2 BACTERIOLOGY. 



ease. It was consideration of the most im- 

 portant questions of biology and pathology, of 

 science and of medicine, that first directed atten- 

 tion towards bacteria. But these subjects have 

 not of course been developed exhaustively by 

 reference to bacteria alone. Small organisms 

 belonging to other groups of the plant king- 

 dom and even to the animal kingdom stand in 

 a similar relation to the questions involved ; 

 and we may speak with greater precision of 

 micro-biology, indicating by that term a vast 

 territory into which investigation has made 

 only an excursion. If we still continue to 

 allot to bacteria the major part of this territory, 

 we are justified for the reason that bacteria are 

 the organisms whose participation in impor- 

 tant biological phenomena was first discov- 

 ered, and because, owing to the development of 

 special methods of bacterial investigation, we 

 at present possess in this group of microbes the 

 most favorable material for research. 



In this chapter we shall consider questions re- 

 lating to bacterial structure. The points which 

 are of the greatest general interest are those 

 bearing upon the constancy and variability 

 of form, and upon the cellular structure which 

 is especially interesting because these organ- 

 isms are ordinarily regarded as the lowest in 

 the scale of life. 



