1 8 PATHOGENIC BACTERIA. 



same doctrine, while in the Georgics Virgil gives di- 

 rections for the production of bees. 



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, 

 and Kircher in his Mundas Subterraneus (chapter " De 

 Panspermia Rerum ") describes and actually figures cer- 

 tain animals which were produced under his own eyes 

 by the transforming influence of water on fragments of 

 steins from different plants. 1 



About 1686, Francesco Redi seems to have been the 

 first to doubt that the maggots familiar in putrid meat 

 arose de novo: "Watching meat in its passage from 

 freshness to decay, prior to the appearance of maggots, 

 he invariably observed flies buzzing around the meat and 

 frequently alighting on it. The maggots, he thought, 

 might be the half-developed progeny of these flies. 

 Placing fresh meat in a jar covered with paper, he found 

 that although the meat putrefied in the ordinary way, 

 it never bred maggots, while meat in open jars soon 

 swarmed with these organisms. For the paper he sub- 

 stituted fine wire gauze, through which the odor of the 

 meat could rise. Over it the flies buzzed, and on it they 

 laid their eggs, but the meshes being too small to per- 

 mit the eggs to fall through, no maggots generated in 

 the meat ; they were, on the contrary, hatched on the 

 gauze. By a series of such experiments Redi destroyed 

 the belief in the spontaneous generation of maggots in 

 meat, and with it many related beliefs." 



In ,1683 Anthony van Leeuwenhoek, justly called the 

 " Father of microscopy," demonstrated the continuity of 



1 See Tyndall : Floating Matter in the Air. 



