42 LOUIS PASTEUR 



imagine the eager curiosity with which the old 

 Dutch investigator, Anton van Leeuwenhoek, 

 examined for the first time the minute creatures 

 which were revealed by his hand-made micro- 

 scopes. Leeuwenhoek lived in the seventeenth and 

 eighteenth centuries (163 2-1723) at a time when 

 the compound microscope was just coming into use 

 and was being applied by Malpighi, Grew and 

 others to reveal the finer structure of animals and 

 plants. He had used his microscopes to observe 

 the stings of bees, the scales of butterflies' wings, 

 and other favorite objects of the amateur micro- 

 scopist, but one day he chanced to examine some 

 drops of stagnant rain-water when, greatly to his 

 surprise, he found them swarming with a variety 

 of minute living creatures, swimming about in all 

 directions in the most lively manner. It was like 

 the revelation of the fauna of a new continent, 

 except that the animals were much more strange 

 and different from what we are familiar with than 

 any animals we should be apt to find in an unex- 

 plored part of the world. Leeuwenhoek sent many 

 notes describing these new and strange creatures 

 to the Royal Society at London which published 

 them in the early volumes of its transactions. Won- 

 derful revelations these! Inevitably they aroused 



