Softening of the lung-tissue is of very rare occurrence; it is altogether distinct from pneumonia, and must not be confounded with Andral's ramollissement (red and gray hepatization); like softening of the stomach, it is a peculiar spontaneous process, and appears under precisely the same conditions as that affection: indeed, as a further proof of their identity, we may add that this disease is almost always combined with gastric softening.

In any part of the lungs we may find an undefined patch of a dirty brown or blackish color, according to the state of the blood at the commencement of the process, and which is so very moist and soft that on the slightest pressure it breaks down into a pulp, which is mixed with a serous fluid and contains black flocculi of carbonized blood. The bronchial mucous membrane is found in the same state for some distance around the diseased spot.

In consequence of the considerable quantity of blood which is always contained in the lungs, there is a resemblance between softening of the pulmonary tissue and the black softening of the stomach, which proceeds from a disease of the blood itself. It may be easily mistaken for diffuse pulmonary gangrene; indeed in very intense cases the diagnosis must depend on the absence of the gangrenous odor, and on the lesser degree of discoloration.