THE GENUS AUROCOCCUS 177 



degrees, the action of the organisms upon milk and gela- 

 tin, and their chromogenic power. The morphological 

 characters upon which this classification was based do 

 not seem to us of great weight. The occurrence of the 

 same coccus in larger or smaller cell groupings, according 

 to varying conditions, is a matter of common observation, 

 and the size of the individual cell is also notably incon- 

 stant. The last three of Unna's types are apparently 

 sarcinae, which occur in larger or smaller growth masses; 

 and the twelve classes under these three types, including 

 fifty-seven cultures, were all alike in failing to acidify 

 milk and liquefy gelatin. The first two growth-types of 

 Unna, micrococci occurring singly or in pairs, included 

 eleven classes, differing in chromogenesis, liquefaction, 

 and lactose fermentation. Of these classes, i, 2, 3, and 

 n, including sixteen cultures, acidified milk, liquefied 

 gelatin, and produced a yellowish growth. Class 9 

 (four cultures) differed in its grayish- white growth; Class 

 5 (one culture) in its white growth and failure to liquefy. 

 Among the non-acid formers, Class 4 included three cul- 

 tures of yellow liquefiers, Class 6, two cultures of white 

 liquefiers, Class 7, a single orange non-liquefying form, 

 Class 8, five white non-liquefiers, and Class 10, two yellow 

 non-liquefiers. 



In this investigation, the fundamental difference be- 

 tween the orange and yellow chromogens was again 

 ignored. The comparative quantitative study of bio- 

 chemical characters in a considerable series of cultures 



