MANUAL OF BACTERIOLOGY 



CHAPTER I. 



GENERAL MORPHOLOGY AND BIOLOGY. 



Introductory. — At the bottom of the scale of living things there 

 exists a group of organisms to which the name of bacteria is 

 usually applied. These are apparently of very simple structure, 

 and may be subdivided into two sub-groups, a lower and simpler 

 and a higher and better-developed. 



The lower forms are the more numerous, and consist of 

 minute unicellular masses of protoplasm devoid of chlorophyll, 

 which multiply by simple fission. Some are motile, others non- 

 motile. Their minuteness may be judged of by the fact that in 

 one direction at least they usually do not measure more than 

 1 fi (o-ginns- inch). These forms can be classified according to 

 their shapes iuto three main groups — (1) A group in which the 

 shape is globular. The members of this are called cocci. (2) A 

 group in which the shape is that of a straight rod — the pro- 

 portion of the length to the breadth of the rod varying greatly 

 among the different members. These are called bacilli. (3) A 

 group in which the shape is that of a curved or spiral rod. 

 These are called spirilla. The full description of the characters 

 of these groups will be more conveniently taken later (p. 12). 

 In some cases, especially among the bacilli, there may occur 

 under certain circumstances changes in the protoplasm whereby 

 a resting stage or spore is formed. 



The higher forms show advance on the lower along two lines. 

 (1) On the one hand, they consist of filaments made up of 

 simple elements such as occur in the lower forms. These 

 filaments may be more or less septate, may be provided with a 



