Inflammation, like congestion, is characterized by the four special symptoms, heat, pain, redness, and swelling. In inflammation, however, these symptoms are all much more intense than in conges tion. In this respect, inflammation may be considered as an advanced stage of irritation. It includes in its different stages all the primary morbid actions previously mentioned; namely, irritation, both active and passive congestion, and depression. On account of its resemblance to congestion it is sometimes not easy to distinguish between the two diseases, especially at the beginning of the morbid condition or process. Indeed, at the beginning there is no distinction, for the inflammatory process is induced by irritation and congestion. The real distinction between inflammation and congestion is not easily perceptible in the early stages, at least before any special results have been produced. Microscopical researches have shown, however, that there is a difference even at this early period which consists in the great increase of white blood corpuscles. This may be very easily observed in the delicate web of a frogs foot placed beneath the microscope. Upon placing the point of a needle or other mechanical or chemical irritant upon the membrane, all of the phenomena of irritation, congestion, and inflammation may be observed occurring in their proper order, the beginning of inflammation proper being indicated by the accumulation of white blood corpuscles in and about the gradually dilated blood-vessels of the affected part. There is every reason for believing that this is exactly what occurs in larger animals and human beings. If inflammation is arrested in its first stages, the effects are only those described. If continuous, however, the morbid action may give rise to the exudation of matters which afterward harden and cause induration of the parts, or the intensely local action may become so great as to occasion death of some of the tissues, involving coagulation of the blood and obstruction of the circulation.

This is what occurs in a boil. When death of the tissues has taken place, the dead parts are treated like foreign substances in order to prevent contamination of the system by absorption of the dead and disorganizing matter. The dead part is separated from the living by a wall of defense which is thrown up about it and by a layer of corpuscles exactly resembling white corpuscles of the blood, but in this case termed pus corpuscles. It is these corpuscles which form the greater part of the whitish or yellowish discharge from abscesses or suppurating wounds. As thus seen, it is wholly devoid of offensive odor, and is termed healthy pus; but when by the breaking down of dead tissues the pus becomes tilled with products of decay, and is watery in character, it is termed unhealthy, or ichorous pus, and often has a very offensive odor. Pus is formed partly from the blood, by the removal of its white corpuscles, and partly from the tissues themselves, which undergo destruction about the dead part for the purpose of loosening it and thus removing it from the body. If a part which has thus died has been loosened and removed, an examination of the surface beneath will show that underneath the purulent matter is a layer of small red prominences termed granulations, which indicate that new tissue is forming. By degrees the cavity left, if not too large, will be filled up with newly made tissue, which is, however, of a somewhat different character from that which was removed. It sometimes happens that in consequence of a still greater intensity of inflammatory action the tissue of the diseased part dies very suddenly, from the stagnation and coagulation of the blood in its blood-vessels. This is termed gangrene, the consideration of which must be left for the section devoted to surgery, to which province it particularly belongs.

Inflammation is generally described as being acute, sub-acute, or chronic, the distinctions between which are the same as those which govern the classification of other diseases. The symptoms above described are those of acute inflammation. In sub-acute inflammation the same 8ymtoms will be noted, though their intensity will be less, and they succeed each other at longer intervals. In both acute and sub-acute inflammation the whole system participates in the disturbance. The greater the extent and the higher the degree of the intensity of the inflammatory process, the greater will be the general disturbance. The temperature of the body as well as that of the diseased part will be found almost invariably to be above normal. When a large and important organ, as a lung, the liver, or the stomach, is affected, the temperature of the whole body may rise to a very high point, while a very slight inflammation accompanying the efforts of the system to expel a sliver from the skin may not at all affect the general temperature. It is the great elevation of temperature which in the majority of inflammations is the thing to be most dreaded and which is the chief cause of a fatal result in a large share of the cases in which death occurs from inflammatory affections.

In what is termed chronic inflammation, the intensity of the vital action is much less than in acute inflammatory affections. Indeed, although the results of so-called chronic inflammation are in some respects similar to those of acute inflammatory action, it appears to us that there are good reasons for believing that there is really no such thing as chronic inflammation, but that the condition generally denoted by this term is really only chronic congestion, either active or passive. We are sure that this is true of a large share of the cases usually included under the head of chronic inflammation, whether it be applicable to all or not, and we have never yet found difficulty in explaining the phenomena of what is generally termed chronic inflammation in accordance with the views expressed. When a part is affected by acute inflammation, if recovery does not take place it finally continues in a state of active or passive congestion, most frequently the latter, which is the condition generally known as sub-acute or chronic inflammation. Inflammations have been classified according to the variety of tissue affected by them, but as this classification is of no practical importance, we need not present it here. The especial characteristics of local inflammations will be given in connection with their description elsewhere.

The Causes of Inflammation

Inflammation may be induced by mechanical or chemical irritants, by poisons generated in the system or received into it from without, through morbid nervous influences, and perhaps by other means. Its general character is the same, however, whatever may be its cause.