PLATES CLXIII-CLXVI FREUND'S complete adjuvant, a mixture of dead mycobacteria and mineral oils, has been widely used in experimental pathology (Freud, 1947(Freud, , 1951. Although its mode of action is still uncertain, the morphological and immunological responses to this material are well documented (Moore et al., 1963; Schoenberg, Rupp and Moore, 1964; Moore and Schoenberg, 1966; Spector and Lykke, 1966). By contrast, the reactions evoked by incomplete Freund's adjuvant-which does not contain a mycobacterial component-have not received comparable attention.Laufer, Tal and Behar (1959) investigated the morphological changes produced by fractions of Freund's adjuvant injected subcutaneously into mice, guinea-pigs and hamsters, but none of the animals was killed until 5 mth after inoculation and the findings in only six organs-liver, spleen, kidneys, heart, lungs and brainwere presented.During the course of other experiments, we have had occasion to examine tissues from mice given injections of incomplete Freund's adjuvant. The reactions observed at the site of injection and also in the regional and more distant lymph-nodes were sufficiently unusual to warrant a more detailed study.
MATERIALS AND METHODSThirty-five male Swiss albino mice were used, aged 4-8 wk and weighing 10-1 5 g. The animals were housed in metal cages and maintained on a pellet diet and water ad libitum.Freund's incomplete adjuvant was obtained from Difco Laboratories, Detroit, Michigan (batch no. 474513). It contained Arlacel A (mannide mono-oleate) 1.5 ml. and Bayol F* (paraffin oil) 8.5 ml.The animals were divided into 2 groups. (I) Twenty-seven mice received an injection of 0.05 ml. incomplete Freund's adjuvant into the left hind foot-pad and were subsequently killed in groups of 3 at the following times after injection: 1, 6, 18, 24, 48 and 72 hr, and 5, 10 and 17 days. (2) Eight mice were used as untreated controls.All mice were killed with ether vapour and the following tissues were removed and h e d in 4 per cent. buffered formaldehyde: hind foot (left); fibromuscular According to White (1967), Bayol F is a mixture of 42.5 per cent. paraffins, 31.4 per cent. monocyclic naphthalenes and 26.1 per cent. polycyclic naphthalenes. J. PATH. BAcT.-VOL. 95 (1968) 41 1
