A MAIS'UAL OF BACTERIOLOaY 



SECTION I 

 THE FORM AND OCCURRENCE OF BACTERIA 



Bacteria are small and simply organized plants. For the most 

 part they consist of single cells, but some consist of filaments 

 made up of separate individuals and show some tendency toward 

 a physiological division of labor. The bacterial cell is supplied 

 with a definite cell wall which incloses living protoplasmic sub- 

 stance. Bacteria multiply by simple division, usually constricting 

 in the middle and forming two new cells from each mother cell. 



The first recorded descriptions of bacteria are those of Leeu- 

 wenhoek, a Dutchman, which were written in 1683. Most of 

 our knowledge of bacteria, however, has been obtained since the 

 year 1869. 



We have learned that bacteria are widely distributed in nature. 

 The soil and natural waters contain large numbers of them. The 

 dust particles in the air carry numbers of germs. In thickly 

 populated regions the number of germs in the air is larger than 

 in sparsely settled districts, while the air over the sea and on 

 the tops of high mountains is quite poor in bacteria. 



We find that bacterial activities are intimately associated with 

 processes of growth and decay, health and disease, life and death. 

 Although there are certain bacteria which cause diseases, yet 

 the sum total of their activities is beneficial to the human race, 

 and it is certain that life as we know it could not long exist on 

 the earth were it not for their action. The study of these organ- 

 isms has led to the solution of many of the important problems 

 of human welfare. 



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