■ W. J V. OSTERHOUT 19 



F, rests upon a board which is held in position by a support not shown 

 in the drawing. The amount of compression of F can be varied either 

 by shifting F or by altering the point at which G is attached to H. 



A and B are provided with tightly fitting stoppers into which the 

 tubes are fastened in air-tight fashion. All other connections should 

 likewise be air-tight. 



The carbon dioxide produced by the organism is absorbed with sur- 

 prising rapidity by the indicator solution, provided a rapid circulation 

 of air is maintained. This is evident from the fact that when known 

 amounts of CO2 are introduced into A the CO2 is at once carried over 

 into B and equilibrium is quickly established. 



Ordinarily it is not important to know the absolute amount of CO2 

 produced by the organism, since we are concerned only with compara- 

 tive values. If for example we wish to, compare the normal rate of 

 respiration with the rate under the influence of ether, we proceed as 

 follows: We place the organisms in A and close the clamp, D, opening 

 C and E so that the air passes through the U-tube^ (containing an 

 absorbent of CO2, such as lumps of NaOH)^ into the indicator solution 

 in B . The indicator solution may consist of distilled water (free from 

 CO2) to which enough NaOH has been added to make its pH value 

 about 7.3; phenolsulfonephthalein is added, so that the solution 

 becomes pale pinkish in color. As the gas passing into B is practically 

 free from CO2 little or no change will be produced by its circulation; 

 it should, however, be allowed to circulate until the color of the indi- 

 cator has become constant.^ The clamps, C and E, are now closed 

 and D is opened, allowing the CO2 given off by the organisms to pass 

 into B . The time required to produce a clearly marked change in the 

 color of the indicator is noted and buffer solutions (contained in 

 Pyrex glass tubes of the same size as B and having the same concen- 

 tration of indicator) are selected which match the color of the indica- 

 tor at the start and finish. The clamp D is now closed; C and E are 

 opened, thus washing the CO2 out of B until the indicator returns to 



' In place of the U-tube a tower or potash bulb may be employed. 

 8 When a volatile reagent, as ether, is added, the substance in the U-tube must 

 be one which does not absorb the reagent. 

 ' Unless the joints are tight CO2 may leak in. 



