CHAPTER THIRTY-SEVEN 



BACTERIA AND THEIR RELATIONS TO LIFE 



The best-known and the most discussed of all the non-green 

 plants are the bacteria. They are so intimately related to human 

 welfare that most persons, even though they have never seen 

 bacteria, know something about them. They are one-celled 

 plants, at once the smallest in size, the simplest in structure, and 

 the most abundant of all plants. They live in immense numbers 

 in the water and in the upper layers of the soil, and they are 

 blown about in dust in the air. Some are too small to be seen 

 except with the highest powers of the microscope. Others may 

 be seen with an ordinary laboratory microscope. They make up 

 for the small size of the individual by their rapid multiplication 

 and by the formation of colonies containing countless numbers 

 of individuals. Bacteria are responsible for many of the diseases 

 of men, animals, and plants, and bacteria affect our lives in 

 almost countless other ways. All our modern methods of sanita- 

 tion, quarantine, surgery, water supply, and sewage disposal, 

 and much of our personal hygiene, are primarily based on our 

 knowledge of the behavior of this group of plants. 



Economic importance of bacteria. Economically the bacteria 

 are of the greatest importance. Together with the fungi they 

 are the principal cause of disease, decay, and the formation of 

 humus. Bacteria bring about the ripening of milk in butter and 

 cheese making, and they produce both the pleasant flavors in 

 these products and the unpleasant flavors that develop in them 

 with age. The bacteria are also the source of much of the 

 available nitrogen in agricultural soils. The drying of hay, 

 vegetables, and fruits, the canning and pickling of vegetables, 

 fruits, and meats, and refrigeration and cold storage are methods 

 of avoiding or making impossible the growth of bacteria. Thus a 

 knowledge of these plants is fundamental to our understanding 

 of thousands of details of our daily life. 



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