What remains after eliminating erysipelas, constitutes a group having so much in common that attempts at further differentiation have led to much disputation, and not even to-day is there such accord in different countries as the writer of a text-book would find desirable. One class of pathologists claims but one common disease with many varieties under different conditions, just as the term _septicæmia_ or _blood poisoning_ has been made to designate a whole class of local and general infections, irrespective of the particular microbes that cause them. Others with greater precision give the disease a name according to the causation by one particular microörganism, or by another, which may be closely related to it in many respects, but which in successive subjects and outbreaks, maintains its own individual characteristics as regards morphology, cultural and staining habits, pathogenesis, etc. The question has been rendered all the more trying, by the occasional association in the same animal system, or in the same outbreak of two distinct varieties of microörganisms, in place of one, giving rise of course to modifications in the symptoms, lesions, progress, mortality, etc. Apart from the microörganism the whole class tends to show a close family relationship in their pathological phenomena shown under different conditions : 1st. Under a large dose, or specially virulent germ, in a particularly susceptible animal, all tend to a manifestation of an acute septicæmia, with generally diffused petechiæ of the skin, mucosæ, serosæ and internal organs, blood extravasations, and an early high mortality. 2d. Under a smaller dose, or a less potent germ, or in a less susceptible animal the tendency is to necrotic processes in the seat of inoculation or the point of election of local lesions. Necrotic ulcers are especially common in cases that survive one, two or three weeks, or that develop in a subacute or chronic form. 3d. With a minimum dose of a germ of little potency, and in a very resistant subject even the necrotic lesions may be absent, and there may be suppuration only or ulceration of serosæ and joints. The question of the primary identity, or disparity of the whole class of germs, causing the septicæmic swine plagues, may be practically ignored in this work; it is important rather with our present knowledge to note the diseases associated with particular germs, or varieties of germs, and to describe these as far as possible as independent affections. This is as permissible as it is to describe smallpox, sheeppox, and cowpox as distinct affections, no matter what may be the truth or falsity as to their alleged original identity. _Rouget_ in Europe and _Hog Cholera_ and _Swine Plague_, as the best established types in the United States deserve primary mention, to be followed by references to additional types which have been found to be associated with other distinct microörganisms.