358 RESPIRATORY METABOLISM 



KOH. Gerard and Hartline (1934) have improved the method by 

 enclosing the tubes in an air tight chamber to ehminate barometric dis- 

 turbances, and by using a screw micrometer to increase accuracy of 

 reading. 



5. CARTESIAN DIVER ULTRAMICROMANOMETER (NEEDHAM AND BOELL, 

 1938) 



This is an appHcation of the principle of the Cartesian diver for use 

 as a constant-volume manometer. The "diver" chambers are constructed 

 from capillary tubing and consist of a bulb partially filled with gas, 

 an open capillary neck, and a solid glass tail to ensure that the diver 

 floats upright. The diver is placed in a closed chamber partially filled 

 with a strong salt solution, the specific gravity of which is such that the 

 diver maintains a position below the surface of the salt solution, and 

 that a small amount of this solution enters the neck. If the amount of 

 gas in the diver is changed by a reaction, more salt solution will be 

 drawn in or forced out of the neck, the specific gravity of the diver 

 will change, and the level of flotation will also change. By changing 

 the pressure on the salt solution, the diver may be brought back to any 

 given level. Therefore, the diver may serve as a constant-volume ma- 

 nometer, and changes in the amount of gas in the chamber may be calcu- 

 lated from the changes in the external pressure which are necessary to 

 maintain the diver at a definite level. This application of the Cartesian 

 diver was suggested by Linderstrom-Lang (1937), and has been used 

 for parts of amphibian embryos by Needham and Boell (1938), who 

 describe the use of this instrument for measurement of O2 consumption, 

 anaerobic glycosis, and respiratory quotient. From Table 3 it may be 

 noted that this instrument when read only to 0.2 mm. has a sensitivity 

 as great as those which employ special reading devices, and that it 

 therefore has the possibility of being made more sensitive. 



Aerobic Respiration 

 1. the normal rate of respiration 



One fundamental essential in measuring the respiration of any bio- 

 logical material is that other material, also capable of respiratory ac- 

 tivity, be absent or very well controlled. This means that bacteria must be 

 absent, or at least must contribute only a negligible amount to the 



