324 GASOMETRIC-VOLUMETRIC METHODS 



chamber. The units are mounted in a vertical bank inside a brass- 

 glass box. Brass clips into which the respirometers fit are rotatable 

 from the outside of the box by means of a metal arm connected 

 thereto by a packed joint. Since the tissue being studied clings to the 

 roof of the expanded end of the unit, a droplet of substrate to be 

 added may be placed on the floor along with a small lead shot coated 

 with celloidin and paraffin. Rotation of a single capillary at any 

 time then causes the mixing ball to drag the reagent around to the 

 tissue. Greasing of the cap-respirometer joint makes it transparent 

 and thus allows visual observation of the tissue being studied." 



(d) Scholander Micrometer Burette Differential Respirometers 



Scholander ( 1942a j adapted his micrometer burette (page 262) 

 to the measurement of small gas changes in volumetric respirometers 

 of his design. One of the respirometers was sensitive to about 0.3 fA. 

 per hour and another to about 0.01 /xl. per hour. Greater refinement 

 would be achieved by reducing the dimensions of the micrometer 

 spindle and the glass parts. In a subsequent publication Scholander 

 and Edwards (1942) described a larger respiration chamber for an 

 apparatus designed for measurements on aquatic organisms such as 

 sand crabs, dragonfly larvae, or water plants. This instrument was 

 sensitive to within 1 ixl. per hour. 



The principle of the apparatus lies in the maintenance of con- 

 stant gas volume in a reaction vessel by the addition of oxygen 

 from a micrometer burette to replace that used up by the respira- 

 tion. The carbon dioxide evolved is absorbed by alkali. The pressure 

 in the reaction vessel is balanced against that in a compensation 

 vessel. 



Respirometer Sensitive to 0.3 Microliter per Hour. This 

 apparatus (Fig. 99) consists of a micrometer burette (1), storage 

 bulb for oxygen (2), respiratory chamber (3), manometer (4), and 

 a compensation vessel (5). The capillary bore is 1 mm. The frame 

 holding the apparatus is held by a rod which passes through a hole 

 (7), and it rests on the water bath at 6. The biological material 

 in 3 is separated from the carbon dioxide absorbent, which is in the 

 bottom of the same vessel. A ground joint, or a syringe needle 

 pushed through a rubber stopper as shown in 3, may be used to 

 connect the respiratory chamber with the rest of the apparatus. 



