Dr. Alison on the Differential Stethophone. 



393 



possible means of hearing, with two ears at ouce, sounds emanating 

 from the same region or surface, for the sides of the head can he 

 applied, of course, to the same sounding surface only in turn or 

 succession. With this instrument we, as it were, place our ears in 

 our hands, apply them where we choose, and listen with thefti both 

 at adjacent or distant points of the same surface, at one and the 

 same instant of time. 



It is not unlikely that the property which the stethophone pos- 

 sesses of pointing out with precision where sound is most intense, 

 may be very usefully employed. It seems possible that it might be 

 turned to account in discovering the points where operations in mili- 

 tary mining may be going on. 



It is, however, in the practice of medicine only that the differential 

 stethophone has been hitlierto applied ; and it may be here permitted 

 to me to point to some of the chief purposes for which it is adapted, 

 and for which it has been employed. 



In respect to respiration, we may compare at once, and without 

 the inconvenience of moving the head, or the ordinary stetho- 

 scope, from place to place, the extent of the respiratory sounds 

 in different parts, so that a very minute difference, an excess in one 

 part or a deficiency in another, may with certainty be discovered. 

 Differences in quality, such as softness or roughness, are readily 

 recognized. The increased length and loudness in one part is accu- 

 rately contrasted with the healthy conditions of another part. In 

 cases where the aspiration has been very full in one place, in order 

 to compensate for deficiency in another place, and where the ea;pira- 

 tion was long and coarse in the deficient part, I have heard the in- 

 spiratory sound only in one ear, and the extjiratory sound in the 

 other ear. The sounds were respectively restricted to the two parts ; 

 and they alternated in a very marked manner. One part has re- 

 mained silent wbile the other has been heard to sound ; and this has 

 been silenced when the other has awoke the ear. 



The diagram represents the soimds occurring alternately in two 

 sides of the chest in a consumptive patient. The dark spots repre- 

 sent the sounds. 



Healthy. 

 Riglit side of chest. 



Unhealtliy. 

 Left side of chest. 



Tlic inllncncc wliicli the acts of respiration exert in heightening 

 and lowering the murmurs in veins, say of the neck, in persons 

 affected with a thin and watery condition of blood, is well exhibited 



