26 MAX LEVINE 



THE SUBSTITUTION OF QUANTITATIVE ACID-PRODUCTION FOR GAS- 

 FORMATION AS A DIFFERENTIAL INDEX IN STUDIES 



ON B. COLI 



Kligler 6 suggests that quantitative acid-production be substituted 

 for gas-formation as an index of fermentation. He points out that 

 in standard meat-infusion sugar-freed carbohydrate broth media there 

 is a rather sharp dividing line between acid-producers and nonacid- 

 producers at 1.5% normal acid, and that quantitative gas-production 

 is variable and unreliable. Of course it is agreed that, as a quantitative 

 test, gas-formation as ordinarily determined in the Smith or Durham 

 tube is of little value; as a qualitative test, however, it may be of 

 considerable significance. If a culture is inoculated into sugar broth 

 and gas is formed, while no gas is produced in plain broth, the organ- 

 ism would most certainly be regarded as a fermenter irrespective of 

 whether more or less than 1.5% acid is formed. 



Kligler apparently regards such an organism as a nonfermenter, 

 for he says : "The members of the proteus group, on the other hand, 

 produced from 10 to 20 per cent, gas in lactose broth tho at no time 

 did they produce more than 1.0 percent normal acid," and he later 

 records this group as lactose-negative. It is not the ^intention to 

 debate at this point whether B. proteus is a lactose- fermenter or not, 

 but it should be pointed out that to say that an organism which forms 

 gas from a carbohydrate is a nonfermenter because the acid titer is 

 low, introduces confusion into the already much maligned and abused 

 term "fermentation." The low titer might be due to a secondary, 

 alkali-production which masks the acid, as suggested by Rogers. It 

 has been repeatedly observed in this laboratory that B. aerogenes in 

 peptone dipotassium-phosphate solution containing 1 or 2% glucose, 

 may be acid to methyl red after 24 hours' incubation, but alkaline 

 after from 48 to 96 hours at 37 C. 



Rogers, Clark, and Evans 7 also determined titratable acid and 

 selected 1% normal acid as the point of demarcation between fer- 

 menters and nonf ermenters,, but they point' out the possible errors in 

 acid-determination and give precedence to gas-formation as indicated 

 in the following: 



"Under certain circumstances which have not yet been definitely deter- 

 mined, the acid from the fermentation of sugar may be masked by a secondary 

 alkaline production, sufficient in some cases entirely to obscure the acid for- 



6 Jour. Infect. Dis., 1914, 15, p. 137. 



7 (a) Jour. Infect. Dis., 1914, 14, p. 411; (b) IS, p. 100; (c) 1915, 17, p. 137. 



