68 Dr. B. W. Richardson on the Audiometer. (_May 15, 



catch all the sound lying between 130° and 107°, until he could 

 remember what he had to listen for. By practising him then to 

 detect the lowest sound that he was physically capable of receiving, I 

 got him to detect this one sound more readily than those which came 

 higher up. By further practice all the intervening sounds became 

 audible with equal facility. These facts, which have been confirmed 

 by another observation on a different person, seem to me to indicate 

 that deafness from imperfection of the tympanum or other parts of the 

 organ of hearing may be increased, beyond the mere physical failure, 

 either from some lost power of automatic adjustment in the auditory 

 apparatus, or from failure of receptive power in the cerebrum itself, 

 so that the memory, rendered imperfect, is slow to assist the listener 

 until by exercise of function its readiness is restored. 



Influence of Atmospheric Pressure. 



By use of the audiometer, the influence of atmospheric pressure on 

 hearing is detectable. In my own case when the barometer is at 80 

 I can hear on both sides close down to zero ; but below 30 I fail by 

 2° on the left side to reach zero. In another person a similar failure 

 extends to a loss of 4°-. 



Observations on Lower Animals. 



I have tried to determine in some of the lower animals whether 

 there is the same sense of hearing as in man. In most animals it is 

 difficult to obtain sufficient quietude to enable the observer to gather 

 from expression or movement of the animal the information sought for. 

 In two dogs, one a terrier, the other a field spaniel, I succeeded in 

 making some good -observations, and in them the range of hearing 

 power seemed to be distinctly lower than it is in the human subject 

 who has perfect hearing. In both these animals, which were healthy, 

 and in the prime of life, the first indication of the detection of 

 sound commenced at 10 G on the scale. The detection was evidenced 

 by the sudden expression of listening, by a slight change of position, 

 and. a slight dilatation of the pupils. This detection was clearly made 

 on the instant, as if the sharp line of hearing were the same in them 

 as it is in the higher animal. 



Practical Memoranda. 



1. The audiometer will, I think, be an essential in all physical 

 examinations of men who are undergoing examination as to their fit- 

 ness for special services requiring perfect hearing, such as soldiers, 

 sentries, railway officials, and the like. 



2. The instrument will be of great use to the physician in determin- 



