Sera from two rabbits bled after one, two and three inoculations of concentrated type 1 poliovirus tissue culture fluid were assayed for neutralizing activity by a quantal and a plaque method. The plaque counts in these tests have been shown to approximate to a Poisson distribution as determined by the relationship between the variance and the mean of replicate counts. However, there is a considerable scatter of the points in such a comparison and this accounts for the absence of the expected increase in accuracy of this plaque method over the quantal.

The relationship between the antibody content of the sera determined by the two methods is non-linear. This can be attributed to inhomogeneity of the antibody produced which increases with the number of antigenic stimuli given.

The amount of virus in nasal and other secretions after infection with coxsackievirus A 21 has been measured daily in ten volunteers. Most virus was found in nasal secretion, less in throat secretion and small amounts were found intermittently in the saliva and faeces.

Virus administered as small drops or on a swab was more infectious for man if put on to the nasal mucosa than on to the throat or outside the nose. It was also infectious by the conjunctival route.

Virus was sprayed in droplets of about the same size range as those found in a natural sneeze. Virus survived better in larger (> 4 μ) than in smaller droplets. About one tissue culture infectious dose of virus in such droplets also infected volunteers.

The symptoms produced by these experimental infections have been analysed. The disease produced was largely independent of the dosage and route of infection. Those with pre-existing antibody resisted infection better than those with no antibody. Antibody rises were detected in about two-thirds of infected volunteers.

Volunteers with colds shed virus in large drops on sneezing, or into the handkerchief on blowing the nose, but virus was recovered from the air only after simulated sneezes by volunteers with high concentrations of virus in their nasal secretions. Virus died off rapidly on fabric at room temperature and humidity, and was only resuspended as airborne droplets when large doses such as 0·02 ml. of virus of high titre (107·5 TCD 50/ml.) were used.

Infection was transmitted from an infected volunteer to an uninfected partner living in the same flat in three out of twenty tests. Infection was not transmitted in experiments when volunteers mixed for a few hours with subjects with colds, or inhaled air into which a subject with a cold had just sneezed.

The protection afforded by a combined enteric and cholera vaccine administered by the intradermal route, and demonstrated by active and passive mouse protection tests and agglutination titres, is excellent and equal to that given individually by the component TAB and cholera vaccines.

In order to reduce the number of injections required and the unpleasant reactions provoked it is suggested that combined enteric and cholera vaccine administered by the intradermal route is of value, where appropriate, for the vaccination of travellers, and for the rapid protection of non-immune persons in the event of natural disasters or mobilization.

Foot-and-mouth disease virus of Type SAT 1 (strain Turkey 323/62) was passaged serially 34 times in cattle previously vaccinated with increasing doses of formol-treated vaccine of the homologous strain. Primary vesicles developed in all the partly immunized animals and secondary lesions occurred in the majority. Virus from the 34th passage was capable of reinfecting a steer only 76 days after primary infection early in the passage series. Virus isolated from the second infection of this animal differed from that isolated from the primary infection in complement-fixing properties and in sensitivity to antiserum, and these differences were of a degree indicative of subtype variation.

The variant strain was transmissible by contact, and virus titres in tongue and foot lesions of partly immunized animals were of the same order as those encountered in susceptible cattle.

These observations suggest one way in which variant strains may arise in the field.

A method of micro-titration for cytolytic antibodies is described. Standard drops of diluent are placed on a subdivided siliconed slide and dilutions are made by rotating a wire loop holding 1 drop of serum in each drop sequentially. One drop of a mixture of cells and complement is then added. The slide is incubated in a moist chamber for 90 min at 37° C. after which a small cover-slip is placed on each drop and the amount of cell lysis, judged by phase-contrast microscopy, is graded.

An analysis of variance of the method has been performed and the method has been found to be reliable, accurate and unbiased.

It allows accurate estimates of cytolytic activity in sera using cell concentrations of 104 to 105 cells per ml. Eight ten-dilution titrations can be carried out with 1 ml. of such a suspension.

A study was made of the ‘latent’ viral flora of simian tonsils. This was followed by isolation of viruses from two batches of sick monkeys whose illness is described. Simian viruses 15, 17 and 32 were isolated from nose and throat swabs obtained from the sick monkeys. A connexion between human and simian adenoviruses is suggested.

Sera from most of the Tristan da Cunha community were tested for toxoplasma antibody. In a comparison with sera from ‘normal’ inhabitants of South Wales there was a significantly higher incidence of dye tests positive at 1/16 or more in the Tristan community at all age groups. The incidence of retinitis was also found to be much higher than in Britain. It appears unlikely that toxoplasmosis caused any cases of mental defect or abortion on the Island.

Photoinactivation of vaccinia virus sensitized by methylene blue had parameters similar to those observed with other viruses. Thus inactivation proceeded exponentially to completion, was irreversible, independent of temperature and the intensity of illumination. Inactivation was dependent on the dose of illumination and the concentrations of both methylene blue and hydrogen ions. The effects of pH appeared to be primarily concerned with the tenacity of dye-virus binding. Inactivation was inhibited by small amounts of nucleic acid but not by their bases or pentoses. Inactivation was only affected by the presence of extraneous protein in relatively high concentration: it was not affected by the enzymes catalase or peroxidase. Attempts to obtain direct chemical evidence of the participation of viral nucleic acid in photoinactivation were unsuccessful.

Recombination experiments strongly indicated the involvement of viral protein in photoinactivation. Immunogenicity was not impaired since good responses of neutralizing antibody were obtained in rabbits immunized with vaccines photoinactivated over a wide range of exposure times.

The possible risks of infection associated with the practice of licking envelopes, stamps and labels were investigated. Although pathogenic bacteria and viruses were not isolated from sample envelopes obtained from various sources, the gums used in manufacture were found to exert a protective effect against death from desiccation on the bacteria and viruses which had been introduced into them. Staph. aureus and Salm. paratyphi B remained viable for several months in dried films of two out of four gums tested. An echovirus could be recovered from similar films for up to 30 days, and an adenovirus for up to 10 days.

Bacterial multiplication occurred in the gum used for the manufacture of postage stamps. The comparison is drawn between the possible consequences of minimal contamination of this gum and of cans of corned beef in the light of recent studies.

1. Residual populations of wild house mice (Mus musculus L.) were trapped alive in premises where poison treatments with 0·025% warfarin bait had been reported to be ineffective.

2. In the laboratory the individually caged mice were fed 0·025% warfarin in a sugar/oil/coarse oatmeal base. In toxicity tests lasting 10 and 21 days, the total mortality was low and the rate of death slow compared with mice drawn from habitats not treated with warfarin.

3. It is suggested that tolerance to warfarin in M. musculus either is polygenically based or is controlled by a single major gene influenced by modifiers and that these hard-to-kill populations have arisen through selection during successive control treatments.

An investigation has been made of the association between weather and the numbers of colds reported on a given day. The seasonal trends were eliminated by working with the differences between the observed values on any day and the expected values derived from smooth curves fitted to the averages for the time of year.

Examination of nine weather variables for the day on which the colds were reported and for each of the 29 preceding days showed that only two, mean day temperature and water-vapour pressure at 9 a.m., were significantly correlated with the numbers of colds. Partial correlation studies showed that the strongest association was with lowered mean day temperature between 2 and 4 days before the reported onset of symptoms.

Regression analysis demonstrated that the magnitudes of the associations were sufficient to account for the greater part of the seasonal variation in the incidence of the common cold in both London and Newcastle. A small effect of atmospheric pollution appeared in this analysis.

These results suggest that some effect of low outdoor temperature promotes transmission of the virus or the development of disease.