47 "Das tuberkelähnliche Lymphadenom," Archiv der Heilkunde, 1870, xi. 6; xii. 1.
48 Untersuchungen über Lymphdrüsen-Tuberkulose, 1871.
Although the typical tubercle is thus constituted, the structural features depend somewhat upon its age. It is generally admitted that the freshest tubercles, as found in the external coat of the smaller arteries of the pia mater, are composed of little else than a circumscribed accumulation of small, round cells, without a distinct reticulum. The giant-cells, the epithelioid cells, and the well-characterized reticulum appear as the tubercle increases in age. It is thought probable that the giant-cells represent the agglomeration of the small, round cells in pre-existing cavities, lymphatics, blood-vessels, or secretory canals. The epithelioid cells in like manner are considered to result from the enlargement or fusion of the smaller cells, while the reticulum represents either a secretion from, or a transformation of, the cellular elements of which the tubercle is composed.
The subsequent history of the tubercle is dependent upon its metamorphoses. These are known as cheesy degeneration, calcification, and fibrous transformation.
The absence of blood-vessels, already stated, and the abundantly cellular nature of the growth, with the possible action of micro-organisms, result in a tendency to the early death of the cells and a necrosis of the tubercle. This is the cheesy degeneration, and is regarded as a form of coagulative necrosis, which begins at the centre, advances toward the periphery, and results in the transformation of the gray into a yellow tubercle. This termination in cheesy degeneration likewise affects inflammatory products surrounding the tubercle, and even relatively normal tissues in which numerous tubercles may lie. This cheesy material either softens or becomes infiltrated with lime salts, calcified. The softening of the tubercle results in the formation of a material capable of removal as a discharge from the surfaces of the body or by absorption through the lymphatics and blood-vessels. In the former event ulcers arise upon, and cavities communicate with, the surfaces of the body opening externally.
The cheesy material frequently becomes calcified, thus remaining as a comparatively inert mass. The earthy salts may be diffused throughout a uniformly cheesy basis, or they may be deposited in a partially softened, cheesy menstruum, when a mortar-like material results.
The tubercle becomes fibrous with the diminution in the number of its cells and the increase in the thickness of the reticulum, with the transformation of the latter into a homogeneous hyaline substance. The cornified, horn-like tubercle is one whose size is diminished from the shrinkage of its cells into glistening flakes, without an evident associated cheesy or fatty degeneration.
The intimate relation of scrofula to tuberculosis has been variously expressed from time to time in accordance with the amount and accuracy of the existing knowledge. At the outset the enlargement of the lymphatic glands, especially of the neck, characterized the scrofulous affection. As the enlargements of the glands were found to present intrinsic differences connected with differing clinical histories, only those glands were regarded as scrofulous which presented the cheesy appearances. With the recognition of the cheesy condition of tubercles the latter were identified with the scrofulous gland, from the cheesy condition common to both.
This identification of scrofula and tubercle prevailed till Virchow showed that cheesy material might have a different origin, and maintained that there were cheesy lymphatic glands without tubercle, as well as tuberculous lymphatic glands which might become cheesy. A distinction was thus drawn between scrofula and tuberculosis. The former term was applied to that condition of the individual which favored the retention and cheesy degeneration of inflammatory products, not only in the lymphatic glands, but elsewhere in the body. Tuberculosis, on the contrary, was characterized by the production of tubercles which were often accompanied by retained inflammatory products, both of which were prone to undergo cheesy degeneration.
The frequent association of well-defined tubercles with what were regarded as antecedent scrofulous disturbances also suggested an intimacy of relation between scrofula and tuberculosis. Virchow49 had always maintained the possibility of regarding tuberculosis as a heteroplastic or metastatic scrofula. The occurrence of cases of tuberculosis without evidence of an antecedent scrofula prevented him from making a more absolute statement of the above relation.