278 A MANUAL OF BACTERIOLOGY 



best culture medium, but even on these the organisms 

 must usually be subcultured every few days, or they die 

 out. Some varieties are hsemolytic, the haemolysis being 

 due to a lysin, others are not hsemolytic. Hsemolytic 

 varieties are common in influenzal pneumonia. On 

 gelatin, which is rarely liquefied, the growth has much the 

 same characters, and is better seen, as this medium is 

 clearer than agar, but it takes some days to attain the 

 maximum. In stab-cultures minute spherical colonies 

 develop all down the line of the stab, but without invading 

 the surrounding medium. In broth a flocculent deposit 

 forms, the fluid sometimes remaining clear, sometimes 

 becoming turbid. There is no growth on potato. Litmus 

 milk is usually acidified and sometimes coagulated, and 

 acid is generally produced from glucose. Most strepto- 

 cocci, with the exception of the pneumococcus, fail to 

 ferment inulin. The indole reaction can be obtained in 

 broth cultures in seven to fourteen days on the addition 

 of a nitrite, but not without. 



The thermal death-point of the streptococci is 55 to 

 60 C., the time of exposure being ten minutes, and they 

 are destroyed by weak solutions of disinfectants, e.g. 

 1-100 phenol, in ten minutes. Streptococci are generally 

 delicate organisms, soon dying out, but some of the 

 faecal varieties may live for weeks or months in water 

 and sewage. 



Much research has been devoted to the differentiation 

 of the streptococci. We have the pioneer work of 

 Andre wes and Horder. Gordon, Houston, Besredka and 

 Ainley Walker on the fermentation reactions of the group. 

 Fermentation reactions carried out with a long series of 

 fermentable substances lead to an almost endless number 

 of varieties. Of more recent work, 1 that of Holman, 



1 See Holman, Journ. Mcd. Research, vol. 34, 1910, p. 378 ; Blake, ibid., 

 vol. 36, 1917, p. 99 ; Adkinson and Walker, ibid., vol. 41, 1920, p. 457 ; 



