From his observations while working in London and Edinburgh hospitals, British physician Joseph Lister concluded that cleanliness was essential to preventing postsurgical infections. The following excerpt from his "On the Antiseptic Principle of The Practice of Surgery" (1867) describes how he was influenced by the "germ theory" of French scientist Louis Pasteur to devise a method for reducing the number of such infections.

In the course of an extended investigation into the nature of inflammation, and the healthy and morbid conditions of the blood in relation to it, I arrived several years ago at the conclusion that the essential cause of suppuration in wounds is decomposition brought about by the influence of the atmosphere upon blood or serum retained within them, and, in the case of contused wounds upon portions of tissue destroyed by the violence of the injury.

To prevent the...