THE EFFECTS OF BACTERIA. 125 



molecule in the bacterial cell is decomposed into 

 smaller particles, during which process heat is given 

 off. I will illustrate this by the ordinary form of 

 fermentation of sugar in which the process is very 

 simple. 



C 6 H 13 6 = 2C 2 H 6 + 2CO 2 

 1 grape sugar = 2 alcohol -f- 2 carbonic acid. 

 Or, 



C 6 H 12 O 6 = 2C 3 H 6 O 3 

 1 grape sugar = 2 lactic acid. 

 Or, 



C 6 H 12 = 8C 2 H 4 2 

 1 grape sugar = 3 acetic acid. 



The organism requires such a source of energy, 

 particularly when it grows in the absence of oxygen, 

 and there is a failure of the source of energy at the 

 command of the aerobic varieties and which consists 

 in the oxidation of absorbed substances by the oxy- 

 gen which has been taken up. Hence all anaerobic 

 varieties are provided with great power of fermenta- 

 tion of sugar, and some facultative anaerobics only 

 give rise to fermentation of a saccharine nutrient 

 when oxygen is excluded. 



In contradistinction to fermentation by the split- 

 ting-up process is the much rarer oxidative fermen- 

 tation, the best example of which is the production 

 of acetic acid from alcohol. Here we find a one-sided 

 metabolic activity of the acetic acid bacteria. These 

 obtain a considerable supply of energy, not by split- 

 ting up, but by oxidation of the absorbed alcohol. 

 The gain in energy occurs simply from a one-sided 

 intensification of the ordinary nutritive processes of 

 bacteria. 



It is evident from these remarks that products of 



