During a period of 13 months, 1273 consecutive samples of water received at this laboratory were submitted to a modified presumptive coliform test which included single tubes of four different media. These were: (1) MacConkey broth, (2) formate lactose glutamate medium (pH 7·5), (3) lactose glutamate medium (pH 7·5), and (4) Folpmers's glucose glutamic acid (pH 6·0). 955 samples gave exactly the same results in all four media, but the remaining 318 samples produced differences which enabled comparisons to be made between the media.

As compared with MacConkey broth, the three glutamic-acid media produced between 24–30% more isolations of Esch. coli, and the formate and the glucose media produced at least the same total number of true coliform organisms (including Esch. coli) with appreciably fewer false positive reactions. The lactose glutamate medium gave no false positive reactions but, through the suppression of coliform organisms other than Esch. coli, reduced by 16% the total coliform yield. MacConkey broth gave the largest early (18 and 24 hr.) yield of positive reactions, but the results at the end of 24 hr. showed the formate medium to be not far behind MacConkey broth and appreciably ahead of the glucose medium.

Further experiments with the formate lactose glutamate medium adjusted to different pH's, ranging from 6·0–7·5, indicated that a medium of pH 6·7 provided optimal conditions for the early development of both acid and gas. It was therefore decided to test this observation more fully with routine samples. During a period of 4 months, 279 unselected consecutive samples of water (of which 78 gave positive results) and 57 consecutive unchlorinated water samples (56 of which gave positive results) were examined by a multiple-tube technique in both MacConkey broth and formate lactose glutamate medium (pH 6·7). In the former series the MacConkey broth contained the inhibitory bile salt previously used; in the latter series this was replaced by a relatively non-inhibitory bile salt. In both series the formate medium yielded an appreciably increased total of coliform organisms (12 and 17%) including an increased total of Esch. coli (27% in the former and 13% in the latter series), and in both series also the results at 18 hr. were abreast with, and at 24 hr. ahead of, those obtained in MacConkey broth.

With certain reservations, it is considered that formate lactose glutamate medium (pH 6·7) can be offered as a suitable alternative to MacConkey broth for the presumptive coliform test of water. Wider trials of this medium would be required before this claim could be fully substantiated.

My thanks are gratefully accorded to Drs W. H. H. Jebb and A. H. Tomlinson of the Oxford Public Health Laboratory for invaluable advice during the investigation and to Dr Ian Sutherland of the M.R.C. Statistical Research Unit for statistic appraisal of the results. I am also greatly indebted to my technicians Mr J. H. Evans, F.I.M.L.T., and Mr G. H. Lowe, F.I.M.L.T., for their unstinting help.

1. A review of the few studies so far made on the high mortality from tuberculosis among elderly men, and a consideration of the available statistics, indicate that urbanization is one of the principal factors responsible.

2. In the present inquiry, which was confined to London, 445 newly diagnosed cases of tuberculosis in men over 40, together with the same number of paired controls, were studied by means of a questionnaire and of personal interview.

3. It was found that the tuberculous patients differed significantly from the controls in the following characteristics; Scots, Irish, Welsh, or foreign nationality; single, widower or divorced; resident in common lodging houses or hostels; inadequate or special diet; history of gastrectomy; a winter cough; shortness of breath; insufficient sleep; and heavy drinking and smoking. On the other hand, overtime or night work, diabetes, rheumatoid arthritis, asthma, and mental illness were distributed fairly evenly in the two groups.

4. Unfortunately no group of elderly women exists in this country living under the same sort of conditions as the elderly men studied here, so that it was impossible to determine how far the various factors considered were responsible for the high rate of late adult male tuberculosis. A study, however, of a population of established civil servants living under ordinary conditions revealed little difference between the observed rates of tuberculosis and those expected on the basis of national notification figures for men and women in the older age groups.

5. It appears that a low standard of personal hygiene, associated especially with heavy smoking and drinking and residence in loading houses, predispose to the development of tuberculosis in the elderly male. Part of the evil effect of living in common lodging houses in particular may be due to the increased risk of exposure to tuberculous infection that it entails.

6. It is tentatively concluded that the casual workers of an urbanized community are one of the principal reservoirs of tuberculous infection in large towns, and since there is no numerically comparable female population, this group, and its immediate male contacts, account in large measure for the difference between the male and female tuberculosis rates in the older age groups.

This work was initiated during the tenure of a Prophit Scholarship of the Royal College of Physicians, and completed with the aid of a grant from the Medical Research Council.

I am indebted to members of the Prophit Committee of the Royal College of Physicians for their support and encouragement, and most particularly to Dr G. S. Wilson, Director of the Public Health Laboratory Service, under whose guidance the work was carried out. Figures relating to the incidence of tuberculosis in the Civil Service are published by kind permission of Dr W. E. Chiesman, Treasury Medical Adviser, and Dr M. C. W. Long, Dr J. W. Parks, and Dr H. Stannus Stannus, whose departmental records were used to compute the figures.

I am greatly indebted to the consultants and staff of the seventeen chest clinics who co-operated in the investigation, for their interest and help in tracing patients, and to the medical superintendents of numerous sanatoria and chest hospitals, and to the surgeons who permitted me to interview patients under their care as controls.

I should like also to acknowledge the assistance received from the medical officers of health of the metropolitan boroughs who kept me informed of notifications from lodging houses in their areas, and supplied information about the accommodation.

1. Results are presented of palatability tests and chronic toxicity tests with five anti-coagulant rodenticides at a variety of concentrations against wild Rattus norvegicus, R. rattus and Mus musculus. These results are compared with similar data for warfarin. Estimates are also given of the acute oral toxicity of two of the five, fumarin and diphacinone, to white rats.

2. The toxicity of the compounds vis-à-vis warfarin is examined from the standpoint of the risks to domestic animals involved in their use as rodenticides.

3. Coumachlor, 2-isovaleryl-1, 3-indandione and 2-naphthyl-1, 3-indandione are considered to be less effective than warfarin against R. norvegicus. Their effectiveness against R. rattus remains to be demonstrated.

4. Fumarin appears to be about as good as warfarin against R. norvegicus and R. rattus at similar concentrations. It appears to be slightly less effective against M. musculus.

5. Diphacinone at 0·0025% is regarded as a good alternative to 0·005% warfarin against R. norvegicus. At 0·0125% it is probably more effective against R. rattus than is 0·025% warfarin. The two poisons are about equally effective at this strength against M. musculus, but diphacinone is probably slightly more dangerous for domestic animals.

6. The results of a small number of field trials with fumarin and diphacinone are briefly summarized.

So many of our colleagues and others have helped at some stage or other of our investigations that it would be tedious to mention them all by name. We must, however, single out for our special thanks Mrs M. Rowe and Miss E. Taylor who carried out a large number of the laboratory tests, Mr A. Taylor on whose chemical experience and facilities we have freely drawn and Mr C. H. B. Worrall, Miss B. Jones, Mr S. R. Surtees and Mr J. H. Cuthbert (Department of Agriculture for Scotland) who carried out the field trials.

The mosquitoes Aedes aegypti, A. triseriatus, Culex pipiens, C. quinquefasciatus, and Anopheles quadrimaculatus were all found to be efficient experimental vectors of Shope's virus-induced fibromas of cottontail rabbits, transmitting the virus during interrupted feedings as well as after long intervals from an infective meal. The reduviid bugs, Triatoma infestans, T. phyllosoma pallidipennis and Rhodnius prolixus, and the bedbug, Cimex lectularius, were also capable of transmitting fibroma by interrupted or delayed feeding.

Evidence from various types of experiments indicated that arthropod transmission is mechanical, the virus being extremely stable in the insects. Some experiments did indicate the possibility of virus proliferation. Although mosquitoes did seem to serve as ‘flying pins’ when transmitting virus by interrupted feeding, they certainly were distinctive in that they maintained their ability to transmit for very long periods of time. To transmit fibromas, arthropods actually must draw virus up between the stylets of the mouthparts; mosquitoes were unable to transmit by feeding through skin moistened with a suspension of fibroma virus or by feeding subsequent to having their mouthparts painted with a virus suspension.

While cottontail tumours at peak virus titres are always infective for suitable insects, the fibromas of adult domestic rabbits generally are not infective, even though the virus titre is equivalent. However, the tumours of suckling domestic rabbits do become infective for insects.

The variables operating in respect of the risk of provoking paralytic poliomyelitis by inoculating children with different prophylactic reagents have been analysed.

It is concluded that the use of combined diphtheria fluid toxoid and pertussis vaccine, administered in early infancy, incurs a minimal risk and is to be recommended because of its immunological effciency, its unquestionable value in helping to maintain a high immunization rate against diphtheria in the child community and for its marked administrative convenience.

Two units, within a mouse-breeding colony, with different breeding systems, have been compared from the point of view of general healthiness of the breeding stock. In one unit the monogamous-pair system, involving post-partum oestrus mating, was employed and in the other the harem system, with isolation of the pregnant females for each litter-down until after the post-partum oestrus. The two units were housed separately and had different staffs. The monogamous-pair unit was accommodated in four small rooms not directly connected; the harem unit in two larger connecting rooms. The methods of cageing, bedding, feeding, watering, care, culling and subsequent procedures were identical for both units and the same system of recording individual detailed information relating to health and breeding was followed for the two units. The size of the two populations studied was 1198 and 1024, respectively, the larger number belonging to the harem unit in which the mice were retained for a significantly longer period. These mice were moved more frequently and handled much more often.

Apart from a small outbreak of Tyzzer's disease (in the harem-bred unit) and sporadic cases in both units spread over the whole period of the survey—some 3–4 years—the general health of the two units was good. There were no cases of salmonella infection, mousepox, pasteurellosis or other serious infections. Throughout the period both units maintained a high standard of productivity and there was no evidence that the mating of the monogamous pairs at the post-partum oestrus led to any weakness or ill health. As would be expected, however, the losses from death and culling were greater among the females in both units.

The health record of the monogamous-pair bred unit was consistently higher than that of the harem-bred unit. There were more cases of Tyzzer's disease in the harem-bred mice and more evidence generally of ill health in this unit. Infertility was three times greater with the harem-bred mice as compared with those in the monogamous-pair unit.

Details of the two systems are discussed and although the records maintained for the two may not be strictly comparable it is concluded that, under the conditions obtaining, the monogamous-pair breeding system yielded a healthier colony of mice than the harem breeding system.

I should like to thank Dr J. S. Patterson and Mr R. Cook for placing many of their records at my disposal, Mr S. Peto and his staff for carrying out much of the tedious compilation of data, and Dr D. W. Henderson, F.R.S., for affording me facilities for this work. To these I am especially grateful for their interest, advice and assistance.

1. The mesenteric lymph nodes and faeces of pigs, cattle, sheep, dogs and cats and the intestinal wall and other organs of chickens in Essex, England, have been examined for salmonellae. These animals were either healthy or were not suffering from clinical salmonella infection.

2. Salmonellae were isolated from the mesenteric lymph nodes of sixty (12%) of 500 pigs, nine (4·5%) of 200 dogs, five (2·5%) of 200 cats and none of 200 cattle and 100 sheep. None was found in the chickens.

3. One (0·5%) of the cats and one (0·5%) of the dogs and six (1·2%) of an additional 500 healthy pigs were excreting salmonellae in their faeces.

4. Of the seventeen serotypes found in pigs, Salm. typhi-murium, Salm. anatum and Salm. cholerae-suis occurred most frequently.

5. All strains of Salm. cholerae-suis were isolated in brilliant green MacConkey broth; selenite broth was unsuitable for this purpose.

6. Despite the high isolation rate from pigs, clinical salmonella infection was diagnosed relatively infrequently at this laboratory. Salm. cholerae-suis was isolated from only one of seventeen epidemiologically unrelated cases of necrotic enteritis in pigs.

7. The results are discussed from the public health and agricultural view points with particular regard to the part infected feedingstuffs may play in causing salmonella infection in animals.

The expenses of the investigation were, in part, defrayed by grants from the Agricultural Research Council, whose help I gratefully acknowledge.

I am grateful to Mr A. J. Harman and Miss Linda Kelly for their capable technical help and to Dr K. C. Sellers for useful suggestions made during the course of this work. I am also indebted to Dr Joan Taylor for typing all the salmonella cultures and to Mr L. G. Smart for collecting the lymph nodes from the cattle, sheep and pigs.

1. An examination of eighty-nine samples of uncooked and thirty-eight samples of cooked food purchased by one particular hospital showed that the purchased food was bacteriologically clean.

2. A similar examination of 173 samples of food after it was cooked and prepared for serving in the hospital kitchens showed that, with the exception of cold chicken, the bacterial flora was greatly reduced by cooking. Ten of forty-six samples of cold chicken, however, were contaminated with fairly large numbers of Cl. welchii.

3. An investigation into the cooking and handling of the fowls indicated that contamination of the cooked fowls with kitchen dust was a probable explanation for the presence of Cl. welchii.

4. Immediate refrigeration of the fowls, well separated on shallow trays, was shown to be a satisfactory method of preventing the growth of contaminating Cl. welchii to any dangerous extent.

5. Six outbreaks of food poisoning, in which there was an association between cold chicken and the clinical symptoms of Cl. welchii food poisoning, are reported and discussed.

I have pleasure in thanking Dr Betty Hobbs of the Food Hygiene Laboratory of the Public Health Laboratory Service at Colindale for the serological typing of numerous strains of Cl. welchii; Mr D. B. Colquhoun for assistance with the phage-typing of the staphylococci; Mr G. Kerr for the photography; and the kitchen staff in the hospital concerned for making possible the numerous samplings of food and the other inquiries into the day-to-day affairs of the hospital catering department.

Re-examination of the U-virus of Philipson & Wesslén has shown it to be a typical ECHO virus closely related to Type 11 of this group. Ultrafiltration and ultra-centrifugation techniques indicate that the virus particle has a diameter of about 27 mν and serological studies confirm its antigenic relationship to the ECHO group.

The virus has been successfully transmitted via the nasal route to volunteer adult subjects. All of them became infected but the clinical picture showed no more than a very mild gastro-intestinal illness or a slight disturbance of the general well-being.

Passage in monkey kidney cells appeared to attenuate significantly when compared with short-term passage in human embryo-lung culture, and this seemed to affect the isolation rate from subjects so infected.

The virus is highly immunogenic. Antibodies to the U-virus have been found in normal persons residing in Great Britain.

We wish to thank the volunteers for their willing co-operation and Miss J. B. Macdonald for help with the clinical observations. Dr A. D. Macrae supplied the ECHO Type 11 prototype virus and immune serum and Prof. C. H. Stuart-Harris supplied the pooled human sera. The Director, Microbiological Research Establishment, Porton, afforded the use of the ultracentrifuge. Monkey kidneys were supplied by the M.R.C. polio vaccine control laboratories. Mr M. C. Brebner and Miss P. K. Pearce assisted with the laboratory work.

The fermentation of mannitol by coagulase-positive staphylococci has been studied. It was found difficult to obtain reproducible results by methods which could be conveniently used in a routine department.

A method of grading based on the fermentation of mannitol has been examined. Organisms of the supposedly most dangerous grade (Grade A) were isolated slightly more frequently from lesions than from carriers, but from all sources a high proportion of strains belonged to this grade.

It was not possible to correlate the grades to which staphylococci were assigned with their production of diffusible antigens.

In this hospital it seems that the proportion of strains assigned to Grade A has become very much higher than it was 15 years ago.

We thank Prof. R. Knox, Mr J. B. Blaikley, Dr W. H. H. Merivale, and Dr R. H. Gorrill for the help and advice they have given us in the course of this investigation and numerous members of the nursing staff of Guy's Hospital for their co-operation in checking records and answering questions.

Skin lesions with histopathology similar to that seen in lesions in man have been produced in calves by the experimental inoculation of cultures of Myco. ulcerans. Sensitization of infected calves to mammalian tuberculin as well as to ulceranin has been demonstrated.

It is considered unlikely that cattle are a reservoir of infection for man.

The expenses of this investigation were met by a research grant from the Board of Management, Alfred Hospital.

We are indebted to Dr A. V. Jackson, Director of Pathology, Alfred Hospital, for the reports on histopathology.

When the manifold system of freeze-drying is used the practice of plugging the tubes containing the product to be dried would seem to be necessary. It should be emphasized that a loose plug implies teased out cotton-wool and not just a loosely fitting one. Virus was recovered from the drying apparatus under various conditions when unplugged tubes were used. No virus contamination could be demonstrated when the tubes were plugged.

The Mahoney, Type 1, poliomyelitis virus had been through six to-and-fro monkey kidney-tissue culture and suckling mouse passages. Early paralysis was produced in groups of mice inoculated directly from infected tissue-culture fluid, but mouse-to-mouse passage failed to produce paralysis except in an occasional mouse. At the 7th tissue-culture mouse passage, the virus harvested from paralysed mice was inoculated into 100 mice. One mouse developed paralysis within 24 hr. From this mouse a variant of Mahoney virus was isolated which has now been through seventy-five mouse-to-mouse passages and produces paralysis in 90–100% of mice within 3 days.

The authors would like to express their deep appreciation of Prof. A. Kipps' constant interest and encouragement.

Experiments were made with five pathogenic serotypes and five non-pathogenic Esch. coli strains to study the competitive growth of mixed coli cultures in nutrient broth. In associations incubated at either 37 or 44°C. the organism inoculated in smallest numbers increased proportionately after 18 or more hours' incubation. The greater the initial disparity, the greater was the increase. Broth culture favoured the pathogenic strains only when these were numerically inferior in the inoculum. The tendency to numerical equation increased with increasing length of incubation.

A study was made of the use of nutrient broth as an aid to the isolation of pathogenic Esch. coli strains from the faeces of infants. 120 positive specimens were examined. Nutrient broth incubated at 44° C. was the most successful method, and when used as a complement to direct plating resulted in an additional 19·6% of positive specimens. The main value of nutrient broth as an enrichment method is in the examination of the faeces of suspected carriers and convalescent patients, in which the pathogen is likely to be outnumbered by non-pathogenic Esch. coli strains.

I wish to thank Prof. Scott Thomson for his advice and helpful criticism, and Dr R. W. S. Harvey for his interest and encouragement.

1. A brief review of the literature on acid-fast bacilli found in skin lesions is given.

2. The characteristics are described of an acid-fast bacillus isolated from a skin lesion found in the South African Xenopus laevis.

3. Reasons are given to support the view that chromogenic acid-fast bacilli cultured from skin lesions belong to the group of ‘Saprophytic acid-fast bacilli’.

4. The possibility of using the Middlebrook-Dubos haemolysin test as a tool to differentiate atypical acid-fast bacilli is discussed.

Thanks are due to Dr Charles Pike for all the histological reports, to Mr T. R. West for the microphotographs, to Dr Piersma (Messrs Lederle) for the gift of special sensitive Old Tuberculin for the Middlebrook test, to Dr Nassau for patients' sera and the ‘Goss’ antigen and finally to Mr W. J. Fincham for the titrations of the haemolysin titres.

A special cabinet was designed to protect the operator, during post-mortem examinations on animals infected with pathogenic organisms, against the risk of enhaling infected material and the surrounding area from becoming contaminated. The cabinet was suitable for small animals including mice and guinea-pigs.

1. The recovery, after poisoning, of the rat population of eight sewer systems was measured by the bait-census method.

2. In three of the systems the mean rate of increase was of the order of 3% per week. This is attributed solely to breeding and is regarded as typical for rats in sewers.

3. Higher rates of increase (up to 11·8%) were also recorded but are believed to have been partly due to immigration or to have been only apparent (as a result of census difficulties).

4. The consequences for control of a rate of increase as low as 3% per week are discussed.

Our thanks are due to eight Local Authorities, their Chief Public Health Officers and members of their staffs, without whose help the work would have been impossible, and to a number of colleagues, especially Mr J. H. Greaves, who helped with much of the census work.

The virulence of nine strains of Klebsiella was tested in mice inoculated by peritoneal and oral routes, the latter being a convenient method of inducing pneumonic infections.

At similar doses, shorter survival was observed in young mice. Injected by the intraperitoneal route, organisms from 16 hr. old cultures proved more virulent than those from older cultures, but no such difference was obtained orally. Repeated subculture of a virulent strain failed to attenuate its oral virulence and killed suspensions of the same strain were without effect. With only two exceptions, all strains were more virulent when administered orally than intraperitoneally. Wherever possible the concept of relative virulence was employed in making statistical comparisons. It is, however, considered that virulence is an unsatisfactory taxonomic discriminant.

We would like to thank Dr I. Friedmann, Dr F. Fulton and Dr G. Meynell for their helpful criticism. We are also indebted to Dr Lynne Reid for her comments and to Mr G. B. Newman for checking the calculations. Thanks are also due to Mr G. D. Breach and Mr G. Latchford for technical assistance, to Mr D. Connolly for preparation of graphs and Mrs A. Gorvin for secretarial assistance.

The National Institute for Water Research of the South African Council for Scientific and Industrial Research has been engaged on extensive research into the conservation of water supplies and into the reclamation of industrial and sewage effluents. Within the framework of this programme, a comparative study of the efficiency in the reduction of bacterial numbers by existing conventional sewage treatment plants has been carried out. The numerical decreases in bacterial populations after primary sedimentation, biological filtration, the activated sludge process, secondary sedimentation (humus tank), and final sand filtration have been compared with the reduction in bacterial numbers attained by the treatment of sand-filter effluent, humus tank effluent, and primary biological filter effluent in units for further biological purification.

Various types of units for this purpose have been investigated, and from available results it appears perfectly feasible to consider the suitability of effectively purified sewage effluents as sources for raw water supplies for industrial and domestic use. Sewage effluents after final further biological purification could be admitted for unrestricted discharge into rivers. The possibility of objections from the point of view of public health and future use is completely ruled out by the fact that the quality of the final effluent is as good as that of river water.

A variety of experimental units for further biological purification of sewage effluents have been studied, and a comparison of the results obtained from grass-plots, artificial vleis (a natural vlei in South Africa is a marshy or swampy depression in the ground in which water collects and which supports a standing vegetation), algal beds, artificial model rivers, and maturation or oxidation ponds have shown that maturation ponds, possibly a number of ponds in series, with an established microflora and microfauna of their own, may provide the final solution of the problem. Further biological purification will play an important role in the conservation of water supplies and will contribute to the raw water sources available for industrial and domestic use.

In parallel with these studies, the effect of the discharge of sewage effluents from conventional treatment plants into a river system has been investigated together with the fate of the sewage bacteria after admission to a natural environment. The manifestations of self-purification have been recorded, and the additional or superimposed effect of run-off and drainage from populated and unpopulated areas, as well as the admission of storm-water, have been considered together with the effects of seasonal variations due to climatic conditions.

The author wishes to express his gratitude to his assistants who bravely bore the burden of the routine work involved, and wishes to thank the S.A. Council for Scientific and Industrial Research for permission to publish this paper.

Five media—MacConkey broth, lactose broth, Teepol broth, lauryl sulphate broth and glucose glutamic acid medium—have been compared as primary media for the isolation of coliform organisms from 1691 samples of water received for examination during a period of 18 months.

Of these samples 1043 (61·7%) gave an identical result in all five media. In the other 648 (38·3%) samples there were differences either in the types of coliform organism isolated or in the rapidity with which the reactions appeared in the different media. The differences in the final yields of coliform organisms and Escherichia coli in the five media are not statistically significant.

There were differences in the number of false presumptive positive reactions given by the different media—lactose broth giving many more false presumptive positive reactions than any of the other media and nearly six times as many as MacConkey broth, which gave the smallest number.

All the reactions tended to appear rather more slowly in glucose glutamic acid medium than in the other media.

Glucose glutamic acid medium has the advantages of being a chemically defined medium and of not containing any substances which are likely to be inhibitory to coliform organisms. Other glutamic acid media may be found on further investigation to give better results than the present glucose glutamic acid medium, but those presented here suggest that media containing glutamic acid are worthy of further investigation.

I am indebted to Dr Ian Sutherland of the M.R.C. Statistical Research Unit for statistical advice and to Dr R. D. Gray of the Public Health Laboratory, Newport (Mon.) and to Dr A. H. Tomlinson of the Public Health Laboratory, Oxford, for much helpful criticism.