Of thirty-six babies delivered at home 72% acquired Staph. aureus in their noses and throats within their first fortnight of life. The carrier rate among the twenty-eight who were subsequently followed was 65% during the first fortnight period. Only 18% acquired penicillin-resistant strains, in contrast to the previously observed hospital-born group, 97% of whom acquired strains resistant to penicillin. Phage typing demonstrated that the home-born babies who acquired Staph. aureus during their first fortnight carried the same strains throughout the 15–25 week observation period. As in the hospital-born babies, many of them tended to lose the strains from the nose while retaining them in the throat. Strains having phage patterns of Groups I and II were most common among the home-delivered babies, whereas among the hospital-born babies Groups I, III, or untypable strains were most frequent. There was no evidence that the penicillin sensitive strains acquired from the home are carried for shorter periods than the penicillin-resistant strains of the hospital. Babies failing to acquire Staph. aureus within the first fortnight tended either to acquire it in the throat alone, or to remain non-carriers. It is suggested that babies who do not become carriers within the first two months of life are unlikely to do so later.

I owe thanks to many people: to the late Prof. Sir Alexander Fleming for generously extending the laboratory facilities of The Wright-Fleming Institute; to Prof. Robert Cruickshank for patient guidance and invaluable suggestions; to Dr R. E. O. Williams for providing materials and laboratory space for the phage typing, and to Dr Joan E. Rippon for instruction in the phage typing technique; to Dr Agnes H. W. Smythe for the co-operation of the Marylebone and Lisson Grove Child Welfare Centres, and to Mrs Eastham and Miss MacGilley who took the swabs there; to Dr W. Howard Hughes, Dr W. G. Booth, and Dr K. Hart for arranging co-operation of the Ealing Public Health Department; to the Ealing midwives who collected the swabs from the domiciliary-delivered babies; to members of the Wright-Fleming Institute technical staff.

Also, I am grateful to the following organizations for personal grants while conducting the study: The United States Educational Commission in the United Kingdom for a Fulbright Scholarship, 1951–53; The University of California for a grant from the Student Aid Fund; Sigma Delta Epsilon for a Fellowship Award.