During the period 1951–58, a study has been carried out of a series of seventeen families in which more than one member developed a staphylococcal lesion.

In eleven of these families, phage typing revealed that spread of infection from person to person had occurred. Once introduced into a household, the staphylococcus demonstrated great persistence; a particular strain could cause recurrent lesions in different members for as long as 6 years. The interval between the first and subsequent infection in another member of the same family was most irregular, but was usually 2–11 months.

The patient with recurrent furunculosis appeared to be mainly responsible for dissemination of strains.

In six out of the seventeen families, although multiple infections were encountered in the household, these were not due to case-to-case spread because more than one phage type of staphylococcus was isolated.

In one family investigated, there had been a dissemination of a hospital-acquired staphylococcus to another member of the household.

No infections were encountered in which the ‘epidemic strain’ 80/81 was responsible.

I wish to express my gratitude to Dr R. E. O. Williams of the Staphylococcal Reference Laboratory, Colindale, for his assistance in this work.

An investigation has been carried out over a period of 7 years of a series of eighty-one patients who first presented in 1951–52 with staphylococcal lesions. In seventy-two oases (89%) the infection was limited to a single, short episode of infection without recurrence. But nine patients (11%) developed recurrent lesions throughout the period. In these patients, from a comparison of the phage types isolated from successive infections, it was inferred that the organism had persisted in the body for over 6 years in two cases, for 4–5 years in five cases and for 1·3 years in three cases.

Nasal carriage also persisted for over 6 years in two cases and for 3–5 years in three cases.

In two cases, chronic skin carriage occurred in the absence of nasal carriage. There was persistence of staphylococci for 3 and 5 years in these cases, and the use of a special technique revealed that carriage in the deeper layers of the skin was particularly important.

The frequency distribution of phage patterns isolated in recurrent cases reflected the high incidence of Group II strains at the time when the strains were first acquired. New infections which arose in 1957–58 no longer showed this preponderance of Group II strains, as only eleven (28%) of thirty-eight new infections were caused by this group.

The bacteriological examinations were mostly carried out by the Central Public Health Laboratory, Colindale, and I wish to express my gratitude to Dr R. E. O. Williams of the Staphylococcal Reference Laboratory, for his assistance in this work. I am also grateful for the laboratory facilities afforded me by Dr Ridley at the Hospital for Tropical Diseases for the performance of the skin carriage testing.

1. Before undertaking a bacteriological survey of the waters of the Hooghly River and the associated canals a detailed epidemiological study over the past 20 years of cholera, as it affected the individual administrative wards of Calcutta, was undertaken. Sampling points were selected in accordance with the results of this study. Samples of water from the various points were collected at intervals extending from December 1958 to August 1959 in 2½–5 l. amounts. The whole sample in each case was filtered through special filter pads. The pads were first cultured in an enrichment medium from which plate cultures were subsequently made for colony isolation, serological and biochemical examination.

2. The sampling points on the canals were all adjacent to areas where the local endemicity was judged to be high; other points were by bathing ghats, etc. A total of eighty-nine samples covering all the sampling points were examined and Vibrio cholerae were isolated from twelve of these samples, eight of which came from twenty-six samples collected from two sampling points on the Chetla and Circular Canals, respectively.

3. The positive isolations were spread fairly evenly over the whole period of the study which covered both epidemic and non-epidemic periods including the monsoon. Although the incidence of cholera in Calcutta may fall to a low level during non-epidemic periods cases continue to occur throughout the year and the relationship of the maintenance of the infection in the city to the continuous potential infectivity of the open natural waters of Calcutta is discussed.

1. Heat labile and heat stable inactivating factors against T-system phages are present in normal guinea-pig and rabbit sera. These may be antibodies.

2. Sera of guinea-pigs immunized with phages T2, T3 and T4 contain heat labile and heat stable antibodies.

3. The heat labile activity is absorbed from guinea-pig serum by phage more readily than the heat stable activity.

4. Dilution of the sera reduces the heat labile activity more than the heat stable activity.

5. Complement has no effect on the inactivation or neutralization of phages T2, T3 and T4 by normal or immune guinea-pig sera.

The development of the molluscum body and of the molluscum contagiosum virus is described. All cells of the molluscum lesion do not form molluscum bodies, but those which do probably show cytoplasmic abnormality prior to the appearance of virus particles within the cytoplasm. Such abnormal cells may reflect the activity of some infective precursor of the morphologically observable virus particle; they may alternatively represent cells which have successfully resisted invasion by the infective precursor.

Cells which have failed to resist invasion gradually become filled with virus particles and the nucleus becomes eccentric. The molluscum body thus formed is virtually a bag of virus particles, the wall of the bag being the peripheral cytoplasm, which seems to resist invasion and in which the nucleus remnant can readily be detected.

There appear to be two kinds of viruses. Development of the commoner virus is compared and contrasted with studies by Morgan and his colleagues of vaccinia and fowl pox. It is akin to fowl pox in its origin from foci of finely dispersed cytoplasm, here called cytoplasmic clouds; it is akin to vaccinia in that no evidence can be found of a denser, finely granular, pre-nucleoid material; it is like both in that the virus does not observably develop within the nucleus; and it is unlike both in that a nuclear change—the appearance of rather unspecific dense bodies—is seen. The structural changes seen in the virus particles during development are similar to those described by Morgan et al., but a slightly different interpretation is given of the behaviour of the transient ‘nucleoid’: they believe that it expands to form a central viroplasm, whereas in this paper it is believed to disperse through an already present central viroplasm.

The second type of virus is of uncertain origin. It may develop from, or at least it seems to be related to, a double-membrane structure seen in abnormal lesion cells.

The antigenic structure of Bordetella pertussis varies continuously with environmental conditions of growth and, under suitable conditions, any of three forms (or modes) with markedly different antigenic surfaces may be developed. High temperatures and certain ions, such as sodium, potassium, halides, formate and nitrate, favour growth like that on Bordet and Gengou's medium at 35° C. Low temperatures and other ions, such as magnesium, sulphate and mono- and dicarboxylic acids with more than two carbon atoms, favour growth with a markedly different antigenic structure and character. These two extreme forms have been called X mode and C mode respectively. A third mode (called I mode) is induced within a narrow range of intermediate temperatures and ion ratios. Bacterial cells in C mode, unlike those in X mode, do not agglutinate red-blood cells, are not haemolytic or agglutinable by heavy metal salts, have no surface antigen related to Bordetella parapertussis or B. bronchiseptica and are serotypically homogeneous.

The influence of ions is a function of their species and ratios and not of their absolute concentrations or total ionic strength. A number of ions has been arranged in a pattern. In this the influence of any salt is represented at the centre of a line joining its component ions, and a measure of the influence of any salt mixture is given by the position of its imaginary centre of inertia. (For calculating this, mass is represented by the product of salt concentration and conductance ratio and radius of gyration by distance.) The influences of ions and temperature appear not to interact since their combined influence is proportional to the sum of their separate influences.

The change from one mode to another (modulation) occurs without mutation or selection, is complete within 7–15 cell divisions and appears to stem from altered rates of synthesis of at least three kinds of antigen molecule. During the process of modulation, antigens not detectable by agglutination in any of the three equilibrium modes (X, I and C) may appear transiently at the surface.

Mutants may or may not modulate. Modulatable mutants may be distinguishable from the wild type in only one mode. Almost all convalescent antibodies are directed against X mode, but C-mode antibodies have been found in several adults with persistent cough and infection.

I wish particularly to thank Dr E. K. Andersen for her generous gifts of sera, Drs P. L. Kendrick, H. Proom, A. F. B. Standfast and A. J. H. Tomlinson for gifts of cultures and Mr M. Breach for his invaluable help in the preparation of media and sera. I am also indebted to the University of London Central Research Fund and the Governors of Westminster Hospital for grants towards the purchase of materials.

Various explanations have been proposed to account for the increased incidence of moniliasis as a result of ‘broad spectrum’ antibiotic therapy, but it is generally believed that the suppression of the bacterial flora enables fungi to proliferate without competition. The pathogenicity of Candida albicans is, in any event, associated with the numbers of cells present and we have undertaken tests in vitro in an attempt to contribute more evidence on the mechanism of their proliferation in the presence of tetracycline-treated bacterial flora. The results are presented here as a preliminary communication.

1. By inoculating conjunctival scrapings into the chick embryo yolk-sac trachoma virus was isolated from twenty-four of thirty patients, whereas inclusions were demonstrated in only eighteen of them.

2. Bacterial contamination of the chick embryos can be greatly reduced by treating the scrapings with streptomycin 20,000 μg./ml.

3. In twenty-four of twenty-five isolations, virus was first detected in embryos inoculated directly with conjunctival material.

4. The viruses usually kill the chick embryos, which may show haemorrhagic lesions, but it is not unusual for embryos to survive a large inoculum.

5. The viruses isolated all appear in the chick embryo yolk sac as elementary bodies similar to other members of the psittacosis-lymphogranuloma group. Of the twenty-four strains, two also induced the formation of compact aggregates of elementary bodies containing a carbohydrate, probably glycogen.

6. It is anticipated that this method of isolation will be useful in studying the virology and epidemiology of trachoma, in assessing the influence of treatment, and as a test of cure.

We are deeply indebted to Dr I. A. McGregor for all the facilities made available to us at the M.R.C. Laboratories in the Gambia. Our thanks are also due to the medical officers and sisters at the research ward for their kindness and unfailing co-operation in the care of those trachomatous patients who had to be hospitalized. The excellent technical assistance of Miss A. M. Fischer is gratefully acknowledged.

1. Faeces from rural, outwardly healthy Bantu school children from a Native Reserve region have been bacteriologically examined seven times at regular intervals over a period of one year.

2. Of 75 children, 44·0% experienced at least one salmonella infection and 29·3% one shigella infection; considering the infections together, salmonellae or shigellae were recovered from 72·0% of the individuals. The observations are discussed and the view is expressed that over a period of one year, practically all children experience one, and many of them several, attacks by these pathogens.

3. In the majority of cases, the infections appeared to be subclinical and of short duration. There was no evidence proving the existence of chronic carriers.

4. Salmonelloses showed a seasonal dependence with the highest incidence in early summer, i.e. December. Shigelloses was distributed evenly throughout the year.

5. The recovered salmonellae were of twenty types. Salm. typhi, Salm. paratyphi A, B and C were not isolated. Members of all shigella groups were encountered.

6. All the recovered strains from the Tlaseng area were sensitive to streptomycin, chioromycetin, terramycin, achromycin and neomycin, and most of them to aureomycin and erythromycin. In comparison, salmonella strains isolated from the Johannesburg urban area showed signs of increased resistance to the same antibiotics.

7. Water was probably implicated in the conveyance of the infections.

We should like to express our thanks to the Director of this Institute, Prof. E. H. Cluver, for permission to publish this paper; to Mr R. G. Robinson for assessing the micro-organisms' sensitivity/resistance to antibiotics; to Dr P. A. Christensen for statistical advice; and to Dr A. R. P. Walker (of the Human Biochemistry Research Unit, Council for Scientific and Industrial Research), who incurred the major portion of the expenses of transport by permitting us to accompany him during his investigation on bilharziasis and nutritional state in the Bantu school children.

A field experiment was conducted from July 1958 to February 1959 in the San Francisco Bay region to test the effect on flea populations of prolonged exposure of the native meadow vole, Microtus californicus, to 5% DDT powder in insecticide-bait-boxes. Previous studies had shown that two important vectors of sylvatic plague, Malaraeus telchinum and Hystrichopsylla linsdalei, could be controlled both on their hosts and in the host nests by this method. However, the question of possible resistance was postulated since the control of H. linsdalei on its host was inferior to control of other flea species.

Bait-boxes with DDT powder were maintained in the field for 6 months. Records of flea populations on Microtus during this period showed equally good control of all flea species. Observations on vole nests at termination of the study revealed deposits of DDT and good control of all flea species in them. During the period of study, the evidence suggested that none of the flea species involved exhibited DDT resistance.

The major portion of the field routine was done by Messrs A. R. Kinney and R. L. Martin. Flea identifications were made by Mr H. E. Stark. Analyses of nests and rodents for DDT were performed by Mr C. Cueto, Technical Development Laboratories, CDC, Savannah, Georgia.