16 The Story of the Bacteria 



One of the most common of the bacteria is a 

 little rod, so small that if you were to put fif- 

 teen hundred of them end to end, the line 

 would scarcely reach across the head of an 

 ordinary pin. If you look at them with a 

 magnifying power so great that, if it could be 

 applied to him, it would make a man look 

 about four times as tall as Mount Washington, 

 they do not look larger than this. We can 

 see, however, that they are made up of a 

 slightly granular material surrounded by a 

 somewhat denser envelope. 



The bacteria appear under the microscope 

 as pale translucent bodies, and the student 

 usually finds it necessary, in order to see their 

 outlines clearly, to stain them with some 

 one of the aniline dyes red, or blue, or violet, 

 when they become very distinct. 



When they are alive and suspended in fluids 

 many of the rod-like and spiral bacteria can 

 perform the most elaborate and astonishing 

 series of movements. They swim slowly, they 

 turn about, they roll over, they wriggle, dart 

 forward, retreat, bang against one another, 

 rest awhile, sway to and fro, plunge off again, 



