154 RELATIONSHIPS OF THE COCCACE^E 



group (8) was marked by the occurrence of the cells in 

 pairs; group (9) by the presence of a capsule; and group 

 (10) by the arrangement of the cells in plates rather than 

 chains. Even without taking into account the over- 

 lapping of the various groups, this classification is scarcely 

 adequate. Virulence and growth on potato are such 

 exceedingly unstable characters as to be of little diagnostic 

 value in this genus. Motility is of extremely doubtful 

 occurrence; no motile streptococcus has been recorded 

 by any good observer during the recent period in which 

 the methods of bacteriology have developed to approxi- 

 mate accuracy. The last three groups include organisms 

 which probably belong to other genera. 



Lingelsheim (1903), in a somewhat less arbitrary 

 fashion, divided the genus into seven species as follows: 



(1) Str. longus, characterized by long chains, positive Gram 

 stain, small colonies on agar, and variable pathogenicity; 



(2) Str. brevis pharyngis, differing in showing short chains, 

 no pathogenicity, and feeble viability in cultures; (3) 

 Streptococcus of Etienne, chains of slender cells decolor- 

 izing by Gram ; (4) Streptococcus of the saliva, non-patho- 

 genic, short-chained form, capable of growth on potato; (5) 

 Sir. brevis liquefaciens , differing from No. 4 in decolorizing 

 by Gram and liquefying gelatin; (6) Str. coli gracilis, 

 differing from No. 5 in showing longer chains with a ten- 

 dency to the formation of tetrads; (7) Leuconostoc, the 

 zooglcea-forming type. 



In this classification the use of several characters in 



