32 MYCOLOGY 



Fermentation is well exemplified in an old and well-known process- 

 the conversion of alcohol into acetic acid by a number of organism 

 morphologically very similar. Hansen considers that there are thrct 

 different species concerned in the acetic fermentation, namely, Bacleriur, 

 acelicum, B. Pasteurianus and B. Kutzingianus, which are non-motile 

 medium-sized rods often in chains and forming pellicles which appea 

 on the surface of the liquid, afterward sinking to form in the liquid : 

 deposit known as mother of vinegar. The changes which take placi 

 in the conversion of alcohol to acetic acid may be expressed as follows 



CH3.CH2.OH -1-0 = CH3.CHO + H2O 



Alcohol Aldehyde 



CH3.CHO -I- O = CH3.COOH 



[Aldehyde Acetic Acid 



This is conducted in barrels with wood shavings, where the alcoholi 

 fluid trickling over the shavings coated with the bacteria, and in contat 

 with the air, is changed to acetic acid. 



Lactic acid fermentation is important to man, because upon th 

 changes in milk by the lactic acid organisms depends the manufactur 

 of a considerable number of valuable products of the dairy, such a 

 buttermilk and cheese. This fermentation is an aerobic process whos 

 optimum is found between 30° and 3S°C. There is a considerabl 

 number of bacteria capable of converting milk sugar into lactic acic 

 such as Vibrio cholera, Bacillus prodigiosus and others, but the true lacti 

 acid bacteria are those which are the cause of the souring of mill- 

 Formerly, they were all classed as Bacterium acidi lactici, but recen 

 investigations have shown that not one species but a considerabl 

 number are at work, sometimes one form; sometimes another bein 

 active. A common kind is a short non-motile rod, 0.5/1 X i to 2/. 

 facultatively anaerobic, known by such names as Bacterium acidi lactic 

 B. aerogenes, and probably comprising several races of one specie; 

 The true lactic acid fermentation is the change of lactose, or mil 

 sugar, into lactic acid. As lactose is not directly fermentable it mus^ 

 be converted into such simple sugars as glucose and galactose. Th 

 following equation approximately represents the chemic chang 

 involved. 



CisHjaOu + H2O = CeHijOo + C^HuO, 



Lactose Water Glucose Galactose 



C„H,20„ = 2C3H6O3 



Lactic Acid 



