Out of these researches arose a famous battle which kept Pasteur hard at work for four or five years — the struggle over spontaneous generation. It was an old warfare, but the microscope had revealed a new world, and the experiments on fermentation had lent great weight to the omne. Vivum ex ovo doctrine. The famous Italians, Redi and Spallanzani, had led the way in their experiments, and the latter had reached the conclusion that there is no vegetable and no animal that has net its own germ. But heterogenesis became the burning question, and Fouchet in France, and Bastian in England.