The effect of fighting on the adrenals, thymus and spleen of the vole, Microtus agrestis.

Abstract

1. An attempt has been made to put Chitty's hypothesis, which explains population cycles in the vole (Microtus agrestis) [Chitty, 1952], to an experimental test by studying the effect of fighting on these animals. 2. When strange voles are added to a cage containing a pair of 'resident' voles, the strangers are viciously attacked by the residents. As a result of these attacks there is a pronounced increase in the weight of the adrenal glands and the spleen, and a decrease in the weight of the thymus, of the strange voles. The observed weight changes in these organs were statistically significant. 3. The weight changes in the adrenals and in the thymus of the strange voles can be explained by assuming a disturbance of the adreno-pituitary system of the animals concerned. Interpretation of the increased weight of the spleen is less straightforward, but the enlargement may indicate that the weakened condition of the strange voles enabled a pathogenic organism to become invasive.