a serologic classification dividing hemolytic streptococci into groups (A-O) that bear a definite relationship to their sources, based on precipitation tests depending on group-specific carbohydrate substances; e.g., Group A contains strains most pathogenic for humans; B, strains from mastitis in cows and from normal milk, including strains from the human throat and vagina; C, strains from various lower animals, including a number from cattle and the human throat; D, strains from cheese and humans; E, strains from certified milk; F, strains mainly from the human throat, associated with tonsillitis; G, strains from humans, a few from monkeys and dogs; and H, K, and O, nonpathogenic strains occasionally from normal human respiratory tracts.