1) Following excision of the carotid sinus nerves of the rabbit blood pressure increased by an average of 29mmHg, and vasoconstriction of the stria vascularis was histopathologically observed, without any destructive changes.
2) Unilaterl or bilateral removal of the superior cervical ganglion was followed by the vasodilatation of the stria vascularis, appearance of nubecula in the endo- and perilymph and swelling of the cells in some organs of Corti.
3) In the control animals acoustic stimulation by a 110 phon white noise for one hour daily for 10 successive days caused no cochlear lesion, while in the treated animals it resulted in the destruction of the hair-cells and other structures of the organ of Corti and the stria vascularis. This acoustic trauma was produced bilaterally in the case of unilateral excision as well, and was marked at the second turn.
4) The reduced C.M. potentials of normal rabbits on exposure to a 110 phon white noise for 30 minutes was restored to normal in 15 to 20 minutes, but in the case of bilateral gangliectomy only a small amount of recovery was observed. The unilaterally gangliectomized animals similarly showed poor recovery on the affected side, with nearly the same recovery on the opposite side as the normal subjects.
5) These results apparently indicate that increased noise susceptibility is caused by the surgical removal of the carotid sinus nerve or superior cervical ganglion.