Mast cells and eosinophils have been identified by differential stainings and counted
in mucous membrane of nasal septum, turbinates and sinus of 77 ewes naturally infected
with Oestrus ovis. Results have been compared with those of nine parasite free lambs.
Anova tests indicate significant differences between infected and parasite-free sheep
for the cell numbers and their distribution among the septum, the turbinates and the
sinus and according to their position in mucous membrane, interglandular chorion of
sub-mucosa. In infected sheep, the mean number of mast cells is twice the number present
in parasite free animals. The burdens of eosinophils are multiplied by 17 for the
septum, 29 for the turbinates and 58 for the sinus. The hypothesis of the development
of an hypersensitivity phenomenon in ovine oestrosis is sustained by these results.