Blood-stage malaria parasites in the vertebrate host can develop either into the asexual, multiplying forms, called schizonts, or into gametocytes, the sexual stages of the parasite. In the present work we studied the differentiation into asexual parasites or gametocytes of the progeny of single, isolated schizonts of the clone 3D7A of Plasinodium falciparum, using monoclonal antibodies specific for the sexual or asexual stages of the parasite. We observed that schizonts obtained from a continuous culture undergoing serial cycles of growth and dilution with fresh red blood cells produced either only gametocytes or only asexual parasites, showing a high degree of commitment to one or the other developmental pathway.

The relative proportion of schizonts which produced gametocytes was very low at low parasite densities in culture, while at high parasite densities a much greater proportion of schizonts produced gametocytes. Nevertheless, at both low and high parasite densities individual schizonts were almost always fully committed to producing only gametocytes or only asexual parasites.

Ouabain applied to adult male Schistosoma mansoni causes a large, non-reversible tension increase of the parasite's musculature and elimination of spontaneous contractions. The tension increase and the time-course of tension development caused by ouabain are dose dependent with significant effects obtained at 3 × 10−6m. Digoxin and digoxigenin act in a similar manner with a relative potency of ouabain ≃ digoxin > digoxigenin. Lowered temperature as well as substitution of Li+ for Na+ increases muscle tension. The membrane potential recorded from the ventral tegument is also affected by treatments which interact with Na+–K+ transport systems. Ouabain (0·1 mm) causes a rapid depolarization without a significant effect on membrane resistance. The tegument is depolarized by temperatures below 30 °C. The effect of temperature is readily reversible and the temperature sensitivity is eliminated by pretreatment with ouabain. Substitution of Li+ for Na+ also causes a depolarization of the tegument. Tracer experiments show both an increase in Na+ and a decrease in K+ in the parasite within 10 min after treatment with ouabain (1 × 10−5m). Decreasing temperature of the bathing medium also causes an accumulation of Na+ as well as a decrease in the animals. The above results indicate a significant role for active Na+–K+ transport in muscle contraction and in maintenance of the tegumental membrane potential. The data also suggest that the Na+–K+ transport in S. mansoni may be electrogenic.

The effects of parasitization by Hyposoter exiguae on the nutritional physiology of Trichoplusia ni were influenced by the dietary sucrose level. The results confirmed that host nutrition plays a significant role in the manifestation of parasitic infection during the insect parasite-host association. Increased dietary sucrose level resulted in an increase in haemolymph trehalose concentration in both control and parasitized insects, but the increase was greater in the latter group. However, when the sucrose level was increased without energetic compensation and the dietary casein level was maintained constant, the haemolymph trehalose concentration was affected very little in unparasitized individuals but was markedly elevated in parasitized hosts. This result suggests that the de novo synthesis of carbohydrate in parasitized T. ni may not be regulated by dietary sugar intake.

A method of breeding and maintaining L. natalensis cultures in the laboratory is described.

The infection of snails with F. gigantica miracidia and the collection of metacercariae is discussed. The mean number of metacercariae arising from cercariae produced by each snail was 652·6, over a period of 8·2 days.

It is shown that after 3 months storage F. gigantica metacercariae are still viable when excysted in vitro by using artificial pepsin and trypsin enzymes.

The author wishes to express his thanks to Dr G. M. Urquhart of the Wellcome Laboratories for Experimental Parasitology, University of Glasgow, Veterinary Hospital, Bearsden Road, Bearsden, Glasgow, who has read through this paper and made the necessary corrections.

Protoscoleces of Echinococcus granulosus absorb the l-amino acids proline, methionine, leucine, alanine, serine, phenylalanine, lysine and glutamic acid by a combination of mediated transport and diffusion. All eight amino acids were accumulated against a concentration gradient. Comparison of Kt and Vmax values suggests that a low affinity for a particular compound is compensated for by a relatively larger number of transport sites for that compound. Four systems serve for the transport of the eight substrates studied: 2 for neutral (EgNl, EgN2) and 1 each for acidic (EgA) and basic (EgB) amino acids. All eight amino acids are incorporated into protein to varying degrees and substantial portions of absorbed l-alanine and l-methionine are metabolized into other compounds.

Through the courtesy of the Editors of Parasitology I have been favoured with an advance proof of the remarks of Dr Woodcock on a former note of mine relating to the procedure of the Recorder of the Protozoa section of the International Catalogue of Scientific Literature and the Zoological Record. In my article I raised three points. (1) In certain cases where the generic names Crithidia and Herpetomonas were placed in inverted commas in the Catalogue, I stated that no direct evidence existed to justify such a procedure. (2) I protested against such meddlesomeness on the part of the Recorder. (3) I stated that the Recorder, who had not worked on the parasites themselves, held, consequently, extreme views. Dr Woodcock's so-called reply has afforded me considerable amusement and it is a matter of surprise to me that he has been so ill-advised as to write such a poor rejoinder—he must know that he has made no answer to my remarks. That the weakness of his position is well known to him is shown by his recourse to the tactics of vituperation and innuendo, where he remarks that my method of criticism is “not straightforward but, on the contrary, distinctly oblique.” Dr Woodcock has no case and so has adopted metaphorically the old, old method of “abusing the plaintiffs attorney,” in the shape of discussing my own papers on parasites not originally under discussion. I am sorry that one who apparently claims to be an authority is reduced to such second-rate methods. While I regret the necessarily severe character of this, my rejoinder, it is impossible to deal otherwise with the numerous side issues raised by Dr Woodcock.

1. The feeding habits of second- and third-instar larvae of Neottiophilum praeustum have been observed and show that this species is a true parasite of birds and feeds by sucking the blood of nestlings.

2. If they are too numerous the larvae may kill the nestlings. Although they will continue to feed upon dead birds, and even penetrate into the viscera, such food is unsuitable for the development of the larvae and they become greatly distended and die within a few days.

3. The morphology of the hitherto unknown second-instar larva is described and is compared with that of the third instar.

4. Within the puparium of Neottiophilum praeustum there is a fourth moult resulting in the formation of a cast prepupal cuticle which resembles that described by Snodgrass in Rhagoletis pomonella and is much better developed than the prepupal cuticle in Calliphora erythrocephala.

5. The better development of the prepupal cuticle in the acalypterates than in calypterates indicates that the presence of a prepupal stage in the cyclorrhaphous Diptera is a primitive character and is progressively reduced until in the higher families it is almost vestigial.

The earliest stages found are groups of small bodies, 1·8 or 2·0μ in diameter. These groups are probably taken up by phagocytic cells and pass through the epithelium of the host into the connective tissue, where a cyst is formed by the host. Within the cyst the bodies grow. In many cysts there is a differentiation into two types: the larger, when mature, attain 40μ in size, are shaped like a pear, and contain at the broad end a chromatic rod. The small bodies reach 3Oμ in length, are also somewhat piriform, and contain two similar structures attached to their nuclei. In some cysts large bodies alone are found.

Development is periodic, the youngest stages being found from January to March and the parasites not reaching maturity until September–November.

Type species P. sociabile, with the features mentioned above: found near the ventral surface of the foot of Buccinum undatum.

Some of the reindeer (Rangifer tarandus) introduced into Scotland from Northern Sweden have become infested with the deer warble fly Hypoderma diana and the deer ked Lipoptena cervi.

Evidence is presented which suggests that the larvae of H. diana proceed to their final site on the back of the host by way of the neural canal, and in this way probably caused the deaths of two reindeer in the winter of 1953–4.

A detailed analysis is presented of the frequency with which various bands of spines occurred on second-stage larvae of H. diana. An analysis of the number of chitinous rings in the two posterior spiracles on second-stage H. diana larvae showed that in any individual larva the two numbers were not independently determined.

On reindeer L. cervi produced puparia in December.

Various stages in the life cycle of Panopistus pricei are reported from Agriolimax agrestis. These are essentially the same as those reported by Krull from Zonitoides arboreus. The excretory system of a developing metacercaria is described.

Surface antigens of Schistosoma haematobium were identified by 125I-surface labelling of schistosomula followed by immunoprecipitation of the solubilized, labelled surfaces. The major antigens, after electrophoresis, formed a continuous smear corresponding to a molecular weight in the range 35–24000; in addition, a 17000 antigen was also identified. These surface antigens, in contrast to somatic antigens, were species-specific, as judged by immunoprecipitation with human anti-S. mansoni serum and serum from mice vaccinated with highly irradiated S. mansoni cercariae. S. haematobium surface antigens, however, were recognized to some extent by serum from mice chronically infected with S. mansoni. It is suggested that this cross-reactivity may reflect the heterologous immunity demonstrated experimentally between these two species, whilst the species-specificity of vaccine sera to surface antigens may mirror the highly specific immunity induced by vaccination.

Paramphistomum daubneyi sp.nov., recovered from Bos taurus in Kenya, East Africa, is described and differentiated from the other species of the genus possessing a Microbothrium type of genital atrium.

Lymnaea truncatula Müller was infected experimentally with miracidia of P. daubneyi and the development in the snail host is briefly described.

Evidence has accrued to indicate that host defence mechanisms enhance the efficacy of many of the drugs used to treat infectious diseases. Because of this, and also because of the likelihood of increased pathogen loads in immunoincompetent hosts, some infections are less likely to be completely cured by normal regimens of chemotherapy in individuals with drastically impaired immune responsiveness. In such circumstances natural selection could result in the accelerated emergence of drug-resistant pathogens.