Again, though the redness, swelling, throbbing, tension, and other symptoms of inflammation are less manifest when the affection is deeply seated, yet their existence is undoubted. When an animal dies from inflammation of the lungs, the air-cells of these organs are found crowded with a larger number of turgid bloodvessels than in the healthy state, and, of course, the parts must appear preternaturally red. Coagulating lymph, or a mixture of fibrine and serum, and even blood, are extravasated in the substance of these viscera, which become heavier, and feel more solid.

The extravasation of coagulating lymph, which is one of the chief causes of the swelling, is also one of the most characteristic signs of phlegmonous inflammation.

Some writers restrict the seat of phlegmon to the cellular tissue; hut this is erroneous, for, had they duly discriminated the nature of common inflammation, they would have allowed that this affection existed wherever the capillaries (or smallest vessels) appeared to he more numerous and enlarged than in the natural state, accompanied with an effusion of coagulating lymph, whether upon the surface of a membrane or a bone, or in the interstices of the cellular substance, and attended with acute pain and a throbbing pulsation in the part.

As Dr. Thompson has observed, the epithet remote, as applied to the causes of inflammation, does not appear to be happily chosen, for under this term are comprehended all those agents, events, and states which contribute immediately, as well as remotely, directly as well as indirectly, to the production of the affection.

The remote causes of inflammation are infinite in number, but easy of comprehension, because divisible into two general classes. The first includes all such agents as operate by their stimulant or chemical qualities; for example, cantha-rides, heat, the action of concentrated acids, alkalies, metallic oxides, and metallic salts, acrid vapours, gases, alcohol, animal poisons, etc.

The second class of causes are those which act mechanically, such as bruises, wounds, pressure, friction, &c

The principle on which the application of cold to a part becomes the remote cause of inflammation is rather difficult to explain. "No subject," says a distinguished professor, "is more deserving of investigation than the effects which are produced in the body by the operation of cold applied to its surface; but the subject is at the same time exceedingly extensive, complicated, and difficult. These effects differ according to the degree in which the cold is applied, and the mode of its application. So diversified, indeed, are these effects, that it requires no mean confidence in theoretical reasoning to believe that the operation of cold in producing them is explicable upon any single general principle."

The operation of cold upon the body affords the best example I can suggest of the production of inflammation from the operation of a power acting upon a part at a distance from that in which the inflammation takes place, such as inflammation of the organs situated within the chest and abdomen.

Again, in some instances cold, or a diminution of temperature, seems to act more directly upon the parts with which it comes in contact, familiar examples being witnessed in the inflammation of the mucous membranes of the nose, trachea or windpipe, bronchiæ, etc, from the inhalation of cold air, and in the production of rheumatic inflammation from the exposure of the body to cold.

From these facts it will be observed that the application of cold seems to have somewhat of a directly exciting effect, and perhaps the same remark is still more applicable to the local effects of cold in the production of inflammation which is usually denominated frost-bite. Touching a solid body, as a piece of metal, the temperature of which has been greatly reduced, or a piece of ice, produces a sensation like that of burning, and may be followed, like the application of a fire, by a blister.

Numerous opinions have been entertained and promulgated respecting the proximate cause of inflammation, but almost every theory has been built upon the supposition of some kind of obstruction in the inflamed part.

While the circulation of the blood was unknown, the opinion prevailed that the liver was the centre of the vascular system, from which the blood went forth by day to the extremities, and returned at night. If, then, any peccant matter irritated the liver, the blood was sent out more forcibly; and if, at the same time, any part of the body were weakened, or otherwise disposed to receive a greater quantity of fluid than the rest, then a swelling was produced by the flow of humours to this place. Fluxions, or flows of humour to a part, might happen either from weakness of it, which allowed the humours to enter more abundantly, or from its attracting the humours in consequence of the application of heat or other agents.

But from the theories of fluxion and congestion, which were quite incompatible with the laws of the circulation of the blood, we will turn our attention to the doctrine of