By interlobular emphysema is meant an infiltration of air into the interlobular cellular tissue, or into the cellular tissue surrounding the large vessels of the lungs, the air occasionally extending from thence to the posterior mediastinum, to the neck, and external parietes of the chest. Unless it arise from external injury and consequent wounds of the lungs, this comparatively rare disease, would appear in every instance to be produced suddenly, during some violent effort made by the individual; hence its occurrence in the adult, from attempts to lift a heavy weight, and from excessive straining at stool or during parturition, and hence its occurrence in infants from fits of crying, gusts of passion, and the laborious or interrupted respiration incident to some cases of hoopingcough and croup. Although supposed to arise from the accidental rupture of one or more air-cells, neither its place nor mode of escape into the cellular membrane, has been clearly made out on inspection after death; and what is very remarkable, it rarely if ever accompanies ordinary vesicular emphysema. On examination, we find that the narrow white lines of dense cellular membrane which naturally unite the lobules together, and which by their interlacings, produce the lozenge-like figures on the surface of the lungs, have undergone a change; they are, as it were, dilated and expanded, and present an appearance of inflated canals proceeding in different directions on the surface of the lungs, dipping down into their substance, and varying from a line or two, to perhaps half an inch or more. These inflated canals sometimes present an uniformity of surface; at other times, they appear to be made up of separate dilatations of the cellular membrane, strung together like so many pearls. Contrary to what is observed in vesicular emphysema, a little air occasionally

escapes beneath the pleura beyond the interlobular spaces, and may be made to move from place to place by the pressure of the finger.

Physical signs.-The pathognomonic signs of this affection, are, the dry crepitation of large bubbles, and the frottement ascendens et descendens, or rubbing sound on the ascent and descent of the ribs, detected by auscultation. The patient himself is occasionally conscious of the crepitation, and the practitioner may now and then feel it by simply pressing his finger between the ribs above the parts affected. By percussion, a naturally, or perhaps a preternaturally clear sound is elicited. Of course when the air finds its way into the cellular membrane of the neck and chest, we have an emphysematous state of these parts.

The only symptom of importance to which it gives rise is great and sudden difficulty of breathing.

Diagnosis.-The dry crepitation of large bubbles, the ascending and descending rubbing, and the clear sound on percussion, together with the suddenness of the attack of dyspnoea, will in uncomplicated cases leave little room for doubt or difficulty. It must be remembered, however, that certain of the signs and symptoms may be obscured by accidental complications. Pneumo-thorax often comes on suddenly with great difficulty of breathing, and is also attended with a clear sound on percussion; but pneumothorax most frequently supervenes on phthisis, or some other disease of the lungs; the ribs are quite immoveable, or nearly so; the crepitation and rubbing are absent; all respiratory murmur is annihilated, unless old adhesions exist; and a faint tubular respiration may sometimes be

heard.

The disease, though sudden in its attack and alarming

in its immediate effects, seldom requires any material interference; the extravasated air appears in general to be quickly absorbed; and all that is necessary is to make a few small punctures through the skin with the point of a lancet, when the emphysema extends to the neck and chest.

PNEUMONIA, OR PERIPNEUMONIA.

PNEUMONIA may be defined to be an inflammation of the air-cells of the lungs, speedily producing an effusion into them, of a serous-looking fluid commonly mixed with blood; causing, if unchecked, such a degree of thickening of their parietes as apparently to fill them up entirely for a time; or leading to the deposition of an albuminous matter, which is either solid or of a puriform character; and seldom, if ever, terminating in the formation of a genuine abscess.

Both the general and local symptoms of pneumonia vary considerably, according to the intensity of the attack, and the age and constitution of the individual; but more particularly, according to the extent to which the bronchi happen to be involved in the inflammatory process. In its simplest form; after chilliness, shivering, feebleness, and depression, the patient experiences for the most part, strongly marked symptoms of febrile reaction, giddiness, confusion, and sometimes intense pain in the head; occasionally delirium, especially towards night; the skin acquires a remarkably pungent heat, generally accompanied by dryness, more rarely by moisture; the pulse is full and strong, perhaps labouring and sluggish; the face is usually more or less suffused with a livid or deep crimson flush, accompanied by an expression of distress; the tongue is foul,

its substance is more injected than in ordinary phlegmasiæ, and in a short time it manifests a tendency to become dry and brownish; the respiration is more or less hurried; but there is seldom pain or any very obvious cough or expectoration, and sometimes none at all; the entire assemblage of symptoms bears a striking resemblance to those of a common continued fever, and often, especially in the aged and cachectic, take on a considerable degree, of the typhoid type.

In a large majority of cases, however, occurring in moderately good constitutions, the smaller, bronchi are involved; so that, together with the symptoms enumerated, we have both cough and expectoration, as well as more strongly marked pain and difficulty of breathing. But even in this more common form of the complaint, neither the cough nor the pain is by any means very urgent, whilst the expectoration is for the most part exceedingly scanty. This scanty expectoration of pneumonia, presents physical characters in a great measure peculiar to, and characteristic of, the complaint. It is so remarkably viscid that it will often adhere to the sides of the containing vessel like so much semifluid gum, and with such pertinacity, that although tremulous, it cannot be made to quit its situation either by reclining or inverting the vessel.

These small viscid masses frequently contain air-bubbles, and present considerable variety of colour, being sometimes semitransparent and pearly or greyish, like the thickest mucilage; at other times, according to the quantity of blood with which it is so often mixed, we have it of a sea-green, apple-green, gamboge yellow, rusty brown or reddish colour; and indeed in some instances, the matter expectorated, appears to consist almost entirely of

blood, when it is perhaps equally or even more copious, but of course less viscid.

When the bronchitic complication is still more considerable, the wheezing and dyspnoea are more urgent, the cough more frequent and violent, the pain or soreness more distressing, and the expectoration much more copious. In such cases the characteristic appearances of the pneumonic expectoration, are often altogether lost amidst the abundant bronchial secretion, or perhaps we find the whole of the latter tinged of a brownish or saffron colour, by the admixture of blood usually observed in the former.

Such are the symptoms usually attendant on the ordinary forms of pneumonia; but although in enumerating and arranging them, it would appear that their severity is to a certain extent determined by the degree of bronchial complication; it is nevertheless true, that without either bronchial or pleuritic complication, the distress of breathing is in some rare instances, extreme; and in a short time, amounts almost to a state of orthopnoea. We have found this form of the complaint associated in a few cases, with myriads of miliary tubercles pervading both lungs, and proving fatal, either in the first or very early in the second stage of the disorder.

On dissection, the appearances differ according to the stage or period of the disorder at which death took place. In the first stage of pneumonic inflammation, we find the lung externally of a dark or violet colour, whilst internally, it presents various shades of red; it feels more substantial and resisting; it retains its tenacity; it still crepitates, but pits upon pressure; and on cutting into it, a considerable quantity of a thin, frothy, and often bloody fluid escapes from the incision; nevertheless the cellular