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 72 , which is exactly 4,722,366,482,869,645,213,696 

 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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