22 METHOD OF STUDYING RESPIRATION 



In case it is desired to withdraw a sample of gas in order to de- 

 termine the amount of O2 consumed, it is only necessary to inter- 

 calate a glass tube in the neighborhood of D, with stop-cocks at 

 each end which can be closed when the tube is removed. 



It is evident that this method is just as applicable to photosynthesis* 

 as to respiration. In studying photosynthesis it may be desirable to 

 introduce known amounts of CO2 into the apparatus at the beginning 

 of the experiment. 



In conclusion it may be added that in carrying out such investiga- 

 tions it is desirable to compare the times required to produce equal 

 amounts of CO2 rather than to compare the amounts of CO2 produced 

 in equal times. The former method compares reaction velocities 

 while the latter may not. 



SUMMARY. 



An apparatus is described which makes it possible to measure 

 rapidly and accurately small amounts of CO2 given off by organisms 

 of ali kinds. The apparatus can also be used to measure photosyn- 

 thesis. 



