EXAMINATION OF LIVING BACTERIA. 27 



locomotion. Moreover, it very frequently happens 

 that these characteristics are not all present in one 

 species ; many are motionless, and yet form spores, 

 and so on. Continually species are being taken out 

 of the class Bacterium, to be included in the class 

 Bacillus, and in the end the former will probably be 

 quite absorbed in the latter. 



We soon observe considerable differences in the 

 movements of bacilli. Some shoot like lightning 

 through the field of vision, whilst others drag them- 

 selves slowly forwards. Again, othefs show oscillatory 

 movements without really moving from one place, 

 whilst yet others swarm about amongst themselves 

 without apparent method, now shooting here, now 

 there, sometimes pausing for a moment, and then 

 turning round, etc. Many bacilli are quite motion- 

 vless, whilst in others these movements may be tem- 

 porarily suspended. 



Distributed amongst these rod-bacteria, we find 

 the motionless ball-bacteria, or Micrococci, which are 

 already known to us. Specimens of a third family, 

 the Screw or Spiral bacteria, may occasionally 

 be found in the meat infusion, bat they more fre- 

 quently occur in an infusion of decomposing plants. 

 They are like little bent rods, which sometimes appear 

 as long threads, twisted into the form of spirals, and 

 sometimes as shorter cells, which present the appear- 

 ance of half the turn of a spiral. The diameter of the 



