THE group of micro-organisms known as the haemolytic streptococci is responsible for a number of acute inflammations in various regions of the body, such as erysipelas, heart disease, and puerperal fever, as well as for such diseases as scarlet fever and certain types of pneumonia. In addition, they are important secondary invaders, attacking those whose resistance is already lowered by some other infection. They spread in the body both by the lymph and the bloodstream and are. frequently found on mucous surfaces in apparently healthy individuals. They are only known as parasitic upon the animal body and appear to maintain themselves in a human population like the meningococcus or pneumococcus, namely, by carriers.