CHAPTER I. 



FORM AND CLASSIFICATION OF BACTERIA. 



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Bacteria may be characterized as unicellular, micro- 

 scopic plants. Their vegetable nature has been established 

 only within comparatively recenl; f^a^i' , Frc *P ne time of 

 Leeuwenhoek, who in 1683 discovered .the first, representa- 

 tive of this group, until 1854 these microscopic' organisms 

 were spoken of as animalculae or minute forms of animal 

 life. Indeed, it was not until about 1875 that the true 

 relationship of bacteria to plants was definitely settled, 

 largely through the labors of Cohn, Naegeli, DeBary and 

 other botanists. 



When studying the exceedingly minute forms of life 

 observed under the microscope, one recognizes that it is not 

 always possible to indicate the dividing line between the 

 animal and vegetable kingdoms. There is no one charac- 

 teristic which will serve for this purpose. Prom the very 

 nature of things it must be expected that the lowest forms 

 of animal and plant life will approach one another. The 

 striking differences which are seen between the higher 

 forms of animal and plant -life gradually disappear as the 

 comparisons are carried down the scale to the lowest forms. 

 The latter merge into one another indicating a common 

 origin in the remotest past. Under these conditions it is 

 evidently impossible to characterize certain forms of life as 

 plants or as animals. 



Inasmuch as bacteria belong to the lowest and simplest 

 forms of life, it cannot be expected that they will show any 

 marked differentiation into plants. They are classified, 

 however, among plants because of their evident relation. 



