1. In intact rats infected with P. berghei spontaneous eradication of infection has occurred by about 4 months after the day of inoculation.

2. These recovered rats show a strong residual immunity to reinfection with a heterologous strain, but this has begun to wane by 15–18 months after cure of the initial infection.

I owe many thanks to Miss W. J. Wall and Miss J. Wrugh of the Ross Institute for maintenance of the rats and assistance with the blood films.

1. The morphology of an Entamoeba from the Sudanese lizards Mabuya quinquetaeniata, M. striata and Tarentola annularis is described. It was similar to Entamoeba coli of man.

2. It is referred to the species E. flaviviridis, Knowles & Das Gupta (1935).

3. An ‘Amoeba’ was observed in Tarentola annularis which was similar in size to the Entamoeba. The nuclear structure, however, was distinctive, with a very large karyosome and no peripheral chromatin. The cysts were uninucleate.

4. It is very similar to the organism described as Vahlkampfia reynoldsi by McFall (1926).

The Chalcidoid wasp, Bairamlia fuscipes, was found parasitising the flea Ceratophyllus wickhami in the nest of the North American Grey Squirrel (Sciurus carolinensis) from Gerrard's Cross.

The larval and pupal stages of B. fuscipes were found in the cocoons of C. wickhami, and the adults were crawling about in the squirrel's nest.

The parasites were scarce, only 7 per cent, of the cocoons dissected at intervals during fifteen months were parasitised.

The parasite has not been reared in the laboratory beyond the second instar larva, though full grown larvae have successfully reached maturity under experimental conditions.

B. fuscipes oviposits through the flea cocoon and fixes the egg on the abdomen of a resting larva or pupa. Only one egg has been found in each parasitised cocoon. The larva feeds externally on the flea, fixing itself to the fourth abdominal segment or thereabouts.

Attempts were made to parasitise larvae of Xenopsylla astia, but without success.

The external anatomy of the full grown larva of B. fuscipes is described.

The humoral responses of Sprague–Dawley rats infected with Brugia pahangi were examined for up to 6 months after infection by ELISA, immunoblotting, and IFAT. In 2 experiments, 50% and 62·5% of rats developed patent, microfilaraemic infections. Mean adult worm burdens at autopsy were approximately 2% of the inoculum, and only patent rats yielded living adult worms. IgG antibody levels against crude somatic extracts (CSE) of all parasite stages and against adult excreted/secreted (ES) products were significantly higher in patent than non-patent rats. Both patent and non-patent rats produced anti-microfilarial surface antibody, as revealed by immunofluorescence. Immunostaining of Western blots by early infection sera showed no consistent difference in recognition of infective larval (L3) antigenic components by IgG or IgM antibody between eventually-patent and eventually-non-patent rats. By 26 weeks, however, patent rats recognized more components. The data suggest that antibodies against L3, adult, and microfilarial somatic antigens, ES antigens and microfilarial surface antigens do not correlate with the subsequent development of microfilaraemia in any individual rat.

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.

Evidence has accrued to indicate that host defence mechanisms enhance the efficacy of many of the drugs used to treat infectious diseases. Because of this, and also because of the likelihood of increased pathogen loads in immunoincompetent hosts, some infections are less likely to be completely cured by normal regimens of chemotherapy in individuals with drastically impaired immune responsiveness. In such circumstances natural selection could result in the accelerated emergence of drug-resistant pathogens.

Host and Record. At least four specimens of the parasite were found attached to the sides and belly of a sail-fish Histiophorus gladius Day caught off the south coast of Ceylon. I was fortunate enough to obtain two of these, both females, complete except for the egg strings. They measured 135 mm. and 157 mm. in their total lengths. One of them, the smaller, is illustrated in Fig. 1.

In 1916 Dr J. C. Becker made the interesting discovery of Bilharzia infection in Physopsis africana collected at Nijlstroom in the Transvaal and obtained the adult flukes in some guinea-pigs he had exposed to infection with the cercariae. The town of Nijlstroom is situated at the source of a tributary of the Limpopo river at an altitude of 3924 feet above the Indian Ocean into which it flows. In 1917 I collected2 infested examples of P. africana at Magaliesburg, a popular picnic place for Krugersdorp residents, situated on a branch of the Little Crocodile river which later joins the Limpopo. Magaliesburg has an altitude of 5000 feet above sea-level. I also obtained infested examples from Rustenburg, thus revealing a further source of infection from tributaries of the Little Crocodile river, at an altitude of over 4000 feet.

The trematodes described below were collected at the Marine Biological Station at Ghardaga, Red Sea.

Type specimens are deposited in the Department of Parasitology of Faculty of Medicine, Abbassia, Egypt.

All measurements are in millimetres.

The British species of Aëdes, A.(Finlaya) geniculatus, lays its eggs on the damp surfaces of tree-holes containing water; or, if the expanse of water in the hole be large, often directly upon the water surface.

A condition with a weak genetic component, but a strong correlation with age, is the summarizing of conferences. It is an art form often resembling the expression of gratitude by a bride on the receipt of her sixth electric kettle. However, our gratefulness now is genuine, because we have been given a wonderfully interesting series of papers. Their authors were chosen with skill to show the manifold variety of genetic interactions between parasites and hosts. The range of these interactions would daunt even the strongest-hearted summarizer, and my task can only be managed by a ruthless subjectivity.

Fertilization phenomena has been observed in the malaria parasite of the Himalayan Flying Squirrel with blood showing heavy infection. The blood was obtained on the slide, put in the moist chamber, dried and stained. Two types of microgametes could be distinguished. One of these two types were found in various stages of the process of fertilization. More than one microgamete were often found to take part in fertilizing a single macrogamete. This is the first recorded case of polyspermy in malaria parasites.

Thanks are due to Mr Nandalal Pau for his help in preparing the Plate incorporated in this paper.

This investigation received financial support from the World Health Organization.

Eimeria phasiani was shown to be pathogenic to young pheasant poults. Doses of 100000 or more oocysts proved fatal to birds up to 3 weeks old. Lesser doses produced losses in the live-weight gain of the host.

Two separate strains of E. phasiani were completely susceptible to 0·006% (w/w) Sulphaquinoxaline, but less so to 0·006% (w/w) Amprolium and 0·0125% (w/w) Zoalene.

I should like to express my sincere gratitude to Dr E. U. Canning for her supervision and helpful advice, and to Professor O. W. Richards, F.R.S., for permission to work at the Imperial College Field Station. I am also grateful to Mr T. H. Blank, of the Eley Game Advisory Service, Fordingbridge, Hants, who gave day-old pheasant chicks for this study.

The work was financed by a scholarship from the Agricultural Research Council.

The survival capacities of Muellerius capillaris (Nematoda: Protostrongylidae) free-living larval stages (L1) of an Israeli desert isolate (Nubian isolate) (92 mm rain per annum) and a French isolate from a temperate habitat (650 mm rain per annum) were compared under humid and extreme dry conditions. Under the dry conditions (7% relative humidity [r.h.] and 33% r.h. at 23 °C), both isolates exhibited the same remarkable survival capacity for periods of 17 and 28 days, respectively (>92% survival, P>0·1). However, during and after recovery from the anhydrobiotic state, different behaviour patterns of L1 were observed in each isolate. Under humid conditions (97% r.h.) for 10 days, both isolates exhibited similarly low survival percentages (13·4±4·6%, S.E., survival for the Nubian isolate, 3±3% for the French isolate, P>0·05). In water, the French isolate was less active, survived better (52±8·4% vs 28·7±3·7, by day 28, P<0·05) and retained a better morphological appearance (shrunk less) than the Nubian isolate. Larval development of the French isolate in the land snail Theba pisana was significantly faster than that of the Nubian isolate, reaching a higher proportion of infective stages (L3) on day 36 post-infection (78·6% vs 56% P>0·05). However, similar infection intensities were recovered in snails infected with either of the isolates (59·8±10·3, S.E., n=14, for the French isolate, 53±6, n=13, for the Nubian isolate, P<0·05).

Trichomonas vaginalis is an extracellular parasite that colonizes the human urogenital tract leading to trichomoniasis, the most common sexually-transmitted non-viral disease worldwide. The immune response plays a critical role in the host defense against this parasite. Trichomonas' DNA contains unmethylated CpG motifs (CpGDNA) that in other microorganisms act as modulators of the immune response. However, the molecular mechanisms responsible for CpGDNA immune modulation are still unclear. As macrophages participate in the first line of defense against infection, we investigated the type of immune response of murine macrophages to T. vaginalis DNA (TvDNA). We observed high expression of the proinflammatory cytokines IL-6 and IL-12p40 in macrophages stimulated with TvDNA. In contrast, the anti-inflammatory response, assessed by IL-10 and IL-13 mRNA expression was delayed. This suggests that the immune response induced by TvDNA is modulated through cytokine production, mediated partly by NADPH-oxidase activity, as TvDNA induced reactive species of oxygen production and a rounded morphology in macrophages indicative of an M1 phenotype. Furthermore, infected mice pretreated with TvDNA displayed persistent vulvar inflammation and decreased parasite viability consistent with higher proinflammatory cytokine levels during infection compared to untreated mice. Overall, our findings suggest that TvDNA pretreatment modulates the immune response favouring parasite elimination.