1. The course of an epizootic of plague in thirty-four colonies of gerbils (Tatera brantsi) was observed by counting, at 4-weekly intervals, the number of burrows which, when they had been closed on one day, were found open on the next. One gerbil could open an average of eight burrows in one night.

2. Regular censuses on the twenty-one colonies which survived until the last phase of the epizootic showed that the gerbil population fell from about 420 at the end of June 1940 to none at the end of January 1941. From May 1941 to August 1942, 3-monthly counts revealed some recolonization, but field officers reported that between 1942 and 1951 the gerbils sometimes died from plague, and the population never regained its former level.

3. During 1940, two to four colonies died out every 4 weeks. The time of year seemed not to influence the course of the epizootic.

4. Pasteurella pestis was detected in some gerbil colonies 4–6 months before they died out.

5. Plague-infected gerbil fleas were found which had been immured in blocked deserted burrows for periods of up to 120 days.

6. The passage of infection was traced from the reservoir in gerbils to other wild rodents (Otomys irroratus, Rattus (Mastomys) natalensis), to house rats (Rattus rattus) and to man.

1. Hospital records of 1469 cases of rheumatic fever (including chorea) up to the age of 14 years were used to study the social distribution of the disease in Melbourne. On this evidence the incidence of rheumatic fever was three times greater in low than in high rental districts.

2. The results of throat-swab surveys and Dick tests on schoolchildren living in different districts showed that children in the poor districts contracted streptococcal infections more frequently than those in well-to-do districts.

3. One factor associated with the carrier rate of Streptococcus pyogenes in the various social groups was the incidence of tonsillectomy. In the better class districts where the tonsillectomy rate was high (60%) the Str. pyogenes carrier rate was 12.5%, whereas the rates in poor areas were 35 and 25.3% respectively.

4. Differences in social incidence of rheumatic fever might therefore be explained by differences in social incidence of streptococcal infection, which, in turn, might be influenced by the incidence of tonsillectomy.

We wish to thank the many persons who so willingly assisted in the collection of data for this study, particularly Dr H. L. Stokes and Dr M. M. Wilson, and Dr R. E. O. Williams for advice on presentation. This work was supported by a grant to one of us (Dr M. C. Holmes) from the Commonwealth Research Fund from the University of Melbourne.

Factors affecting the growth of Streptococcus faecalis on glucose-yeast extract-sodium azide agar have been studied. Both the high temperature of incubation used (45° C.) and the presence of azide reduced the proportion of cells able to form colonies, the inhibitory action being much more marked with cultures which had become attenuated, either through age or through prolonged immersion in water, than with comparatively young and vigorous cultures. This inhibitory action was found to be largely overcome if the inoculum was subjected to a preliminary period of ‘resuscitation’, by incubating it with double-strength glucose broth before adding the azide-agar portion of the medium and allowing the mixture to set.

Neutral red was so inhibitory to some strains of Str. faecalis that it could not be included in the medium. Phosphate, as the potassium salt at a concentration of 0.7%, if autoclaved with the remaining constituents of the medium, exerted a depressing effect on the counts. Added separately it showed no inhibitory action.

The spinning-bottle technique (Allen et al. 1952) was adapted for Str. faecalis. When used for samples containing a mixed flora the method, described in the Appendix, permitted the growth only of Str. faecalis.

This paper is published by permission of the Department of Scientific and Industrial Research.

Three methods have been investigated for determining Most Probable Numbers, using lactose-bile salts broth for Bacterium coli and glucose-yeast extract-azide broth for Streptococcus faecalis. In the ‘direct’ method inoculated tubes of medium are incubated directly in a water-bath, at 44° C. for Bact. coli or at 45° C. for Str. faecalis. In the ‘subculture’ method primary incubation at 37° C. is followed by subculture of positive tubes to tubes of fresh media which are incubated at the higher temperature. In the ‘resuscitation’ method each medium is divided into 2 parts. The inoculum is mixed, in McCartney bottles or tubes, with the first part of the medium, containing the sugar and the peptone, and the mixture is held at 37° C. for 1–2 hr. to resuscitate organisms weakened by age or by long immersion in water. The second part of the medium, containing the bile salts or the azide, is then added and the bottles or tubes are incubated at 44 or 45° C. With samples of polluted waters the ‘subculture’ method gives significantly higher counts than the ‘direct’ method for Str. faecalis but not for Bact. coli. The ‘resuscitation’ method gives significantly higher results than the ‘subculture’ method for both organisms, it requires less time for completion, and is specific for the organism concerned.

These results were obtained with media containing 0.003% brom-cresol purple as indicator; neutral red was found to be inhibitory.

This paper is published by permission of the Department of Scientific and Industrial Research.

On the basis of previously published work, the skin test for toxoplasmosis has been judged to be a convenient and sufficiently reliable method for carrying out epidemiological group investigations intended to elucidate the spread of the disease. With it one can probably detect as many persons with serologically demonstrable antibodies against toxoplasma as when the same persons are examined by means of the routine dye test. An investigation employing skin testing has been carried out on 648 persons between the age of 0 and 45 years, all living in or adjacent to a town in Central Sweden. The reagent used (toxoplasmin) was prepared from toxoplasma cultures grown on embryonated hen's eggs by the State Bacteriological Laboratories, Stockholm. Amongst 379 children under the age of 15 years, only one gave a positive reaction, whereas in the higher age groups the frequency of positives rose rather rapidly to 40% in the age group 30–45 years. The results show fair agreement with those previously reported from similar investigations, with one very noticeable exception: in North Sweden skin reactions have proved positive in a bare 10% of adults studied. The significance of this observation is discussed in regard to the epidemiological characters of the disease. Having due regard to our incomplete knowledge of the subject, attention is drawn to the possibility that reservoirs of infection are extrahuman and that transfer of the disease to human beings occurs through the medium of biting insects or contaminated food.

1. The effects of poison treatments on the rat populations of two sample districts of heavily infested sewers in a London borough were studied.

2. Each district had a maximum rat population represented by a census figure of about 10,000 g. wheat eaten per day, corresponding to at least 400 rats.

3. Poison treatments after prebaiting, at intervals of 6 months, reduced the rat population of each district to less than 10% of the maximum. A rapid restoration of the population followed, and the level reached in 6 months was near the maximum.

4. In both areas, direct poisoning with sodium monofluoroacetate ‘1080’ was as effective as a prebaiting treatment. Direct poisoning with zinc phosphide was relatively unsuccessful.

5. When both areas received double treatments, consisting of direct poisoning with sodium monofluoroacetate followed by a prebaiting treatment, the estimated population of one district was reduced to about 3% of the maximum. In the other area, rain made the second poisoning ineffective.

6. The rate at which the population was restored from the 3% level was even higher than the rates previously observed, and was probably too high to be accounted for solely by breeding. Evidently, invasion from the surface played a part.

7. No relationship could be established between the estimated sewer rat population densities within each district, and the known sites of surface infestation.

We are grateful to the Council and officers of the Borough in which the work was done, for unstinted help throughout the inquiry. We also owe thanks to H. V. Thompson for help in the early stages; to him and to Miss M. D. A. Lawrence for discussing the work during its progress; to Miss M. M. Spencer for help in the analysis of the records and in checking calculations; and to A. G. Jenson for mapping the districts and for drawing the figures.

The complement-fixation technique described in this paper was designed as a simple and rapid micro-method. It is derived from the method published by Fulton & Dumbell (1949), but a number of modifications have rendered it less laborious to perform and more flexible in application. Using rabbit, human and guinea-pig antisera, this technique has been successfully applied to the serological examination of the viruses of influenza, vaccinia and Newcastle disease, and experience with other materials, such as gonococcal antigen and extracts of chorio-allantoic membrane and mouse lung, suggests that it is of general application.

Thomas & Van den Ende (1941) and Puck and his collaborators (Puck, Hamburger, Robertson & Hurst, 1945; Puck, Robertson, Wise, Loosli & Lemon, 1946) have shown that the application of small amounts of oil to bedclothes reduces the quantities of dust and bacteria liberated during bedmaking. Joyce Wright in her first investigation (Wright, Cruickshank & Gunn, 1944) found that oiling bedclothes was, consequently, effective in reducing the incidence of cross-infection, but this was not confirmed in her later work (Wright, Begg & Smellie, 1947), or by Krugman & Ward (1951). Barnard (1952), however, has recently shown that cross-infection can possibly arise by interchange of bacteria in blankets during laundering. Oiling of bedclothes may, therefore, be a very useful hygiene measure.

1. An investigation has been carried out into the conditions necessary for the production of immuno-conglutinin in rabbits.

2. The inoculation of complement adsorbed on sensitized cells stimulates the production of immuno-conglutinin. We have called this procedure hetero-stimulation.

3. Immuno-conglutinin also results from the inoculation of untreated but killed bacteria. This procedure for its production we call auto-stimulation. Gram-negative bacteria appear to be more effective stimulants than Gram-positive bacteria. Soluble antigens did not appear to be as effective as bacterial suspensions.

4. The necessity for clarifying the part played by immuno-conglutinin in in vivo immune processes has been stressed.

The authors would like to thank the following for gifts of experimental materials: Mr H. I. Field, strains of S. pullorum; Dr J. Boissard, strain of C. hofmanni; Dr C. H. Lea and Dr R. S. Hannan, purified casein; Miss Dunkerley, Bence Jones protein. Cx polysaccharide for testing acute phase protein in rabbit serum was made available by the kindness of Dr McCarty of the Hospital of the Rockefeller Institute for Medical Research, New York; and much of the work on this aspect was done in consultation with Dr H. C. Anderson, to whom we are most grateful.

Cases of paratyphoid fever are often not diagnosed until the second, third or subsequent weeks of illness. When calculating clearance rates of a series of cases the calculations must be based only on the numbers known to be positive at the week under consideration. If based throughout on the total number of cases the rates of clearance in the early weeks are greatly reduced.

Cases for which laboratory records are incomplete must not be entirely rejected when calculating clearance rates but must be retained in the population for as long as they were known to be positive.

Analyses designed to show the duration of infection in paratyphoid fever can only be made with accuracy under the most favourable conditions.

A large number of cases of paratyphoid fever were repeatedly examined bacteriologically to establish the duration of the infection as distinct from the clinical illness. After an initial lag the proportion of cases remaining infected fell logarithmically until the carriers revealed themselves.

We are grateful to many medical officers for information about their cases, and to Dr Lewis Fanning and Dr Ian Sutherland for much helpful criticism.

Purified tuberculin in concentrations equivalent to 1x/20 standard Old Tuberculin had no apparent effect on the outgrowth in vitro of liver and kidney epithelium derived from sensitized guinea-pigs.

Acknowledgement is made with thanks to Miss Florence Taylor for technical assistance, and to Mr L. Jones for help with the microphotography.

In three cattle vaccination experiments, with three strains of the virus of foot-and-mouth disease, it was shown that virus passaged in culture in cattle tongue epithelial tissue was as effective an antigen as virus passaged in cattle.

With two virus strains, the virus content of the culture at the peak of infectivity was about the same as that of vesicle epithelium from the tongues of reacting cattle. Variable and less satisfactory results were obtained with the third strain, but one culture passage yielded tissue of sufficiently high virus content for the preparation of vaccine of adequate potency.

No modification in the antigenic behaviour of the strains was detected as a result of passage in culture.

It is a pleasure to acknowledge the technical assistance given by Mr W. J. Brownsea.

This investigation has been concerned with the changes that occur in the coliform and faecal coli content of water samples on storage at room and refrigerator temperatures for 6 hr. as compared with those occurring after 24 hr. storage.

The examination was conducted by a 70-tube method using twofold diminishing volumes.

The percentages of samples showing a significant change corresponding to at least a doubling or halving of the coliform content on storage were: (a) at room temperature after 6 hr. 24.7%, and after 24 hr. 38.3%; (b) at refrigerator temperature after 6 hr. 25.0%, and after 24 hr. 33.9%. The percentages of samples showing a significant change in the faecal coli content on storage were: (a) at room temperature after 6 hr. 18.7%, and after 24 hr. 34.6%; (b) at refrigerator temperature after 6 hr. 10.4%, and after 24 hr. 25.0%. The changes were preponderantly decreases and most of the large changes occurred after 24 hr.

The investigation has shown that fewer changes occur after 6 hr. storage than after 24 hr. storage, and that storage for 6 hr. at refrigerator temperature is preferable to storage for 6 hr. at room temperature. Even so, some samples show significant changes after 6 hr. storage at refrigerator temperature; the coliform content is significantly altered in 25% of samples and the faecal coli content in 10% of samples.

Samples of water should, therefore, be examined as soon as possible after collection, certainly within 6 hr., and during the period of transport to the laboratory they should be kept cold, if possible by ice.

A quantity of 0.1 ml. of a 3% solution of crystalline sodium thiosulphate in a 6 oz. bottle is sufficient to neutralize up to 5 p.p.m. of residual chlorine; the use of large quantities of thiosulphate is unnecessary, except possibly for some swimming-bath samples. The investigation has shown that this amount of thiosulphate has no significant effect on the coliform or faecal coli content of non-chlorinated water samples during 6 hr. storage at refrigerator temperature. There therefore appears to be no disadvantage in adding this amount of thiosulphate to all water sampling bottles.