Influenza vaccines used in trials appeared to stimulate a small increase of saline-reactive anti-A1 antibodies in group O volunteers. There was no evidence that haemolysins were elicited by adjuvant vaccine. It is unlikely that influenza vaccines would cause ABO haemolytic disease in infants.

The mechanism of spread of an epidemic of variola minor (alastrim) occurring in 1956, in Vila Guarani, a semi-rural school district of the City of São Paulo, Brazil, is examined. Cases were grouped according to time and space relationships corresponding to either a household or a school class, as once variola minor was introduced into a household or a school class spread was independent of occurrences in neighbouring social units. The constant occurrence of a single introduction in school classes and households implied that the chance for transmission of the disease outside the homes or the school was very small. The secondary attack rate was higher in households than in school classes. Twenty households with cases had more pre-school children and school children and a lower vaccination level than twenty-two neighbouring households without cases but also including one or more persons who were known to have had personal contacts with patients.

Examination of the chain of contagion clearly shows that spread in the school was directly and indirectly responsible for the majority of cases in the epidemic, for the peak of the epidemic curve and for the extent of topographical spread of the epidemic. This predominant role of the school was accentuated by incomplete preventive measures (vaccination campaign and isolation of patients) applied late in the epidemic and it is attributed to the following facts, (a) There was a single school in the district, and school children were thus concentrated, (b) The school was the only place of the district where persons living in different neighbourhoods had regular, repeated contacts, (c) The great majority of school children had had no previous variola and many had no vaccination scar, (d) The social activities of school children gave them the highest potential as transmitters of variola minor.

Two hundred and ninety-three milk ring test-positive individual milk samples were examined by whey complement fixation and agglutination tests and the results were compared with the isolation of B. abortus by cultures made from the milk.

There was a closer correlation between whey CF tests and isolation of the organism than between whey AG tests and isolation. Brucella organisms were not isolated from 116 MRT-positive milk samples when the whey CF titre was < 1/10; whereas 9/104 (9%) isolations were made from milk when the whey AG titre was < 1/20.

Because of its closer correlation with culture results it is suggested that the whey CF test would be valuable in an eradication programme for the detection of infected udders.

The limitations of the milk ring test for the examination of individual milk samples are emphasized and it should be used only as a preliminary screening test. In the individual milk samples examined, 32% of the MRT-positives showed no evidence of infection by either the whey AG, whey CF, or culture tests.

The results of a survey of the foot-and-mouth disease carrier state in three localities of an FMD enzootic area of Botswana are presented. The collection, storage and handling of the samples is mentioned and the isolation of virus on calf thyroid monolayer tissue cultures is described. Type SAT 3 virus was isolated from up to 20% of the animals sampled at periods between 7 and 12 months after natural infection. Sera were tested for all the animals from which virus was recovered and compared with similar numbers of sera from virus-negative animals. No correlation was found between the carrier state and serum antibody titres.

Antigenic studies are described which indicated not only an antigenic variation of some carrier viruses isolated from the outbreak strain but also antigenic differences between strains of carrier virus from different animals in the same herd. There was no evidence at the time of sampling of the persistence as carrier virus of the attenuated vaccine strains of FMDV used previously in the cattle sampled.

The results suggest that transference of carrier virus from animal to animal may occur in the absence of clinical infection.

The capacity of certain strains of Streptococcus pyogenes to produce opacity in aged horse serum has been studied. Cells from all stages of the growth cycle are able to produce opacity. Maximal activity is reached towards the end of the exponential phase of growth.

Examination of cell fractions obtained by mechanical breakage and differential centrifugation suggested that the cell-bound activity is predominantly associated with the membrane fraction. Extraction with sodium deoxycholate yields a soluble fraction of high activity.

There is considerable strain variation in heat stability of the serum opacity factor. Cell-bound activity is often quite resistant to heat, whereas extracted activity is less stable.

Low concentrations of divalent cations have an activating effect, whereas high concentrations inhibit the serum opacity reaction. High concentrations of uni-valent cations are without effect on the cell-free enzyme but have an activating effect on the cell-bound enzyme.

For both the cell-bound and the cell-free enzyme the pH optimum was 5·8.

Although sensitive to trypsin and pepsin, the serum opacity factor appears to be resistant to streptococcal proteinase. Its activity is destroyed by formaldehyde and by periodate but is unaffected by a number of reducing agents.

Pre-heating of the serum or the addition of iodoacetate did not affect the serum opacity reaction. The enhanced cholesterol esterification previously described with fresh serum appears to be a secondary reaction. Even when isolated by relatively gentle methods, α-lipoprotein serves as a substrate only in the presence of crystalline serum albumin.

The serum opacity reaction (SOR) is produced by some streptococci of group A, but not by streptococci of groups B, C, D, F and G. The production of this reaction was found to be closely related to serotype as determined by M and T antigens. The SOR of an individual strain was found to be consistently stable over a period of time both in strains maintained in the laboratory and in strains isolated sequentially from individual patients following streptococcal infections. Strains for which the demonstration of an M-antigen by the precipitin method was difficult or impossible in general produced a SOR, while strains more easily typable generally failed to produce this reaction. Laboratory selected variants of type 12 strains showed an inverse relationship between M protein and lipoproteinase production, whereas M positive and M negative variants of other serotypes showed no variability with respect to lipoproteinase production.

An investigation was carried out on the influence of the mode of transport at ca. 21° C. on the fate of S. typhimurium, E. coli, Ps. aeruginosa, Staph. aureus, Str. pyogenes and spores of B. cereus collected from surfaces by swabbing with cotton and alginate.

Transport at relative humidity 0·58–0·95 leads to losses in viable counts sometimes exceeding two log cycles. In Stuart's medium and Ringer-calgon particularly Enterobacteriaceae showed growth when transported at 21° C. Reduction of the pH value of Stuart's medium led to losses of far over one log cycle in some types of bacteria and could therefore not be recommended.

Slight chilling of the medium, e.g. to 12° C., and insulation during transport appeared to maintain counts of the organisms studied at their original level in both Stuart's medium and Ringer calgon for 10–12 hr.

Oxoid dehydrated MacConkey broth was compared with laboratory prepared MacConkey broth, Teepol broth and three modifications of glutamic acid media, by participants in eleven laboratories. A variety of chlorinated and unchlorinated water samples were used. The Oxoid MacConkey broth was shown to be a satisfactory standard for comparison. Teepol broth was found to be a satisfactory alternative to MacConkey broth. Gray's improved glutamate medium was shown to be the best of the glutamate media and it gave results superior in most respects to MacConkey broth. In particular more Escherichia coli were obtained as well as more coliform organisms. Organisms surviving marginal chlorination were recovered more readily. Growth was sometimes slower than in MacConkey broth but this could possibly be improved by closer attention to pH adjustment and mineral composition.

A field survey conducted amongst children in a semi-rural area of Ceylon has revealed a high rate of Schick negative conversion early in life. A high carrier rate of C. diphtheriae in cutaneous ulcers which probably accounts for this early Schick conversion has been detected. The role of cutaneous diphtheria and that of non-toxigenic organisms in the acquisition of natural immunity to the disease is discussed.

Rabbits were immunized by multiple intradermal injections followed by six intravenous doses of vaccinia virus inactivated by heating to 65° C. Particular attention was paid to confirming that the virus used was fully inactivated and incapable of reactivation. The immunized rabbits developed neutralizing and other antibodies to a titre comparable with those developed in response to live virus, but multiple intravenous injections were required to elicit a maximum titre. A qualitatively different response was seen only in immunodiffusion tests in agar gel where two or three fewer lines developed with antisera to heated virus than with those to live virus. The rabbits were subsequently challenged intradermally either with vaccinia and cowpox or with rabbitpox. They showed some immunity to vaccinia and cowpox, compared with normal controls, but less than that elicited by live virus. Their resistance to lethal doses of rabbitpox was life-saving though some rabbits did develop lesions. Later rechallenge of the rabbits showed that they had not developed further immunity, in distinction from the normal controls. The implications of these findings are discussed.

I wish to thank the National Fund for Research into Poliomyelitis and Other Crippling Diseases for their generous support in providing a Research Fellowship during which this work was done. I wish to thank also Professor A. W. Downie F.R.S. and the Staff of the Department of Bacteriology, University of Liverpool, for their encouragement and assistance respectively.

Two isolations of Arizona from humans were made in Sheffield in 1966. The first was from a 3-year-old girl with a history of gastro-enteritis; the second was from her 5-year-old brother who was a symptomless excretor. Infection was traced to pet terrapins recently purchased from a local pet shop. The relative epidemiological significance of Arizona infection and the potential hazard of pet terrapins has been reviewed.

We wish to thank Dr V. G. S. Damms for his help and co-operation and for allowing us to publish details of his patients, Dr J. G. Wallace for his work on the preliminary identification of the organism, and Dr Joan Taylor and Dr E. H. Gillespie for their helpful advice and criticism.

Pigs were infected by the intranasal instillation of a large dose (ca. 107·0 ID 50) of a highly virulent strain of African swine fever virus (ASFV) and the progress of the infection was studied by the ‘routine titration approach’ (Mims, 1964) using pig bone marrow cultures.

Virus growth was established within 16–24 hr. in the retropharyngeal but not in the alimentary or nasal mucosae or the tonsils. By 24–40 hr. the virus was consistently present in the retropharyngeal lymph nodes, almost invariably the medials; titres in these nodes exceeded those in the associated mucosa by 48–72 hr. Generalization, presumed to have occurred via the tracheal lymph ducts and the blood stream, was generally demonstrable after 72 hr., i.e. by the time of the onset of pyrexia or 24 hr. prior to this.

On average 11% of the total infectivity in the blood was present in the plasma, with the rest assumed to be cell-associated. A mean of about 45% of the total infectivity was recovered in erythrocyte fractions in which the concentration of leucocytes had been materially reduced; fractions with increased leucocyte counts contained relatively little virus and it was concluded that the great majority of circulating virus was closely associated with the erythrocytes. Adsorption of ASFV to normal pig erythrocytes was demonstrated in vitro.

The greatest concentrations of virus were recorded in the lymph nodes, especially those of the cephalic region, and in the spleen, where titres commonly attained 108·0 to 109·0 HAD 50/g. and exceeded those in the blood. They were, therefore, thought to be the source of much circulating virus, although there was some evidence that the liver, lungs and bone marrow may also have contributed, at least in some animals. There was no evidence that the mucosae of the alimentary and respiratory tracts or the kidney, myocardium and brain were a source of significant amounts of virus. The virus demonstrable in Peyer's patches did not exceed that in the intervening ileal mucosa.

Although contact transmission of ASF does not normally occur during the first 12–24 hr. of fever, considerable amounts of virus were usually present in the nasal and intestinal mucosae at 72 hr. It was probable that this infectivity was due to the blood content and that excretion did not occur until the epithelium was breached.

Three pigs, all of which had lesions of a portal cirrhosis, showed a delayed or restricted generalization of virus, in comparison with the other twenty-eight animals which behaved according to a regular pattern.

We are grateful to Mrs M. O'Sullivan and Mrs E. Douglas for painstaking technical assistance and to Mr C. S. Rampton, A.I.M.L.T., for the preparation of the figures.

Details of confirmed outbreaks of food poisoning due to heat-sensitive Cl. welckii are given. In 4/5 incidents heat-sensitive Cl. welckii were isolated in large numbers from the majority of the faeces. In the remaining outbreak the faecal samples were not collected until 7–9 days after the illness. The causative organism was isolated from the food in 3/5 instances.

In addition four outbreaks of food poisoning in which both heat-sensitive and heat-resistant Cl. welckii were isolated are described.

The role of heat-sensitive Cl. welckii in food poisoning outbreaks is discussed and a suggested method of examining faeces for Cl. welchii is given.

We are indeed grateful for the assistance given in collecting faecal specimens and obtaining detailed information on the food preparation, etc., by Drs G. C. Turner, J. Epsom, J. G. Wallace, P. J. Wormald, H. D. Holt, D. G. Fleck, J. M. Graham, E. Tanner and J. D. Abbott. We would also like to thank Mrs I. Batty of the Wellcome Research Laboratory for carrying out toxicological examinations for us.

One of us (R.G.A.S.) is attached to the Commonwealth Department of Health, Australia, and is at present the holder of a Public Service Board Postgraduate scholarship.

Norbormide at 1·0 and 0·5% and zinc phosphide at 5·0 and 2·5% were each tested in four types of cereal bait, after prebaiting and as direct poisons, against infestations of R. norvegicus on forty-eight farms in Montgomeryshire.

The relative success of treatments was measured by the reduction in the number of takes from wheat baits put down for 2 days, 13 or 16 days before, and 5 days after, poisoning.

Treatments with zinc phosphide were significantly more successful than those with norbormide, irrespective of the cereal bait, concentration of poison or method of treatment used, and in spite of conditions on many farms that partially restricted the distribution of the baits containing zinc phosphide.

Differences between these results and results of laboratory tests with the same rodenticides are discussed.

Norbormide is recommended for use in situations where zinc phosphide cannot be used efficiently without risk to livestock.

We are indebted to Messrs Tavolek Laboratories Limited, Slough, for the free supply of norbormide made available early in the trial; also to Messrs. Lloyd and Pritchard, who were responsible for all the treatments; to Miss E. J. Taylor and Miss P. Cullen for assistance with some of the census baiting, and to J. H. Greaves for permission to examine original data and present them in Table 3.

The coagulability of the plasma of blood taken from the retro-orbital sinus of untreated and warfarin-treated wild house mice (Mus musculus L.) was determined. Individual differences were observed in the resting clotting times of animals drawn from three different sources, so-called ‘normal’ (N) mice, home-bred warfarin resistant (HBR) mice and field-caught suspected warfarin resistant (FR) mice. Mice from the three sources also showed wide individual variation in response to injected doses of 1, 5 and 50 mg. of warfarin/kg, body weight. The overall response shown by HBR and FR mice, particularly females, was less than that shown by N animals. Some FR females failed to respond to a dose of 100 mg. of warfarin/kg, body weight.

Normal mice showed a similar response to two identical doses of warfarin (1, 5 or 50 mg./kg. body weight) given at an interval of 3 weeks. They developed a tolerance to repeated daily injected doses of 1 mg. of warfarin/kg, body weight but not to the higher doses (5 and 50 mg./kg.) to which some HBR animals became tolerant.

In comparative 21-day feeding tests with 0·025% warfarin in medium oatmeal, the mortality in N, HBR and FR mice was 100% (27), 64·5% (40/62) and 22·7% (10/44) respectively. Whereas the plasma of all N mice was rendered uncoagulable after 3 days and the animals died within 12 days, the clotting times of the surviving HBR and FR mice (24/59 males and 32/47 females) either were not at any stage appreciably increased or had declined to near normal values by the end of the test period.

In similar tests with 0·025% warfarin in oatmeal bait containing 5% mineral oil, it was found that the clotting ability of the plasma of N, HBR and FR mice was impaired earlier and that mortality in HBR and FR animals was significantly higher (62/67, 92·5% and 7/8, 87·5% respectively).

Three of seven HBR mice died after prolonged feeding on various warfarin baits but only after 186, 197 and 209 days respectively. The inclusion of mineral oil in bait containing 0-0·25% warfarin was more effective in decreasing the coagulability of the blood of these mice than either increasing the concentration of warfarin (to 0·1 and 0·2%) or including sulphaquinoxaline or corn oil.

Studies on mice given warfarin by injection and in feed indicated that in females the level of resistance to warfarin may be assessed on the basis of their response to a single injected dose of warfarin.