Formates by B. coli communis. 



467 



Quantitative Study of the Rate and Extent of Decomposition of Sodium Formate 

 and Glucose by an Artificially Selected Non-gas-producing Strain of B. coli 

 communis when grown on them either separately or together. 



In order to determine the causes of the greatly increased gas production 

 observed when B. coli communis was grown on a mixture of sodium formate 

 and glucose, the change was followed quantitatively. For this purpose it 

 was necessary to determine the weight of formic acid and glucose consumed 

 in the reaction and the total carbon dioxide and acid produced, and also to 

 measure the gas production from time to time. The method which was 

 employed would be suitable for the examination of the decomposition of 

 many other substances by bacteria, and it is therefore described in detail. 



A quantity of 50 or 100 c.c. of 2 per cent, glucose in 1 per cent, peptone 

 water is sterilised and inoculated with the organism. The cotton-wool plug, 

 which should fit loosely, is pushed half-way down the neck of the flask, and 

 the flask is connected with a Schiff's gas burette by means of a rubber 

 stopper provided with a two-way tap. The burette, which is filled with 

 mercury, is in connection with a reservoir for adjusting the pressure, as in 

 the apparatus described by Harden, Thompson, and Young (1910). Before 

 beginning the experiment, air may be removed from the flask by putting it 

 in connection with the burette. On lowering the reservoir air passes into 

 the burette. Nitrogen is then admitted to the flask by reversing the tap, 

 and this process is repeated four or five times, when the oxygen will have 

 been practically all removed. The flask is well immersed in a water-bath 

 maintained at 37°. When it is desired to stop the reaction, the flask is 

 removed from the water, and the contents are, after turning the two-way 

 tap so as to put the flask in connection with the apparatus described below, 

 carefully brought to the boil, the gas driven out displacing the mercury 

 from the inner tube A (see figure). 



Details of the Use of the Gas Collecting Apparatus. — The object of the 

 apparatus is to collect all the gases which remain in the fermentation flask 

 both free above the surface of the medium and dissolved in the fluid. 



A is an ordinary Liebig's condenser set vertically and connected by a 

 three-way tap D with a gas burette B accurately graduated. By putting D 

 in connection with the pump or by raising the tube C, which must be filled 

 with mercury, the mercury rises to fill B ; the tap E is then closed. The 

 ta,p D may now be reversed and mercury drawn up into the inner tube A 

 from the reservoir I/" to the level L'. A circulation of water in the Liebig's 

 condenser is not necessary for the condensation of the steam, but helps in 

 keeping the temperature of the collected gas constant. To collect the gases 



