[Comparative-quantitative investigations of brains of wild and laboratory rats]

By means of serial sections at equal intervals through the brains of 8 Norway rats and 8 laboratory rats the fresh volume sizes of the optic regions lateral geniculate nucleus (pars dorsalis), striate area, superior colliculus and tractus opticus were determined. Furthermore the sizes of neocortical white matter and grey matter were measured in the same way. On the basis of the intraspecific allometric relation between brain size and body size differences in size of the structures between wild and domestic animals could be established. Especially the subcortical terminal regions of visual input and the striate area showed size reductions of different intensity from Norway to laboratory rats, whereas the optic tract underwent increase. The volume of grey matter showed decrease too and for the white matter no size differences between both groups came out as a result. These changes in size of nervous tissue from Norway rats to laboratory rats were partly discussed as due to the special changes of environment through domestication but in this special case also as due to the effect caused by the albinism of the investigated laboratory rats.