Arecoline hydrobromide was tested for its efficiency in causing dogs to purge and in removing hydatid worms by infecting, dosing and autopsying 157 dogs. Doses were given by mouth in water at various rates, by mouth in meat, and by subcutaneous injection.

The tabulated results indicate that the median efficiency of hydatid-worm removal, with doses of or above grain/10 lb. weight, are 95% or more. Dosing in meat is almost equally efficient but the action is slower, taking usually over 1 hr. instead of 15–30 min. Injections of arecoline caused purgation but not worm removal. Increasing the dosage rate above grain/10 lb. body weight increased the proportion of dogs that vomited and caused convulsions in some, but did not markedly increase efficiency in worm removal. The dose recommended for general use is grain/10 lb. body weight; though half or double this dose is about equally suitable. None of the dogs tested was killed by arecoline.

Repeated doses were given to see how many were required to ‘clear‘ a dog. Dogs usually gave negative results after three doses that caused purging.

Arecoline showed a similar high degree of efficiency against Taenia species and Dipylidium; usually removed about half the Toxocara specimens present, and had no significant effect against hookworms.

Solutions of arecoline were tested in vitro on isolated Taenia segments arranged to record. Solutions of 0.001% or more in Ringer's solution almost invariably caused extreme relaxation of the segment, its normal rhythmical contractions ceasing. The segments were not killed.

Arecoline hydrobromide appears to exert its anthelminthic action: first, by causing the muscles of cestodes to relax, so that the hold on the host's intestine is lost; secondly, by causing the host to purge, so that the detached worms are removed from the host's body.

The writer wishes to thank Sir Louis Barnett, Dr Hercus and other members of the Hydatid Committee for their interest and support. She especially thanks Miss D. Medley, Hydatid Assistant, who has carried out the heavy share of the infecting of dogs and handling of faeces. Thanks are also given to Mr L. K. Whitten, Agricultural Parasitologist, for technical advice; to Mr Grimmett, for analysing arecoline-content of pills; and to the various members of the Medical School staff who have given helpful advice.

The life history of Ornithodorus delanoei acinus under laboratory conditions at 30°C. may be summarized thus:

Thanks are due to Prof. P. A. Buxton, F.R.S., in whose departmemnt the work was done, and to Dr A.D. Lees of the Insect Physiology Unit, Agricultural Research Council, who made final observations on some of the later nymphal stages and adults.

1. Membranes prepared from chicken skin provide a suitable medium through which Aëdes aegypti females may be induced to gorge.

2. Under suitable conditions the proportion of female A. aegypti which will gorge through membranes, though more variable than when a living chick is offered, is great enough for experimental purposes.

3. It is shown that the gorging reaction in A. aegypti is provoked by a heat gradient between the environment and the food-limiting membrane.

4. The feeding reactions of A. aegypti towards whole blood, fractions of blood, and other sub-stances have been studied. It was found that (a) whole blood, and red corpuscles in saline when ingested through membranes go directly into the stomach which becomes fully distended; (b) haemoglobin in plasma or distilled water is ingested to a lesser degree than whole blood or red corpuscles in saline, and plasma alone is rarely ingested, but all these pass to the stomach; (c) sweet solutions containing glucose or honey are seldom imbibed through membranes and pass to the stomach or diverticula, but only the diverticula are fully distended.

When offered as open drops (a) blood is seldom ingested, but if ingested passes to the stomach; (b) haemoglobin in plasma or water, or plasma alone, are very rarely ingested, but pass mainly to the stomach; (c) sweet solutions containing honey or glucose, or mixtures of blood and honey are readily ingested and pass mainly to the diverticula which become fully distended, though traces may be found in the stomach.

5. Aëdes aegypti may be infected with Plasmodium gallinaceum by allowing them to gorge on drawn infected chicken blood through a membrane. Infection rates comparable to those obtained when the mosquitoes are fed directly on living chickens may be obtained by this method.

6. If infected mosquitoes are allowed to gorge upon uninfected blood through membranes they eject viable sporozoites into the blood. When young chicks are injected intravenously with blood so infected, infections are produced which in period of incubation and intensity are comparable with those resulting from the bites of infected mosquitoes.

7. The ejection of sporozoites through membranes in this manner provides a ready means of obtaining sporozoites free from glandular tissue.

8. Sporozoites collected by this method will be suitable for in vitro experiments upon the action of drugs on sporozoites, and also as a source of material for studying in tissue cultures the developmental stages of the malaria parasite arising directly from the sporozoite.

We wish to thank Prof. D. Keilin, F.R.S., and Dr P. Tate for helpful criticism and advice during the course of the work.

A description is given of the processes of copulation, formation of the egg and spermatozoon, cleavage, embryogeny and hatching in B. phlebotomum. These processes were found to be essentially similar to those in other strongyle nematodes.

The anatomy of the first three larval stages is described and the observations of Conradi & Barnette (1908) and Schwartz (1924) were largely confirmed.

Penetration of the skin of calves by the infective larva was observed histologically. The larvae were found to have reached the dermis within 30 min. and to have penetrated the cutaneous blood vessels within 60 min. of application to the skin. The larvae were found in the lung where the third ecdysis was in progress 10 days after penetration of the skin. A description is given of the growth of the third-stage larva in the lung, the changes which take place during the third ecdysis, and the anatomy of the fourth-stage larva.

The fourth-stage larvae exsheath in the lungs and travel to the intestine. After a period of growth in which sexual differentiation takes place, the fourth ecdysis occurs and the adult parasite emerges. The time required for the attainment of maturity was found to be somewhere between 30 and 56 days after penetration of the skin.

This paper was written at the Ministry of Agriculture and Fisheries Veterinary Laboratories, Wey-bridge, and the writer would like to express his gratitude to the Director, Prof. T. Dalling, also to Dr W. R. Wooldridge, chairman of the Council of the Veterinary Educational Trust for their help and encouragement. The writer's thanks are also due to Dr H. A. Baylis, Prof. R. T. Leiper and Dr E. L. Taylor for their advice and help on technical points, and to Mr R. A. O. Shonekan, African laboratory assistant, for his able co-operation.

Investigations were carried out on the influence of the local environment on the preparasitic stages of B. phlebotomum and the following observations were made.

1. The infective larvae are positively thermo-tropic and positively phototropic. These observations confirm those of Schwartz (1924). The larvae are not negatively geotropic and do not climb grass, but remain in the dung, gaining access to the host by adherence of the dung to the skin.

2. Lack of air, such as would occur in tightly packed faeces; immersion of the faeces in water; temperatures below 10° C.; and lack of moisture, are all inhibitory to development. Infective larvae are resistant to at least 5 days‘ direct exposure to an atmosphere of relative humidity 75 at a temperature of 25° C.; in dry faeces they are resistant to 14 days‘ exposure to the same atmosphere.

3. In Northern Nigeria desiccation is the most important inhibitory factor in development. The extreme dryness of the pastures in the dry season prevents development of the larvae and adherence of dung to the skin. Penetration of the skin of the host probably occurs only in the rainy season, maximal penetration probably occurring just after the rains are regularly established.

4. The female lays 600 eggs in 12 hr. in the early rains, but the output of eggs by the females varies considerably throughout the year. It is greatest in the early rains and lowest in the later months of the dry season.

5. The female hookworm burden of nomadic cattle fluctuates throughout the year. The maximum burden occurs in the later months of the dry season.

6. Three factors, all probably bound up with a single factor, i.e. moisture, seem to influence the degree of pasture infectivity. (a) Inhibition of larval development; (b) failure of faeces to adhere to the skin; (c) fluctuation in the egg-laying rate of the female hookworms. The fluctuating pasture infectivity results in a fluctuating hookworm burden.

7. The period of maximum hookworm burden in nomadic cattle more or less coincides with the period of incidence of a disease in Stock Farm cattle, associated with hookworm infestation.

In the discussion an attempt is made to correlate these observations both in accounting for the seasonal incidence of ‘hookworm disease’ and in suggesting methods of control.

This paper was written during the tenure of a Cooper Centenary Fellowship for which the author is indebted to the Council of the Veterinary Educational Trust. The writer's thanks are also due to his laboratory assistant in Nigeria, Mr R. A. O. Shonekan.

1. The oxidation-reduction potential in cultures of E. histolytica has been studied. It was found that a close relation exists between the potential in the culture and the growth, encystation, and excystation of E. histolytica. The small differences observed in different cultures indicate the reproducibility of the potentials and the reliability of the potential condition in explaining these biological activities of the amoebae in culture.

2. The best growth of trophozoites was observed at potentials between −350 and −425mV., less at potentials between −275 and −350mV., still less at between −200 and −275mV. At potentials between −150 and −200mV. a bare increase in number of trophozoites was noticed. Between potentials of −50 and −150mV. no increase of growth was observed. Trophozoites were found dead in 12 hr. or more at potentials between −50 and +50mV., and died and disintegrated in a couple of hours between potentials of +100 and +200mV.

3. The life span of a culture of E. histolytica was also found to be related to the potential condition. The longer the potential in the culture remains below −150mV., the longer the culture remains positive.

4. Excystation of E. histolytica, no matter in what media, took place only at potentials of −115mV. or lower.

5. Mass encystation of E. histolytica was induced in cultures in which a ‘sharp rise of potential’ occurred after a greatly increased rate of multiplication of trophozoites after 22–24 hr. of incubation. Maturation of cysts occurred during this period of ‘sharp rise of potentials’. If the potential went down shortly after its sharp rise, the cysts failed to become mature and disappeared in about 12 hr.

6. Trophozoites and cysts observed in cultures with very low potentials (below −300mV.) and a rapid multiplication were definitely smaller than those in cultures having higher potentials and trophozoites multiplied slowly.

7. In cultures of amoebae in which mass encystation failed to occur, or mass encystation occurred but cysts failed to become mature, some success was observed in a few trials by artificially creating the ‘sharp rise of potential’ by oxygenation.

8. The pH values noticed in cultures at times of encystation ranged from 6.4 to 6.8. This pH range was a little lower than that observed previously. Mass encystation failed to occur at the change in potential if the pH was 7.2 or higher.

9. It is felt that the process of encystation requires, at least, two extrinsic and one intrinsic factors. The first two are the potential change from more favourable to less favourable conditions and the pH. The last one is the tendency to encyst possessed by the amoebae.

10. The low potential condition in a culture of E. histolytica was found chiefly provided by the activity of the accompanying bacteria. It is, therefore, felt that the indispensability of a bacterial flora for cultivation of amoebae may be explained, partly if not entirely, by the potential relation. To verify this statement, it is hoped to propagate E. histolytica in cultures in which a strongly reducing condition is provided without the presence of bacteria.

The author wishes to acknowledge the kindness of Dr David Weinman of this department in making many invaluable corrections of this manuscript, and he is very grateful to Mrs Elizabeth B. Keller and Mrs Wanda Reed for their help in preparing the graphs accompanying it.