DYSENTERY AND ALLIED BACILLI 9 



medium) and H-ion determinations were made by the dilution method. In 

 chart 2 the data are shown graphically. 



The rate of acid production was observed qualitatively by the use of brom- 

 cresol-purple and in some instances with the china-blue rosolic acid indicator. 

 Inoculation was made from 24-hour agar slants; incubation was at 37 C. in 

 the ordinary manner; acidity was recorded after 6 hours. At this time all 

 strains of B. alkalescens and B. dispar, one B. flexneri and the 2 B. dys. 

 Sonne were distinctly acid as indicated by. a distinct or dirty yellow with brom- 

 cresol-purple. All other strains produced acid less rapidly. They showed a 

 distinct purple (more alkaline than P H 6.3) with brom-cresol-purple and with 

 the china-blue mixture were colorless or light blue. 



Q? 



i 



S.O 



6.0 



Chart 2. Rate of acid production: Inoculations made from 24-hour broth cultures and 

 H-ion determinations made by dilution method. 



It may be concluded from the observations of glucose fermentation that B. 

 alkalescens and B. dispar produce acid more rapidly and then revert to a 

 distinctly alkaline reaction that may be indicated qualitatively, by phenol-red 

 or brom-cresol-purple. The use of brom-cresol-purple, however, would require 

 experience and care, whereas phenol-red necessitates a prolonged period of incu- 

 bation. The most desirable indicator for qualitative differentiation would be one 

 which changes at P H 6.5 showing a distinct coloration on the alkaline side. 



A SIMPLIFIED SOLID MEDIUM FOR GROWTH AND ISOLATION OF 

 DYSENTERY BACILLI 



After a number of preliminary experiments it was found that by the addi- 

 tion of a small amount of glucose (0.03-0.05) to peptone-phosphate agar, 

 growths as luxuriant, if not more so, than on nutrient agar could be obtained. 

 As facilities for determination of the optimum H-ion concentration were not 

 available at the time in France a series of experiments were carried out to 

 determine the optimum concentration of dipotassium phosphate for growth of 

 dysentery bacilli in a medium not requiring any further adjustment of reaction. 



