In various toxic-infectious conditions a type of brain lesion has been described to which has been given the names "brain purpura," "hemorrhagic encephalitis," and "perivascular hemorrhages"; none of these titles gives an adequate idea of the pathologic nature of the disease, though each contains some element of truth. The nature of the process, the nomenclature, the type of cell involved in the pathologic reaction and even the type of lesion which should be included in this group are sufficiently ill defined to make a survey of the field both desirable and useful. In 1903, Rosenfeld1described a pathologic process in the brain to which he gave the name "hemorrhagic encephalitis." This condition had apparently been overlooked up to this time. His article was followed, in 1905, by a more thorough investigation by Schmidt,2who first used the term "brain purpura." Schmidt preferred the latter term, though the lesion