264 GAS METABOLISM OF BACTERIA 



of the tubercle bacillus to containers of Ba (0H)2 and found that the organisms failed 

 to grow. From this they concluded that free CO2 was essential for growth. These au- 

 thors explained the lag period in the development of cultures as a quiescent interval 

 during which the CO2 was accumulating to the optimum concentration. 



Rockwell' studied the gaseous requirements for the growth of various bacteria 

 and, from a large series of investigations/ has come to the conclusion that all bacteria, 

 yeasts, and molds require free CO2 for their growth and that the gas is used as a source 

 of carbon. He inoculated the surface of agar plates and incubated them over alkali; 

 in many of his experiments the growth of the organisms was inhibited. The lack of 

 growth was not due to the drying of the medium as the use of more vigorous dehydrat- 

 ing agents such as HjSO^, CaCL, and glycerol permitted excellent growth despite 

 marked desiccation. The negative results, i.e., the cases in which no inhibition was 

 evidenced over alkali, were explained by the lack of control of all or any one of five 

 factors, which are: the presence of carbohydrate in the medium, the protein content 

 of the medium, the amount of inoculum, the acidity of the medium, and the concen- 

 tration of salt. The conclusion that free CO2 is utilized as a source of carbon by all 

 organisms is not warranted from the data presented. In fact, the work on respiratory 

 quotients already mentioned proves that such an utilization does not take place. 



A more plausible theory of the influence of COj on the growth of organisms is 

 that developed by Novy and Soule, but as yet unpublished. In an attempt to ac- 

 count for the conflicts in the existing data, an extensive series of investigations has 

 been carried out. From these experiments, and based on the fact that bacteria can 

 grow luxuriantly on agar surfaces in the absence of free CO2 when this substance is 

 removed by aeration, and that it is impossible to inhibit the growth of micro-organ- 

 isms in a liquid medium by either of the methods mentioned, the conclusion has been 

 reached that it is the intracellular CO2 which plays the important role in the life of the 

 germ. If this intracellular CO2 is removed by exposure to alkali, or by other means, 

 inhibition, and even death, may result. Any method that will maintain the intracellu- 

 lar CO. equilibrium will prevent or overcome the inhibiting action of alkali and permit 

 growth to take place. 



GAS METABOLISM UNDER ANAEROBIC CONDITIONS 



No phase of the gaseous metabolism of bacteria has been more thoroughly inves- 

 tigated than the growth of organisms under anaerobic conditions. The bacteria of the 

 colon group were early recognized as gas-producers, and because of their importance 

 have received considerable attention. It was early recognized that CO2 and H2 pre- 

 dominate in the gases produced under anaerobic conditions. Although CH^ has been 

 reported as a by-product of the anaerobic growth of B. coli, there is no evidence that 

 such is the case. It is relatively simple to determine the ratio of H2 and CO2 produced 

 when only traces of other gases are formed. An alkali is introduced into the liquid 

 trapping the gas; the CO, present unites with this substance leaving the hydrogen 

 intact. By measuring the total volume of gas formed and the decrease in volume due 



' Rockwell, G. E.: ibid., 28, 352-56. 1921. 



' Rockwell, G. E., and Highbcrger, J. H.: ibid., 40, 438-46. IQ27. 



