AN HISTORIC SKETCH OF THE STETHOSCOPE
By D.M. CAMMANN, M.D.
New York Medical Journal
April 24, 1886
Mr. President and Gentleman:
I will not consider whether the idea
of the stethoscope originated with Hippocrates, Bayle, Hook, or
Laennec. Laennec made the idea practically useful. His first instrument
was a cylinder of paper compactly rolled and kept in shape by
paste. The longitudinal aperture, always left in the center of
the paper thus rolled, led accidentally, in his hands, to its
discovery. The stethoscope that he subsequently adopted was a
cylinder of wood, an inch and a half in diameter and a foot long,
perforated longitudinally by a bore three lines wide and hollowed
out into a funnel shape at one end to the depth of an inch and
Piorry introduced a more slender instrument
with ivory cap, and later this was altered and made of wood only.
Instruments with a trumpet-shaped end were evised by Dr. Williams
about 1843. Since then the modifications of the monaural stethoscope
have been numerous and more than thirty may be found scattered
through the files of medical journals. Some hav been hollow and
others solid. They have been made of wood, metal, vulcanite, papier-mache,
and other materials, either alone or in combination. Among others
may be mentioned the stethoscopes of Walshe, Quain, Loomis, Cammann,
and Clark. Preious to 1850 M. Landouzy, of Paris, constructed
a binaural instrument having a number of gum-elastic tubes by
which several persons could listen at once. This required three
hands for its application and was not found of any prectical use.
many years before this, Dr. Williams, of London, was accustomed
to a stethoscpemade of two metal tubes attached to the bell of
an ordinary stethoscope with flat earpieces. This conveyed sounds
with exaggerated intensity , but was inflexible and awkward of
application. The double stethoscope of Dr. leared. shown at the
International Exhibition of 1851, was a great improvement. It
consisted of two gutta-percha tubes attached to teh ear-pieces.
These tubes, being drawn apart and applied to the ears, were kept
in place by their own elasticity.
In 1851, Dr. Marsh, of Cincinnatti,
patented a double stethoscope. This had a membrane stretching
over its objective end, and two gum-elastic tubes leading from
the chest-piece to the ears. In this instrument the earpieces
were inconvenient; it required two hands for its application,
and the sounds conveyed were muffled and confused. These circumstances
rendered it of little value. Dr. Cammann was familiar with these
two instruments, Landouzy's and Marsh's, and it was chiefly the
fact that Marsh's was patented which introduced Dr. Cammann to
devise a better one and give it freely to the profession. His
binaural stethoscope, therefore, was not a new invention, but
was, and is now, the best instrument of the kind devised. It was
only after much labor and considerable expense that a satisfactory
result was attained. The instrument was perfected in 1852, and
descrivbed in the "New York Medical Times" of January,
1855. It is light, durable, easily carried, and a good conductor
of sound. The ear-pieces are the best that have been devised ,
but room for improvementin this respect still remains. The attachment
of a rikm of soft rubber to the chest-piece, as devised by Dr.
Snelling, is of advantage in applying it more closely to the inequalities
of the chest. In most of the instruments now made the rubber band
which serves to draw the two tubes together is replaced by a spring.
In the latest improvement the spring is placed in the screw which
binds the tubes together.
Great care is required int eh construction
of the stethoscope, and many defective ones are sold. The knobs
on the ear-pieces must neither be too large nor too small; if
too small, they cause pain by their pressure; if to large, they
allow external sounds to enter the ear. The tubes must be curved
so tht they enter the ear in the direction of the meatus. The
flexible tubes must not be too stiff nor too long, and their movements
must be noiseless.
A considerable variety of flexible
stethoscopes is now in use. They may be generally described as
consisting of a chest-piece, long flexible rubber tubes, and round
ear-pieces. The ear-pieces are held in place wither by being firmly
pressed into the meatus, or by a spring passing over the head
or under the chin. A flexible stethoscope is described by Mr.
Brown in the "Lancet," March 3, 1877, in which the ear-pieces
are oval. When placed in teh ear with the long diameter vertical,
they are said to remain readily in position. The differential
stethoscope of Scott Alison is similar in mechanism to Cammann's,
but had two chest-pieces--one for each ear, enabling the sounds
from different regions of the chest ro be conveyed to the ears
at the same time. The value of this stethoscope has been a matter
of considerable controversy. It is claimed that it is capable
of offering aid in diagnosis in two ways:(1) By the consecutive
observation of the sounds of two regions of the chest byt he different
ears, and (2) by their simultaneous observation. We can listen
over different parts of the chest with either ear by removing
one or the other chest-piece, and thus can compare the counds
heard over different regions with great rapidity, and detect slight
differences which might escape us in a prolonged examination.
If we listen at two points simultaneously, and sound of the same
quality but of different intensity is heard at each point, the
weaker is eclipsed or nullified, and thus, by the eclipsing of
a weaker impression through one ear by a stronger impression throuh
the other, differences may be recognized which might otherwise
escape detection. When hearing is impaired in one ear, this stethoscope
can not be used satisfactorily.
The hydrophone is another instrument
devised by Alison. It consists of an India-rubber bag about the
size of a large watch and filled with water. Another inventor
had previously constructed a wooden instrument filled with water,
but it was not practically useful. Alison found that when water
was interposed between two conducting media, sound was conveyed
to the ear with greater intensity. The hydrophone may be employed
as an instrument by itself or in aid of the stethoscope. The increase
of sound varies much with the material through which it is conducted.
With firm, non-flexible, or solid stethoscopes, the hydrophone
acts as a damper and diminishes sound. The more a stethoscope
becomes a mere air instrument and departs from the character of
a solid conducting medium, the more water adds to its acoustic
value. This may explain why such opposite results have been obtained
in the use of the hydrophone by different observers.
Some years ago the idea of a stethoscope
containing an air-chamber in the chest-piece was suggested by
Dr. Leaming. In 1884 ("Diseases of the Heart," by Constantin
Paul;william Wood &Co., 1884) Dr. Constantin Paul devised
a stethoscope with two flexible tubes leading to the ears, and
a hollow chamber in the chest-piece, connected with a rubber bulb
by a long flexible tube. If the air in the hollow chamber is exhausted,
the instrument is held firmly against the chest.
My modification of Cammann's stethoscope
("New York Medical Journal," January 3, 1885) can be
screwed on in place of the usual chest-piece.
In the pectoral end is an air-chamber
which is completely closed by pressure against the chest, the
inner and outer rims of the chamber being on the same level. Connected
with this chamber by a small tubular opening is a rubber bulb
through which the the sound conducting tube passes. By pressure
upon this bulb when the instrument is held in position, the air
is exhausted in the hollow chamber, and the stethoscope is held
firmly to the chest-wall. It requires some practice to use this
modification successfully. The bulb should be strongly sompressed,
and then frim and even pressure made against the chest-wall, when
the pressure upon the buld should be at once relaxed. If this
be done, the instrument is held in place during the examination,
or at least for a considerable time.
I have used this instrument for more
than a year, and am confirmed in y opinion of its value. By its
use the closest possible contact is obtained with the parts under
examination. Sound, in passing to the ear, is conveyed through
two hollow chambers--one in the chest-piece, and the rubber bulb--both
of which act as resonators and increase its intensity. Not only
is the intensity of the sounds increased, but their true quality
is better appreciated. Another advantage is that the two hands
of the auscultator are left free to practice the method of auscultatory
percussion--a method which has not yet received the attention
it deserves, and which, it is to be hoped, will come into more
Dr. Platt said it might be that his
lack of success with Dr. Cammann's modified instrument, with which
he had been pleased a tfirst, had been due to the fact that he
had not accustomed himself sufficiently to it. It was, of course,
very convenient to have both hands at liberty, expecially in auscultatory
percussion. But an objection, as it seemed to him, was that the
suction of the bulb displaced the skin and subcutaneous tissuem
somewhat interfering with the transmission of soundm and at the
same time there seeme dto be a continuous slight roaring sound
produced which he could not connect with any physiological state.
Dr. E.D. Hudson asked further regarding
the principle governing the difference in action of the improved
and that of the original Cammann.
Dr. Cammann replied that the air reached
the ear directly from the part of the chest to which the instrument
was applied, as in the unmodified stethoscope, but hte inside
and the outside chambers seemed to act a sresonators, and as a
matter of fact the intensity of the sound was increased.
The President remarked that the double
stethoscope undoubtedly did intensify the sound, but it also changed
the quality , which was a disadvantage in studying pulmonary disorders.
But, if one wished to compare cardiac sounds which were in close
approximation to one another, it would enable the listener to
locate the point of maximum intensity much better than with the
naked ear. He had used Dr. Cammann's modified instrument somewhat,
and had got the impression that it was only of advantage in auscultatory
percussion. The ordinary stethoscope without the bulb was much
more satisfactory to him generally than the modified one, but
that might be due to the fact that he had not become accustomed
to Dr. Cammann's modification.