Tuberculous infections of the skin have been divided into two categories as to their source. There are those of exogenous origin and those of endogenous or metastatic origin. Cutaneous tuberculosis of exogenous origin usually manifests itself as a single progressive lesion which spreads by continuity or contiguity of tissues. Once the type has become well established in the individual case it usually remains characteristic throughout its duration. Tuberculosis spreading hematogenously has been subdivided into two classes, the one spreading by tumor formation and the other exanthematous. The exanthematous subdivision comprises lichenoid tuberculosis, papulonecroctic tuberculosis and erythematous rosacea-like tuberculosis with lupoid characteristics.
In order to comprehend the nature and significance of metastatic tuberculosis it is necessary to review the evolutionary mechanism in experimental animals. The classic experiments of Lewandowsky1 on hematogenous tuberculosis showed that when tubercle bacilli were injected into the arterial blood of the ventricle of a normal guinea