ORGANIZATION OF THE BACTERIA. 43 
was thus demonstrated that there was a flagellum at both ends of the or- 
dinary B. termo. 
“Tt 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.— Or THE DirrerENT Moves or 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 : — 
1. Form of a little chain: Torula, Leptothria. 
— The usual method of multiplication among the 
bacteria is by fission (“ scissiparité’’); each cor- 
puscle divides transversely, and gives birth to two 
