CONTROL AND USE OF BACTERIA 397 



In these liquids the oxidation of alcohol is due to the action 

 of bacteria. In the making of sauerkraut and other kinds of 

 pickles, as well as in the curing of silage, bacterial fermenta- 

 tion is used. In the work of the dairy, from the souring of the 

 milk and cream to the curing of cheese, bacteria are used at 

 several points. Cheeses of the Cheddar type and various 

 cream cheeses, as well as butter, depend for their flavors upon 

 the particular species of bacteria present during the souring. 



It is very likely that bacteria play a part in the curing of tobacco 

 and in the making of hay, although the problems connected with 

 these processes have not been thoroughly worked out as yet. In the 

 preparation of indigo dye from the extracts of certain plants of the 

 bean family, it is likely that an oxidizing ferment from certain bacteria 

 performs an essential part of the work. In the preparation of hides 

 for tanning, certain of the changes are brought about by bacterial 

 ferments. 



In the disposal of sewage in large cities, a process of converting 

 the decaying mass of organic matter into harmless or less offensive 

 forms through the action of bacteria has come into extensive use. 

 The sewage is collected in large tanks. After the fermentation the 

 " sludge " may be used as a fertilizer. 



