THE GENUS MICROCOCCUS 217 



own series of cultures we have examined twenty-four 

 strains of yellow cocci from the body. In Gram reaction, 

 fermentative power, and rate of gelatin liquefaction, as 

 well as in chromogenesis, they resembled the saprophytic 

 micrococci, and differed from Aur. aureus. It seems 

 more probable, therefore, that this subtype is a form of 

 M. flavus, which lives on the surface of the body and may 

 at times acquire pathogenic properties, rather than a form 

 of Aur. aureus, which has lost its Gram reaction and its 

 power to break up dextrose and lactose, changed its chro- 

 mogenesis and weakened in its ability to act on gelatin. 



Another common type of the micrococci differs from 

 M.flavus in its ability to reduce nitrates. This appeared 

 to be the second form in abundance in our investigation, 

 thirty-one of the one hundred and fourteen cultures ex- 

 amined showing the power of attacking nitrates. As in 

 the case of Aur. mollis, discussed in Chapter VIII, some 

 cultures formed ammonia only, some nitrites only, and 

 some both. The first case was the most common. For 

 the present it seems best to include all these forms under 

 a single type, until further study shows how significant 

 the differences may be. 



In other respects the biochemical characters of this 

 type correspond to those of M . Jlavus, with a single excep- 

 tion; eight of our thirty-one cultures failed to liquefy 

 gelatin. In the genus Aurococcus a similar phenomenon 

 was noted. Nitrate reducers (Aur. mollis) generally lique- 

 fied gelatin, but occasionally cultures were found which 



