mation is, commonly, cold applied to the body, obstructing perspiration, and determining to the lungs; while, at the same time, the lungs themselves are exposed to the action of cold. These circumstances operate especially when an inflammatory diathesis prevails in the system; and, consequently, upon persons of the greatest vigour; in cold climates; in the winter season; and particularly in the spring, when vicissitudes of heat and cold are frequent. The disease, however, may arise in any season when such vicissitudes occur.

Other remote causes also may have a share in this matter; such as, every means of obstructing, straining, or otherwise injuring, the pneumonic organs.

Pneumonic inflammation may happen to persons of any age, but rarely to those under the age of puberty; and most commonly it affects persons somewhat advanced in life, as those between fortyfive and sixty years; those, too, especially of a robust and full habit.

The pneumonic inflammation has been sometimes so much an epidemic, as to occasion a suspicion of its depending upon a specific contagion; but I have not met with any evidence in proof of this. See Morgagni de causis et sedibus morborum, epist. xxi, art. 26.

346. The pneumonic, like other inflammations, may terminate by resolution, suppuration, or gan

gréne; but it has also a termination peculiar to it. self, as has been hinted above, (259); and that is, when it is attended with an effusion of blood into the cellular texture of the lungs, which soon interrupting the circulation of the blood through this viscus, produces a fatal suffocation. This, indeed, seems to be the most common termination of pneumonic inflammation, when it ends fatally; for, upon the dissection of almost every person dead of the disease, it has appeared that such an effusion had happened.

347. From these dissections also we learn, that pneumonic inflammation commonly produces an exudation from the internal surface of the pleura ; which appears partly as a soft viscid crust, often of a compact, membranous form, covering every. where the surface of the pleura, and particularly those parts where the lungs adhere to the pleura costalis, or mediastinum; and this crust seems always to be the cement of such adhesions.

The same exudation shews itself also by a quan tity of a serous whitish fluid, commonly found in the cavity of the thorax; and some exudation or effusion is usually found to have been made likewise into the cavity of the pericardium.

348. It seems probable, too, that a like effusion is sometimes made into the cavity of the bronchia: for, in some persons who have died after labour

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ing under a pneumonic inflammation for a few days only, the bronchie have been found filled with a considerable quantity of a serous and thickish fluid; which, I think, must be considered ra ther as the effusion mentioned, having had its thinner parts taken off by respiration, than as a pus so suddenly formed in the inflamed part.

349. It is, however, not improbable, that this effusion, as well as that made into the cavities of the thorax and pericardium, may be a matter of the same kind with that which, in other inflammations, is poured into the cellular texture of the parts inflamed, and there converted into pus; but, in the thorax and pericardium, it does not always assume that appearance, because the crust covering the surface, prevents the absorption of the thinner part. This absorption, however, may be compensated in the bronchiæ by the drying power of the air; and therefore the effusion into them may put on a more purulent appearance.

In many cases of pneumonic inflammation, when the SPUTA are very copious, it is difficult to suppose that the whole of them proceed from the mucous follicles of the bronchiæ. It seems more probable, that a great part of them may proceed from the effused serous fluid we have been mentioning; and this, too, will account for the sputa being so often of a purulent appearance. Perhaps the same thing may account for that purulent expectoration,

as well as that purulent matter found in the bronchiæ, which the learned Mr. de Haen says he had often observed, when there was no ulceration of the lungs and this explanation is at least more probable than Mr. de Haen's supposition of a pus formed in the circulating blood.

350. To conclude this subject, it would appear that the effusion into the bronchiæ, which we have mentioned, often concurs with the effusion of red blood in occasioning the suffocation, which fatally terminates pneumonic inflammation; that the effusion of serum alone may have this effect; and that the serum poured out in a certain quantity, rather than any debility in the powers of expectoration, is the cause of that ceasing of expectora tion which very constantly precedes the fatal event. For, in many cases, the expectoration has ceased, when no other symptoms of debility have appeared, and when, upon dissection, the bronchiæ have been found full of liquid matter. Nay, it is even probable, that, in some cases, such an effusion may take place, without any symptoms of violent inflammation; and, in other cases, the effusion taking place may seem to remove the symptoms of inflammation which had appeared before, and thus account for those unexpected fatal terminations which have sometimes happened. Possibly this effusion may account also for many of the phe nomena of the Peripneumonia Notha.

351. Pneumonic inflammation seldom terminates by resolution, without being attended with some evident evacuation. An hemorrhagy from the nose happening upon some of the first days of the disease, has sometimes put an end to it; and it is said, that an evacuation from the hemorrhodial veins, a bilious evacuation by stool, and an evacuation of urine with a copious sediment, have severally had the same effect; but such occurrences have been rare and unusual.

The evacuation most frequently attending, and seeming to have the greatest effect in promoting resolution, is an expectoration of a thick white or yellowish matter, a little streaked with blood, copious, and brought up without either much or violent coughing.

Very frequently the resolution of this disease is attended with, and perhaps produced by, a sweat, which is warm, fluid, copious over the whole body, and attended with an abatement of the frequency of the pulse, of the heat of the body, and of other febrile symptoms,

352. The prognostics in this disease are formed from observing the state of the principal symptoms.

A violent pyrexia is always dangerous.

The danger, however, is chiefly denoted by the difficulty of breathing. When the patient can lie on one side only; when he can lie on neither side,