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 reaching, 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 all other living things they must have parents. What probably took place at the beginning of the world we cannot consider here but one thing is certain that, at the present day, no living matter is produced from non-living matter; “life from life” is the only theory that will stand scientific tests and this has been the case ever since the simplest microscopes were thought of and thousands of years before that. Any substance, however liable to decay, if rendered germ free and kept germ free, will retain its fresh condition indefinitely. Could bacteria or germs, call them what you will, simply happen it would be useless attempting to fight against them.