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Bacteria are now considered to belong to the vegetable kingdom, 
being able to derive nourishment from ammonia compounds. They 
differ from the higher vegetable cells in being unable to split up 
carbonic acid into its elements. This is said to be due to their 
not possessing chlorophyl, or green colouring matter. Bacteria 
may be defined as minute vegetable cells devoid of nuclei ; the 
cell-walls consist of cellulose, the contents being protoplasm, which 
varies in its constitution, as shown by the different manner in 
which chemical agents for staining them act. In some instances 
they contain starch granules, and then of course they will stain 
a dark colour with iodine. Others contain sulphur granules, and 
in others again certain colouring matters. 
Bacteria differ in shape. Sometimes they appear as micrococci, 
or round or egg-shaped cells. These increase by fission, or 
division ; sometimes the two divisions remain attached at one 
end, and then you have a diptococcus. These may again divide ; 
so that you may get a string of them, when they are strepto- 
cocci. Division may take place in two or three directions, so 
that four or eight cells may result from the division of one. 
Bacilli are rod -shaped bodies ; when short called bacteria, 
when long bacilli ; when bent, they are called vibriones. Some- 
times they have a corkscrew form, and are called spirilli. Under 
the microscope some appear to be endowed with locomotive 
powers, and others are motionless. They can be readily observed 
in any vegetable infusion which has putrefied. It is considered 
by some that the movements are only molecular, and are not 
independent. Undoubtedly some move by contraction of their 
protoplasm, as they have a filamentous termination, which lashes 
about freely. As before mentioned, their multiplication may take 
place by fission, or division, or by spores, as in anthrax bacillus. 
Some bacteria require oxygen, and others can derive their 
nourishment from oxygenised compounds in the medium in 
which they grow. Pasteur on this account divides them into 
aerolic and anaerobe. They require nitrogen to build up their 
protoplasm, and carbon also ; water is likewise necessary. A 
practical proof of this is found in the preservative qualities 
of sugar, the addition of which to preserved fruit prevents the 
formation of fungoid growths by absorbing the water. 
In order to cultivate the various forms of microbes, very 
various media are required ; some thriving in one medium, 
