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.

The survival characteristics of free-living cercarial populations of Transversotrema patialensis were described and shown to be age-dependent. The maximum life-span was found to be 44 h with a 50% survival at 26 h. Activity and infectivity of the larvae were also characterized by age-dependence, and were demonstrated to be closely correlated with one another. For individual cercariae, both activity and infectivity had dropped to extremely low levels many hours before death occurred. An attempt was made to interrelate activity and infectivity, in a theoretical manner, with the availability of energy reserves.

Conceptual understanding of the biological processes involved was aided by the formulation of simple mathematical models.

An experiment was carried out to investigate the effect of soil moisture stress upon the hatching behaviour of Nematodirus battus. The method involved the use of polyethylene glycol solutions to maintain a steady osmotic pressure around a soil containing N. battus eggs, which were ready to hatch. Different concentrations of polyethylene glycol (creating different moisture stresses) were found to affect the numbers and the rate of egg hatching markedly.

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.

The behaviour which enables the cercariae of the ectoparasitic digenean, Transversotrema patialensis, to establish themselves on the surface of their fish hosts has been described experimentally using anaesthetized fish. Specialized regions of the cercarial tail, the arm processes, seem to be adapted for both specific recognition of, and rapid attachment to, the outer surface of a fish. Each arm process bears an array of nine ciliary sensory structures, the mammiform receptors, which have been tentatively identified as contact chemoreceptor organs involved in host recognition. Also present on each arm is an adhesive pad that mediates the initial attachment to the host. It is a differentiated region of the distal cytoplasm of the epidermal syncytium which invests the whole arm process. The cytoplasm of the pad region contains membrane-bounded adhesive granules, the contents of which are released during activation of the pad.

During a series of experiments on the ecology of Nematodirus battus observations were made on the uptake of water by eggs containing third-stage larvae. It was found that, as they approached hatching, the water content of the larvae increased markedly, then fell immediately after they escaped from the shell. The method of measuring the water content, using interferometry, is also described.

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.

The ultrastructural and cytochemical changes accompanying intracellular digestion and cellular defecation in the haematin cell of Diclidophora merlangi have been described. Blood proteins of the host-fish are sequestered by endocytosis and degraded within an interconnecting network of channels that form an integral, but changing, part of the cell. The digestive enzymes involved originate in the granular endoplasmic reticulum and are packaged in the Golgi apparatus and transferred to the channels in Golgi vesicles. The rate of haemoglobin absorption and the activity of the Golgi, as judged by vesicle counts and staining intensities for thiamine pyrophosphatase activity, are stimulated by the introduction of host protein into the gut lumen. The haematin residues of digestion are extruded periodically into the lumen by exocytosis involving membrane fusion. The process is a continuous one and, in worms starved of food, can result in the complete evacuation of pigment from the cell. It is suggested that a lysosomal system operates in the digestive cycle of the haematin cell.

Observations were made on the histology of tissues from the first 6–10 m of the small intestine from both sheep infected with Trichostrongylus colubriformis and from uninfected controls. In uninfected animals, and in distal samples from infected lambs, villi were tall and covered by tall columnar epithelium, the intestinal crypts were convoluted and the lamina propria was only moderately cellular. In tissues with sub-total villus atrophy and a convoluted surface, the superficial epithelium was usually low columnar, often with an indistinct brush border. More severely affected mucosa was flat, with low surface epithelium and protruding crypt openings. The flat surfaces frequently had leaks of eosinophilic material and polymorphonuclear cells between enterocytes, or through erosions in the epithelium. Such defects were smaller and less frequent in mucosa with a convoluted surface. There were increased mitoses in intestinal crypts and a heavy inflammatory cell infiltrate in the lamina propria. Mast cell, globule leucocyte and theliolymphocyte numbers were not increased in infected sheep.

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.

Second-instar larvae of the gypsy moth, Porthetria dispar (L.) were infected with Beauveria bassiana (Balsamo) Vuill. by allowing larvae to crawl over sporulating cultures of the fungus. Virulence of the pathogen was increased by inoculating larvae of the wax moth, Galleria melonella (L.), twice in serial succession. Observations were made on the infectivity and histopathology of the parasite in the host. Penetration of the cuticle occurred 24 h after inoculation and at 64 h post-inoculation the interior was completely filled with hyphae. Penetration of the gut wall was also observed.

Increased permeability of capillaries and venules, labelled with colloidal carbon, was observed in the superficial mucosa of the small intestine of sheep infected with Trichostrongylus colubriformis. The labelled vessels were restricted to infected portions of the gut, and the intensity of labelling appeared to be related to density of the worm population. Open junctions were seen between endothelial cells in permeable vessels. In moderately atrophic infected intestine, enterocytes were domed, had sparse, short, distorted microvilli and many polyribosomes. Tight junctions between enterocytes seemed to be intact and distended intercellular spaces were seen. In more severely atrophic mucosa, enterocytes had distended mitochondria and endoplasmic reticulum, bizarre shapes, and the continuity of the epithelial sheet was occasionally disrupted. There was oedema in the lamina propria and neutrophils were seen in migration to the lumen of the gut. The possible mechanisms inducing these changes and their significance in terms of plasma protein loss and intestinal function are discussed.

Serum taken from mice 12–15 weeks after a primary infection of Sehistosoma mansoni transfers to normal recipients a partial resistance to subsequent schistosome challenge. The transfer of immunity is evident not oniy in the reduced recovery of mature parasites from the liver, but also in the diminished numbers of invading schistosomula recovered from the lungs. Since the recipients of immune serum exhibit a level of resistance equivalent on average to 47 % of that found in actively immunized animals, the results suggest that humoral factors play a major role in the effector mechanism of schistosome immunity.

The ability of three species of avian trypanosome, Trypanosoma corvi, T. bouffardi and T. everetti, to protect against heterologous and homologous challenge has been studied in susceptible birds. None protects against challenge with either or both of the other two species and mixed infections can be obtained experimentally. With T. bouffardi, both apparently sterile and premune states exist after initial infection and the host is immune to challenge with homologous strains; heterologous strains sometimes break this immunity and produce shorter, lower parasitaemias. T. everetti remains in the circulating blood for long periods at low levels and challenge doses with the homologous strain result in a slightly elevated parasitaemia for a few days. T. corvi produces a degree of immunity after the initial infection which usually results in a reduced second parasitaemic peak of shorter duration when birds are challenged with a homologous strain.

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 haemocytic reactions of larvae of Drosophila algonquin leading to encapsulation and melanization of eggs of the hymenopterous parasite Pseudeucoila bochei are characterized in part by the premature mass differentiation of plasmatocytes to lamellocytes. Normally this transformation of blood cells occurs at the time of pupation. The data suggest the haemocytes are stimulated to differentiate by chemotactic means. In susceptible host larvae the parasite appears activately to inhibit the immune reactions by blocking cellular differentiation.

Five species of parasitic copepods are described based on the material collected during cruise 16 of R/V Anton Bruun. They are: from the gill chambers of macrourids, Chondracanthodes deflexus Wilson, Lateracanthus quadripedis Kabata and Gusev and Brachiella annulata Markevitch; from the anal fin of a macrourid, Nudiclavella galapagoense gen.nov., sp.nov.; and from the gill filaments of brotulids, Naobranchia maxima sp.nov. All fishes were caught with FVSL (free vehicle set lines) in the deep sea off the Galápagos Islands, ranging from 1710 to 3330 m.

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.

Host suitability, reproduction, effects of temperature on reproduction and pupal development, effects of humidity on pupal development and the effects of photoperoid on puparial deposition, pupal development and adult emergence were studied in a laboratory colony of Pseudolynchia canariensis. Flies were observed to lack strong host specificity. Puparia were produced at regular 24 h intervals by flies maintained at 30 °C, averaging 8·8 puparia per female. Optimum temperature for colony maintenance was observed to range between 26·6 and 30·0 °C. Temperatures of 13 and 37 °C were lethal to pupae. Humidity and photoperiod did not markedly affect pupal development. Puparial deposition and adult emergence occurred only during the photoperiod.