. 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 chloro- 

 phyll, 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 i //, (o-^^o- inch). These forms can 

 be classified according to their shapes into three main 

 groups (i) 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 proportion 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 fuller description of the characters of these 



