By measuring potential drop produced by a constant current across the partition between scala media and scala tympani the average resistance of this partition was found to be 4700 ohms at the round window, 3500 ohms at the first turn, 1200 ohms at the second turn and 600 ohms at the third turn. Just preceding or simultaneously with a drop in d.c. potential there was a drop in resistance in response to loud sound. Recovery of the resistance preceded recovery of d.c. potential. Anoxia first lowered d.c. potential, then resistance. Both appeared to recover at nearly the same time. Destruction of the fourth, third and second cochlear turns did not affect d.c. potential or microphonics in scala media recorded from the first turn through the round window. Both were abolished upon destruction of the first turn. No spread of current was found from one turn to another. Implications of these results are discussed.
Using a potassium chloride reference microelectrode and an antimony-Cerroseal alloy active microelectrode, the pH of the perilymph exposed to the atmosphere was found to be 7.8–8.0 and the endolymph in situ 7.3–7.5 in the guinea pig. The acidity of these fluids in situ appears to be very sensitive to changes in carbon dioxide tension.
Oxygen tension of the endolymph in the scala media of the guinea pig cochlea was measured using a micro-polarographic technique. Near the stria vascular is the oxygen tension was 55 to 70 mm Hg. Deeper in the scala media it decreased gradually to 16 to 25 mm Hg. Effects of sound, hypoxia, hyperoxia, and hypercapnea were studied. Oxygen tension decreased with hypoxia and sound, and it increased with hyperoxia and hypercapnea. A technique to check the integrity of a metallic-plated microelectrode is described.
Oxygen tension of the endolymph in the scala media of the guinea pig cochlea was measured using a micropolarographic technique. Near the stria vascularis, the oxygen tension was 55–75 mm Hg. Deeper in the scala media it decreased gradually to 16–25 mm Hg. Following sound the oxygen tension fell below normal with very gradual recovery. Breathing pure nitrogen reduced the oxygen tension rapidly. On rebreathing air it usually returned to normal as rapidly overshooting for one or two minutes. If recovery from anoxia was slow no overshoot occurred. Breathing 10% carbon dioxide in air increased the oxygen tension more than pure oxygen. On return to normal air the oxygen tension fell back to normal or slightly below if the animal had previously breathed pure oxygen.
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