MICROBES, OR BACTERIA. 117 
the aid of purely inorganic substances. Animals and 
plants devoid of chlorophyl get their nutriment by 
unmaking the complex substances elaborated by the 
green parts of plants, and these act in the same way 
for their own profit in those organs which have no 
chlorophy]l ; as, for instance, in the seed and embryo. 
ITX.—A£ROBIES AND ANAROBIES. 
We have seen that microbes, at different epochs 
of their existence, and in accordance with the nature 
of their environment, can assume very diverse forms. 
Thus the organism, which at first appears in the forin 
of globules (micrococeus), either isolated or united in 
more or less numerous colonies by a kind of muci- 
laginous envelope (4oogloea), when it again becomes 
free, may be elongated in the shape of the figure 8, 
which is formed of two cells about to separate; or 
a large number may be included in the form of a 
straight, articulated rod (Bacterium), or in a rod 
which is curved, waved, or even spiral (Vibrio, 
Spirillum, Spirochete), always more or less mobile; 
or, again, the cells may form long, stationary filaments 
(Bacillus), ete. 
So also the habitat and mode of life divide the 
microbes into very distinct classes). Some can only 
subsist when they breathe the natural oxygen they 
withdraw from the atmosphere; they can only exist 
