note a spasm of the extreme vessels; and this constituted their proximate cause of the disease. Dr. Darwin considers them as the effect of a torpor of the capillaries of the skin, which forms a material link in his chain of the theory of fever; while Dr. Brown and Dr. Rush appear to view them as the consequences of mere debility, or deficient excitement in the system.

52. It would be superfluous at this day to attempt to refute the opinion of Dr. Boerhaave. Suffice it to say, that no such lentor or viscidity of the blood as he describes is found to happen: and his theory is now universally exploded. Almost equally superfluous would it be to controvert Dr. Cullen's imaginary doctrine of spasm; for there is no evidence of the existence of such a state of the blood-vessels, and if there was it would be insufficient to explain the subsequent symptoms of fever. His theory is accordingly also very generally rejected. The torpor of the capillary vessels, supposed by Dr. Darwin to occur in fever, very probably exists in the state of predisposition; but it cannot be presumed to be the proximate cause of the disorder, unless it continues during its whole progress, which, however, it is not alleged to do. The conjectures of Dr. Brown and Dr. Rush are as unsatisfactory as all the others we have mentioned; for extreme debility may exist in the body, and yet those appearances which take place in fever are not produced by that debility. There will be no "retreat of the blood towards the viscera," according to the remark of Dr. Rush. The vessels under the skin will not shrink and disappear, nor will the action of the heart and the respiration be oppressed.

53. To what then, I ask, are those peculiar symptoms of fe ver to be ascribed? The answer is obvious. They can be ascribed to no other cause than the reversed action of the capil laries and small arteries. This morbid action, by its recurrence in fever, and its continuance during the disorder, is competent to produce all its various modifications; and by means of it alone can we account for the various appearances and symptoms

of the complaint. We accordingly find no difficulty in explaining the third class of phenomena we have mentioned; to wit, the sense of oppression in the body, and the unusual excitement in the action of the heart and large arteries. These are the natural and necessary consequences of the reversed action of the extreme parts of the arterial system, giving a preternatural resistance to the free circulation of the blood, and accumulating it in unusal quantity in the system of large vessels in the inte rior parts of the body.

54. Let us now see how our doctrine applies to the different stages and states of fever. Debility, either direct or indirect, I have said, is the predisposing cause of all fever. This debility, in the vascular parts of the body, whose muscular fibres habitually act in succession to each other, always produces a disposition to that derangement of the natural order of motion which happens from their acting in a reverse direction. And this reversed action is always more easily induced in the vascu lar organs, and by less powerful causes than convulsive action: hence it generally precedes, and seldom or never follows convulsive action. The action of the heart and arteries then, in common with other muscular action, becomes weak in the in'cipient state of fever. It ceases to extend its influence to the system of capillary vessels-They become doubly debilitated, both from internal and external causes-Their trains of contractions are no longer governed by the impulse of the blood from the heart-They yield to the operation of other stimuli, which now produce a greater relative effect-Their circular fibres are excited into action at their minute extremities; and the contractions necessarily follow each other in succession up the course of the arteries, in a direction opposite the natu ral order of motion. In consequence of this reversed action of the capillaries, the circulation is retarded, the secretions are diminished, the skin becomes dry, the extreme vessels lose their fulness, and the blood accumulates in the large arteries. This accumulation of blood produces a preternatural distention

of the vessels nearest the heart, and offers an uncommon resistance to the action of that organ. It becomes oppressed, and labours to overcome the unnatural obstacles opposed to its power, in the same manner that its action is increased from the accumulation of blood produced by the pressure of the muscles in violent exercise. Its motion is accordingly accelerated. Its contractions are usually more frequent than natural, often irre gular, and sometimes depressed. The respiration becomes difficult and laborious, and the functions of life disordered. This commotion in the circulation is commensurate in degree and duration with the degree and duration of the reversed ace tion in the extreme vessels. And this, according to the various conditions of the system, under all the varying circumstances of animal life, produces all the different states of fever.

55. In the common intermittent fever, the reversed action of the capillaries produces first the cold stage, and afterwards, by preternaturally exciting the action of the heart and large arteries, gives rise to the hot stage and its attendant symptoms. This fever, more than any other, is accompanied with a sensation of chilliness, because, as I suppose, the frequent exposure of the body to alternate heat and cold has no small share in producing the predisposition to it in the system, and the sensibility of the skin is left either unimpaired, or perhaps preternaturally in. creased. Besides, as this exposure of the body to heat and cold is for the most part periodical, owing to the greater heat of the day than of the night, it may induce a corresponding periodical habit of alternate excitement and debility, which will explain, in some measure,' the periodical recurrence of the pa roxysms. It is to be remarked also, that as those causes which predispose to this fever, act primarily and principally on the external surface of the body, the capillaries of the skin are first affected, and the capillaries in the other parts of the body se condarily by association. And this too may explain why the affection of the skin, that is, the coldness and chilliness in the commencement, and the heat and redness in the progress of

the paroxysm is greater than in most other fevers.

With this

also is to be connected the consideration, that, as in this fever the surface of the body is the part primarily affected, there is no great degree of debility induced in the whole system, and the weakness of the action of the heart in its commencement is rather the consequence of association with the capillary ves sels than of general debility or specific weakness of that organ; and that hence it is soon excited into such vigorous action by the stimulus of the accumulated blood, as to overcome the re, versed action in the capillaries, and to extend the natural ex citement and wholesome action to the surface of the body, when the paroxysm subsides, and the fever terminates periodically. In some cases of malignant intermittents, however, attended with great general debility, the action of the heart continues so much enfeebled and oppressed, as to be utterly incapable of overcoming the reversed action of the capillaries; and death consequently happens in the cold stage. In these cases it is observed that no sensation of chilliness occurs, and the large arteries are found, on dissection, to be surcharged with blood, similar to what happens in other malignant fevers. These cir cumstances indicate at once the great degree of debility, and the great degree of reversed action subsisting in those fatal conditions of fever.

56. In the simple inflammatory fever which happens most commonly in the cold season of the year,not in consequence of periodical exposure to alternate heat and cold, but in conse. quence of long-continued exposure, first to cold and afterwards to heat, the capillary vessels are more generally affected. Not only those of the skin, but the more deep-seated ones become immediately debilitated; and accordingly the reversed action is at first more extensive than in intermittents, and afterwards more permanent. This fever, therefore, assumes a more continued type, and remits only in consequence of the general habit of the body, with respect to periodical excitement and debility from the difference of temperature to which it may

have been habitually exposed, from the coldness of the day, and the warmth of a bed at night.

57: In milignant fever, which happens when the body has been exposed to a continuance of excessive heat and moisture, and where the exciting causes are of a deleterious nature, there is always great and universal debility. In this case the action of the heart becomes often suddenly oppressed, and its feeble power sinks under the accumulation of the circulating fluid produced by the reversed motion of the capillaries. Its force is insufficient to subdue the morbid action in the extreme vessels; and death consequently ensues.

58. The limits of this essay will not permit me to be more particular in the application of my doctrine to the different states and circumstances of fever. Enough has been said to show that it will furnish an ample, and, we trust, a satisfactory explanation, of the most important and characteristic phenomena of the disorder.

59. Thus, I have given a rude sketch, an imperfect outline of a theory of the proximate cause of fever. As it differs materially from all other preceding theories adopted by writers on medicine, it may be properly called the reversed theory of fever, to distinguish it from the metaphysical theory of Stahl, the mechanical theory of Boerhaave, the spasmodic theory of Hoffman and Cullen, the putrid theory of Pringle, the sthenic and asthenic theory of Brown, the sympathetic theory of Darwin, and the convulsive theory of Rush.

60. On the subject of the proximate cause of fever I have ever entertained but one opinion, since I began to study the book of nature, instead of the speculations of authors. None of the prevailing opinions satisfied my mind, or appeared sufficient to explain the nature of the disorder. I accordingly embraced the doctrine I have delivered in the early period of my studies, and have been more and more confirmed in the conviction of its truth by subsequent reflection and observation. By adopting this theory we avoid the insuperable difficulties of