356 RESPIRATORY METABOLISM 



The above titration methods are applicable only to quite large num- 

 bers of organisms. It seems possible that these methods could be im- 

 proved by the use of accurately controllable microburettes, smaller vol- 

 umes of liquid, and so forth, but it is doubtful whether they could 

 be made as accurate and reliable as some of the manometric procedures 

 discussed below. Also, respiratory quotients are not easily obtained by 

 titration methods. 



2. GAS ANALYSIS 



Soule (1925), Amberson (1928), and Root (1930) have applied the 

 standard Haldane-Henderson methods of gas analysis to respiration of 

 the Protozoa. These methods are adequate for use with rather con- 

 centrated suspensions and pressures, and possess certain definite ad- 

 vantages when Oo or especially CO, tension is being varied experimen- 

 tally and would have to be determined separately if manometric methods 

 were used. Whenever gases other than COo are evolved by an organism, 

 gas analysis seems to be the only satisfactory method of measurement. 

 The details of gas analysis methods are discussed by Peters and van 

 Slyke (1932). Soule (1925), for studies of the metabolism of Leish- 

 mania tropica and Trypanosoma leivisi, used gas analysis, supplemented 

 by readings of an insensitive manometer, the purpose of which was 

 principally to indicate when gas exchange was taking place (method 

 described in detail by Novy, Roehm, and Soule, 1925). 



3. STANDARD MANOMETRIC METHODS 



The principle of the manometric method is somewhat as follows: 

 the organisms, in a suitable immersion medium, are placed in a closed 

 flask large enough so that a considerable air space is present. The flask 

 is connected to a capillary manometer tube partially filled with a liquid. 

 Alkali may be present in a separate small container inside of the flask. 

 If so, then CO, is absorbed, and the amount of Og consumed may be 

 measured by means of the movement of fluid in the manometer tube 

 as changes in volume (Haldane, Thunberg, Winterstein, Duryee, and 

 Dixon types), or in pressure at a given volume (Warburg), or as the 

 resultant of simultaneous changes in both (Barcroft difl^erential type). 

 Manometric methods, although very simple in outline, are filled with 

 pitfalls for the inexperienced investigator, and a careful reading of the 



