The variable refractivity of the protein or polypeptide hormone-producing cells showing a unique luminescence in the dark-field microscope.

When cryostat sections of endocrine tissue were examined in a dark-field microscope, a brillant granular luminescence was revealed in the endocrine cells thought to be concerned with protein or polypeptide horome production. The sections were prepared from fresh materials either frozen in a cryostat chamber at --25 degrees C, in dry ice-acetone, or fixed in formalin-calcium for 24 hr. The neurosecretory substance in the hypothalamus and the posterior lobe of the pituitary showed a blue luminescence; the acidophil cells of the anterior lobe of the pituitary, orange; basophile cell, green or blue; intermediate lobe cells, no luminescence; thyroid C cells, white-blue; pancreatic A cells, blue; B cells, orange; adrenomedullary cells, greenish blue; enterochromatin cells, green; and other endocrine cells in the gastrointestinal tract, blue or orange. After tearing and spreading the pituitary and hypothalamus with a pair of needles on a glass slide, and examining the teased specimen by dark-field microscopy, various cells of different lumunescent colours became apparent in the anterior lobe of the pituitary, a blue fluorescent substance in the posterior lobe, and neurosecretory cells bodies in the hypothalamus. The different colours appear to be inherent in the granules of living tissues.