I. 



SPONTANEOUS GENERATION. 



ALL antiquity, down to the end of the Middle 

 Ages, believed in the spontaneous generation 

 of both plants and animals, that is to say, their ori- 

 gin directly from the earth or other dead material 

 without a previous germ or egg. Three centuries 

 before the Christian era Aristotle taught the spon- 

 taneous origin of eels and other fish out of the 

 slimy mud of rivers and marshes; also that certain 

 insects originated from the dew deposited upon 

 plants, that lice were spontaneously engendered in 

 the flesh of animals, and that caterpillars were act- 

 ually the product of the plants upon which they 

 feed. Von Helmont, who died in 1644, described 

 in detail the conditions necessary for the spontane- 

 ous generation of mice! Dr. William Harvey, the 

 discoverer of the circulation of the blood, has (he 

 credit of first propounding the principle that no 

 life could exist without pre-existing life. He main- 

 tained that all living things proceeded from eggs, 

 but just what he meant by eggs seems to be uncer- 

 tain, though he probably included in the term seeds 



and germs of all kinds. 



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