1. A highly selective medium for H. pertussis has been made by incorporating 4:4'-diamidinodiphenylamine dihydrochloride (M & B 938), penicillin and sodium fluoride in a partially defined base.

2. M & B 938 has an interesting selectivity which is much influenced by its environment, especially by the ionic composition of the medium. No pattern has emerged from a study of the effects of eighty salts and many other substances on its activity; but the gain in selectivity for H. pertussis produced by cysteine and magnesium malonate has been usefully exploited.

3. In a strict comparison with Bordet-Gengou the new medium yielded 28% more positive cultures from per-nasal swabs and 75% more from post-nasal swabs. With the new medium the incidence of serious rival growth from any part of the nasopharynx has been about 4% and, in contrast with Bordet-Gengou, postnasal swabs have yielded as many positive cultures as per-nasal swabs.

4. The new medium is simple to make, stable, reliable, economical of material and time and suitable for routine use with per-nasal, post-nasal or supralaryngeal swabs, sputum or vomit.

5. The new medium grows H. parapertussis poorly; but a highly selective medium for H. parapertussis is easily made by adding streptomycin and penicillin to Bordet-Gengou.

6. Whatever the medium, the nature and number of swabs are important factors affecting the isolation of H. pertussis: with the new medium positive diagnoses from per- and post-nasal swabs taken at the same time were about 40% more than from either swab alone.

7. A statistical analysis strongly supports the opinion of Bradford & Slavin (1940) that the relatively poor results with post-nasal swabs on Bordet-Gengou medium are due to the overgrowth of H. pertussis by rivals rather than to the absence of H. pertussis from the pharynx. It also indicates that the expectation of isolating H. pertussis on Bordet–Gengou varies directly with the numbers present and inversely with the numbers of rivals, especially of diphtheroids and streptococci.

8. Addition of 32 μg. stilbamidine di-isethionate and 0·25 unit penicillin/ml. to Bordet–Gengou makes an effective selective medium for oral streptococci related to, or of, groups K and L, but not for H. pertussis.

I wish to thank my clinical colleagues, especially Dr N. O. Richards and Dr A. Bogdan, for kindly sending swabs from their patients, Professor R. J. V. Pulvertaft for his continuous support, Dr J. A. Fraser Roberts for advice and help with the statistics, Dr A. J. Ewins and Dr H. J. Barber, May and Baker Ltd., for gifts of aromatic diamidines, Dr H. King for gifts of alkyl diamidines and Mr M. Breach, F.I.M.L.T., and Mr A. Drake, F.I.M.L.T., for their help with the preparation of sera, media and routine cultures. I am indebted also to the Central Research Fund of London University and to the Governors of Westminster Hospital for grants for the purchase of materials.

Over 500 medical students have been examined for nasal carriage of Staph. pyogenes at weekly intervals over a period ranging from 3 to 12 months.

Nasal carriers were classified as persistent, intermittent and occasional. Of the students, 39% were persistent or intermittent carriers in whom the staphylococcus was believed to colonize the skin of the vestibule of the nose; 42% were occasional carriers in whom the staphylococcus was only a chance inhabitant of the nares.

Staph. pyogenes was isolated from the anterior nares of persistent carriers on at least 90% of the occasions on which they were examined, and was of the same phage type on each occasion. From intermittent carriers it was isolated less regularly, but on at least 10% of occasions on which they were examined, and it remained of one phage type. Staph. pyogenes was isolated at less than 10% of swabbings from occasional carriers, and at each the organism was of a different phage type.

Eighty-nine per cent of persistent and intermittent carrier strains, and 54% of occasional carrier strains could be typed with phage filtrates. The strains not typable with phage filtrates, and found predominantly among occasional carriers, were considered worthy of separate classification, and it is suggested that typability with phage be used as a criterion of pathogenicity for Staph. pyogenes.

We wish to thank Prof. T. J. Mackie for his continued interest and advice; Dr J. P. Duguid for criticism and advice; Dr R. E. O. Williams and Miss Joan Rippon of the Staphylococcal Reference Laboratory, Colindale, who very kindly instructed one of us (J.C.G.) in bacteriophage typing; Dr Donald Cruickshank for taking nasal swabs from patients; Dr Cumming of the Blood Transfusion Department, Royal Infirmary, Edinburgh, for permission to swab blood donors, and the medical students who so willingly co-operated in this work.

In a school with 250 pupils all under the age of 10, sixty-four suffered from diarrhoea and abdominal pain. The victims sickened on 5 and 6 February, but it was not until 12 February that the first cases (bacteriologically confirmed) were notified to the Health Authority. All the notified cases were between the ages of 6 and 9 years and attended the same school. Older children, who attended other schools, were not affected.

Vitamin E-deficient rats, as well as normal and vitamin E-deficient chicks, failed to discriminate between two diets which were identical in all respects except that in one there was a deficiency of vitamin E and in the other there were adequate levels of vitamin E.

Grateful thanks are due to G. Crook for assistance in the care and management of the experimental animals.

1. The existence of passive immunity to myxomatosis was demonstrated by the inoculation of normal young rabbits with either myxoma-immune serum or saline, and their subsequent inoculation with the standard laboratory strain of myxoma virus. All the passively immunized animals lived longer than the control animals and a few survived.

2. Passive immunity could also be demonstrated in the offspring of myxoma-immune mothers. When these were challenged by mosquito bite inoculation with the standard laboratory strain of myxoma virus they either failed to become infected, or survived infection for several days longer than the progeny of normal does. When challenged by the intradermal inoculation of a slightly attenuated strain of myxoma virus 25 % of the progeny of immune does survived the infection, whereas none of the normal kittens survived.

3. The survival times of young rabbits in both the normal and passively immunized groups was influenced by their age, very young animals dying several days earlier than rabbits 4 and 6 weeks old.

4. The possible epidemiological consequences of passive immunity in the behaviour of myxomatosis in populations of wild rabbits are discussed.

Field observations on myxomatosis in wild rabbit populations of the Riverine Plain of south-eastern Australia, extending between August 1951 and March 1953, were reported. General observations on vector abundance and disease incidence were made over a large area. Detailed analysis of the population counts, age structure and immune status of the rabbit population, and the occurrence of insect vectors, were made at one site, Lake Urana.

The case-mortality rate in the first epizootic was in the neighbourhood of 99·8%, whereas in the second epizootic it was about 90 %, and many more chronically sick rabbits were observed in the later outbreaks. The virulence of eight strains of virus recovered from mosquitoes at Lake Urana in December 1952 and four strains recovered at Corowa at the same time was found to be somewhat reduced when they were compared with the original standard laboratory strain of virus. It is thought that this attenuation is the major reason for the observed change in the case-mortality rates.

The mosquitoes, Anopheles annulipes and Culex annulirostris were by far the most important insect vectors of myxomatosis in this region.

Thanks are due to Messrs F. N. Ratcliffe, B. V. Fennessy, and H. J. Frith of the Wildlife Survey Section of C.S.I.R.O. for helpful discussion and assistance during the field work and in the preparation of the paper. The technical assistance in the field of Messrs C. S. Hale and K. L. S. Harley is gratefully acknowledged, as is the generous help afforded by the landholders of Lake Urana, especially Mr J. Muldoon, and by Mr W. Quirk, rabbit inspector.

1. A quantitative comparison has been made of the observed mortalities from respiratory tuberculosis with those expected from a simple scheme of generation mortality.

2. This scheme gives a good account of the observed rates until about 1930, but is unsatisfactory thereafter.

3. It is concluded that these discrepancies cannot be due to chance, and that the generation effect has become obscured by other factors.

4. In particular the shift of maximum mortality into later life is not directly explained by the hypothesis, nor is such a shift a necessary consequence of the generation hypothesis of mortality.

I am greatly indebted to Dr J. C. McDonald for advice and constructive criticism during the writing of this paper; my thanks are also due to Dr G. S. Wilson for his comments.

In earlier reports on the physique of Oxford undergraduates attending the pilot student health service from 1947 to 1950 emphasis was laid on body shape. Parnell (1952) pointed out the tendency for centrally placed Sheldonian somato-types, that is those with more balanced mid-range body proportions, to occur more frequently in the Oxford sample than in American universities, a tendency incidentally which advances further according to the level of university performance attained. Tanner (1952) emphasized the tendency for Oxford students to show less mesomorphy, that is muscle and bone development, than American students but he reports a comment from Sheldon himself that the distribution at Harvard resembled the Oxford distribution more closely. This approach, by the analysis of body shape, to the problem of physical characteristics accompanying academic selection is of particular interest, but in calculating the somatotype, height is deliberately ignored by being placed as the denominator of all the body proportions employed. Height, however, is an index of body size, as opposed to body shape, and has an importance of its own. This report concerns observations on Oxford undergraduates in which more attention is paid to body size, and particular attention also to variation of weight during university residence.

1. Non-avid tetanus antitoxin appears to have a higher titre in relation to an avid standard if titrations are made against test toxins with a high toxoid content. The least avid serum tested appeared to be 2·87 times as potent when titrations were made against a toxin grown for 35 days than when a 2-day growth was used. Using the same test doses avid sera did not show this discrepancy.

2. A mixture of short-growth toxin and formol toxoid reacted similarly to the long-growth toxin.

3. Some non-avid tetanus antitoxic sera showed evidence of difference in goodness of fit with two test toxins; one serum was 2·49 times the titre of another when tested against one toxin and only 1·37 times when tested against another toxin.

4. Diphtheria toxoid has less affinity than toxin for antitoxin; this difference is greater with formol toxoids of poor immunizing efficiency; the difference is further accentuated if non-avid anti-toxin is used.

5. The Danysz effect may be very small if non-avid antitoxin is used.

6. In the presence of excess antitoxin, toxin or formol toxoid can combine with 3, 4 or more times its equivalent as judged by in vivo titrations for free antitoxin.

7. The serum ratio, i.e. in vivo titre/in vitro titre of high or low ratio antitoxin in multiple combinations is nearer unity than that of the original antitoxin.

In certain types of titrations the experimental results are obtained as percentages, say of mortality, at different dilutions in geometric progression of the test material. The result of a titration is then expressed as the 50% end-point which is estimated by interpolation as follows.

In a previous paper (Bailey, 1953a) I discussed the distribution of the total size of a stochastic epidemic, involving both infection and removal, in a given group of homogeneously mixing susceptibles. The model employed was of the ‘continuous infection’ type, according to which infected individuals continue as sources of infection until removed from circulation by recovery, death or isolation. This may be contrasted with the chain-binomial type of model which entails short periods of high infectivity and approximately constant incubation periods (see, for example, Greenwood, 1931, 1949; Lidwell & Sommerville, 1951; Bailey, 1953b). The basic assumptions are that, with x susceptibles and y infectious persons in circulation, the chance of one new infection taking place in time dt is βxy dt, while the chance of a removal is γy dt, where β and γ are the infection and removal rates, respectively.

A bacteriological study of burned patients and of the staff and environment in a burns unit was made with the purpose of discovering the principal reservoirs and routes of transfer of Ps. pyocyanea.

Infected burns appeared to be the most important reservoirs. About 3 % of the stools of normal subjects and of patients with intestinal symptoms carried the organism, which was also isolated from the nose, throat, nasopharynx, skin and ear of a small proportion of patients and staff in the burns wards.

The hands of nurses in the wards were often contaminated with Ps. pyocyanea, and presented a likely vector in the transfer of the organism by contact—e.g. from the bandages of infected patients, and from furniture and other objects near to their beds.

It was shown by slide agglutination that a new type of Ps. pyocyanea admitted to one of the wards spread freely in that ward but hardly at all to the other ward. Since patients from both wards used the same dressing station and operating theatres, it seemed from this finding that a large proportion of the cross-infection occurred in the wards.

Polymyxin dusting powder was shown in a controlled trial to protect exposed burns against contamination by Ps. pyocyanea.

These results are discussed in relation to the mechanism of transfer of the organism and the methods of preventing cross-infection. The need to use several methods concurrently is emphasized, since none of those which have been investigated contributes more than a partial effect. Cubicle wards are advocated, since much cross-infection is shown to occur in open wards.

We are much indebted to Dr G. T. Cook for kindly letting us use results obtained by him at the Oxford Public Health Laboratory. We also wish to thank Prof. J. F. D. Shrewsbury of Birmingham University and our colleagues at the Birmingham Accident Hospital for their valuable co-operation, and Dr A. C. Cunliffe of King's College Hospital for information on the typing of Proteus from patients in our wards.

In the period following the last war a large acceleration has occurred in the rate of decline of the death-rates of the younger age groups. The oldest age groups have not shared in this improvement. This course of the death-rates is in striking contrast to the predictions of two decades ago when it was thought that any substantial improvement in the age specific rates was most likely to occur at the older ages. A large part of the fall at younger ages has been due to the decrease in mortality from infectious diseases and tuberculosis. The death-rates at ages 5–24 are now probably almost at a minimum and if a further appreciable improvement is to be made in them the death-rate from violence must be reduced. Violent deaths account for roughly one-third of all deaths in this age range.