What Bacteria Do 15 



unknown to man, which still linger in the 

 primitive simplicity which we imagine to have 

 belonged to the earth's earliest denizens. 

 These are the bacteria. 



So small are the bacteria, and so simple in 

 their structure and activities, that it has not 

 been an easy task 

 for scientific men 

 to decide whether 

 they belonged 

 among animals or 

 plants. It is now 

 definitely settled, 



J FIG. I. FORMS OF BACTERIA 



however, that they 



are plants, and are closely related to the sea- 

 weeds. 



Bacteria vary a good deal in shape, but 

 in general they are either spheroidal or ovoidal, 

 like a billiard-ball or an egg; or rod-shaped, 

 like a lead-pencil; or spiral-shaped, like a 

 cork-screw. Some are separate, some clus- 

 tered. Fig. i: 



They are in general so very small that we 

 can hardly form a conception of them except 

 by comparison with some well-known objects. 



