210 FOUNDATIONS OF BIOLOGY 



experimentation for academic discussion and hearsay. By 

 the simple expedient of protecting decaying meat from con- 

 tamination by flies, he demonstrated that these insects are 

 not developed from the flesh and that the apparent trans- 

 formation of meat into maggots is due solely to the develop- 

 ment of the eggs deposited thereon by flies. 



But the time-honored doctrine of spontaneous generation 

 was not overthrown by this experiment nor the long series 

 which Redi made. The presence of parasites within certain 

 internal organs of the higher animals , as in the brains of 

 sheep, baffled Redi himself. Also, the improvements of the 

 microscope revealed an unknown microcosm whose origin 

 seemed plausibly explained as spontaneous. BIOGENESIS, or 

 all life from preexisting life, was placed on a secure foundation 

 only within the past half-century by the working out of the 

 remarkably complex life histories of internal parasites, which 

 showed that they all arise from parents like themselves, 

 and by the classical demonstrations of Pasteur and others 

 that microorganisms are not the result, but the cause of de- 

 cay. The latter fact is at the basis of, and is attested by, the 

 methods now universally used in food preservation and 

 aseptic surgery to mention but two instances. 



At the present time, we may consider it as established that 

 all known forms of life arise from preexisting life by reproduc- 

 tion. But if we accept the testimony of astronomer and 

 geologist, the Earth was at one time in a condition in which 

 life as we know it could not exist, and so we are face to face 

 with the problem of how it came to be established on the 

 Earth in the past the remote past, since the geological 

 record affords convincing proof that life has existed continu- 

 ously on the Earth for some hundreds of millions of years. 



Unless one is willing to ascribe life's origin to SPECIAL 

 CREATION which at once removes it from the sphere of 



