STREPT. ERYSIPELATIS AND STREPT. LACTICUS. 179 



First, 2,500 cubic centimeters double-strength bouillon of the above 

 composition was prepared as follows: 2,500 grams chopped lean beef 

 was placed in 2,500 cubic centimeters distUled water for twenty-four 

 hours at 15° C. (tliis infusion was strained through two layers of cheese- 

 cloth) ; 50 grams Witte's peptone and 25 grams NaCl were mixed together 

 in a smooth paste, with 500 cubic centimeters of the strained infusion. 

 Care must be exercised to leave no unbroken globular masses of peptone. 

 Add the peptone emulsion to the rest of the infusion and make up to the 

 required volume. Autoclave fifteen minutes under 15 pounds' pressure. 

 Adjust the reaction to very faint pink for phenolphthalein by the addition 

 of n/1 NaOH;^ then autoclave for forty-five minutes, and filter through 

 Swedish filter paper. Control the volume. Place 200 cubic centimeters 

 of the bouillon thus prepared into each of eleven Erlenmeyer flasks (500 

 cubic centimeters) and sterihze in the autoclave for tliirty minutes. The 

 remaining portion may be employed to estimate the hydrogen ion con- 

 centration as previously described; that is, at first an approximate re- 

 action is determined by the colorimetric method, ^ then finally electrically.^ 

 The following table indicates the various amount of n/1 NaOH or n/1 

 HCl and distilled water (sterilized) to be added separately * to obtain the 

 different hydrogen ion concentrations desired : — 



Table I. — Preparation of Media. 



Sets 1 and 2 were prepared at the same time. 



Ph — exponent of hydrogen ion concentration, explained previously. 



Inoculation was made with 1 cubic centimeter of forty-eight hour lactose broth culture. 



' This manipulation is found to be necessary in order to have the bouillon remain clear. 



2 It has been described previously on p. 161. * It has been described previously on p. 163. 



' It has been described previously on p. 145. * This has been treated on p. 161. 



