Eight 7-month-old sheep were dosed continuously with Trichostrongylus colubriformis larvae and 4 sheep were killed at 5 and 10 weeks from the commencement of infection. Flattening of the mucosa and villous atrophy were commonly present at slaughter, and parasites were often found in superficial channels parallel with the luminal surface. At 10 weeks the mucosa was thickened and highly cellular. Leucine aminopeptidase, alkaline phosphatase and maltase activity were reduced in the proximal third of the small intestine. Liver vitamin A was reduced in 3 of 4 infected sheep at 10 weeks, but serum vitamin A levels were comparable with those of worm-free control sheep throughout the experiment.

Nippostrongylus brasiliensis infections in mice were terminated more rapidly than in rats and immunologically induced damage occurred earlier. Like rats, mice expelled damaged worms more rapidly than normal worms. Recipients of cells from the spleen or mesenteric node of immune mice expelled their worms by day 8 of the infection. Recipients of cells alone or antiserum alone did not expel their worms by day 5 but mice given both cells and antiserum expelled their worms by this stage of the infection. Damaged worms were expelled more rapidly than normal worms from mice given immune cells. This work indicates that antibodies and cells collaborate to expel N. brasiliensis from mice as has been shown to occur in rats.

Two lines of Plasmodium chabaudi differing in three characters have been crossed, using a technique previously described for P. yoelii. One line, termed 47AS, was characterized by an electrophoretic form of 6-phosphogluconate dehydrogenase, denoted 6PGD-2, a form of lactate dehydrogenase, denoted LDH-3, and was pyrimethamine-resistant. The second line, termed 10AJ, possessed enzyme forms 6PGD-3 and LDH-2 and was pyrimethamine-sensitive. The cross was made by permitting mosquitoes to feed on a mixture of the two lines and infecting rodents with the resulting sporozoites. The products of the cross were cloned by dilution and examined for enzyme-type and drug-response. Results showed that recombination had occurred between each of the three characters. Clones characterized by 6PGD-2/LDH-2 and 6PGD-3/LDH-3 demonstrated recombination between the enzyme markers. The drug-resistance character segregated independently of either enzyme marker.

Skin penetration by infective Ancylostoma tubaeforme larvae has been investigated cinematographically and using in vitro techniques. The dermal tissue appears to cause little hindrance to larval migration but complete penetration through the skin from the dermal direction did not occur, although total penetration from the epidermal surface was frequently accomplished. No evidence could be found for enzymic secretions emanating from the worms under conditions that gave positive results from Necator americanus and Strongyloides fülleborni infective larvae. The results indicated that A. tubaeforme was able to penetrate without the use of enzymic secretions and an alternative, mechanical mechanism for penetration is advanced.

The level of free amino acids in Diclidophora merlangi is high, comprising over 500 μmoles/g ethanol extracted dry weight. A single amino acid, proline, constitutes some 70% of the total pool. Analysis of parasite protein and host blood and mucus revealed low proline levels, suggesting that the high free pool content was not related to a requirement for protein synthesis or to its abundance in the diet of the worm. Experiments revealed that proline was not involved specifically in osmoregulation, and the reasons for the large amounts present in Diclidophora remain unknown.

A robenidine-resistant strain of Eimeria maxima was found to be drug-dependent and developed satisfactorily only in birds which were receiving the drug in the diet. Normal parasite development occurred in the presence of 132 ppm of robenidine in the food.

The sexual development of the microgametocyte of Plasmodium yoelii nigeriensis may be subdivided into microgametogenesis which includes exflagellation, dispersal of the gametes and fertilization. Under our experimental conditions microgametogenesis takes about 8–15 min at 20 °C, the duration of this period being inversely related to temperature. Exflagellation takes less than 1 min, subsequent dispersal of gametes may continue for 40 min. We find that exflagellation is totally inhibited in vitro by temperatures of 30 °C and above, and by certain invertebrate tissue culture media. Exflagellation may occur within a persistent host cell plasmalemma, which seriously impedes the escape of the 8 microgametes. Microgametes move by sinusoidal or helical waves which may be rapid (10 waves/s), slow (< 1 wave/s) or they may be immobile. Microgamete activity, which is alternately rapid/slow or slow/immobile, declines linearly with time. Fertilization which takes less than 1 min results from characteristic behavioural changes by the microgamete; vibratory waves are responsible for the penetration of the macrogamete by the microgamete. The microgamete completely enters the macrogamete and therein continues its cyclical activity.

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 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.

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.

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%.

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.