Tapetum lucidum in the pigmented and albino ferret.

Light and electron microscopy showed that the tapetum lucidum in the pigmented ferret is morphologically indistinguishable from that in the albino ferret. The matrix of the rods of the tapetal cells was strongly osmiophilic, but glutaraldehyde fixation before osmium tetroxide treatment caused a dissolution of the matrix material. It has been proposed that the tapetal cells are modified melanocytes and that the tapetal rods are composed of melanin, but it can be concluded from our data that the matrix of the tapetal rods is not melanin. Further studies by plasma-atomic emission spectrometry showed that the tapetal cells are very rich in zinc, with similar levels in pigmented and albino ferrets. Excessive concentrations of other metals were not observed. Histochemical demonstration of heavy metal showed that the zinc is present in the tapetal rods and indicated a localization mainly in the rod membranes.