MORPHOLOGY 595 



the veins leads to a septicaemia fatal in 24-48 hours ; streptococci are present 

 in the blood in very large numbers. 



With a less virulent organism, localized foci of suppuration form on serous 

 surfaces ; from these the animal may recover but death often takes place 

 within 10-20 days. In such cases streptococci are not found in the blood. 



C. Intra-peritoneal inoculation. Inoculation into the peritoneal cavity is 

 followed by as severe an infection as inoculation into the veins. A virulent 

 streptococcus will kill a rabbit in 24-72 hours. 



The virulence of a given streptococcus for the rabbit may be indefinitely increased 

 by passage through rabbits. Marmorek, for instance, was able to increase the viru- 

 lence of a streptococcus to such an extent that one-millionth and even one-thousand- 

 millionth of a cubic centimetre of a broth culture was sufficient to kill a rabbit 

 when inoculated into the peritoneal cavity. 



Mice. Mice are almost as susceptible to infection with streptococci as 

 rabbits. A virulent streptococcus inoculated beneath the skin will kill a 

 mouse in 2472 hours. In the case of less virulent organisms death does not 

 occur so soon and is preceded by the formation of abscesses. 



Guinea-pigs. Guinea-pigs are less susceptible than rabbits and mice. The 

 inoculation of a virulent streptococcus beneath the skin generally gives rise 

 to a local abscess which ultimately resolves. 



If the virulent passage streptococcus of Marmorek be inoculated into the peritoneal 

 cavity in quantities of not less than 0'2 c.c., a purulent peritonitis and bacteraemia 

 results which is fatal in about 15-20 hours. 



Large animals. Of the larger animals, asses and horses are moderately 

 susceptible to infection with streptococci [of average virulence], the latter 

 somewhat less so than the former. Dogs and sheep, on the other hand, are 

 relatively immune. 



Man. Numerous experiments have been carried out on the human sub- 

 ject. The results of inoculation have often been negative, but, on the other 

 hand, in several instances a typical erysipelas has been produced and in one 

 case the experiment terminated fatally. 



SECTION II. MORPHOLOGY. 

 1. Microscopical appearance and staining 1 reactions. 



Streptococci consist of non-motile cocci arranged in chains. 



*' 



** % / ' :S r\ 



%% "k '"'{ 



s ,. r v ; 







FIG. 279. Streptococcus. Film from 



FIG. 278. Streptococci in pus. Jenner's stain. a broth culture Carbol-crystal- violet. 



(Oc; 2, obj. Atfi, Zeiss.) (Oc. III. obj. ^th, Beich.) 



