1. Samples of whey from individual cows and herds infected with R. burneti and from uninfected cows and herds have been tested for R. burneti antibodies.

2. The haemolytic complement-fixation test, the conglutinating complement-absorption test, the direct agglutination test and the anti-globulin sensitization test were compared for sensitivity in detecting whey antibody.

3. The direct agglutination test was generally more sensitive than either of the complement-fixation tests, particularly when it was enhanced by centrifugation of the sensitized rickettsiae. The anti-globulin sensitization test, however, gave the highest titres andit appeared to be specific.

4. The practical application of these techniques and certain theoretical considerations are discussed.

Preliminary observations in a systematic study of fifteen bacteriophages isolated from Pseudomonas aeruginosa are described. The evidence as to size, morphology and plaque appearance indicates that this group of phages comprises several distinct types. The electron microscope reveals some of the phages to be simple spheres, but the majority are tailed particles.

The importance of this group in the study of the phenomenon of lysogenicity is pointed out.

The sensitivity of different culture media for isolating salmonellae from the faeces of man, dog, horse, cow, sheep, pig, chicken, duck and turkey has been investigated. Suitable dilutions of tissue fluids of animals that had died from salmonella infection, and in which the numbers of viable salmonellae could be accurately estimated, had previously been added to the faecal specimens. Tissue fluids containing Salmonella dublin, typhi-murium, thompson, cholerae-suis, gallinarum and pullorum were used.

Selenite and tetrathionate media were greatly superior to liquid desoxycholatecitrate medium, liquid Wilson and Blair medium, cacotheline broth and brilliant green peptone water. By the use of either selenite or tetrathionate media it was usually possible to recover salmonellae from faecal specimens to which less than ten salmonellae had been added. They could nearly always be recovered from specimens containing 100 salmonellae.

Salmonellae were more easily recovered from the faeces of some species of animals than others. For selenite, the order of ease of recovery was horse, followed by sheep, human, cow, chicken, pig, turkey, dog and duck faeces, and for tetrathionate, horse, sheep, human, dog, pig, cow, turkey, chicken and duck faeces.

Selenite medium was preferable to tetrathionate for examining cow and chicken faeces but the reverse was true in the case of dog faeces; slight differences only were noted in the other species. Taken as a whole, selenite was slightly superior to tetrathionate, butbest results were obtained by the use of both media.

Some types of salmonellae were easier to recover from faeces than others.Of six salmonella types, Salm. thompson was easiest to recover followed by Salm. typhi-murium, dublin, gallinarum, pullorum and cholerae-suis, in that order.

Erroneous results were obtained when laboratory cultures were used instead of infected tissue fluids.

It was necessary to add several thousand salmonellae to faeces before they could be recovered by direct culture on desoxycholate-citrate-agar or Wilson and Blair solid medium.

Salm. cholerae-suis and Salm. abortus-ovis were exceptional in that direct plating was superior to the use of enrichment media.

With lightly infected specimens an incubation period of 24–30 hr. was optimum for selenite and tetrathionate media. A longer period was detrimental with tetrathionate but not with selenite medium.

The combination of selenite and solid Wilson and Blair medium was sometimes too inhibitory to permit the growth of salmonellae.

There was little advantage in preparing selenite medium with mannitol instead of lactose.

1. Mice infected intracerebrally with M. tuberculosis H 37 Rv in doses of 400,000–1,300,000 bacillary units gave a graduated series of responses whose regression provided an arbitrary 100% standard of mouse virulence for human tubercle bacilli.

2. Under certain experimental conditions this standard remained stable and its confidence limits could be defined.

3. The relative virulence of other strains of tubercle bacilli could be assessed quantitatively in relation to this standard, and expressed as a (percentage) virulence ratio.

4. 100% virulence was defined as that of a strain showing a threshold of response of 600,000–1,300,000 bacillary units, lethal cerebral lesions at 8–20 days or necrotic pulmonary lesions at 20–30 days, and a mean 50% mortality time of less than 36 days.

5. Qualitative and quantitative responses characteristic of intermediate and very low virulence were also defined.

6. Higher proportions of virulent cells were obtained from 3 to 7 days than from older cultures in Tween-albumin liquid media, but inocula were more suitably standardized by obtaining cells from 11 to 12-day cultures.

7. Passage in the mouse and guinea-pig failed to alter the virulence of H 37 Rv. A slight increase was effected by passage in the lung of the rabbit.

8. The technique employed was a measure essentially of the ability of the organism to multiply in, and damage, resistant tissues.

A relatively simple and safe apparatus for the study of airborne infection is described.

Cloud sampling and assessment techniques are described and critically discussed. Evidence is given concerning the satisfactory reproducibility of in vitro and in vivo assays.

Limitations to the usefulness of the apparatus are noted.

A vertical closed circuit wind tunnel is described in which a spinning top sprayer is used as a source of homogeneous particles of pathogenic organisms. The dry particle size may be set at any figure between 1 and 20 µ, and the cloud concentration can be varied over wide limits. Provision is made for humidity control. Animals may be exposed to the cloud, and samples taken from it. The apparatus can be sterilized with flowing steam and formalin.

An appendix giving details of the operational technique is available on request.

Experiments were carried out in a test chamber of 16,500 cu.ft. capacity with air conditioned at 68° F. and 54% relative humidity. Ventilation was controlled at 3·0 changes/hr., air being recirculated with 0·5 air change/hr. of fresh air admitted. By spraying into the air ducting a concentrated suspension of Chr. prodigiosum a bacterial cloud was introduced into the chamber of over 5 × 106 organisms/cu.ft. of air as l μ particles. Viable organisms were still present in the atmosphere after 6 hr.

When a heat-generated vapour of hexylresorcinol was introduced in a concentration of between 6 and 7 μg/cu.ft. of air the bacterial count dropped from nearly one million organisms per cu.ft. to fewer than ten in 35 min.

When the bacterial suspension was sprayed into the chamber with hexylresorcinol vapour present, the peak concentration reached was about one-quarter and on stopping the spray, the bacterial count fell from one million per cu.ft. to fewer than ten in less than 25 min.

Hexylresorcinol is also effective when the bacterial aerosol is in particles of 6–7 μ in size (approx. 100 bacteria per particle).

Hexylresorcinol has no effect against a bacterial aerosol of B. subtilis spores in 1 μ particles.

No attempt has been made to analyse the mode of action of hexylresorcinol in diminishing the bacterial content of the air. The evidence collected clearly indicates the necessity for further study of this problem.

Antibacterial sera against C. diphtherias gravis (serological type I), intermedius and mitis were prepared in horses. The details of the immunization and the preparation of the sera are described. The sera contained a minimal amount of antitoxin.

The anti-gravis serum in the dose used, when it was given to guinea-pigs 1 hr.before the subcutaneous injection of ten lethal doses of the homologous organism, saved the life of 75 % of the animals. Those which died lived longer than the controls, and C. diphtheriae was recovered less often from the local lesion and the liver than at the same sites in the controls; it was not recovered from the heartblood of the animals which received the experimental serum, whereas cultures from the heart-blood were positive in about 40 % of the controls.

In these experiments the degree of invasiveness of the strain, as judged by the frequency of its recovery in cultures from the heart-blood and the liver of the control animals, corresponded with earner observations (Robinson & Marshall,1934), which showed that in routine virulence tests carried out by the subcutaneous inoculation of guinea-pigs C. diphtheriae could often be cultivated from the local lesion, the liver, the pleural fluid and the heart-blood, and that gravis and intermedius strains were more invasive than mitis strains. This was one of the main facts which suggested that an antibacterial factor might prove to be a useful adjunct in the treatment of diphtheria.

The anti-gravis serum, when given as a supplement to the routine doses of antitoxin to patients with severe diphtheria, had a definitely beneficial influence on the local lesion. Moreover, the serum improved for a time the general condition of some of the patients, including those who died later. The death rate of the group to which anti-gravis serum was administered was similar to that of the control group but, on the other hand, the patients who received the serum lived, on the average, longer than the control patients notwithstanding that treatment of the former group was begun later in the disease. The clinical evidence in favour of the anti-gravis serum cannot be assessed quantitatively, but, since it is based on critical observations, it should not be disregarded.

Consideration of the results as a whole leads us to conclude that the anti-gravis serum used in the tests contained a specific antibody which, within limits, had a beneficial action. We suggest, therefore, that the role of the antibacterial factor in the pathogenesis and control of diphtheria merits investigation.

This investigation has been concerned with the changes that occur in the coliform and faecal coli content of water samples on storage at room and refrigerator temperature for 20–24 hr.

On examination by a seventy-tube method, using twofold diminishing volumes, twenty-three out of 151 samples of water stored overnight at room temperature showed a significant increase in the presumptive number of conform organisms and twenty-nine a significant decrease. Of the same number stored in the refrigerator, ten showed a significant increase and twenty-six a significant decrease.

Of 111 samples examined for faecal coli, eight showed a significant increase on storage at room temperature and twenty-nine a significant decrease. Of the same number stored in the refrigerator, seven showed a significant increase and fifteen a significant decrease. The effects of the source of the water, the time of year and the original number of coliform organisms in the sample were examined.

The present investigation has shown that in a considerable proportion of samples a significant change in the conform and faecal coli content does occur on overnight storage at room or refrigerator temperature. It may, perhaps, be safe to store samples under some conditions for shorter periods, but this is a matter for future investigation.

1. A quantitative study has been made of the activity of C′1, C′2 and C′4 in the complements of the horse, cat, pig, man, guinea-pig and rabbit.

2. Evidence is presented which suggests that either there may be two types of C′4, the one haemolytic and the other conglutinating, or else that the manifestation of this complement component varies under conditions not yet understood.

3. In certain complements it appears that the serum proteins functioning as C′1 with the bovine anti-sheep red cell antibody are distinct from those functioning as C′1 with an antibody of similar specificity from an immune rabbit serum.