Francesco Redi

Experimental toxicology

In 1664 Redi wrote his first monumental work Osservazioni intorno alle vipere (Observations on Vipers) to his friend Lorenzo Magalotti, secretary of the Accademia del Cimento. In this he began to break the prevailing scientific myths (which he called "unmasking of the untruths") such as vipers drink wine and shatter glasses, their venom is poisonous if swallowed, the head of the dead viper is an antidote, the viper's venom is produced from the gallbladder, and so on. He explained rather how snake venom is unrelated to the snake’s bite, an idea contrary to popular belief.^[13] He performed a series of experiments on the effects of snakebites and demonstrated that venom was poisonous only when it enters the bloodstream via a bite, and that the fang contains venom in the form of yellow fluid.^[9][14] He even showed that by applying a tight ligature before the wound, the passage of venom into the heart could be prevented. This work marked the beginning of experimental toxinology/toxicology.^[15][16]

Entomology and spontaneous generation

Redi is best known for his series of experiments, published in 1668 as Esperienze intorno alla generazione degl'insetti (Experiments on the Generation of Insects), which is regarded as his masterpiece and a milestone in the history of modern science. The book is one of the first steps in refuting "spontaneous generation"—a theory also known as Aristotelian abiogenesis. At the time, the prevailing wisdom was that maggots arose spontaneously from rotting meat.^[6]

Redi took six jars and divided them into two groups of three: In one experiment, in the first jar of each group, he put an unknown object; in the second, a dead fish; in the last, a raw chunk of veal. Redi covered the tops of the first group of jars with fine gauze so that only air could get into them. He left the other group open. After several days, he saw maggots appear on the objects in the open jars, on which flies had been able to land, but not in the gauze-covered jars. In the second experiment, meat was kept in three jars. One of the jars was uncovered, and two of the jars were covered, one with cork and the other one with gauze. Flies could only enter the uncovered jar, and in this, maggots appeared. In the jar that was covered with gauze, maggots appeared on the gauze but did not survive.^[17][18]

Redi continued his experiments by capturing the maggots and waiting for them to metamorphose, which they did, becoming flies. Also, when dead flies or maggots were put in sealed jars with dead animals or veal, no maggots appeared, but when the same thing was done with living flies, maggots did. His interpretations were always based on biblical passages, such as his famous adage: omne vivum ex vivo ("All life comes from life").^[4][19]

Parasitology

Redi was the first to describe ectoparasites in his Esperienze intorno alla generazione degl'insetti. His notable illustrations in the book are those relevant to ticks, including deer ticks and tiger ticks; it also contains the first depiction of the larva of Cephenemyiinae, the nasal flies of deer, as well as the sheep liver fluke (Fasciola hepatica). His next treatise in 1684 titled Osservazioni intorno agli animali viventi che si trovano negli animali viventi (Observations on Living Animals, that are in Living Animals) recorded the descriptions and the illustrations of more than 100 parasites. In it, he also differentiates the earthworm (generally regarded as a helminth) and Ascaris lumbricoides, the human roundworm. An important innovation from the book is his experiments in chemotherapy in which he employed the "control"', the basis of experimental design in modern biological research.^[2][4][20] He described some 180 species of parasites. Perhaps, his most significant observation was that parasites produce eggs and develop from them, which contradicted the prevailing opinion that they are produced spontaneously.^[21]