No sound reaches the ear directly. It only hears the vibration of the inner rubber diaphragm and the diaphragm receives only a very minute part of the original sound which reaches the ear.
The minute hole in the rod allows of the entry and escape of the outer air. Thus each side of the ear drum receives an equal pressure of the external atmosphere.
When very heavy gunfire has to be withstood, care must be taken that the outer disc fits airtight into the tube of the ear. A little vaseline or other antiseptic ointment round the edge of this disc makes an airtight joint, or a third rubber disc is added, but the two discs are ample for pistol shooting.
The ear protector is easily kept clean and antiseptic by washing occasionally in a weak antiseptic solution.
There is no inconvenience in wearing these ear protectors and they are not very noticeable.
With some other forms of protectors, made of hard vulcanite which are forced in to make an airtight closure, pain and soreness arise if they are worn for any length of time and this unyielding vulcanite may displace the anvil and bones of the middle ear, or a sore may be caused and set up grave inflammation. Any ear plug which requires forcing or stretching the ear passage is dangerous or painful to wear.
CHAPTER XLIV
EYESIGHT