6 THEORIES OF SPONTANEOUS GENERATION 



crayfish and various molluscs originate from wet earth and 

 decaying slime, eels and some other fishes from marine silt, 

 sand and decaying water weeds. Even frogs, and under 

 certain circumstances salamanders too, can arise from the 

 ciu'dling of slime. Mice arise from damp earth. Some higher 

 animals also arise in a similar way, first manifesting them- 

 selves in the form of worms. " For this reason, and concern- 

 ing human beings and quadrupeds ", Aristotle wrote, " if 

 they were sometimes earth-born, as some people maintain, 

 one may postulate two methods of arising, either from worms 

 which form themselves first, or from eggs." 



However Aristotle did not merely describe various cases 

 of spontaneous generation. An important feature of his work 

 was that he gave a theoretical analysis of this phenomenon 

 and founded his theory of spontaneous generation. In the 

 course of time it seems that his views changed, but in the 

 last analysis they served as the basis of the idealistic 

 hypotheses concerning the origin of life. 



Aristotle considered that living things, like all other 

 concrete objects (substances), are formed by the conjunction 

 of some passive principle, ' matter ' (by this word Aristotle 

 obviously meant what we now call material), with the active 

 principle of ' form '. The ' form ' of living things manifests 

 itself in the ' entelechy of the body ' — the soul. This shapes 

 the body and sets it in motion. Thus matter does not possess 

 life but is infused with it. It is adapted and organised by 

 means of a spiritual force ; an orientating internal substance 

 (entelechy) brings matter to life and sustains the living 

 thing. The spirit, however, is already inherent in the actual 

 elements from which living things are formed, it is inherent 

 in a smaller degree in the earth and in a greater degree in 

 water, air and fire. Because of this, that which is created by 

 the spirit depends substantially on the preponderance of this 

 or that element. Earth produces mainly plants ; water, 

 aquatic animals ; air, the inhabitants of the land ; and fire, 

 the supposed inhabitants of the celestial bodies, in particular, 

 the moon. For their ' form ' living things which arise from 

 others like themselves depend on ' animal warmth ' and 

 when they arise by spontaneous generation on ' solar 



