 His experiments showed that crushed leaf extracts from infected tobacco plants remain infectious after filtration.Ivanovsky suggested the infection might be caused by a toxin produced by bacteria, but did not pursue the idea.In 1898, the Dutch microbiologist Martinus Beijerinck (1851–1931), a microbiology teacher at the Agricultural School in Wageningen repeated experiments by Adolf Mayer and became convinced that filtrate contained a new form of infectious agent.