346 



SCIENCE. 



[Vol. IX., No. 318 



Eobeson, at the naval attack on Fort Fisher, found 

 that the continued exxjlosion of fifteen-inch shell 

 at close quarters gave rise to very disagreeable 

 ringing in the ears, which finally benumbed the 

 hearing sense so much that he could not hear an 

 order given on deck for several days : the disabil- 

 ity, however, was but temporary. 



I am in receipt of a communication from Med- 

 ical Director Henry O. Mayo (retired), U.S.N. , 

 giving his own experience as to the effect on the 

 ear of the concussion of great guns, which is of 

 much interest, since it shows the effect of repeated 

 injuries. He says, " I first felt the effects of con- 

 cussion from big guns the summer of 1861, on 

 board the frigate Savannah, while engaged in a 

 scrimmage with some rebel gunboats at the mouth 

 of the James River. As the affair promised to be 

 of a bloodless character, from the respectful dis- 

 tance kept by the enemy, I seated myself in the 

 bridle-port, on the gun deck, to watch the perfor- 

 mances. My hearing was quite impaired for a 

 day or two, but in a short time the effects of con- 

 cussion passed off entirely. 



"Just at the close of 1864, I was attached to 

 the U. S. steamship Powhattan, of Admiral Por- 

 ter's fleet, and was engaged five days (three atone 

 time and two at another) in the bombardment of 

 Fort Fisher and the other batteries at the entrance 

 to "Wilmington. Having occasion to go on deck 

 at times during the action, I could only do so by 

 the cabin companion-way, which was but a few 

 feet from the eleven-inch pivot gun. This chanced 

 to be discharged two or three times, just as my 

 head was about on a level with it, going up or 

 down the hatch, and the concussion was tremen- 

 dous. Once I thought the gun had burst, and 

 taken my head along with it. Upon reaching 

 home, a month or two afterward, I found the 

 hearing of the left ear much impaued, but the 

 right still served me so well that I was enabled to 

 continue my ordinary duties on the active list. 



"In the early part of 1870 I went to China as 

 surgeon of the Asiatic fleet. During this cruise 

 I was exposed for one entire day to the concussion 

 of big guns engaged at target-firing on board the 

 flagship Colorado. This gave the coup de grace to 

 the hearing of the left ear, and still further im- 

 paired that of the right. In 1875 I was retired on 

 account of deafness." 



Dr. Mayo is of the belief that the cause of the 

 defectiveness lies in the transmitting mechanism 

 of the middle ear, and not in the inner ear, or 

 auditory nerve-tract. The Eustachian tube of the 

 left (worst) ear has always seemed abnormally 

 pervious, while the right was considerably ob- 

 structed. He cannot hear the loudest-ticking 

 watch pressed against the left ear, and only faintly 



in the right. He can converse pretty well with 

 one person, at close range, who speaks slowly and 

 distinctly. 



In general, it may be said that the concussion 

 of great guns is much less in the rear of the piece 

 than just over it or at one side, and that the more 

 in advance, the greater the exposure to the blast. 

 On shipboard a gun's crew is usually stationed 

 from four to eight feet to the rear of the muzzle, 

 and, when protected by bulwarks and decks, ex- 

 perience no special inconvenience ; but, if the ear 

 happens to be on the same plane as the face of the 

 muzzle, the effect at a distance t'f afew feet is dis- 

 agreeable, or even painful, and causes temporary 

 deafness. 



The force of impact upon the drum-head will 

 depend somewhat on the size and curvature of the 

 external auditory canal and the rigidity of its 

 cartilaginous walls ^ of course, the more straight 

 and large the passage, the greater the injury. 



The size and tensile strength of the drum-head 

 must be taken into account : if large and brittle, 

 from trophic changes, it is much more easily 

 ruptured. 



The facing of the person exposed must also be 

 considered : usually the ear directed toward the 

 object from which the concussive force is propa- 

 gated suffers most ; but in the case of Ingram it 

 was otherwise, the sound-waves having been re- 

 flected. 



The immediate effect of the blast-impact in the 

 cases injured by the shell-explosion at Sandy 

 Hook was undoubtedly upon the exterior surface 

 of the drum-head mainly. While it is true that 

 atmospheric tension is almost equal on both sides 

 of the drum head, yet a current of air passes 

 much faster along the comparatively large tube 

 comprising the external auditory canal than along 

 up the-small Eustachian tube ; and hence, in most 

 of these cases, the drum-head was driven in with 

 great force, and contused against the inner wall 

 of the tympanum and the retained air. The effect 

 of such violent concussion is to cause the death of 

 the membrane. 



The momentum of sound-waves may ordinarily 

 be estimated by the application of the law of cen- 

 tral forces, the force being inversely to the square 

 of the distance. The effects, practically, of such 

 intense concussive force, however, carmot be 

 measured by rules governing sound ordinarily, 

 since it has been found by experience, that, in- 

 stead of finding himself surrounded near the 

 breech of the gun by highly rarified air, the ex- 

 perimenter may be subjected to quite an opposite 

 condition ; namely, one of condensation. In the 

 former, intra-tympanic air would rush outwardly, 

 carrying the drum-head before it. In confirma- 



