1. A new species of tick, I. theileri from South Africa, is described. Hitherto it has been collected only from birds.

2. Existing descriptions of I. daveyi Nuttall 1913 and I. brunneus Koch 1844 are amplified, and the synonymy of I. frontalis (Panzer, 1795) discussed.

3. Diagnostic characters, whereby I. daveyi, I. brunneus, I. frontalis and I. theileri may be separated, are tabulated.

The life history of Ornithodoros graingeri under laboratory conditions at 28° C. and 95% humidity, can be summarized as shown in Table 4. These figures, except for the fourth-stage nymphs, include the interval between emergence and willingness to feed.

A spirochaete, S. graingeri n.sp., was isolated from batches of Ornithodoros graingeri from caves near Tiwi, south of Mombasa. Very scanty infections were caused in white rats and mice, and a persistent parasitaemia in a general paralytic. Guinea-pigs, a monkey, and a young rabbit were insusceptible. There was evidence that unlike most tick-borne strains the spirochaete was only slightly neurotropic.

1. Strains of P. berghei resistant to sulphadiazine, pyrimethamine, and methylene blue were produced by treating acute infections with low doses of drug.

2. The strain resistant to methylene blue was sensitive to pamaquin, mepacrine, sulphadiazine, proguanil, pyrimethamine, and 2 : 4-diamino-6 : 7-camphano-pteridine.

3. The pyrimethamine-resistant strain was cross-resistant to proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-camphanopteridine, 2 : 4-diamino-6 : 7-(l′-ethylindolo)-pteridine, and 2 : 4-diamino-5-p-chlorophenylpyrimidine.

4. The sulphadiazine-resistant strain was cross-resistant to pyrimethamine, sulphanilamide, proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-dinhexylpteridine, and 2 : 4-diamino-6 : 7-diisopropylpteridine. It was as sensitive as the parent strain to quinine, mepacrine, chloroquin, pamaquin, methylene blue, and M 3349.

5. The action of sulphadiazine against the sulphadiazine-resistant strain was inhibited by the same doses of p-aminobenzoic acid and folic acid as were required with the parent strain, although the dose of sulphadiazine was increased 30-fold.

The purpose of this paper is to describe a new tick of the genus Ornithodoros Koch, from South Africa. Specimens were received through the courtesy of Dr Zumpt of the South African Institute of Medical Research, after being collected from the burrow of a striped mouse, Rhabdomys pumilio (Sparrman), near Cathcart, Cape Province, in April 1952. Interest in the ‘burrow haunting’ Ornithodoros of Africa has increased in recent years, because certain of these ticks have been found to transmit spirochaetes of rodents and other small mammals. These spirochaetes may be evolutionary precursors of those that infect man, and cause the well-known sporadic relapsing fever of tropical Africa. Two live Ornithodoros larvae from the burrow were emulsified and inoculated into a white mouse but no spirochaete was isolated (Zumpt, personal communication).

1. Entamoeba moshkovskii was isolated from a sewage plant in North London.

2. The morphology and metacystic development is similar to that of E. histolytica and other histolytica-like amoebae, but with differences in minor details.

3. The cysts of E. moshkovskii remain viable when kept at 4° C. for periods up to 10 months providing they are not allowed to dry.

4. If the amoebae are placed in hypotonic solution, the amoebae attempt to eliminate excess water by means of contracting vacuoles, but they eventually die.

5. Experiments have shown that E. moshkovskii is an anaerobe.

6. The optimum temperature for growth is about 24° C. as encystation does not occur at 37° C.

7. E. moshkovskii is not infective to rats or to larvae of the common frog (Rana temporaria) and Salamandra maculosa.

Types. Four mature females (NM. 5728) from Myotis tricolor, Town Bush Cave, Pietermaritzburg, March 1952.

For the purpose of determining the suitability of malaria for some work on experimental epidemiology, it was necessary to study the reciprocal immunity produced between a number of species and strains of avian plasmodia maintained in canaries. Some of this work has been a repetition of that previously described by other authors, but some new observations have been made, involving a number of geographically widely separated species and strains, which seem worth putting on record.

1. The width and length of eggs of Haemonchus contortus, Cooperia curticei, Trichostrongylus axei, T. vitrinus, Bunostomum trigonocephalum, Chabertia ovina, Oesophagostomum venulosum and Ostertagia spp. were measured.

2. Frequency distributions of the linear dimensions of the eggs of each species are given, together with the frequencies calculated on the assumption that the distributions are normal.

3. A method of species differentiation based on egg measurements is described, the method being based upon the statistical chances of eggs of different species falling into particular size classes.

4. The application of the method and the construction of a classifying scale are described.

Among approximately eighty larvae of Trachea secalis, gathered from the same locality near Cape Town, South Africa, the incidence of microsporidian infection has been found to be 100%. In the majority of cases the parasite had heavily involved the lower portion of the gut, whereas the rectum and the upper portion of the gut were never infected. In severe cases the gut tissue was practically destroyed and replaced by an almost solid mass of spores. Except during the stages preceding spore formation, the infected portion of tissue can be detected by the unaided eye. When spores have been produced in large numbers, the involved area, which may be no larger than the head of a pin, and is usually located within the posterior third of the gut, becomes white and opaque, and contrasts sharply with the healthy surrounding tissue. The latter is transparent, and appears dark, owing to the colour of the contents. At a later stage it is not unusual to find the infected zone in the form of a narrow band which encircles the gut. The infection then spreads upwards and downwards. Finally, the entire lower portion of the gut becomes white and chalky. With the exception of the gut contents the parasite has not been found elsewhere in the body of the host.

On 7 March 1953 I received several specimens of Locusta migratoria from Mr T. Singh, who found them dying in the breeding cages at the Imperial College, London. Microscopic examination showed that the fat body contained large numbers of oval-shaped spores belonging to a microsporidian.

At one of the meetings of the Royal Society of Tropical Medicine and Hygiene, I made a very short communication on the three blood-sucking midges (Jobling, 1929). My particular reference was to Culicoides vexans, which is the most troublesome and commonestspecies in spring, in the northern and the north-western suburbs of London. At that time I had been studying the life history of this midge, including the morphology of its eggs, larvae and the pupa, but this work was not completed.

The nematodes described here were collected by biologists of the Australian National Antarctic Research Expedition based at the subantarctic stations at Macquarie Island and Heard Island, over the years 1948–51.

1. A description is given of a sporozoan parasite occurring in the coelomic fluid of P. minutum.

2. The four stages described include two types of schizonts (each enclosed in a tough envelope), merozoites, trophozoites, and encysted gamonts. The schizonts occur in the haematids of the coelomic fluid, the ‘cysts’ in amoebocytes.

3. The life history and possible affinity of the parasite with the Haemogregarinidea are discussed.

4. Attempts to verify the suggested life history by experimental means are described.

In tests for chemotherapeutic activity, mice were infected with Eperythrozoon coccoides, treated with drugs for 2 days, splenectomized, and treated with drugs for a further 2 days. Blood films were examined from the second day after splenectomy, when control mice showed heavy blood infections.

Neoarsphenamine, aureomycin and terramycin were active.

Tryparsamide, Chloromycetin, alloxan and polyoxyethylene ether, D2, were slightly active.

Many drugs, listed in Table 3, were inactive.

Neoarsphenamine cleared E. coccoides from the blood very rapidly. This action was inhibited by dimercaprol (BAL).

E. coccoides closely resembles Haemobartonella muris in its sensitivity to drugs. Both micro-organisms probably have affinities with the Rickettsiae.

When reviewing the status of Ixodes frontalis Panzer in an earlier paper (Arthur, 1952) the reference to Acarus (Ixodes) turdi Scopoli was not included, for the description might well apply to any tick. This is equally true for Panzer's description, and this name has been retained through popular usage. Neumann (1899) was the first worker to present a fairly clear account of this species but, as his host range shows, it may well have been clouded by reference to Ixodes brunneus Koch. The available descriptions refer to the female. Larvae have hitherto been neglected or else described as similar to the female, with the addendum that ‘in the larva the scutum is as broad as long’. Examination of ticks from a large number of birds has convinced me that in the past the immature stages of many species of ticks have, on this basis, been incorrectly determined. This may possibly be one reason for the suggested rarity of records of the immature stages of I. frontalis. In the present paper the larva of this species has been described. This description has been based on larvae sent to me by Mr John Ash.

Up to the present time the polyhedral viruses of insects have been considered to be extremely specific in their infectivity, and cases of cross-infection, even between closely related species, were regarded as rare occurrences. Recently, however, we have recorded results which suggest that there is no such specificity of infection (Smith & Xeros, 1952). In the following paper we describe the results obtained in an extensive series of cross-inoculations among a heterogeneous collection of lepidopterous larvae, selected entirely at random. The results obtained appear at first sight to be compatible with one clear-cut explanation of straightforward cross-infections with differential multiplication of two different viruses in different hosts. Other complications, however, cannot be excluded and one or two possible situations are discussed later in the paper.