438 I. J. KLIGLER AND J. DEFANDORFER 



addition either of nutrose or bile produced a marked improvement 

 of the medimn, the former surpassing the latter in this respect. 

 Further study showed, however, that other factors were con- 

 cerned, and finally, by elimination and new cultivation, a medium 

 was evolved which offered distinct advantages for the cultiva- 

 tion of the dysentery bacilli. The modification consists in the 

 substitution of sodium bisulphite as recommended by Robinson 

 and Rettger (1916) and the accurate adjustment of the hydrogen 

 ion concentration to a Ph value of 7.6-7.8. The medium as ordi- 

 narily prepared with a phenolphthalein reaction of +0.2 gives 

 an end reaction, after the addition of the sodium-sulphite which 

 is alkaline, ranging from P^ 8.4 to 8.8. This degree of alkalinity 

 is inhibitive to the growth of the Shiga bacillus. 



Either meat-infusion or beef-extract agar may be used. We 

 use a beef-extract medium prepared as follows : 



Peptone 10.00 grams 



Beef extract 3.00 grams 



NaCl 5.00 grams 



Agar 15.00 grams 



Water 1000 cc. 



All the ingredients except the agar are dissolved first; the 

 agar is then added and the mixture autoclaved for one hour at 

 15 pounds pressure. It is then cooled to 50°C., white of egg 

 added (2 eggs to 5 liters), and steamed in the Arnold for thirty 

 minutes. The reaction is then adjusted to P^ 7.4, with phenol- 

 sulphonephthalein as the indicator, the medium boiled on the 

 free flame for six to seven minutes, filtered, flasked, and auto- 

 claved. 



This constitutes the stock^ medium from which all the special 

 media — brilliant green, Endo, etc. — ^may be prepared. Before 

 pouring the Endo plates the reaction is adjusted to Ph 7.6-7.8, and 

 the lactose and the fuchsin-sulphite are added in the usual 

 manner. It has been our experience that about 0.8 cc. n NaOH 



^ This agar can be used for all purposes. The reaction is favorable for the 

 growth of all common bacteria. In places where a large amount of medium is 

 used, and in the field, it is especially advantageous to have a single stock that 

 can serve as a basis for the various modified media. 



