1 6 THE STORY OF THE BACTERIA. 



about four times as big as Mount Washington, 

 they do not look larger than this. We can 

 make out, 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 distinctly, 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, 

 and so on through varying phases of move- 

 ment until the head swims and the eye tires in 

 following them. This movement, in some of 

 the bacteria at least, is induced by a little hair- 

 like projection from the end of the organism, 

 which vibrates rapidly to and fro. It is very 

 difficult to see these little projections or cilia, 



