The _identity_ of the microbe with other streptococci of animals and man has been claimed. Arloing alleges that, by culture of the microbe in the blood or peritoneum of the live rabbit, he exalted the virulence, and obtained in succession a streptococcus capable of producing _erysipelas_; _gangrenous erysipelas_; _suppurating_, _sloughing erysipelas_; _pseudo-membranous peritonitis_; _metastatic abscesses_; and _fulminant septic peritonitis_. Hill, Jensen and Sand, and Lignieres, as the result of cultures and inoculations claim that strangles streptococcus is identical with that of contagious pneumonia. Courmont, on the other hand, as the result of his cultures and inoculations, concludes that the microbe of strangles and that of erysipelas are independent organisms. The clinical evidence is decidedly against the theory of identity. In epizoötics of strangles we meet with a constant succession of cases of strangles and in districts into which contagious pneumonia has never been introduced, no single case of that disease ever comes in to break the monotony of the sequence and to start a series of cases of the latter affection. Conversely, in an outbreak of contagious pneumonia in a locality heretofore free from strangles, strangles do not develop. Again, no matter how prevalent nor how constant strangles may be in a locality, and how habitually men have their wounded hands covered with the pus of the abscesses, no epidemic of erysipelas is entailed in man. Strangles spreads with remarkable rapidity through a stable, but not to the often more than equally exposed human attendants, nor to any animal apart from the genus equus. The absence of strangles from Iceland (Jonsson) endorses that view. As a practical question of sanitary science, we occupy a sound position in differentiating the germs of strangles and contagious pneumonia, and further that of erysipelas of man, as a wise health officer would differentiate the microbes of cowpox and smallpox. Whatever may be true or false as to their primary identity, or as to the transition of one to the other in successive inoculations on animals of other genera, they are essentially diverse pathogenically as we meet with them in practice, and our measures may be safely based on this practical diversity. _Accessory Causes._ _Youth_ strongly predisposes, most cases occurring between two and five years, and seventy per cent. before five years. It may, however, appear at any age, being congenital in some cases (Nocard, etc.), in others appearing a few weeks after birth, and in still others at over twenty years, if the subjects have not contracted it earlier. _Dentition_ which is active in these early years, induces congestion about the head and general constitutional disturbance, which make the system more receptive.