http://www.biology.clc.uc.edu/courses/bio114/spontgen.htm: It is easy in hindsight to regard earlier views with smug superiority, for the notion of "spontaneous generation" is of course ridiculous on the scale of complex organisms. However, past generations aceepted "spontaneous generation" only as applicatble to certain lower animal, for which that belief was supported by good evidence and was well accepted by reputable authority, in particular by Aristotle.

http://www.accessexcellence.org/AB/BC/Spontaneous_Generation.html: It was not until quite late that careful experimentation demonstrated that not even bacterial life arises by spontaneous generation. Louis Pasteur devised the clinching experiment in 1859.