Methyl benzoquate at 20 ppm or clopidol at 250 ppm in the diet show true coccidiostatic activity in infections with Eimeria tenella in the chick. Lerbek, a synergistic mixture yielding 8·35 ppm methyl benzoquate and 100 ppm clopidol, produced a partially coccidiocidal effect; relapses following restricted periods of medication were less severe, and suppression of parasite development following delayed medication was quicker and more effective than with either component of the mixture used alone.

Ultrastructural observations of the surface of Diplocystis schneideri reveal a folded, multilaminate membrane, similar to that found in other eugregarines, covered with a layer of fibrous material. It is suggested that this fibrous material is a product of the haemocytes of the host, Periplaneta americana.

The activities of monensin, lasalocid and halofuginone against Eimeria tenella, E. brunetti and E. necatrix have been studied under laboratory conditions. Complete control of experimental infections in the chick, separable from toxicity, was not obtained with monensin, but was achieved with the other two compounds at levels of 150 and 6 ppm in the food respectively. All three compounds appear to inhibit coccidial development very early in the life-cycle, and to have a fairly rapid lethal effect, monensin and lasalocid more so than the febrifugine derivative. In vivo observations have been supplemented with in vitro studies. Some discussion of the difficulties of relating laboratory experiments to field performance is given.

Young schistosomes collected after penetration through isolated mouse skin (3 h schistosomula) were cultured in medium containing immune rhesus monkey serum with a high titre of antibody known to kill schistosomula in the presence of complement. Morphological signs of damage in electron micrographs were confined to the surface tegument of the schistosomula. Antibodies in immune rhesus serum were shown to bind to the surface membrane of 3 h schistosomula using an antibody-enzyme bridge technique involving labelling with horseradish peroxidase and histochemical localization of the enzyme at the ultrastructural level. Schistosomula recovered from the lungs of mice 4 days after infection did not bind monkey antibodies at the surface and these 4-day schistosomula are not susceptible to damage by immune serum in vitro. Mouse erythrocyte antigens were detected on the surface of 4-day schistosomula using an appropriate antibody-enzyme bridge but these host antigens could not be found on 3 h schistosomula. This correlation between the presence of mouse host antigens on the surface of schistosomula and the inability of immune monkey antibodies to bind to the surface membrane is consistent with the hypothesis that host antigens are acquired by young schistosomes and serve to protect the surface membrane against antibody-mediated damage.

The ultrastructure of the intestinal-cloacal junction of the male nematode Heterakis gallinarum is described. A sphincter muscle seals the lumen of the alimentary tract at this point by squeezing on the posterior cells of the intestine. These posterior cells of the intestine are unusual in that they contain numerous microtubules, and are very different from the other cells of the intestine. Electron-dense granules lie at the base of these cells where they abut on to the portion of the sphincter muscle which contains the myofilaments. It is suggested that a build-up of pressure in the intestinal lumen, brought about by the pumping action of the pharynx and/or contraction of the muscle network around the intestine, is the most probable means of opening the sphincter at defecation. On the other hand, the structure of the posterior cells of the intestine suggests that they may act as a stretch receptor which communicates with the sphincter muscle by means of a pharmacologically active substance held in the electron-dense granules which lie in the basal region of these cells.

The humoral encapsulation reaction of larvae of Chironomus has been reproduced and studied in vitro. This reaction is activated by entomogenous fungi and certain foreign bodies as well as by nematodes. The different stages of encapsulation and the duration of the process have been determined. In the larvae of a given species of Chironomidae encapsulation does not vary with age or sex. In contrast, the duration of the process differs according to the species of Chironomidae and is modified by temperature or by parasitism of the host by Mermithidae.

The capsules contain melanin. Their formation is prevented by glutathion, an inhibitor of phenoloxidase.

The humoral type of encapsulation also occurs in vitro in the haemolymph of larvae of the nematocera families, Culicidae and Chaoboridae. However, the reaction of these insects differs in the amount, distribution and pigmentation of the capsular material.

The results demonstrate similarities between humoral and cellular encapsulation.

The fine structure of trophozoites, schizonts, merozoites and macrogamonts of Eimeria acervulina found in goblet cells of the duodenal epithelium of chicks is described and compared with the corresponding stages formed in other epithelial cells. Complete schizogony, with the formation of mature merozoites, occurred freely in goblet cells. Developing macrogamonts (but no microgamonts) were rarely found in goblet cells. The stages observed were confined to the cytoplasm of the host cell above the Golgi apparatus and were usually seen between the mucous granules. The stages seen appeared normal, and contained similar structures to corresponding stages developing in other cells. The finding of developing stages of E. acervulina in goblet cells provides further evidence that site specificity of Eimeria at the cellular level is not as strict as previously thought.

Biomphalaria glabrata selected for genetic differences in susceptibility to infection with a Puerto Rican strain of Schistosoma mansoni were exposed to miracidia of a strain of S. mansoni from St Lucia. The St Lucian strain was less infective than the Puerto Rican. Results suggested that in snails susceptible to the Puerto Rican S. mansoni, differences in susceptibility to the St Lucian strain were determined by a single gene, with insusceptibility dominant.

Immune serum accelerated the expulsion of Trichuris muris when transferred into normal mice on days 0 and 3 after infection, but had no effect when the recipient mice had been immunosuppressed by sublethal irradiation or by cortisone treatment. Delaying serum transfer until days 7 and 8 in normal mice failed to accelerate expulsion, although immune mesenteric lymph node cells (MLNC) accelerated expulsion whether transferred early or late in infection.

Expulsion from NIH mice, normally complete by 12 days, was prevented by sublethal irradiation given as late as 9 days after infection, but could be restored by subsequent transfer of immune MLNC or, to a lesser degree, non-immune MLNC. Immune MLNC were unable to restore worm expulsion in mice irradiated before infection.

These results are interpreted as showing that the immune expulsion of T. muris from mice during a primary infection requires the sequential activities of antibody-mediated and lymphoid cell-mediated components.

When eggs of the monogenean Dictyocotyle coeliaca, a parasite from the body cavity of Raja naevus, are incubated in alternating 12 h periods of light and darkness at 12 °C the marginal hooklets appear between 75 and 90 days after collecting the eggs from the host's body cavity and hatching begins after about 102 (96–109) days. Hatching occurs continuously throughout the light and dark periods so that there is no daily hatching rhythm, and host skin mucus and fluid from the host's body cavity (previously deep frozen and thawed before use) are ineffective as hatching stimulants. The significance of these observations in relation to host behaviour is discussed.

Cattle were inoculated with dilutions of Theileria parva (Muguga) stabilate without concurrent antibiotic treatment. The dilutions were selected to induce severe East Coast fever infections, which in some cases would lead to death. Serum samples were collected and the complement fixation (CF), indirect haemagglutination (IHA) and indirect immunofluorescence (IFA) tests were used to detect T. parva serum antibodies. Sera were fractionated on Sephadex G200 to determine the activities of specific immunoglobulin fractions. Sequential production of IgM antibody followed by 7SIg antibody was demonstrated by the IHA and CF tests. All IFA activity was restricted to the 7SIg fraction. Serologic reactions in the IHA test were detected as early as 4 days after inoculation of the stabilate, CF activity after 8 days and IFA activity after 21 days.

Three groups of chickens were fed small numbers of ova (3, 5 or 9 ova per bird) of Heterakis gallinarum in a quantitative study of the transovarial transmission of Parahistomonas wenrichi by the nematode. Subsequent incidence rates of Parahistomonas infections in recipient birds were analysed according to the methods of Chiang & Reeves (1962). The results indicated that at least 25 % of Heterakis ova, passed in the faeces of birds with concomitant Parahistomonas infection, carried the protozoon. The appearance of Parahistomonas in a bird which retained all its challenge nematodes indicated that the protozoon can be released by living worms. Data on the pre-patent periods of Parahistomonas infections are consistent with a hypothesis that the protozoon is typically released at the time of the final (fourth) moult of the nematode.

Larvae of the cattle tick Boophilus microplus will attach to thin (0·3–0·5 mm) slices of cattle skin and engorge on a partially denned medium at 35 °C. Forty-seven to 83% of the larvae had engorged by 8 days, and 51–71% of these moulted to nymphs. Tissue culture medium alone allowed little growth unless supplemented with dialysed, freeze dried bovine serum (7%, w/v). This medium could be further defined by substituting purified bovine serum albumin (Cohn fraction V) for the dialysed bovine serum. In one experiment, nymphs of Haemaphysalis longicornis engorged and later moulted to adults. Skin slices were used fresh or after freeze-drying and storing at − 25 °C. The possible uses of the culture method are discussed.

The thoracic lymph duct of rats infected with Trypanosoma brucei and with T. congolense was cannulated at different stages of infection. Trypanosomes were always present in the lymph of rats infected with T. brucei, whereas they were absent or very scarce in the lymph of rats infected with T. congolense. There were greater fluctuations in the numbers of trypanosomes in the blood than in the lymph. The intra- and extravascular populations of T. brucei differed: stumpy forms were present only in blood; dividing forms were usually more numerous in lymph.

Samples of rabbits were obtained throughout each month over the 4-year period 1967–70. All fleas were removed, sexed and counted and the reproductive condition of the rabbits recorded. Rabbit fleas Spilopsyllus cuniculi (Dale) were present on both sexes of rabbit at all times of the year. In each year significantly high numbers of fleas were found on the rabbits in January, February, March and April and significantly low numbers in August, September and October. Mean flea counts were significantly higher on female rabbits than on males during April, May and June. During the rest of the year counts from each sex of host did not differ significantly. There were significant differences in flea numbers between years. More female than male fleas were found on both sexes of host throughout the year. The rabbit population sampled is shown to be typical of post-myxomatosis populations with regard to breeding performance and juvenile mortality. The relationship of the observed patterns of change in flea numbers to host and flea breeding and to host behaviour, population size and structure is discussed.

An examination of 235 Plica umbra and 167 Uranoscodon superciliosa (Sauria: Iguanidae) from Belém, Pará, Brazil, has revealed a number of hitherto undescribed blood parasites. These include Fallisia audaciosa, F. simplex, Garnia multiformis, Plasmodium vacuolatum and Trypanosoma plicae spp.nov., all in P. umbra, and G. uranoscodoni sp.nov. in U. superciliosa. In addition, both species of lizards showed occasional Eperythrozoon and microfilaria infections. Among the haemosporines, F. audaciosa is particularly interesting in its restriction to the neutrophils; and G. multiformis for its early development in erythroblasts of the bone-marrow, and its variable morphology in subsequent stages of the infection in the peripheral blood. Mixed infections of the different haemosporines resulted in 18 combinations of parasites in P. umbra, indicating the importance of examining a large number of these animals when preparing descriptions of the individual organisms. T. plicae is a large, broad trypanosome, averaging ∼ 57·0 × 16·0 μm. Isolation of the parasite was made from four out of six P. umbra, after the culture of heart blood in NNN medium: the fact that none of the four positive lizards showed detectable trypanosomes in the peripheral blood suggests a high incidence of occult infections. The incidence among the remaining 229 P. umbra, as given by the direct examination of blood-films, was only 10·0%.

Judged by oocyst production, infections with Eimeria acervulina in birds immunized with E. maxima were consistently higher than in birds which had not been immunized. Oocyst production of E. maxima in birds previously infected with E. acervulina was greater, in three out of four experiments, than in control chickens, but some of the differences were slight. The findings are discussed but no satisfactory explanation can be offered. In general there was little or no difference between the oocyst production of the individual species when present as single or mixed infections.

The life-cycle of Tetrameres mohtedai in the fowl involving a hitherto unknown intermediate host, Setomorpha rutella, is described and methods for laboratory demonstration are given. Development to infectivity in the intermediate host took less than 2 weeks under laboratory conditions. Infections could be established using infective larvae dissected from the intermediate host. The pre-patent period in the fowl averaged 36 days. Experimental evidence is given for infection of the final host by ingestion of either infected adult or infected larval Setomorpha. Development of the parasite to the infective stage does not depend on metamorphosis of the intermediate host.