There is a certain class of medical literature and teaching that is made so positive and dogmatic, as to create doubts and suspicions of its reliability. Many very good teachers err in supposing that unless they state the facts of medicine in the most positive way, it never can impress the student. Often medical text-books are written in this spirit, and students and readers who accept them as final, have much to unlearn in after life. While it is not quite true that the positive dogmatic man, on questions of science, is a quack, it is true that empiricism depends on the positiveness by which it is proclaimed. Darwin expressed the truth when he said: "Ignorance more frequently begets confidence than does knowledge; it is those who know little and not those who know much who so positively assert that this or that problem can never be solved by science."