140 RELATIONSHIPS OF THE COCCACE^E 



during dichotomously branching chains during repeated 

 cultivations. This author believes that differences, both in 

 chain formation and in the manner of growth in broth, are 

 markedly influenced by the reaction of the medium. He 

 states that a streptococcus which forms long chains and 

 shows sediment in acid broth will grow in short chains 

 and show a uniform turbidity if the broth be made slightly 

 alkalin. The Gram stain is usually positive with the 

 streptococci, especially in cultures freshly isolated from 

 the body. Cultivation in artificial media produces more 

 variable results. 



The streptococci are essentially parasitic forms. Their 

 habitats are the various surfaces of the animal body, from 

 which they penetrate the tissues in acute disease. Their 

 growth on solid media is always feeble. On potato it is 

 generally so sparse as to be invisible. Cultures die out 

 very rapidly in successive transfers. Cultivation under 

 anaerobic conditions is often more successful than in the 

 presence of air. In broth, cultures grow well for a few 

 transfers, producing turbidity and, later, sediment if the 

 growth is active, or sediment alone if it is less vigorous. 

 Sugars are favorable for development, and are generally 

 fermented; milk is coagulated by some strains but not by 

 all; other biochemical reactions are generally negative. 

 The virulence of the streptococci is extremely variable. 

 When grown on culture media they rapidly become non- 

 pathogenic. Repeated passage through animals, on the 

 other hand, may produce so high a virulence that a very 



