By the mix-culture of Bact. coli groups, which were isolated from the sound man's feces, with Sal. typhi in bouillon, the author found the following results: 1) There was observed the difference of bacterial antagonism due to the difference of types of Coli groups, but no difference due to that of the generations of mix-culture. 2) By the mix-culture, Coli communis and communior came to show the paragglutination with anti-typhoid serum (particularly with O-serum), and it was raised from generation to generation till the 10th generation and then fell down. This paragglutination tended to appear and disappear suddenly. The paragglutination after the enough repeated generations of mixculture was relatively stable. 3) The Bact. coli which was mix-cultured with Sal. typhi did not show any variation of its biological natures.