Household Bacteriology 13 77 



germs that are not harmful 



Some bacteria are of great value in the economy of nature. Man's 

 bacterial friends have been found not less active than, and many times 

 as numerous as, his bacterial foes. To his bacterial friends he owes the 

 fertility of the soil by which plants are nourished. They tear down 

 organic matter and pass it back to its simpler elements through the process 

 of decay, thus ridding the earth of many harmful substances. This is 

 the work of so-called nature's scavengers. There is advantage in what 

 is called incipient decay. When bacteria grow in food the products of 

 decomposition are different from the original nature of the food and 

 produce new odors and tastes. We often need the flavors thus produced 

 to stimulate the flow of the digestive juices. The gamy taste of meat is 

 due to the beginning of decomposition of some of its constituents, and 

 the strong flavor of limburger cheese is owing to the same cause. Gamy 

 food, however, soon becomes objectionable; and cheese is ruined by the 

 development of a too strong flavor of putrefaction. 



The most common substances that owe their flavor largely to the 

 presence of bacteria are butter, cheese, and vinegar. Without bacteria, 

 butter, like " apple-pie without the cheese," lacks flavor; while cheese 

 without bacteria would be like ' ' the play ' Hamlet ' with Hamlet left 

 out ' ' — ■ an utter impossibility. When you next enjoy the acidity of 

 a pickle, remember to give credit for that pleasant sourness to certain 

 tiny plants, such as -those that you have seen massed together in enormous 

 quantities in " mother " of vinegar. Whenever a liquid containing a 

 small amount of alcohol cider, for example, is exposed to the air, bacteria 

 find therein a home and food. A film similar in nature to " mother " 

 spreads over the top of the liquid and before long the alcohol becomes 

 acetic acid, with vinegar as the result. 



Our Puritan grandmothers would have thought us bewitched had we 

 been able to tell them that their cheeses, on which they spent so many 

 watchful hours, owed their making and their flavor largely to invisible 

 plants. Even now scientists are unable to explain this process fully, 

 although they are certain that there could be no cheese without bacteria. 



From none of the harmless bacteria do we get more real enjoyment 

 than from those found in butter. Long before the science of bacteriology 

 and the days of cream separators, it was known that cream set to rise 

 by its own lightness, skimmed, and left standing for several days would 

 " ripen " and make far better butter than fresh cream. Butter made 

 from ripened cream was found to taste better, keep better, and be made 

 more easily than that made from unripened cream. We needed the 

 bacteriologist to find the cause and to prove it to be the presence of bac- 

 teria; but long before his day the thrifty housewife had made use of the 



