262 GAS METABOLISM OF BACTERIA 



tubes or preferably agar plates in containers the atmospheres of which may be varied. 

 It is essential that the absolute amount of oxygen which is present, at the tension 

 under consideration, be sufficient to meet the requirements of the organism. These 

 conditions may be illustrated by the following experiment of Novy and Soule: 



It had been determined from a study of the respiratory quotients that the human tuber- 

 cle bacillus, in order to produce a rich growth, must be provided with about loo cc. of O2 or 

 about 500 cc. of air. With this fact in mind, they grew this organism on agar slants in con- 

 tainers which progressively increased in size as the tension of oxygen in the confined gas de- 

 creased. Atmospheres of 6, 3, i, and 0.5 per cent were provided in containers of 2,000, 3,300, 

 7,700, and 20,000 cc. respectively. Each receptacle had previously received one freshly in- 

 oculated agar slant. After drawing a sample of the gas for analysis each chamber was placed 

 at 37° C. The experiment was conducted over a period of six weeks with analyses at frequent 

 intervals. At the end of this time all of the oxygen in each container had been consumed and 

 CO2 produced. The respiratory quotients were very nearly the same as those obtained under 

 ordinary aerobic conditions. An excellent though varying growth was present in each tube, 

 conclusive evidence that the tubercle bacillus can grow in the culture tube under any de- 

 crease in the oxygen tension and that it can utilize this element to the last free molecule. The 

 only limit imposed is the size of the container which, for reasons stated, must be of such 

 capacity as to provide approximately 100 cc. of oxygen. It was plainly evident that respira- 

 tion ceased when the oxygen was gone, as there was no increase in the CO2 content of the 

 jars after this time. The growth of an aerobic organism under diminished oxygen tensions 

 is of necessity slower than under ordinary air conditions. 



Several other aerobic organisms have been investigated by the same methods, and all 

 have given similar results. It may be tentatively concluded that a true aerobic organism can 

 utilize free oxygen under any diminished tension, but a visible growth will be obtained only 

 when the absolute volume of this element is present in the amount required under ordinary 

 air conditions. 



INCREASED AND DIMINISHED CO^ TENSIONS 



Mention was made earlier in this paper that all growing organisms utilize oxygen, 

 whether free or combined, and liberate CO2. Some writers have felt that this waste 

 product plays an important role in the metabolism of bacteria, and that it is required 

 in certain tensions for the growth of the cells. Ample proof has been advanced to 

 show the favoring influence of the presence of this gas when making primary isola- 

 tions from infected material, but after the organisms have become adapted to culti- 

 vation on artificial medium the beneficial action of added CO, is lost. 



Many organisms have been grown in the presence of high tensions of CO2, and by 

 way of illustration one of the experiments of Novy and Soule with the tubercle bacil- 

 lus may be cited: 



Freshly inoculated glycerol agar slants were placed in jars of about 2,000-cc. capacity; 

 the atmospheres of the jars were adjusted to tensions of 30, 40, 50, and 60 per cent CO2 with 

 an adequate supply of oxygen present. The jars, after the analyses of the gas contents, were 

 incubated for fifty-nine days and then samples of the gases were withdrawn and analyzed. 

 Excellent cultures were obtained in each tube. The data showed that the growth of the or- 

 ganisms had altered the original composition of the gas by utilizing the oxygen and increas- 

 ing the CO2 tension. Calculations of the respiratory quotients demonstrated that the pres- 

 ence of the high CO2 tensions had no intluence on the respiratory relations. In another ex 



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