All dermatologists are aware of the great progress that has been made in recent years in our knowledge of cutaneous tuberculosis. We have kept abreast of the advances with the knowledge of tuberculosis elsewhere and have followed the research in related fields. We have attempted to apply the new facts as each was established to what was known about cutaneous tuberculosis, but despite our considerable present knowledge, despite all the advances in the fields of allergy and immunology, we have been unable to find an explanation for the great variance in the morphologic aspects of the various tuberculoderms as we know them today.The finding of the tubercle bacillus in lupus vulgaris lesions, both by culture and inoculation, disclosed that this cutaneous disease is in general tuberculous. This was a great advance, but it did not explain why in certain tuberculous patients there should develop such a slow, almost benign, form of cutaneous tuberculosis, even though its manifestation in the skin was a destructive and serious malady in itself. Other cutaneous dis¬ eases less destructive than lupus vulgaris had been suspected of being closely related to lupus, but proof of their tuberculous causation was slow in coming. Gradually evidence was accumulated that some of these, for example acnitis, were also caused by the tubercle bacillus, and one by one a number of diverse cutaneous conditions were proved to be of tuberculous causation or, because of certain constant observations, were strongly suspected of being tuberculous. When this relationship, real or suspected, of tuberculosis was applied to a large series of poorly described cutaneous lesions, a nosologie terminology evolved which to this day makes the subject incredibly involved and complex.In 1896 Darier propounded his theory of the tuberculids, and a new nomenclature was evolved. Lesions which were suspected of being tuberculous, but in which the tubercle bacillus could rarely if ever be found, were called "tuberculids," and the enthusiasm of some allowed a large number of cutaneous conditions to be included in this ill defined nosologie group.As certain cutaneous lesions which either had been proved to be tuberculous or were still strongly suspected of being so became better known and were reported with greater regularity, an effort was made to classify them. Some students of the subject decided that certain types arose from inoculation in virgin soil, and they classified these types as external cutaneous tuberculosis, while other forms developed from endogenous infections and these they called internal types. Other classifica¬ tions were based on the mode of spread and on the suspected manner of sowing of the bacilli in the skin.The way the patient who harbored various tuberculous lesions reacted to tuberculin provided explanation for the pathogenesis of certain types and hence another means of classification. The course and prognosis of the disease revealed the close relationship of some of these diverse conditions.Regardless of which classification one accept...
