Thirty strains of Pseudomonas aeruginosa, isolated from routine clinical material, were investigated, with particular reference to the metallic lytic effect and the bacteriophages they carry. From the filtrates of these strains, twenty-five bacteriophages or phage variants were isolated, and the effect of these on the various bacterial strains and some of their variants were investigated.

It has not been possible to elucidate the nature of the agent responsible for the metallic lytic effect. The true phages isolated, however, present many features of interest which warrant their more detailed study.

Part of this work was carried out in the Nkana Kitwe and C.S.I.R. virus research unit at the U.C.T. Pathology Department.

A survey of the extent of bovine type human tuberculosis in Northern Ireland has been made from unselected material during the past 5 years.

Only one case of bovine type pulmonary tuberculosis was found out of more than 1000 cases.

The proportion of bovine type cases in the non-respiratory group was 4·3%; 3·3% of meningitis cases were of bovine origin.

A marked decline in the extent of bovine type infection is shown to have occurred during the past 10 years. This is believed to be due to a great increase in the pasteurization of milk during this period. Milk was a particularly valuable food during the war, and pasteurization facilitated its distribution.

1. Thirty-four vaginal Corynebacteria have been grouped and subgrouped according to their cultural and biochemical characters. Owing to their instability and to the rigid taxonomy of the Corynebacteria, the exact identity of many of the strains is uncertain, but their characters have been compared with some of the Corynebacteria which have been given specific rank.

2. The majority of strains were carbohydrate-fermenters and many were of the hyperacid type. These may be associated in some way with a normal high vaginal acidity.

3. Many instances of resemblances to C. diphtheriae in morphology, in staining reactions, and in cultural appearances relating to the different dissociative phases, were encountered in the examination of these strains, and, in fact, some of the cultural types seen were analogous to those of C. diphtheriae described by Mcleod.

4. Intradermal tests on rabbits showed that many of these strains, including some from each group, were capable of inciting inflammatory reactions in their tissues, and it is suggested that they may play a secondary part in some infections.

The British Standard Code of Practice and other authoritative guides, recommend minimum rates of ventilation related to the size and use of rooms, and structural means for providing them. But the difficulty of measuring actual ventilation rates suggests that it is seldom done.

1. An account is given of the relationship of Bact. coli type O55 B5 H6 to cases of infantile gastro-enteritis.

2. In Aberdeen this organism has now largely replaced the O111 variety (alpha) which had been the prevalent type during 1947 and 1948 in its association with the disease.

3. A brief description has been given of the clinical findings, which show no marked deviation from those found in similar cases elsewhere. The actual severity of the illness as judged by the mortality rate has been greatly lessened.

4. The value of medication with chloromycetin in a small number of cases has been discussed. It is believed that the use of the drug eliminates the organism from the bowel in certain cases and helps to reduce the number of cross-infections even in a cubicle ward. The average weekly weight increase of children on chloromycetin was almost double that of a group of healthy, untreated children.

5. Several small outbreaks of infantile diarrhoea associated with the O55 B5 H6 type in wards and institutions have been recorded. In some the numbers of symtomless carriers of the O55 type have exceeded those of clinical cases also harbouring the same organism.

6. ‘O’ and ‘H’ agglutination tests made with suspensions of the prevalent strain of Bact. coli on sera from cases examined early in the disease were mostly negative. Such positive titres as were obtained were low. Examination of paired acute and convalescent sera from 29 cases gave some evidence of increasing titre during the course of the disease in eight cases, but such increase was of low order.

7. The present bacteriological evidence suggests that further specific types of Bact. coli will be found to be associated with the disease.

A technique for carrying out the anti-globulin test with Salm. typhi O suspension in described; this technique has been used to examine a number of human sera. The degree of amplification of agglutinin titre and the final titres obtained were appreciably greater in the sera of individuals with a history of Salm. typhi infection, some of whom were carriers, than in the sera of normal individuals.

A paper on biological assays and biological standards might be expected to start with a definition. What is a biological assay and what is a biological standard? However, I shall for the moment make the somewhat doubtful assumption that we all know the answer to those questions but shall return to them later, making a start meanwhile by discussing some aspects of the history of our subject.

1. Five anto-horse sera which did not contain antibodies for horse-serum crystalbumin have been shown by absorption experiments to contain horse-serum crystalbumin.

2. All five sera precipitated when mixes with other anti-horse sera containing anti-crystalbumin, precipitation being due to the presence of horse-serum crystalbumin in one antiserum and of anti-crystalbumin in the other.

3. Antigen and its homologous antibody were never found together in the serum of an animal, and contradictory results in other experiments are probably due to impure multiple antigens.

4. It is concluded that anti-horse sera may contain some of the antigenic components of injected horse serum together with antibodies to other antigens of the horse serum, but not homologous antigen and antibody. Consequently, the ‘mutual’ precipitation of anti-horse sera is due to the presence of a number of antigens in horse serum, one or more of which, present in one anti-horse serum, in the absence of its homologous antibody, may precipitate when mixed with another anti-horse serum which contains the homologous antibody.

5. The use in these experiments of a single α-procedure optimum as the indicator of an antigen-antibody reaction illustrates a method enabling the investigation of problems involving single antigen-antibody reactions, even though the available reagents consist of mistures of antigens and mixtures of antibodies.

The recorded mortality from tuberculosis has fallen greatly in England and Wales since the middle of the nineteenth century when records were first available. The fall in rate has not occurred uniformly in all age groups however, and one result of this is that the maximum mortality rate in males is now occurring at a much later period of life than formerly.

1. The paper represents an attempt to estimate the error of the standard 10 ml. Haldane gas analysis apparatus under routine conditions of use.

2. The ultimate error of the instrument under optimum conditions has been obtained from duplicate mercury calibrations of the same instrument and corresponds to s.d. = 0·013% gas. A significant day-to-day variation in calibration was found.

3. The accuracy in routine use has been determined by replicate estimations of CO2 and O2 in air and from estimation of CO2 in designed experiments. The data show an error corresponding to s.d. = 0·027 to 0·13%. This is far larger than that described by Haldane.

4. Examination of the distribution of terminal digits in burette readings shows that the smallest scale division is in fact not being divided into ten parts by the worker. Preference for certain digits varies with the individual, with time, and with the accuracy required.

5. There is a marked tendency for a worker to obtain an ‘expected result’, whether this is derived from a previous estimation of the same sample or from knowledge of the expected result; such bias tends to reduce the apparent error of estimation. Bias of replication—‘prejudice error’—may play a part in many forms of measurement.

6. The results and conclusions are discussed in relation to other published data on errors of measurement in general.

1. Salmonella antisera from a number of animals, including man, have been examined by conglutinating complement-absorption and haemolytic complement-fixation tests for the presence of anitbodies. Both a soluble antigen and a particulate antigen of washed suspended orgainsms have been used. The behavior of the antisera was comparable with that previously recorded with the mallein antimallein system, in so far as the reactions obtained with the different complements followed the same general pattern.

2. Two factors were found to explain the failure of certain antisera, in conjunction with the antigen, to adsorb certain complements. On the one hand, a few antibodies themselves appeared incapable of fixing a particular complement. On the other hand, although some antisera failed to fix specific complements, their antibodies, isolated from the serum, were able to fix the complements concerned. In these cases it appeared that the heated serum contained a non-specific factor that prevented the adsorption of the complements.

3. The existence of such non-specific factors in certain heat-inactivated sera is illustrated in Figs. 11–14. An examination of the mechanism involved does not appear to implicate the procomplementary effect of sera, although this effect in itself is a complex problem requiring further elucidation. The few experiments carried out indicate that the factor in the inactivated serum does not come into play and inhibit the adsorption of complement by an antigen-antibody complex without the initial intervention of some component of complement. Only after this has occurred is the inhibitory factor able to block any further complement adsorption.

4. We have discussed the implications of these experiments and their possible relationships to the complementoid phenomena described by previous workers.

Techniques for the fractionation of C′ 1 and C′ 2, and for the specific inactivation of C′ 4 of horse complement are described, and shown to be satisfactory. These three components of complement and also conglutinin are found to be essential to the process of conglutination.

The experiments reported do not exclude the possibility of additional or unidentified fractions of horse serum playing a part in the reaction. Whether or not C′ 3 is essential to the process of conglutination could not be determined from the evidence available.

It was found that by the procedures employed the C′ 4 fraction may be supplied either from the horse complement or from the heated bovine serum added as a source of conglutinin or from both.

When horse complement and bovine antibody against sheep cells are used it is found that conglutination will only result when the complement components are absorbed on to the immune complex in a particular sequence. The sequence is that C′ 1 is absorbed first on to the sensitized cells, and then C′ 2 and C′ 4 are absorbed together. Both these components must be presented together to the sensitized cells carrying C′ 1 if conglutination is to result. Finally, conglutinin acts on the sensitized cells which have absorbed the three complement components, and conglutination results.

The significance of these findings, together with matters of a more general nature, is discussed.

(a) This paper is a study of a poliomyelitis epidemic in the Central Auckland Health District which commenced in November 1947, and by the end of April 1949 had produced 345 cases in a population of about 350,000.

(b) Incidence per 10,000 reached 8·0 in the city, 15·4 in the country districts, and 21·5 in certain urban areas lying between city and country.

(c) In general, incidence was inversely related to population density. Abnormally high incidences in some urban areas was attributed to influx of rural dwellers in recent years. Unusually low incidence in one city area may have been related to the periodic effect of race meetings in increasing the local density.

(d) The three previous Auckland epidemics showed a successively declining incidence, and were linked by periods of grumbling activity. The present epidemic was preceded by a lull, and its toll has approached that of the 1916 epidemic. It is probable that a new cycle has begun which will imitate the first, but on a lower scale.

(e) Spot maps showed that the disease was already widespread before the first positive cases revealed its presence. Some ebb and flow, but no actual movement from one area to another, occurred during its course. An interesting feature was the comparative rarity of cases in the neighbourhood of the city's sewage-polluted bathing beaches.

(f) An inverse correlation was noted between the ratios of ‘suspect’ to positive cases established in a previous inquiry, and the incidence of cases with paralysis or paresis in various age/sex groups. High ratios indicated lower severity.

(g) It was estimated that by the end of April 1949, all boys 10–15 years in Auckland had been affected by poliomyelitis, either ‘suspect’ or positive. Less than half the girls of this age had been affected. Estimates are given for the other age groups.

(h) Families of cases showed no significant difference in composition from the average in the area.

(i) No correlation, whether inverse or direct, was found between sanitary conditions in schools and the incidence of positive cases.

(j) The cycle of poliomyelitis in the community is discussed in the light of these findings.

Filtrates prepared from suspensions and broth cultures of Brucella vaŕiants were examined for the presence of Brucella bacteriophage. Smooth Brucella, when mixed with decimal dilutions of these filtrates in broth, (1) contained typical bacteriophage plaques when inoculated on solid medium, and (2) gave a heavy turbidity in broth after suitable incubation, but frequently failed to yield visible growth upon plating these broth cultures to a solid medium. These data were discussed in terms of Brucella bacteriophage, and it is concluded that the presence of this virus best accounted for the phenomena observed.

Woodhouse's experiments on the carcinogenicity of ten different fractions for the skin of mice have been analysed statistically. Two experiments separated by a considerable period of time were performed on each fraction.

A number of different measures of carcinogenicity were used. All agree in showing that

(1) The apparent carcinogenicity was greater in the 2nd series of experiments.

(2) There were significant differences in carcinogenicity. The fractions can be divided into three groups within which the carcinogenicities were about the same, viz. F H I K, B D G L E, M.

To estimate the number of viable streptococci present in the air of occupied places, airborne bacteria were collected in a slit-sampler on a nutrient agar medium containing 5% sucrose, 5% horse serum, 0·25 mg./100 ml. crystal violet, and 1·0/100 ml. potassium tellurite. This medium inhibits the great majority of the staphylococci and micrococci found in the air. On it colonies of Strep. salivarius are readily recognized by their mucoid form. The number of other streptococci was estimated by picking and examining a random sample of the colonies.

Streptococci were recognized in the sample by three different methods: (1) by microscopic examination of a nigrosin film made from the original colony; (2) by examination of a nigrosin film and also subculturing the colony to a ditch plate having blood agar on one side and serum agar containing 40% or bile on the other; or (3) by subculture to bile-agar ditch plates alone, the bile agar in this case containing aesculin and ferric citrate. By method (1) streptococci could be distinguished from micrococci; by methods (2) and (3) this distinction could be made with more confidence, and in addition enterococci could be distinguished from other streptococci.

A number of tests of the efficiency of the method were carried out, and it was concluded that some 20–40% of the viable streptococci in the air were missed.

The standard errors of the mean of a number of streptococcal counts in schoolrooms were calculated and found to be of the order of 14% of the mean when our standard routine was followed; increasing the size of the sample of colonies picked for examination by 30% would probably have had only a trivial effect on the standard error of the mean, since the greater part of the variation was due to differences between the counts in different rooms.