Carbohydrate Fermentation by Bacteria. 45 



Thus, in all, there were 294 combinations, including variable 

 amounts of peptone, lactose and phosphate from zero to and 

 slightly above that used in ordinary media. Both the hydrogen 

 ion concentration and the amount of gas produced were recorded 

 daily for three weeks, thus giving us 294 curves. 1 



The analysis of these curves brought out the following facts: 



Increase in the concentration of lactose generally increased 

 the rate of acid production (given constant concentration of 

 peptone and buffer-salts). 



Thus, when the amount of buffer-salts is not sufficient, the 

 increase in concentration of the carbohydrate inhibits the growth. 



With any concentration of carbohydrate, the amount of free 

 acid indicated depends of course on the concentration of the 

 buffer-salts. 



Concentration of peptone affects the amount of free acid 

 indicated partly in the same manner as does the concentration of 

 neutral salts, but in addition the amount of sugar attacked is 

 smaller as the concentration of peptone in the medium is increased. 

 Thus, when 1 per cent, or more of peptone is used in the medium, 

 the amount of carbohydrate has to be increased in proportion in 

 order to obtain sufficient amount of free acid (amount of neutral 

 salts being constant). 



The amount of gas produced changes inversely with variations 

 in the hydrogen ion concentration, other conditions being equal. 



Therefore, other conditions being equal, the amount of gas 

 produced increases directly with concentration of buffer. 



Given constant concentration of carbohydrate and buffer 

 salts, the amount of gas produced changes directly with the con- 

 centration of peptone. 



These findings suggest that the number of discrepancies in 

 results of the fermentation experiments are largely due to the fact 

 that media are not usually compared with sufficient attention to 

 factors above mentioned. The variations in sugar content and 

 especially in buffer content of the media are not guarded against 

 sufficiently in routine procedure of making media. Moreover, 



1 While in this paper we refer only to the part of the experiment which dealt with 

 the production of acid and gas, the complete records will cover also the data on 

 nitrogen and carbohydrate metabolism, including the gas analysis and the curves of 

 multiplication. 



