No gas produced in peptone; pleomorphic forms not uncommon Bacteroides p. 424 (See also Sphaerophorus gulosus.) 10. Halophilic, requiring more than 4 per cent salt for growth; gas produced from peptone Bacteroides p. 4^4 {B. halosmophilus) Not halophilic 11 11. Very pleomorphic; gas produced from peptone Sphaerophorus p. 44I {S. necrogenes and S. necrophonis and possibly S. varius and S. bullosus) Bifurcated cells; gas production from peptone doubtful Bacteroides p. 4^4 {B. fur cos us) 12. Acid produced from lactose 13 No acid produced from lactose 16 13. Motile Bacteroides p. 424 (B. variegatus) Non-motile 14 14. Non-pleomorphic, /«si/orw cells growing poorly on plain agar (?) Fusobacterium p. 4^6 Not as above 15 15. Gelatin liquefied; very pleomorphic on ordinary or blood agar Sphaerophorus p. 44-1 {S. glycolyticus) and Bacteroides p. 4^4 {B. uncatus) Gelatin liquefied; not pleomorphic Bacteroides p. 424 {Bacteroides exigmis, B. uniformis, B. tumidus and some strains of B. distasonis) Gelatin not liquefied Bacteroides p. 4^4 16. Motile; fusiform rods; pleomorphic Fusobacterium p. 436 {F. praeacutum) Non-motile 17 17. Very small rods capable of passing through a Chamberland L2 filter; acid produced from glucose, sucrose and mannitol; recorded from the respiratory tract of man Dialister p. 44O Not as above 18 18. Organisms dependent on serum or ascitic fluid for growth; pleomorphic Sphaerophorus p. 44^ {S. floccosus and S. abscedens) Not as above 19 19. Slender, pointed rods Fusobacterium p. 4S6 {F. polyinorphuui and F. vescum) Rods with rounded ends Bacteroides p. 4^4 {B. cylindroides, B. capillosus, B. fragilis, B. perfoetans, B. uncatus and B. succino- genes) 20. Acid from fructose Sphaerophorus p. 44^ {S. siccus) Not as above 21 21. Organisms require serum or ascitic fluid for growth; pleomorphic Sphaerophorus p. 4P (S. caviae) Not as above; not pleomorphic Bacteroides p. 4^4 {B. putidus, B. putredinus and B. coagulans)
