2S8 



GAS METABOLISM OF BACTERIA 



theria bacillus, the addition of glucose to the medium increased the quotient, showing 

 that when glucose is present it is utilized, more or less completely, by the organisms 

 as a source of energy. 



If only glucose were oxidized the quotient would be i.o. It will be seen from Table 

 II that this value is very closely approximated by several organisms. On the other 

 hand, it is also clear that some combustion of the proteins or amino acids in the medi- 

 um is taking place at the same time that glucose is being oxidized and that, as a result, 

 the observed quotient represents the sum of all of the oxidations. 



Since the quotient for protein is 0.81, it follows that complete combustion of a 

 mixture of protein and glucose would yield a value intermediate between 0.8 and i.o, 

 depending upon the relative amounts burned. 



Furthermore, the utilization of any free amino acids that may be present in the 

 medium may influence the quotient to a marked extent. Thus, the c^uotient for gly- 

 cine and asparagine is 1.33, while for alanine it is 1.0 and for leucine it is 0.80. Hence, 



TABLE II 

 Average of Corrected Real Respiratory Quotients Obtained in Jar Experiments* 



* The figures in parentheses give the number of experiments. 



depending upon which amino acid is being utilized, the observed respiratory quotient 

 will be greater or lower than 1.0. 



Another factor which tends to raise the respiratory quotient above the theoretical 

 value is the decarboxylation of amino and other organic acids, because CO2 is liberated 

 without oxygen consumption. 



As shown in Table II, the quotient for B. suhtilis, when grown on glucose agar, is 

 unusually high. This may be due solely to the two factors just mentioned. On the 

 other hand, it is possible that a slight reaction, in the nature of alcoholic fermenta- 

 tion, produces an additional excess of CO2 sufficient to give a quotient of 1.4 or even 

 higher. 



It appears that glycerol is an important source of energy. The energy thus ob- 

 tained permits complete utilization of such nutrient substances in the medium as are 

 needed by the organism. It is worthy of note that the human \-ariety of the tubercle 

 bacillus, which is unable to grow on plain agar, multiplies readily on glycerol agar and 

 gives a respiratory cjuotient corresponding closely to the theoretical value. 



On plain agar, serum agar, and blood agar the organisms obtain the required en- 

 ergy by breaking down protein matter or by utilizing the free amino acids present. 



