DEPARTMENT OF BACTERIOLOGY 



159 



the ones which are frequently spoken of as germs, microbes, or 

 raicro-organisms, and whose proper botanical name is hacteria. 

 As has been intimated, the bacteria are the smallest plants of 

 which we have any knowledge. Because of their extreme mi- 

 nntenesSj their existence was not known until the microscope 

 came as an aid and an extension to ordinary vision. After 

 their discovery comparatively little information of importance 

 m regard to their nature and function was acquired until the 

 latter half of the present century. 



The form and ^structure of bacteria are extremely simple, 

 and shQw so little variety that, in appearance, different species 



Fig. 54. Forms of Bacteria. 



resemble one another very closely. Three principal forms are 

 recognized: those which have the shape of little balls or spheres 

 known as micrococci', those which are elongated and round, 

 like a short pencil, known as bacilli; and those which are spiral 

 or corkscrew-shaped known as spirilla. Fig. 54 shows the dif- 

 ferent forms as they appear under a moderately high power of 



