During the past twenty years, with the application of improved methods and more extensive tests, a number of the natural groups or species of the streptococci have become fairly clearly defined. Among the more adequately described groups are those typified by Streptococcus pyogenes, the "animal pyogenes," Streptococcus equi, Streptococcus mastitidis, Streptococcus lactis, Streptococcus fecalis, Streptococcus liquefaciens, Streptococcus zymogenes, Streptococcus bovis and Streptococcus thermophilus. On the other hand, some of the streptococci which have been well known since the relatively early days of bacteriology have not been extensively studied by the more modern methods, and the differentiation of these forms from some of the better established groups is not entirely clear. In such a state are the characteristic non-hemolytic streptococci of the human throat, commonly designated as the "viridans group," Streptococcus mitior, Streptococcus salivarius, Streptococcus mitis, etc.The present study was limited to the predominating streptococci in the throats of healthy and presumably normal persons. The isolations were made by the application of quantitative dilution methods to freshly taken swab samples, so as to eliminate not only organisms of fortuitous occurrence, but also even streptococci native to the throat which may occur in small numbers.Under these quantitative restrictions true beta-hemolytic streptococci were not obtained among the 322 cultures which were isolated at various times from 20 healthy individuals. 263 on July 16, 2020 by guest
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