THE GENUS AUROCOCCUS 175 



out that, when kept in tap water or distilled water, the 

 orange staphylococcus lost its orange color and again 

 recovered it after animal inoculations. In an earlier 

 communication (Winslow and Rogers, 1906) we have 

 shown that exposure to as low a temperature as 50 to 55 

 degrees may produce a subsequent loss of chromogenic 

 power. Too strong ligjit, or too long cultivation in 

 complete darkness, as well as the presence of chemical 

 poisons, are said to hinder chromogenesis (Neisser and 

 Lipstein, 1903). 



Differences in pigment production appear also to 

 arise among the cocci as the result of spontaneous 

 variations, — not, as in the cases quoted above, in response 

 to unfavorable environmental conditions. Conn (1900) 

 and Sullivan (1905) note that on a plate, sown from a 

 pure culture, there may develop colonies varying appre- 

 ciably in shade, from which, by selection of the extremes, 

 quite distinct types can be derived. Neumann (1897) 

 records the sudden appearance of widely different strains, 

 as sectors in old and carefully sealed stab cultures. We 

 have observed both phenomena in our own work, but 

 are inclined to attribute the second to contamination. 



Medical bacteriologists, from practical experience, have 

 recognized the pyogenic staphylococci as a fairly well 

 defined natural group; and in view of the unstable 

 character of the pigment-producing power they have 

 generally considered the orange and white forms as only 

 varietal types. Published descriptions were, however, 



