The ultrastructure of the sweat glands of the ox, sheep and goat during sweating and recovery.

The ultrastructure of the sweat glands of cattle, sheep and goats was studied before, during, and after, exposure of the animals to controlled warm environments. In cattle, sweating induced little ultrastructural change in the gland, although fluid-filled spaces appeared between the myo- and secretory epithelial layers. The mechanism appears to be one of fluid transport and exocytosis of secretory vesicles, which in this species seem to be derived from the Golgi apparatus and/or mitochondria. The glands of the sheep and goat also displayed signs of vesicle exocytosis and of fluid transport during sweating. The sweating 'fatigue' in these species was apparently due to failure of the secretory cells, some of which ruptured and were extruded into the lumen. The evidence during subsequent recovery indicates that neighbouring cells spread to make contact, encase remnants of atretic cells between them and the underlying myoepithelium, and engulf them. Sweat in these species appears to be formed (a) by secretion and (b) from cells which can no longer meet the demands of stimulation. The role in sweating of cell replacement, and of undifferentiated cells found between the myo- and secretory epithelia, is discussed.