1 8 Introduction 



find Cardan asserting that water engenders fishes, and that 

 many animals spring from fermentation. Van Helmont 

 gives special instructions for the artificial production of 

 mice, and Kircher in his " Mundus Subterraneus " (chapter 

 "De Panspermia Rerum") describes and actually figures 

 certain animals which were produced under his own eyes 

 by the transforming influence of water on fragments of 

 stems from different plants.* 



About 1671, 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 de- 

 cay, prior to the appearance of maggots, he invariably ob- 

 served flies buzzing around the meat and frequently alight- 

 ing 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 putre- 

 fied in the ordinary way, it never bred maggots, while meat 

 in open jars soon swarmed with them. For the paper he 

 substituted 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 permit 

 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 

 arteries and veins through intervening capillaries, thus 

 affording ocular proof of Harvey's discovery of the circula- 

 tion of the blood; discovered bacteria, seeing them first in 

 saliva, discovered the rotifers, and first saw the little glob- 

 ules in yeast which Latour and Schwann subsequently 

 proved to be plants. 



Leeuwenhoek involuntarily reopened the old contro- 

 versy about spontaneous generation by bringing forward a 

 new world, peopled by creatures of such extreme minuteness 

 as to suggest not only a close relationship to the ultimate 

 molecules of matter, but an easy transition from them. 



In succeeding years the development of the compound 

 microscope showed that putrescent infusions, both animal 

 and vegetable, teemed with minute living organisms. 

 * See Tyndall: " Floating Matter in the Air." 



