MATILDA M. BROOKS 185 



would pass through the distilled water before going into the indicator 

 tube. After the rate of production of CO2 under these conditions 

 had been determined, a drop of NaOH was added to this inserted 

 tube and its effect upon the apparent rate of CO2 production, in- 

 dependent of any effect upon the bacteria, was measured. Equilib- 

 rium is very rapidly attained, since there is very little NaOH pres- 

 ent in proportion to the amount of CO2 produced, and since the 

 method of stirring is very efficient. The NaOH in this tube was 

 then replaced by distilled water and a drop of the alkali of the same 

 concentration was placed in the tube containing the bacteria. The 

 difference between the results in the two cases would measure the 

 action of the NaOH upon the organisms themselves. (When this 

 experiment was varied by using 0.75 per cent dextrose in place of dis- 

 tilled water the results were essentially the same.) 



It was found that the addition of one drop of 0.1 n NaOH had no 

 measurable buffer effect. This was also the case when the alkali was 

 added to 2 cc. of an emulsion of dead bacteria in the side tube instead 

 of to distilled water. The addition of alkali to the dead bacteria 

 would of course simulate more nearly the buffer effects of the actual 

 experiments. 



It is not proposed to discuss at length in this paper the theo- 

 retical basis for the reactions governing the distribution of CO2. 

 in the apparatus. Equilibrium in the different carbonate-bicarbo- 

 nate systems seems to be established almost simultaneously. Regu- 

 lar readings may be obtained as quickly as 5 minutes after the intro- 

 duction of a solution. The hydrogen ion concentrations in the three 

 tubes (bacterial suspension, side tube, and indicator tube) differ 

 even when in equilibrium with the same CO2 tension because the 

 amount of base in the three tubes differs. They may be supposed to 

 be in equilibrium at the beginning of a reading. After this, as the 

 CO2 is produced by the organisms there is an increase of CO2 tension 

 in the circulating air from which CO2 is absorbed by the solutions in 

 the tubes. The indicator tube being farthest from the source of CO2 

 naturally may be expected to lag very slightly behind the side-tube 

 in its change toward equilibrium, because the latter absorbs part 

 of the CO2, thus lowering the CO2 pressure in the air which passes 

 through it. In these experiments the side tube contained only 2 cc. 

 of liquid, which had no measurable effect. 



