Louis Pasteur and Emile Roux were sometimes in disagreement in their approach to disease. Pasteur was an experimental scientist, whereas Roux was more focused on clinical medicine. They also held different religious and political beliefs, with Pasteur being a right- leaning Catholic, and Roux being a left-leaning atheist. Given their many differences, they clashed often as they worked towards vaccines against anthrax and rabies. The main issues between Roux and Pasteur regarded the ethics of human experimentation, specifically, the amount evidence from animal experimentation on the rabies vaccine needed in order to justify giving the vaccine to humans. Roux was more reluctant to give the vaccine to humans without further evidence that it was safe in animals.