Leprosy appears in two forms, which are clinically pretty sharply distinguishable, and were named by Danielssen and Boeck “nodular” and “anæsthetic.” This nomenclature, introduced by these authors in their pioneer work, _Om Spedalskhed_, Christiania, 1847, _Traité de la Spedalskhed_, Paris, 1848, is so far important as it characterizes the common and most prominent symptoms of the two forms, viz., in the one, the nodular eruption on the skin, in the other, the anæsthesia which results from the widespread affection of the nerves. On the other hand, regarded from a strictly scientific standpoint, the nomenclature is scarcely the happiest: firstly, because the one form is named from the eruption on the skin, and the other from the results of the affection of another organ, the nerves; and secondly, because the nerves are affected in the nodular as well as in the other form, though the result of the affection, the anæsthesia, does not so dominate the appearance of the disease. As Danielssen and Boeck recognised, skin eruptions are present in both forms, and since, as we shall later point out, the eruptions differ both clinically, and also somewhat in their anatomical formation, it would perhaps be more strictly correct to describe the two forms as Lepra tuberosa (tuberculosa) and Lepra maculosa or lævis. But, in the first place, it is of questionable advantage to change a universally accepted nomenclature; and secondly, it is very frequently the case that one sees the patient for the first time after the disappearance of the macular eruption with anæsthesia only, so that the name Lepra anæsthetica exactly describes the case. But in order to give to the skin eruption in the anæsthetic form its proper place in the nomenclature we will describe the two forms of the disease as _Lepra tuberosa_ (tuberculosa), and _Lepra maculo-anæsthetica_. And thus we hope to have done justice both to the founders of the scientific study of Leprosy, and to the clinical appearances of the disease.