4. The Theory of Germs
The discovery of the germ theory by Louis Pasteur was a major breakthrough in the medical field as it brought to notice the real reason behind the origin of deadly diseases like anthrax, cholera and rabies. The theory emphasized on the importance of sanitation and cleanliness to keep away germs which were the cause behind many of the diseases. It is because of this theory that the prevention of these deadly diseases has been possible extending the human life.