THE GENUS MICROCOCCUS 213 



It will be noticed that motile forms are not excluded by 

 this definition. The half-dozen cocci which have been 

 described as showing flagella and motility, under certain 

 conditions of cultivation, resemble similar non-motile 

 forms in all other respects. A single character, of a 

 transitory nature, does not seem to warrant the creation 

 of a separate genus. Exaggerated importance has per- 

 haps been attached to this property because of the idea 

 that morphological characters, alone, are of systematic 

 value, and because of the dearth of such characters 

 among the cocci. With the characterization of genera 

 by the correlation of biochemical characters and habitat, 

 the motile forms may be relegated to a more modest 

 rank. 



The genus Micrococcus as thus denned is a remarkably 

 simple and homogeneous group. In our own work we 

 have studied one hundred and fourteen strains which 

 apparently belong to it. Thirty-one of these were isolated 

 from the body, thirteen of them from pathological con- 

 ditions; twenty-eight were from water, twenty-three from 

 earth, and thirty-two were from the air. It is apparent 

 that altho these organisms may occur upon the body, 

 their normal habitat is not confined to it, as in the genera 

 of the Paracoccaceae. Twenty-five strains were consist- 

 ently Gram-positive, thirty-eight variable, and fifty-one 

 consistently Gram-negative. The surface growth in one 

 hundred and one cases of the one hundred and fourteen 

 cultures was good to abundant. In dextrose broth nine- 



