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.

Phage adsorption by resistant staphylococci was studied.

Staphylococcal cultures previously allowed to adsorb phage to which they were resistant remained as sensitive to their appropriate phages as normal cultures of the same strains.

When pooled related and unrelated phages were incubated with their propagating strains, the results resembled those obtained when these phages were incubated separately with the same strains.

The lytic effects of thirty-two phages at test dilutions were tested singly and when pooled into five mixtures. All the phage-propagating strains and over 500 strains received for typing were tested. The results were in agreement.

Thirty-two phages at their test dilution in nutrient broth remained stable, whether pooled or not, at 0 to + 5° C. for various times. Briefly summarized, serological group A phages were stable for at least 1 month, and group B phages were stable for only 2–3 weeks.

Broth cultures of staphylococci incubated for 18 hr. at 30° C. were as phage-sensitive as the same cultures when left at room temperature for 24 hr.

A new method of phage typing staphylococci by means of phage pools, as satisfactory as the standard method, and less laborious, is described.

Tetanus antitoxic horse sera were fractionated with sodium sulphate and by electrophoretic separation. The activity of the native serum and of fractions was determined in vivo in the mouse and guinea-pig and in vitro by the flocculation method. All the sera and fractions showed several zones of flocculation. The flocculation optimum corresponding to the toxin-antitoxin complex was selected by absorption of antitoxin to the floccules. The distribution of activity amongst the electrophoretic components of the native serum was computed from electrophoretic analysis, refractive increment measurements and assays of the activity of the electrophoretically pure fractions.

In all the sera examined the antitoxin was associated with both β- and γ-globulin. The γ-globulin antitoxin had a shorter flocculation time and a higher in vivo/in vitro ratio than β-globulin. The in vivo/in vitro ratio of γ-globulin was two to three times that of β-globulin antitoxin, its exact value depending on the toxin concentration against which the antitoxin was measured. The avidity of γ-globulin antitoxin was greater than that of β-globulin antitoxin judged by two independent ‘dilution’ tests, namely a comparison of the mouse unitage using two concentrations of toxin and a comparison of the values obtained with one concentration of toxin in the mouse and in the guinea-pig. The in vivo values of the various antitoxins varied with the toxin employed in the test.

During the first course of immunization in a horse the γ-globulin antitoxin rose to a constant value; β-globulin antitoxin increased to a still higher value later in the course. The avidity of the serum, as measured by the two ‘dilution’ ratios, also increased during immunization.

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.

1. Colonies of wild Rattus norvegicus Berkenhout were kept in closed rooms containing nesting sites. The conditions permitted breeding.

2. Seventy-six experiments, each lasting 6–35 days, were done to test the rats' food preferences. In each experiment except two, a choice was given between two foods, both available in excess. In the two exceptional experiments a choice between three foods was given.

3. Although marked preferences were shown, a food was rarely quite rejected in favour of an alternative.

4. Among cereals, wholemeal was preferred to wheat grains, but wheat grains were preferred to white flour; little or no white flour was eaten if wholemeal was available. Wheat germ was eaten only in small quantities when an alternative cereal was available, but in larger quantities if the alternative was sugar or a sugar-cereal mixture.

5. The addition of sugar or saccharin to cereals increased acceptability; sugar was preferred to saccharin.

6. The addition of arachis oil to wholemeal or wheat increased acceptability.

7. Cod-liver oil at 2·4 % acted as a deterrent.

8. Total calorific intake remained steady over short periods, but over several weeks rose as the mass of the rat colony increased. The higher the mean weight of the rats in a colony, the lower the calorific intake per unit weight of rat.

9. The amount of food eaten was partly determined by its calorigenic capacity: in particular, wet foods were eaten in much larger quantities than dry foods.

10. The food preferences of wild rats differ in several respects from those of white Rattus norvegicus.

11. Apart from palatability or flavour, the main factors influencing food preference were (a) previous experience and probably (b) the nutritional value of the food. The effect of previous experience was often observed when rats, accustomed to one food, gradually changed from the accustomed food to another. The stages of a change to a new food, or the establishment of a particular preference, varied, and are discussed in detail.

1. The incidence of haemolytic streptococci in the patients of a Hospital School for rheumatic children was determined over a period of 1 year.

2. In the total of 1644 throat and 1644 nasal swabs, group A strains were isolated from 20 throat and two nasal swabs. Eighty-seven strains of Lancefield's groups C and G and 54 strains of groups other than A, C, or G were isolated

3. There was no evidence of cross-infection.

4. Factors contributing to the low incidence of group A strains and the absence of cross-infection are discussed.

5. The carriage of groups C and G strains did not appreciably affect the erythrocyte sedimentation rate.

6. Although no direct evidence is available, the experience of the present study suggests that the incidence of streptococci in an institution for rheumatic children may be reduced by: (a) bacteriological screening before admission; (b) regular swabbing and Lancefield's grouping of streptococci isolated for the early detection of group A strains; and (c) administration of penicillin or sulphadiazine prophylactically to even a limited number of children.

We thank Prof. R. S. Illingworth for his advice in the writing of this paper, Dr J. L. Emery for laboratory facilities, Dr R. E. O. Williams for his advice in the planning of the investigation, and the matron and sisters of Ash House Hospital School, Sheffield, for their assistance.

The expenses of the investigation were defrayed by a grant from the Medical Research Council.

1. The haemolytic complement-fixation test and the conglutinating complement-absorption test, as well as the agglutination reaction and the antiglobulin sensitization test, have been used to study a change which occurs during egg adaptation of the Christie strain of R. burneti.

2. Antigens were prepared from yolk sacs of the third to the ninth passages inclusive. Irrespective of numbers of rickettsiae, antigens from the third and fourth passage failed to fix complement with homologous (human) antiserum, unless the latter was in very low dilution. From the fifth passage, however, antigens fixed complement with high dilutions of the same antiserum and thus resembled the classical Henzerling strain antigen.

3. Third-passage antigen failed to fix conglutinating as well as haemolytic complement with high serum dilutions. The agglutination reaction and antiglobulin test, however, showed that third-passage antigen absorbed antibody almost as well as ninth-passage and Henzerling strain antigens.

4. It was not possible to find out if the change in behaviour was due to a true antigenic variation or to non-specific hindrance of complement absorption. Heating failed to alter the behaviour of the antigens and the results of absorption tests were inconclusive.

The way in which rats and mice eat whole grains of wheat, barley, oats and maize has been studied.

Rats (Rattus norvegicus and R. rattus) hold grains with the long axis parallel to that of the body and eat the germ end of the grain in preference to the rest.

Mice (Mus musculus) hold grains with the long axis at right angles to that of the body and attack first the cheeks of all grains except maize, of which only the germ and scutellum are eaten.

It is suggested that texture is in the main responsible for the selection of a particular part of a grain.

A method for the estimation of chloramphenicol in faeces and bile is described. It has been shown that the bile contains high concentrations of the antibiotic, but the faeces small amounts. It is considered that the faecal concentration is dependent on the biliary supply.

The action of chloramphenicol on the gut flora is described and the dominance of yeasts on complete suppression of the conforms is reported, drawing attention to the possibility of intestinal moniliasis following unrestricted use of the antibiotic.

An explanation of ‘relapses’ in the chloramphenicol treatment of typhoid fever is given, and the possible effect of chloramphenicol on immunity response is discussed.

This paper is a short exposition of the mathematical and statistical theory of the growth of bacterial populations subject to mutation.

A mathematical model for the long-term development of a mixed population with two types of organism is proposed. The proportion of organisms which are of the mutant type eventually approaches an asymptotic value, which is independent of the initial composition of the population. A procedure is outlined for estimating the forward and backward mutation rates from a long-term experiment.

The exact interpretation of the constants representing mutation rates requires some assumption about the point of time, during an individual life cycle, at which mutations occur. The usual assumption is that mutations can occur with equal frequency at all instants during the cycle.

In short-term experiments, in which the proportion of mutants is at all times negligible, it is important to consider the variation between the numbers of mutants developing in replicate cultures. The theoretical distribution of Lea & Coulson may be disturbed by the failure of any one of a number of assumptions; the effects of such disturbances are considered in some detail.

Various methods of estimating the mutation rate from an observed series of replicate cultures are examined. Two of the main sources of disturbance of the theoretical distribution may be delay of phenotypic expression, and the existence of multinucleate cells with dominant mutation. These factors affect particularly the lower tail of the distribution, and it is suggested that a fairly safe procedure may be to estimate the mutation rate from the upper quartile of the observed distribution. Tables 3 and 4 enable the estimate of the mutation rate, together with 95% confidence limits, to be readily calculated.

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.

The results of an investigation into the incidence of canicola fever amongst owners of dogs infected with L. canicola is described.

Visits were made to forty-six households in which infected dogs lived. Altogether 137 household contacts were examined and blood samples from 99 or 72·3 % were tested for agglutination against L. canicola. All the sera proved negative.

A detailed classification of the kinds and conditions of housing and of householders is given.

Some of the difficulties in explaining the relationship between the disease in dogs and man are discussed; the results of the present survey and the experience with some reported cases of human canicola fever show that there is great variation in the risk of infection to owners and others hving in the same house with diseased dogs.

Some other source of infection common to man and dog is possible.

It is recommended that in the light of present knowledge greater attention should be paid to the preventive aspect and that more propaganda should be directed to make dog owners aware of the possibilities of infection and of the importance of observing hygienic principles when handling dogs and particularly when dealing with dejecta.

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.

Chemical and bacteriological examination of muds from sources differing widely in the degree of pollution to which they were subject showed great differences in the contents of carbon, nitrogen and sulphide. These differences were not correlated with differences in the severity of faecal pollution. The amount of organic matter available for growth of micro-organisms in the mud of different depths was not reflected in the figures for organic carbon. A convenient index of this factor was obtained by measuring the volume of gas evolved during anaerobic digestion over a prolonged period of incubation. The rate of evolution was increased by the addition of an inoculum of digested sludge from a sewage works.

Sulphate-reducing bacteria appeared to be of two different types. In samples of mud from fresh-water lakes much higher counts were usually obtained in a medium containing comparatively low concentrations of inorganic salts and of lactate than in a medium containing much higher concentrations of these constituents. In samples from locations where conditions were more saline the reverse was usually true.

Counts of Bact. coli and of Strep, faecalis together probably constitute the best index of faecal pollution in the examination of samples of mud. These organisms are, however, largely confined to the surface layers.

Biochemical and serological investigations were made upon Bact. coli O 55 B 5 strains isolated from infants with diarrhoea and vomiting. On the basis of their reactions with six fermentable substances and of their H antigen types, the strains could be differentiated into three sero-fermentative types, I, II and III, which comprised, respectively, those having H6, H2 and H7 antigens.

We wish to acknowledge our thanks and indebtedness to the following: the Chairman and Members of the Tottenham Group Hospital Management Committee, and Dr T. H. C. Benians, Dr W. I. Leslie and Dr R. Swyer, for facilities for research in the laboratory and wards of St Ann's General Hospital; Mr L. G. C. Maslen for most valuable advice and assistance; the entire laboratory staff for their willing and efficient help.

It has been shown that the cells in exudates produced by the injection of tuberculin into the serous cavities of sensitized animals are alive and not dead as claimed previously. Such cells consumed oxygen and glucose at the same rate as cells obtained similarly from normal animals but moved somewhat less actively. Purified tuberculin had no specific effect on the respiration in vitro of macrophages or neutrophil leucocytes derived from sensitized animals.

Evidence for the isolation of a virus from this epizootic disease of shearwaters is based upon the reproduction of a similar condition in ducklings and pigeons and upon the development of characteristic histological changes with cytoplasmic eosinophilic inclusions in inoculated chorio-allantoic membranes of chick embryos.It was not possible to reproduce the original disease exactly by inoculation of shearwaters with egg-passage virus from the previous season because the birds did not develop blisters at the site of inoculation of the web. Nevertheless, three out of four birds died and the agent was re-isolated from the spleen of one of them.The ability of the virus to cause blisters on duckling webs was neutralized by shearwater serum taken at the convalescent but not at the acute stage of the disease, and complement fixation was obtained with convalescent shearwater serum.

Previous studies on natural virus infections of birds have been mainly limited to psittacosis and ornithosis, the pox viruses, Newcastle disease virus and some of the neurotropic viruses. However, the failure to infect mice by any route, and the ability of the shearwater virus to pass through filters with an A.P.D. of 48 mμ, seemed to rule out the psittacosis group as a cause of the infection. The ability of the virus to cause vesicles and the intracytoplasmic eosinophilic inclusion bodies suggested a member of the pox group of viruses, but the small size of the agent renders a relation to either the pox group or Newcastle disease virus unlikely. Several of the neurotropic viruses which infect birds, for example, Japanese B virus, are about the size of the shearwater virus, but they do not cause the formation of inclusion bodies and they are all pathogenic for mice. Foot and mouth disease virus is also of small size and produces vesicular lesions, but it is unlikely that the shearwater virus is the same since it was unable to infect a cow or the pad of a guinea-pig, and it grew in eggs more readily than foot and mouth disease virus.

There has obviously been insufficient work on the agent to postulate a new virus, but the properties described do not justify its classification in any of the known virus groups. The name puffinosis which was originally suggested still seems suitable for this disease of Puffinus puffinus puffinus.

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.

Fusiformis is a multicellular organism having the cytological characters of the Eubacteria, and normally reproducing by fission.

A few cells of all the strains examined pass through the L cycle; usually the initiation of this process follows the patterns described in Proteus and the Morax-Axenfeld bacillus. It has not so far been possible to grow these L-forms of Fusiformis in culture without immediate reversion to the bacillary form.

The stable forms described by other workers appear to be produced by a process analogous to the sexual conjugation seen in the Actinomyces.

The evidence suggests that passage through the L cycle is a normal function of Fusiformis in its natural habitat.