"The ultimate test of a scientific theory is its practical application."

"As soon as I had found the tubercle bacillus, I found it also in the sputum of phthisical patients."

"A doctor must be able to do two things: see microscopically and think logically."

"The greatest obstacle to progress is not ignorance, but the illusion of knowledge."

"The isolation of disease-causing microorganisms is the first step towards controlling them."