208 THE CONTINUITY OF THE RACE 



Roman emperor Augustus, expressed the accepted belief of his time when 

 he wrote: 



By this sure experiment we know 



That living creatures from corruption grow: 



Hide in a hollow pit a slaughtered steer, 



Bees from his putrid bowels will appear, 



Who like their parent haunt the fields, and 



Bring their honey harvest home, and hope another spring. 



The warlike steed is multiplied, we find, 



To wasps and hornets of the warrior kind. 



Cut from a crab his crooked claws and hide 



The rest in earth, a scorpion thence will glide 



And shoot his sting; his tail in circles tossed 



Refers the limbs his backward father lost; 



And worms that stretch on leaves their filmy loom 



Crawl from their bags and butterflies become. 



The slime begets the frogs loquacious race; 



Short of their feet at first, in little space 



With arms and legs endued, long leaps they take, 



Raised on their hinder parts, and swim the lake, 



And waves repel; for nature gives their kind. 



To that intent, a length of legs behind. 



Such beliefs appear again and again in the literature of the Middle 

 Ages and seem to have been almost unquestioned until well into the 

 seventeenth century. It was recognized, of course, that men and domes- 

 tic animals were born from parents, but even here there was much 

 mysticism and sometimes willingness to credit occasional instances to 

 spontaneous origin. 



The first clear case of doubt of the actuality of the spontaneous origin 

 of common small animals was that which led an Italian naturalist, 

 Francesco Redi, to perform some simple experiments about 1680. (At 

 this time, Vesalius' great treatise on human anatomy, based upon actual 

 dissection, was already more than a hundred years old.) Redi tested the 

 spontaneous origin of maggots from decaying meat by placing bits of 

 meat in three glasses. The first was left uncovered, the second was covered 

 with fine netting, and the third was covered with parchment. He soon 

 discovered maggots on the meat in the first glass, a few maggots on the 

 fine netting over the second glass, and no maggots at all in the third glass, 

 although in all the glasses the meat appeared equally spoiled. Further 

 observations proved to him that the maggots originated not in the meat 

 but from flesh flies which, attracted by the odor of the decaying meat, 

 came to deposit eggs or living maggots; that the eggs hatched into mag- 

 gots, the maggots fed and grew and transformed into flies, and that these 

 flies, in turn, produced more eggs. 



