Over 500 medical students have been examined for nasal carriage of Staph. pyogenes at weekly intervals over a period ranging from 3 to 12 months.Nasal carriers were classified as persistent, intermittent and occasional. Of the students, 39% were persistent or intermittent carriers in whom the staphylococcus was believed to colonize the skin of the vestibule of the nose; 42% were occasional carriers in whom the staphylococcus was only a chance inhabitant of the nares.Staph. pyogenes was isolated from the anterior nares of persistent carriers on at least 90% of the occasions on which they were examined, and was of the same phage type on each occasion. From intermittent carriers it was isolated less regularly, but on at least 10% of occasions on which they were examined, and it remained of one phage type. Staph. pyogenes was isolated at less than 10% of swabbings from occasional carriers, and at each the organism was of a different phage type.Eighty-nine per cent of persistent and intermittent carrier strains, and 54% of occasional carrier strains could be typed with phage filtrates. The strains not typable with phage filtrates, and found predominantly among occasional carriers, were considered worthy of separate classification, and it is suggested that typability with phage be used as a criterion of pathogenicity for Staph. pyogenes.We wish to thank Prof. T. J. Mackie for his continued interest and advice; Dr J. P. Duguid for criticism and advice; Dr R. E. O. Williams and Miss Joan Rippon of the Staphylococcal Reference Laboratory, Colindale, who very kindly instructed one of us (J.C.G.) in bacteriophage typing; Dr Donald Cruickshank for taking nasal swabs from patients; Dr Cumming of the Blood Transfusion Department, Royal Infirmary, Edinburgh, for permission to swab blood donors, and the medical students who so willingly co-operated in this work.

1. An examination of eighty-nine samples of uncooked and thirty-eight samples of cooked food purchased by one particular hospital showed that the purchased food was bacteriologically clean.2. A similar examination of 173 samples of food after it was cooked and prepared for serving in the hospital kitchens showed that, with the exception of cold chicken, the bacterial flora was greatly reduced by cooking. Ten of forty-six samples of cold chicken, however, were contaminated with fairly large numbers ofCl. welchii.3. An investigation into the cooking and handling of the fowls indicated that contamination of the cooked fowls with kitchen dust was a probable explanation for the presence ofCl. welchii.4. Immediate refrigeration of the fowls, well separated on shallow trays, was shown to be a satisfactory method of preventing the growth of contaminatingCl. welchiito any dangerous extent.5. Six outbreaks of food poisoning, in which there was an association between cold chicken and the clinical symptoms ofCl. welchiifood poisoning, are reported and discussed.I have pleasure in thanking Dr Betty Hobbs of the Food Hygiene Laboratory of the Public Health Laboratory Service at Colindale for the serological typing of numerous strains ofCl. welchii; Mr D. B. Colquhoun for assistance with the phage-typing of the staphylococci; Mr G. Kerr for the photography; and the kitchen staff in the hospital concerned for making possible the numerous samplings of food and the other inquiries into the day-to-day affairs of the hospital catering department.

Strains of Staphylococcus pyogenes able to grow in 0·1 unit/ml. of penicillin produced penicillinase and were regarded as resistant. The majority of the remaining strains had the same sensitivity as the standard sensitive staphylococcus.Five hundred and three strains were isolated from pre-clinical medical students from 1950 to 1953, and 24% were penicillin-resistant. Two per cent were streptomycin-resistant and none were resistant to chloromycetin, aureomycin or terra-mycin. Two hundred and forty-six of the strains were isolated from persistent and intermittent carriers, but only 14% were penicillin-resistant.Another 183 strains were isolated from persons unattached to hospital, and 14% were resistant to penicillin. Only one strain was streptomycin-resistant; one was chloromycetin-resistant and none were resistant to the other antibiotics.Among persistent and intermittent carriers, more than 7 times as many penicillin-resistant strains were isolated from those who had had previous penicillin therapy as from those who had not.It was concluded that the administration of antibiotic increases the number of resistant strains in the community.