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.

The design of mass and targetted community-based chemotherapy programmes for the control of the major helminth infections of man is discussed in relation to the population and transmission dynamics of the parasites. Rapid reinfection following a single mass or targetted anthelmintic application is shown to be a universal feature of helminth transmission, as a consequence of the regulatory or feed-back mechanisms controlling population abundance within both individuals and the community as a whole. Control of reinfection requires repeated community treatment where the intensity of application and the interval between treatments are dependent on the reproductive life-expectancy of the adult worm, the net force of transmission prior to control (the basic reproductive rate) and the factors which create aggregation in the distribution of parasite loads within the population. Selective or targetted treatment is shown to be most effective for the control of morbidity as opposed to the control of transmission. The impact of targetted treatment depends critically on the factors that generate heterogeneity in parasite burdens and on whether or not selectivity is based on a single or repeated identification of the ‘wormy’ fraction of the community. Monte Carlo simulation studies are employed to assess the likely impacts of different control strategies on average parasite abundance/person and the distributions of parasite loads within populations. Future epidemiological research needs are discussed in relation to theoretical work and recent field studies of predisposition to heavy infection.

In this paper an account is given of new forms discovered by the writer during a survey of the parasites of mussels and cockles, obtained chiefly from the estuary at Conway, but also from other beds on the North Wales coast. The trematode parasites of shellfish in this area have not previously been dealt with, although several forms have been described from the Liverpool Bay area by the late Prof. Johnstone and his colleagues. Few additions have been made to our knowledge of the early stages of British marine Trematodes since the publication of a series of papers by Lebour (1912) and Nicoll (1914).

In the laboratory, transmission of Schistosoma mansoni to and from Biomphalaria glabrata can occur in artificial sea water at or below a concentration of 12-5%. Miracidia can also emerge and infect snails in 25 % sea water, but this concentration is inimical to the survival of the snails or their eggs. The parasite thus appears to be better adapted to brackish water than is the intermediate host. Epidemiological studies are needed to assess the limits imposed by brackish waters on the natural transmission of schistosomiasis.

Three morphologically distinct types of muscle fibres isolated from the platyhelminth Schistosoma mansoni have been studied with whole cell current- and voltage-clamp techniques. Fibres showed a marked time-dependent decrease in membrane resistance in response to depolarizing current injections. Voltage-clamp experiments revealed the presence of two distinct voltage-gated outward currents. The most prominent current is a slowly activating, slowly and incompletely inactivating potassium current similar to delayed rectifier currents which have been described in a variety of cell types from a variety of organisms. Also present is a faster activating, quickly and completely inactivating potassium current that shares functional characteristics with ‘A’-currents. All three of the cell types studied possess a delayed rectifier current, but only two of the three types have ‘A’-currents. Though depolarization with high K+ leads to contraction of the dispersed fibres, no voltage-gated inward currents could be detected by whole cell voltage-clamp under any of our conditions.

Specimens of Plectanocotyle gurnardi were obtained by the writer from the gills of Trigla cuculus L. and T. gurnardus L. during trawling operations at the Irish Atlantic Slope fishing grounds in August 1938 and July 1939. One specimen of Plectanocotyle gurnardi was collected from a Trigla gurnardus and seven specimens of the same parasite from eight specimens of T. cuculus, the greatest degree of infestation encountered being 3 parasites per host fish. Plectanocotyle gurnardi has been recorded previously, under one or other of the synonyms listed above, from Trigla gurnardus by van Beneden & Hesse (1863), T. Scott (1901, 1905), A. Scott (1904), Lebour (1908), and Little (1929); from T. lucerna L. by A. Scott & Little; and from Trigla ‘sp.’ by Monticelli (1899). It will be noted that the present records of the parasite are from its usual host T. gurnardus and from a new host T. cuculus.

1. Four trematodes, Gastrothylax crumenifer, Cotylophoron cotylophorum, Paramphistomum explanatum and Fasciola gigantica have been used for quantitative analysis of their inorganic constituents.

2. Calcium, magnesium and phosphorus content have been determined.

3. All the four trematodes contain large amounts of phosphorus (0·61–1·05%); but the amounts of calcium (0·025–0·045%) and magnesium (0·029–0·065 %) are small.

The genus Lecithocladium was erected by Lühe in 1901, with L. excisum (Rud. 1819) as the type species. In addition to the type species, the genus contains L. excisiforme Cohn, 1902, L. gulosum Linton, 1910, L. longicaudum Shen, 1934, L. psenopsis, L. magnacetabulum and L. pagrosomi Yamaguti, 1934, and L. johnii Yamaguti, 1938. L. barbatum Cohn, 1902, has been transferred to the genus Dinurus Looss, 1907, and L. crenatum (Molin, 1859) is regarded by Looss as a ‘species inquirenda’, while Lühe maintains that it is synonymous with L. excisum. The author (1937) has added two more species from Indian hosts to the genus. These are more fully described in the present paper.

1. A survey of 227 rooks (Corvus frugilegus frugilegus L.) and seventy jackdaws (C. monedula spermologus Vieill.) was conducted in Hertfordshire. The birds were examined by means of cultures of their peripheral blood, or (in the case of eleven rooks and one jackdaw only) bone-marrow, on N.N.N. medium. Twenty-seven rooks (11·9%) and six jackdaws (8·6%) were found to be infected.

Some of the rooks were examined at a time of year when the trypanosomes are not present in the peripheral circulation; other rooks were examined in the first year of their life before adults of Ornithomyia avicularia (the vector of this parasite) were present. Ignoring birds of these two groups, twenty-six out of seventy-eight (33·3 %) adult rooks were found to be infected. This value probably approximates to the natural infection rate among adult rooks (and perhaps jackdaws).

2. The trypanosome in question is a large spindle-shaped form, measuring an average of 48·2µ in length (excluding flagellum) and 5·5µ in width. There is a tapering aflagellar region extending 14·1µ (on the average) beyond the kineto-plast. This trypanosome is assigned to the species T. avium Danilewsky, 1885.

1. The anatomy of three digenetic trematodes from Conger conger (Linn.), Skrjabiniella aculeatus (Odhner), Lecithochirium rufoviride (Rud.) and Sterrhurus fusiformis (Luhe) has been described. The technique employed is given, and in each case the history of the species has been traced.

2. The discussion on the nomenclature of Skrjabiniella aculeatus explains why this generic name used by Issaitschikow (1928) has been adopted in this work in place of Prosorhynchus, and a key to the genera Prosorhynchus s.str. and Skrjabiniella has been suggested. A table showing the proposed division of Odhner's genus Prosorhynchus is included.

3. In the discussion on the hemiurid worms it is pointed out that there is no sound basis for the separation of the genera Lecithochirium and Sterrhurus as they stand.

Previous observations, which showed that treatment of mice with hydrocortisone acetate around the time of their infection with Schistosoma mansoni reduced the mature worm burden, have been confirmed. The number of eggs produced by the surviving worms during early patency was also significantly reduced. Cyclophosphamide and another steroid immunosuppressant, betamethasone, also caused a reduction in fecundity of S. mansoni when given at the time of infection, as did T-cell deprivation of the mice by adult thymectomy and injection of anti-thymocyte serum 1 month before infection. There was no effect of these three treatments on worm numbers. In contrast, injection of mice with anti-thymocyte serum at the time of infection marginally increased the size of the mature worm burden. The deleterious effects of hydrocortisone acetate on S. mansoni worm numbers and fecundity were only apparent if the steroid was given within 1 week of infection. Indomethacin, a compound which inhibits tissue inflammatory reactions by inhibiting prostaglandin synthesis, and which therefore mimics one of the actions of corticosteroids, had no effect on S. mansoni worm maturation and fecundity.

Oncospheral agglutination given by sera immunized with Hymenolepisnana eggs is described as a new way of assessing H. nana infection. All sera of mice which possessed acquired protective immunity against reinfection by H. nana eggs had the potency to induce oncospheral agglutination in vitro. Only oncospheres, which had been hatched, agglutinated, no agglutination occurred in sera from uninfected mice. Oncospheral agglutination was carried out by mixing 0·1 ml of serial two-fold dilutions of serum and 0·1 ml of Hanks' balanced salt solution containing about 600 hatched oncospheres. Titre of agglutinins was indicated as a reciprocal of the final dilution capable of giving agglutination clusters made of three or more oncospheres. Agglutinins developed within 14 days after a primary infection with 500 shell-free eggs. There was no rapid increase of agglutinins within 4 days following a secondary infection. The titre increase coincided with the increase in dosages of eggs. Agglutinins were thought to be immunoglobulins, because the potency of the serum to agglutinate oncospheres was extinguished after absorption of globulins with rabbit anti-mouse globulin serum.

Agglutinins were produced in rabbits by intravenous injections of shell-free eggs. The titres of the rabbit sera were much higher than those of mouse sera.

Blastocrithidia familiaris were found to be parasitic in the midgut, ileum and rectum of Lygaeus pandurus. The host—parasite relationship is described. Attachment of parasites in the midgut and ileum occurs by interdigitation of expanded flagella over and between the microvilli. No attachment to microvilli was observed where extracellular membranes form well-organized layers which lie parallel to the gut wall and completely separate the microvilli border from the lumen. The extracellular membranes originate from delamination of the outer unit membrane of microvilli which consists of a double plasma membrane. The function of the extracellular membrane layers and their possible role as a peritrophic membrane in preventing parasite attachment is discussed in relation to previous studies on midgut cells in Hemiptera with a similar apical coat on midgut microvilli. In the rectum, parasites attach to the cuticle of the gland cells and not to the rest of the rectal wall. Attachment to the cuticle occurs by the formation of hemidesmosomes. A comparison of the relationship of B. familiaris and its host to previous ultrastructural studies of associations between kinetoplastid flagellates and their respective hosts is discussed.

The development of drug resistance by the present Houghton strain of Eimeria tenella to the quinolones, methyl benzoquate and buquinolate, was found to take place after a single experimental passage. The development of resistance was independent of drug selection pressure and showed cross resistance to other quinolones, but not to amprolium and robenidine. When the Weybridge, Beltsville and Elberfeld strains of E. tenella were compared under similar laboratory conditions, the Weybridge and Elberfeld strains developed resistance to methyl benzoquate after 6 passages and the Beltsville after 5. Studies on the response of the Houghton strain to methyl benzoquate and buquinolate revealed that the drugs did not completely control the infection as measured by weight gain and that oocyst production was not suppressed. These observations indicate that the strain had already acquired some resistance to these drugs. This was confirmed by examining the resistance to methyl benzoquate of a culture of the Houghton strain of E. tenella which had been stored frozen in liquid nitrogen since 1969. This showed full sensitivity to the drug and developed resistance after 8 passages. This suggests that drug tolerance has been acquired by the Houghton strain since 1969.

Oocyst lines were established from the Houghton strain by infecting single birds with approximately 10 oocysts. Eleven of these lines were found to be sensitive to methyl benzoquate, and nine to give rise to resistant parasites. It is concluded that the Houghton strain is contaminated by a small number of resistant oocysts which can be eliminated from a culture by dilution of the challenge inoculum. One of these Houghton oocyst lines, sensitive to methyl benzoquate, developed resistance after 8 serial passages.