1. Cultures of tubercle bacilli were obtained from 204 cases of lupus.

2. According to their cultural characters the strains could be divided into two main groups, one containing 102 strains with the characters of human tubercle bacilli and the other containing 102 strains with the characters of bovine tubercle bacilli.

3. Virulence tests were carried out on a large number of animals, and in one instance over 100 animals were used for testing strains from a particular case.

4. Of the 102 culturally human strains 41 were highly virulent for the guineapig, and for the monkey when this was tested, producing progressive and rapidly fatal tuberculosis. The remaining 61 strains (59.8%) showed varying degrees of attenuation.

5. Of the 102 culturally bovine strains 34 were highly virulent for all the animals tested, producing in them severe and rapidly fatal general tuberculosis identical with that set up by standard bovine bacilli. The remaining 68 (66.7%) were of lower virulence for the rabbit, and for the calf and goat when these animals were tested, than standard bovine strains, but they all produced in one, two, or three of these species more extensive tuberculosis than human bacilli. For the guineapig, and for the monkey when tested, these strains fell below the virulence of standard bovine strains, except for a few whose virulence was only slightly lowered for the rabbit.

The relationship of Esch. coli 0.26, 0.55 and 0.111 to the incidence and spread of infantile gastro-enteritis in a defined area has been studied over a period of 5 years in the Public Health Laboratory, Southampton.

In the main, the study was concerned with infants up to 1 year of age suffering from gastro-enteritis, and from this age group faecal specimens from 1234 individuals were examined for three sero-types of Esch. coli (0.55 and 0.111 from the autumn of 1949 until September 1954 and 0.26 from May 1953 until September 1954). Esch. coli O.111 was isolated from 66 infants of whom 56 had enteritis, type 0.55 from 159 infants of whom 126 had acute symptoms, and type 0.26 from 14 infants all but two of whom had enteritis.

During widespread outbreaks there were sometimes multiple foci of infection. The determination of the H-antigen carried by the O sero-types showed, for instance, that the 0.55 outbreak in 1952 was almost entirely due to subtype 0.55 H.2, but that a second subtype 0.55 H.7 was also incriminated. Similarly, an 0.111 outbreak in 1953 was due to a mixture of two subtypes (0.111 H. 2 and 0.111 H. 12), but in 1954 the former subtype was not seen and only O. 111 H. 12 was identified.

During epidemic times Esch. coli 0.55 was isolated from 37·2% of the infants examined, whereas in non-epidemic periods the figure was only 1·2%. In the case of type 0.111 the figureswere 26·9 and 1·4% respectively.

Symptomless excreters were found throughout the period of the study and at all ages, but the proportion as compared with cases was significantly higher in children over 1 year of age. Nevertheless, there were several symptomless excreters less than 4 weeks old. While there was some evidence to suggest that the young child who was a symptomless excreter might be responsible for maintaining a low-grade infection in a community, there was no indication that the rare adult-carrier played any significant part in this.

The specific types of these coliform organisms can survive for long periods outside the body. Naturally infected dust contained viable organisms 12 days after it was first found to be so contaminated; the dust was maintained in a cool shady room.

There is great variety in the clinical severity of the disease as seen in comparable groups of infants, from a very grave illness to the very mildest of diarrhoeas. The very young and those with some other complicating illness are always at a greater risk.

The pattern of the outbreaks as seen in this study suggests a gradual enhancement of virulence of the two main types of Esch. coli with local spread at first and then wide dispersal throughout the district followed by a reversion to the poorly invasive type.

The mouse-protection test is discussed as a routine procedure. It has been shown that the assay is exceptionally subject to variation and that an average slope of 1·47 has been found over a year. With this slope and tests involving 90–180 mice it is possible tobe reasonably sure that a vaccine actually 3 times as potent as needed passes a test which lays down that the lower fiducial limit (P = 0·95) should exceed the specified requirement. For a vaccine only 1·5 times as potent as needed, much more extensive laboratory work would be necessary.

Four series of tests, A, B, C and D, have been considered in detail. In the first two series, to obtain the values of the ImD 50, percentages of survivors were transformed into probits, and the best-fitting straight lines connecting the probits with the logarithms of the doses were obtained by the method of maximum likelihood. This is the most accurate method to use. These results showed that the error of the test was large, but there were no significant differences in the slope of the probitlog dose relation in the results of tests from any one laboratory. The slope (1·46 ± 0·09) obtained from series A was greater than that from series B (0·79 ± 0·06). with a consequent increase in accuracy.

1. A survey has been made of the serum levels of immuno-conglutinin in apparently healthy persons.

2. The level of immuno-conglutinin is raised in infective diseases and in other diseases where an antigen-antibody interaction is incriminated in the aetiology.

3. The significance of immuno-conglutinin is discussed.

Experiments were performed which show that virulent strains of Salmonella paratyphi A contain an additional antigen which has all the properties of a Vi antigen.

The anti-Vi immune serum combined in suitable proportions with an anti-0 immune serum exerted maximal bactericidal effect on virulent strains.

An outbreak of encephalomyclitis of unknown actiology occurred in the Royal Free Hospital Teaching Group in 1955. The disease which affected about 9% of the population was probably a viral infection spread by personal contact. People of all ages were attacked but those under 30 were most susceptible. Institutional life was an important factor in determining the case incidence which was highest among nurses, orderlies and resident domestic staff. The clinical picture was one of encephalomyelopathy, with lympho-reticular reaction and relapsing myalgia.

A detailed investigation has been made of the pock-counting method for titrating vaccinia virus on embryonated eggs with a view to eliminating the wide scatter of results hitherto inseparable from the technique, and of assessing the precision of which it is capable. A detailed description is given of the technique evolved.

Reasons are given for supposing that the distribution of counts should follow the Poisson series, and considerable progress is claimed towards the achievement of such a distribution.

The duration of bacteraemia in guinea-pigs following the subcutaneous inoculation of brucellae can be used as a measure of the virulence of the strains. Strains of low virulence (e.g. Brucella abortus S19) are almost always cleared from the blood stream within a week, whereas virulent strains produce a bacteraemia that regularly persists for 4 weeks and may last very much longer.

All of four strains of Br. melitensis isolated from cow's milk in Great Britain behaved in the same way as the typical and virulent strains of Br. abortus and Br. melitensis tested, regularly producing prolonged bacteraemia. These results do not support the suggestion that the strains of Br. melitensis isolated in this country are of low virulence.