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very different degrees; so that, whatever attention it may deserve in practice, there is no fixing such limits to it as to admit of establishing a species under the title of Putrid.

73. Beside differing by the circumstances already mentioned, fevers differ also by their being accompanied with symptoms which belong to diseases of the other orders of pyrexiae. This sometimes happens in such a manner, as to render it difficult to determine which of the two is the primary disease. Commonly, however, it may be ascertained by the knowledge of the remote cause, and of the prevailing epidemic, or by observing the series and succession of symptoms.

74. Most of our systems of physic have marked, as a primary one, a species of fever under the title of Hectic; but,■as it is described, I have never seen it as a primary disease. I have constantly found it as a symptom of some topical affection, most commonly of an internal suppuration; and as such it shall be considered in another place.

75. The distinction of the several cases of intermittent fever I have not prosecuted here; both because we cannot assign the causes of the differences which appear, and because I apprehend that the differences which in fact occur may be readily understood from what is said above (25, 26, and 27), and more fully from our Methodical Nosology, CI. I, sect. 1.

CHAP. IV.

OF THE REMOTE CAUSES OF FEVER.

76. As fever has been held to consist chiefly in an increased action of the heart and arteries, physicians have supposed its remote causes to be certain direct stimulants fitted to produce this increased action. In many cases, however, there is no evidence of such stimulants being applied; and, in those in which they are applied, they either produce only a temporary frequency of the pulse, which cannot be considered as a disease; or, if they do produce a permanent febrile state, it is by the intervention of a topical inflammation, which produces a disease different from what is strictly •ailed fever (S).

77. That direct stimulants are the remote causes of fever, seems farther improbable; because the supposition does not account for the phenomena attending the accession of fevers, and because other remote causes can with greater certainty be assigned.

78. As fevers are so generally epidemic, it is probable, that some matter floating in the atmosphere, and applied to the bodies of men, ought to be considered as the remote cause of fevers: and these matters present in the atmosphere, and thus acting upon men, may be considered, either as Contagions, that is, effluvia arising directly or originally from the body of a man under a particular disease, and exciting the same kind of disease in the body of the person to whom they are applied; or Miasmata, that is, effluvia arising from other substances than the bodies of men, producing a disease in the person to whom they are applied.

79. Contagions have been supposed to be of great variety; and it is possible this may be the case: but that they truly are so, does not appear clearly from any thing we know at present. The genera and species of contagious diseases, of the class of pyrexias, at present known, are in number not very great. They chiefly belong to the order of fevers, to that of exanthemata, or that of profluvia. Whether there be any belonging to the order of phlegmasia, is doubtful; and though there should, it will not much increase the number of contagious pyrexiae. Of the contagious exanthemata and profluvia, the number of species is nearly ascertained; and each of them is so far of a determined nature, that though they have now been observed and distinguished for many ages, and in many different parts of the world, they have been always found to retain the same general character, and to differ only in circumstances, that may be imputed to season, climate, and other external causes, or to the peculiar constitutions of the several persons affected. It seems, therefore, probable, that, in each of these species, the contagion is of one specific nature; and that the number of contagious exanthemata or profluvia is hardly greater than the number of species enumerated in the systems of nosology.

80. If, while the contagious exanthemata and profluvia are thus limited, we should suppose the contagious pyrexiae to be still of great and unlimited variety, it must be with respect to the genera and species of continued fevers. But if I be right in limiting, as I have done, the genera of these fevers (67-70), it will appear likely that the contagions which produce them are not of great variety; and this will be much confirmed, if we can render it probable that there is one principal, perhaps one common source of such contagions.

81. To this purpose it is now well known, that

VOL. I. F

the effluvia constantly arising from the living human body, if long retained in the same place, without being diffused in the atmosphere, acquire a singular virulence ; and, in that state being applied to the bodies of men, become the cause of a fever which is highly contagious.

The existence of such a cause is fully proved by the late observations on jail and hospital fevers: and thaf the same virulent matter may be produced in many other places, must be sufficiently obvious: and it is probable, that the contagion arising in this manner, is not, like many other contagions, permanent and constantly existing; but that, in the circumstances mentioned, it is occasionally generated. At the same time, the nature of the fevers from thence, upon different occasions, arising, renders it probable, that the virulent state of human effluvia is the common cause of them, as they differ only in a state of their symptoms; which may be imputed to the circumstances of season, climate, &c. concurring with the contagion, and modifying its force.

82. With respect to these contagions, though we have spoken of them as of a matter floating in the atmosphere, it is proper to observe, that they are never found to act but when they are near to the sources from whence they arise; that is, either near to the bodies of men, from which tfcey immediately issue; or near to some substances which,

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