Bauhaus-Universität Weimar

its ordinary construction, the stethoscope conducts sounds to the ear in 
two ways,—namely, by its solid portion, which receives the sonorous 
undulations from the solid body yielding the sound, and transmits them 
to the solid parts of the head around the organ of hearing; and by the 
column of air in its interior, which receives the sound also from the 
solid body, but transmits them through the air of the meatus externus 
to the membrana tympani. The interior column of air is a much less 
effective conducting medium than the wooden tube around, on account 
of the difficulty attending the transition of sonorous vibrations from 
solids to air, but it is of use by its resonance. Hence a simple solid rod 
does not answer the purpose of a stethoscope. Sounds may be heard, 
however, very distinctly by means of a mere rod, if the ear'be stopped 
by a plug of chewed paper, and the one end of the rod be applied, not 
to the plug itself, on account of the sound of friction which would be 
produced, but to the external ear near it. Here the sonorous undula¬ 
tions are communicated more completely to the walls of the external 
meatus by means of the plug, and are thence propagated to the mem¬ 
brana tympani. 
In cases of deafness, where the undulations of the air do not make 
sufficient impression even with the aid of an ear-trumpet, it is some¬ 
times of use to convert the undulations of the air into undulations of 
solid bodies, and conduct these to the organ of hearing by solid media. 
This is best effected, when the object is to hear the voice of another 
person, by causing him to direct his voice into a basin, whence it is 
conducted to the ear by a rod held between the teeth, or applied to a 
plug inserted into the meatus auditorius of the deaf person.* 
3. Jlcoustic properties of the labyrinth. 
The fluid of the labyrinth, aquula Cotunnii, or perilymph, first claims 
our attention as the most general and constant of the acoustic provisions 
of the labyrinth. In all forms of organs of hearing, the sonorous vibra¬ 
tions affect the auditory nerve through the medium of a fluid. On this 
account, the vibration of the particles in the nerve itself will probably 
be much more uniform in character than if merelv the surfaces of the 
nerve had been in contact with solid parts; in which case, the more in¬ 
ternal particles of the nerve, being distant from the surface of the solid 
bone, would be acted on in a different manner from the more superficial 
particles. Muncke (Gehler’s Physik. Wörterb. iv. 2, p. 1211,) remarks, 
with reference to the fluid of the labyrinth, that water, although ill- 
adapted for the generation of sound, is nevertheless an excellent con¬ 
ductor of it, even a better one than air. This I cannot admit; it can 
be true only with respect to the velocity of the propagation of sound; 
the undulations of air are conducted with least loss of intensity by air, 
those of water bv water. 
___ * 
The passages called aqueducts appear to me to merit no consideration 
in relation to the physiology of hearing. They contain neither mem¬ 
branous canals nor fluid, nor even venous trunks, but merely serve to 
bring the periosteum of the cranial bones and dura mater into connection 
* All the experiments of this kind on the hearing of deaf persons by means of solid conduc¬ 
tors, are collected in the works of Chladni, (Akustik, p. 262, 286,) and Lincke (op. cit. p. 530.)


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