BACTERIAL CLASSIFICATION 21 



marked by the correlation of several distinct characters. 

 The first type, of which the ordinary parasitic strepto- 

 cocci are examples, produces a faint veil-like growth on 

 agar, shows under the microscope pairs or chains or 

 small groups of cells, generally stains by Gram, fails to 

 reduce nitrates or liquefy gelatin, and produces a strongly 

 acid reaction in dextrose and lactose broth.* The 

 second and third types include the forms characterized 

 by orange and white growth, respectively (the common 

 staphylococci of the skin). For these two types we 

 have suggested the generic names, Aurococcus and 

 Albococcus. Both resemble the streptococci in parasitic 

 habit and generally positive Gram reaction. Both, like 

 the streptococci, differ from the other three types in the 

 fact that they occur in small cell aggregates (never in 

 packets), and in their power of fermenting dextrose 

 and lactose, altho they show larger cell aggregates and 

 form less acid than the streptococci. Nitrate reducers 

 and gelatin liquefiers are found in both groups, but the 

 orange liquefiers act much more vigorously than do 

 those of any other type. The frequency curves for 

 this character are plotted in Fig. III. 



The other three groups of the cocci include the sapro- 

 phytic, yellow and red chromogenic forms. Cocci of 

 both types may of course be found on the body, but they 

 are the prevalent forms in water and earth, as the white 



* The quantitative basis of these definitions is discussed in Chapter 

 III. 



