REDl'S EXPERIMENTS 17 



ophy, Descartes tried to relate the qualitative diversity of 

 natural phenomena to matter and its movement. 



Thus, according to Descartes, the living organism does not 

 need to be explained by any special obedience to ' a vital 

 force '. Descartes postulates nothing other than a machine, 

 very complicated certainly, but of completely intelligible 

 construction, whose movements depend exclusively on the 

 pressures and interactions of particles of matter as do the 

 movements of the wheels in a clock. Thus different kinds of 

 living beings can arise spontaneously from the surrounding 

 lifeless matter. In particular, when moist earth is exposed 

 to the rays of the sun or when putrefaction occurs, there 

 develop all kinds of plants and animals such as worms, flies 

 and a variety of insects. But for this to happen there is no 

 need for any intervention whatsoever by any ' spiritual prin- 

 ciple '. Spontaneous generation consists only of the natural 

 process of self-formation of complicated machines, a process 

 which takes place invariably when certain circumstances, not 

 yet fully investigated by us, are fulfilled. 



Thus, do^vn to the middle of the seventeenth century, the 

 actual possibility of spontaneous generation had not been 

 seriously questioned by anyone. The dispute between the 

 mystical doctrines irom the Middle Ages and the materialism 

 noAV in violent spate was only concerned with the theoretical 

 treatment of the phenomenon: was spontaneous generation 

 to be regarded as a manifestation of ' a spiritual principle ' 

 or as a natural process of self-formation of living beings? 

 However, the study of living nature was all the time becom- 

 ing both wider and more accurate in its approach, and the 

 assurance of those who had accepted spontaneous generation 

 as a ' fact ' now began to be shaken. 



Redi's experiments. 



In this matter the experiments of the Tuscan physician 

 Francesco Redi (1626-1697) can justly be counted as the 

 turning point. To Redi fell the honour of being the first 

 to emerge with the support of experiment from the 

 belief in spontaneous generation which had ruled without 

 interruption for so many centuries. In his treatise Esperienze 

 intorno alia genemzione degV insetti (1668) he describes 



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