The most prominent feature of tertiary syphilis consists in the formation of granulation tissue, and this takes place on a scale considerably larger than that observed in lesions of the secondary period. The granulation tissue frequently forms a definite swelling or tumour-like mass (syphiloma), which, from its peculiar elastic consistence, is known as a _gumma_. In its early stages a gumma is a firm, semi-translucent greyish or greyish-red mass of tissue; later it becomes opaque, yellow, and caseous, with a tendency to soften and liquefy. The gumma does harm by displacing and replacing the normal tissue elements of the part affected, and by involving these in the degenerative changes, of the nature of caseation and necrosis, which produce the destructive lesions of the skin, mucous membranes, and internal organs. This is true not only of the circumscribed gumma, but of the condition known as _gummatous infiltration_ or _syphilitic cirrhosis_, in which the granulation tissue is diffused throughout the connective-tissue framework of such organs as the tongue or liver. Both the gummatous lesions and the fibrosis of tertiary syphilis are directly excited by the spirochætes. The life-history of an untreated gumma varies with its environment. When protected from injury and irritation in the substance of an internal organ such as the liver, it may become encapsulated by fibrous tissue, and persist in this condition for an indefinite period, or it may be absorbed and leave in its place a fibrous cicatrix. In the interior of a long bone it may replace the rigid framework of the shaft to such an extent as to lead to pathological fracture. If it is near the surface of the body--as, for example, in the subcutaneous or submucous cellular tissue, or in the periosteum of a superficial bone, such as the palate, the skull, or the tibia--the tissue of which it is composed is apt to undergo necrosis, in which the overlying skin or mucous membrane frequently participates, the result being an ulcer--the tertiary syphilitic ulcer (Figs. 40 and 41). _Tertiary Lesions of the Skin and Subcutaneous Cellular Tissue._--The clinical features of a _subcutaneous gumma_ are those of an indolent, painless, elastic swelling, varying in size from a pea to an almond or walnut. After a variable period it usually softens in the centre, the skin over it becomes livid and dusky, and finally separates as a slough, exposing the tissue of the gumma, which sometimes appears as a mucoid, yellowish, honey-like substance, more frequently as a sodden, caseated tissue resembling wash-leather. The caseated tissue of a gumma differs from that of a tuberculous lesion in being tough and firm, of a buff colour like wash-leather, or whitish, like boiled fish. The degenerated tissue separates slowly and gradually, and in untreated cases may be visible for weeks in the floor of the ulcer. [Illustration: FIG. 40.--Ulcerating Gumma of Lips.