Dr. J. P. Caplan (1949) of the Ministry of Pensions Tropical Diseases Unit, Queen Mary's Hospital, Roehampton, reported that in the course of 8 years he had observed several hundred cases of creeping eruption am, ong ex-prisoners-of-war from the Far East and that more than 98 per cent, of them had Strongyloides infection.

According to Napier (1949), who comments on this condition, at least 90 per cent, of these patients had worked in Siam on. the notorious railway. One of Napier's cases came from the Assam-Burma frontier and one of Caplan's from Java. Professor J. J. C. Buckley, who was consulted, was of the opinion that morphologically the parasite in the faeces of these patients was in no way different from S. stercoralis Bavay, 1876).

The writer decided to undertake this investigation, with Professor Buckley's permission, on ascertaining that a friend of his, an English doctor on leave from Malaya who had worked on the Siamese. Railway under the Japanese, was harbouring Strongyloides infection and had creeping eruption.

The majority of normal sera proved in vitro to be cercaricidal to larvae of S. mansoni. Of 502 normal sera. 21 per cent, were noncercaricidal whereas the remainder exhibited varying degrees of cercaricidal potency.

The cercaricidal factor was thermolabile and disappeared during storage. It bore several points of similarity to complement.

The cercaricidal factor was present to a varying degree in sera from all species investigated. Apparently normal sera from all cattle and different proportions of other species, caused an enveloping precipitate to form around the cercariae. This bore no obvious relationship to the nematode worm burden or presence of F. hepatica.

An enveloping precipitate formed around cercariae of S. mansoni when placed in vitro in immune sera and incubated at 87°C. This occurred in serum immune to S. haematobium as well as to S. mansoni. It is not known-whether age and weight of infection influence the rate and extent of envelope precipitation.

An experiment on six pairs of twin lambs earned out in 1946–6 was repeated in 1946–7, comparable results being obtained in the two years. One of each pair of twins was given 10,000, 15,000 or 20,000 infective larvae of Trichostrongylus axei when one month old; and four months later all the lambs were given 40 daily doses of 4,000 infective larvae of Trichostrongylus axei. Egg counts and weight gains were recorded weekly and when they were nine months old the surviving lambs were killed and examined post-mortem. The results show that the smaller doses of larvae given to lambs one month old increased their resistance to the second infestation but that the high doses (20,000 or more) decreased the resistance. There was an intermediate dosage level at which no effect, either of increased or decreased resistance, was observed.

The results of this experiment are discussed in relation to the work of other authors on resistance in animals to superinfection with parasites. It is suggested that the resistance to parasitic gastritis developed by sheep in the field may be partly a result of the intake of small numbers of larvae early in life and that it may actually be beneficial to expose young lambs to light infestations. It is, however, dangerous to expose them to a high level of infestation at an early age and because of the difficulty of assessing the dose of larvae necessary to stimulate resistance in a particular lamb, even by artificial infestation, it is impossible to make precise practical recommendations.