516 INFECTION AND IMMUNITY. 



in wound infections and septicemia, and gave to 

 the organism the name of Streptococcus pyogenes. 

 Morphology. The typical streptococcus is a spherical or 

 spheroidal cell, about one micron in diameter, 

 which grows in the form of chains of varying 

 length. Division takes place in one direction 

 only. Variations in form, such as diplococcus-like 

 cells in pairs or chains, or elongated cells resem- 

 bling bacilli, represent accidental stages or anoma- 

 lies in division. Streptococci commonly appear as 

 diplococci in the blood and tissues of the infected. 

 Unusually large cells may be involution forms. 

 The difficulty of distinguishing the pneumococcus 

 from the streptococcus has been mentioned. At 

 one time it was thought that streptococci could 

 be separated into those which grew in long chains 

 (8. long us) and those which produce short chains 

 (8. brevis) . Although these names are still used 

 for convenience, they are not well grounded, since 

 the length of the chains is not an inherent prop- 

 erty; one form may be changed into the other by 

 appropriate methods of cultivation. Similarly the 

 8. erysipelatis of Fehleisen is not a specific or- 

 ganism for erysipelas, since strains from other 

 sources are able to cause experimental erysipelas 

 in man. Streptococci growing in short chains may 

 be cultivated from the normal mouth cavity and 

 they are usually of low virulence for animals. On 

 the other hand, 8. longus is more often obtained 

 from wound infections, septicemia and malignant 

 ' tonsillitis. Capsulated strains of high virulence 

 are occasionally found in the body. Ordinarily, 

 however, streptococci are not surrounded by a cap- 

 sule. The Streptococcus mucosus may be a pneu- 

 mococcus. Although streptococci are described 



