The form of the killing curve obtained by bombaring micro-organisms with high energy electrons enables an estimate to be made of the numbers of individual viable organisms present in the aggregates or clumps comprising the sample. Samples of Staph. aureus collected from the air of two hospital wards have been found to consist of aggregates containing, on the average, only about four viable cocci per air-borne particle. These samples were taken during quiet periods and during periods of active dispersion of the organism but there was no active spread of staphylococcal disease at any time.

The work on the linear accelerator was carried out with the aid of grants provided by the Treasurer and the Board of Governors from the Discretionary Fund of St Bartholomew's Hospital, to whom we wish to express our gratitude.

Studies on reproduction in a colony of albino mice before and after length of daylight was made constant show no change in litter size. However, there was an increase in the number of post-partum pregnancies after light was made constant and, during the first month thereafter, females were older at first parturition than in previous months.

1. Whole cultures of Clostridium welchii, Type C (organisms plus toxin), produced enterotoxaemia and death when fed to new-born piglets.

2. The disease could rarely be produced by suspensions of washed organisms given in the same way but was readily initiated by feeding bacteria-free toxin from Type C cultures.

3. Piglets dying from enterotoxaemia induced by bacteria-free toxin showed all the extensive pathological changes of the natural disease; their intestines contained Type C organisms and far greater quantities of toxin than had been given by mouth.

4. Type C organisms could not be demonstrated in the intestines of piglets from healthy litters of the same age, although such animals were carriers of the Type A strain.

5. The clinical signs, with particular reference to the development of hypo-glycaemia, and the pathology of both natural and experimentally induced cases of enterotoxaemia are described.

6. In the light of these findings the pathogenesis and epidemiology of enterotoxaemia in the piglet are discussed.

We wish to thank Mrs B. L. Wardale and Mr P. J. D. V. Brett for general assistance. This study was aided financially by a general grant to one of us (R.F.W.G.) from the Agricultural Research Council.

The distribution of salmonella agglutinins among 2117 normal sera from 1054 male and 1063 female adult population of Ibadan is described, and the relation of the distribution of the agglutinins with the antigens of salmonella strains isolated over 2-year period in a hospital in Ibadan, Nigeria, is discussed.

We wish to thank Prof. B. G. T. Elmes and Dr J. B. Lawson for their help with the collection of specimens. Our thanks are due to Mr R. J. Leeming, F.I.M.L.T. for his technical assistance.

(Part of the material upon which this paper is based is included in a thesis for submission for the Cambridge M.D. degree by one of us (D.M.).)

Calculations have been carried out which suggest that as few as 6 × 104 molecules of anti-poliovirus antibody per millilitre of serum may be sufficient to prevent the clinical disease under certain epidemic conditions. Other calculations have been made involving therapy of the experimental disease in monkeys and certain factors required for successful serum therapy have been discussed.

1. Bacteriological surveys of more than forty popular bathing beaches around the coasts of England and Wales have been made during the past 5 years. The great majority of the beaches studied were subject to contamination with sewage.

2. A rough grading of the beaches studied gave a similar ranking order whether the results of the presumptive coliform test or faecal coli counts were used as the basis of grading.

3. Grading of beaches was valid only when surveys were carefully planned to ensure representative sampling from the areas on the beaches concerned where bathing actually took place.

4. The coliform test as used in the bacteriological examination of drinking waters was the main test procedure used but had certain limitations. Promising results with plate counts on relatively non-inhibitory media were obtained.

5. Various salmonella serotypes, notably Salm. paratyphi B, were isolated in small numbers from a high proportion of sea-water samples. The proportion of positive results for salmonella isolation increased from 13·3% in samples with less than 1000 coliform organisms per 100 ml. to 40·1% in samples with over 10,000 coliforms per 100 ml. Comparison of the numbers of salmonellae isolated with what is known of the minimum infective doses of these organisms suggested that very large volumes of sea water would require to be ingested for infection to occur.

6. Poliovirus was not isolated from a small series of sea-water samples examined. Because of the very large dilution factor, special concentration procedures would probably be required to isolate this virus from sea water.

7. Four cases of paratyphoid fever probably due to bathing were recorded. Surveys of the two associated beaches had given median presumptive coliform counts of more than 10,000 per 100 ml., and both showed gross macroscopic pollution with sewage.

8. A statistically controlled study of the bathing histories of 150 poliomyelitis cases in children living permanently by the seaside gave no evidence that bathing had played any part in causing the disease.

1. Salmonella incidents in Northern Ireland from 1951–58 are compared with the published findings in England and Wales.

2. Caecal swabs from 489 pigs killed in two bacon factories showed a salmonella isolation rate of 2%.

3. Salmonella organisms were isolated from twenty-three out of 100 samples of caecal faeces and from only six of 100 caecal swabs taken from the same animals. Three per cent of meat samples from these pigs and 70% of sausage samples from this meat contained Salmonellae.

4. Rectal swabs from 162 pigs on five farms producing infected pigs showed Salmonellae in 9% of those examined.

5. Twenty-four per cent of pig-meal samples taken on these farms contained Salmonellae, and the same salmonella types were found in the meal at the mill and in fish meal and bone meal before mixing.

6. It is probable that some salmonella types pass from feedingstuffs through pigs to human food and cause human infections.

We should like to express our thanks to Dr Joan Taylor of the Salmonella Reference Laboratory, Colindale, for typing many of the Salmonellae; to Mr J. Stuart of the Veterinary Division, Ministry of Agriculture, Northern Ireland, for help in sampling at an abattoir and on the farms; to the staff of the Northern Ireland Hospitals Authority, Central Laboratory, for technical assistance; to Mr J. Patton and Dr D. Luke for much help and advice at many stages of this inquiry; to Miss A. McCann for the secretarial work; to the Northern Ireland Hospitals Authority for a grant towards the expenses in 1958; and to our colleagues in the Local Authorities, General Practice, on the farms and in the factories who were always most helpful and co-operative.

1. Neonatal serum proteins and those of maternal colostrum have been examined in the Spinco analytical ultracentrifuge and the Perkin-Elmer electrophoresis apparatus. To facilitate correlations between the two types of result, certain protein fractions have been prepared electrophoretically and examined in the ultracentrifuge.

2. The electrophoretically distinguishable components of precolostral serum, albumin, α and β globulin and traces of γ globulin sedimented mainly as a single boundary which showed evidence of a slower component (probably fetuin) with a sedimentation constant of about 3S. A small proportion of a macroglobulin component (S020 ≅ 16S), associated with the α globulin, was also present. In conformity with the very low γ globulin, there was a complete lack of globulin with S020 ≅ 6·5–7·0S. The β globulin and the bulk of the α globulin sedimented closely with albumin, whose sedimentation constant in an electrophoretically isolated fraction was somewhat lower than normal, probably as a result of α-globulin contamination.

3. The electrophoretic and ultracentrifuge analysis of postcolostral calf serum showed evidence of passive absorption from the maternal colostrum of immune lactoglobulin. There was a rise in the concentration of total serum protein of which up to 51·6% was immune lactoglobulin, of sedimentation constant 6–6·5S. No such component occurs in precolostral sera. The electrophoretic and ultracen-trifugal characteristics of this globulin were not significantly altered as the result of absorption. The acquisition of immune lactoglobulin was accompanied by a simultaneous fall in serum albumin concentration.

4. Examination of colostrum, rennin-produced colostral whey, and of electrophoretic fractions prepared from colostrum showed the presence of a small proportion of a macroglobulin (S020 ≅ 18S), a well-defined immune lactoglobulin of S020 ≅ 6·4S and electrophoretic properties in the γ-range, and a group of electrophoretically more mobile components with sedimentation constants ranging downwards from 3S.

5. Electrophoretically prepared fractions from the serum of a deprived calf 27 days old showed sedimentation properties in conformity with the results on precolostral sera, with the macroglobulin component being again associated with α globulin. The remainder of α and β globulin sedimented alongside albumin and the additional γ-globulin component in a single boundary of S020 ≅ 6·5–7S.

6. The concentration of autogenous γ globulin developed by calves which had been deprived of colostrum increased with time and was generally in fair agreement with that of the 6·5–7S component.

The authors wish to thank Sir Alan Drury, F.R.S., for his interest and encouragement during the course of this work, Mr N. Buttress, Mr D. Hardman and Miss J. Mallon for technical assistance and Mr J. Clark for assistance in the care and handling of the calves.

1. The influence of the thyroid gland on the production of antitoxins to two alum-precipitated bacterial exotoxins has been investigated in different animal species.

2. Rats, rabbits and mice produce more circulating antitoxin when thyroidectomized, and less when made hyperthyroid by thyroxine administration, than control animals.

3. Guinea-pigs produce slightly less antitoxin when thyroidectomized, and markedly more when thyroxine treated, than control animals.

We are grateful to Dr J. S. F. Niven for histological examination of tissues, and to Miss M. V. Mussett, B.Sc., for statistical analyses. The alum-precipitated tetanus toxoid XW 2044, and tetanus toxin XW 1322, were kindly supplied by Miss Mollie Barr, M.Sc., of the Wellcome Research Laboratories, Beckenham, Kent, and we are also grateful to Mr P. Rodican of the Lister Institute, Elstree, for a supply of tetanus toxin 829.

1. The susceptibility of mice of different ages to intramuscular, intraperitoneal, and oral administration of EMC virus, and to intracerebral and intramuscular injection of both the Texas and the Connecticut-5 strains of Coxsackie virus have been studied. In all cases susceptibility decreases with age. The development of resistance to a given virus may vary in rate and extent according to the route by which the virus is given.

2. The multiplication of small amounts of EMC virus in muscle, and of the Texas and Connecticut-5 strains of Coxsackie virus in both muscle and brain, has been studied in mice of different ages. A very high degree of multiplication of all three viruses was observed in both muscle and brain of young mice, but no significant multiplication of the EMC virus in older muscle could be detected with these small inocula, nor of either of the Coxsackie strains in older muscle or brain.

3. Multiplication of EMC virus in young mice was shown to take place within the muscle itself. Haemagglutination tests showed that less haemagglutinin, as well as less infective virus, was produced in the muscles of older mice following the injection of small amounts of virus.

4. Multiplication of EMC and GDVII viruses could be demonstrated even in older mice if a sufficiently large amount of virus was inoculated initially.

5. The rapid initial disappearance of infectivity from the site of inoculation was shown to be mainly due to dispersal of inoculated virus around the body.

6. The simplest hypothesis which will accommodate the observed data on virus multiplication and on the development of resistance with age appears to be that the accessibility of the host cell to virus decreases with age. We found no evidence that the ability of the host cell to support virus multiplication declines with age.

This work was done in the Department of Zoology, Oxford University. One of us was in receipt of a Medical Research Council training grant. The expenses of the research were met by a grant from the Nuffield Foundation, to whom we should like to express our gratitude.

Good fixation of complement was obtained with the infective virus fraction of the Mahoney Type 1 poliomyelitis virus which had been adapted to suckling mice. The presence of a soluble antigen, specific to Type 1 virus, was also demonstrated but was small in amount.

The infective virus fraction of the suckling mouse adapted MEF1 Type 2 poliomyelitis virus produced as good fixation of complement as did Type 1, but the fixation of complement by the MEF1 soluble antigen was far greater than that obtained with the Mahoney strain.

The author would like to thank Prof. A. Kipps for his interest and encouragement and Miss M. Butchart for her valuable technical assistance. She is also indebted to Dr H. Malherbe of the Poliomyelitis Research Foundation, Johannesburg, for the Type 1 monkey immune serum.

1. The question of a possible eclipse phase during the first week of experimental mouse tuberculosis has been examined.

2. Using fluorescence microscopy to examine sections and to perform counts of stainable bacilli for comparison with counts of culturable bacilli in the lungs it was found that bacilli multiplied very slowly during the first 5 days, and rapidly from about the sixth day onwards.

3. At all times there was close agreement between stainable and culturable bacilli in the lungs.

4. During the lag phase, the bacilli occurred as widely scattered, often weakly acid-fast cells that were difficult to defect by Ziehl–Neelsen staining.

5. Active removal of bacilli by phagocytes is believed not to be important at this stage.

6. After 5 or 6 days, clusters of bacilli, rapidly increasing in number and size and strongly acid fast, were readily detected in the lungs.

Colorimeters and non-recording spectrophotometers for visible and ultra-violet light have been used for many years and are to be found in most microbiological laboratories. With the need for greater speed of operation, recording instruments are now coming into more general use. During the last two decades recording infra-red spectrophotometers have been developed and these have enabled the absorption measurements on micro-organisms to be extended into the infra-red region of the spectrum. Two factors have tended to retard the use of infra-red spectrophotometry. One is the high initial cost of the equipment and the other is the large absorption of infra-red radiation by water. Despite these difficulties, a considerable amount of work has now been done and it seems profitable to review the varied applications to which infra-red spectroscopy has already been put and to indicate the results which have been obtained by its use.

1. Experiments have been carried out to estimate quantitatively the survival of Sh. sonnei at various R.H.'S and two different temperature ranges.

2. A fraction may survive for 7–10 days under favourable conditions.

3. At R.H.'S of 40–60% the organism survives less well than at higher or lower values.

4. Survival is better at temperatures of 5–10°C. than at 20–30°C.

I am very grateful to Mr T. Nash for his advice during the course of this work, and also to Col. H. J. Bensted for his comments on the MS.

Ambient temperature profoundly affects the mortality rate and symptomatology in rabbits infected with an attenuated strain of myxoma virus. Simulated summer temperatures allowed at least 70% of infected rabbits to recover, whereas only 8% recovered when held at simulated winter temperatures. Similar fluctuating high temperatures did not reduce the lethality of rabbitpox or of a highly virulent strain of myxoma virus.

On the chorio-allantoic membrane of developing chicken embryos the proliferation of myxoma virus was almost completely inhibited at 39° C., but the yield of rabbitpox virus was not reduced at this temperature.

The serological response and viraemia in rabbits held under different conditions of ambient temperature were investigated. Low temperatures resulted in high titres of circulating virus and soluble antigens, whereas at high temperatures anti-body appeared early. Haemolysin production was not affected by ambient temperature.

The widely variable response of rabbits infected with the attenuated strain of myxoma virus when held at mild temperatures indicates that there is a considerable variation in the innate resistance of the host to the invasion of the virus. This resistance is enhanced by high and reduced by low ambient temperatures, so that the host response is relatively uniform under these conditions. The precise nature of this innate resistance has not been elucidated.

Now that attenuated strains of virus are common and many rabbits exhibit enhanced genetic resistance, seasonal temperatures will have an important influence on the mortality rate in epizootics of myxomatosis.

It is a pleasure to acknowledge the skilled technical assistance of Mr A. Brand.

1. Methods are described for altering the susceptibility of the surviving allantois to infection by influenza viruses.

2. Under natural conditions susceptibility is a linear function of age between 10 and 18 days of incubation. The drop is 0·11 log10 unit per day for all strains of influenza tested.

3. In whole eggs this decline is masked by the effect of acid allantoic fluid which prevents infection when the pH falls below 6. The effect is not directed against the virus particle, nor does it do permanent damage to the cell, as surviving tissues are equally susceptible whatever the pH of the allantoic fluid that bathed them in ovo.

4. Surviving membranes can be made less susceptible by incubating the eggs at 35° rather than 38° C.; by maintenance for 24 hr. in vitro; by use of deficient or inappropriate medium. These methods lower susceptibility more for some strains than for others.

5. All treatments which lower susceptibility also increase its variation from egg to egg.

1. A new phage-typing scheme for Salm. typhi-murium is described which initially defines thirty-four types of the organism.

2. Types recognizable with the older scheme of Felix and Callow remain distinct with the new system. However, the latter method offers a finer subdivision of the organism than does the former.

3. Thirteen of the twenty-nine typing phages used in the new scheme were prepared by adaptation of Salm. paratyphi B typing phage 3b, and nineteen are serologically indistinguishable from this phage.

4. The lysogenic properties of the new types are discussed. Twenty-three out of the thirty-three type strains yielded both thermolabile and thermostable phages and a further three yielded thermolabile phages only. No phages could be isolated from the remainder.

5. The distinctive host ranges of the phages carried by most types can be used for type identification.

I am indebted to Miss Alison M. Dykes for her valuable assistance with this work; to Mr F. J. Flynn for help in the preparation of phage stocks; and to Dr E. S. Anderson for many helpful discussions and advice in the preparation of this paper.

Guinea-pigs immunized with alum-precipitated diphtheria toxoid (APT) become hypersensitive to diphtheria toxin and toxid. This hypersensitivity is probably due to a mixture of immediate (Arthus-type) reactions and delayed (tuberculin-type) reactions, the former increasing as the level of circulating precipitating antitoxin rose and tending to mask the latter. In a hyperimmune guinea-pig the residual damage following the intradermal injection of toxin is due, at least in part, to hypersensitivity to toxin; toxicity probably contributes relatively little to the extent of the lesion in animals with a high titre of antitoxin.

The technical difficulties of proving the presence of a delayed allergic reaction in animals with an early allergic reaction are discussed.

I am grateful to Dr C. G. Pope, who has been closely associated with this work, not only for providing highly purified materials, but also for his advice.