1. The average lethal dose of fluoracetamide for wild R. norvegicus was found to be 13 mg./kg. of body weight and the LD95, about 43 mg./kg.

2. Wild rats offered bait contatining 0·5, 1 and 2% fluoracetamide, after a period of conditioning, seemed to find it palatable and, on the average, ingested the equivalent of 18–100 LD50's. Warning symptoms appeared in about an hour or longer and included short convulsive spasms.

3. The speed of onset of warning symptoms leading to cessation of feeding was studied in albino rats dosed with the equivalent of 2 LD50's of sodium fluoracetate, zinc phosphide or fluoracetamide. Feeding ceased soonest in the case of sodium fluroacetate. Zinc phosphide gave very variable results, but it is thought that if wild rats had been used, feeding would have stopped nearly as soon as with sodium fluoracetate.

4. It is considered that field trials to compare the efficiency of 1% flouracetamide and 2·5% zinc phosphide, both with ‘prebaiting’, would be well justified.

5. Fluoracetamide at 2% may also prove to be a good alternative to 0·25% sodium fluoracetate as a ‘direct’ poison for controlling rats in sewers.

We are indebted to Miss Y. Larthe and Miss E. J. Taylor who took part in the bioassay and in one of the experiments with the marked rats.

1. When chick embryo cell monolayers were infected with ultrasonically treated elementary body suspension by a short period of adsorption some of the adsorbed virus lost infectivity in a few minutes. This was followed by a more gradual loss during incubation of the cultures. The lowest point was reached at 4–6 hr. followed by a rise in titre due to production of new virus at 7–8 hr. The quantitative assessment of these changes is discussed.

2. In such cultures, titration of intact and disintegrated cells after incubation for 4–5 hr., indicated an eclipse phase by showing an absence of infective virus in cells which ultimately produced it. The process of eclipse continued for several hours. With inoculum that had not been subjected to ultrasonic treatment it was not possible to show this by infecting HeLa cell monolayers.

3. Ultrasonically treated inoculum, compared with a similar, but untreated inoculum, had a three to flvefold higher titre. The virus units in it were more uniformly capable of infecting cells. After its adsorption to monolayers a rapid loss of some infective virus occurred within a few minutes which was not demonstrable with untreated inoculum. During incubation of monolayers infected with treated inoculum the loss of infectivity was faster, there was a more rapid production of new virus and a greater yield. The nature of the changes in the virus which were brought about by ultrasonic treatment have not been explained, but the use of such an inoculum markedly affected the results of experiments.

4. Treatment of infected monolayers with trypsin or EDTA caused the cells to shed as much as half their virus. This virus would not be released spontaneously into the medium or removed from monolayers by washing. This applied to all periods of incubation up to 24 hr. or more when marked increase of virus had occurred.

5. The disintegration of infected cells by ultrasonic treatment was efficient in releasing infective virus from them, although it was not possible to be certain all the virus in the cells was rendered detectable by this technique.

6. The effect of some technical procedures on the interpretation of results is discussed.

1. The reaction of slowly growing pathogenic bacteria with specific fluorescent antibody provided a means for their rapid identification.

2. Fluorescein isothiocyanate was used to label the globulins of antisera as it had a number of advantages over fluorescein isocyanate.

3. Several other isothiocyanates and a few sulphonyl chlorides tested were inferior to flurescein isothiocyanate as labelling agents. Some of the compounds caused protein precipitation, and others gave a less intense or less distinctive fluorescence than did dluorescein isothiocyanate.

4. The tests were performed by taking impressions of bacterial micro-colonies on glass cover-slips, drying and fixing the preparations, staining them with labelled antiserum, washing in saline and mounting in glycerol saline. The preparations were than examined microscopically under ultra-violet light.

5. Micro-colonies of Br. suis, Past. tularensis and Past. pestis, when treated with homologous labelled antiserum, fluoresced brightly under ultra-violet light and the individual bacteria were sharply defined and stained at the periphery.

6. Micro-colonies of these and other bacteria stained with normal labelled serum, or heterologous labelled antiserum, showed either very dim fluorescence under ultra-violet light, with poor definition of in dividual bacteria, or no fluorescence at all.

7. The technique described permitted specific identification of Br. suis, Past. pestis and Past. tularensis within 20 hr. of inoculation of agar plates with material suspected of containing one of these organisms.

This investigation arose out of a line of work suggested by Dr G. S. Wilson. We should like to thank Dr D. W. Henderson and Major L. H. Kent for providing facilities for the work, Mr E. O. Powell for continual encouragement and supervision of the microscopy, Dr D. W. Henderson, Dr M. C. Lancaster and Dr D. A. L. Davies for supplying antisera, and Mr T. W. Pearce for valuable technical assistance and the photographs.

One of the major difficulties in determining the cleanliness of blankets for use in hospital wards is the estimation of bacterial contamination remaining on the blanket after washing. Present procedures are either cumbersome or not readily reproducible. Procedures for measuring bacterial contamination on fabrics may be based on dispersion of the bacteria as an aqueous or as an airborne cloud. As aerial sampling has the advantages that it may be rapid and simple and can be used to sample blankets which have been washed with a bactericide the possibilities of this principle were investigated. A simple method has been developed (Blowers & Wallace, 1955) in which the blanket is scraped manually by the edge of an agar plate so that the bacterial dust is thrown on to the exposed agar surface, but this procedure is difficult to control. There are wide differences in surface properties of blankets, and consequently in the amount of fibrous material shaved off by the Petri dishes. Puck, Robertson, Wise, Loosli & Lemon (1946) worked on the principle of hitting an area of taut blanket and sampling the aerial cloud so formed, but as their apparatus was not convenient for routine sampling in wards an improved version has been developed.

Part I

1. The following disinfectants were investigated for use in bar-soaps: Hexachlorophene (G11) (2:2′-dihydroxy-3:5:6:3′5′:6:′-hexachlorodiphenylmethane); Actamer (2:2′-thiobis, 4-6-dichlorophenol); DCMX (dichloro-m-xylenol); TMTD (3:4:5-tetramethyl thiuram disulphide); TCC (3:4:4′-trichlorcarbanilide); TBS (3:4′:5-tribromsalicylanilide) and TCS (3:3′:4′:5-tetrachlorsalicylanilide).

2. The concentration required for bacteriostasis of Staph. aureus was 2·5 p.p.m. for DCMX and 0·1 p.p.m. for TCS, the other disinfectants falling between these values. None were effective against E. coli, 12·5–50 p.p.m. being required for bacteriostasis (Tabel 1).

3. In the presence of serum the concentration required for bacteriostasis was increased (Table 4).

4. The soap inactivation coefficient (S.I.C.) is a value derived from zone diffusion tests. Zone diameters of the same disinfectant are compared in soap and soap-free solution so that the S.I.C. measures the effect of soap on disinfectant activity.

5. DCMX is inactivated by soap (S.I.C. = ∞). The activity of G 11 is much reduced by soap (S.I.C. = 200). Actamer and TMTD are active in soap, whereas TCC, TBS and particularly TCS is more active in soap than soap-free solution (S.I.C. = 0·32) (Table 3).

6. Another test based on zone diffusion is described which measures the effect of soap-soluble skin substances on disinfectant activity. Zone diameters of the same disinfectant are compared in fresh soap and used soap solutions.

7. Of the disinfectants tested only TMTD lost some of its activity in the presence of soap-soluble skin substances (Table 5).

Part II

8. Conventional bacteriological plate-counting technique was used to enumerate bacteria in wash-water. The bacteria were removed from hands by using a standardized washing procedure with bar-soap but without scrubbing.

9. Bacteria were not removed uniformly when washing was carried out twelve times in succession, significantly more bacteria being removed at the beginning of of the washing procedure.

10. When the same individuals were tested at weekly intervals the rate at which bacteria were removed in successive washes was found to vary significantly.

11. Using a single standardized wash the variation in the count of twenty individuals was followed for a period of 16 months. The count from one individual could vary by a factor of 10.

12. A design for a handwashing test, to take account of these variables is described. The bacterial counts of the wash-water when subjects used control soap for 1 week was compared with counts obtained from subjects using disinfectant soap. Subjects and soaps were randomized according to multiple Latin squares.

13. This handwashing technique was used to test the disinfectants described in Part I of this paper. All these disinfectants were effective but tetrachlorsalycilanilide (TCS) was the best. Soap containing 0·5% TCS caused an 84% reduction (Table 9).

The authors wish to thank Dr H. Wilkinson for the ideas he contributed and the interest he has shown in this work, and the Directors of Unilever Limited for permission to publish this paper.

Experiments performed on spore formation in B. anthracis, in a wide range of closed atmospheres of chemically controlled humidity, showed that the sporing time of B. anthracis is prolonged considerably as the humidity decreases, both at 26 and 37° C. The effect is less noticeable at the lower temperature.

Experiments performed on spore germination in the same organism showed that a temperature range of 20–44° C. permitted germination of the five strains tested. Above a temperature of 39° C. and below 30° C. germination time lengthened considerably.

Experiments performed on the influence of humidity on spore germination, both at 26 and 37° C. showed that no germination could take place at a relative humidity of 80% or below. Germination time was considerably prolonged when the humidity value fell below 100%.

This work formed part of a thesis for the degree of M.D. in Bristol University. I wish to thank Dr G. S. Wilson for his advice in preparing this paper.

Immunization experiments in guinea-pigs with high egg passage Flury virus gave the following results:

1. Intracerebral inoculation of the vaccine protects against subsequent intracerebral or peripheral challenge with fixed virus.

2. Intramuscular administration results in the development of a good immunity status to peripheral challenge.

3. Intramuscular or intravenous inoculation of the vaccine fails to protect against intracerebral challenge.

Polluted water from a stream caused three cases of infection with Salm. paratyphi B belonging to two phage-types. These phage-types and two others were isolated from the water.

One woman, aged 81, with a history of enteric fever 20 years previously was discovered to be a prolific carrier of at least three of these phage-types, and to be the source of the pollution.

We are greatly indebted to Mr G. K. Anderson, County Sanitary Inspector, Midlothian, and to his staff for the large volume of field work they carried out; to Dr E. S. Anderson and Dr A. Bernstein, Central Enteric Reference Laboratory and Bureau, Colindale, London for the phage-typing on which this survey is based; and to Mr James Sutherland, F.I.M.L.T., for his enthusiastic technical assistance.

A carrier has been found of at least three phage types of Salmonella paratyphi B. Investigation has shown that phage-mediated conversion could account for this multiplicity of types according to the following scheme.

It is not possible, however, to exclude the actual occurrence of repeated infection with different phage types.

I am grateful to Dr E. S. Anderson of the Central Enteric Reference Laboratory, Colindale, for his interest and advice during the course of this investigation, and to Dr Helen A. Wright of the University of Edinburgh who provided the many cultures and so introduced me to this problem.

The serological properties of the two strains of Trichomonas foetus (strain B and strain M) isolated from uterine infections in cows in Belfast and in northern England, respectively, and two strains isolated from the caecum of pigs were in vestigated with rabbit antisera to each of the four strains by direct agglutination and by precipitation of a saline extract of the dired organisms in tubes and in gel-diffusion plates.

There was considerable cross-reaction between the four strains. By the use of predominantly polysaccharide fractions from strains B and M and the predominantly protein fraction TF 4 from stratin B, the polysaccharide complex of lines could be distinguished from the protein lines.

The major protein antigens were common to all four strains, but the major polysaccharide antigens were only partially shared.

The cow strains B and M were readily distinguished from each other but had a variable though slight serological relationship. The two pig strains were very closely related to each other but were not identical. Cross-reaction revealed a relation between the cow and the pig strains. The cow strain B was more closely related than the M strain to the pig strains.

The serological distinctions do not justify the separation of the pig and the cow strains of T. foetus into two species.

I wish to thank Prof. W. T. J. Morgan, F.R.S. for preparations of diethylene glycol extracts and kind advice and Dr Winifred Watkins for ethanol fractionation of antigen and for enzyme preparations. I am also grateful to Dr A. E. Pierce of the Institute of Animal Physiology at Babraham for the isolation of clones from the S2 strain.

1. ‘Resistant’ and ‘susceptible’ species of animals appear to be more or less equally susceptible to lung infection with equal doses of tubercle bacilli. Therefore it is pertinent to ask whether recognized natural differences in species resistant are in fact significant. For example, in terms of death rates (i.e. of overall resistance) the C57 mouse is at least as susceptible to tuberculosis as the guinea-pig and much more so than man.

2. Resistant, moderately susceptible and susceptible strains of mice as determined by death rates when exposed to large infecting doses, were equally susceptible to intranasal infection with small numbers of tubercle bacilli.

3. A state of tolerance of the parasite by the host lasting for about 3 weeks was observed in all mouse strains, regardless of ultimate strain resistance.

4. Pre-allergic deaths commenced in all groups when the tuberculous processes left insufficient normal lung to support life, but the deaths stopped first in the resistant strain and last in the susceptible strain, coinciding approximately in each strain with the onset of allergy.

5. Acquired immunity, once established, appeared not to vary in quality from one mouse strain to another, at least during 3 months' observation.

6. Racial or strain variations in the resistance of mice to tuberculosis are therefore natural, only in the sense that speed of onset of acquired immunity is probably genetically determined for each strain.

7. It is suggested that both species and racial variations in natural resistance to pulmonary infection are insignificant. Differences in the subsequent course of the disease appear to be explainable by the rapidity, efficiency and duration of the acquired immune response.

An outbreak of Salmonella typhimurium infection in a large general hospital is described. The outbreak was spread over some 20 weeks and gave rise to 102 cases of enteritis and there were at least 150 symptomless excreters of the organism.

Evidence is presented to support the view that the method of spread was by cross-infection, not by contamination of food in bulk. Control measures, which ultimately brought the outbreak to an end, were instituted on this basis.

We wish to thank Dr A. J. H. Tomlinson and his staff at the Public Health Laboratory, County HallS.E. 1 for the generous assistance they gave us in examining all the specimens from the hospital staff during the outbreak. The resources of the Department of Bacteriology of the Postgraduate Medical School were at that time largely devoted to teaching and adequate investigations could not have been made without this help. Dr Tomlinson also gave us much advice both during and after the outbreak for which we are most grateful.

Dr E. S. Anderson, Director of the Central Enteric Reference Laboratory and Bureau, Colindale, London, N.W. 9, very kindly undertook the phage-typing of many of the strains of Salmonella typhimurium isolated and we wish to express our thanks to him for this and other help he gave us in the investigation of the outbreak.

Our thanks are also due to Dr Joan Taylor, Director of the Salmonella Reference Laboratory, Colindale, for her help and interest.

Discussions with Dr R. M. Fry and Dr Joan Boissard in Cambridge in connexion with their investigations of a similar outbreak were most interesting and valuable and it gives us pleasure to thank them.

We also acknowledge gratefully the help and co-operation of our colleagues at Hammersmith Hospital, especially Dr C. E. Roberts, the Medical Superintendent, and of those at the Postgraduate Medical School.

A total of 849 samples of pig sera were tested for antibodies to L. canicola, L. icterohaemorrhagiae, L. pomona, L. ballum, L. sejroe, L. grippotyphosa, L. hyos (mitis Johnson), and L. bataviae. Positive results were obtained in 57 samples to all but the last three serotypes.

I wish to thank Mr J. Norval of Edinburgh and Mr W. R. P. Hildebrand of Belfast for supplying the sera and Dr A. Wilson Taylor for his interest and supervision.

I am greatly indebted to the late Dr J. C. Broom of the Wellcome Laboratories of Tropical Medicine for the supply of leptospira.

1. Many immunologically related components occur in bovine serum and colostrum, but certain components in each are absent in the other (specific components). Two components (or groups) occur in colostrum which do not appear in serum, and these can be associated with electrophoretically slow and fast colostrum components.

2. Pre-colostral and adult urines contain low concentrations (<0·2 g./ 100 ml.) of protein which, though immunologically related to serum proteins, does not closely resemble any major serum component in physical properties.

3. Urines collected during the period of proteinuria contain increased concentrations of protein (up to 2 g./ 100 ml.) which is immunologically related to both serum and colostrum. From the presence of material related to specific colostrum components (and the absence of specific serum components), the added protein evidently originates from colostrum rather than serum. The total added protein possesses components with electrophoretic mobilities covering a wide range, with appreciable protein faster than albumin at pH 8. From sedimentation studies, the added proteins resemble the slower sedimenting colostrum proteins (β-lactoglobulin and lactalbumin) and contain no observable material with the sedimentation behaviour of immune lactoglobulin.

4. Immunologically, the added protein is related only to the electrophoretically faster of the specific colostrum components, and this applies also to post-colostral lymph in spite of its very high content of immune lactoglobulin. It follows that the specific electrophoretically slower colostrum components represent only a small proportion of the total immune lactoglobulin fraction.

5. The presence in urine, collected during the period of proteinuria, of antibody activity (deriving originally from the calf's mother), and of protein with the approximate electrophoretic mobility of, but without the sedimentation behaviour of γ-globulin, is to be explained probably on the basis of molecular degradation at some stage between absorption from the intestine and excretion in the urine.

6. The low molecular weight colostrum components, though present in low concentration in the lymph, are absent or below the detectable threshold in post-colostral sera (containing much material derived from immune lactoglobulin), and this is thought to be partly due to selective action by the kidney, allowing the passage of, and causing concentration of low molecular weight protein in the urine, whilst retaining higher molecular weight protein in the serum.

7. The results show that the proteinuria of the new-born calf arose mainly from low molecular weight protein in the colostrum which was absorbed from the gut together with the immune lactoglobulin. Owing to the small molecular weight, this, the former protein, was subsequently cleared from the circulation probably by glomerular filtration, accounting for the difficulty of detecting them electrophoretically and ultracentrifugally. On the other hand, the immune lactoglobulin with its much higher molecular weight was not so cleared from the circulation and is readily detected there.

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