276 



PHYSIOLOGY OF NUTRITION. 



Vo 



1,000 (l + at) 



If V was the volume at the commencement of the experiment, 

 and Fj_ the volume calculated at the end of say six hours, then 

 V 1 Vis the volume of Carbon dioxide given off during that time. 

 Since in vacuo the initial volume was zero, V l directly indicates 

 the volume of Carbon dioxide evolved. 



It is often desirable to be able to compare the rate of intra- 

 molecular respiration with that of normal respiration, and in order 

 to do this we must arrange beside the barometer tube a second 

 glass tube of the same size, and into this introduce seedlings as 

 nearly as possible of the weight and in the same stage of develop- 

 ment as those in the vacuum. To prevent them falling back, we 

 push a small cork down the tube. This is then inverted in mer- 

 cury, and about 20 c.c. of the 

 atmospheric air present in it is 

 removed by suction, the mer- 

 cury naturally rising to that 

 extent (see Fig. 102). To so 

 remove a portion of the air 

 from the tube we use a glass 

 flask, closed by a rubber 

 stopper, through Avhich passes 

 a bent glass tube carrying a 

 piece of rubber tubing. We 

 warm the flask, close the 

 tubing with a clip, and then 

 introduce the end of it into 

 the tube. The flask is allowed 

 to cool, and on releasing the 

 clip it acts as a suction ap- 

 paratus, by means 

 of which the mer- 

 cury is easily caused 

 to ascend in the 

 tube. We now 

 finally cover the 

 mercury in the tube 



FIG. 102. Apparatus for determining the quantity of 

 Oxygen which plant structures can take up in respiration. 



with a layer of water about 3 mm. thick, make the necessary 

 readings for determining the volume of air in the apparatus, and 

 introduce a fragment of caustic potash into the tube. The 



