CLASSIFICATION OF BACTERIA 121 



Classification. A consideration of the classification of 

 bacteria is quite unnecessary for the purpose of our work, 

 inasmuch as they are so minute that no one without the 

 aid of a powerful microscope will ever be likely to see 

 these organisms. Their activities are seen on all sides, 

 but the organisms themselves are totally below ths reach 

 of our vision. It is sufficient, therefore, to give a few 

 facts concerning their general appearance. 



Bacteria are the simplest organisms known. They are 

 far simpler than molds and even simpler than yeasts. So 

 minute are they, and so simple in their structure, that 

 very little is known in regard to them at the present time 

 except their external appearance. They are almost uni- 

 versally regarded as plants, although many of them are 

 endowed with a power of motion and for this reason might 

 readily be mistaken for animals. Biologists have learned, 

 however, that many plants can move ; bacteria need not, 

 therefore, be classed with animals on that account if they 

 resemble plants more closely in other respects. 



Flagella. The fact that many bacteria are endowed 

 with the power of motion suggests that they must have 

 locomotive organs, and these, indeed, are easily seen by 

 proper microscopic study. They consist of minute hairs 

 which ^project from the body of the bacteria. Sometimes 

 there is a single one from one end, sometimes they occur 

 in tufts, and occasionally they may be scattered all over 

 the bodies of the bacteria as shown in Fig. 48. These 

 little hairs are capable of waving to and fro, and by this 

 motion they drive the bacteria through the water. Not 

 all bacteria possess such locomotive organs, and one 

 means by which scientists classify these organisms is by 



