19 



A perusal of the table will show that Bact. coli produces a large 

 amount of acid whereas the acidity produced by Bact. aerogenes is very 

 much less. This is particularly noticeable with respect to acetic and 

 lactic acid. It will also be noted that the Bact. aerogenes produces about 

 twice as much carbon dioxide as Bact. coli and that the volume of hydro- 

 gen gas formed is more nearly the same. They observed further that Bact. 

 coli utilized only a part of the available carbohydrate whereas the Bact. 

 aerogenes strains completely exhausted the sugar. They conclude from 

 these observations that the two organisms act upon glucose in a totally 

 different manner and must therefore be regarded as separate and distinct. 



The Voges Proskauer Reaction. If the products of glucose de- 

 composition enumerated above are summed up, it will be found that 

 only 69 percent of the carbon is accounted for in case of Bact. aerogenes 

 and 87 percent with Bact. coli. This led Harden to search for the discrep- 

 ancy which he accounted for by the presence of a crude glycol. This con- 

 sists for the most part of 2:3 butyleneglycol (CH 3 CHOH-CHOH-CH 3 ), 

 On oxidation it yields acetyl-methyl-carbinol (CH 3 , CHOH, CO. CH 3 ), a 

 volatile reducing substance, which, when mixed with potassium hydroxide 

 in the presence of peptone, imparts an eosine-like coloration to the mixture 

 on standing. Butyleneglycol is oxidized to acetyl-methyl-carbinol by Bact. 

 aerogenes but not by Bact. coli. 



Neither acetyl-methyl-carbinol nor butyleneglycol give the eosin-like 

 coloration when mixed with potassium hydroxide. In the presence of 

 peptone, however, the coloration develops on standing in the case of the 

 carbinol but not with the glycol. According to Harden the reaction is 

 due to further oxidation of the carbinol (CH S CO.CHOH.CH 3 ) to diacetyl 

 (CH 3 CO.CO.CH 3 ) which reacts with some constituent of the peptone. In 

 a later study Harden and IN orris report that in the presence of strong potas- 

 sium hydroxide solution diacetyl reacts with proteins to give a pink color- 

 ation together with a green fluorescence. With arginine, creatine, dicyan- 

 amide and guanidine acetic acid, the pink coloration is also obtained but 

 the fluorescence is absent. The reaction depends on the presence of the 

 group NH:C (NH 2 ) N:HR. The exact significance of R. has not been de- 

 termined. Harden ascribed the Voges-Proskauer reaction to the production 

 of acetyl methyl carbinol. 



The reaction takes its name from the fact that it was first observed 

 by Voges and Proskauer in 1898, in their studies on the "Bacteria of Haemor- 

 rhagic Septicaemia." They describe this observation as follows: 



"On addition of caustic potash, we observed a new interesting color 

 reaction. If the tube be allowed to stand 24 hours and longer at room 

 temperature, after the addition of the potash, a beautiful fluorescent color 

 somewhat similar to that of a dilute alcoholic solution of eosin forms in the 

 culture fluid particularly at the open end of the tube exposed to the air. 

 We have investigated a few of the properties of this coloring substance, 

 which is not produced by the action of the alkali on the sugar, and have 

 found that it is fairly resistant to the action of the external air. After a 



