600 THE STREPTOCOCCI OF MAN 



latter type. No relation has been established between the virulence for man 

 and the virulence for the lower animals. 



[Andrewes and Horder found that streptococci of their pyogenes and 

 anginosus groups, which include 145 out of 194 strains examined, were patho- 

 genic to mice when first isolated from the body ; those of the salivarius and 

 JoBcalis groups were non-pathogenic. In their experience a streptococcus 

 may be the cause of a septicaemia or of an inflammatory affection in man 

 and yet produce little or no effect when inoculated into a rodent, and they 

 formed the opinion that while there was a general correspondence in patho- 

 genic effect upon man and rodents it was not universal.] 



Method of increasing the severity of experimental streptococcal infections. 

 (a) The pathogenic power of a streptococcus for a rabbit may be increased by 

 inoculating with it sterilized culture of Proteus vulgaris (Roger and others). 



(b) Vincent has shown that the streptococcus is more virulent for laboratory 

 animals when associated with the typhoid bacillus and its products. 



A streptococcal culture, 0'25 c.c. of which inoculated into the veins of a rabbit 

 caused no rise of temperature, led to a fatal septicaemia in an animal which had, 

 previously to inoculation with the streptococcus, been inoculated with a culture 

 of the typhoid bacillus. Cultures of the typhoid bacillus, sterilized by filtration, 

 and inoculated at the same time as a streptococcus render the latter much more 

 virulent. A highly immune animal such as the guinea-pig dies of a streptococcal 

 septicaemia* if it be inoculated intra-peritoneally with a mixture consisting of 2 c.c. 

 of a filtered culture of the typhoid bacillus and 1 c.c. of a streptococcus the virulence 

 of which has not been artificially raised. 



Exaltation of virulence. (a) The method recommended for obtaining a very 

 virulent virus for the preparation of toxin is that of Marmorek who increases 

 the virulence of the organism by passage through rabbits. The technique 

 is as follows : 



Inoculate a fatal dose of the streptococcus into the ear vein of a rabbit. As soon 

 as the animal is dead, sow some of the heart blood in a tube of human-blood-serum. 

 Incubate at 37 C. for 48 hours and then inoculate a second rabbit with the culture. 

 Sow a second culture and inoculate a third rabbit and so on indefinitely. The viru- 

 lence can only be maintained by repeated passage through animals. After passage 

 experiments extending over 2 months Marmorek found that the streptococcus was 

 so virulent that 0-000,000,000,01 c.c. sufficed to kill a rabbit. (This exceedingly 

 minute dose diluted with 1 c.c. of broth and inoculated into the peritoneal cavity 

 led to death from septicaemia in 30 hours.) 



(b) In a similar manner, Aronson increased the virulence of streptococci 

 by passage through mice. 



2. Bio-chemical reactions. 



Formation of indol. Streptococci do not form indol in culture. 



[Neutral red. Using ordinary broth tinted with the dye it has been found 

 that some streptococci after anaerobic cultivation for 48 hours change the 

 colour of the medium from cherry red to orange green, while others leave the 

 original colour unaltered (vide infra). 



[Fermentation reactions. Gordon tested ten " representative " streptococci 

 obtained from disease processes and other sources upon 33 substances of the 

 carbohydrate, glucoside and polyatomic alcohol series. 



The medium was made up thus : 



Lemco, ... 1 per cent. 



Peptone, - - 1 



Test organic substance, 1 



Sodium bicarbonate, ...... O'l 



10 per cent, watery solution of ordinary solid litmus, - 10 



Water, 87 



and the cultures were incubated for 3 days at 37 C. 



