It would not be stretching things all that much to say that the work attributed to Louis Pasteur ( see also Pasteur) is the hingepoint which transformed medicine from a systematic discipline somewhat akin to alchemy to a rigorous science. It is going to be a shock to most of you to discover that as late as 1860 the concept of spontaneous generation ( see also SG and SG ) was widely accepted among scientists and doctors. Not only that but bloodletting, often by leeches, was still standard medical practice especially in many rural areas as was discussion of the four humours. Pasteur changed all that. In particular the discovery and proof that microbiotic bacteria invisible to the naked eye was responsible for many diseases in one fell swoop swept away over 20 centuries of medical thinking.