8 BACTERIA, YEASTS, AND MOLDS 



(1688) maggots, as well as mice and eels, were tmderstood 

 to need living ancestors. Redi even went further and made 

 a statement that was not by any means proved by. his ob- 

 servations, and which was indeed quite startling to his con- 

 temporaries ; he claimed, in fact, that life comes only from life. 



Nevertheless, the belief in spontaneous generation still 

 persisted. Microscopes had shown that decaying liquids 

 were fuU of minute living creatures. It was observed that 

 if any organic liquid was kept for a few days, even in a 

 tightly stoppered bottle, these microscopic beings were sure 

 to appear in it. Where did they come from if they did not 

 spring spontaneously into life within it? Of course we do 

 not believe this to-day ; if we did, we should not be so con- 

 fident that we can save food by canning it. But for about 

 a century and a half the subject was very hotly disputed. 



About the middle of the eighteenth century a scientist by 

 the name of Needham tried to settle the question by boiling 

 an infusion of meat, or something of similar nature, in order 

 to kill aU living things in it ; he then sealed it hermetically 

 in the vessel in which it had been boiled and set it aside to 

 see what happened. Any housewife who has tried to can 

 some vegetable, which does not contain much sugar or any 

 acid, by the open-kettle method (or even by the cold-pack 

 method if the jars were merely allowed to stand in boiling 

 water) has a fairly ^ood idea of what is likely to happen in 

 such cases. She knows that her vegetables canned in this way 

 often go bad ; in fact, they practically always go bad unless 

 she allows them to stand in boiling water for a few hours. 

 So Needham found that although his boiled infusions some- 

 times remained clear, they were very often filled with living 

 organisms after standing a few days. He believed that these 



