M. H. SOULE 



259 



As a rule, the observed quotient is in excess of the theoretical value (0.81), and the 

 reason for this must be sought in the factors already discussed. 



THE GAS EXCHANGE 



The jar method serves not only to determine the respiratory quotient but also to 

 supply data as to the extent of the gas changes brought about by the culture in a 

 single tube. With 10 cc. of medium in a tube the surface area represents about 15 

 sq.cm. of culture. Undoubtedly, it would be preferable to have the exact weight of 

 the organisms which have developed in a tube in order to make comparisons of the 

 gas exchange of various germs and the different media. It is more important, how- 

 ever, to determine the total dissolved CO2 in the medium, and to do this the weight 

 of the growth must be sacrificed. 



Out of a large mass of data, much as yet unpublished, the values given in Table 

 III have been selected. They show the volumes of CO2 produced and of O2 consumed, 

 per culture tube, by a number of organisms. In the last column of the table is given 

 the volume of air corresponding to the Oo consumed. It will be seen from these values 

 that many of the organisms can and do require relatively large amounts of air. 



It has been shown in Table II that an organism when grown on a medium which 

 contains no sugar yields a respiratory quotient of less than i.o. This is because of the 

 fact that the volume of the O2 consumed is greater than that of the CO2 produced. A 

 glance at Table III will serve to bring out this difference in the gas exchange. Failure 

 to appreciate the nature of the chemical change involved has led some writers to mis- 

 interpret the meaning of this difference. The fact that the volume of CO2 produced 

 is less than that of the O2 consumed does not mean that the difference represents the 

 volume of O2 assimilated or retained by the organism. The difference represents the 

 volume of oxygen used to oxidize hydrogen to form water. 



It will be noted on reference to Table III that 10 gm. of sterile raw potato con- 

 sumed the oxygen present in 552 cc. of air in ten days. These data are included be- 

 cause of the importance of this plant tissue in anaerobic culture. Novy' has furnished 

 conclusive evidence that it is this marked gas exchange that favors anaerobic growth 

 by the rapid and complete removal of the oxygen that may be present. 



INCREASED AND DIMINISHED OXYGEN TENSIONS 



The first real tests of the influence of high partial pressures of oxygen on pure cul- 

 tures of micro-organisms were made by Moore and Williams.^ In their work slanted 

 tubes of agar inoculated with the test cultures were placed in a bell jar containing 

 varying percentages of pure oxygen. Samples of the gas in the jar were withdrawn for 

 analysis at the beginning of the experiment and at various intervals during the incu- 

 bation period. The net result of these investigations, which were extended by Adams^ 

 working in the same laboratory, was that out of twenty-six cultures tested in partial 

 pressure of 500 mm. or more of oxygen, the growth of only the tubercle bacillus and 

 B. pest is was inhibited. These organisms had not been killed, as subsequent incuba- 



' Novy, F. G., Jr.: /. Infect. Dis., 36, 343-82. 1925. 



' Moore, B., and Williams, R. : Biochem. J., 4, 177-90. 1909. 



^ Adams, A.: ibid., 6, 297-313. 1911. 



