DUST, MOLDS, AND BACTERIA OF THE AIK 93 



New bacteria are produced by division of the old ones. 

 After one has grown to adult size it may divide into two, 

 each of which may continue to grow and divide. The divi- 

 sion may be repeated as often as once in every twenty 

 minutes, though usually not so frequently. Like other de- 

 pendent plants, bacteria feed upon and destroy plant and 

 animal materials and, on account of the rapidity with which 

 they multiply, are usually found in very large numbers. 



FIG. 48. Photomicrographs of bacteria 



These photographs were taken through a high-power microscope. The small, dark 

 bodies are the bacteria, very highly magnified. Photographs by Dr. N. M. Harris 



105. Study of yeasts, molds, and bacteria. The study of 

 these forms of life is of great importance, and the methods 

 that must be used in studying them are different from those 

 used in studying larger plants. One who wishes to know 

 much about them must give his attention to this branch of 

 science alone. On account of the danger to man from disease- 

 producing bacteria, the science of bacteriology has been taught 

 largely in connection with the study of medicine, but its im- 

 portance in other respects is coming to be more commonly 

 recognized. Yeasts and molds have little relation to disease, 

 but are of great importance in daily Me and in industry 

 because of the changes which they produce in food. 



