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.

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.

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.

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.

Suspensions of Strep. pyogenes, Staph. aureus, Ps. pyocyanea and micrococci in serum, distilled water, saline and oleic acid solution were allowed to dry on cover-slips. The numbers of bacteria surviving after periods of exposure were estimated from viable counts of extracted cover-slips.

All the organisms tested showed after drying a fall in viable count that was absent in aqueous suspensions not allowed to dry. Ps. pyocyanea was shown to have a lower survival rate on drying than the other organisms.

Serum afforded moderate protection to the suspended organisms during the period of drying.

0·1 mg./ml. oleic acid caused a rapid destruction of Strep. pyogenes and a significant destruction of Ps. pyocyanea as well as of Staph. aureus and micrococci in drying films of these organisms. The similarity of the fate of Staph. aureus and micrococci during drying in low concentrations of oleic acid is in contrast to the previously reported greater sensitivity of Staph. aureus to higher concentrations of oleic acid (1–10 mg./ml.) in the test-tube.

The implications of these findings are discussed in relation to skin and wound flora, and to environmental hygiene.

1. The lysis of Bact. coli by glycine is inhibited completely by various treatments: (a) by heating the bacteria at 65 or 100° C.; (b) by the action of Cr, Fe, and Al salts at concentrations which cause agglutination of the organisms, (c) by various heavy metals, including particularly Hg and Ag salts, at low concentrations (d) by lethal concentrations of formaldehyde and phenol.

2. The lysis is not inhibited by sodium fluoride, potassium cyanide, or sodium monoiodoacetate at concentrations which suppress the action of certain enzymes.

3. This evidence on the whole supports the rejection of the view that a simple physical process is responsible for lysis by glycine, but does not yet enable us to distinguish between the other possible mechanisms of the lysis because the treatments used might equally interfere either with the structural proteins of the bacteria, or with the hypothetical enzymes which might be concerned in producing the lysis.

1. Australian wild rabbits which had recovered from myxomatosis acquired in the field contained in their serum antibodies which could be detected by complement-fixation or neutralization tests for a long period (more than 18 months) after their recovery. The titre of complement-fixing antibody fell fairly rapidly during the first few months, and remained at a steady level thereafter. No change could be detected in the titre of neutralizing antibodies throughout the observation period.

2. Inoculation of such rabbits with myxoma virus was sometimes followed by the development of a local lesion at the inoculation site, and in these rabbits the titre of complement-fixing antibody rose, but there was no alteration in the neutralizing power of the serum. In other animals no lesion developed and there was no change in the antibody titre.

3. Serum was collected from a total of 824 wild rabbits from seventeen localities in eastern Australia with varying histories of myxomatosis since December 1950. Examination of 135 of these sera by both neutralization and complement-fixation tests showed that the results obtained by the two methods were in close agreement.

4. In many areas in which the disease was absent in the summer of 1950–1 and produced a violent epizootic in 1951–2, the majority (70–90 %) of the sera collected from rabbits 2–5 months after the height of the epizootic contained antibody to myxoma virus, i.e. the majority of the survivors had recovered from the disease.

5. Counts of the rabbit population before and after a violent epizootic in the summer of 1951–2, and the proportion of immune animals amongst the survivors in these areas showed that the case-mortality rate was between 99·4 and 99·8%.

6. Consideration of the results obtained in the serological surveys showed that the case-mortality rate was probably of this order (about 99·5%) in all areas in which there had been no disease or a negligible outbreak in 1950–1, whether they had a grade I or grade II kill in 1951–2.

7. In certain other areas, in which a grade I outbreak in 1950–1 was followed by a grade II or poorer kill in 1951–2, the observed immune rate was considerably higher than would be expected if the case-mortality rate (assuming that the whole rabbit population was susceptible) was 99·5%. The possible causes of this are discussed. Survival of immune survivors from the first epizootic through the second may be a factor of some importance, but it is probably not the only factor involved.

8. The areas just mentioned were exceptional. In most places there was either no build-up of population after the 1950–1 epizootic, or a second effective epizootic destroyed the majority of rabbits in the small population which had developed by reproduction of the survivors of the first outbreak.

1. Antibodies to the flagellar antigens of salmonellae are frequently present in the urine of Egyptians.

2. In many individuals, who are not urinary carriers but have schistosomiasis and have received T.A.B. vaccine, these urinary antibodies are derived from the plasma due to exudation or bleeding into the urinary tract.

3. In urinary enteric carriers, the urinary antibodies are due, at least in part, to the local production or release of antibodies within the urinary tract, as shown by the ratios of urine titre to serum titre with different H suspensions.

4. The production of antibodies within the urinary tract is considered to be an example of production or liberation of antibody by cells at, or close to, the site of infection.

The stock diet for rats and mice, diet 41 cubed, can be rendered sterile to broth by autoclaving at 15 lb./sq. in. for 20 min. without impairment of the nutritive value for breeding mice.

1. Second attacks of typhoid fever are uncommon. In the literature this has been taken to imply that an attack of typhoid fever confers a high degree of immunity which, nevertheless, may be overcome by such factors as re-infection by a large dose, an organism of a different strain, or one of high virulence.

2. Two large outbreaks of typhoid fever in the same community within 5 months produced eleven examples of second attacks. Clinical descriptions of four of these are given.

3. Details are given of the population at risk and the attack rates in various groups.

4. The evidence of these facts and figures, though inconclusive, suggests that an attack of typhoid fever does not confer more than a moderate degree of specific immunity. The influence of chloramphenicol upon immunity remains sub judice.

The investigation of 10,436 fermented tubes arising in the presumptive coliform examination of samples of water at six laboratories in England and Wales has shown that, with unchlorinated supplies, the unconfirmed presumptive test gives sufficiently accurate results. Full confirmation of all presumptive positive tubes of these waters is impracticable as a routine and ‘colony-confirmation’ gives a correction of only 0·5%. With chlorinated waters, however, ‘colony-confirmation’ discloses an error of 5·5%, largely due to the presence of anaerobes. This error can also affect the faecal coli (44° C.) count and may be so large in individual samples that assessment of chlorinated supplies should not be based on the presumptive test until this has been checked at least by plating.

1. A study of factors involved in the transmission of haemolytic streptococci has been made by experiments with healthy carriers and individuals whose upper respiratory passages were contaminated with Chromobacterium prodigiosum.

2. The following conclusions were reached: (a) Expulsion of haemolytic streptococci in droplet spray is determined by the nature of the expiratory activity (Fig. 1), the concentration of the organism in the saliva (Table 3) and the volume of salivary flow (Fig. 6).

(b) Droplets and droplet-nuclei are less important vehicles of transmission because of the extremely low content of haemolytic streptococci in them (Figs. 2–5)

(c) Dust particles carrying haemolytic streptococci and liberated by agitation of handkerchiefs more effectively pollute the air than violent expiratory activities (Figs. 4 and 5).

(d) Hands and clothing readily become contaminated by heavy nasal carriers (Table 4) and the former serve as the principal means of contaminating the environment and other individuals.

3. A diagram showing probable mechanisms of transmission is given (Fig. 7) in which hand contact is represented as a more important pathway of spread than air-borne dust which, in turn, is more important than either droplets or droplet-nuclei.