1896 - 97 .] Dr Albert A. Gray on Direction of Sound. 447 
intensity did not vary in the least even with repeated experiments. 
From this case, therefore, it is evident that the reflex does not 
occur through mechanical irritation of the branches of the fifth 
nerve in the tympanic membrane. 
The experiment was again performed upon a brother of the 
case just narrated. He suffered from perforation and suppuration 
of both ears, but with treatment the suppuration was cured; and 
I prevented adhesions forming, so that he hears well in spite of 
the perforations. When the experiments were performed on 
him the same results were obtained as from individuals with 
normal ears. 
It may be concluded, therefore, that stimulation of the nerve 
within the labyrinth of one ear produces a change in some 
structure in the opposite ear which enables the latter to hear 
sound more acutely. The next step is to consider what change 
occurs in the ear opposite that in which the stimulus has been 
produced by pushing the malleus (and other bonelets) inwards. 
Poliak (Med. Jahrbucher, Wien, Oct. 1892, p. 308) has shown 
that when one ear is stimulated by a sound the tensor tympanum 
of that ear and also of the opposite ear are set in action ; he has 
further shown that this reflex is produced better by high notes 
than by low ones. Another fact of importance is that observed 
by Urbantschitsch, that stimulation of one ear by sound increases 
the hearing power of the opposite ear; in other words, binaural 
audition is more acute than monaural. Urbantschitsch attributes 
this fact to the passing of auditory sensation from the cerebral 
cortical centre of one side to that of the other, and hence the 
intensity of the sound appears to be greater. In the light, how- 
ever, of my experiments above described, I would be inclined to 
attribute the increased hearing power in the case of binaural 
hearing to reflex action of the intrinsic muscles of the ear. In 
these experiments, at anyrate, the increase of the intensity of the 
sound cannot be due to reflex sensation from one cortical auditory 
centre to the other, because the stimulus applied to one ear was 
not auditory at all. 
When we come to the question as to what structures take 
part in the reflex, we have two matters to consider: (1) Evidence 
of a similar reflex occurring between the two ears; (2) the 
