46 MORPHOLOGY OF THE BACTERIA. 
The petalococcos and petalobacteria of Billroth 
correspond with the mycoderma of Pasteur. 
4. Swarms. — We have seen that the filiform 
and spiral bacteria do not, usually, form zooglea. 
These microphytes are either disseminated and free, 
or united in swarms. This formation may be seen, 
for that matter, in all the bacteria, when, thanks 
to abundant nourishment, they multiply rapidly | 
and gather together in considerable masses. They 
are very active in these swarms, whilst in the 
zooglea the corpuscles are motionless, because of 
the intermediary glairy substance. 
Pulverulent precipitate. — When the nutritive 
elements are exhausted in a liquid, the bacteria 
cease to multiply, fall to the bottom of the recep- 
tacle, and the liquid gradually becomes clear. The 
deposit formed in this manner may acquire a thick- 
ness very appreciable to the naked eye. The bac- 
teria which form this precipitate are not dead, but 
in a state of temporary repose; and if a new sup- 
ply of nutritive material is added to the liquid, 
they are seen to multiply anew, until this has been 
exhausted (Cohn). 
