Toxascaris versterae sp.nov. from hyenas in South Africa is described. T. versterae is compared with Toxascaris leonina, the only other member of the genus.

I thank Professor J. F. A. Sprent for his advice and criticism. This work was supported by grants from the Australian Research Grants Committee and from the U.S. Department of Health, Education and Welfare, No. AI-07023–03.

The frequency distribution of parasites among hosts is used as the basis of the quantitative assessment of the nature of parasitism. The host–parasite system is regarded as an ecological relationship between populations of two different species of organisms. From the overdispersed frequency distributions exemplified by the Negative Binomial distribution a specially truncated form is derived and shown to fit the data of Hynes & Nicholas (1963). The theoretical consequences are discussed and these form the basis of a definition of parasitism.

I am indebted to Professor H. B. N. Hynes who so readily understood my general aims and freely provided detailed information about his work. I also have great pleasure in thanking Professor John H. Whitlock, not only for the original computing facilities which he so generously provided, but also for his many other kindnesses. I am also very grateful to Dr Charles Henderson Jun. for his work on the original computer program and to Dr Mark Westwood for his ingenuity and labours in producing a new approach to the computations.

Tissue stage and erythrocytic stages of a new malaria parasite Rayella hylopetei n.sp., is described from a Particoloured flying squirrel Hylopetes alboniger Hodgson encountered in Darjeeling. Tissue stages are represented by schizonts in the form of cystic bodies occurring in characteristic foci of infection occurringi n the liver. Schizonts are absent in the erythrocytes, and it appears that all immature stages in the erythrocytes directly develop into gametocytes. Haemozoin pigments occur in the form of black granules. The infected red blood cells are slightly enlarged and are without stippling.

The investigation received financial support from the World Health Organization.

In order to learn more about the nature of the chemical bonds stabilizing the surface membranes of the cercariae and schistosomula of Schistosoma mansoni, these organisms were treated with a variety of reagents. The cercarial surface was dissolved by 8 M urea alone (pH 9·0) but was protected from such dissolution if a certain critical concentration of cation or anion was included in the 8 M urea solution. Divalent cations were more effective than monovalent cations in this protective effect. The 8 M urea was also unable to dissolve the cercarial surface at any pH below 5·8. The cercarial surface was very rapidly dissolved by sodium hydroxide solutions at pH 11·4 and above. The divalent cation calcium, if included in the sodium hydroxide solution, slowed down the rate of surface solution by sodium hydroxide. The schistosomular surface was stable to 8 M urea at pH 9·0 but was readily dissolved in 8 M urea at pH 10·7 and 11·7. The schistosomular surface was stable in aqueous sodium hydroxide solutions at pH 12·0. Anionic detergents were very effective in dissolving the cercarial surface at concentrations above 0·001%. Cationic and non-ionic detergents were ineffective at 0·01% or below. A saturated solution of digitonin if diluted 1:100 caused destruction of the cercarial surface. At higher concentrations it caused expansion and stabilization of this surface.

It is suggested that in both the cercarial and the schistosomular surface, bonds between carboxyl (—COO′) and amino (—NH3+) groups are very important in maintaining structure. The origin of the —NH3+ group is possibly from —NH2 lysyl group in cercariae, and a guanido group in schistosomula. The suggestion that cations are incorporated into the cercarial surface and stabilize it during and after penetration has been tested by treating schistosomula with EDTA. The EDTA had no visible effect on the surface, nor did it labilize the surface to other reagents.

I should like to thank very warmly Dr S. A. Ibrahim, in whose Department this work was carried out. My grateful thanks are given to the Medical Research Council (U.K.) for a grant. I should also like to thank Mr J. R. Lauder, Mr Ahmed Gandour and Mr Saleh for their help during the work. I am very grateful to Dr J. A. Clegg and Dr S. R. Smithers for helpful discussions.

The base compositions of DNA from some species of malarial parasite have been estimated by measurement of density in CsCl gradients and of thermal denaturation temperatures. Species from avian (Plasmodium gallinaceum) and rodent (P. berghei and P. vinckei) hosts – often used as model systems in malarial studies – contain single DNA components with base compositions of about 20% G + C. By contrast, species from primate hosts (P. knowlesi and P. falciparum) contain major DNA components of about 40% G + C and minor ones of about 20% G + C. These differences could be reflexions of markedly different genomes within these two groups of the genus Plasmodium.

Apart from differences in base composition, the physico-chemical properties of the main components of DNA from primate and rodent malarial parasites are very similar to those of DNA from mammalian cells. DNA from avian malarial parasites appears to have some unusual properties.

One of us (P.I.T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking and Dr J. Williamson for many helpful discussions, Dr W. H. G. Richards, Dr A. Voller and Dr D. C. Warhurst for the provision of some of the strains and Miss Jane Dunnett, Mrs A. C. Gutteridge and Mr T. Scott-Finnigan for technical assistance.

Babesia rodhaini infected mouse and rat red cells were non-infective after receiving 40 or 60 krad irradiation from a 60Co source.

Rats inoculated with irradiated infected red cells were subsequently found to show strong resistance to homologous challenge.

Mice, which are more susceptible to B. rodhaini, showed less resistance to challenge, following immunization with irradiated B. rodhaini infected red cells.

Splenectomized rats were immunized with irradiated infected blood. There was a delay compared with the controls in the onset of acute fatal parasitaemias in these rats. A population of parasites was isolated by taking and mixing blood from each of the splenectomized rats during the patent parasitaemia following challenge. This population appeared to be an antigenic variant of the original immunizing population.

I thank Mrs J. Page for excellent technical assistance and Dr K. N. Brown for criticizing the manuscript.

The structure of the cysticercoid of Raillietina cesticillus has been studied with the aid of light and electron microscopes. While the ultrastructure of the superficial parts of the scolex closely resembles that of other cestodes, the fine structure of the cyst wall differs from both these. The arrangement and functions of the tissues in the cyst wall are discussed and interpreted with reference to the tissues of the scolex of the cysticercoid of R. cesticillus and to the tissues of other cestodes. R. cesticillus cysticercoids, subjected to various histochemical tests, were shown to contain proteins and carbohydrate materials.

The author wishes to thank the Principal and Governors of West Ham College of Technology, a constituent college of the North-east London Polytechnic, for their general and financial support of this work. Thanks are also due to the Directors and Governors of the several institutions whose electron microscopes the author used. The work described here forms part of a thesis approved by the University of London for the degree of Ph.D.

Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in the parasitic nematodes Rhabdias bufonis (Schrank, 1788) and R. sphaerocephala (Goodey, 1924). Both species are parasitic in the lungs of their amphibian hosts and feed entirely upon blood drawn from the lung capillaries.

Three gland cells are present in the oesophagus, one in each sector. The two subventral ducts open, by way of ampullae, into the lumen of the oesophagus about a quarter of its length from the anterior end. The dorsal gland opens similarly into the base of the buccal capsule. It is suggested that the glands produce a B-esterase, in an histochemically inactive form in situ, which is responsible for haemolysis and the bulk of extracellular digestion. Only one cell type is present in the intestine and this is entirely absorptive in function.

The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion involving the B-esterase and acid phosphatase which are present in association with the microvilli. Haematin results from this process and is precipitated in the gut lumen. A smaller proportion of haemoglobin is taken up by the gut cells and is broken down intracellularly by lysosomes, originating in Golgi in the basal gastrodermis. These show endopeptidase activity and later acid phosphatase in some of the bodies of the lysosomal sequence and only at the light microscope level. The iron-containing pigment haemosiderin resulting from digestion is retained in the lysosome residues and forms the pigment granules in the gastrodermis. The products of extracellular digestion absorbed by the gastrodermis are synthetized into lipid by a lipase, probably produced by GER.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.

Histological, histochemical and ultrastructural methods have been used to study gut structure and digestive physiology in Cosmocerca ornata (Dujardin, 1845). The nematode is parasitic in the small intestine and rectum of Rana temporaria, and feeds solely upon the gut contents of the host, primarily bacteria and cellular debris rather than fluid material.

Only a small buccal capsule is present and no host tissue is ingested. Rigid channels at the tips of the oesophageal radii and a spiral arrangement of the corpus lumen are probably concerned in expressing any fluid in the food while retaining the particulate matter. The latter is then shredded by three large valvular flaps projecting into the lumen of the posterior oesophageal bulb. One gland is present in each sector of the bulb. There is some evidence that two secretions are produced in each subventral sector, an electron-dense one posteriorly which is released into the lumen below the valve flaps, and an electron-lucid one synthesized more anteriorly which is released in the anterior region of the bulb. Only one secretion is produced in the dorsal gland, similar to that in the anterior subventral sector, and which is poured into the lumen of the posterior corpus. The intestine is not differentiated into distinct regions and contains no gland cells. A prominent striated border of microvilli is present, varying from 25 μm in the foregut to 0·5 μm in the hindgut. They have a prominent core composed of minute fibrils and an outer glycocalyx covering.

Digestion is entirely extracellular, bacteria and cellular debris in the ingesta being broken down by a C-esterase present in the oesophageal gland secretions. It is completed by a process of contact digestion with the same enzyme adsorbed on to the glycocalyx. Acid phosphatase, also produced by the oesophageal glands and present on the microvilli, may be concerned in the absorption of the resultant digestion products and any simple solutes in the food made available by host extracellular enzymes. GER and free ribosomes present in the distal regions of the gastrodermis are probably concerned in the assimilation of the absorbed materials into glycogen which is stored in large quantities in the gastrodermis.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board.

Histological, histochemical and ultrastructural methods have been used to study the gut structure and digestive physiology in the parasitic nematode Cyathostomalari E. Banchard, 1849. The nematode is parasitic in the orbito-nasal sinuses of its host and feeds exclusively upon blood.

Three gland cells are present in the oesophagus, one in each sector. The two subventral gland ducts open into the lumen of the oesophagus at the level of the nerve ring, and the dorsal gland duct into the base of the buccal capsule. It is suggested that the latter gland may produce an anticoagulin, histolytic and/or haemolytic secretions, histochemically-inactive in situ. The intestine is syncytial, with no differentiation into secretory components, and its distal surface is provided with a prominent brush border of long microvilli.

A non-specific esterase, thought to originate in the oesophageal gland secretions, causes haemolysis of ingested erythrocytes. The major part of haemoglobin digestion is extracellular, partly by a process of contact digestion on the microvilli, initiated by the esterase, and the protein is then further broken down by an exopeptidase of the ‘leucine aminopeptidase’ type, and the products absorbed into the gastrodermis possibly with the aid of an acid phosphatase present on or in the microvilli. An insoluble iron-containing compound, which is not haematin, results from breakdown of the prosthetic group. A smaller proportion of haemoglobin is taken up by the gastrodermis and digested intracellularly by the action of lysosomal hydrolases. An endopeptidase and an acid phosphatase are present in the gastrodermis, possibly in sacs of GER which are suggested to be primary lysosomes and which fuse with the endocytosed heterophagosomes. The insoluble pigment haematin results from digestion within the heterolysosomes, and this gives rise to the iron-containing gastrodermal pigment granules. The products of extracellular digestion are absorbed by the gastrodermis where they are synthetized into lipid by a lipase, which probably resides in whorls of GER.

This investigation was supported in part by Research Grant AI 06295 of the United States Public Health Service. The final manuscript was prepared during the tenure of a Postdoctoral Fellowship from the British Egg Marketing Board. I wish to extend my gratitude to Dr J. B. Jennings for advice and encouragement throughout this work.

The immune reaction of the mouse to the cestode, Hymenolepis microstoma, has been investigated. The mouse can carry a worm burden of up to 500 mg wet wt and there is no evidence either of rejection of the parasite by the mouse or a slowing down of growth rate of the mouse as a result of the parasite.

The nature of the antibody response has been investigated with regard to the type of antibody, onset of production, and titre.

The nature of the antibody is discussed together with the fact that there is no rejection of the parasite. The possibility that a cellular immune response might be necessary for rejection is also discussed.

I should like to express my thanks to Dr T. S. C. Orr of Fisons Research Laboratories, Loughborough, for many helpful comments and suggestions during the course of this work.

My thanks are due also to Professor C. A. Hopkins who put the facilities of the Wellcome Laboratory at my disposal at all times. My thanks, too, to Miss Gillian Moore whose technical assistance was invaluable.

The work was in part supported by a Grant from Fisons Ltd.

The intraperitoneal inoculation of chickens with 100–170 mg of Statolon, an artificial interferon inducer in mammals, induced the production of a virus interference factor in the serum. Chickens, 3 and 5 weeks old given 40–170 mg Statolon i.p. produced significantly fewer oocysts after infection with E. maxima than untreated chickens.

Only three serum samples (from a large number examined) taken from chickens 1, 4 or 6 days after E. tenella infection or 6 h and 6 days after E. maxima infection showed slight but significant antiviral effects.

Demodex carolliae, a parasite of the bat Carollia perspicillata, is described for all stages of its life cycle. The sequences and adaptive features of this life cycle are detailed. Some information is presented on the population structure and the pathogenicity of this species.

This research was supported in part by Grant W83–1 to Dr F. Lukoschus from the Netherlands Foundation for the Advancement of Tropical Research (WOTRO).

The culture method developed by Geiman and co-workers has been modified to give average multiplication rates for Plasmodium knowlesi of at least six-fold in 24 h.

Individual modifications have been assessed on the basis of parasite multiplication and [3H]leucine incorporation into parasite protein. The second cycle of in vitro development which is particularly influenced by the conditions of culture was improved by: (i) culture of washed parasitized red cells in a medium containing dialysed homologous serum screened for its ability to support parasite growth; (ii) addition of ATP, Co-enzyme A (or pantothenate) and glutamine.

We thank Mr E. D. Dennis and Miss Susan Wanstall for technical assistance. This work was supported by grants from the Medical Research Council and the World Health Organization.

The present study includes five new and three known species of trematodes from marine fishes of India. Records of new hosts and new localities are given. The new species are: Plagioporus longicaudus, Opegaster paramacrorchis, Pseudopecoelina elongata, Pseudopecoeloides scomberi and Hamacreadium leiognathi. The known species are: Podocotyloides parupenei (Manter, 1963) Pritchard, 1966, Hamacreadium mutabile Linton, 1910 and H. krusadaiensis Gupta, 1956. Hamacreadium leiperi Gupta, 1956 is considered a synonym of H. mutabile.

The author wishes to express his gratefulness to Dr Ather H. Siddiqi for his guidance and to Professor H. W. Manter of the University of Nebraska, U.S.A. for his valuable comments. The present study was financially supported by the Council of Scientific and Industrial Research, New Delhi.

Trypanosoma avium bakeri ssp.nov. has been recorded from naturally infected red-whiskered bulbuls (Otocompsa jocosa Linn.). This trypanosome resembles T. avium Danilewsky, 1885 in general morphological features but it is larger in every respect. The parasite can also infect chicks, black-breasted quails and pigeons.

The division stages of the parasite are also very interesting. Considering the different morphological criteria, division stages and loose host specificity, the parasite is designated as subspecies of T. avium.

For the first time division stages of an avian trypanosome have been studied in detail in the peripheral circulation and bone marrow of the bird. The parasite multiplied by longitudinal binary fission and two types of plasmotomy.

Our thanks are due to Dr S. Mookerjee, Professor and Head of the Department of Zoology, Presidency College, Calcutta for providing the necessary laboratory facilities and constant encouragement and for going through the manuscript and to Dr J. R. Baker, Department of Medical Protozoology, London School of Hygiene and Tropical Medicine, for his valuable suggestions in the preparation of this article. The financial support provided by the Indian Council of Medical Research (for H.N.R.) and the University Grants Commission (for D.K.C.) is gratefully acknowledged.

Isoenzyme patterns of normal adult Nippostrongylus brasiliensis were compared with those of damaged worms permanently affected by immunity and adapted worms which show increased resistance to immunity.

Isoenzymes of acetylcholinesterase, found in glands of the head end of the worms, showed changes in damaged and adapted worms which can be related to the effects of immunity.

Aminopeptidases and non-specific esterases from the same glands were unchanged in worms affected by immunity.

Isoenzymes of acid phosphatase found in the gut of the worms were altered in damaged and adapted worms; these changes are probably secondary to the changes in acetylcholinesterases.

Of the enzymes studied, acetylcholinesterase is the enzyme most likely to be the antigen which stimulates host immunity, but final proof of this is required.

We are most grateful to Dr Valerie E. Jones for many helpful suggestions.

Sections of salivary glands from adult R. appendiculatus ticks and sections of the whole bodies of nymphal R. appendiculatus ticks were studied to obtain data on the incidence and development of T. parva during feeding. Since, in their previous instars, all the ticks had dropped engorged from a parasitaemic calf on the same day, it was possible to compare the resultant infection rates in nymphs and adults.

In the adult ticks, the highest percentage infection (45%) and the greatest number of infected acini (45 from 20 ticks) were observed after 3 days feeding. Mature parasites were first seen after 4 days. In the nymphs, the highest percentage infection (35%) was observed after 3 days feeding. Equal numbers of infected acini (14 from 20 ticks) were observed in unfed nymphs and in those which had fed for 2 or 3 days. Mature parasites were first seen after 2 days, and all were mature after 3 days.

It was concluded that a batch of nymphs would contain more parasites per gramme than a corresponding batch of adult ticks. This fact, together with the observed uniformity of maturation of the parasites in nymphs, may make nymphs a more suitable choice than adults for the preparation of ground tick stabilates.

We are most grateful to Mr M. P. Cunningham, who inoculated the calf on which the ticks fed, and to Mr A. Musoke who observed the subsequent clinical reaction of the calf.

This work was carried out as part of the programme of the Immunological Research on Tick-borne Cattle Diseases and Tick Control Project which is supported by the United Nations Development Programme/Special Fund, with F.A.O. as the Executing Agency, in collaboration with the East African Community. The assistance of our colleagues on the Project is gratefully acknowledged. This paper is published by kind permission of Mr A. Rashid, the Director of the East African Veterinary Research Organization.