The Story of Progress and DiscoveryYou have probably heard it said that if you put a horsehair in a
You have probably heard it said that if you put a horsehair in a container of rainwater and place it in the sunshine, a snake will develop. It is hard to convince people even today that this is not true, yet it is not difficult to get a horsehair and some rainwater to try the experiment. Since very early times men have believed that living things could come from non-living things. Some people thought that frogs and toads developed from the mud of ponds, rats from the river Nile, and insects from dew or from rotting waste. Vergil wrote that slime begat frogs. Centuries later, other men wrote that water produced fishes and that mice came from old rags. This notion that living things can come from lifeless matter is known as the theory of spontaneous generation. Today we know that living things can come only from living things. Redi, in the seventeenth century, was the first to experiment to prove that insects do not originate from rotting matter. From his experiment, Redi concluded that maggots appear in decaying meat simply because the eggs of flies hatch there, and not from spontaneous generation .
At the time of Leeuwenhoek the microscope was not well developed, but with it he discovered bacteria. The study of these tiny forms of life which looked like specks to him was not practical until more than 150 years later, when microscopes were much improved. However, the discovery led some medical men at the time to think that contagious diseases were due to germs passed from the sick to the well.
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