ORGANIZATION OF THE BACTERIA. 43 



was thus demonstrated that there was a flagellum at both ends of the or- 

 dinary B. termo. 



" It will of course be understood that it is by no means an easy matter 

 to secure the demonstration ; and whenever we repeat it, it must always 

 be with nearly the same amount of trouble and patience, although we 

 can now with the ordinary condenser detect the vortical action, both in 

 front and (occasionally) behind the termo, as we never did before. But 

 the demonstration of the ultimate structure of a fixed object — as for 

 instance Amphipleura pellucida — must be looked upon as a matter of 

 great ease in comparison ; and that for many reasons, the foremost 

 being the motion and the minuteness of the object, the swift play of the 

 flagella, their similarity in optical properties to the fluid in which bacte- 

 ria live, the difficulty of retaining them in focus, and of getting them in 

 such a position in relation to the light as to make demonstration possible. 

 Of course, all this would be removed if dead bacteria would answer, but 

 they very rarely (indeed only once) have done so with us. The flagel- 

 lum needs to be in slow motion to properly show itself ; for even with 

 the more delicate and minute monads it is a difficult thing to show the 

 flagella in dead forms, since in the majority of cases they appear to be 

 attracted round the body of the creature." 



§ 2. — Of the Different Modes of Grouping 

 of the Bacteria. 



The bacteria are found in different media in 

 two states, — free, isolated (unicellular bacteria), 

 or united several together, either in chains, in 

 filaments, or in masses of greater or less extent, 

 and sometimes by the aid of a mucous substance 

 in which they are imbedded. 



The free unicellular bacteria are found in the 

 Spirillum, Bacillus, Monas, etc. When they are 

 united, they are grouped in the following 

 modes : — 



]. Form of a little chain: Torula, Leptothrix. 

 — The usual method of multiplication among the 

 bacteria is by fission (" scissiparite") ; each cor- 

 puscle divides transversely, and gives birth to two 



