Bacteria 



The habits and way of life of some bacteria are very 

 remarkable. One great group of them is unable to exist 

 in free oxygen, but obtains what oxygen they require by 

 the alcoholic fermentation of sugar and allied material. 

 They and the other fungi and plant cells which act like 

 them are therefore responsible for alcohoUsm. 



Sunlight at once destroys most bacteria. A young 

 (three hours old) Micrococcus prodigiosus dies in one 

 minute of sunlight. Old colonies (that is, ten to fifteen 

 hours old) may survive longer but are killed in three 

 to five minutes.^ 



A colony or <' culture " of bacteria isolated from the 

 world in a test-tube or glass shell, and growing in blood- 

 serum or peptone broth, not only extracts and absorbs 

 from this liquid or jelly whatever food it requires, but 

 also excretes out its own waste products. This is just 

 as necessary for bacteria as for any other plant or 

 animal. As we saw in the last chapter, carbonic acid 

 is a waste product excreted by plant roots, and is in 

 excess poisonous to them. 



A disease germ living in an animal's body gives off 

 a series of complex waste products or toxins which are 

 deadly poisons to the animal cells. The dead substance 

 of these poisoned cells is then absorbed as food material 

 by the bacterium, which in consequence thrives and 

 multiplies. 



When cultivated artificially in test-tubes or glass 

 boxes (Petri's shells) a colony of disease germs will in 

 process of time exhaust all the food material in its 

 little '^ world " or test-tube, but it will become itself 

 diseased and die long before it has done so, for its 

 own waste excretions will have so pervaded and 

 poisoned its world that it becomes uninhabitable. 



Pasteur suggested that when disease germs in an 

 animal body eventually die out, as is found to be always 



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