a1 (Research Student, Department of Parasitology, London School of Hygiene and Tropical Medicine.)
The differential blood count of the normal laboratory rat shows at all times a greater proportion of lymphocytes than of neutrophiles. In rats infected with 400–600 larvae there is within 2–4 days of the infection a great relative, and possibly absolute, neutrophilia with a corresponding lymphocytopenia, which becomes less marked as the infection progresses, though the percentage of neutrophiles remains above, and that of lymphocytes below, the normal average. This neutrophilia is accompanied by a moderate left shift in the Cooke polynuclear count which may persist for a considerable period. At the same time the infection is immediately followed by a relative eosinopenia or aneosinophilia which persists for 1–5 days and is probably due to the setting up of a local eosinophilia in the sub-mucosa of the intestine. Thereafter the eosinophilia becomes generalised and reaches its maximum in 7–16 days after infection, with considerable fluctuations from day to day, finally settling to a low-grade eosinophilia which may persist for some months. The degree of eosinophilia appears to be only generally related to the severity of the infection and depends on the individual host animal. Persistence of aneosinophilia is an unfavourable prognostic sign.