Science and human health both took a great leap forward thanks to French chemist Louis Pasteur (1822–1895), who made world-changing discoveries about germs and vaccinations. Pasteur had a profound effect on animal health as well, finding methods to prevent rabies and other lethal illnesses.
Probably more than any other individual, Pasteur helped mankind understand the importance of cleanliness in preventing the spread of disease. Naturally he had great admiration for the cleanest of animals, the cat.