CAPILLARY RESPIROMETRY 323 



tion chamber in a large compensation vessel which is sealed off to 

 make the system independent of barometric changes. Volume 

 changes within the capillary chamber are so small in comparison to 

 the volmiie of the compensation vessel that these changes can be 

 considered completely undamped, and the arrangement makes for 

 great stability in measurement. An improvement initiated by Tobias 

 and Gerard in this type of respirometer is the use of ten or more of 

 the capillaries at the same time in a single compensation vessel. 

 Gas volume changes of the order of 0.0005 to 0.001 microliter per 

 minute can be followed at minute intervals with individual readings 

 varying from the mean by about 8%. For five to ten minute inter- 

 vals the accuracy is about 2%. 



Apparatus. The respirometer is made by sealing a 90 mm. 

 length of 0.2 mm. glass capillary tubing into a 30-40 mm. length of 

 1.2-1.5 mm. thin-walled glass tubing with DeKhotinsky cement. The 

 wider tube serves as the reaction chamber while the capillary con- 

 tains the index droplet by means of which gas vol. changes are 

 measured. It has been found that isodecane (2,7-dimethyloctane) 

 is superior to other index fluids for small capillaries. Bits of filter 

 paper soaked with acid or alkali, and separated by dry paper guards, 

 may be used in the reaction chamber to absorb certain gases during 

 the reaction. The absorbing materials and the tissue are placed in 

 the reaction tube. The open end of the latter is then sealed with 

 plasticine. The isodecane droplet is placed in the capillary and the 

 respirometer is mounted on a central thick-walled capillary tube 

 connected to the glass stopper of the compensation vessel (Figs. 

 97, 98) . A number of the respirometers may be mounted around the 

 central tube as shown. The glass stopper bearing the respirometers 

 is then fitted into the compensation chamber, which is supported 

 horizontally. The entire glass unit is submerged in a thermostat 

 bath. By rotating the stopper, individual capillaries can be brought 

 into the field of the horizontal micrometer microscope employed to 

 determine the positions of the index droplets. At the end of an ex- 

 periment the small capillary is broken off and the diameter of the 

 lumen at the end is measured with an ocular micrometer. 



Certain mechanical improvements have been introduced (Tobias, 

 1943) : "Permanent, heavy-walled capillary units, expanded at one 

 end to accommodate tissue and absorbing reagents, replace the fine 

 capillaries. A small ground-glass cap instead of plasticine closes the 



