CHAPTER III. 
VITAL PHENOMENA OF BACTERIA—MOTION, HEAT 
AND LIGHT PRODUCTION—CHEMICAL EFFECTS. 
Motility. Many bacteria when examined under the 
microscope are seen to exhibit active movements in 
fluids. This motility is produced by the fine hair-like 
flagella attached to all motile species. The movements 
are of a varying character, being described as creeping, 
waddling, rotary, undulatory, sinuous, snake-like, ete. 
At one time they may be slow and sluggish, at another 
sorapid that any detailed observation is impossible. 
Some bacteria are very active in their movements, dif- 
ferent individuals progressing rapidly in different direc- 
tions, while with many it is difficult to say positively 
whether there is any actual motility or whether the 
organism shows only molecular movements—so-called 
‘* Brownian ’’ movements—a dancing, trembling mo- 
tion possessed by all finely divided organic particles. 
If in doubt in such cases it is best, where the matter is 
of importance and one is skilled in the technique of 
staining, to stain the organisms for flagella, and also to 
examine them in a 0.1 per cent. bichloride of mercury 
solution, when, if the movements continue, they are 
purely molecular. Not all species of bacteria which 
have flagella, however, exhibit at all times spontaneous 
movements; such movements may be absent in certain 
culture media and at too low or too high temperatures, 
or of either an insufficient or excessive supply of oxygen. 
