i8 : ^PA THOGENIC BACTERIA. 



that "sometimes animals are formed in putrefying soil, 

 sometimes in plants, and sometimes in the fluids of other 

 animals." He also formulated a principle that "every 

 dry substance which becomes moist, and every moist 

 body which becomes dried, produces living creatures, 

 provided it is fit to nourish them." 



Three centuries later, in his disquisition upon the 

 Pythagorean philosophy, we find Ovid defending the 

 same doctrine: 1 



"By this sure experiment we know 

 That living creatures from corruption grow : 

 Hide in a hollow pit a slaughter' d steer, 

 Bees from his putrid bowels will appear, 

 Who, like their parents, 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 toss'd 

 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 frog's loquacious race ; 

 Short of their feet at first, in little space, 

 With arms and legs endued, long leaps they take, 

 Raised on their hinder part, and swim the lake, 

 And waves repel ; for nature gives their kind, 

 To that intent, a length of legs behind." 



Not only was the doctrine of spontaneous generation 

 of life current among the ancients, but we find it persist- 

 ing through the Middle Ages, and descending to our own 

 generation to be an accidental but important factor in 

 the development of a new branch of science. In 1542, 

 in his treatise called De Subtilitate, we find Cardan as- 

 serting that water engenders fishes, and that many ani- 

 mals spring from fermentation. Van Helmont gives 

 special instructions for the artificial production of mice, 



1 Ovid's Metamorphoses, translated by Mr. Dryden, published by Sir Samuel 

 Garth, London, 1794. 



