314 GASOMETRIC-VOLUMETRIC METHODS 



1. Capillary Respironietry 



The technique of vokimetric capillary respirometry is based on the 

 measurement of changes in the gas volume in a capillary tube con- 

 nected to a chamber in which the respiring sample has been placed. 

 The position of an index droplet placed across the lumen of the 

 capillary serves as an indication of the volume at any given moment. 



The history of the use and development of capillary respirometers 

 has been documented in a review by Tobias (1943) and need not 

 be presented here. In the following a description will be given only 

 of a few of the more modern designs adapted to measurements on the 

 histo- or cytochemical level. 



The differential instruments consist essentially of two chambers 

 connected by a capillary tube containing an index droplet. One 

 chamber contains the biological material, medium, and reagents, 

 and the other only the medium and reagents. Changes in the amount 

 of gas which result from the biological action are followed by meas- 

 urements of the displacement of the index droplet. In the closed sys- 

 tem used, barometric fluctuations are without effect. When both 

 chambers, drilled in a block of heat-conducting material, are of 

 nearly the same size, temperature variations are of significance only 

 in so far as they influence the rate of the reactions measured, and 

 changes occasioned by the medium alone are cancelled. However, 

 in this case, the displacement of the index droplet is only about half 

 that obtained if the end of the capillary were open to the air. By 

 employing a compensating chamber which is very large with respect 

 to the reaction chamber, the movement of the index droplet in the 

 differential instrument can be made to approximate that in the open 

 type ; but more careful temperature control will be required, since a 

 given variation in temperature will take longer to exert its full effect 

 on the larger chamber. 



(a) Cunningham-Bar th-Kirk Differential Respirometer 



Cunningham and Kirk ( 1940) described a differential respirometer 

 with chambers of approximately equal size, which has the advantages 

 of enabling substitution of different capillary tubes, alteration of 

 chamber volume, filling of the chambers with various gas mixtures 

 as desired, and mixing of solutions during an experiment by means 

 of an electromagnetic "flea" (page 179). Since the symmetrical 



