370 



GASOMETRIC-MANOMETRIC METHODS 



4. Slowly push the diver, with the stopper partway in its mouth, 

 down to the bottom of the flotation vessel. 



5. Release the forceps and push the stopper deeper into the 

 mouth with the tip of the forceps. The diver will not rise if the 

 charge has been properly calculated. However if the diver should 

 rise, push the stopper deeper into the mouth. 



Hollow stoppers must not have a specific gravity less than that 

 of the medium or they will float out of the mouth seal. A stopper 

 is removed from a mouth seal by inverting the diver, dipping its 

 mouth into water, and letting the stopper fall out. 



-^M- 



A~ 



a 



A~. 



D 



u o 



a b 



I 



Fig. 130. Various arrangements for respiration measurements. 



From Holler (1943) 



In the figure, 1 shows the cylindrical diver for use when the main require- 

 ment is small volume : a, gas exchange between R and gas phase sufficient, also 

 when the surface of R is small; b, the gas exchange requires a large surface of 

 R (only possible in case of oi-ganisms that can rest on an air meniscus). 2 shows 

 the flask-shaped diver for use when the main requirement is a large surface 

 of R and when air support is not tolerated by the organism : c, relatively large 

 gas space; d, gas space as small as possible; the neck diameter and the length 

 of M depend on the importance of preventing the gas loss by diffusion. In 3 is 

 seen the glass stopper for use when the main requirement is that the diver be 

 as gas-tight as possible : e, glass stopper in ; /, glass stopper in M. 



The type of diver used and the arrangement of the seals will be 

 determined by the particular experiment to be performed. The 

 following basic set-ups (Fig. 130) were given by Holter (1943) for 

 a simple measurement of respiration which requires only one aqueous 

 neck seal (sodium hydroxide to absorb carbon dioxide): "Sugges- 



