(a.) If the granulations were regarded as swollen, and consequently obliterated, air-cells, they could neither exhibit the above anatomical relations, nor could they present the metamorphoses which, regarding them as inflammatory products, we have represented that they undergo; that is to say, if we take an unbiassed view of the subject.

(b.) Even the greatest swelling of the air-cells could not modify the volume of the hepatized lung, while our theory perfectly explains this phenomenon.

(c.) If the third stage, or that of purulent infiltration, were a suppuration of the interstitial tissue, a recovery from it without abscess and solution of continuity could not be possible; whereas it takes place by partial expectoration and partial absorption of the dissolved exudation, without any ulcerous destruction of tissue, in which case anatomical investigation shows, that, in purulent infiltration of the lungs the texture is altogether undestroyed, and of a spongy, cellular nature.

(d.) Finally, the same process, as a general rule, extends to the terminal ramifications of the inflamed lung.

Even from what has been already said, it appears that, in relation to its anatomical elements, we may regard pneumonia as a croupous process on the pulmonary mucous membrane,or, in other words, as a parenchymatous croup. It exhibits, even within the limited circle of its anatomical relations, a perfect identity with the croupous process on other mucous membranes; we shall, however, subsequently develope this view in a more extended and general manner.

We very often find the three stages coexisting, and can observe all the transition-stages passing into one another. Purulent infiltration and gray hepatization generally predominate in the central and inferior part of the inflamed lobe; there is grayish-red or red hepatization towards the periphery; above this there is inflammatory engorgement; while, finally, simple stasis, and very frequently acute oedema in different stages, are present in the adjacent tissue.

Pneumonia may prove fatal in any of these stages; it may also retrograde from each to the normal condition. Besides the above-described termination in purulent fusion of the inflammatory product (purulent infiltration), it may in rare cases give rise to abscesses or induration, or may end in other ways, which can be more suitably noticed in a future part of the work.

If the pneumonia has reached the third stage, and is proceeding towards a cure, we observe the following phenomena: - The purulent fluid is gradually removed, and an exhalation of serum commences from the pulmonary mucous membrane; the pus which still remains is gradually rendered thinner by this admixture, and is finally converted into a floc-culent, turbid serosity, which becomes mixed with air-bubbles as soon as the air again begins to penetrate. The parenchyma, at the same time, becomes paler, and of a grayish-yellow tint, and retains this color for a considerable time; it crepitates less distinctly than in the normal state, is softer and moister, is more or less oedematous, and easily torn.

The lung can also retrograde from the second stage, that of hepatization, to the normal state, without the purulent liquescence of the exudation. This process is undoubtedly one of the most difficult which the healing powers of nature can accomplish; for it always takes place somewhat slowly, and undoubtedly the more so in proportion, on the one hand, to the plasticity of the product, and, on the other, to the exhaustion following the effusion, whether the exhaustion be dependent on the disease, or be induced by the activity of the treatment. The granulations, together with the tissue, gradually become paler, and a serous fluid, which is secreted in the cells, seems by degrees to cause a fusion of the granulations, layer by layer. The tissue still retains a granular character, but the granulations always become smaller, of a pale red or reddish-gray color, and are bathed in a serous fluid, which is mixed with tolerably consistent, pale reddish or whitish flocculi, and which gradually becomes frothy from the entrance of air. When the granulations are thus finally melted down, the parenchyma remains for some time in a state of serous infiltration, and is redder, firmer, and more resistant than in the normal state, owing, apparently, to a still existing infarctus of the walls of the air-cells and of the interstitial tissue. This retrograde process does not go on with equal or uniform rapidity at all parts; and we can often confirm our diagnosis by finding dense and still hepatized patches in tissue which has more or less returned to the normal state.

Finally, pneumonia retrogrades from the first stage - that of inflammatory stasis - to the normal condition; this is very frequently the case when those favorable influences are present which it is the great object of the healing art to induce. The inflammatory stasis, after it has deposited a moderate infiltration of turbid serous fluid, is converted into simple stasis, and after this is resolved, the tissue again becomes normal, but remains for some time the seat of hyperemia which may easily relapse into inflammatory stasis.