[Editor's note: Joseph Lister was the son of J. J. Lister, a prosperous Quaker wine merchant whose hobby was the development of the achromatic microscope. J. J. Lister formulated the mathematical basis for removing chromatic aberrations from lenses and, with Thomas Hodgkins, examined many tissues of the body, discovering the striation of voluntary muscle and establishing the biconcave shape of erythrocytes, among many other pioneering discoveries. His son, Joseph Lister, did his first work examining pus using his father's invention and became interested in the fermentation activity of bacteria; he soon established the antiseptic principle, which completely altered the mortality from surgery and gave that field the impetus to grow. Aseptic methods were developed later.] 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 occurrence of suppuration with all its attendant risks was an object manifestly desirable, but till lately apparently unattainable, since it seemed hopeless to attempt to exclude the oxygen which was universally regarded as the agent by which putrefaction was effected. But when it had been shown by the researches of Pasteur that the septic properties of the atmosphere depended not on the oxygen, or any gasous constituent, but on minute organisms suspended in it, which owed their energy to their vitality, it occured to me that decomposi-