522 H. J. CONN, CHAIRMAN 



FERMENTATION OF SUGARS, ALCOHOL AND GLUCOSIDES 



This may be determined in either sohd or liquid media accord- 

 ing to which the organisms to be investigated prefer for their 

 best growth; but the committee recommends that solid media 

 be used whenever possible. 



The method recommended for determining fermentation in 

 solid media is that described by Conn and Hucker (1920). 



When solid media are to be inoculated, use the following agar 

 slant method: Prepare two lots of agar media, one the regular 

 beef extract agar and the second a peptone-free agar having the 

 following composition : 



NHtHjPOj 1.0 gram Adjusted to pH 7 by the addition 



KCl 0.2 gram of NaOH. About 6 cc. normal 



Agar 15.0 grams NaOH required 



Water 1000 cc. 



To both of these media add 1 per cent of the fermentable sub- 

 stance to be investigated and 2 cc. per liter of a saturated aqueous 

 solution of brom cresol purple. Distribute these two media in 

 test tubes and cool in a slanting position. The tubes should be 

 inoculated either on the surface alone like an ordinary agar 

 slant, or partly on the surface and partly in a stab at the base of 

 the tube. The tubes should be inoculated at 37°C. or 25°C. 

 according to the optimum temperature of the organism under 

 investigation. Examine after twenty-four hours and then as 

 often as seems necessary according to the rapidity of the growth 

 so as not to overlook any changes in reaction. Acid can be 

 readily determined by the yellowing of the indicator. A very 

 good idea as to the amount of acid can be obtained by noticing 

 the size of this zone of yellow. This method is only roughly 

 quantitative yet gives fairl}'^ satisfactory results. A convenient 

 method of denoting results is the following: use a single -|- sign 

 if acid is produced but the yellow zone does not extend to the 

 base of the slant, denote ++ ii the acid zone extends to the base 

 of the slant but no further, -|- 4- + if it extends half way from 

 the base of the slant to the bottom of the tube and + + 4- -(- if 

 the whole tube of agar has turned to its acid color. Use the 

 symbol (0) to indicate no change in reaction. 



