THE COLON BACILLUS GROUP 237 



2C 6 H 12 O 6 -f H 2 = 2C 3 H 6 3 + CH 3 COOH + C 2 H 5 COOH -f 2CO, + 2H 2 

 Grape-sugar. Water. Lactic acid. Acetic acid. Ethyl alcohol. Carbonic Hydrogen. 



acid. 



ACID PRODUCTION FROM SUGARS BY COLON BACILLI. When suffi- 

 cient sugar is present the amount of acid produced is quite uniform. 

 In many it proceeds until the acidity is sufficient in quantity to stop 

 the growth of the bacilli. In milk this acidity becomes about 12 per 

 cent, f, acid to phenolphthalein. There are reasons to think that lactic 

 acid is first produced and that from this other acids and products de- 

 velop. Under aerobic conditions lactic is produced in excess of acetic 

 acid, while in the absence of oxygen the reverse is apt to be true. 



GAS PRODUCTION. When colon bacilli are grown in a solution of 

 glucose, CO 2 and H 2 are produced, 1CO 2 to 1H 2 up to 1CO 2 to 3H 2 . 

 Anaerobic conditions aid gas formation. Some colon varieties produce 

 gas from no sugars and some from a few only. Nearly all produce gas 

 from glucose, and about 60 per cent, of varieties produce gas from 

 milk-sugar. Very slight traces of gases other than H and CO 2 are pro- 

 duced. The amount of gas varies in different varieties; the closed arm 

 of the tube half -filled, and the II and CO 2 in the proportion 2 to 1, 

 is the characteristic type. It is also true of Gartner's B. enteritidis. In 

 another type the whole of the closed arm is filled, H 2 :CO 2 =1:2 or 3. 

 This type is usually called bacterium cloacae. In a third type the arm 

 is nearly filled, H 2 :CO 2 =1:1. This type is the bacterium lacticum 

 aerogenes. 



Concerning the gas and acid produced the following rules have been 

 established : 



1. The quantity produced varies with the amount of bacteria and 

 their activity as well as with the type of organism. 



2. It depends upon the living organisms. 



3. The products have a less heat value than the sugar from which 

 they were formed. 



4. The fermentation is not a simple hydrolytic action, but one in 

 which combinations between the C and O atoms are sundered and 

 formed. This is not an oxidation process, but a change through break- 

 ing down that is, a true decomposition. What oxidation takes place is 

 chiefly due to the oxygen liberated from splitting the sugar molecules. 



USE OF SUGAR LITMUS AGARS TO DIFFERENTIATE BETWEEN COLON AND 



TYPHOID BACILLI. 



Color of media after 24 hours' growth of culture. 

 List of sugars. 



Colon bacillus. Typhoid bacillus. 



Grape-sugar . . . Ked. Red. 



Saccharose .... Bed. Red. 



Mannite .... Red. Red. 



Cane-sugar . . . Blue. Blue. 



Maltose Red or moderately red. Red or pink. 



Milk-sugar . . . Red. Blue. 



Dextrin .... Blue. Violet blue. 

 To bouillon used for acid and gas formation no sodium hydrale or carbonate should 

 be added. 



