Tóm tắt
1. A new technique has been developed for the preparation of a permanent parotid fistula in the sheep. The advantage over the Pavlov‐Glinski operation is that the saliva drips from the dependent point of a skin teat. The secretion rate may be unobtrusively observed without fixation of any apparatus to the animal. Thirty‐seven sheep with parotid fistulæ have been studied.2. The presence of a parotid fistula for 6–93 weeks did not involve any anatomical or histological deviation from normal in the parotid gland.3. A sheep with a parotid fistula lost each day 1–4 l. of hypertonic alkaline saliva containing 160–650 m.equiv. of Na+. The animal could be maintained in good condition indefinitely provided enough Na+ was given to replace that lost from the fistula. Digestion proceeded normally.4. The rate of parotid salivary secretion increased during eating and rumination, and decreased during starvation or water depletion.5. The response of the animal to Na+ depletion was examined under strictly controlled conditions. The sheep has remarkable parotid and renal mechanisms of electrolyte regulation. The salivary Na+ concentration falls commensurately with Na+ depletion from a normal of 180 m.equiv/l. to as low as 10 m.equiv/l., and the salivary K+ concentration rises equivalently from 10 m.equiv/l. to 180 m.equiv/l. This allowed the sheep to establish a new Na+ equilibrium at a particular level of Na+ depletion. It could survive for weeks even though depleted of several hundred m.equiv. of Na+. Because of the nature of the fluid dynamics of digestion in the ruminant, the mechanism of conservation of salivary Na+ during Na+ depletion may have survival value under stringent environmental conditions such as drought.6. A sheep with a parotid fistula licked 5–15 g./day off a salt block which was provided in its cage. Prior to operation a normal sheep usually licked off only 0·5–2 g./day.
