66 Dr. Scott Alison, [Feb. 18, 



If there be a material diiFerence at the two spots examined, sound is 

 heard only by that ear connected with the more intense point. The 

 test is absolute ; for in one ear there is no hearing, and in the other 

 there is hearing. There is consequently no room for error in judgment 

 as to degree, as in the case of consecutive observations with one ear 

 only, with the ordinary stethoscope. 



The human ear being capable of hearing many sounds at the same 

 moment, (if one be not extremely intense,) and as the principle so to 

 speak of restriction of hearing to the favoured ear holds in the case of 

 all, it follows that if one can be favoured with a major impression of 

 fifty sounds, they shall all be heard through that ear, and through that 

 ear only. And if some of these fifty sounds be carried in major inten- 

 sity to one ear and some in major intensity to the other ear, some of 

 these sounds will be exclusively heard through one ear, and some 

 exclusively through the other ear ; a division of sounds thus virtually 

 taking place. Indeed, if we possessed fifty ears, and if of fifty sounds 

 one could be carried in a major intensity to each of these fifty ears, 

 each of the fifty sounds would be heard exclusively through one ear, 

 i.e. each ear would hear one sound exclusively. 



This apparent division of sounds may be effected by placing a 

 watch upon a musical box. If both cups of the stethophone be placed 

 so as to receive sound from these bodies equally well, both sounds will 

 be perceived through both ears, and if one cup be placed nearer these 

 two bodies than the other cup, both sounds will be heard in the ear con- 

 nected with this cup ; but if one cup be held a little nearer the musical 

 box than the other cup, and if this other cup be held a little nearer 

 the watch, i.e. if one cup be a little favoured in respect of one sound- 

 ing body, and the other cup be a little favoured in respect of that of 

 the other sounding body, the musical box will be heard through that 

 ear only which is favoured in respect of it, and the watch will be heard 

 exclusively through that ear that is favoured in respect of that body. 

 "When two murmurs occur at the heart, one at the base and another at 

 the apex, possessing as they usually do different characters, (say one 

 being '* blowing " and the other being *' rasping,") and they blend 

 together, they may be thus sensorially separated by placing one cup at 

 the base, and the other at the apex, points of major intensity of the two 

 murmurs respectively. 



Of the amount of difference which shall suffice to render one ear as 

 it were sensationless and to effect a monopoly of sensation in the 

 other, it is difficult to speak with great precision. The difference 

 must be considerable, but need not be very great. In the case of a 

 watch, if one cup be placed fully on the watch, and the other one- 

 third or one-half off" it, sensation is limited to the ear connected with 

 the first ; if the cup wholly on the watch be now moved off" the watch, 

 but kept within half an inch of it, sensation is limited to the other ear ; 

 and if the cup half or one-third off the watch be now moved wholly off* it, 

 to the distance of an inch or more, sensation is again transferred to the 

 other ear. Transitions of sensation may be thus indefinitely carried 



