Data are given showing the concentration of pure ozone required to inhibit the growth of, and to destroy, various micro-organisms when growing on agar, in nutrient broth, a synthetic medium, or simply suspended in water. The following is shown:

1. Different organisms vary in their susceptibility towards this gas. Achromobacter and Pseudomonas strains, such as occur on chilled meat, are the most resistant. On the whole, mould fungi are about as susceptible as bacteria.

2. Very much higher concentrations are required to arrest established growth than can be used if inoculation and admission of inhibitor are coincident.

3. Lower concentrations are inhibitory at lower temperatures. These results are ascribed to dissipation of the ozone by combination with products of bacterial metabolism. It seems that any factor which diminishes growth will augment the effectiveness of ozone.

4. Comparatively small concentrations (less than 10 p.p.m.) suffice to destroy bacteria suspended in water. Somewhat larger concentrations inhibit growth in a synthetic medium.

5. Still larger quantities (several hundred p.p.m.) are required in nutrient broth.

6. Nutrient broth treated with ozone will support little or no bacterial growth, due to change of pH, growth taking place slowly if the pH is restored to its original value. Inhibition of growth in such a medium is therefore a complex process depending in part upon the secondary effects of decomposition of the medium.

7. To kill them, bacteria require still more ozone (in some cases several thousand p.p.m.) if growing on agar. These results are ascribed to combination of ozone with the supporting medium.

8. When applied to organisms growing on food, combination with ozone not only spoils the food, but it makes it difficult to interpret the effect on the microbes in terms of the ozone applied.

9. The inhibitory concentrations are higher than humans can tolerate.

10. Ozone destroys the dehydrogenating enzymes of the cell, and it is suggested that its germicidal action may be partly due to interference with cellular respiration.

The work described in this paper was carried out as part of the programme of the Food Investigation Organization of the Department of Scientific and Industrial Research.

The importance of the accuracy of serological tests for syphilis has become more than ever emphasized by widespread testing and more efficient therapy. The problems are reviewed in the light of present knowledge of the specificity and sensitivity of standard serological tests for syphilis. Richardson's modification of the Wassermann reaction is described. The results of this test when applied to ninety-two cases giving doubtful or discrepant reactions by routine tests are presented and classified. The cases were followed up clinically. The results indicate that this simple test is a reliable and valuable adjunct to routine methods, and should be employed widely as a verification procedure.

The importance of the haemagglutination-inhibition test does not need to be stressed. It is a fact that the inhibition titre of a single serum has no constant value, but may vary in repeated estimations. This may be due to the use of different virus or erythrocyte suspensions or to differences in environmental circumstances, such as temperature. Duplicate tests carried out at the same time and with the same materials yield identical results. This makes it necessary to compare a serum obtained during convalescence from the same case. The ratio between the two titres shows whether an influenza infection has taken place or not. Although it is commonly accepted that a titre rising by two twofold dilutions (a fourfold rise) is significant, some workers will accept even a twofold rise (Sartwill & Long, 1948; Rasmussen, Stoles & Smadel, 1948). Such observations have been made on pairs of sera taken from the same indicidual with not more than a 5-week interval between them.

1. Some sources of error in the testing of quaternary ammonium compounds for bactericidal activity have been investigated. These resolve themselves into (a) errors caused by bacteriostasis, and (b) errors caused by the clumping of bacteria.

2. A suitable technique, free from these errors, is described.

3. Cetavlon in 0·1% solution is a powerful bactericide even in the presence of moderate amounts of organic matter.

4. One per cent Cetavlon will not kill spores at room temperature even when contact is maintained for several days.

5. Bacteria surviving the action of quaternary ammonium compounds retain their virulence.

Change of flagellar antigenic phase in the Salmonellas is considered as resulting from the mutation and back mutation.

A rapid method of determining the phase of numerous colonies of Salmonella typhi-murium is described; melted sloppy agar containing antibody for one phase is layered on tplates on which colonies have grown. On brief incubation, colonies of the agglutinated phase produce narrow dense sharp edged zones of opacity, while colonies of the other phase wide diffuse zones of swarming organisms.

A theoretical analysis shows that if the growth rates of the phases are equal the proportion of cells of ‘mutant’ phase in a culture initially all in one phase and maintained in continuous logarithmic growth will (at first) increase linearly with the number of generations at a rate proportional to the mutation rate. In one strain of Salm, typhi-murium experiments showed the rates of growth of the phases to be equal; the proportion of cells of mutant phase in cultures of this strain during long periods of continuous growth has been measured; linear rates of increase were found, and the mutation rates are calculated.

The variance in proportion of cells of mutant phase in replicate cultures has been measured; the findings are correlated with theoretical considerations.

Certain anomalous decrease in proportion of cells of mutant phase during prolonged growth are described, and a possible explanation is proposed.

Eight further strains have been investigated by the same methods; in the nine strains, the rates of mutation from group to specific phase range from 10-4 to 4.7 X 10-3per bacterial generation cycle, and the rates of the reverse mutation from 10-5 to 8.6 X 10-4. In all the strains, including two of variety binns, the rate of mutation from group to specific is higher than the rate of the reverse change; it is shown theoretically that such strains will tend towards an equilibrium composition in which the specific phase will predominate; in one rapidly mutating strain such an equilibrium has been demonstrated.

In a limited experiment, alteration of medium and of temperature of incubation caused to detectable alteration of rate of mutation per bacterial generation.

Stable O mutants, and poorly flagellated mutants which back-mutate to the fully motile form, are described.

The experimental findings are compared with reports in the literature on the phase of Salm. typhi murium as isolated. The behavior of strains of variety binns is discussed, and it is suggested that this description should not now be applied to strains in which a specific phase can be demonstrated. The biological funtion of mutablility of phase is discussed.

The following conclusions were drawn from these experiments with bovine group B streptococci:

1. A relationship existed between lethal power and the number of living organisms inoculated, and, therefore, the number of living organisms inoculated must be determined when the killing power of a strain is under investigation.

2. Equal doses of the same strain were likely to kill more mice, but less rapidly, when inoculated intravenously than when inoculated intraperitone-ally.

3. Virulence for mice might be related to serological type.

4. The disease caused by intraperitoneal inoculation of strain S 13 was a rapidly fatal peritonitis with concomitant bacteraemia.

5. The disease caused by intravenous inoculation of strain S13 was a fatal bacteraemia with a tendency for the streptococci to form dense clumps in widely separated tissues.

1. A strain of Boot, coli adapted to growth in high glycine concentrations, which had lost the power of producing ‘gas’ from sugars, was shown to be devoid of formic hydrogenlyase.

2. Formic acid was prominent among the products of fermentation of sugars by this strain.

3. The appearance of formic hydrogenlyase in vitro, in bacteria grown in such a way as not to contain the enzyme, was inhibited by glycine at high concentrations.

One of us (J. G.) is indebted to the Medical Research Council for a grant-in-aid for expenses.

1. None of forty-eight strans of Brucella abortus, ten of Br. melitensis and seven or Br.suis were shown to be lysogenic.

2. It was not possible to ‘adapt’ bacteriophages that were active upon other species of bacteria to lyse brucellas.

3. Thirty samples of faeces, mainly from cows, four sewage samples, twelve specimens of uterine fluid from cows that had aborted, and twenty samples of bulk milk failed to yield bacteriophages active upon brucellas.

There were nearly 400 cases of gastro-enteritis in Brisbane from May to October 1947. About half represented the endemic level then prevailing, and the remainder formed a virulent epidemic, which was responsible for most of the deaths. Salmonella bovismorbificans was isolated from a sufficient proportion of these cases to justify the belief that it was the cause of the epidemic.

Of recognized infections with S. bovis-morbificans 77 % were in babies under 1 year old, 19 % in those 1–2 years old, and 4 % in older children and adults. The infection was most severe in the under-1-year-old group, and severity varied during the epidemic, reaching a maximum in August and thereafter declining steadily.

Nearly two-thirds of the infections were institutional.

Infants were found to be infective during the incubation period and also for periods up to 6 months after clinical recovery. Their faeces provided the greatest mass of infective material. Infections in older age groups were relatively unimportant in relation to the rate of epidemic spread, but significant secondary centres of infection developed in mice and cockroaches in the hospital wards.

The path of infection was traced from the faeces to the sinks and brushes used for cleansing soiled napkins, to mice and cockroaches which had access to the sinks, and to ward wash-basins and nailbrushes used by the nursing staff. Possible indicators of faecal contamination were found on nurses' hands, in ward kitchens, and in milk mixtures prepared for babies' feeds.

Control is believed to be practicable and to depend, first, on making medical officers and nurses aware of the dangers; and secondly, on improved ward hygiene, of which elimination of washing napkins in wards, reduction of contamination when changing napkins, rigid segregation of ‘clean’ and ‘dirty’ nurses, and improvements in food preparation and administration, are regarded as the most important.

Floor dust has been collected for bacteriological examination by three methods: (1) with a miniature vacuum cleaner in which the ‘bag’ consists of a paper Soxhlet extraction thimable, (2)by sweeping, and (3)by blowing the dust on to the surface of a culture plate. The dust on to the surface of a culture plate. the dust from on to the first two methods was shaken with broth and an aliquot sample plated out on crystal-violet blood ager plates.

Surface inoculation of the plates was found to give somewhat higher counts than the use of pour plates, but otherwise minor variations in the routine were without great effect on the count.

Analysis of the results obtained in examining a number of specimerns from schoolrooms and day nurseries showed that, though the counts of streptococci in successive samples from one dust suspension agreed well, there was wide variation between the counts from duplicate samples of dust, however collected; the frequency distribution of the counts in rooms was of the log-normal type. It is clear that in routine work, all the dust collected from the whole floor of a room should be examined, in order to give the most reliable result.

Of 185 specimens in which four colonies of haemolyt streptococci were grouped, 67% had all four strains of group A. Ofniety-four samples in which four group A strains were typed, 55 % had all four strains of the same type; more than one type was found in 20 %.

1. Strains of Bact. coli and related bacteria possess a life cycle resembling that of Myxobacteria. The vesicular, resting nucleus is contained in a microcyst, which is formed by a process suggestive of sexual conjugation.

2. The microcyst germinates by the transformation of the resting nucleus into the chromosome-like bodies typical of active, vegetative cultures. These may be analogous to the chromosome complexes of yeasts. The period of germination of microcysts corresponds to the lag phase of cultures.

3. The nucleus remains permanently in the mitotic condition during the active, vegetative phase of growth, and reproduces by an asexual and a sexual method.

4. Older cultures may be transformed directly into microcysts or may first adopt a secondary, vegetative phase, in which the nucleus is in the form of a single, central body.

5. Microcyst formation differs from spore formation in that it lacks the obvious reduction processes associated with spore formation, upon which a few original observations are included.

Information relating to post-partum mating has been described in guinea-pigs kept in six small colonies containing variable numbers of the sexes running together continuously in floor pens of standard size. Litters were born on the floor and rearing was communal (Method 1). Three other like colonies were similarly maintained, except that the females in late pregnancy were separated from the male to avoid post-partum mating (Method 2). The conditions of farrowing and rearing were similar to those of Method 1. The data given by thirty-four sows of a closely recorded (stock) colony bred in units of six females and one boar, but in which every litter was born and reared under ‘cage’ conditions (Method 3), were used for comparative purposes only.

Post-partum mating was considered to have occurred only when the interval between the births of any two consecutive litters of the same sow did not exceed 70 days. Of litters born under Method 1, 80% were conceived at post-partum oestrus; the mean gestation period was 68 days. The average inter-parturition interval of all sows breeding under Methods 1 and 2 was 74 and 118 days respectively. The optimal ratio of the sexes in a colony breeding by both methods was judged to be twelve females to one male.

Litter size varied between 3·98 (Method 1) and 3·69 (Method 3) and by all three breeding methods, the proportion of young already dead or that died at birth was about 5%. Deaths were more common in summer months when litter size was maximal.

The post-natal death-rate during the first 28 days of life among young reared communally (Methods 1 and 2) was 10% and was fivefold that observed in litters reared separately by their mothers (Method 3). This death-rate was highest during the winter months due to the difficulty of providing adequate amounts of fresh green vegetables.

The annual output of young guinea-pigs from colonies bred under Method 1 was 62% greater than that from other colonies bred by Method 2. The more rapid sequence of littering did not affect the quality (body weight) of the young at birth or at weaning.

Attention has been drawn to a possible deleterious effect of intensive breeding to the health of the females and their lessened resistance to infection. It has been suggested that, for this reason, the breeding life of the sows should be limited to 1 year.

The effects of radiation from the surroundings on the impressions of freshness of 106 men and 39 women members of the staff of the Building Research Station were investigated during the first 6 months of 1948. Subjects were exposed to three types of environment: (1) where the walls were cooler than the air, (2) where the walls and air were at the same temperature, and (3) where the walls were warmer than the air. The tests were carried out in calm air.

It was found that the difference between the mean radiant temperature and the air temperature affected freshness impressions, but the effect was relatively slight. Environments which felt cool tended to feel fresh, yet a rise in the mean radiant temperature—which would increase the warmth of the environment—tended to produce an impression of greater freshness. At a given equivalent temperature, environments with the surroundings warmer than the air were found to be definitely fresher than cold- and neutral-wall environments. This was thought to be mainly due to the fact that the humidity of the air in the warm-wall environment was lower than that in the other two environments. Changes in humidity insufficient to affect sensations of warmth affect impressions of freshness. Under the conditions of these experiments, and to keep freshness impressions constant, a rise of 1° F. in the temperature of calm air must be compensated by a fall of about 5% in the relative humidity.

The subjects had a distinct preference for the warm-wall environment; 73% of them found it pleasanter than either the cold- or the neutral-wall environment.

Freshness impressions are considered to be related to transient fluctuations in the rate of heat loss from the head.

1. Sodium fluoracetate (1080) has been tested in the field as a poison for Rattus norvegicus and R. rattus.

2. Direct poisoning (without Prebaiting) was used in thirteen tests on R. norvegicus. In eight of these tests censuses showed kills of at least 89% in three tests the poison failed, and in two the results were equivocal.

3. Of three similar tests against R. rattus two were successful and one was a failure.

4. Six tests of 1080 after prebaiting gave five successes (including one against R. rattus), and one in which the estimated kill was about 82%.

5. In five out of six tests populations of R. norvegicus which had survived baiting with 1080 showed shyness (refusal) of the poison when it was given in a new bait base.

6. The LD 50 of 1080 for a strain of white rats was found to be 3·8 mg./kg. (approx. range 2·8–5·2).

7. A number of wild brids and some domestic animals were accidentally killed during the tests despite stringent precautions taken in laying the bait and in warning occupiers.

8. It is concluded that: (a) although 1080 is probably more effective in direct poisoning than other poisons used in the past, it does not give as consistent results as the standard poisons do after prebaiting; (b) 1080 is too dangerous for general use.

An expectation of life limited to n years is properly defined by

to which the approximation usually used is

A heterogeneous sample consisting of eighteen specimens of semen provided by eleven patients was examined. Smears were supravitally stained at 3, 8 and 27 hr. Counts of living and dead spermatozoa, classified into normal and fourteen types of abnormal forms, showed that whereas five abnormal forms were always dead, the remaining types showed varying proportions of dead and living cells. Their rate of mortality was somewhat greater than that of normal spermatozoa.

A survey of both the prevailing and the desirable conditions for housing small laboratory animals, with particular reference to rats and mice, is described. The data surveyed are confined to laboratories in Great Britain and include requirements of space, heating, ventilation and building construction, with such accessories as cages, feeding devices and other equipment.

1. A preparation containing 0·7% scilliroside (the glucoside of red squill) had been tested as a poison for Rattus norvegicus and R. rattus.

2. The preparation has been found to be effective in the field against norvegicus but not against rattus.

3. Assayed against a strain of white rats, the preparation had an LD 50 for males of about 25mg./kg., and for feamales of about 5 mg./kg.

4. The LD 50 for adult Rhode Island Red fowls was greater than 400 mg. /kg. Pigs, dogs and cats were treated with doses up to 16mg./kg. without fatal results.

5. Silmurine was unpalatable to pigs, dose and cates, but fowls readily consumed a mash containing 1% Slimurine.

The amount of clerical work involved, and the ramifications of the record system used, in an animal laboratory, are conditioned by the purpose for which the colony is maintained, and dependent upon how anxious its custodians are to control its size and guide its future. If, for instance, ease of operation and minimization of clerking is to be the overriding consideration one may secure a good supply of young rats by the simple process of allowing a flock of adult animals the freedom of a warm room containing bedding and food. One enters at intervals to clean and feed, and, eventually, to remove, for experimental work, those youngsters that look big enough to fend for themselves, taking care, at the same time, to leave a few of each sex to grow to maturity and guarantee the next generation. An occasional census of population and production is all that is necessary in the way of records.