362 GASOMETRIC-MANOMETRIC METHODS 



is narrow, the calibration mark will come high enough on the stem 

 to avoid contact with the diver, and in this case a hair loop or a 

 glass ink mark may be used. 



(8) FILLING THE DIVER 



The Bottom Drop. According to the calculations of Linder- 

 str0m-Lang (1943), the general rule follows that the thickness of 

 the layer of the bottom drop of reaction mixture must not exceed 

 0.5 mm. if the rate of gas diffusion through the drop is not to become 

 the limiting factor for the rate of the gas exchange to be measured. 

 This refers to gas changes in the range of those to be expected in 

 the usual biological systems (of the order of 0.01 ix\./hr.). For all 

 other cases, the equations given by Linderstr0m-Lang (1943) should 

 be applied to check the conditions. 



It is essential that the bottom drop spread to reduce the thick- 

 ness of the liquid layer. The cleanliness of the diver is an important 

 factor. If the reaction mixture does not wet the glass, recourse may 

 be had to one of the following devices: 



1. Addition of a surface-active substance, such as 0.1% sodium 

 taurocholate, provided that the substance will not interfere with 

 the reaction. 



2. A very short centrifuging, or whirling by the arm while 

 holding the diver (the diver must be held with cloth or filter paper 

 to prevent the fingers from touching it) . 



3. If centrifuging is not sufficient, and it is permissible in the 

 experiment, moistening the wall of the diver bulb before the bottom 

 drop is added by filling the bulb to within 1 mm. of the neck with 

 a suitable liquid and then sucking it out as completely as possible. 

 It will be necessary to correct the volume of the bottom drop for 

 any of the liquid not removed. When the moistened part is less 

 than 2 mm. from the lowest neck seal there is danger from creeping; 

 this may be obviated by a wax ring, described on page 363. 



In order to avoid injuring cells, or damaging the tip of the braking 

 pipette used to transfer them by having the tip touch the glass 

 bottom of the diver, a small amount of a suitable liquid (about 

 0.1 [xl.], termed a "forerunner" by Holter, is placed into the bottom 

 of the diver first. The "forerunner" is introduced with a slender 

 flexible pipette which will not break if it touches the bottom of the 

 diver. It is necessary to avoid evaporation of the "forerunner" by 



