376 GASOMETRIC-MANOMETRIC METHODS 



(about 30 sec), displace it by means of the fine screw on the 

 pressure regulator. 



(e) If the two readings check, take the time of the second 

 adjustment within 1 min. as the time of reading. 



note: Observe the shape of the menisci of the seals during measurement. 

 If they do not wet the neck properly they are apt to be deformed and the 

 accuracy of the measurement may suffer. It is sometimes helpful to vary 

 the pressure quickly to about 10 cm. on each side of the equilibrium value 

 to cause the menisci to move over the glass in their immediate locality 

 and thus wet it. Of course it is necessary as a rule to employ control divers 

 in each experiment. The use of the air bottle renders therm obarometer 

 divers superfluous. 



(11) REVIEW OF THE EXPERIMENTAL PROCEDURE 



As an example of the steps in an actual experiment, Holter (1943, 

 page 460) gave the procedure to be followed in a measurement of 

 the respiration rate of echinoderm eggs. The experiment described 

 was carried out in air, and two experimental divers and one control 

 diver were used. The following is Holter's own description (page 

 references, however, refer to this book) : 



Choosing the Proper Size and Type of Diver. Since the assumed oxygen 

 consumption is large (about 5 X 10"'' /xl./hr.), the diver need not be smaller 

 than "standard size." The total gas volume of these divers being about 10 fj.\., 

 the oxygen consumption will correspond to a change in equilibrium pressure of 

 about 50 mm. per hour. As the oxygen used in the reaction drop is supplied only 

 by diffusion, we need a reaction drop having a large surface and forming a 

 thin liquid layer (this excludes filling a in the schedule on page 000. Naked 

 echinoderm eggs do not stand direct contact with the surface of water (ex- 

 cludes filling b). No glass stopper is needed (excludes filhng e and /) since the 

 experiment is to be of short duration (2-3 hours) and since the pressure changes 

 are expected to be so large that a slight gas loss by diffusion through the diver's 

 mouth plays no appreciable role. On account of the magnitude of the antici- 

 pated effect we choose among fillings c and d the former, which also by its 

 better utiHzation of the area of the diver bottom, gives the largest surface of 

 the bottom drop. 



Manipulations : 



(1) If the flotation medium has not been in use for a long time the flota- 

 tion vessel is, not later than 1 hour before the beginning of the experiment, 

 shaken with air (page 374). 



(2) The air bottle in the thermostat is connected to the outside air (page 

 374). 



