256 GAS METABOLISM OF BACTERIA 



It follows, therefore, that the respiratory quotient = ^p>^ ~^^i- I^ the respiratory 



quotient is high, carbohydrate is supposedly being oxidized in the body; and, if low, 

 fat is undergoing change. 



The respiratory quotients of micro-organisms, as a rule, have been computed 

 from the analysis of the gases over the cultures, but the values thus obtained can at 

 best be considered only approximate. The direct use of analytical data, uncorrected 

 for the changes in pressure, is wrong, since it gives an apparent respiratory quotient 

 which is usually higher than the real quotient. A further and common error is the 

 failure to determine the amount of CO2 dissolved, free or chemically combined in the 

 medium. Another point which must be considered is the period of incubation, which, 

 with some organisms, may be without appreciable, effect; with others, on account of 

 secondary changes in the medium such as decarboxylation, a longer period may re- 

 sult in an increased CO, production, and hence in a higher final value. 



In Table I are presented, by way of illustration, the results of a determination of 

 the respiratory cjuotient of B. suhtilis when grown on i per cent agar containing 5 per 

 cent glycerol. 



A jar (Fig. 2) received two inoculated tubes (20X150 mm.), very loosely plugged, 

 each containing 10 cc. of the medium; also one open tube with 10 cc. of boiled dis- 

 tilled water, the latter to supply the recjuisite aqueous tension. In order to hasten the 

 production of this tension five drops of water were placed on the bottom of the jar. 

 Thereupon the jar was closed, clamped, and attached to a manometer and placed in 

 the hotroom at 32° C, with stopcocks i and 3 closed. It was equilibrated four hours 

 later. 



In ten days the manometer showed a pressure of — 20 mm.; on the thirteenth day 

 it had reached — 21, and remained at that point until the nineteenth day when its con- 

 tents were analyzed. It will be seen from the table that the O2 was practically all gone, 

 and evidently this state had been reached about the tenth day. The culture in the 

 two tubes produced 233 cc. of CO2 and consumed 275 cc. of O2 at 0° and 760 mm. The 

 close approximation of the respiratory quotient thus obtained with the theoretical 

 oxygen quotient of glycerol should be noted. 



The errors often seen in the published work on gas metabolism are brought out 

 in Table I. Thus, the calculated apparent respiratory quotient is the one usually 

 given and is incorrect since it is based on data uncorrected for temperature and pres- 

 sure changes and does not include the dissolved CO2. The calculated, real respiratory 

 quotient, corrected for changes in volume, does not include the dissolved CO2. The 

 corrected, real respiratory quotient is based on all of the CO, produced and all of the 

 O2 consumed, corrected for changes in pressure, and converted to standard conditions. 



The value of the manometric reading as a check on the analysis is apparent. 

 When such agreement does not exist, it shows that an error is present which may be 

 in the analysis of the control or of the culture. Apart from this, the error may be due 

 to formation of a gas, such as N2, by the culture. The manometer is therefore a serv- 

 iceable indicator of the production of such a gas or of products which have high 

 vapor tensions. 



The respiratory quotients for a number of organisms arc presented in Table II 



