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The contributions against the spontaneus generation
The theory that
every livings comes from others of the same species has been acquired
from the men of the past, for degrees. The studies were made also thanks
to the invention of the microscope by Leeuwenhoek. Francesco Redi, scientist
who lived in XVII the century, was the first one to demonstrate that '
animaletti' that they form themselves on the meat come from the eggs that
the flies place on the meat.
After there was the discovery of the protozoans, the argument that existed
one spontaneous generation returned outside. Spallanzani demonstrated
that also the microscopical livings develop themselves from other livings
and not from the contained substances in the infusions. Subsequently with
the discovery of the bacteria Pasteur'll say its opinion against the spontaneous
generation. Finally with the discovery of the virus was understood how
much little was the difference between virus (the livings), and some chemical
substances (the enzymes).
Here the problem is more complicated and difficult because the virus need
of the participation of the cells of the organism that accommodates them
to reproduce.
Now
we do not believe to the spontaneous generation because we know that living
frogs, flies, worms and other beings do not form themselves from the mud
but from other frogs, flies and worms.
Thanks to the experiments of Redi the metamorphosis of the bugs have been
discovered that it has been studied in deep way in the successive centuries.
Moreover the ' spontaneous generation ' is a nonexistent hypothesis also
for the microscopical living beings, like Spallanzani demonstrated through
him experiments on the infusions.
The consequences of Spallanzani's and Redi's experiments have repercussions
on us about the conservation of foods: the meat are conserved in the refrigerator
at low temperatures, the water are conserved in closed bottles. 
All this has been possible thanks to their studies and those of others, like Pasteur that demonstrated that also the bacteria derive from other livings of the same species.
Some problems there will be after the discovery of the virus: the problem of the ' spontaneus generation' will be still debatable even if the scientists will understand like the virus succeed to reproduce themselves to use the organisms that accommodate them.
