It has been demonstrated that under prolonged experimental conditions lipid is utilized most quickly under optimal conditions of tonicity, gaseous exchange, pH and sensory stimulation. There is good evidence that activity may be an appreciable energy-consuming process. It has been deduced, however, that the low Reynold's number means viscous forces dominate locomotory energy consumption, and work done is proportional to the square of the velocity. Osmoregulation in hypotonic media and tolerance of hypertonic media do not require appreciable energy.

Locomotion is only possible in limited environmental conditions, and these may also be conditions of peak basal metabolism. Larvae are able to enter quiescence which is not energy-demanding, in poor conditions. Larvae can survive anaerobiasis, but finally die without reduction in lipid and cannot convert lipid to carbohydrate for anaerobic metabolism.

The help of Mrs Helen Foreman in staining the larvae and for statistical analyses, and of Mr J. M. Smith is greatly appreciated. I would like to thank Dr Elizabeth U. Canning for kindly providing the microdensitometer and Professor G. S. Nelson and Dr D. A. Denham for enabling us to establish A. tubaeforme in our cats. The generous support of the British Medical Research Council is much appreciated.

Quantitative paper chromatography and radioactive tracers were used to study the flux of alanine through the sporocysts of Cercaria emasculans in vitro. The following evidence indicates that simple diffusion is the main mechanism of permeation: (1) the sporocysts cannot accumulate alanine against a concentration gradient; (2) the concentration of alanine in the sporocysts is a direct linear function of the concentration of alanine in the external environment; (3) addition of 10−2 M glucose to the medium does not enhance permeation; (4) neither heat-killing the sporocysts nor treating them with 10−3 M iodoacetate slows the rate of permeation; (5) the Q10's for the permeation are similar to those to be expected in a process involving simple diffusion; (6) the amino acid molarities in the parasite and host tissues in vivo are strikingly similar. No utilization of alanine during the course of 3 h incubations could be detected by autoradiography.

The dynamic nature of the equilibrium between the sporocysts and the external environment is emphasized by the exchange of alanine that occurred even under isotonic conditions.

Fresh sporocysts leaked alanine and proline during 1 and 4 h incubations in vitro. The significance of this is not known.

The ultrastructure of the adult stage of T. colubriformis and H. placei was studied. The cuticle of both nematodes was composed of (1) a membrane-bound layer, (2) external cortex, (3) inner cortex, (4) matrix, (5)–(7) three fibre layers, and (8) a basal lamella. Pear-shaped bodies embedded in the matrix layer in H. placei occur, along the length of the animal, once per annulus. A thin hypodermis enlarged to form lateral, dorsal and ventral cords which contained hypodermal cells, nerves and excretory canals. The muscle cells were large and multilobular. Two sizes of myofilaments, present in the contractile part of the cell, conformed to the filament arrangement of obliquely striated muscle. The mouth, buccal cavity and oesophagus of the alimentary tract were lined with cuticle. The oesophagus contained gland cells, muscle cells and apical cells. The lumen of the intestinal cells of both species had a well-developed microvillar border. In H. placei each microvillus was encircled by a ring of apparently spirally orientated vesicles or tubules.

The authors are grateful to Dr D. W. Brocklesby for his help and advice. They would also like to thank Dr D. L. Lee and Dr W. G. MacMillan for helpful discussions.

An electron microscope study has been made of some of the events which occur during the beginning of the relationship between Moniliformis dubius and its intermediate host, Periplaneta americana. The acanthor penetrates through the intestinal wall and is encapsulated by host haemocytes. This encapsulation is typical of the haemocytic reaction of insects to foreign bodies. A proliferation of the acanthor's surface membrane then takes place and forms a coat of microvilli. The formation of this coat by the parasite is accompanied by the dispersion or disintegration or both of the encapsulating haemocytes. The coat of microvilli constitutes a major component of the envelope surrounding early larval stages of M. dubius. There is no evidence for the presence of host connective tissue in the envelope.

We are grateful to Dr A. V. Grimstone, Department of Zoology, for use of the electron microscope, and to Mr David Barnard and Miss Valerie Furber for technical assistance. We thank Dr George Salt, F.R.S. for his criticism of the manuscript.

An activity cell apparatus to facilitate quantitative measurements of motility of small nematodes in saline is described. The effects of salines with a pO2 either greater than 120 mmHg or less than 12 mmHg upon the motility of adult N. brasiliensis females was studied. The worms were found to require an oxygen tension greater than 12 mmHg to be able to maintain their motility.

I am grateful to Professors J. Brough and D. Bellamy for providing the facilities during the course of this study. I should also like to thank Dr R. A.Hammond for his supervision, help and criticism throughout the project, and Mr C. Welsby for his technical assistance in the construction of the activity cell.

This work was carried out during the tenure of a Scientific Research Council Studentship.

The growth curve, rate of neutral unbound lipid synthesis, and relationship between morphogenesis and lipid reserve have been studied at 30 °C. The feeding process, including a theoretical calculation of bacterial requirements of preinfective larvae, is presented, together with some measurements of the most important variables in ingestion, expulsion of water through the anus, and its dependence on larval posture is described.

Larval stages have been tracked on agar; L1 are so inactive that no tracks were obtained; L2 show short, irregular tracks, and infective larvae strong, long and straighter tracks. The locomotory activity of L2s is primarily for feeding, whereas L2s are adapted for dispersion and host location.

I thank Mr J. M. Smith for tracking the larvae and Mrs Helen Foreman for staining them, Dr Elizabeth U. Canning for making available the scanning microdensitometer and Professor G. S. Nelson and Dr D. A. Denham for enabling us to establish A. tubaeforme in cats. Finally the generous support of the British Medical Research Council is appreciated.

During 2 min incubations of Trypanosoma gambiense (bloodstream form) with [U-14C]glucose (1 mM) over 60% of absorbed label was detected in free alanine. In the presence of 12·5 mM unlabelled alanine, the amount of alanine synthesized from glucose was reduced by less than 10%. These data support previous observations on the high level of transaminase activity in African human trypanosomes.

Alanine, aspartate and glutamate were metabolized to various other free amino acids whereas a significant amount of label derived from [14C]arginine could not be accounted for by amino acid assay.

The sulphur containing amino acids, cysteic acid and taurine, were apparently synthesized from alanine, glutamate and arginine. The significance of these syntheses is poorly understood.

Following incubations of trypanosomes for 2 min in exogenous amino acids the internal free pool became imbalanced due to accumulation and metabolism of the substrate amino acid.

Evidence obtained indicated that the level of free endogenous glutamate may be rate limiting for the glutamate-pyruvate transaminase system.

The fine structure of the shell formed round developing zygotes of an acanthocephalan has been described and compared with the descriptions from light microscopy. The origin of layer 1 from globules in the ovum has been postulated and a sequence of elaboration of the three shell layers has been suggested. The layers of the shell should continue to be numbered rather than labelled with descriptive terms until their origin and chemical composition have been established.

I should like to thank the Avon and Dorset River Authority for collection of the fish.

The anatomy of the choriothete and its relation to certain features of the tsetse uterus, such as the previously unnoticed radial, uterine ridges, are described. The results of this study suggest that the choriothete is an organ for support of the developing embryo or larva and this role is taken over by the uterine ridges when the larva reaches a sufficient size. The choriothete then appears to degenerate due to stretching of the uterus until the beginning of the next breeding cycle.

Hatching takes place with the aid of a labral egg-tooth as in some other dipteran larvae and does not require the additional presence of the choriothete.

The uterine ridges also help to form a pool of milk gland secretion around the anterior end of the second-instar larva by locking its body wall to that of the uterus.

I am grateful to Dr E. J. Popham and Col. H. W. Mulligan for reading the text and would like to thank Dr T. A. M. Nash of the Tsetse Research Laboratory, Bristol, for the provision of tsetse material. The work was carried out during tenure of a grant from the Ministry of Overseas Development.

An extract of blood from Aotus monkeys infected with Plasmodium falciparum contained all the clones of malaria precipitins so far identified in human blood.

We are grateful to the Medical Research Council and Overseas Development Administration of Great Britain and to the World Health Organization for their financial assistance.

The results of several experiments that included variation of the pH and concentration of the extracts and analysis of the role of enzymes separated from midgut fluid by electrophoresis indicated that hatching involved two or more proteolytic enzymes that digested the cytoplasmic layer and embryophore. Amylases from T. molitor and other sources were shown to play no part in hatching. A defined medium based on analyses of midgut fluid and containing trypsin, chymotrypsin and peptidases was shown to digest the embryophore and effect the release of hexacanths in a time comparable to that obtained with T. molitor extracts. The specificity of the enzymes attacking the cytoplasmic layer remains unknown.

The binding of chloroquine to DNA isolated from P. knowlesi has been investigated. In the presence of increasing concentrations of malarial DNA, the absorption spectrum of chloroquine exhibited strong hypochromism in the range 325–350 nm, small red shifts of the absorption maxima and an isosbestic point at 300 nm. The fluorescence emission of the drug at 380 nm (excitation 330 nm) was quenched five-fold by malarial DNA. Chloroquine itself protected malarial DNA from thermal denaturation. These data are consistent with binding of the drug to malarial DNA as has been suggested from studies with DNA from bacteria and mammalian cells. The binding affinity for malarial DNA is of the same order as that for mammalian DNA.

The effect of chloroquine on the metabolism of P. knowlesi in culture was also investigated. There was a direct correlation between concentrations of drug which affect the morphology of parasites and those which affect markedly the incorporation of 3H-adenosine into DNA and RNA, 14C-isoleucine incorporation into protein and the formation of lactate as a result of respiration. However, all processes were inhibited to the same extent, indicating that binding to DNA is not the only action of the drug.

The mode of action of chloroquine and the question of resistance to it are discussed.

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 K. N. Brown for reading through the manuscript, and Miss Jane Dunnett, Mrs A. C. Gutteridge and Mr T. Scott-Finnigan for skilled technical assistance.

The course of single infections of Nematodirus battus was studied and the developmental phases of the fourth larval stage described. The third moult occurred between days 2 and 4 after infection and the fifth between days 8 and 10. The period of maximum larval penetration of the intestinal mucosa occurred around day 4 and most of the larvae had returned to the mucosal surface by day 6, during the middle of the fourth-stage. Some larvae remained deep in the mucosa and moulted to the fifth-stage in this site.

The relationship between growth and morphological development was not constant and was different in worm populations from different sites. Some larvae grew very rapidly during the early fourth-stage and then entered a period of lethargus while continuing to develop sexually, while others grew and developed throughout the larval stage.

The worms recovered from the second 30% of the small intestine were consistently smaller and less advanced morphologically than those from the first 30%. The worms in the posterior region of the small intestine were preferentially lost from the mucosa in the third- and fourth-stages between days 2 and 4 and from the mucosal surface as adults between days 12 and 16.

Over 90% of Hymenolepis diminuta cysts administered by stomach tube become established in CFLP, and Porton strains of mice. The rate of growth of single worm infections in terms of dry weight and length was determined. The rate of growth of H. diminuta in mice is slower than in rats even in worms only a few mm long. In most mice growth ceases abruptly on day 10±1 day when the worm is 4–30 cm long, destrobilation usually occurs leaving a scolex and neck often 0·5–2 mm in length. Destrobilated worms can survive for at least 47 days but little if any regrowth occurs unless the worms are surgically transplanted into rats or previously uninfected mice. Normal growth appears to be resumed within hours in both recipient hosts. The cause of destrobilation is probably not physiological; position of establishment and forward migration during growth of the worm in mice is similar to that in a rat. Destrobilation occurs well before the worm fills the small intestine lengthwise. Strong evidence of an immunological response being involved is given by the fate of a secondary infection given 22 and 28 days after the primary. Lower % recoveries were recorded in secondary infections killed 6–9 days later, and the worms were severely stunted. The various lines of evidence are discussed and it is concluded no reasonable doubt exists that H. diminuta is rejected by CFLP and Porton mice as a result of an immunological response.

Histochemical analyses of the pigment accompanying lung mite infections in Old World monkeys indicate that, contrary to other endogeneous pigments, this pigment is not homogenous, but consists of at least three components. One fraction is formed by fine granular or amorphous cleavage products of mucin substances, the second portion appears to be large granules of haemosiderin and/or lipofuscin, and the third component consists of needle-like crystals of unknown chemical nature. The source and nature of the pigment are discussed.

I am grateful for the technical assistance of Mrs J. A. Silva and the support by Drs R. T. Damian, S. S. Kalter, R. E. Kuntz and B. J. Myers; Southwest Foundation for Research and Education, San Antonio, Texas.

This study was funded in part by U.S.P.H.S. Grants RR-00361, RR-00278 and RR-00451 and WHO Grant Z2/181/27.

Worm counts, faecal egg counts and erythrocyte losses are recorded for lambs which were exposed on a naturally infected pasture for different periods in different years. After each exposure period the lambs were kept under conditions in which no further infection could occur; at varying times, usually after the infections had had time to maturo, the lambs were killed and examined. A detailed analysis of the results is given. It is concluded that the negative binomial distribution of worms among sheep within a flock is not a reflexion of the pasture distribution of infective stages but is the result of a combination of Poisson distributions, these distributions being generated by genetic subsets within the flock. There is a remarkable correlation between the numbers of Haemonchus present and the numbers of worms of the other genera. It is suggested that there are host-mediated common elements in the biomass regulating parameters of mixed trichostrongyle infections and that there is a resource-allocating device. Three main hypotheses are proposed. The hypotheses are: (1) The dimensional constraints on the host-parasite system are the results of various kinds of pace-setters or biological clocks. In each annual cycle the parent worms programme the rate of development through each generation. (2) The rate of development of the worms is tied stochastically or deterministically to the rate of senescence and death. (3) The rate of development and death for each trichostrongyle is set at the start of each season by a host factor which acts on a comparable area of the genome in each trichostrongyle. Methods of testing these hypotheses are discussed and the work related to other systems.

In rats treated with compound 48/80 or histamine, worm expulsion was inhibited. Treatment with a histidine decarboxylase inhibitor accelerated worm expulsion. Treatment with compound 48/80 elevates histamine and histidine decarboxylase levels and reduces circulating reagin titres. These results show that histamine is not responsible for worm expulsion.

Compounds such as isoprenaline and theophylline which increase cellular levels of cyclic 3′,5-AMP, prevented worm expulsion.

It is concluded that the evidence that amines are involved in worm expulsion needs reassessing and that cellular release mechanisms in general may be affected by drugs thought to act solely on amine release. In particular, the release of effector substances from sensitized lymphocytes on contact with antigen may be affected by these treatments.

The skilful technical assistance of Miss R. Keist and Miss I. Beeger is gratefully acknowledged. We thank Mr H. Berchtold, Biostatistisches Zentrum der Universität Zürich, for the statistical evaluation of the data.

It has been demonstrated that under normal laboratory conditions Lymnaea truncatula infected with Fasciola hepatica are not able to shed all their cercarial loads before their death. Cercariae are irregularly released over an extended period and considerable variations (4–1789) occur in their output.

Laboratory studies have revealed that the green parts of grass (Dactylis glomerata) are preferred to the brown, dead parts by the cercariae of Fasciola hepatica for metacercariae formation. More cysts are formed on the lower surface of submerged leaves than on the upper surface.

There is vertical zonation of metacercariae on grass in water. More cysts occur on the upper parts of submerged grass than on the lower parts.

Vertical migration of cercariae after settling does not usually occur before cyst formation.

The results are tabulated and discussed and correlated with conditio s in the field.

This work was undertaken in the Department of Zoology, University of Bristol, Bristol, under the supervision of Dr H. D. Crofton, to whom I wish to express my gratitude.

Rats were infected with 1000 larvae at the time of mating and they were given a second infection while suckling a new-born litter some 3½ weeks later. Although they did have significantly more worms than immune controls such rats were nevertheless highly resistant to challenge with infective larvae. However, when challenged with adult worms, immunized lactating rats were unable to eliminate the second infection.

That the failure of self-cure in this case was not because adult worms are less antigenic in lactating rats was shown in the third experiment. Lactating rats were immunized by infection either with adult worms only or with larvae allowed to complete their life-cycle. When subsequently challenged with infective larvae during the same lactation, both groups were equally resistant. It is therefore concluded that in lactating rats the gut phase of N. brasiliensis infection is in some way protected from the self-cure mechanism. This may be due either to absence of an essential factor operating late in the process, or to the presence of a potentiating factor which allows the worms to survive.

The author would like to thank Professor W. I. B. Beveridge in whose Department this work was carried out, and the Agricultural Research Council for their financial assistance. It is also a pleasure to acknowledge the technical assistance of Mr J. A. Wilson and Mr P. W. Holmes.

Microfilariae belonging to the genera Brugia, Loa and Wuchereria have been stained by a wide variety of histochemical methods. The results are recorded in eight Tables.

The sheath of the microfilaria contains polyanionic material, probably polysulphate, periodate reactive mucosubstance, sulphur-protein and complex lipids. The fluid within the sheath is also polyanionic.

The cuticle of the microfilaria is stabilized by disulphide bonds possibly in a collagen but it was not possible to demonstrate collagen by staining. The cuticle also contains a periodate reactive G mucosubstance and complex lipids. The annular grooves of the cuticle also contain a periodate unreactive mucosubstance. Certain areas of the cuticle, around the excretory pore, the pores of the Schwanzgebilde, and the cephalic structures - oral ring, hook and spines - are hardened by deposition of a keratinous scleroprotein. Some reactions of the cuticle may be masked by the presence of basic protein.

The excretory vesicle contains polyanionic material but there was no clear evidence that the polyanionic material within the fluid in the sheath came from the excretory vesicle. The excretory vesicle, the anal vesicle and the subcuticular cells contain periodate reactive G mucosubstance. Most RNA staining was found in the excretory vesicle, the excretory cell, the anal vesicle, the rectal cells and the G cell.

The pharyngeal thread, the Innenkörper, the rectal cells and the anal vesicle represent the modified gut of this first stage larva. The pharyngeal thread appears to consist largely of a protein-mucosubstance complex that can be unmasked by oxidation. The Innenkörper contains a basic protein and acidic mucosubstance, possibly sialomucin, complex that can be unmasked by adjusting the electrolyte concentration of the staining media.

The relevance of some of these techniques in the analysis of possibly unique invertebrate structures is discussed briefly.

We thank Dr D. A. Denham, Mr P. R. N. Pester and Dr T. Ponnudurai in particular, and many other correspondents, for supplying us with microfilariae for staining. This work was supported by a grant from the Medical Research Council of Great Britain.