1. The efficiency of plating of phage 13 on the semi-resistant strain Ps. LIII-3bi decreases as the initial bacterial population on the plate is diminished. Addition of Ps. LII extract to the phage before plating with low bacterial concentrations increases the plating efficiency (exhibition effect).

2. An extract of a strain Ps. LIII-lb which is fully sensitive to phage 13 also causes exhibition of this phage on Ps. LIII-3bi.

3. It is suggested that dissolved phage 13 receptors present in extracts of Ps. LII and Ps. LIII-lb have an affinity not only for the phage but also for suitable bacteria and thus cause exhibition. Inhibition (e.g. of phage 14 by the Ps. LII extract) is due to phage receptors having no tendency to adsorb to bacteria.

4. The phage-exhibiting and inhibiting properties of a freeze-dried extract of Ps. LII active when dissolved in 0.85 % NaCl are lost if the solid is dissolved in water and the solution so obtained further diluted with 0.85 % NaCl. Activity is recovered slowly if NaCl is added to the aqueous solution, instantly if the solution is freeze-dried and the residue dissolved in 0.85 % NaCl.

5. The inhibitory properties of the Ps. LII extract for phage 14 are more sensitive to heat and acidity or alkalinity than the exhibitory properties for phage 13.

6. The absence of cross-precipitin reactions between Ps. LII and Ps. LUI-lb suggests that the phage 13 receptors of the two organisms are non-antigenic or different. I am grateful to Prof. M. van den Ende and my colleagues in this Unit for helpful discussions.

It is generally agreed that the administration of the 11–oxysteroid hormones of the adrenal cortex to the commonly used experimental animals, the rat and the rabbit, produces involution of lymphoid tissue. Since lymphoid tissue is an important site of formation of antibody, several workers have attempted to correlate the effects of adrenal steroids on lymphoid tissue with their effects on immunity. The effect of the 11–oxysteroid adrenal hormones on the immunity of experimental animals, as judged by the amount of circulating antitoxin present in the blood, is not, however, a matter of general agreement. Different workers have obtained widely diverse and conflicting results.

1. Myxomatosis was first recorded in England in October 1953 and persisted over the following winter. It was anticipated that an epizootic, similar to those in Australia, would develop during the spring or summer of 1954 and that mosquitoes might be the principal vectors. A study of the sylvan mosquitoes in the area of the first myxomatosis outbreak was therefore made, from April 1954 onwards.

2. These mosquitoes (Aëdes spp.) overwinter as larvae, pupate in early May and are adult from mid-May to September. Throughout this period, in 1954, myxomatosis spread slowly in the study area and infected rabbits were abundant.

3. Despite the presence of large numbers of Aëdes (particularly A. cartans and A. annulipes) and their persistent attacks upon man, the mosquitoes (except in one case) were not attracted to healthy domestic rabbits exposed in the woods. Aëdes can have little, if any, part in the spread of myxomatosis. Observations made in the cool summer of 1954 were confirmed in the hot summer of 1955.

4. Engorged mosquitoes (apart from those which had just fed on the human collector) were never found, so precipitin tests could not be made. The source from which these woodland mosquitoes normally obtain their blood meals remains a mystery.

5. In the laboratory, the Aëdes were reluctant to feed on normal, healthy rabbits but fed readily (round the eyes and on the nose) on normal anaesthetized rabbits or comatose myxomatous rabbits. Biting experiments indicated that Aëdes may remain infective for up to 36 days after an infective blood meal.

6. Infected Aëdes were recovered from woods containing myxomatous rabbits, and tame rabbits infected by the bites of these mosquitoes developed myxomatous tumours on the nose. Although some Aëdes were thus feeding on wild myxomatous rabbits, the evidence that the mosquitoes did not feed on healthy rabbits indicates that Aëdes were of negligible importance as vectors of myxomatosis.

Evidence is presented that outbreaks of myxomatosis among domestic rabbits at Newhaven in Sussex were spread through the agency of Anopheles atroparvus. The habits of this insect are discussed in relation to its possible importance as a vector of myxomatosis.

Anopheles labranchiae atroparvus which have gorged on myxoma-infected rabbits may retain their infectivity for as long as 220 days in a period covering the winter months. Virus titres in infected mosquitoes may also remain stable for several weeks at summer temperatures; virus has been recovered after 36 days in summer.

Virus in these Anopheles is, in most instances, to be found only in the head and mouthparts. Survival on mouthparts of killed mosquitoes, on the other hand, has been only for a few days.

One strain of virus (Newhaven strain) isolated from wild A. atroparvus produces flat erythematous lesions on intradermal inoculation into rabbits, and deaths occur later than with typical strains.

The possible role of over-wintering atroparvus as a reservoir of infection of myxomatosis is discussed.

The possibility is considered that transmission of infection by Anopheles is not purely mechanical, but that limited multiplication occurs in the insects.

1. A new method for the preservation of bacteria by drying is described.

2. Marked differences between organisms were found with respect to the relationship between growth phase and recoveries after drying.

3. Recoveries of several strains of neisseriae and vibrios, both immediately after drying and after storage, were considerably higher than any previously recorded for similar species of these genera.

The main object of the experiment which this note describes was to determine whether influenza virus could be preserved by the ‘peptone-plug’ method of drying which has recently been found to be very effective for bacteria (Annear, 1956). Two other methods of preservation were also compared in parallel with it: (a) the centrifugal freeze-drying technique (Fry & Greaves, 1951) and (b) deep-freezing.

Air-borne bacteria collected from occupied schoolrooms and cultivated aerobically on serum agar yielded a mean count of' general bacterial flora' (principally various micrococci) of about 70 colonies/cu.ft. with a 95% range of 19–251 colonies/cu.ft. Of a number of other occupied places examined, none except busy public offices yielded as high an average count.

When the air samples were cultivated on a medium designed to suppress micrococci, a count of 1.0–1.5 colonies of streptococci/cu.ft. was observed. About 25 % of the streptococci were levan-producing Streptococcus salivarius.

An analysis was made of factors that might affect the number of bacteria found in the classroom air. The principal findings were that Str. salivarius was correlated with the amount of talking among the room occupants and that the general count was correlated with the ventilation rate and to a less extent with talking. Both counts were correlated less strongly with the general level of activity among the occupants.

In classrooms with ultra-violet irradiation, the numbers of Str. salivarius were reduced and the correlation with talking was less than in the unirradiated rooms, being little greater than the small correlation with activity.

It was concluded that most of the Str. salivarius in the air of the schoolrooms were derived directly from the upper respiratory tract of the occupants, and these seemed to be sensitive to ultra-violet irradiation. A smaller proportion were probably dispersed from secondary reservoirs and were less sensitive to the irradiation.

Most of the organisms comprised in the general bacterial flora were probably derived from such secondary reservoirs as clothing, but some, including the enterococci, were almost certainly derived from floor dust. We are greatly indebted to Mrs Eileen Woods for her help in the computations on which this paper is based.

An attempt has been made to assess the value of counts of bacteria in the air of occupied rooms as indices of the risks of air-borne cross-infection in these rooms. Data collected during a field trial of ultra-violet irradiation in schoolrooms have been analysed to establish the correlation between counts of Streptococcus salivarius or of the general flora and classroom secondary attack rates for measles and the incidence of four groups of respiratory affections. Variations in classroom environment and child age and behaviour were taken into account in the analysis.

The Str. salivarius count has been shown to be significantly related to the risk of classroom transfer of measles, but not to the incidence of respiratory disease. For the general flora counts the reverse was true.

A discussion of these results in the light of the effects of ultra-violet air disinfection on the incidence of presumably air-borne diseases leads to the conclusion that the Str. salivarius count may reasonably be taken as index of the risk of classroom transfer of measles, but that no such assumption is possible about the value of general flora counts in the measurement of air hygiene in relation to respiratory diseases.

An investigation in an urban area of south-east Kent of 160 patients who had had either pneumonia or unexplained fever during the period from the end of 1948 to the beginning of 1954 revealed that twenty-three (14%) had probably had Q fever.

A comparison of the epidemiological histories of patients who had had Q fever with those of the remainder showed that the use of a household supply of raw milk was commoner among the former.

Occupational exposure to animals (or animal products), visits to potentially infectious places, or residence near potential sources of infection were not significantly more frequent among the Q-fever cases as compared with the controls.

The isolation of Rickettsia burneti from the bulked milk of some local herds supplying retail dairies in the towns, together with the general epidemiological evidence, suggested that Q fever in the towns was predominantly milk-borne.

The epidemiology of Q fever in the residents of two rural areas, respectively, the Romney Marsh in Kent and Chatteris-Witchford rural districts in Cambridgeshire, has been studied.

In the Romney Marsh some 14 % of persons who had suffered from pneumonia or undiagnosed fever probably had Q fever. No cases of Q fever were detected in Chatteris-Witchford R.D.

Two sources of infection—sheep and infected cows' milk—were found in the Romney Marsh, and the infection of some of the cases of Q fever could be attributed to them. There was also a group of cases who were probably not infected from milk or by direct exposure to sheep. They may, however, have been indirectly infected from sheep.

The absence of Q fever in the Chatteris-Witchford area is of interest in view of the use of raw milk by a substantial proportion of the inhabitants of this area and also because of their contact with cattle. Investigation, however, failed to reveal any infection of the cattle with Rickettsia burneti.

Incomplete antibodies demonstrable by the Coombs antiglobulin technique were found in almost all guinea-pigs inoculated subcutaneously with Brucella abortus. They were detected between the 20th and 30th day after infection and reached a peak between the 50th and 70th day, at which time their titre was 4—8 times that of the ordinary agglutinins.

Paper electrophoresis of sera from infected guinea-pigs showed a great increase in y-globulin as infection developed. Smaller increases in α1- and β-globulin were observed.

1. Three strains of virus were isolated in suckling mice from the blood of three patients suffering from dengue during a local outbreak of the disease.

2. One strain was adapted to adult mice and identified as a dengue virus of type 1. The identification was confirmed by workers in America.

3. Evidence is presented that the other two strains of virus are similar to the one fully identified.

4. Attention is drawn to the need for detailed work to find a more sensitive method of isolation for dengue viruses.

Of 629 fresh fish (sixty-five species) and forty-two samples of fish-washings obtained from a fish-market in Colombo, and investigated bacteriologically for the presence of Salmonella, thirty-nine fish (twenty-four species) and five samples of washings were found to be harbouring the organisms.

Of fifteen salmonella types found, all except Salm. chittagong and Salm. oranienberg had been previously isolated from human and animal sources in Ceylon.

The presence of Salmonella in the intestines of fresh fish examined suggested that the organisms had entered the live fish, whilst their isolation from the gills and fish-washings was evidence that the fish could have been contaminated post-mortem.

The significance of these findings in relation to hazard to health is discussed.

The observations reported here show that the T Vi antigen is effective in stimulating antibodies when it is attached to the cells. It is also clear that the Vi antigen is readily removed in aqueous solutions, but in such organic solvents as acetone, chloroform, ether, alcohol, carbon tetrachloride and benzene it is retained by the cell. In alcohol-water mixtures the Vi antigen is progressively more soluble in those solutions where the alcohol concentration is less than 70 %. However, its solubility in water is limited, and by making progressively heavier suspensions it was found that a point is reached at which Vi antigen is retained by the cell, the suspending solution apparently being saturated. Such an aqueous suspension is able to stimulate the production of Vi antibody.

The administration of dried organisms in peanut oil resulted in the production of antibodies against both O and Vi antigens. This was in contradistinction to the results obtained when mineral oil, mineral oil + saline, or peanut oil + saline were used: in these cases the O antibody titre was lower and Vi antibodies were produced in low titre or not at all. It seems clear that the presence of water in the vaccine has the effect of removing the antigenicity of the Vi hapten; water-free, vegetable-oil vaccine is suggested by these studies as an effective agent for immunizing against all of the antigens of Salmonella typhi. The use of such a vaccine in producing active and passive immunity in animals is discussed in the paper which follows.

A method is described for the preparation of a vaccine, consisting of a suspension of bacterial cells in a vegetable oil, which retains the antigenic activity of both Vi and O antigens of S. typhi. The ability of such a vaccine to induce active and passive protection in mice is demonstrated.