BACTERIA 



they are essential to brewing and tanning; they 

 act as scavengers over the face of the earth, break- 

 ing up a mass of decaying animal and vegetable 

 matter into simple chemical substances which can 

 then be used again as food for plants; some of 

 them also can take a gas called nitrogen, from the 

 air, and pass it on to green plants. 

 I What are these active little creatures ? The 

 question is a natural one. They are merely very 

 minute, one-celled plants. Each one possesses a 

 firm cell-wall, filled with living matter; in an 

 earlier chapter, we described the one called protean 

 animalcule and, although it was composed of but 

 a single cell it had no definite wall. This is one of 

 the essential differences between plants and animals, 

 both of them are made up of one or more, maybe 

 millions of cells, but each plant cell is surrounded 

 by a well-defined wall, animal cells have no such 

 svalls. The exact position of the bacteria in the 

 Dlant world is still open to doubt. Most scientists 

 Dlace them amongst the fungi; for, with very few 

 exceptions they possess no chlorophyll. One or two 

 )f them, however, do possess a green colouring 

 natter which, if not chlorophyll is very near to it; 

 )n this account other scientists are of the opinion 

 hat they are related to the seaweeds. It is a 

 Qatter, however, that does not concern us very 

 leeply, for our purpose it is sufi&cient to know that 

 hey are plants. When they were discovered, nearly 

 ,hree hundred and twenty-five years ago, they were 

 vDoked upon as minute animals and it is curious 



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