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.

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.

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 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.

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.

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.

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.

In lactating rats examined 3 weeks post infection, adult Nippostrongylus brasiliensis were found in the duodenum close to the pylorus. Worms migrated from the predilection site, shown by Brambell (1965) and Alphey (1970) to be approximately 25% down the intestine, during the second week of infection. A similar migration took place in neonatally infected rats.

It was suggested that the migration was an active response to immunological damage. It could be prevented by early betamethasone treatment but only modified by treatment given late in infection.

The effect of immune inhibition on the pleomorphism of Trypanosoma brucei was studied by counting trypomastigotes and their granules on agar. A statistical analysis is presented. Busulphan 32 mg/kg, given 24 h before inoculation, caused an inhibition of the infection detectable at 72 h, but not thereafter. Immune inhibition caused by busulphan was associated with increased numbers both of agranular forms and forms containing lipid (type II) granules. After 96 h, treatment did not alter the proportion of agranular to granular forms. The remission was delayed 24 h in treated rats, the remaining trypomastigotes being more sluggish, more fragile and containing more numerous granules of increased size. We conclude that the remission is not produced by the immune reaction but by an innate process of dissolution of the ageing trypomastigotes.