88 RELATIONSHIPS OF THE COCCACE^ 



form good surface growths, produce a moderate acidity 

 in sugar broth, grow well, but with poor pigment produc- 

 tion, at 37 degrees, and generally produce a considerable 

 liquefaction of gelatin. The red-pigment-producers occur 

 often in packets, are generally Gram-negative, grow 

 abundantly, ferment dextrose slightly but not lactose, 

 form nitrites, but not ammonia, in nitrate solution, and 

 generally fail to liquefy gelatin. 



With these general relations of the four color-types of 

 the Coccaceae in view, it is possible to interpret more 

 intelligently the differences which appeared when the 

 cultures isolated from the body were compared with those 

 of saprophytic origin. The average results cited early in 

 this chapter were naturally imperfect because cultures 

 taken from the skin include stray saprophytic cocci and 

 vice versa. As a matter of fact 31 per cent of the cocci 

 isolated from the skin were of the yellow type and 16 per 

 cent of those from water, earth, and air were orange 

 chromogens. On the whole, however, the average 

 character of each flora was determined by its predominant 

 component types. Grouping similar forms together and 

 referring them to the respective habitats in which they 

 occur in greatest numbers, it is clear that the white and 

 orange forms belong with the streptococci as parasitic 

 Coccaceae, while the yellow and red chromogens form a 

 saprophytic division of the family. The common charac- 

 ters in each of these two habitat-groups are so many, and 

 the mutual contrast between them so marked, as to leave 



