M. H. SOULE 251 



what complex and often gave very inexact results. In 1913 the literature was re- 

 viewed in detail by Frieber' and, during the following year, by Rogers, Clark, and 

 Davis^ who contributed a valuable supplement to Frieber's study; in both papers the 

 untrustworthy nature of the recorded bacteriological gas analyses was deplored and 

 new methods were suggested. In each of these investigations the metabolism of B. 

 coli was studied. This germ, ordinarily considered an aerobe, was grown in broth, 

 in vacuo, under anaerobic conditions, and the gases formed were analyzed. Anderson^ 

 modified the technique of Rogers and his co-workers and made accurate quantitative 

 estimations of the gaseous components evolved by several strict anaerobes. The pro- 

 cedure at best has a very limited application. 



METHODS 



As already stated, the methods which have been employed in the study of gas changes by 

 bacteria as a rule have been somewhat complex. It is beyond the scope of this article to re- 

 view these earlier investigations on gas metabolism. The recent studies of Novy, Roehm 

 and Soule^ have resulted in methods which are of general applicability. They are equally 

 suitable for the study of the respiration of organisms when grown on solid or liquid media, 

 in tubes, flasks, or on plates, either in an atmosphere of air or in varying concentrations of 

 O2, CO2, N2, or other gases. The technique not only permits of accurate manometric observa- 

 tions over extended periods of time, but also allows the easy withdrawal of samples of the 

 contained gases for the purpose of analysis. These methods have been utilized in the study 

 of a large number of organisms, including various protozoa as well as plant tissue. For full 

 details the reader is referred to the original memoirs. 



It is essential in the study of gases to be able to observe the pressure changes which take 

 place within the respiratory chamber. A manometer usually not only reveals whether an or- 

 ganism is alive and growing, but also indicates the point when growth or respiration ceases. 

 Some investigators have made use of ordinary manometers attached to their culture flasks. 

 The instrument devised by Barcroft^ is well known and, as modified by Brodie,^ has been 

 used for diverse respiration studies such as those on excised tissues by Warburg^ and others. 



It is desirable to have a manometer which is highly sensitive and yet independent of 

 variations in atmospheric pressure. These conditions are realized in the compensation mano- 

 meter. This instrument is shown in Figure i, attached to a glass-capped //-tube of about 

 loo-cc. capacity; in Figure 2 it is connected to a Novy jar. For details of construction and 

 calibration the original paper should be consulted. 



When an experiment is in progress the apparatus is kept at constant temperature and 

 cocks I and 3 on the manometer remain closed. The system is not subject, therefore, to 

 changes in barometric pressure, and any variation in the mercury level is due entirely to the 

 gas exchange of the germs. This is extremely important when an experiment extends over a 

 period of time. 



The purpose of stopcock 2 is twofold: (i) to shut off the manometer when the gas pres- 



' Frieber, W.: Centralbl. f. Baktcriol., Abt. I, Orig., 69, 437. 1913. 



^Rogers, L. A., Clark, W. M., and Davis, B. J.: /. Infect. Dis., 14, 411-75. 1914. 



3 Anderson, B. G.: ibid., 35, 213-81. 1924. 



'' Novy, F. G., Roehm, H. R., and Soule, M. H.: ibid., 36, 109-67. 1925. 



5 Barcroft, J.: Ergehn. der Physiol., 7, 772-75. 1908. 



^ Brodie, T. G.: /. Physiol., 39,391-96. 1909-10. . ■; ■',*■ / 



> ■ -^ ^ t\ "^ 

 7 Warburg, O.: Biochent. Ztschr., 100, 230-70. 1919; 1923; 1924. / .;*. < ■ 



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