RESPIRATORY METABOLISM 355 



single protozoan cells, micromanometric methods have been devised 

 (Kalmus, 1927; Rowland and Bernstein, 1931). More recently, still 

 better micromanometric methods have come into existence, but these have 

 not yet been applied to the respiration of protozoa. Table 3 gives the 

 sensitivity of various types of manometers, some of which have not yet 

 been used to measure the respiration of Protozoa. It should be remem- 

 bered that whenever a respirometer is made more sensitive to changes 

 in gas volume produced by organisms, it simultaneously becomes more 

 sensitive to slight changes produced by the environment (thermal and 

 barometric effects) and to inaccuracies arising from imperfect design 

 and construction (ground-glass connections and stopcocks, surface phe- 

 nomena at the meniscus of manometer fluid, inaccuracies of capillary bore 

 and so forth). Therefore, stability of the apparatus, on which final ac- 

 curacy must depend, becomes more and more difficult to obtain. For that 

 reason the most sensitive types should be reserved solely for those prob- 

 lems in which concentrated suspensions are undesirable or unobtainable. 

 By comparison of Tables 3 and 4, it should be possible to determine ap- 

 proximately the type of respirometer necessary for any one of a variety 

 of problems. 



1. TITRATION METHODS 



a. Dissolved O^ determinations. For any aquatic animal it is possible 

 to measure Oo consumption by placing the organisms in a closed chamber 

 filled with water of known 0„ content and by measuring the amount of 

 O2 left after a definite period of time. For this purpose a modified Win- 

 kler titration method is usually used {Standard Methods of Water Analy- 

 sis, 1936). Special precautions are necessary whenever the animals can- 

 not be removed from the solution, or if iron is present. This method has 

 been used by Lund (1918a, 1918b, 1918c) and Leichsenrmg (1925) 

 on Paramecium and Colpoda. 



b. Measurement of CO2 production. Production of CO2 may be 

 measured by placing the organisms in a small amount of solution in a 

 small open container. This is placed inside of a larger closed container 

 in which an alkali, preferably Ba(OH)2, is present. The COo given off 

 by the organisms is absorbed by the alkali, which can then be titrated 

 with acid in the presence of an indicator. This method was recom- 

 mended by Lund (1918d) for use with Paramecium. 



