IN two previous papers (Henderson andWilliams, 1961, 1963) some observations were reported on the part played by nasal staphylococci in staphylococcal infection of surgical wounds and also the extent to which the environment of the patients in a surgical ward became contaminated by staphylococci. Daily bacteriological samples were taken and in this way serial pictures were built up of the spread of the staphylococci. The part, if any, played by the operating theatre as a source of staphylococcal infection was not considered, however, in either of these papers and the present study was planned to provide, if possible, some information on that source.One hundred clean operations were studied over a period of a little more than 3 years. They were all major operations, e.g., radical mastectomies (59), cholecystectomies (31), and gastrectomies (2). The remainder (8) were miscellaneous. Ninety-one of the IOO operations were drained by a tube through a stab wound separate from the main incision. The operations were all performed by the same surgeon. The operating theatre is not of modern design and working space is limited. There is, however, an arrangement under which fresh air from outside is sucked in by a fan and pumped through filters into the operating theatre. This has been geared to give a flow of filtered air passing through the theatre and into the outside corridor at a rate of approximately 10-12 changes per hour. The patients were examined daily until either the wound had healed and the stitches were removed, or sepsis, if any, was established. The author took all the swabs and attended all the operations, thus assuring uniformity of method. The surgical team changed, naturally, in the 3$ years, as new house-surgeons and nurses replaced others, but otherwise the lines on which the investigation was carried out did not materially alter throughout the period.
METHODSPatients were seen as soon as possible after they had been admitted and a nasal swab was taken, usually about 15 minutes to I hour after admission. The swabs were on wooden sticks and, after being moistened in sterile saline, the same swab was rubbed six or seven times around the inside of each anterior naris. The next day a second nasal swab was taken and usually on the third day the patient underwent operation. If it was delayed for any reason daily nasal swabs were taken until the day of operation. At