The ultrastructure of the normal caecum of chickens and of chickens infected with Trichomonas gallinarum has been investigated. In infected caeca some villi and crypts of LieberkÜhn appear normal whereas others show marked changes in structure of the epithelial cells. The most obvious changes are loss of microvilli and glycocalyx and an increase in number of vesicles which stain metachromatically with Azur II. T. gallinarum has been detected between epithelial cells and in the lamina propria. Bacteria often, but not always, accompanied the protozoa in the tissues.

When ring-stage parasites are grown to the late trophozoite stage in vitro, the incorporation of [3H]adenosine into parasite DNA and RNA is in the ratio of ~ 1:1·5 and not 1:4 as expected from direct biochemical analysis of the parasite. A method is described by which large quantities of infected blood can be grown in vitro from the ring to the trophozoite stage thus allowing direct biochemical analysis of parasites grown in vitro. The results of direct biochemical analysis indicated that parasites grown in vitro have similar DNA and protein contents to those grown in vitro but that RNA contents are much less in vitro. Quantitative histochemical studies also indicated a deficiency in RNA in parasites grown in vitro. It is concluded from the evidence of three distinct methods that RNA synthesis is defective during the first asexual cycle in vitro. In the second cycle all three macromolecular biosyntheses studied are reduced when compared to the first so that the actual rate of RNA synthesis is further reduced when compared to that in vitro. It is suggested that the successive decrease in RNA synthesis parallels the reduction in multiplication obtained on subculture of the parasite.

Ultrastructural examination of the parasite-host interface of three tetraphyllidean cestodes of Raja naevus (sectioned attached to the intestine) indicates that while the strobilar tegument of each closely follows the typical cestode pattern that of the bothridia has several modifications probably associated with attachment. Microtriches similar to those of the strobilum are absent, although small spines on Echeneibothrium sp. and Phyllobothrium piriei and wart-like structures on Acanthobothrium quadripartitum bothridia are considered to represent the osmiophilic tips of specialized microtriches. The bothridia of the three species have no apparent function in the absorption of food but evidence suggests that the apical pad of the myzorhynchus of Echeneibothrium is specialized for the uptake of nutrients directly from the submucosa of the host intestine to which it is applied. Attachment and sensory roles by the myzorhynchus are also indicated. Echeneibothrium and P. piriei bothridia severely damage the host mucosal surface, while those of A. quadripartitum do little harm. This difference is probably associated with the size, mobility and mode of attachment of the cestodes. There are indications that the bothridia of Echeneibothrium upset the metabolism of mucosal cells in the attachment region. The tips of the strobilar microtriches of A. quadripartitum are shown to function in the attachment of the strobilum to the host mucosa, and in the protection of the microthrix proximal surfaces by a filtering action.

A method for detecting antibody activity in vitro against the invasive stages of E. tenella and E. maxima is described. Treatment of cultured chick kidney monolayers with serum (or a globulin fraction thereof) from immunized birds caused a reduction in the numbers of intracellular stages 24 or 48 h after inoculation of sporozoites. This reduction was seen when serum was incorporated in the culture medium at the time of sporozoite inoculation and also, but to a lesser extent, when the monolayers had been pretreated with the antibody-containing medium which was washed off prior to infection. The results correlated reasonably well with those obtained when the sera were tested in embryo (E. tenella) or in vivo (E. maxima). Similar treatment of cultured CAM monolayers in which infection with E. tenella was well established (101 h), did not greatly affect the development of the parasite. This suggests that the anti-coccidial activity is either effective against the sporozoite stages only, or is unable to affect parasites within cells.

Detailed descriptions are given of the larvae of the three species of British metastriatan ticks, with particular reference to the arrangement and dimensions of setae.

A description is given of a Babesia-like parasite found in the erythrocytes of two Cercopithecus pygerythrus monkeys probably from East Africa. Morphologically it seems identical with a parasite found by Mayer (1934) in Macaca irus monkeys from Java and named by him Entopolypoides macaci. On the other hand, the present African type differs from the Javan one in that it does not readily infect M. irus or M. mulatta monkeys; and it might well be named provisionally E. macaci (cercopitheci). Morphologically, the early forms are fine rings with a large vacuole but the more mature parasites form several fine long processes which are best seen under phase-contrast illumination. The cycle in the erythrocytes probably ends by division into four new parasites and it takes 3 days to quadruple the number. There is no synchronicity, such as occurs with malaria. The parasite was passed by syringe into Erythrocebus patas, Papio papio and Cercocebus galeritus monkeys in which it produced a light parasitaemia if they were intact, or an intense one (up to 70% erythrocytes parasited) if they were splenectomized. In both cases the bouts of parasitaemia are prolonged for weeks, and they may continue with relapses apparently for years. A light transient infection was produced in one splenectomized Macaca mulatta and in one out of two intact M. irus monkeys, but not in one M. arctoides (splenectomized), one Cebus albifrons, one C. apella, two Aotus trivirgatus and two Pan troglodytes (one splenectomized). Apparently the parasite readily infected African lower primates, hardly infected Asiatic ones, and did not infect American ones. Even in susceptible splenectomized monkeys, in which it produced prolonged intense parasitaemia, the parasite causes little pathogenic effect beyond a moderate anaemia. Attempts were made to transmit it through Rhipicephalus sanguineus, Dermacentor andersoni, Ornithodoros (sp.), Ornithonyssus bacoti and Aedes aegypti but they were unsuccessful. Probably the vector is an Ixodid tick. Chemotherapeutically the parasite was sensitive to a babesicidal compound, Imidocarb (3,3′-bis-(2 imidazolin-2yl) carbanilide) and to primaquine but not to chloroquine, pyrimethamine, pentamidine, Berenil or homidium.

Chicks hatched from eggs laid in the third and fourth weeks after inoculation of the hens with oocysts of E. maxima excreted fewer oocysts in response to a challenge inoculum of E. maxima given at 1 week of age than controls hatched from the eggs of uninfected hens. A λ-livetin fraction prepared from the yolks of eggs laid by hens 14–22 days after a single inoculation of oocysts of E. maxima and injected subcutaneously into 2-week-old chicks caused a similar reduction in oocyst yield from a challenge inoculum. The serum of the donor hens, obtained at the corresponding time intervals was protective. These results confirm that immunity to infection with E. maxima is, at least in part, mediated by humoral antibodies.

A modification of the ‘floating raft’ method of in vitro penetration study is described. This allows replication of results and additional conveniences in operation. Filter paper membranes have shown characteristics similar to those of skin and have been used for quantitative studies. A method of digesting penetrating larvae from skin has been used to reduce the variability inherent in whole skin. Neither chloroform soluble skin products nor gravity were found to have a significant effect on the number of larvae entering membranes. Exsheathment of larvae was not essential prior to penetration and no specific stimuli for exsheathment appear to be necessary. Scanning electron micrographs have shown that entry may be by either hair follicles or desquamations of the stratum corneum. No evidence of enzymic activity during the invasion process has been found so far and the results suggest that a mechanical rather than chemical system obtains.

Goldfish were experimentally infected with different population densities of the acanthocephalan Pomphorhynchus laevis, and maintained at different temperatures. The density of infection had no effect upon the establishment of the parasite, but a 12°C rise in water temperature reduced the recovery after one week by 30%. Thereafter there was a continuous loss of parasites during the course of infection. The rate of this loss was independent of worm burden and temperature, but increased under conditions of host starvation. Both male and female parasites attached themselves in the same region of the alimentary tract, with a mean position about 19% along its length. They remained in that region throughout the course of infection, and the population did not migrate down the intestine with increasing age. In starved fish, the region of attachment was nearer the oesophagus, at low temperatures nearer the rectum, and when crowded the occupied region extended anteriorly. Male worms were unable to establish as easily as females, but once established survived better, and the sex ratio after two weeks was in favour of males. The results are compared with the results of studies on other acanthocephalans and on fish-cestode systems. It is recognized that although the establishment of fish acanthocephala is affected by temperature to a lesser extent than that of some fish cestodes, temperature in conjunction with changes in fish diet is a major control upon the flow of parasites through acanthocephalan-fish parasite systems. The significance of the results to the interpretation of data based on field observations is discussed.

Cortisone, methotrexate and anti-lymphocyte serum were all found to suppress the rejection by SPF CFLP male mice of H. diminuta, which normally occurs between days 9 and 12. Worms continued to grow in mice given immunosuppressants and matured on days 16–18 as they would in a rat, by which time they stretched from the stomach to, and sometimes into, the caecum. Worms in mice given methotrexate ceased to grow after day 16, but this was believed to be due to the deterioration of the host's intestine wall; in mice receiving cortisone growth was faster than normal and worms continued to increase in size until the end of the experiments on days 20–24. The mouse/H. diminuta system is discussed, emphasizing that, as far as is known, H. diminuta (which has no hooks) has no close contact with the tissues and that this is a case of a mammal responding against an organism living freely in the lumen.

The immune reaction of larvae of O. caesarion against the nematode H. autumnalis is characterized by melanization of the cuticle of the parasite and the accumulation and fusion of host haemocytes to form a homogeneous, multinucleated capsule around the parasite. The immune reaction is manifested as a change in the haemocyte picture of the host long before there is any visible evidence of melanization and encapsulation. Differential haemocyte counts from host larvae at various stages of infection showed a decrease in the number of oenocytoids. These data, together with histological studies, indicate that oenocytoids play an important role in the melanization and encapsulation of the nematode. The apparent increase in the number of circulating haemocytes in parasitized larvae suggests that the haemocytes are stimulated to move out of areas where they are normally located and to react against the parasite.

The third-instar larval cuticles of Hypoderma bovis and H. diana and the puparial cuticle of H. bovis are described. The observations on and the descriptions of these cuticles are compared with the work of Enigk & Pfaff (1954) on H. bovis larval cuticle. The cuticles of the Hypoderma species are compared with the typical dipteran larval cuticle described by Dennell (1946) for Sarcophaga and found to approximate very closely to this basic pattern. In view of this it has been necessary to revise the terminology of the cuticular layers as originally described by Enigk & Pfaff for Hypoderma bovis. A description of the puparial cuticle and its specialized structure and the histological appearance of the pupal suture or line of weakness is given.

The distribution of larval ticks in relation to vegetation cover was studied on two coastal farms in the Port Alfred district of the Cape Province. The following five species were found: Boophilus decoloratus (Koch), Amblyomma hebraeum Koch, Ixodes pilosus Koch, Haemaphysalis silacea Robinson and Rhipicephalus evertsi Neumann. B. decoloratus predominated in short protected vegetation, I. pilosus and H. silacea in short covered vegetation and A. hebraeum in medium-to-tall protected vegetation. R. evertsi was collected in too small numbers to allow any correlation to be established. Both I. pilosus and H. silacea demonstrated activity peaks during the winter months. Microclimatic measurements indicated that larval ticks were not usually collected in microhabitats which experienced midday saturation deficits in excess of approximately 10 mm Hg. Behavioural studies on larval ticks climbing glass rods demonstrated the possible association of larvae with a definite vegetation height. The optimal vegetation heights were correlated with field data. The water balance of some tick species was studied and it was found that at 26 °C a relative humidity of 70% or more (i.e. above 7·53 mm Hg saturation deficit) was required by these larvae. Larvae lost water to the atmosphere at humidities lower than this value and took up water vapour from the atmosphere at values higher than 70% R.H. They were shown to be able to imbibe water through the mouthparts, and this possibly has survival value.

Toxocara vajrasthirae is described from the hog-badger (Arctonyx collaris) of Thailand. Of the species in the genus Toxocara, it most closely resembles T. canis. It differs in the possession of proportionately shorter and narrower cervical alae, relatively longer spicules, a coarse, reticulate pattern on the eggshell and an undivided part of the uterus which is longer than the divided part.

Ultrastructural observations on Moniliformis dubius, combined with measurements of envelope volume and composition at various stages during the parasite's development, suggest that production of envelope material is essentially complete by the stage at which elevation occurs. Elevation is associated with the production of an inner layer. In vitro observations on acanthors show that membranous coat material can be produced in the absence of haemocytes.

In chickens kidney-cell culture gametogony of E. tenella usually occurs in a limited number of selected cells in the form of nests of gametocytes. Some cells contain only macrogametocytes, others only microgametocytes and some cells contain both sexes together. Mixed nests of gametocytes are evidence for genetic sex determination. By using PAS staining the origin of macrogametocytes and microgametocytes can be retraced to the merozoites and schizonts of the last generation, which are differentiated by this technique.

The growth of Hymenolepis microstoma in weanling (21–23 days old) and adult (> 10 weeks old) rats has been investigated. Growth proceeded normally until the worms were about 9 days old. They then destrobilated, leaving only the scolex attached to the duodenum or bile duct. In only 1% of the rats did growth of the worms continue beyond 10 days and these large worms caused the bile ducts of their hosts to become distended. Immuno-suppressants had no effect on the growth of the worms, and tests suggested that there was no serological reaction to infection. It was concluded that the rat is a poor host for Hymenolepis microstoma but that it is not completely refractory.

The structure of the various stages of Eimeria tenella grown in the chorioallantoic membranes of the chick embryo has been shown to be similar to the stages in the caecum of the bird. The effects of the anticoccidial drug, Robenidine, on the fine structure of the various stages of E. tenella, grown in the chick embryo and in the caecum of the bird, have been described. The first noticeable change occurs in the endoplasmic reticulum, including the nuclear envelope, and in the Golgi complexes of all stages. The nucleus itself, and the mitochondria, do not appear to be affected by the drug until much later, and this effect is probably due to the degeneration of the cell. It is suggested that the drug may have a direct effect upon protein metabolism of the parasite, resulting in swelling of the granular endoplasmic reticulum and Golgi complexes, or that it may have a primary effect upon some other organelle or metabolic process, and that the swelling of the endoplasmic reticulum and Golgi complexes is a secondary or tertiary phenomenon.

The behaviour of the third-stage larvae of Nippostrongylus brasiliensis has been studied on rat, mouse and human skin. Locomotion in thin films of moisture is by two-dimensional, undulatory propulsion on skin, and by three-dimensional, undulatory propulsion on hairs. In drops of water or in thick films of moisture locomotion is less efficient than in thin films. It is suggested that the thin film of moisture around larvae on the skin may become coated with a thin monolayer of lipid which could reduce evaporation from the surface of the nematode and from the film of moisture, thus extending the period before desiccation begins. Studies with the electron microscope have shown that the larvae move horizontally into the stratum corneum and later penetrate the epidermis and dermis by separating the constituent cells of these tissues. In the dermis there is dissolution of collagen around the larvae. It is suggested that this separation of cells and dissolution of collagen need not be brought about by enzyme action, as similar effects can be brought about by changes in pH or ionic composition of the bathing medium.

A survey in Busoga District, Uganda, where an outbreak of sleeping sickness was detected, has yielded an infection rate with T. brucei subgroup in G. fuscipes of 4.8%. Isolation of the infected flies was by feeding of the flies on mice, followed by trituration and inoculation of a suspension of the triturated flies into mice. The mice were treated with cyclophosphamide to reduce the immune response. The percentage infection as determined by inoculation of triturate was 4.1%, whilst that by feeding on mice was 1–8%. Amongst the 19 strains of T. brucei subgroup isolated, four were identified as T. rhodesiense by the BIIT method.