18 PA THOGENIC BA CTERIA. 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, long1 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 Helmorit gives special instructions for the artificial production of mice, and Kircher in his Mundus Subterraneus (chapter l ( De Panspennia Return") describes and actually figures cer- tain animals which were produced under his own eyes by the transforming influence of water on fragments of sterns from different plants.2 1 Ovid's Metamorphoses, translated by Mr. Dryden, published by Sir Samuel Garth, London, 1794. 2 See Tyndall: Floating Matter in th? Air.