Bacteria 
of several Iron-bacteria, which form the peculiarly un- 
pleasant-looking slime in the stagnant water of marshes 
where there are iron-pipes. 
There are but a few examples of the manifold 
activities of these minutest of vegetable organisms. It 
is really impossible to do justice to them in a short 
space. It is they who especially take charge of all 
dead vegetable and animal matter, which they thoroughly 
break up and work down to some simpler chemical 
condition, in which it can be again used by the vege- 
table world, Their small size and wonderful rapidity 
of growth enables them to do this in a very efficient 
manner, 
A single bacterium will grow up and divide into two 
bacteria in the space of 20 minutes. So that in one 
day of 24 hours, the progeny of one bacterium would 
be 2”, which is exactly 4,722,366,482,869,645,21 3,696 
individual germs, Indeed in a very few days the whole 
earth would be one weltering mass of bacteria if all the 
descendants of a single microbe continued to live and 
multiply at this unconscionable rate. But this is an un- 
likely thing to happen, for they require food material, and 
would very soon commit bactericide by carbonic acid 
poisoning. 
Cheese, butter, curds and their various varieties are 
due to special bacteria. In concert with yeasts and 
some other fungi they produce many fermentations, 
and especially assist in making beer, wine, ginger-beer, 
and vinegar. It is they also who spoil and destroy the 
same deleterious drinks. Tobacco is the result of 
bacterial activity. The making of hay, ensilage, and 
linen, or the tanning of raw hides, can only be carried 
out with the help of bacteria. The art of man in all 
these cases consists in checking their action at the 
moment when some useful substance has been pro- 
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