BACTERIA 



reason, weak alkalies are sometimes added to milk. 

 Acids and alkalies, of equal strength form neutral 

 solutions, so that, when the milk bacteria begin 

 their activities which result in the formation of acid, 

 it is at once made neutral by the alkali. By this 

 means, curdling is postponed for a little while, 

 though there comes a time, of course, when all the 

 alkali is used up, then the acid gains the upper hand 

 and curdling takes place. We could if we wished 

 continue adding more and more alkali to keep pace 

 with the formation of acid, but too much alkali 

 would be as unpalatable as too much acid, so 

 nothing would be gained. 



Before we bring out our microscope to examine 

 these lowly plants, we will first of all kill a myth 

 which has survived, in the non-scientific mind, since 

 the eighteenth century and then describe briefly the 

 life history of a typical bacterium. Now for the 

 myth. Bacteria are so minute, their activities so 

 great and the results of their activities so far reach- 

 ing, that it is hardly surprising to learn that, even 

 at the present day, bacteria are supposed simply 

 ''to happen." We talk of thunder turning milk 

 sour, but thunder can no more sour milk than can 

 a passing train or an air raid or a burst in a water 

 main. True, milk turns sour more quickly in 

 thundery weather than in frosty weather, because, 

 when thunder threatens, the air is warm and the 

 milk-souring bacteria increase more rapidly in warm 

 weather than in cold. We must remember always 

 that bacteria are living beings and in common with 



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