Questionnaire survey of the drift mines of the British Isles revealed that the presence or absence of rat infestations could be related to the size of the mine in terms of manpower, large mines being more commonly infested than small ones. In addition, various features of drift mines and their surroundings, i.e. the presence of urban areas, nearby rat concentration points, canteen and surface stables, horses, the absence of buildings and the type of surface sanitation are all related to infestation. Field survey has shown that the extent of dilapidation and piling of waste material assists infestation. It has also indicated that the greater infestation of pits with large numbers of workmen is due to some extent to the extra cover provided by the greater number of surface buildings, these being few or lacking altogether in small pits.

At a mine at which changes in the rat population were studied it was seen that unsuccessful poisoning could leave a breeding nucleus of rats, but that there could also be a speedy re-invasion even after successful poison treatments. Whilst the surface rat population in the buildings of this mine was controlled there were no underground infestations. It appears, therefore, that regular inspection and control of surface infestations should in most cases prevent underground infestation.

This work was carried out under a research grant from Safety in Mines Research Establishment, Ministry of Power, and I am indebted to the Ministry for permission to publish the results. I should like to express my gratitude to the several members of the staff of the Safety in Mines Research Establishment, Sheffield, for the help they gave, in particular Mr C. S. W. Grice. I should like also to thank Prof. L. E. S. Eastham in whose department the work was carried out, Dr E. T. B. Francis who supervised it, Miss B. B. Jones of the Ministry of Agriculture, Fisheries and Food, and the many employees of the National Coal Board who assisted at various times.

Observations are reported on the mechanism of transmission of a neurotropic strain of Newcastle disease virus from infected to normal baby chicks. Infection appeared to be mediated mainly by large or very labile air-borne particles. Other factors examined were the time of maximum infectivity of chicks, the effects of duration of contact, of the social habits of the chicks and of the type of cage used to house them.

Results obtained by contact experiments were supported by tests in which settling virus particles were collected in Petri dishes placed at various distances from infected chicks.

A modification of the metabolic inhibition test for titrating poliomyelitis antibody is described. The method depends on the substitution of galactose for glucose in the initial medium to eliminate colour change during the period of virus activity. Neutralization is detected by the addition of glucose at the end of the period, when the usual colour changes associated with this type of test occur. A statistical analysis of the results obtained is given.

This method can also be used for titrating antibodies to other enteric viruses.

Thanks are due to Dr Hélène Mair, Dr D. R. Gamble and Dr A. D. Macrae for strains of enteroviruses, and to Miss Patricia Jerram, for valuable technical assistance in the early days of this work.

Experiments have been described in which mice were infected by the inhalation of a mono-dispersed aerosol of Salm. typhimurium. The disease so produced was characterized by a specific primary pneumonia. The lethal dose was very much smaller than that required by ingestion, and was approximately equal to the intraperitoneal lethal dose. Possible implications have been discussed.

The authors wish to thank Mr S. Peacock for his invaluable help in the operation of the Henderson apparatus, and Messrs A. V. Lowle and C. M. R. Pitman for technical assistance. We also wish to thank Dr J. S. Paterson for supplying some of the bacterial strains, and for much advice and encouragement.

The number and some characteristics of the colds experienced by office workers in London and Newcastle upon Tyne are described.

Age was the only factor found to be strongly associated with the number of colds experienced by an individual. Female staff suffered only 10–15% more colds than male staff. The presence of children in the household had little or no effect. The daily use of public transport also appears to be unrelated to the number of colds suffered.

We are grateful to the Ministry of Pensions and National Insurance for affording us the facilities necessary for the carrying out of this investigation, and particularly to the staffs of the offices who collaborated with us in providing the records and to the members of the Establishment Department and to the staff representatives for their help in the organization of the study. We are also indebted to the Medical Department of the Ministry for their interest and advice. We also wish to record our gratitude to the Shell Petroleum Company, its officers and staff, and particularly the chief medical officer, for their assistance and collaboration, to the management and staffs of the two other London offices studied and to the nurses, Mrs E. Hodgson, Miss M. Petts, Miss L. Waddell and Mrs E. A. Wilson, who collected the records.

Analysis by epidemiological methods of the spread of the common cold among office workers and their families has failed to account for more than a fraction of the infections as a consequence of known exposure to infected individuals. Infections too mild to be recorded as colds, survival of the virus in the environment and its subsequent dispersal are considered as possible explanations of this.

The distribution of serial intervals between colds suffered by members of the same family indicates that the median interval between the onset of an infection and the first symptom in infection apparently arising from it as cross-infections was between 21½ and 31½ days. This is only slightly longer than the median interval, 2·4 days, observed between nasal installation and the onset of symptoms in experimental infections.

There is some epidemiological evidence that susceptibility to the common cold is reduced during the weeks following a cold.

We should like to repeat, in this the second paper in this series, our thanks to the Ministry of Pensions and National Insurance and to the Shell Petroleum Company, to those members of their staffs and to the nurses and others who helped us in this investigation.

1. A 0·005% solution of the sodium salt of pindone was found to kill wild house-mice (Mus musculus) in 4–6 days. Mice offered a choice between this solution and water drank more water, but the difference in consumption was not statistically significant.

2. The addition of 1% sugar did not appreciably alter the palatability of a 0·005% solution, but a solution of the anti-coagulant containing 10% sugar was more readily accepted than water. This preference was maintained with solution 4 months old.

A study was made of the effect of chlorine solutions on broiler chicken carcasses that had been artificially infected with salmonellae. One hundred and sixteen carcasses were infected with widely varying numbers of seven different salmonella serotypes.

Treatment of carcasses with 200 p.p.m. of chlorine for 10 min. usually prevented the subsequent recovery of salmonellae when fewer than 1000 organisms had been inoculated. When larger numbers of organisms were inoculated or when lower concentrations of chlorine were used, salmonellae were usually recovered from the treated carcasses.

It is suggested that the incorporation of chlorination with 200 p.p.m. for 10 min. into the routine processing of poultry carcasses would greatly reduce the number of contaminated birds leaving processing factories.

We wish to thank the management of a local poultry-packing factory for their co-operation, without which this investigation would not have been possible. We are also grateful to Miss P. E. Ellis for technical assistance.

During a recent epidemic of poliomyelitis three viruses isolated (one Type 1 and two Type 2) elicited both Type 1 and Type 2 CF and precipitating antibodies in the patients whilst only the homotypic neutralizing antibodies were present. These viruses inoculated into animals produced specific CF and neutralizing antibodies, but precipitating antibodies to both types were present in a significant number of animals. These findings suggest that certain polioviruses have complement-fixing and precipitating antigens common to both Type 1 and Type 2 viruses.

We would like to thank our colleagues in the Virus Research Unit for their helpful advice and criticism and Dr J. Hampton (Poliomyelitis Inst., Johannesburg) for the concentrated Type 1 poliovirus vaccine.

A simple device by which the characters of an unknown organism can be com pared with those of named genera and species is described. The comparison is made by using ‘diagnostic tables’ of characters found to have differential value.

Separate tables for Gram-positive and Gram-negative bacteria were made; the first stage indicated the probable genus into which the unknown fell and a second (and occasionally a third) stage was needed to identify the species or subspecies.

We wish to thank Dr Ruth E. Gordon for much unpublished data which were invaluable in constructing Table 1 gg, Miss Helen E. Ross for helping with Table 1f, Dr Oleg Lysenko for letting us use data from a paper about to be published, and Mr W. Clifford for the photographs and figures.

The survival rate of mice actively or passively immunized against intracerebral challenge with Bordetella pertussis, was independent of the size of challenge dose within the range of 20–2000 LD.

This unexpected result appears to be due to the anatomical peculiarities of the infected organ, in which circulating antibody does not pass the normal blood-brain barrier easily. The pertussis infection does not cause sufficient inflammation to induce a pathological increase in the permeability of the barrier until the number of living microbes in the brain reaches 10 to 10. Since this stage in the brain consistently occurs after 4–5 days, independently of the size of the inoculum within the range 20–2000 LD, the outcome of infection in the immunized animal depends solely on the degree of specific immunity.

In the non-immune mouse, the increase in permeability of the barrier persists until death. In the immunized mouse, the elimination of the infection leads to a restoration of the normal barrier at about the 6th day.