The survival rate of mice actively or passively immunized against intracerebral challenge with Bordetella pertussis, was independent of the size of challenge dose within the range of 20–2000 LD.

This unexpected result appears to be due to the anatomical peculiarities of the infected organ, in which circulating antibody does not pass the normal blood-brain barrier easily. The pertussis infection does not cause sufficient inflammation to induce a pathological increase in the permeability of the barrier until the number of living microbes in the brain reaches 10 to 10. Since this stage in the brain consistently occurs after 4–5 days, independently of the size of the inoculum within the range 20–2000 LD, the outcome of infection in the immunized animal depends solely on the degree of specific immunity.

In the non-immune mouse, the increase in permeability of the barrier persists until death. In the immunized mouse, the elimination of the infection leads to a restoration of the normal barrier at about the 6th day.

1. Wistar-albino rats showed no significant difference from albino mice in their response to pulmonary tuberculosis. This conclusion was reached after a detailed comparison of bacillary multiplication, lung involvement, death rates and the rate of conversion to the immune state as determined by footpad reaction to tuberculin in the two species.

2. These findings support the theory that the key to species differences in resistance to tuberculosis is the rate of onset of acquired immunity and it is therefore unrelated to natural resistance.

1. In one Australian study area where the selection pressure of annual epizootics of myxomatosis has been extremely high, the innate resistance of the rabbits was found to have increased to such an extent that only 26% died when inoculated with a strain of myxoma virus which kills 88% of genetically unselected rabbits.

2. The level of innate resistance in a rabbit population varies with the total experience of the disease.

3. In combined field and laboratory trials it was shown that the mortality rate in the field is influenced by innate resistance at least as much as under the sheltered conditions of an animal house. The effect was apparent with both an attenuated and a highly virulent strain of virus.

4. The moderately high ambient temperatures during the field experiments probably contributed to the sparing effect.

The method of multi-regression analysis as applied to data which are classified in a non-metric manner is discussed, and a set of data relating the risk of post-operation sepsis to various factors is analysed in this way.

Age over 60, male sex, long duration of operation, incision over 6 in. long and the insertion of a drain in the wound are all found to be associated with increased risk of post-operative sepsis. Operations for appendicectomy and those on the gall bladder have a relatively high basic risk of developing sepsis while operations for gastrectomy or those on the thyroid, and probably thoracic operations, have a low basic risk. The substantial differences in the gross risk of post-operative sepsis associated with the operations performed in the different hospitals included in the analysis are shown to be almost entirely accounted for by differences in the operations performed in them.

1. The incidence of infectious hepatitis calculated from official notifications fluctuated between 5·7 and 11·4 per 10,000 during the years 1949–57, while reports of the Workers' Sick Fund indicated a rate three to four times greater. The highest rates were between the ages 1 and 9, two-thirds of the cases being under 10. Mortality was very low.

2. Highest attack rates were seen under conditions of crowding, i.e. in agricultural schools, communal settlements and new immigrant towns. This fact, together with the winter peak of incidence, suggests a contact-respiratory form of spread.

3. Immigrants, regardless of country, showed particular susceptibility during their first year or two in Israel. In the long run there was no difference in attack rate between immigrants from Western and from Middle Eastern countries, in spite of the known endemicity of the disease in the Middle East. In communities such as those from Yemen and North Africa, with large families and with, on the whole, a lower economic status, the mean age at onset was significantly younger. Among the non-Jewish population, the incidence was lower than expected due partly to under-reporting and partly, perhaps, to a mild form of the disease in the very young.

Airborne virus particles of vaccinia, influenza, Venezuelan equine encephalomyelitis, and poliomyelitis have been tested for viable survival in the dark at controlled temperatures and relative humidity (R.H.) for up to 23 hr. after spraying.

Viable survival at each R.H. level was better at lower temperature than at higher temperature. Poliomyelitis virus showed best survival at high R.H.; the other three viruses survived best at low R.H.

Three tubular electrostatic precipitators are described for the assay of bacterial and bacteriophage aerosols. Particles can be sampled directly on agar or on agar-impregnated paper in a wide range of aerosol concentrations, or sampled into a fluid for the assay of airborne micro-organisms. Rapid consecutive sampling is possible with the samplers and a collection efficiency approaching 100% is readily obtained. Their sampling efficiency is compared with that of the slit sampler and the liquid impinger.

The infectivity of Pasteurella tularensis clouds decreases with age, for guineapigs challenged by the peritoneal and respiratory routes. No decrease occurs in mice challenged peritoneally. The loss of infectivity depends to some extent on age of culture but more especially on culture medium used. Cultures grown in a partially hydrolysed casein medium and aged 2–3 weeks lose infectivity severely in clouds held 20 hr. at 85% r.h., whereas if grown in cysteine broth with catalase (CBC) no loss occurs in this time until cultures are aged several months. Chloride ion, yeast extract and casein hydrolysate are shown to be infectivity depressors when used in culture media or when added to suspensions before spraying. Sodium chloride in CBC can be replaced adequately by sodium sulphate or sodium phosphate for growth of the organism.

The literature on the dissemination of helminth ova by flies is reviewed. In experiments using various species of filth flies, it was shown that ova of Taenia saginata Goeze 1782 can be passed out for periods of up to 11 days after ingestion, and viability of such ova was demonstrated for three days after ingestion. The possible methods of dissemination of ova are discussed together with the longevity of ova on pasture and the dispersal habits of flies. It is suggested that in Kenya, filth flies may play an important role in the epizootiology of bovine cysticercosis.