The pineal gland of the horse. Morphological and histochemical results. (With notes on the donkey and mule pineal).

The horse pineal gland has been investigated by morphological and histochemical methods. Particular care has been given to the cellular types, to the eventual presence of neurosecretory activity and to the nature of the pigments. Even in the horse pineal, it is possible to distinguish two populations of pinealocytes, morphologically but not histochemically distinct. A great number of pinealocytes are positive for the Masson- Hamperl reaction, and for Gomori- Bargmann 's chromic haematoxylin-phloxine and Gomori's paraldehyde-fuchsin. Along the connective septa, many brown- blackish pigmented cells were present; their pigment was positive for the Lillie and the Masson-Fontana reactions for the determination of melanin pigment. Another type of pigmented cells, carrying a brown yellowish pigment of lipofuscin nature was present, particularly in older animals, along the connective septa.