The instrument which has received the name of stethoscope (derived from στῆθος, pectus, and σκοπέω, speculor or exploro), was invented by M. Laennec; and the idea of it occurred to him from reflecting on the well-known fact in acoustics, that the impression of sound is augmented, when conveyed through certain solid bodies, as, when we hear the scratch of a pin at one end of a piece of wood, on applying our ear to the other. In examining a disease of the heart, he first made use of a quire of paper rolled into a cylindrical form, and, satisfied with the result, he soon proceeded to investigate the various phenomena afforded by the vibrations of air within the chest, through the medium of the stethoscope; which he constructed from the suggestion already mentioned.
After making various experiments as to the form of the instrument, and the kind of material, he found most success in using a wood of medium density, as cedar. This proves very favourable for conveying the delicate vibrations caused by respiration, from the walls of the chest to the ear. For the information of those who have never seen the instrument, I may observe, that it is of cylindrical form, shorter in length, but larger in diameter, than the common flute. It has a cylindrical perforation throughout its whole length, and is divided into two parts for the convenience of using the whole or half length, according to the situation of the patient in bed. The end of each part terminates in a funnel-shaped cavity, the one to receive the separate half of the instrument, and the other to receive the part acting as a stopper, which latter has a short pipe, made of brass or silver to enter the bore of the cylinder.
The instrument is used without the stopper, when employed to ascertain the state of respiration; and with it, either to examine the action of the heart, or the signs afforded by the voice, in certain states of disease affecting the lungs, or the pleural membrane.
In using the stethoscope, care is to be taken that it is kept perfectly flat upon the part to which it is applied, in order that sound may not escape, nor air be admitted; for which purpose it is convenient to hold it at its lower part, while the other end (with the even surface) should be in close contact with the ear, so that the aperture of the instrument be in direct communication with the internal ear. Silk covering, as causing a creaking sort of noise, and thick dress, as obscuring the sound of respiration, should be removed; but the linen or flannel dress may remain on the person without disadvantage. A beginner will be very apt to fail in his early trials, from inattention to some of these points, and from the difficulty which at first attends the tuition of the ear.
A skilful use of the instrument requires much practice. It is not, as some may imagine, a simple matter of hearing a delicate sound. Tact is necessary, but this will be acquired by perseverance. For two days of my own study, I was frequently at a loss to distinguish the peculiar sound or murmur of respiration, and almost despaired of success. I mention this circumstance, that others beginning with the practice of this instrument, may not be deterred from proceeding, by the awkwardness and disappointment which they at first encounter.
At La Charité, the best informed students are great enthusiasts in the practice of this discovery, and regard it as an indispensable source of information in the diagnosis of the diseases of the chest. Such reliance on the stethoscope is very natural, when constant proofs are afforded of the accuracy of opinion formed by M. Laennec, and others, who are competent in using it. The proofs of sure diagnosis are derived from dissection; as, necessarily, the diseases of the lungs and of the heart, allow frequent opportunity of obtaining this test of the physicians’ judgment.
I will relate one instance which came within my immediate knowledge; although equally strong proofs are so numerous, that the regular observer can no more doubt the merits of the stethoscope, than the mathematician can distrust a resolved problem.
In the clinical record of a case of consumption, M. Laennec had stated his opinion, that the upper portion of one lung was the exclusive seat of ulceration. The patient died, and examination was made. The lungs were removed from the chest, and the expected evidence of disease did not appear. M. Laennec, making a closer inspection, discovered that a small part of the upper lobe had been left in the chest, and upon its removal, the ulceration was found exactly as he had predicted.
Some persons assert, that the discovery of the precise situation of an ulceration of the lung is merely a matter of curiosity, as when arising from tubercles, they consider it incurable; but surely this is not a good medical objection. Our art may improve so as to enable us to remedy these evils; and assuredly our chance of success will be increased by a knowledge of the seat of tubercles, their commencement, and their progress. While those persons therefore who have made use of the stethoscope with success, praise it in terms which may seem romantic and beyond the truth; others, and perhaps those chiefly who have never even seen the instrument, speak of it with ridicule, or censure it as a piece of quackery.
It is not just that any one wholly unacquainted with the stethoscope, should assume the right of pronouncing an opinion on its properties. It certainly does not deserve the imputation of quackery; for this opprobrium belongs to the concealment of a remedy; or to some mysterious plan of practice, studiously kept secret for the mere purpose of gain. Candour is most honourable to the educated mind; and to be sensible of our ignorance on any particular subject, is the first step to the acquirement of knowledge.