The modern concept of infectious diseases is generally considered to date from the experiments in which Pasteur, in the years preceding 1860, exploded the theory of spontaneous generation. Without in the least detracting from these epoch-making discoveries demonstrating the role of bacteria in the production of disease, it should be pointed out that even as early as 1836, Agostino Bassi had discovered that a peculiar epidemic in silkworms known as mal calciniaccio or mal segno was associated with a fungus later identified as Botrytis bassiana and that, in 1837, Schonlein had identified a mold which he called a Favus. In 1845, Remak grew this organism on an apple section and successfully transferred a culture to his own arm. Somewhat later Gruby was transferring Favus from man to animal and vice versa. As early as 1841, Gruby had recognized the relationship between this fungus and a certain type of alopecia which