Values are given for the median equivalent diameters and for the inter-quartile range, of airborne particles carrying a variety of micro-organisms.

Organisms associated with human disease or carriage were usually found on particles in the range 4–20 μ equivalent diameter.

Many fungi appeared to be present in the air as single spores.

We should like to acknowledge the collaboration of Dr Yvonne M. Clayton in the collection and examination of the fungal samples.

A comparison was made of three methods for the removal of dust from a hospital ward floor.

The viable bacterial counts of impression plates from the floor showed a mean reduction of 51 % after cleaning with fresh oiled mops, 40 % after cleaning with a tank model vacuum cleaner and 5 % after sweeping with a broom.

The mean proportions of airborne bacteria, compared with viable counts before cleaning, were 192 % during and 194 % after cleaning with a broom; 128 % during and 103 % after cleaning with an oiled mop, and 82 % during and 48 % after cleaning with a vacuum cleaner. On repeated use the oiled mop dispersed almost as much dust as a broom, but this settled rapidly from the air.

The effects of these cleaning methods on counts of presumptive Staph. aureus on the floor and in the air were similar to those found in counts of total organisms.

We wish to thank Mr M. D. Wilkins for valuable assistance, the Domestic Superintendent and staff and the nursing staff for their co-operation, and Messrs Leeming Brothers Limited for supplies of ‘Kex’ mops and equipment.

Optimum forms of moving averages are derived for the estimation of LD 50 in the situation where no assumptions are made about the form of the dose-response distribution. The theory is also applied to uses of moving averages based on the angular transformation of the percentage response. A numerical example illustrates this application, and its results are compared with the corresponding probit and logit estimates.

Twenty-eight adult volunteers were inoculated intranasally with para influenza 2 virus and eight developed illnesses; twenty-eight volunteers were given flanks' saline and one became ill. The illnesses occurred in volunteers given between 2 × 104 and 2 × 106 TCD 50 of virus. The most prominent symptoms were sore throat, nasal stuffiness and coryza; four of the eight volunteers had sufficient coryza to be regarded as having mild colds. Although only eight volunteers had clinical evidence of infection, twenty-four had laboratory evidence of infection as judged by virus re-isolation or antibody response. Neutralization, haemagglutination-inhibition and complement-fixation tests on paired sera showed that sixteen individuals had a fourfold or greater antibody response by one or more tests including five of the eight volunteers who were ill. Twenty volunteers, including seven who were ill, had reciprocal neutralizing antibody titres of eight or more before inoculation of virus so it seems that the illnesses were due to re infection in the presence of antibody. Evidence is presented which suggests that although illnesses occurred in the presence of antibody they were due to the para influenza 2 virus and not some other agent in the inoculum. The results of these experiments seem to fulifi the third of Koch's postulates for para-influenza 2 virus as a cause of respiratory disease in adults.

We wish to thank Dr P. A. J. Tyrreil for his advice during the course of this work and in the preparation of the manuscript. We also thank Dr K. V. Shah (The Johns Hopkins University, Baltimore, U.S.A.) for help in some of the early experiments and Miss B. Ridgwell for valuable technical assistance.

An outbreak of food poisoning caused by Salmonella typhi-murium, phage-type 12, in which 122 persons were infected, is described.

Isolation of the same organism from the drains of two large abattoirs, from pig faeces at one abattoir, and from the floor drains of fifteen out of fifty-four butchers' shops and bakehouses examined, together with records showing that this organism had been recently isolated from pigs and cattle in the neighbourhood, suggested that meat was the vehicle of infection.

We are indebted to Dr E. S. Anderson and the staff of the Central Enteric Reference Laboratory and Bureau, Colindale, for phage-typing the cultures of S. typhi-murium.

We should like to thank Prof. Scott Thomson for his encouragement and advice in the preparation of this paper and Mr J. Morgan and Mr B. M. Jones of the Public Health Laboratory, Cardiff, for their technical assistance.

Diphtheria toxoid lozenges were given to eighty-eight children aged 10–12 years who had previously been immunized by parenteral injection, and the antitoxin titres before and after administration were compared with those in a similar group of forty-six children who received formol toxoid by injection.

The results showed that a course of two lozenges at an interval of 1 week was a satisfactory means of reinforcing immunity in the children. The antitoxin response was less than that after injection, but a substantial response occurred in the children with low initial titres.

It is suggested that the lozenges might replace an injection as a means of reinforcing immunity in children aged 10–12 years and that they might be a valuable means of rapidly reinforcing the immunity of a large number of children in an epidemic.

The lozenges must be given under supervision to ensure that the children allow them to dissolve slowly in their mouths.

We should like to thank Dr J. D. Abbott of the Public Health Laboratory, Manchester, for separating the sera.

Certain strains of Ps. aeruginosa produce, in addition to pyocines, substances which inhibit pyocine activity. These pyocine inhibitors are probably proteolytic enzymes.

In order to investigate the production of pyocines by various strains of Ps. aeruginosa, aeruginosa, nutrient agar medium was devised in which the action of the pyocine-inhibiting substances is suppressed by incorporating 10–5M iodoacetic acid, 0·1 % sodium citrate and 0·1 % dipotassium hydrogen phosphate. This medium also diminished slime production.

Pyocine production is a stable characteristic which is not lost on repeated sub-culture or prolonged storage, and might form the basis of a typing system for Ps. aeruginosa.

I wish to thank Dr M. T. Parker, Director of the Cross-Infection Reference Laboratory, Public Health Laboratory Service, for constant encouragement and helpful advice.

The number of bacteria on the hands of nurses using 2 % hexachlorophene soap intermittently was compared with the numbers of bacteria on the hands of nurses using ordinary soap. No significant differences were observed.

This study would not have been possible without the whole-hearted co-operation of the Matron, Miss M. Schurr, the Deputy Matron, Miss G. Davies and the Sisters and Nursing Staff of Fulham Hospital.

We are also indebted to Mr T. Ridgewell, Mr T. F. Fletcher and Miss Julia Fisher for technical assistance, and to Messers Bibby and Co. For their generous gift of soap.

If Rift Valley fever virus (RVF), of which the main component has a sedimentation constant (S20) of about 450, is centrifuged under conditions adequate to secli ment MEF1 poliomyelitis virus (S20 = 156) completely, about 1 % of the original infective particles remain in the supernatant fluid. This slowly sedimenting (S10W) fraction was shown by centrifugation to contain infective components ranging in sedimentation constant from 4 to 19 Svedberg units. Density gradient centrifu gation showed that the densities of these particles varied from 1 to < 1 g./cm. The components were neutralized by RVF immune serum but were not affected by ribonuclease or deoxyribonuclease. In gel diffusion-filtration experiments the S10W virus behaved as substances having very low diffusion constants. Its filtration end-point using graded collodion membranes, is approximately two to three times higher than the ‘whole’ virus. It is suggested that particles comprising the S10W virus fraction contain lipoid material and may be filamentous.

The authors wish to express their gratitude to Prof. A. Kipps and R. A. Alexander for their continued interest in this work and to Dr T. H. Mead for many helpful suggestions during preparation of the manuscript.

This investigation was supported in part by a Public Health Service research grant Al 04044–02 from the National Institute of Health, Bethesda, U.S.A.

Twenty-three strains of rhinovirus were isolated from 102 patients who had common colds on arrival at a Royal Air Force recruit centre during a 6-month period from June to November, 1960. Three of these strains were M type rhino-viruses similar to ECHO 28 virus. Twenty strains were H type rhinoviruses which fell into six or more different antigenic types. Two of these types were similar to the prototypes Sal/1/58/H and Sheffield/1/60/H. Three types were antigenically distinct from those previously reported in this country and several strains are still unclassified. Other human respiratory viruses were not isolated from common colds occurring at this time among the population studied.

We are indebted to the Senior Medical Officer of R.A.F. Cardington for providing facilities for the investigation, to Squadron Leader M. Shearer for his help in collecting convalescent blood specimens, and to the Director-General of the Royal Air Force Medical Service for permission to publish this paper.

We wish to acknowledge the excellent technical assistance of Miss Ann Deacon. We should also like to thank Dr H. E. M. Kay of the Royal Marsden Hospital for supplying human embryo kidney.

A scheme is described for the identification of enteroviruses in tissue culture by neutralization with composite antiserum pools. The method for making these pools is given. Antisera to twenty-seven enteroviruses were included in the pools which were used to examine 115 viruses consisting of ninety-eight recently isolated viruses and seventeen prototype strains. The results indicate that this scheme provides a useful screening method for identifying enteroviruses. It has proved to be practicable, time saving and very economical in tissue culture.

We are grateful to Dr C. M. P. Bradstreet who made available some of the rabbit antisera.

The virulence of Pseudomonas aeruginosa appears to depend on both its ability to grow in the serum of animals and its ability to produce various types of extra-cellular toxins. No strain of Ps. aeruginosa lacking either of these qualifications was ever found to be virulent to animals.

The ability of various sera of animals to inhibit growth of Ps. aeruginosa appears to depend largely on their content of specific antibodies to each serological type of the surface antigens (the slime layer) and, therefore, susceptibility of animals to the infections of Ps. aeruginosa, even within one species, varies considerably from one individual to another.

This work was supported by a research career development award of the U.S. Public Health Service to the senior author (GM-K3–15).

A comparative study of the susceptibility of monkey kidney, Hep 2 and HeLa cells to enteroviruses and adenoviruses is made. It seems that this Hep 2 cell line is as effective as the monkey kidney cells in their susceptibility to vaccine strains of polioviruses and far better than monkey kidney cells in their susceptibility to strains of ECHO 6 and ECHO 11 from clinical material. It is as effective as, or slightly better than, HeLa cells for the isolation of adenoviruses. It also compares favourably with monkey kidney cells for the isolation of other enteroviruses.

We are most grateful to Glaxo Laboratories Ltd. for the supplies of monkey kidney cells used in this investigation.

1. A retrospective survey has been made to determine the amount of cross-infection caused by Staphylococcus aureus of one particular phage-type, 83 A, in four main hospitals of a provincial hospitals group, over a period of 2½ years.

2. The total number of strains considered was 1131. Of these, 776 were resistant to tetracycline and therefore the most likely to be of significance in cross-infection. Of these 776 strains, about one-third belonged to phage-type 83 A. In the hospital where 83 A strains were most prevalent, they formed about one-half of the tetra cycline-resistant strains; in that where they were least prevalent, about one- quarter.

The clinical sources of the tetracycline-resistant strains are described.

3. It was found that type 83 A strains were the most likely to show resistance to erythromycin, chloramphenicol or novobiocin.

Of a series of 214 type 83 A strains sensitivity tested against methicillin, using a disk-plate method, none was found to be resistant.

My thanks are due to Prof. R. E. O. Williams, St Mary' Hospital Medical School, for his helpful criticism of this paper and, in his previous capacity as Director of the Staphylococcus Reference Laboratory, Central Public Health Laboratory, Colindale, to him and his staff for supplying me with typing phages, and instructing me in their use. I should also like to thank Dr M. T. Parker, Director of the Cross Infection Reference Laboratory, Colindale, for a continued supply of these phages; the Hon. the Viscount Waverley, F.R.C.P., for allowing me to quote from the case history of a patient under his care; and Mr K. Allen, F.I.M.L.T., and other members of my technical staff for their assistance.

By using a specially designed apparatus it was possible to study the yield of airborne organisms when various hospital textiles, artificially and naturally contaminated, were shaken under reproducible conditions. The results indicated that contaminant organisms are most effectively liberated when a textile is shaken in contact with a second fabric. The yield of airborne organisms was approximately doubled under the conditions used. Similarly, a 95 % removal of surface con taminants was also demonstrated by shaking in contact with a second textile, compared to 52 % removal when the textile was shaken alone.

These findings confirm those described in an earlier study of the spread of air borne organisms in a ward environment. It is suggested that this increase in aerial spread of infectious particles, previously referred to as a ‘counterpane effect’, is due to friction between the contaminated textile and its covering material.

Other points which emerged in the course of this work were the demonstration that cotton blankets tended to yield higher airborne counts than woollen ones and that the size distribution of bacterial particles dispersed by textiles is the same as that of the particles which contaminate the textiles.

It is with pleasure that we acknowledge the encouragement and advice of Prof. Walsh McDermott, in whose Department at the Cornell Medical College, New York, this work was carried out. We are also grateful to the National Institutes of Health, Bethesda, for financial support under Grant No. E-635(C 7).

Studies on the use of gamma radiation for the elimination of salmonellae from whole egg, frozen horse-meat, desiccated coconut and bone meal show the extent to which the nature of the medium influences the resistance of these organisms to gamma radiation. There is also a variation in radiation resistance between different serotypes; S. typhi-murium was consistently the most resistant of those examined.

Based on experiments with artificially inoculated or naturally contaminated products, and also on dose/survival curve data, the dose requirement for the elimination of salmonellae from frozen whole egg is estimated at 0·5 Mrad., which gives a 107 reduction in numbers of S. typhi-murium; for frozen horsemeat 0·65 Mrad., giving a 105 reduction; and for bone meal between 0·5 and 0·75 Mrad., giving between 105 and 108 reduction. A dose of 0·45 Mrad. appears effective for desiccated coconut, with a reduction of 103, but such a radiation dose affects the quality of this product.

We are grateful to Dr E. S. Anderson of the Enteric Reference Laboratory for phage typing and for the provision of a strain of S. typhi-murium for experi ments. Also we thank Dr Joan Taylor of the Salmonella Reference Laboratory for the serological typing of salmonellae, and Miss M. E. Smith and other colleagues of the Food Hygiene Laboratory who carried out the routine bacteriological examination.

We wish to thank Mr N. C. Roberts of J. Rannoch Ltd. for his co-operation in the large-scale frozen egg experiment, and also Mrs G. M. Ison of S. Wallace Ltd. in respect of the experiment on frozen horse-meat.