STRUCTURE OF BACTERIA 



119 



difficult, while special devices are required to preserve 

 food indefinitely. 



To the housewife bacteria are of little value and are 

 foes, like the molds, rather than allies, like the yeasts. 

 This does not mean that they have no utility. On the 

 contrary, they are of the most fundamental importance in 

 nature, and it is no exaggeration to say that the very 

 continuation of life is dependent upon their activity. To 

 the farmer 

 they are abso- 

 lutely essen- 

 tial. They 

 are the dairy- 

 man's close 

 allies, and 

 they are in- 

 dispensable friends of many industries. By their action 

 are produced some of the articles for our tables (vinegar) 

 and also the flavor of butter and cheese. However, these 

 phenomena do not directly concern the housewife, and, 

 with a few individual exceptions, bacteria are her foes. 



Fig. 47. Comparative size of the point of the finest 

 cambric needle (6), a particle of dust (a), and bac- 

 teria (c). 



Structure of Bacteria 



Size. Bacteria are much smaller than yeasts, and only 

 the high powers of the microscope can disclose their 

 presence (Fig. 47). Many are not more than a fifty 

 thousandth of an inch in diameter, and even the larger 

 ones are not much more than a ten thousandth of an 

 inch. But bacteria are far more abundant in nature than 

 yeasts. They are present in great numbers in the earth, 



