Trypanosoma equiperdum was found to take up glucose, mannose, fructose and glycerol but not galactose. Data with inhibitors suggested that the absorption of these compounds occurred by mediated processes. The inhibitory activity of various compounds indicated that three separate sites were involved in transport, two for glycerol and one for the hexoses.

Crude globulin fractions were prepared from the pooled serum of chickens 14 days after their inoculation with oocysts of Eimeria maxima (‘immune’ globulin) and from the pooled serum of similar but coccidia-free chickens (‘normal’ globulin). The fractions were injected subcutaneously into young chicks which were challenged with large numbers of oocysts and whose weight gains over the next 7 days were measured. The weight gains in all infected groups of chicks were lower than in uninfected and uninjected controls, but the gains in groups of chicks injected with ‘immune’ globulin preparations were higher than in groups given ‘normal’ globulin. Oocyst production in the groups given ‘immune’ globulin was very much lower than in the control groups, untreated or given ‘normal’ globulin.

The reduction of oocyst production by antisera given by the subcutaneous and oral routes was compared. The weaker of two antisera had no effect when given orally but caused some reduction in oocyst numbers when given subcutaneously. A stronger antiserum produced some effect when given orally but was considerably more protective when given subcutaneously. The findings are discussed in relation to the mode of action of antibodies in protecting against infection.

The cercaria and sporocyst of Bucephaloides gracilescens are described from Abra alba (Wood). Observations were made on the behaviour of the cercaria and the mechanism of release from the first intermediate host. The metacercaria was obtained experimentally for the first time using Ciliata mustela (L.), a species of Gadidae from rock pools, as second intermediate host. It has not previously been recorded from this fish. Unsuccessful attempts were made to infect species of fishes from three other families, namely, Bothidae, Pleuronectidae and Gobiidae, confirming the high degree of host specificity of the metacercaria to Gadidae. The metacercaria, its development and effect on the host are briefly discussed. It was linked with the adult on the basis of comparative morphology and ecology of the hosts.

Metacercariae of Parvatrema timondavidi were successfully cultivated in vitro to adults which produced eggs capable of embryonation and miracidial formation. The worms were grown in NCTC 109 supplemented with 20% inactivated bovine or chicken serum with a gas phase of 8% CO2 in air at 37 or 41°C. The use of the roller tube technique produced considerable promotion of growth in the worms. Heat inactivated bovine serum had a more salutary effect than unheated serum.

Previously immunized rats of different ages were exposed either to one large, or several small challenge infections with the nematode, Nippostrongylus brasiliensis. The number of secondary worms harboured by each of these rats was then determined on the fourteenth day after exposure to challenge. It was found that worms adapted more efficiently to host immunity when both (a) the rats were less than 11 weeks old when challenged and (b) the challenge was given in small repeated doses over a period of weeks. The age of the rats on exposure to the immunizing primary infection, however, had little or no affect per se on the subsequent establishment of immune-adapted worms. It is tentatively suggested that the failure of worms to adapt effectively to the acquired immunity of older rats resulted from the acquisition by these rats of a fully competent cellular immune response.

Fallisia effusa gen.nov., sp.nov. (Haemosporidiidea: Garniidae) is described in the teiid lizard, Neusticurus bicarinatus, from Pará State, north Brazil. Schizogony and gametogony both take place within thrombocytes and white cells of the peripheral blood. There is no development in the red blood cells, by which character the organism is differentiated from Garnia, the other known genus within the family. Another species, Fallisia modesta gen.nov., sp.nov., is described in the iguanid lizard, Tropidurus torquatus hispidus, also from Pará, Brazil. It is distinguished from F. effusa by its development principally in the lymphocytes, as opposed to the thrombocytes. There are other, striking morphological differences between the two species. It is recommended that great care is needed in the interpretation of so-called ‘exo-erythrocytic stages’ of saurian plasmodia, which may well really belong to members of the Garniidae, in mixed infections.

Allophryxus, a new genus of hemiarthrinid isopod, is described. The only species, A. malindiae, is a parasite of the common Indo-West Pacific coral-associated shrimp Coralliocaris superba (Dana). The parasite attaches to the anteroventral aspect of the host's abdomen. Allophryxus is the only hemiarthrinid genus definitely known to have seven pereiopods on the short and four on the long side of the body. The presence of four pairs of biramous pleopods and the absence of telson and uropods from the abdomen distinguish this parasite from related forms.

The rate of expulsion of penetration gland material was determined from photomicrographs of Hymenolepis diminuta hexacanths stained with neutral red dye at intervals after hatching in vitro. Identical secretory rates were recorded for hexacanths incubated in either Tyrode's solution or Tyrode's solution plus an extract of the midgut of Tenebrio molitor. In both media the reduction in stained material observed in the glands after 135 min incubations was equivalent to that observed for hexacanths that had had opportunity to penetrate in vivo during the same time period. These results were interpreted as indicating that the in vivo secretory pattern was similar to that observed in vitro, and that chemical stimuli from the tissue extracts were not required to initiate secretion. Microdensitometric readings also demonstrated a quantitative decrease in dye within the glands as incubation time increased. Ultrastructural examination of the glands showed that their secretory inclusions were exported via ducts to the epithelial cytoplasm where they accumulated in discrete blebs enclosed by the surface membrane. These inclusion-filled, membrane-bounded blebs were apparently formed and released continuously until, after approximately 2 h, only a few inclusions remained in the penetration glands.

The malaria parasites, Plasmodium berghei yoelii and P. vinckei chabaudi, run comparable courses of infection in mice. When mice were treated with betamethasone infections with P. v. chabaudi were enhanced while those of P. b. yoelii were depressed. Antibody levels in betamethasone-treated mice infected with either P. b. yoelii or P. v. chabaudi were depressed to similar extents. The differences in parasitaemias in the two different infections are attributed to the suppression of reticulocyte production by betamethasone. P. b. yoelii preferentially invades reticulocytes and the patterns of parasitaemia follow the level of reticulocytes in the blood. P. v. chabaudi has no preference for reticulocytes and the pattern of parasitaemia is influenced by the depressed immunological response of the host.

The factors responsible for stimulating activation of cystacanths of Polymorphus minutus in vitro have been investigated. Under the conditions used, the optimum temperature for activation was found to be 42–44 °C, at a pH of 7·0. A marked enhancement of activation rate was observed after preincubation in a 1 mM solution of sodium taurocholate and in solutions of sodium cholate, sodium glycocholate or sodium deoxycholate. This apparent effect of bile salts has been compared with that of other detergents, and a significant enhancement of activation rate above control was observed with saponin and sodium fusidate. Trypsin did not affect the rate of activation, and some inhibition occurred with lipase. The osmotic pressure of the surrounding medium has an effect on activation, the rate of which varies inversely with osmolarity. The conditions for activation in vitro are compared with those of the physicochemical environment in vivo.

Most successful parasitoids are able to avoid the encapsulation reaction of their host. A similar avoidance was observed with particles of a weakly acidic cation exchanger which was not encapsulated following its injection into the haemocoele of an insect. The ionic nature of the surface of the acidic cation exchanger and the two species of parasitoid eggs appeared to be similar. A weakly basic anion exchanger was readily encapsulated following injections into the haemocoele of a host. The encapsulation of the basic anion exchanger was prevented by coating the surface with fluid from the calyx region of the female parasitoid ovary. The importance of the fluid from the calyx region of the parasitoid and the ionic nature of the surface in avoiding the encapsulation reaction of the hosts haemocytes is discussed.

The effects of different and repeated doses of Oesophagostomum columbianum larvae on the survival of the adult parasite, its length and the fecundity of the female worm in sheep were studied. Adult worm burdens were dependent on the numbers of larvae administered when sheep were infected once, but not when they were infected twice. It was concluded that these effects were caused by non-specific elimination of worms following a single infection, related to competition for space among larvae and to inflammatory reactions stimulated by them in the gut mucosa which increased with the numbers of larvae given. When sheep were infected once with large numbers of larvae or when they were infected twice the surviving adult population was also influenced by the adaptive immune responses of the host. Parasites recovered from sheep given a single infection of 5000 larvae were stunted compared with worms from sheep given fewer larvae. After a second infection all the worms were stunted and the females produced fewer eggs than did female worms following a single infection; but the numbers of larvae administered did not influence these effects. Egg production was also delayed after a second infection. The reduced fecundity of female worms in the immune host was not related to stunting of the worms, because stunted female worms from sheep infected once with 5000 larvae produced as many eggs as females from sheep infected once with smaller numbers of larvae. It is suggested that the different manifestations of protective immunity in sheep were elicited when threshold levels of infection were exceeded. These levels were represented by between 2000 and 5000 larvae in first, and fewer than 500 larvae in second infections.

The fine structure and organization of schistosome tail musculature has been investigated by transmission electron microscopy. A three-dimensional reconstruction is presented and the relationship between morphology and cercarial behaviour is discussed.

Immunity to Eimeria maxima, judged by oocyst production resulting from a low challenge inoculum, was evident when the challenge was given as early as 3 days after the immunizing dose of 250 or 500 oocysts. Immunity was complete, i.e. no oocysts were produced, to challenge at 7 days after an initial inoculum of 500 oocysts, or at 14 days after 250 oocysts. Judged by the above criteria 250 oocysts of E. tenella did not induce immunity to challenge given at 3, 5, 7 or 14 days. The findings are discussed.

Chicks were treated with cyclophosphamide during the first 3 days of life in order to effect chemical bursectomy. They subsequently showed a reduced capacity for the production of serum agglutinins to Brucella abortus and immunolysins to sporozoites of Eimeria tenella. They also developed a reduced immunity to E. tenella or E. maxima compared with that produced in normal birds. The evidence provided by these experiments for the role of circulating antibodies in immunity to coccidiosis is discussed.

The effects of cercarial concentration and length of exposure on the infection of mice by St Lucian Schistosoma mansoni cercariae were investigated in a running-water habitat.

For all exposure times, mice exposed to cercarial concentrations from 2·5 to 40 cercariae per mouse acquired no infections. At higher concentrations, infection rates and worm burdens of mice increased in direct proportion to cercarial concentrations and exposure times. The highest infection rate (57·9 %) and worm burden (46 worms) were obtained in mice exposed for 256 mm to 1280 cercariae per mouse.

Cercarial concentrations are low in St Lucian running waters, a fact suggesting that the risk of persons becoming infected while fording, collecting domestic water, washing clothes and swimming in habitats with reasonable flows is very low. It appears that most infected individuals acquire a low worm burden over a rather long period of time.

When incubated at 13°C in alternating 12 h periods of light and darkness eggs of Acanthocotyle lobianchi rarely hatch. Hatching was not induced by shadowing or by mechanical disturbance. When skin mucus from the host ray was added to eggs which were more than 15 days old, hatching occurred almost immediately in about 60% of all eggs tested. Susceptibility to host mucus increased with the age of the eggs so that after 26–30 days of incubation over 80% of the eggs tested hatched. Some oncomiracidia were found to remain alive for up to 83 days in the egg, although they appeared to be fully developed at 15 days. Lipid droplets in the body of the 15-day-old oncomiracidia gradually disappeared as the eggs aged and it is suggested that these droplets serve as a food store for resting larvae.

The growth rates of the intramolluscan stages of the parasite Fasciola hepatica were determined at three temperatures 16°, 20° and 25°C. A graphical relationship of growth rate with respect to temperature was produced and a growth array was calculated from this. Meteorological data were summarized in the form of a temperature array. These arrays were then used in conjunction with a simple equation to simulate parasite growth within the snail host. A digital computer was employed to solve iteratively the simulation equation, initially by checking its application against experimentally determined results. It was then employed with the meteorological data to simulate growth with respect to environmental temperatures and the results obtained were compared with those derived from field collections. Estimates were also made of the duration of the shortest life-cycle under field conditions.

When eggs of the monogenean parasite Entobdella hippoglossi, from the skin of the halibut (Hippoglossus hippoglossus), are incubated at 7 °C in alternating 12 h periods of dim blue light (intensity about 3 nW/cm2) and darkness, free-swimming larvae are recovered mostly at the end of the first 2 h of the period of darkness. Larvae do not emerge in significant numbers when the eggs are mechanically disturbed during the light or dark periods, or when the eggs are placed in shadow for periods of 5–25 min during the illumination period. The treatment of fully developed eggs with washings from halibut or from sole or with halibut skin mucus failed to produce hatching.

The free-swimming life of the larvae at 7 °C is in excess of 24 h and within 4 h of hatching at 4 °C some larvae are able to attach themselves to halibut skin and shed their ciliated epidermal cells.

The relationship between the hatching pattern of the eggs of the parasite and the behaviour of the halibut is discussed.

When neonatal rats were exposed to a small (200 larvae) primary infection of Nippostrongylus brasiliensis the worms that became established in the intestine were found in the mid-jejunum on both the seventh and the fourteenth day after infection. By day 21 most of the worms had migrated to the duodenum where they remained subsequently.

When similar rats were exposed to a heavy primary infection (1500 larvae) the worms were found to be distributed along the length of the duodenum and jejunum by the seventh day. By day 28, however, a proportion of worms equal to that formerly located in the jejunum had been expelled, leaving a population of about 300 worms in the duodenum.

It is suggested that the increased longevity of those worms that survive the effects of host immunity is dependent on their location at the duodenal site. The possibility is raised that the duodenum may be an immunologically privileged site for N. brasiliensis in young rats.