BACTERIA 



The writer whom we have just quoted calcu- 

 lated that a single bacterium weighs about 

 0.000,000,000,024,243,672 of a grain, that forty 

 thousand millions weigh one grain and that two 

 hundred and eighty-nine billions weigh a pound. 

 The descendants of one bacterium weigh 1/2666 of 

 a grain, after twenty-four hours ; more than a pound 

 after two days, and sixteen and a half million pounds 

 after three days. The assumption in this case, also, 

 is that no harm comes to any of them; the mor- 

 tality amongst bacteria is, clearly, very great. 



Sometimes, owing to external conditions, such as 

 lack of food certain bacteria produce spores. The 

 power of spore formation is not possessed by all 

 bacteria and those which are able to bring it about 

 are difficult to kill for the spores, which contain 

 the living material of the bacterium are surrounded 

 with walls which will resist boiling, drying, freezing 

 and all manner of ill treatment. The spore forma- 

 tion of bacteria is very simple, all or part of the 

 living contents of the bacterium becomes surrounded 

 by a tough wall and remains so surrounded till cir- 

 cumstances are favourable, when the wall bursts, 

 its contents escapes and becomes a bacterium, cap- 

 able of founding a new colony by the method of 

 splitting we have already described. 



Now let us try to find out what sort of plants 

 we are to look for, when we are searching for 

 bacteria, under our microscope. They exist in many 

 forms, to which special names have been applied, 

 and it is unfortunate that, very often, their external 



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