When the swan-neck flasks failed to show these same microbial growths, Pasteur concluded that the structure of the necks blocked the passage of atmospheric dust into the solution.[5][6] From the two experiments, Pasteur concluded that the atmospheric dust carried germs responsible for the 'spontaneous generation' in his broths.[6] Thus, Pasteur's work provided proof that the emergent growth of bacteria in nutrient broths is caused by biogenesis rather than some form of spontaneous generation.