Although today it may seem obvious it is obvious, for millennia man has ignored the fact that microscopic organisms caused certain diseases.
Until 1600, the so-called theory of spontaneous generation was considered valid, according to which some organisms can spontaneously be generated from non-living matter. The classic example is that of the larvae, believed to be able to be generated from nothing in a piece of decomposing meat.
The first to invalidate this theory was Francesco Redi, personal physician to the Grand Duke of Tuscany. Redi put two pieces of fresh meat in two separate containers, leaving the first open and protecting the second from flies with a retina. After a few days he noticed that only the open container was crawling with larvae. Redi, therefore, showed that the larvae are not generated from nothing but derive from the eggs laid by flies.
The existence of microorganisms began to speak only in the eighteenth century, thanks to the studies of the Modenese Lazzaro Spallanzani, who first coined and introduced in the medical literature the term "germ". However, the discovery of bacteria is attributed to Antony Leeuwenhoek (1632-1723), a textile merchant with a passion for microscopes.
Leeuwenhoek observed how, after brushing his teeth, "living creatures" were present in the tartar deposits. This discovery was made possible by the optimization of the optical microscope, which Leeuwenhoek himself had built, and which subsequently improved further.
The advent of the modern microscope, however, opened new questions on the theory of spontaneous generation. From the first observations, in fact, it seemed that the simple exposure to air of an organic substance led in a short time to the development of germs on its surface.
The French biologist Louis Pasteur intervened to deny the hypothesis of spontaneous microbial generation. Pasteur boiled some broth in a long-necked glass flask, equipped with a special S-shaped beak to prevent dust (and bacteria in it) from entering. Pasteur observed that, thanks to these devices, no bacteria were generated in the broth and that, therefore, the germs are not generated spontaneously.
