He made other observations on the generation of insects, but with acute scientific analysis never allowed his conclusions to run ahead of his observations. He suggested, however, the probability that all cases of the supposed production of life from dead matter were due to the introduction of living germs from without. The good work begun by Redi was confirmed and extended by Swammerdam (1637-1681) and Vallisnieri (1661-1730), until the notion of the spontaneous origin of any forms of life visible to the unaided eye was banished from the minds of scientific men.
Fig. 89.—Francesco Redi, 1626-1697.
Redi (Fig. 89) was an Italian physician living in Arentino, distinguished alike for his attainments in literature and for his achievements in natural science. He was medical adviser to two of the grand dukes of Tuscany, and a member of the Academy of Crusca. Poetry as well as other literary compositions shared his time with scientific occupations. His collected works, literary, scientific, and medical, were published in nine octavo volumes in Milan, 1809-1811. This collection includes his life and letters, and embraces one volume of sonnets. The book that has been referred to as containing his experiments was entitled Esperienze Intorno Alla Generazione Degl'Insetti, and first saw the light in quarto form in Florence in 1668. It went through five editions in twenty years. Some of the volumes were translated into Latin, and were published in miniature, making books not more than four inches high. Huxley says: "The extreme simplicity of his experiments, and the clearness of his arguments, gained for his views and for their consequences almost universal acceptance."
New Form of the Question.—The question of the spontaneous generation of life was soon to take on a new aspect. Seven years after the experiments of Redi, Leeuwenhoek made known a new world of microscopic organisms—the infusoria—and, as we have seen, he discovered, in 1687, those still minuter forms, the bacteria. Strictly speaking, the bacteria, on account of their extreme minuteness, were lost sight of, but spontaneous generation was evoked to account for the birth of all microscopic organisms, and the question circled mainly around the infusorial animalcula. While the belief in the spontaneous generation of life among forms visible to the unaided eye had been surrendered, nevertheless doubts were entertained as to the origin of microscopic organisms, and it was now asserted that here were found the beginnings of life—the place where inorganic material was changed through natural agencies into organized beings microscopic in size.
More than seventy years elapsed before the matter was again subjected to experimental tests. Then Needham, using the method of Redi, began to experiment on the production of microscopic animalcula. In many of his experiments he was associated with Buffon, the great French naturalist, who had a theory of organic molecules that he wished to sustain. Needham (1713-1784), a priest of the Catholic faith, was an Englishman living on the Continent; he was for many years director of the Academy of Maria Theresa at Brussels. He engaged in scientific investigations in connection with his work of teaching. The results of Needham's first experiments were published in 1748. These experiments were conducted by extracting the juices of meat by boiling; by then enclosing the juices in vials, the latter being carefully corked and sealed with mastic; by subjecting the sealed bottles, finally, to heat, and setting them away to cool. In due course of time, the fluids thus treated became infected with microscopic life, and, inasmuch as Needham believed that he had killed all living germs by repeated heating, he concluded that the living forms had been produced by spontaneous generation.
Spallanzani.—The epoch-making researches of Spallanzani, a fellow-countryman of Redi, were needed to point out the error in Needham's conclusions. Spallanzani (Fig. 90) was one of the most eminent men of his time. He was educated for the church, and, therefore, he is usually known under the title of Abbé Spallanzani. He did not, however, actively engage in his churchly offices, but, following an innate love of natural science and of investigation, devoted himself to experiments and researches and to teaching. He was first a professor at Bologna, and afterward at the University of Pavia. He made many additions to knowledge of the development and the physiology of organisms, and he was the first to make use of glass flasks in the experimental study of the question of the spontaneous generation of life.
Spallanzani thought that the experiments of Needham had not been conducted with sufficient care and precision; accordingly, he made use of glass flasks with slender necks which could be hermetically sealed after the nutrient fluids had been introduced. The vials which Needham used as containers were simply corked and sealed with mastic, and it was by no means certain that the entrance of air after heating had been prevented; moreover, no record was made by Needham of the temperature and the time of heating to which his bottles and fluids had been subjected.
