The erythrokinetics of three baboons were studied over a twelve week period after infection with 3 000 cercariae of S. mansoni and compared with three uninfected control animals. In addition to monitoring changes in haematological and parasitological parameters several radioisotopic techniques were used concurrently to measure alterations in red cell kinetics. In particular 51Cr-labelled red cells and 59Fe-ferric citrate were used to measure red cell production, circulating volume, survival time and routes of loss.

All the animals remained in good condition despite heavy infection and the pathophysiological changes were in general mild and transient in nature. The principle alterations were associated with patency and consisted of a modest fall in haematocrit, some inappetence and the appearance of blood-stained mucus in the faeces. Red cell survival was reduced in the infected animals and this was correlated with an increase in faecal blood loss and haemodilution. There was no evidence of haemolytic factors or depressed erythropoiesis having any aetiological role in the anaemia.

The results confirmed the complexities of schistosomal anaemia as well as the ability of primates to withstand heavy parasitic burdens for short periods with minimal pathophysiological disturbance.

The efficiency of five different methods of infection of mice with Schistosoma mansoni or S. intercalatum cercariae was compared; of these the ring method, the tail immersion technique, and the paddling method were found to be the most effective.

A new radioisotope assay system for cercarial host-finding capacity is described. This employs the tail immersion technique with radiolabelled S. mansoni cercariae. The amount of tail-bound radioactivity retained after exposure to radiolabelled cercariae was used to measure the host-finding capacity of the cercariae under various experimental conditions. A direct proportionality was found to exist between the number of penetrating radiolabelled cercariae and the subsequent tail-bound radioactivity. Also, a direct proportionality was demonstrated between the number of labelled larvae available in the suspension and the subsequent tail-bound radioactivity. The influence of light and of length of exposure period on cercarial host-finding was analysed. After an exposure period of 30 minutes the amount of radioactivity confined to tails in the light greatly exceeded that of tails exposed in total darkness. However, after 60 minutes comparable radioactivity levels were achieved in the tails exposed in the light or in total darkness, respectively. In the light, maximum tail-bound radioactivity was achieved after 20 minutes exposure and no further change was observed in the radioactivity level at 40 and 60 minutes.

Praziquantel (Droncit) is a new anthelminthic agent with a strikingly wide therapeutic index. The efficiency of the drug against Diphyllobothrium latum was tested in vivo and in vitro. With a drug dose of 50 mg/kg, artificially infected hamsters were completely cured. The threshold value of the active dose was between 2·5 and 10·0 mg/kg. Clinical trials with Praziquantel against human diphyllobothriasis show great promise, all of ten patients treated with 25·0 mg/kg of the drug being cured. Praziquantel had little effect on larval or adult diphyllobothriids in vitro.

Stunkardia minuta sp. n. was recovered from the small intestine and rectum of 5 box-tortoises (Cuora amboinensis) in Malaysia. The average body size (L × W) is 11·42 × 2·35 mm; oral sucker 1·51 × 1.02; oral pouches 0·21 × 0·18; ventral sucker 1·67 × 1·43; oesophageal bulb 0·54 × 0·54; ant. testis 0·95 × 0·98; post. testis 0·94 × 0.94; seminal vesicle 0·82 × 0·24; ootype 0·21 × 0·41; ovary 0·41 × 0·34; and egg 121 × 83 μm. Although morphologically similar to S. dilymphosa, S. minuta is distinct from any other reported member of the Paramphistomidae.

Metacercariae of the trematode Microphalloides japonicus (Osborn, 1919) were cultivated in various media to gravid adults, and the results were compared with those in vivo. A few eggs were produced in the uterus even in balanced salt solution, although cultivation in Eagle's MEM and NCTC 109 media was much better. Addition of heat-inactivated serum resulted in even better development. Encysted metacercariae also produced eggs in some media, but most of them were incomplete and without shells.

Two strains of laboratory white mice, CFLP and LACA, were infected with the metacestodes of Taenia crassiceps. The serum from each infected mouse was tested for antibodies on double-diffusion gel plates and the number of antigen-antibody precipitin lines formed related (a) to the duration of the infection and (b) to the volume of metacestodes. There was a significant increase in the number of antigen-antibody precipitins with regard to the time infected but not to the volume of metacestodes. The pattern of development of the antigen-antibody precipitation system was also examined.

The humoral response of guinea pigs infected with doses of 500, 1000, and 1500 infective Toxocara canis ova were measured by counterimmunoelectrophoresis and indirect haemmagglutination tests one to five weeks after infection. The antigens used in these measurements were prepared from adult T. canis. Counterimmunoelectrophoresis showed lower titres than haemagglutination method, but it was performed rapidly and with case. The possible use of these techniques for immunodiagnosis of human visceral larval migrans is discussed.

An in vitro larval precipitate test using second-stage Toxocara canis larvae and an indirect fluorescent antibody (IFA) test employing cuticles of T. canis larvae as antigen were evaluated using antisera produced in pigs experimentally infected with T. canis, T. cati, Ascaris suum, Toxascaris leonina and Parascaris equorum. The former test was both specific and sensitive and is suggested as a reliable and simple method of detecting Toxocara antibodies in pigs. The latter test was considered unsuitable because of cross-reactions that occurred when sera from pigs infected with other ascarids were tested. An IFA test for Ascaris antibodies, employing cuticles of A. suum larvae as antigen, is described. The degree of specificity of this test suggests that it may be of value in the detection of antibodies to Ascaris in pigs under natural conditions.

From original observations and from data in the literature, a key to cercariae of British strigeoids for which life-cycles are known has been compiled. The value of various characters of systematic importance is discussed.