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Impetigo contagiosa may be defined as an acute, superficial infection of the skin characterized by exudation and crusting. In this country it is at present mainly seen in children, although it has been an important cause of minor illness among troops in wartime. It appears to have become much less common in the last 10 years, though a recent increase in incidence has been reported (Sneddon, 1953). In the 90 years since the original clinical description of Fox (1864) there appear to have been repeated fluctuations in the prevalence of the disease, and also differences in frequency, severity and predominant clinical type in different parts of the world. It is not surprising, therefore, that there have been great discrepancies between the bacteriological findings of various workers, and that the controversy between the supporters of the staphylococcal and the streptococcal theories of the aetiology of the diseasehas continued for almost 60 years. Most dermatologists nowrecognize the existence of at least two clinical types of impetigo, associated respectively with haemolytic streptococci and with Staphylococcus aureus, though it is not always possible to make such a clinical distinction in the individual case (Epstein, 1940).The investigation reported here falls into two parts, the first of which was carried out in association with Dr L. C. Martin in Cambridge in the years 1941-2 and was concerned with impetigo in young adult service men. The second was occasioned by an increased prevalence of impetigo in the City of Salford in 1953(Burn, 1954, particularly during the last few months of the year. There was an unusually high proportion of severe cases, many of which were of the bullous type.The Cambridge investigation showed that a large proportion of Staph. aureus strains from impetigo cases (and a much smaller proportion from other sources) had the ability to inhibit corynebacteria. The Manchester investigation showed that most of the impetigo staphylococci belonged to a single unusual phage type, members of which were usually able to inhibit corynebacteria and were penicillinresistant, and that the haemolytic streptococci were largely confined to two particular serological types.

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SUMMARYA collection of 346 strains of Streptococcus milleri from a variety of human sources was examined culturally and biochemically, and for the presence of Lancefield group antigens. Most of the strains were non-haemolytic and ungroupable, but 25 % were fi haemolytic and 19 % were a haemolytic; 28 % possessed a group antigen (A, 5 %; C, 6 %, F, 14 %, G, 3 %). These antigens were present in 69 % of f8-haemolytic but in only 13 % of a-haemolytic or non-haemolytic strains; fi haemolysis occurred in 82 % of group-F strains, 43 % of other groupable strains and 11 % of ungroupable strains.The following reactions were given by > 80 % of S. milleri strains: hydrolysis of arginine and aesculin, a positive Voges-Proskauer reaction, and acidification of trehalose, lactose, salicin and sucrose. A minority of strains showed enhancement of growth by CO2, bile tolerance, NaCl tolerance, and ability to acidify other sugars, notably mannitol, raffinose and melibiose. Departures from the modal pattern of biochemical reactions showed a weak correlation with the type of haemolysis and the presence or absence of a group antigen but were not sufficiently systematic for clear-cut subdivisions to be recognized within the species. S. milleri therefore appeared to comprise a 'central' group of non-haemolytic strains that rarely formed a Lancefield-group antigen, in which the aesculin reaction was nearly always positive, lactose was usually acidified, and a considerable minority showed enhancement of growth by C02 and bile tolerance.Deviations from this pattern were of two main types. (1) 'Loss' of one or more of these reactions, which tended to be associated with ,-haemolysis and presence of a group antigen. In these respects, a-haemolytic strains tended to occupy an intermediate position. (2) 'Gain' of the ability to acidify additional sugars, notably raffinose and melibiose or mannitol; this occurred mainly among otherwise typical non-haemolytic strains that were rarely groupable.Only 12 % of isolations from the bloodstream of patients suffering from systemic infections were , haemolytic and only 18 % possessed a group antigen, but a considerably greater proportion of those from visceral abscesses were fi haemolytic (28 %). Among isolations from superficial lesions in some body sites there were considerably greater proportions of f8-haemolytic and groupable strains; thus, nearly one-half of those isolated from the abdomen other than the female genital tract were f,-haemolytic and over one-half were groupable. On the other hand, strains from the teeth and gums were nearly always non-haemolytic and