62 
HOUSEHOLD BACTERIOLOGY 
These are the agents which make the vinegar. 
Not all vinegar used in the household is made from 
cider. The large manufactories usually use alcohol 
or wine as the base of the process. Alcohol and acetic 
acid contain the same elements in different porportions, 
the former having less oxygen. The bacteria of 
mother-of-vinegar are able to take oxygen from the 
air, cause it to unite with the alcohol, and thus make 
acetic acid. In actual practice a weak alcoholic solu¬ 
tion is allowed to trickle 
lowly over beechwood shav- 
lgs. In this way a large sur- 
ice is exposed to the air. It 
found that if the shavings 
‘e sterilized, that is, if all 
icro-organisms are removed, 
o acetic acid is formed, thus 
proving that here again we 
are indebted to our dust-plant 
friends. 
FIG. 38. Bacteria in 
“Mother-of-Vinegar.” 
Butyric Lactic acid, the acid of sour milk, and acetic acid, 
Acid the acid of vinegar, are two desirable acids due to 
bacterial growth, while a third, butyric acid, not desir¬ 
able to the housewife, results when such growth takes 
place in fats. This is the chief cause of rancidity in 
butter and other oily substances and the similar taste 
or smell in old milk. To the housewife this means 
loss of food supplies and therefore comes under the 
unfriendly work of dust-plants. 
