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.