Chemical and ultrastructural changes in tapetum of beagles with a hereditary abnormality.

We have defined the defect in the tapetum of beagles with an inherited tapetal abnormality to be the absence of both zinc and cysteine from the tapetal rods. This was demonstrated by direct measurement of zinc and cysteine and by histochemical localization of zinc. The latter method also indicated an interesting substructure in tapetal rods from normal beagles, in which the zinc is apparently distributed in two concentric rings. The chemical changes involved in different methods of fixing this unique tissue have been examined and correlated with the ultrastructure.