Obstruction to the circulation increases its activity; for the vessels are excited by distention, and, when the extent of the circuit is curtailed, those behind act with greater energy. Thus tying up the finger will bring on inflammation in the whole hand. While, then, the accumulated irritability first excites the sensorial power, the spasm contributes to accelerate the circulation; and, in the weakened state of the brain, this increased action diminishes the nervous power in other parts of the body. The paroxysm is closed by the spasm relaxing, since there is no instance of continued spasm, except by continued irritation; and the spasm relaxes at different periods by the laws established in the system, which we explained under the article Diaeta. It is a fact, that fevers attack at the periods of the regular exacerbation, and yield at the times these constantly regular paroxysms are resolved. Every paroxysm is either resolved or remits at the end of twenty-four hours; the diurnal revolution, established by the regularly returning periods of sleep and watching; the discharge of the alvine excretions, of appetite, etc. It is not so easy to assign a reason why, in a fever consisting of successive paroxysms, the disease should yield only at a given time; except that a septenary period prevails, at the end of which the solutions of the usual exacerbations are more perfect. Of this, however, we have no certain evidence.

It appears singular that increased action should ever have formed a part of the theory of fevers. It is obvious in the sanguiferous system; but the opposite state-is singularly conspicuous in every other part. Even when in delirium, the voluntary muscles are, for a time, violently exerted; it is the energy of a moment, generally accompanied with tremor, and succeeded by the most considerable debility. A tone, an apparent temporary-strength, is seemingly kept up by fever, as greater weakness is felt at its solution than during its course. But it can only be said, that, if the debility is in excess afterwards, it is considerable while the disease continues; and this apparent tone is evidently kept up by the increased action of the vessels in the brain, from which also the delirium proceeds. In short, after watching fevers with attention for thirty-five years, we have never seen any appearance of increased action, except in the sanguiferous system, and even in these vessels the circulation is not apparentlyfree.

It has been objected to the doctrine of spasm, that sweats are sometimes copious. Undoubtedly, at the first view, the argument seems invincible. Yet, if we examine fevers, we shall usually find the skin dry and hot. If we press the palms of the hand, though the hand appear otherwise cool, a heat will be felt there: and the impression communicated to the fingers is not the soft unctuous feel of the healthy skin, but the harshness of dry parchment somewhat warmed. In the profusest sweat, excited by stimulants, the same sensation is perceptible; and as we find this so constantly in fevers; as we find, too, that such sweats not only do not relieve, but add to the oppression, while the soft healthy perspiration is attended with freedom and cheerfulness; we have been led to think these cutaneous evacuations arise from different sources. We have pointed out the distinction under the article Diaphoretica; but whatever be the opinion formed of it, the proper perspiration certainly does not come on till the solution of fever, and it is equally certain that sweating does not supply its place.

The objection that debility is not a cause, since great debility often occurs without fever following, is of still less importance. In this case the sensorial power is affected; the energy of the brain is lessened. In hectics, in dropsy, and in the various nervous diseases where the debility is very considerable, the vital and animal functions only suffer: the mind remains free and unaffected. In fever, the alienation of mind occurs in the first attack; and it is remarkable that in hectics the mind only suffers during the paroxysm.

The principal effect of this state of debility, independent of the irregular action, which is its most constant consequence, appears to be the altered determination. The fluids are confined to the larger vessels; and as the veins, which, by their union, form the vena portae, have no power of impelling the increased load, it is chiefly felt in the liver. We pointed out also the apparent anxiety of nature to keep the vessels of the brain in a state of sufficient tension, and the structure of the sinuses adapted for this purpose. It will be obvious, from these considerations, that the head also should largely share in this accumulation. These circumstances should be kept fully in view, as they are of the greatest importance in practice. From debility, then, and an altered determination, or, in other words, from a change in the balance of the circulation, all the ap-pearances in fevers may be deduced. When, at the conclusion, an apparently putrid dissolution of the blood takes place, it is owing to a diminution of the principle of life, which alone prevents the usual changes of dead animal matter taking place in the living system.

When fevers were supposed to consist in increased action, the remote causes were sought in stimuli of every kind; but if stimulus would alone produce fever, exercise and heat would be its most frequent causes, and common language might be safely transferred to science. But if the effects of exercise and heat are fevers, fever is not a disease; for the warmth and accelerated circulation produce no inconvenience, no function is injured, and, with common precautions, they disappear without the slightest inconvenience. More attentive observation has shown the remote causes to be contagion, and the effluvia from marshes; nor do we distinctly see the exclusive operation of any-other, at least of very few others.

Contagion, in this place, has a very extensive meaning. If many men are confined in a comparatively small place, their health is gradually undermined; their complexions become sallow; their appetite and spirits fail. No real disease may be observable in them; yet, to others, they will sometimes in this state communicate fever, and fever will appear to arise spontaneously among themselves. We see that this poison undermines the springs of life; and though its gradual increase accustoms its action, yet in another it will produce the disease. When the fever is actually formed, it is well known that it may be communicated by its effluvia. Another kind of contagion produced in the body, is that of purulent matter absorbed from an abscess. This we know from its effects to be of an highly sedative nature; and we have much reason to think that it may, in some cases, be communicated to others by effluvia.