22 BIOLOGY: GENERAL AND MEDICAL 



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't 

 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 parts and swim the lake, 

 And waves repel; fo^ nature gives their kind, 

 To that intent, a length of legs behind." 



During the middle ages Cardan, in 1524, declared that 

 water engendered fishes, and that many animals spring 

 from fermentation. Van Helmont published special 

 directions for the experimental generation of mice. 

 Kircher describes and figures certain animals which he 

 declares were formed, under his own eyes, through the 

 transforming influence of water upon the stems of 

 plants. 



Children and ignorant persons still believe in the 

 spontaneous generation of many living things and in the 

 country districts many persons of otherwise good 

 judgment believe that frogs and mosquitoes arise spon- 

 taneously in marshes, while the belief that a horse-hair 

 placed in a water trough will be transformed to a thread- 

 like worm, is widespread. 



No one seems to have doubted that maggots were 

 spontaneously developed in putrid meat until Redi 

 became interested in the subject about 1680 and dis- 

 proved it by a simple scientific demonstration: 



"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 upon 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 them. For 



