All of these somewhat detailed statements lead up to a consideration of the difference between the old surgery and the new. Thirty years ago when an operation was to be performed or an accident cared for we laid out our instruments which were visibly clean, used them with hands which were as clean as those of any gentleman, and applied soft linen rags, lint, and other dressings. To-day we know that these apparently clean instruments, hands, and dressings are covered with bacteria, which produce infection, and, therefore, suppuration, and frequently run riot in blood-poisoning, erysipelas, lockjaw, and death. How does a modern surgeon perform an operation? All bacteria can be killed by heat. Cold has no effect upon them, but the temperature of boiling water (212° Fahr.) is sufficient to destroy them all usually within fifteen or twenty minutes; hence, first, instruments are all boiled; and, secondly, dressings are either steeped in such solutions as have been found to destroy the bacteria, such as carbolic acid or corrosive sublimate, or other preparations, or, still better, are placed in sterilizers, that is to say, metal cylinders, which are then filled with steam, usually under pressure, so as to obtain a temperature of 240° Fahr., and thus make sure of the death of the bacteria. Unfortunately, our hands cannot be boiled or steamed, but the modern surgeon first uses soap and water most vigorously over his hands and arms up to the elbow. The nails are cut short and the scrubbing-brush is especially applied to the nails so as to clean the fingers at the ends. Then by various means, such as pure alcohol, which is one of our best disinfectants, or solutions of corrosive sublimate, and other means too technical to mention, the hands are sterilized. Rubber gloves are frequently used, so as to preclude infection, as they can be steamed to 240° Fahr. Removing at least his outer clothing, the surgeon puts on a cotton gown which has been steamed and so made free from bacteria. Not a few surgeons also wear sterilized caps, so that any bacteria in the hair will not be sifted into a wound, and some wear respirators of sterile gauze over the mouth and beard for the same reason. All the dressings have been sterilized by superheated steam. All the threads by which blood-vessels are tied have been either boiled or otherwise sterilized. All the material for sewing up the wounds, and the needles with which they are sewn, have been similarly disinfected. The skin of the patient is also sterilized, usually the day beforehand, in the same manner in which the surgeon’s hands have been disinfected, and are disinfected a second time just at the moment of the operation. If the case is one of accident, such as a crushed leg from a trolley-car, all of the dirt is most carefully washed away with soap and water, and the parts are disinfected, not only on the exterior, but also by prolonged washing with some cleansing agent in the interior of