STBEPT0C0CCU8 PYOGENES AND STREPTOCOCCUS AGALACTIA 597 



antigenic analysis, using antisera to eight of the strains, showed considerable diversity of 

 antigenic structure, but many group reactions. The two main types differentiated on 

 colonial appearances were shown to be antigenically distinct. Finally, those strains that 

 were tested for heat resistance were found to be killed by heating to 58-60° C. for 30 

 minutes. Stone (1940), who studied 26 strains from partiu-ient women, divided them into 

 three groups according to their growth in 10 or 40 per cent, bile, and was able to demonstrate 

 the presence of at least two acid-extractable antigens havmg some relation to those met 

 with in the laon-anferobic types of streptococci. 



It may be noted that the pathogenicity of anaerobic streptococci for laboratory animals 

 appears to vary widely. Wegelius (1909) produced small abscesses in the peritoneal cavity 

 of mice. Marwedel and Wehrsig (1915), with one strain examined, produced an acutely 

 fatal infection in a guinea-pig. Prevot (1925) records pathogenic lesions of a suppurative 

 gangrenous or oedematous type, sometimes fatal, with most of his strains. Harris and 

 Brown (1929) found that three of 57 strains derived from cases of puerperal fever killed 

 mice within 24 hours. Colebrook and Hare (1933) tested seven puerperal strains by sub- 

 cutaneous injections into mice. Two of them gave rise to small caseous foci at the site of 

 inoculation, but none of the mice died. 



Anaerobic pneumococci have also been described (Smith 1936). 

 We append a summarized description of the more important species, or groups, 

 to which names, or labels, can at the moment be attached. 



Species, Groups and Types 

 Str. pyogenes 



Morphology. — Cocci, usually spheroidal, about 0-5-0-75 ft in diameter, arranged in 

 chains of varying length, but usually including ten or more cocci. Capsules usually absent 

 or poorly develoiJed in tissues ; frequently present in young serum broth cultures of 

 freshly isolated strains. Non-motile. No spores. Gram-positive ; not acid-fast. 



Growth Requirements. — When first isolated may grow poorly on ordinary nutrient 

 agar. Growth is markedly improved by the addition of blood or serum. Optimal tem- 

 perature 37° C. Grows at temperature slightly over 40° C. Poor growth below 20° C, 

 and usually fails to grow at 10° C. Aerobic and facultatively anaerobic. 



Type of Growth. — On solid media after 24 hours' incubation, the colonies are small, 

 about 0-5-0-75 mm. in diameter, opaque, slightly raised, circular, with an entire margin, 

 a slightly granular surface, and a granular structure, when viewed by transmitted light, 

 showing some differentiation into a more opaque central portion, and a more translucent 

 periphery. Aft«r further incubation (48 to 72 hours) the colony may extend in diameter, 

 and become differentiated into a raised central portion, smooth or contoured, and a flatter 

 peripheral zone. The colonial forms presented by different strains are subject to consider- 

 able variation ; and a plate from a single strain may show colonies of very varying appear- 

 ance ; particularly with regard to the smoothness, contouring, or granularity of the surface, 

 and the degree of differentiation between the central and peripheral zones. 



Streaked cultures on solid media give a relatively scanty growth, with a tendency for 

 a majority of the colonies to remain discrete. The growth emulsifies easily, but usually 

 gives a granular suspension. 



In blood agar plates. — The colonies are surrounded by a zone of /^-haemolysis (see above), 

 best seen in the deep colonies. A filtrable haemolysin is formed in fluid cultures, which 

 is oxygen-labile. An oxygen-stable ha^molysin is also 2)roduced. 



In broth, or serum broth. — When first isolated, the growth may be finely granular, or may 

 form a powdery deposit at the bottom of the tube, or cling to its sides. Turbidity of the 

 medium may be moderate, or slight. After subculture, and particularly when repeatedly 

 subcultured at short intervals, the turbidity may increase markedly, and the granular 

 deposit decrease, or disappear ; but the turbidity almost always remains of a finely granular 



