108 A MANUAL OF BACTERIOLOGY 



Exercise 150. The Fermentation of Vinegar 



This fermentation takes place in some weak alcoholic solution, 

 such as cider or wine. The process is carried out by several 

 species of bacteria which are common in the air. Inoculation of 

 the liquids is not, therefore, required for vinegar manufacture. 

 The brown gelatinous mass found in vinegar barrels, known as 

 " mother of vinegar," is the zoogloeum formed by these bacteria. 



The process of fermentation involved is one of oxidation, which 

 is most simply expressed by the equation 



CH 3 - CH 2 OH + 2 = CH 8 COOH + H 2 O. 



In reality, however, the oxidation process is more complex 

 than the above equation would indicate. 



1. Obtain the film from the surface of some old vinegar and 

 inoculate several water blanks. 



2. Plate out the organisms in the water blanks, using wort 

 agar. Incubate the plates at 25 C. 



8. When colonies appear, transfer organisms from them to 

 tubes of wort agar. Incubate tubes at room temperature and at 

 37 C. 



4. Prepare liquid cultures in flasks containing 50 cc. of liquid 

 wort plus 1 per cent alcohol. Inoculate them from the films 

 obtained in 1. Incubate one flask at 15-20 C., one at 30 C., 

 and one at 40 C. Leave two flasks uninoculated for controls. 



5. Examine the flasks daily and note the formation of films. 

 Remove organisms with the sterilized platinum loop, stain with 

 carbol-fuchsin, and examine with the microscope. Use the method 

 described in Exercise 61 to demonstrate the gelatinous capsule. 

 What differences in morphology at different temperatures ? 



6. On every second or third day add a small quantity of 

 alcohol. At the end of the experiment, filter the solutions and 

 titrate them with -^ N NaOH to determine acidity. 



Exercise 151. Study of Mucor 



Mucor is one of the molds common everywhere, especially 

 upon starchy substances. It is especially common upon bread, 

 cooked potatoes, and bananas. It forms a floccose, aerial layer of 



