270 



CHEN CHONG CHEN AND LEO F. RETTGER 



three and rive-day periods. The additional forty-eight hours' 

 incubation has returned all of the aerogenes strains to their 

 proper indicator ranges in the synthetic as well as in the Witte 

 peptone medium. The peak of the curve in the synthetic medium 

 is now located at pH 6.5 instead of 5.7, the whole curve covering 

 a pH scale of 6.0 to 6.8. In the Witte peptone medium the pH 

 scale extends from about 6.0 to 7.6, whereas the peak lies at 6.8. 



ICO 



If 



1l 



«0 



is- 



55" 

 Se 

 W 



Ji- 



30 



_,_/ 



7.i 7.* 7-X 7" 4.8 44 4.* 41 4.0 St SJ, S¥ 4> *o tl f4 t» 



Chart II. Aerogenes Type (Soil) 



Five days' incubation at 30°C. Unbroken line, synthetic medium; barred 

 line, Witte peptone-glucose-phosphate medium; barred and dotted line, Difco 

 peptone-glucose-phosphate medium. 



When substituting Difco peptone for the Witte in the peptone- 

 phosphate-glucose medium, certain discrepancies occurred, even 

 after prolonged incubation. It is seen that 26 of the aerogenes 

 strains entered the methyl red positive range. 



Chart III gives the results of 20 coli cultures isolated from soil, 

 and grown in both the synthetic and the Witte peptone media 

 for three days at 30°C. Chart IV gives the results of the same 

 20 coli strains in all three of the media after an incubation period 

 of five days. 



