9 o EVOLUTION OF THE EARTH 



says that a dead horse breeds wasps, a mule produces hornets, 

 while from an ass arise bumble bees. Van Helmont, one of 

 the founders of chemical physiology, gives particularly specific 

 directions for the experimental production of scorpions and 

 mice, while Kircher actually figures animals which he avers 

 arose under his own eyes through the influence of water on 

 the stems of plants; an instance, perhaps, not of spontaneous 

 generation but of the transformation of plant into animal, 

 which was also a notion prevalent at the time. The ironical 

 reflections of one Ross, aroused by the scepticism of Sir 

 Thomas Browne in regard to mice arising by putrefaction, are 

 quite typical of seventeenth-century opinion. He says: "So 

 we may doubt whether in cheese and timber worms are gen- 

 erated, or if beetles and wasps in cow-dung, or if butterflies, 

 locusts, shellfish, snails, eels, and such life be procreated of 

 putrefied matter, which is to receive the form of that creature 

 to which it is by formative power disposed. To question this 

 is to question reason, sense, and experience. If he doubts 

 this, let him go to Egypt, and there he will find the fields 

 swarming with mice begot of the mud of Nylus, to the great 

 calamity of the inhabitants." 



That such ideas of the origin of life were prevalent and their 

 truth untested by experiments is an eloquent commentary on 

 the general state of the scientific method before the Renais- 

 sance. It was Francesco Redi, an eminent Italian scholar, 

 physician, and naturalist, who, not content with tradition, but 

 with great faith in observation, made a study of the origin 

 of maggots in decaying animal matter. By the simplest of 

 experiments he found that maggots never developed in meat 

 to which flies were not allowed access and that the seeming 

 transformation of meat into maggots was the result of flies 

 laying their eggs on the meat. When this was prevented, no 

 matter how he varied the materials of his experiments, he 

 obtained the same result, and naturally concluded that the sup- 



