The effect of actinomycin D on the growth of African horse sickness virus in monkey kidney cells was studied. It was found that actinomycin D inhibited the yield of virus. It is suggested that African horse sickness virus is either a DNA containing virus or an RNA virus whose replication is DNA-dependent.

Foot-and-mouth disease virus of type O (strain Israel 1/63) was passaged serially fourteen times in cattle previously vaccinated with increasing doses of formol-treated vaccine of the homologous strain. Primary and secondary lesions developed in the majority of the animals. Virus from the 14th passage, which proved to be capable of reinfecting animals only 34 and 35 days after infection with the original strain, differed from the original strain in complement-fixing properties and in sensitivity to antiserum. These changes were of a degree indicative of subtype variation.

Virus titres in the saliva, in the tongue vesicles and in the foot vesicles of partly resistant cattle were very great and would have constituted a danger to other stock under field conditions.

The experimental data confirm previous observations on the infection of partly resistant cattle and on the isolation of variant strains during passage of FMD virus in tissue cultures containing specific antiserum.

1. In the course of the examination of sputum from cases of lobar pneumonia, observations have been made on the incidence of the chief types of pneumococci. In the district from which the material was obtained, there was an apparent local diminution in the number of cases of lobar pneumonia due to Type II; the figures were 32·6 per cent. of Type II cases in the period 1920–22, and only 7·4 per cent. in the period 1924–27. The incidence of Type I was approximately the same in the two periods, the percentages being 30·6 and 34·3.

2. Several different serological varieties of pneumococci have been obtained from the sputum of each of several cases of pneumonia examined at various stages of the disease. This has occurred most frequently in cases of pneumonia due to Type I, and in two instances four different types of Group IV were found in addition to the chief types. The recovery of different types is facilitated by the inoculation of the sputum (preserved in the refrigerator), together with protective sera corresponding to the various types in the order of their appearance.

3. Two interesting strains of Group IV pneumococci have been obtained from pneumonic sputum.

One was an R strain which produced typical rough colonies, yet preserved its virulence for mice and its capacity to form soluble substance. This R pneumococcus developed a large capsule in the mice, which died of a chronic type of septicaemia. A strain producing smooth colonies was obtained from it in the course of a prolonged series of passage experiments.

The second strain, which was proved not to be a mixture, agglutinated specifically with the sera of two different types. In the peritoneal cavity of the mouse the specific soluble substance of each type was produced.

4. A method of producing the S to R change through ageing of colonies on chocolate blood medium containing horse serum is described. After two to three days' incubation small rough patches appear in the margins of the smooth colonies, and from these pure R strains can be isolated.

5. It has been shown that the R change is not equally advanced in the descendants of virulent pneumococci which have been exposed to the action of homologous immune serum. Some R strains form traces of soluble substance in the peritoneal cavity of the mouse; these revert readily to the virulent S form and, in addition, are able to produce active immunity. Others show no evidence of S antigen; spontaneous reversion takes place with difficulty, if at all, and they are incapable of producing active immunity. The stronger the immune serum used, the more permanent and complete is the change to the R form.

6. Restoration of virulence to an attenuated R strain, with recovery of the S form of colony and of the original serological type characters may be obtained by passage through mice. The change from the R to the S form is favoured by the inoculation of the R culture in large doses into the subcutaneous tissues; but the most certain method of procuring reversion is by the inoculation of the R culture, subcutaneously into a mouse, together with a large dose of virulent culture of the same type killed by heat.

Incubation of such a mixture in vitro does not induce reversion.

7. Reversion of an R strain to its S form may occasionally be brought about by the simultaneous inoculation of virulent culture of another type, especially when this has been heated for only a short period to 60° C., e.g. R Type II to its S form when inoculated with heated Type I culture.

8. Type I antigen appears to be more sensitive to exposure to heat than Type II antigen, since the former loses the power to cause reversion when heated to 80° C, whereas Type II culture remains effective even after steaming at 100° C.

9. The antigens of certain Group IV strains appear to be closely related to that of Type II, and are equally resistant to heat. Steamed cultures of these Group IV strains cause the R form derived from Type II to revert to its S form, while they fail to produce reversion of the R form derived from Type I.

10. The inoculation into the subcutaneous tissues of mice of an attenuated R strain derived from one type, together with a large dose of virulent culture of another type killed by heating to 60° C., has resulted in the formation of a virulent S pneumococcus of the same type as that of the heated culture.

The newly formed S strain may remain localised at the seat of inoculation, or it may disseminate and cause fatal septicaemia.

The S form of Type I has been produced from the R form of Type II, and the R form of Type I has been transformed into the S form of Type II.

The clear mucinous colonies of Type III have been derived both from the R form of Type I and from the R form of Type II, though they appear to be produced more readily from the latter. The newly formed strains of Type III have been of relatively low virulence, and have frequently remained localised at the subcutaneous seat of inoculation.

Virulent strains of Types I and II have been obtained from an R strain of Group IV.

11. Heated R cultures injected in large doses, together with small doses of living R culture have never caused transformation of type, and only rarely produced a reversion of the R form of Type II to its virulent S form.

12. The results of the experiments on enhancement of virulence and on transformation of type are discussed and their significance in regard to questions of epidemiology is indicated.

Samples of yellow-fever vaccine prepared from homogenized chick embryos, and of an experimental measles vaccine prepared from chick embryo cells, have each been shown to contain a contaminant virus similar in properties to an avian leukosis virus. Young adult males injected with the yellow-fever vaccine did not develop neutralizing antibodies for Rous sarcoma virus.

The incidence of positive toxoplasmin skin test among subnormals in hospital was compared with that in subnormals attending day training centres and among normal children taken into County Council children's homes. Twelve out of 120 subnormals below the age of 20 attending day training centres were positive to the test, and 23 were positive out of 233 subnormals of the same age tested in hospital.

There was only 1 positive out of 71 children under the age of 18 in the County Council children's homes, compared with 29 out of 296 subnormals of this age who were tested.

The incidence of positive skin test among 115 mongols under the age of 50 was about 11% in each age range, whereas that in 709 other subnormals rose from 5% in those below the age of 10 to 30% in those over the age of 30.

Although factors similar to those causing admission of normal children to County Council care often determine the admission of subnormals to hospital, the children in County Council homes did not share the high incidence of infection which was found in subnormals.

It is suggested that the majority of infections among subnormal children are postnatally acquired. Since the incidence was the same in subnormals living at home as among those in hospital it is suggested that some personal habit commoner among subnormal than among normal children exposes the subnormals to an increased risk of infection.

The comparative efficiency of cultures of rectal swabs and faecal specimens in detecting salmonellas in asymptomatic carriers was determined and then correlated with the number of salmonellas excreted per g. of faeces (wet weight). In six short-term salmonella carriers, 82% of rectal swab cultures taken daily for 11 consecutive days were positive for salmonellas, whereas 94% of faecal specimens cultured were positive. Similarily, in 8 long-term carriers, 58% of the rectal swab cultures were positive as compared with 91% of faecal specimens. The inferiority of the results of rectal swab cultures correlated with their inefficiency in detecting salmonellas when fewer than 1000 salmonellas per g. of faeces were present.

The patterns of salmonella excretion as depicted by estimated salmonella content of faecal specimens showed that all carriers had irregular day-to-day variations. The average number of salmonellas excreted per g. of faeces by short-term carriers was greater than that by long-term carriers, although both groups revealed the same wide variations in number of organisms excreted.

The effect of delayed processing and shipment of specimens upon recovery of salmonellas was also studied. No deleterious effects were noted when specimens were shipped and processing was delayed for up to 3 days.

During 9 months the author observed 309 cases of infection with Salmonella enteritidis, of which 88% were hospital infections in six childrens' wards of three different hospitals. The foci were connected epidemiologically. In 97·7% of those examined, the bacteria were detected in faeces, in 68% in urine and in 27·5% in the upper respiratory tract. Bacteraemia was found in 17·2%. The bacteria were also detected in two air-samples and in two swabs from linen and furniture. All isolated strains were highly resistant to antibiotics and to drying, but sensitive to the action of chloramine. In infected patients with parenteral localization of bacteria, the agglutination test with specific gm antigen was positive in 80% of cases. Many patients were persistent carriers for 5–10 months. In adults a short faecal carrier state was usually observed. The epidemic spread by contact, though in some cases it was probably air-borne. Such epidemics are very difficult to bring to an end.

The remarkable paper by Fred. Griffith on the significance of pneumococcal types, reproduced in the preceding pages of this Journal, in which it was first published 38 years ago (Griffith, 1928), describes a series of careful and painstaking experiments which show beyond doubt that the ability to produce a polysaccharide capsule can regularly be restored to ‘rough’ (R) strains of pneumococci which have lost it, by the subcutaneous inoculation of mice with a mixture of a small number of the living R bacteria and an excess of heat-killed, capsulated (S) virulent bacteria. The inoculated mice frequently died from septicaemia and virulent, capsulated S organisms could be isolated from the blood. On the other hand, in control experiments, the injection of suspensions of heat-killed S bacteria alone never yielded living organisms, while recovery of virulent S organisms by (mutational) reversion, following inoculation of living R bacteria alone, was a rare event. Griffith called this phenomenon ‘transformation’ and, at least in the field of bacterial genetics, this name is still specifically used to describe it.

Opaque colonies of group A streptococci, detected on clear agar plates with obliquely transmitted light, are composed of extremely long chains of cocci. The mucopeptide layer of the cell-wall is involved in the formation of enhanced intercellular bridges. It is suggested that this exaggerated chaining results in an altered growth pattern which gives the appearance of granular opacity to surface colonies.

A study was made of the development of skin resistance and delayed hyper-sensitivity to vaccinia virus after immunization with inactivated vaccinia virus in rabbits. These vaccines are shown to increase skin resistance, and it is also shown that the development of this resistance is dependent upon the virus content of the vaccine. Skin resistance is shown to be related to the titre of circulating antibody rather than to the degree of delayed hypersensitivity. Possible reasons for conflicting reports in the literature on this subject are discussed.

An unusual skin reaction was seen in some animals when challenged with live virus after immunization with inactivated vaccine. The nature of these reactions is discussed.

Using Moore's swabs in four abattoirs, six strains of subgenus III salmonellas were isolated—four diphasic strains belonging to one serotype and two monophasic strains belonging to another. The serotypes differed in the length of time needed to ferment lactose. There was some evidence that the diphasic serotype could have had an ovine origin.

An epidemiological survey of salmonella infection in a closed herd of pigs is reported. The main cause of cross-infection resulted from the movement of animals, with subsequent mixing of infected and clean stock and exposure of non-infected animals to infected faeces. Pen-to-pen infection carried by farm attendants also proved important.

An extended survey is at present being conducted to gain further information on the processes of cross-infection.

The median lethal dose of orally administered norbormide for wild Rattus norvegicus found to be 9·0 mg./kg. of body weight and the LD 95 about 17·0 mg./kg.

In tests in which various concentrations of norbormide or zine phosphide were added to the food of individually caged wild rats, mortality increased with concentration of poison, though more slowly with norbormide than with zine phosphide. The mortality that occurred among rats offered a choice between unpoisoned food and the same food with added norbormide or zinc phosphide indicates that in control treatments in the field the optimum concentration of norbormide in bait would be about 0·;5% and that this might be expected to give results comparable with those obtainable with 2·;5% or 5·0% zine phosphide. Other methods of estimating suitable field strengths indicate that concentrations of norbormide higher than 0·;5% may be preferable.

Some animals that survived exposure to a choice of plain food and the same Food poisoned with norbormide or zine phosphide at field concentrations avoided mating lethal amounts by reacting to the taste of the poison. Others learned to use the taste of the food, not that of the poison as a cue and later avoided eating the food when it contained no poison.

When either poison was presented to rats in the more palatable of two foods in the choice situation mortality was relatively high. Some of the surviving animals subsequently rejected the more palatable food in preference to the normally less palatable alternative.

FMDV strains were titrated in pigs by inoculation of the bulb of the heel of the foot, the coronary band region of the foot, and the tongue. Heel inoculation gave end-points approximately 300-fold higher than did the other two methods.

Parallel titrations in cattle and mice gave infectivity estimates approximately 10-fold and 100-fold higher, respectively, than did heel titration of pigs.

The average variance of individual end-points determined for heel titration was 0·46 (log10 units) and that determined for coronary-band titration was 0·74. The sources of variations in end-points given by heel titrations are discussed.

Rabbits immunized with whole streptococci of group B, type II, produce two immunologically distinct type-specific antibodies which are essentially equal by weight in protecting mice against infection with homologous type strains.

The capsular antigen with which these antibodies react is a polysaccharide containing galactose, glucose, glucosamine, and a labile component which has not been chemically identified. Extraction of the bacteria with TCA yields this ‘complete’ antigen, whereas extraction with HCl yields a partial antigen without the labile component. This degraded antigen can also be derived from the TCA antigen by treating the latter with hot HCl, and is indistinguishable from that extracted directly from the bacteria with HCl.

One of the antibodies produced, the TCA antibody, is directed against the labile component of the polysaccharide. The other, the HCl antibody, is directed against a β-d-galactoside determinant; and the precipitin reaction with this antibody is not masked in the ‘complete’ TCA antigen by the presence of the labile component.

The group-specific polysaccharide, which is located in the cell-wall, is also extracted with either TCA or HCl but can be eliminated from the preparations by fractional precipitation with ethanol. Although it is known that the type-specific polysaccharide is located in the streptococcal capsule, it is not at present clear in what form this substance occurs in the living streptococcal cell. It may be present partially as the degraded HCl form, or possibly wholly as the intact TCA form. Further immunological and chemical studies of these type-specific polysaccharides are in progress, and will be presented in another communication.

The neutralization of a constant dose of Semliki Forest virus by various doses of different antisera was studied. The presence of complement (1/200, v/v) in the neutralization mixture inhibited the neutralization by high concentration of antiserum and somewhat potentiated neutralization by low serum concentration. Because the experiments were biased towards a measure of irreversible neutralization, the inhibition observed in the presence of complement appeared to be an inhibition of irreversible neutralization. This inhibition was interpreted as a dissociation of a complement binding virus–antibody complex. The antibodies involved appeared to be virus-specific.

Modern contact insecticides (like DDT) in powder form are ideal for combating widespread lousiness; but for various reasons they are not suitable for disinfecting small numbers of infested people under civilized conditions. It appears that the most convenient, efficient method in these circumstances is a small-scale fumigation of the infested garments, in either a metal bin or a plastic bag. Ethyl formate, one of the liquid fumigants suggested for this purpose by W. A. L. David in 1944, has been further tested and found efficient. In a plastic bag the size of a potato sack (about 30 × 40 in.), four blankets can be deloused by a dose of 100 ml. with an hour's exposure or a quarter of this dose with an exposure of 5 hr. or more. An overnight treatment with this dose would be safe and convenient, costing about Is. and the actual operations would take only a few minutes.

The relationship between chickenpox and yaws epidemics occurring among children in a village in Netherlands New Guinea is analysed using the mathematical model for a simple deterministic epidemic. It is shown that the yaws epidemic accelerated significantly in the month following the chickenpox epidemic, but that it reverted to its previous rate in the succeeding months. The number of yaws cases attributable to the influence of the chickenpox is estimated from the projected course of the yaws epidemic. It is statistically verified that those children contracting chickenpox were more likely to become yaws cases in the subsequent month.

These results point to the danger of yaws's spread being much more rapid among a population which has recently been subject to an epidemic of chickenpox.

1. Streptococci causing neonatal infection in piglets have been identified serologically as belonging to group D.

2. Glycerophosphate, glucose and xylose have been identified as components of the group substance isolated from these micro-organisms.

3. The streptococci isolated from piglets with this disease in England appear to belong to a single serological type characterized by a capsular polysaccharide.

4. Glucose, glucosamine and galactosamine have been identified as components of the type-specific substance.

5. It is suggested that these streptococci should be designated Capsular Type 1 in Streptococcus suis, a new subgroup in group D.

The colicine type and antibiotic resistance have been determined on strains of Sh. sonnei derived from 9419 incidents of Sonne dysentery in London between October 1956 and March 1965.

The most striking observation has been the appearance of strains with patterns of colicine production and antibiotic resistance new to the area. These changes are best regarded as a result of the interaction and transfer of characters between Sh. sonnei and other intestinal organisms.

The general tendency has been for strains of Sh. sonnei to become increasingly resistant to antibiotics but this has not been an uninterrupted process. The proportion of drug-resistant strains at any one time depended on the properties of the current epidemic strain.

Spread of Sonne dysentery was essentially local, but some strains of Sh. sonnei were found to spread much more widely than others. Most, but not all, of the strains resistant to streptomycin and tetracycline possessed only limited powers of spreading.