of the blood, which supplies both of its elements —the solid and the fluid part. The more the secretion eliminated abounds in solid parts or matters formed at the cost of the solid constituents of the blood, the more is the blood impoverished in these elements—the more is its mass of globules diminished. Absorption then begins, as in the preceding case, to make up the quantity of circulating fluid ; and if this faculty have only fluids to work upon, it is evident that, as in the case of bloodletting, the blood will become more serous than before. The perspiration and the alvine secretions act in this manner, and nature makes use of these, especially of the former, to temper the burning heat of paroxysms of fever. Art but imitates nature in the treat ment of acute diseases ; she strives to procure action of the skin, and especially action of the bowels. The use of diaphoretics and pur gatives is therefore plainly borne out by the principles which have been laid down. The alvine secretions are those especially that carry off the largest proportion of solid matters from the blood, and which therefore, when excited, prove the most permanently efficient in keep ing down the temperature of the body. There is another important reason for preferring the intestinal canal to the skin as the means, in the generality of instances, of reducing tem perature in the treatment of disease, which ought not to be lost sight of : this is, that we can excite the intestinal evacuations to a great extent witbout arousing the circulating system in almost any degree; very different from what occurs when we attempt to unload the vessels by the way of the cutaneous exha lants, in which it is generally impossible to produce abundant diaphoresis without arous ing the heart and arteries to unwonted action as a preliminary. Purgative medicines, there fore, next to the direct abstraction of blood, are the most potent means of tempering the heat of the body by modifying the consti tution of the blood. Nothing that influences the economy can have an effect in one direc tion only. It were foreign to our purpose, however, to enter upon any other than that which bears immediately upon our subject.
There is another natural process analogous in its effects, which the preceding consider ations place in a new point of view. This is the influence of diet and regimen. Low diet does not act merely in preventing the ex citement which always follows the ingestion of solid food ; it further alters the constitution of the blood. This fluid, receiving a more scanty supply of solid matters, continues nevertheless to supply the natural secretions as before, and consequently very speedily undergoes by this alone a diminution in the proportion of its globules, in the direct ratio of the duration of the system of spare diet. Low diet is there fore a means which acts in the same way as bloodletting and purging, with this difference however, that it is slower in its operation, and in the first instance less marked in its effects.
This, therefore, is the slowest and least efficaci ous of the immediate means of reducing tem perature when employed alone, although its conjunction is indispensable to the success of any of the others.
Of all these means, one only is the proper effect of art, namely, the application of cold ; the others are processes of the same nalura medicatrix, and processes which we merely imitate. These act directly in modifying the constitution of the blood, and thus definitively influence the nervous system. The other exerts its influence directly on the nervous system, in calming the excitement or violent action which it has engendered in the sangui ferous system, and those that depend on it.
The application of heat becomes necessary in morbid states the reverse of those that have just been discussed. The proper employ ment of this means depends especially on two general principles bearing upon animal heat, which we have considered above. 1st, The one is, that the economy has the capacity of bearing heat in the same proportion as the function of respiration is extended. In those cases in which this function is limited, or, what comes to the same thing, where any part that requires an accession of heat is indiffer ently supplied with arterial blood, it is neces sary to be extremely cautious in its applica tion. 2nd, The other, that the effects of ex ternal heat are not confined to the simple interval during which it is applied, but remain after it has been removed, and even increase the faculty of producing heat. The applica tion of warmth is therefore not merely pallia tive or supplementary of lost heat ; it has further a directly remedial influence, which may even be excited in excess. When the lesion of the calorific faculty has been great, without much or any organic lesion, other means of greater force than those usually re sorted to by art, or employed by nature in such circumstances, must be called in to assist. Art has happily discovered what seems the most effectual means of winding up the nervous system, and enabling the calorific faculty to be re-established in its normal con dition. This means is quinia, the first of tonics. This powerful medicine is conse quently never administered in acute diseases until all violence of action has ceased, and the functions have resumed their habitual rythm. We find that the action of this medicine is exerted directly upon the nervous system from this, that it seems to have no effect on the secretions, or when it does in fluence these, we are convinced by the tri fling amount of the effect, that it is not through them that the cure is accomplished. As it acts during the intermission, by restoring the normal production of heat, we have no reason to expect the phenomena which characterize the fit—the shivering, &c.; and then the vio lent reaction which we have in the hot stage becomes useless, and in fact is no longer ob served.