An historic sketch of the stethoscope
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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 a half.
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 have 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. Previous 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 stethoscope made 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 the 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 described 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 improvement in this respect still remains. The attachment of a rim 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 in the 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 that 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 the 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 by 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 sounds 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 through 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 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 compressed, and then firm and even pressure made against the chest-wall, when the pressure upon the bulb 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 my 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 general use.
Dr. Platt said it might be that his lack of success with Dr. Cammann's modified instrument, with which he had been pleased at first, 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, especially in auscultatory percussion. But an objection, as it seemed to him, was that the suction of the bulb displaced the skin and subcutaneous tissue somewhat interfering with the transmission of sound and at the same time there seemed to 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 the inside and the outside chambers seemed to act as resonators, 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.