When staphylococcal strains from hospital patients are plotted in a frequency curve according to the size of the growth-free zone in a disk test for sensitivity to penicillin-G, this curve is trimodal. This implies that, besides the sensitive, there are two populations of resistant staphylococci: the moderately and the highly resistant, In a hospital-wide survey of coagulase or mannite positive staphylococci isolated in North Carolina Memorial Hospital between October 1964 and October 1965 it was inferred that: (1) there was a statistically highly significant difference between the distributions of the moderately and the highly resistant strains over duration of hospital stay prior to the time of isolation; (2) the highly resistant strains were seldom introduced from outside; and (3) there was no significant association between use of penicillin-G by a patient harbouring a strain and the frequency with which such a strain was found to be highly resistant to this drug. The latter finding is in contrast to significant associations found when the penicillin resistance is moderate, or when the drug used is other than penicillin-G. It is concluded that a fall in the incidence of staphylococcal strains highly resistant to penicillin-G in patients who did not receive other antibiotics may well be a valid index of the efficacy of programmes to control hospital infection. If so, there is a practical merit in adopting the routine of distinguisning between two groups of penicillin-resistant staphylococci, which behave, epidemiologically, as two distinct bacterial populations.

Mycoplasma pneumoniae is a common respiratory pathogen in the south of England. Of 1150 sera from normal people, 19% had antibody against this organism. Antibody was found with significantly greater frequency in patients with chronic bronchitis.

The growth of vaccinia and cowpox in RK13 cells was studied by measurement of infective virus production, gel diffusion and haemagglutination. The effects of virus growth inhibitors on the normal course of infection were then followed. Although the results with the two viruses were essentially similar some differences were detected between them. Inhibitors of DNA synthesis permitted production of many virus-specific soluble antigens. Compounds which inhibit DNA function and compounds that affected energy-yielding reactions had more dramatic effects. The different results obtained suggested that the synthesis of virus-specific materials was sequential and a possible part of the sequence is suggested.

Two groups of calves were dosed orally with 104, 105, and 106S. typhimurium at approximately 2 days of age and at 14–21 days of age. No obvious clinical signs were observed with this strain, but younger calves excreted the salmonellas in the faeces for longer periods than older animals. The younger animals also excreted more salmonellas per gram of faeces in the first week following dosing. These observations may explain why salmonella cross-infection is likely to occur where very young calves are congregated. Following cessation of excretion of salmonellas in the faeces and subsequent slaughter of calves, examination of all the mesenteric, caecal, and colic lymph nodes showed these to be the most useful sites for recovery of salmonellas.

Provided good nutrition and hygienic conditions prevail, calves retained on their farm of origin for longer periods are more likely to recover from neonatal salmonella infections.

Sheep, after infection with louping ill virus and after re-infection with the same strain of virus 19–21 months later, were bled at intervals and their sera examined for neutralizing and haemagglutinin-inhibiting antibodies. Each antibody type was measured by the constant serum/variable virus and constant virus/variable serum methods. The persistence of each type of antibody and its significance in epidemiological studies is discussed. The relationship of antibody levels in ewes and their lambs was also examined.

Visits have been made to thirty operating suites in the British Isles. Each suite was visited three times at approximately 4-month intervals and observations made on an average of five half-day working sessions on each occasion. Measurements were made of air temperature, humidity, air movement and radiation temperature and many details of the suites and working conditions recorded. At suitable intervals the operating room staff were questioned as to their feelings of thermal comfort using Bedford's 7-point scale. Over 2500 sets of replies were obtained. Visible sweating was also noted.

The effect on comfort and the extent of visible sweating of the many items recorded was then explored by means of a sequential multiple regression analysis. Although air temperature was by far the most important factor affecting thermal comfort, all the variables named above exerted a significant effect. In addition, a number of other conditions including age, sex and race produced minor differences.

Surgeons and anaesthetists were found to differ from other staff in their thermal preferences, the surgeons liking a cooler and the anaesthetists a warmer environment. Although most surgeons were comfortable at temperatures around 66·5°F. (19°C.), at 50% relative humidity and 25 ft./min. air movement with the average amount of thermal radiation from the operating room lamp, it would be necessary to keep the temperature down to 64·5°F. (18°C.) if no more than one surgeon in twenty was to be uncomfortably hot. At this temperature nearly half the anaesthetists, who mostly preferred temperatures around 71°F. (21·5°C.), would feel too cold. Variation in the clothing worn by different staff members seems to be the only way of resolving this difficulty.

The average temperature in the operating rooms visited was over 72°F. (22°C.), and 75°F. (24°C.) was exceeded on about 25% of occasions.

A comparison was undertaken of several serological tests in determining the response of chickens and turkeys experimentally infected with the A 514 strain of Mycoplasma gallisepticum.

After a single intratracheal inoculation of chickens with a culture of the organism, the highest titres were obtained by the indirect complement fixation (ICF) test, followed by the tube agglutination (TA), haemagglutination inhibition (HI), slide agglutination (SA) and metabolic inhibition (MI) tests. By all these tests positive titres were observed within the first week and peak titres between the first and second weeks. At 5 months there was no positive reaction by the ICF test but most chickens gave positive readings by the TA, HI and SA tests for at least 14 months after infection, but turkey sera became negative by all tests after 3 months.

A disadvantage of the ICF test was that sera up to a dilution of 1/8 and 1/16 for chicken and turkey respectively were anticomplementary, and in turkeys this masked the ICF titre, which presumably was low following one intratracheal inoculation. Titres in turkeys with the TA, HI and SA tests followed the pattern seen with chickens and were generally lower than those found by other workers probably because of the avirulent nature of the inoculum used.

The WB test was the least sensitive of the agglutination tests but is useful as a flock test which can be undertaken on the farm.

The MI test gave the lowest titres of all and antibodies could be detected for only 4 months following one intratracheal inoculation. Even with serum prepared by multiple inoculations in chickens the titre was never higher than 1/32 compared with 1/1024 for serum similarly prepared in rabbits.

Precipitins were detected by the agar gel method in the sera of chickens and turkeys after two intratracheal inoculations but in only some of the chickens and none of the turkeys after one inoculation.

By all tests higher titres were observed with chicken than turkey sera and antibodies persisted for a longer time.

Re-infection of chickens when antibodies to the initial infection had become low, and of turkeys when antibodies were no longer detectable, gave rise to an anamnestic response with titres which were higher than before.

Antiserum to M. gallisepticum prepared in chickens is comparable with that prepared in rabbits except for low titres by the MI test.

Wet spores of fourteen strains of Clostridium, representing eight species, were enumerated in four different types of thioglycollate agar and in a similar medium in which thioglycollate was replaced by cysteine-HCl. Thioglycollate appeared to be toxic, in principle, to almost all strains tested, although the degree of toxicity was influenced by other components of the medium. These experiments entirely confirm earlier observations and must lead to the conclusion that the use of thioglycollate in sterility test media should be discontinued and that cysteine-HCl should be used as the redox potential reducing compound instead.

Colony counts on mice given the same number of Salmonella always differ considerably. However, the standard error of the mean log count does not increase after the first 1·5 hr. of infection until the 8th or 10th day. These infections therefore appear to pass through an initial stage lasting a few hours, in which a varying proportion of the inoculum is killed, followed by a prolonged second stage in which the scatter in individual colony counts remains constant.

A commercial swine fattening ration containing animal origin ingredients was shown to be related to the salmonella excretion of market pigs being sent to slaughter from a well-managed farm. When similar animals from this farm were fed a ration of much lower salmonella content, due to exclusion of ingredients of animal origin, their excretion declined as measured by both rectal and caecal swabs. When subsequent lots of pigs consumed a pelleted weaner ration and the special supplement only, before being exposed to a supplement containing the usual level of contamination, they seemed to be refractory to infection. Probably, this was a function of age at first exposure.

With prospective methods it was possible to show that salmonellas from the abattoir environment could infect pigs, that they would excrete them within a very short time, and that organisms from this source could be demonstrated at slaughter and shown to be a cause of carcass contamination.

While these findings support the view that the build-up of salmonellas hi pigs is by contact with a contaminated environment, they indicate that the primary source of the contamination is most probably the salmonella-excreting pig which has consumed contaminated feed ingredients on its farm of origin.

If the great majority of pigs went to slaughter salmonella-free they would not serve as a source of infection to other pigs being sent to slaughter. Their intestinal contents could not contaminate carcass sides in the slaughtering process. This should help to prevent the contamination with salmonellas of the food preparation area of both homes and commercial eating establishments.

Trimethoprim, a 2,4-diaminopyrimidine derivative which inhibits the growth of some bacteria by interfering with folic acid synthesis, inhibited the growth of several strains of the trachoma agent. Inhibition was most clearly demonstrated by measuring prolongation of mean death time of groups of chick embryos inoculated with a single lethal dose of agent. Over a certain range, prolongation was proportional to the logarithm of concentration of inhibitor; higher concentrations were toxic for the embryo. On a weight basis, trimethoprim was not as active as sulphafurazole. Inoculation in conjunction with sulphafurazole resulted in slight potentiation of activity. A related pyrimidine derivative, the antimalarial drug pyrimethamine, also significantly inhibited the growth of one strain of trachoma.

In cell culture, trimethoprim decreased the number of inclusions formed by a suspension of the trachoma agent and induced morphological changes in the inclusions similar to those caused by sulphafurazole.

Inhibition of the growth of the trachoma agent in the chick embryo was reversed by leucovorin calcium. It is concluded that, as with bacteria, the drug acts by blocking the folio acid cycle and that the trachoma agent most probably contains a dihydrofolate reductase.

The possibility of developing a living oral cholera vaccine with naturally avirulent El Tor cultures isolated in a Middle East country or from water sources in Calcutta in the absence of cholera El Tor in these areas has been further studied.

In an extended series of experiments the markedly low pathogenicity of the proposed vaccine strains in laboratory animals has been confirmed. The vaccine strains have been shown to get established and multiply regularly in the ligated intestinal loops of adult rabbits and in the intestine of infant rabbits without producing pathogenic reactions.

The apathogenic character of the vaccine strains has been found to be stable. When propagated serially in these two laboratory models of experimental cholera the vaccine strains show no enhancement of pathogenicity.

Intra-intestinal administration of the live vaccine has been shown to protect adult rabbits fully in the intestinal loop test. Immunized animals were also protected against challenge with V. cholerae strains, though to a somewhat lesser extent. Protective immunity could not, however, be demonstrated in infant rabbits probably because of the immunity-forming mechanism being still rudimentary.

Immunization with live vaccine was found to inhibit the growth of homologous strains in the ligated intestinal loop of the adult rabbit. The growth rate of pathogenic V. eltor and V. cholerae strains was also seen to be markedly reduced throughout the 24 hr. period of observation, but more markedly during the first 4–8 hr. However, the total count of pathogenic V. eltor and V. cholerae strains at 24 hr. after inoculation in ligated ileal loops of immunized rabbits reached levels that invariably caused inflammation and accumulation of fluid in normal rabbits' loops. The absence of gut-inflammatory reaction in immunized rabbits under these conditions has been discussed in relation to the nature of the immunity produced by administration of live vaccine.