THE GENUS MICROCOCCUS 221 



M. tenacatis, Chester; M. tetragenus-citreus, Vincenzi; M. 

 versicolor, Fliigge; M. vesiculiferus, Migula; M. viridis- 

 fiavescens, Guttmann. Some of the characterizations 

 (M. plumosus, M. stellatus, etc.) are based upon supposed 

 differences in colony-morphology; but these seem too 

 uncertain and unimportant for the definition of species. 



The three types so far defined, M. flavus, M. citreus, 

 and M. luteus, are the only micrococci with which we 

 have come in contact in our own work. A great many 

 references in the literature make it apparent, however, 

 that a coccus is often found in earth, water, or air which 

 has the other properties of the species last defined, M. 

 luteus, but fails to form any appreciable amount of yellow 

 pigment. Its colonies are generally described as porce- 

 lain-white. This type was observed as long ago as 1886 

 by two observers; in that year, Fliigge called it M. candi- 

 cans, and Bolton, M. aquatilis. 



The second of Gordon's staphylococci of the skin, found 

 in considerable numbers on the scalp, apparently corre- 

 sponds to this type. It resembles Fliigge' s M. candicans 

 in positive Gram stain, and cannot be sharply separated in 

 this respect from M. luteus, in which the reaction is some- 

 times positive. It shows the low fermentative power of the 

 genus Micrococcus, failing to act on lactose, maltose, or 

 glycerin, but producing acid in mannite. It fails to 

 liquefy gelatin and does not reduce nitrates or neutral 

 red. 



None of our cultures of Micrococcus, characterized by 



