A simple method, applicable in routine work, for simultaneous air sampling of total bacteria, on serum agar, and Str. salivarius and Bact. coli on specific media, is described.

Simultaneous air sampling including, in addition to detection of total bacteria, Str. salivarius and Bact. coli as indicators of buccal and faecal air-borne bacteria, respectively, reveals the kind and source of air-borne pollution much better than the simple total bacterial count.

The air in various medical and public institutions was examined; the results are presented and discussed. The air pollution of the premises examined was relatively high, especially in the operating theatres. The air of infants' wards was found to be heavily polluted with Bact. coli as a result of poor nursing technique and this might have had bearing on the epidemic of infant diarrhoea.

The air of operating theatres ventilated by powerful extractor fans was sampled during operations with special media for Cl. welchii and Staph. aureus, and also for total organisms. Counts made with the slit-sampler showed the presence of Cl. welchii in all samples in a range slightly higher than that of Staph. aureus (mostly between five and twenty-five colonies per 100 cu.ft.). There was no evidence of a build-up of either Cl. welchii or Staph. aureus during the course of operations, nor were there any consistent peaks of contamination during operations.

Settle plates exposed on numerous days in the operating theatres showed similar counts of Cl. welchii and Staph. aureus—the latter slightly more abundant in this series. Settle-plate counts from many parts of the hospital and from the road outside provided evidence that airborne Cl. welchii comes into the hospital from outside, while Staph. aureus is contributed to the air inside the hospital. This view was supported by study with the slit-sampler and with settle plates in a dressing station ventilated with filtered air, where Cl. welchii was rarely found and Staph. aureus momentarily abundant during dressings; staphylococci but not Cl. welchii were dispersed by the operators in a mock operation. The numbers of airborne Cl. welchii inside and outside the hospital were higher in dry than in rainy weather.

Of the patients in the Burns Unit 35% had at some stage Cl. welchii in their burns; contamination was commoner in the more extensive burns. In contrast to Staph. aureus, Cl. welchii was usually present in small numbers and for a short period.

Cl. welchii was found in the burns of twenty out of thirty (66%) patients whose rectal swab taken on admission showed the presence of Cl. welchii; a significantly smaller proportion of patients whose rectal swabs were free from Cl. welchii picked up the organism while in hospital (eight out of thirty-two, 25%; x2 = 9.4, P < 0.01). This observation supports the view that burns and possibly other wounds acquire Cl. welchii by self-infection at least as often as from the environment. While it is obvious that plenum ventilation of operating theatres with filtered air is desirable, it is uncertain to what extent this will reduce the small hazard of post-operative gas gangrene.

We wish to thank Miss G. Hogg and Mr L. Hurst, F.I.M.L.T. for technical assistance, the surgeons and nursing staff of the Birmingham Accident Hospital for their co-operation, Mr N. R. Gill for photography, and Professors A. A. Miles and C. L. Oakley for kindly sending us strains of Cl. welchii.

An investigation has been made of methods of estimating the antitoxin content of small samples of human sera by haemagglutination procedures.

The direct agglutination test appears to be satisfactory when dealing with groups of sera, but was unreliable for testing individual sera.

The discrepancies observed in the direct agglutination test were greatly reduced by adopting an agglutination inhibition test at the LA/100 level of test.

The difference in agglutinating capacity of both avid and non-avid sera per in vivo unit of antitoxin did not appear to be related to avidity.

Ringtail in infant rats is shown to depend on humidity over a wide temperature range. It is not due to infection or diet, but probably to chronic cooling by evaporation, convection and conduction.

Rats should either be bred in cages with solid floors, or else be given environmental conditions resembling those in the natural nest, which keep the young at a low saturation deficit during the early post-natal period.

I am glad to express my thanks to M. Potter, Senior Animal Technician, for his invaluable aid in keeping the records of the experimental programmes, and to G. Dimmock for his help in building and maintaining apparatus. I am also grateful to the University of London for the loan of a Cambridge portable potentiometer.

Children in a residential home whose tonsils had been removed had lower attack rates for streptococcal sore throat than tonsillectomized children. Tonsillectomy did not have a consistent effect on respiratory tract illness.

Tonsillectomy has a similar effect on the outcome of individual exposures to streptococcal infection; the difference was more marked for illness than for simple colonization.

The apparent benefit from tonsillectomy could not be attributed to the ageing of the child, and was considered real. Its magnitude did not seem, however, great enough to justify a policy of extensive tonsillectomy, particularly in view of the possible risks to the child.

A child who had been ill with infection due to one streptococcal type rarely became ill when re-exposed to the same type. In addition there was some evidence in children with tonsils of an immunity, perhaps short lived, which was clearly not type-specific.

In a residential home for children, 367 cases of streptococcal illness were observed in a period of 30 months. The children lived in groups of about twelve in separate cottages. There were 194 occasions on which a streptococcus was thought to have been newly introduced into and produced illness in a cottage; on 132 of these 194 occasions there were no secondary cases of illness. The remaining 62 cottage introductions were followed by one or more secondary cases.

In 27% of the 194 introductions, the primary case of illness seemed to have been infected from a healthy person in the cottage. In all, 30% of introductions of a new streptococcus into a cottage could be attributed to recognized contacts with one or more known infected children.

The most important factor determining spread within the cottage seemed to be the carrier state of the primary case, spread following more often when the primary case had streptococci in the nose either on admission to hospital, or in convalescence.

There was no evidence that spread within cottage bedrooms was of great importance.

In about 35% of the incidents with spread, the initial spread to secondary cases seemed to be from the incubation-stage carriage of the introducer; in 42% it was from his or her convalescent carriage.

The carrier rate in the healthy cottage-contacts was generally higher in cottages experiencing clinical spread of infection than in those that had single-case introductions. There was a strong correlation between the carrier rate in the first week after an introduction and the final bacteriological attack rate, and a weaker correlation with the final clinical attack rate.

Continued spread of infection in a cottage was commonly due to the arrival of new children and was almost always associated with the presence of nasal carriers of streptococci.

The 194 cottage introductions could be grouped into sixty-three overlapping Village epidemics, each apparently derving from a new importation of the particular type into the Village, although the evidence for this was often merely the absence of known infections within the previous few months. Only 13% of the introductions resulted in more than 10 cases, and some 80% had 5 or fewer. Introductions were more frequent in the cottages receiving children new to the homes than in those for the more permanent residents.

The principal factor found as determining the spread from the first cottage to others was the attack rate in the first cottage. Introductions in cottages for school-age children, and especially those in which a child attending the school in the Village grounds was the first to be attacked, also seemed to lead to spread more often than others.

The interval between successive Village introductions of one type did not appear to affect the extent of spread at the second; but the number of cases occurring in the first of two introductions had a notable effect: in no case did two successive introductions both result in a large number of cases of illness.

1. A collection of 1389 strains of Staphylococcus aureus of human origin was examined by the following tests: phage typing, antibiotic resistance, ability to inhibit the growth of Corynebacterium diphtheriae, the egg-yolk reaction and the serum opacity reaction.

2. Nearly all strains of Staph. aureus Type 71 were penicillin resistant, inhibited C. diphtheriae, gave a negative egg-yolk reaction, and produced a zone of opacity on horse-serum agar.

3. The penicillin resistance of Type 71 strains is unlikely to have arisen as a result of the therapeutic use of penicillin, and is probably a natural characteristic of the type.

4. Staph. aureus strains which gave a negative egg-yolk reaction and a positive serum opacity reaction occurred almost exclusively in superficial lesions. The majority of them were members of Type 71, or were penicillin-resistant members of phage-group III. It is suggested that these organisms can cause superficial inflammation, but are usually unable to invade deeper tissues.

I wish to thank Dr A. J. H. Tomlinson for valuable information about his unpublished work on impetigo. Thanks are also due to many colleagues who have provided cultures and clinical information, to Dr R. E. O. Williams for typing phages, and to Mr L. E. Simmons for technical assistance.

Ultra-centrifugation of emulsions from suckling mouse brains infected with the MEF1 strain of poliomyelitis virus separates a non-infective antigen, or soluble antigen, from infective virus. This antigen is responsible for most of the complement fixation and explains the high titres obtained. On the other hand, the same virus, and also Mahoney, Type 1 poliomyelitis virus, grown in monkey kidney tissue culture, fail to produce this soluble antigen, and this is probably a factor in the low complement-fixing titres obtained in tests with these fluids.

The author would like to express her appreciation of Miss M. Butchart's valuable technical assistance.

The antigenic response of guinea-pigs to live poliomyelitis viruses of all three types has been studied and the loss of antigenicity involved in inactivation by formaldehyde and by ultra-violet light have been determined.

We wish to acknowledge the debt we owe to the late Prof. M. van den Ende for his great help and interest in this work, and we are grateful for the assistance received from Dr H. Malherbe and Ruth Harwin in carrying out many of the titrations, and from Dr T. Mead for synthesizing some 1:4-diphenylbutadiene for use as a filter for ultra-violet light.

We also have to thank G. S. Turner, T. Norcott, Doreen Deeks and Margaret Pakes for their technical help.

The inactivation rates of tissue-culture polio virus have been determined and these have been applied to the irradiation of formalinized vaccine, as an additional inactivation process, using a simple irradiator.

The antigenic potency of the vaccine was apparently unimpaired.

We wish to thank the late Prof. van den Ende for his keen interest and criticism; Dr H. Malherbe and his staff for carrying out many of the titrations; Dr P. D. Winter for co-operation in irradiating samples of vaccine, and Margaret Pakes for invaluable technical assistance.

1. During the years 1954–56 large number of salmonellae, comprising six sero-types and a number of Salm. typhi-murium phage types, were isolated at the Bradford abattoir.

2. Most of the cultures were derived from pigs; the animals presented no sign of clinical illness.

3. Human salmonella infections in Bradford over the same period were closely related to the abattoir findings.

4. It seems probable that individual pigs are infected on the farms and when brought to the abattoir may infect others in the lairages.

5. Limiting the duration of stay in the lairages and prevention of overcrowding may substantially reduce the proportion of animals found infected at slaughter.

We wish to express our thanks to Dr John Douglas, Medical Officer of Health, Bradford, for his interest and encouragement in this investigation and to Mr F. H. Myres, Mr J. Noble, Mr E. Root and Mr R. Butterfield of the Bradford Health Department for their enthusiastic help. Thanks are also due to Dr Joan Taylor and Dr E. S. Anderson and staffs of the Salmonella and Central Enteric Reference Laboratories, Colindale, for their assistance in typing Salmonellae, and to a number of our colleagues who have kindly read the script and offered valuable criticisms.

The sources of airborne bacteria within living quarters are minute droplet nuclei which remain suspended in the air following expulsion from a carrier and contaminated particles which have become suspended from dried environmental deposits. Since group A streptococci may be isolated from environmental deposits in populations experiencing an epidemic of streptococcal respiratory disease (Loosli, Lemon, Wise & Robertson, 1952), it has been assumed that contaminated particles of dust serve as an important reservoir of infection. Indeed, many of our measures employed to control respiratory infection in recent years have been directed against this reservoir.

Annually for 4 years groups of young Australian wild rabbits have been captured during non-epizootic periods from areas in which myxomatosis has occurred during the previous summer. The intensity of the preceding epizootic was measured by testing a sample of survivors for antibody. The captured young rabbits were raised in the laboratory until they were about 4 months old and then inoculated intradermally with small doses of the slightly attenuated myxoma virus strain Aust/Corowa/12–52/2 (KM 13), all samples of virus being derived from the same batch which has been stored at -70°C.

The results show there is a significant negative correlation between the mortality rate and the degree of exposure to myxomatosis of the forbears of the tested animals. Passive and active immunization have been excluded and this result is ascribed to increased genetic resistance.

We are greatly indebted to Mr. F. N. Ratcliffe, Officer in Charge of the Wildlife Survey Section of the Commonwealth Scientific and Industrial Organization, and to his officers, especially Messrs W. E. Poole, K. E. Myers, G. Douglas, B. V. Fennessy, H. Frith and K. Keith for their invaluable assistance in collecting rabbits and serum samples.

We have had valuable discussions with Dr W. R. Sobey, Dr P. J. Claringbold and Dr G. S. Watson on genetical and statistical aspects of the problems under study.