and care, the true sound is liable to be masked by a clack of the air beneath. To do justice to the quality of sound, the pleximeter should gently compress and measurably displace any tissues adapted to prevent the natural vibrations of the part percussed.

In accomplishing this end, nothing is found to answer so well as one of the fingers. For convenience, we take either the index. or the middle finger of the left hand. This is easily adapted to any irregularities of the surface to which it is applied, and is, in every respect, decidedly superior to any artificial instrument that human ingenuity can invent.

Ordinarily, the palmar surface of the finger should be presented to the body of the patient, and the percussion should be made on the dorsal surface. The reason of this direction is, the softer portion of the finger best adapts itself and covers the part from which we wish to gather the sound; while the harder portion, by means of its density, best conveys and represents the sound to the ear. In some conditions, however, it is convenient and desirable to reverse the finger. By its natural curve, for instance, it better fits certain depressions, as those above or behind the clavicle, some places between the ribs, and other parts; and the advantage gained in the matter of adaptation may more than counterbalance any consequent defect in the communication of the sound.

In percussing certain symmetrical portions of the body—of the chest particularly-,when we wish to compare one sound with the other, a caution or two must be observed;-Do not make one of the above-named applications of the finger to one part, and the other to the other part. It may prevent a discriminating comparison of the sounds. Be careful, also, to press the finger equally firm, and to apply it in analogous directions, in both instances, as well as on analogous portions. In comparing the two sides of the chest, for instance, we must percuss at equal distances from the sternum, and in corresponding intercostal spaces or over corresponding ribs.

For the purpose of giving the blow in percussion, an instrument has been contrived by Dr. Jacob Bigelow of Boston, Mass. It consists of a handle, about six inches in length, made of whalebone or tough but slightly elastic wood, to one extremity of which is attached a ball, about an inch in diameter. This ball is made in

ternally of some solid substance, and covered pretty thickly with velvet or buckskin, so as to be externally quite elastic. Besides, however, the trouble of preparing it and keeping it by one for use, it muffles the sound, and forbids an accurate discrimination.

Incomparably the best percussor every one has received as the boon of nature. It is found in the right hand simply. Of this, we may use directly one or both of the index and middle fingers; or with these two we may unite, also, the ring finger, taking care to place them so that their extremities shall form a line, and all be equally impressed on the finger of the left hand used as a pleximeter. The phalanges should be so arranged that the third set shall form nearly a right angle with the first, and constitute the head, so to say, of a light mallet or hammer. In that position they must be firmly retained. Of course, the blow brings only the extremities of the fingers in contact with the pleximeter.

The act of percussion should be performed, as far as possible, without any motion of the arm, or even of the forearm. The wrist becomes the moveable point or hinge, and the metacarpus the handle of the percussor. By using any portion of the arm, we almost necessarily strike a blow too firm for the convenience of the patient or for delicacy of sound. We almost necessarily, too, allow the contact to exist for a moment instead of instantly withdrawing the fingers. The consequence is, we prevent the proper vibration of the parts concerned, and thereby obscure the sound. When motion is made from the wrist only, it is much more easy to give suddenness to the impulsion, and thus to favor the reaction of elasticity.

When percussing over thick adipose tissue or tissue infiltrated with serum, we must necessarily use more force than is desirable where the parietes are thin and the internal organs delicately sensitive. In such a case, we should not fail to employ together, the three fingers before named; but we must be particularly careful to have them suddenly rebound after the blow. It is the quickness, rather than the force of the impulsion, which gives the proper clearness and sharpness to the sound. On the contrary, when we are concerned with tissues unusually thin,-when, for instance, we are percussing the chests of children, or of persons greatly

emaciated, the degree of elacticity is such as to render preferable the use of but a single finger.

Percussion is extensively applicable in detecting the condition of organs both in the thorax and in the abdomen. Its importance, however, is much greater, in the former case than in the latter.

The degree of resonance or dulness is different in different portions of the body, while in health. In the abdomen, the alimentary canal is ordinarily distended partly with gaseous substances; and, hence, percussion directly over this canal gives considerable resonance. On the other hand, over the solid viscera,-over the liver, for instance, we get a degree of dulness.

In the thorax, the resonance, cæteris paribus, is greatest over those portions of the lungs, in which the vesicles and smallest bronchial tubes are most numerous, because the thin parietes of those cells and tubes favor the vibration of air within them; while, on the other hand, the thick and rigid walls of the large bronchial tubes allow of comparatively little vibration, and render, in percussion, a degree of dulness. The sound, however, is very much modified by the character of the parietes of that part of the thorax on which we percuss. Thickness of muscular, adipose, or osseous substance creates dulness. The heart is a substance much more solid than the lungs. Hence percussion on the præcordia gives a duller sound than over any portion of the lungs.

In general, the resonance, the thoracic viscera being normal, is greatest in the axillæ, on the sides, along the lower part of the anterior margin of the chest, and below the scapulæ, posteriorly; while, at the summit and at the root of the lungs, the sound is comparatively dull. Where a portion of the left lung overlaps the heart, the sound, of course, is intermediate between the natural dulness at the centre of the præcordia, and the resonance where the vesicles are most abundant.

In judging whether there is disease of any viscus, we compare, in our minds, the sounds heard with such as we believe health ought to render. Where, too, there are analogous parts, we directly compare the sound of one part with that of the other.

CHAPTER IX.

AUSCULTATION.

The most important of all the means of physical diagnosis is auscultation. By this is meant the art of detecting the condition of internal organs by means of the sounds produced by vital internal movements. It was invented by Laennec. Any organ, which, in either of the grand cavities of the body, yields a sound, when the purposes of the vital economy are being fulfilled, may be examined by auscultation; and, by the existence and the quality of the sound, knowledge is often gained respecting the healthy or the diseased condition of that organ.

In regard to the abdomen, however, this art is of less practical value than percussion. The sound of the fœtal heart in an advanced state of pregnancy may be recognized by auscultation. So, too, may a peculiar thrill of the larger arteries; and certain intestinal movements in the abdomen give evidence of peculiar internal conditions. But it is to the viscera of the thorax that it principally applies. By it various conditions of the lungs and of the heart are determined with much accuracy. These, in subsequent pages, are to be made the subject of careful and extended remarks.

SECTION I.

THE MODE OF APPLYING AUSCULTATION.

Auscultation is either mediate or immediate. Mediate auscultation supposes, for the purpose of conveying the sound, the intervention of a tube between the part of the patient to be ausculted and the ear of the auscultator. Immediate auscultation, on the contrary, supposes the ear to be applied directly to the part to be examined.

Laennec employed mediate auscultation. Having, accidentally, in a sense, rolled a piece of paper into the form of a cylinder and applied it to the chest of a person whose heart was diseased, he

was struck with the distinctness of the cardiac sound; and this gave origin to the systematic use of an acoustic instrument, which took the name stethoscope, from its being primarily and principally applied to examinations of thoracic viscera.

Since the first adoption of mediate percussion, stethoscopes of various materials and various forms have been employed. The kind of instrument originally used by Laennec was crude and unwieldly, and, with great propriety, has been laid entirely aside.

The sounds to be communicated to the ear are variously created, and require a somewhat peculiar instrument of conduction. Those originating in solids are best transmitted by a solid; and those originating in air are best transmitted by air. Indeed, the more nearly the conducting substance agrees, in density and structure, with that giving origin to the sound, the better is the sound conducted.

For a stethoscope, then, we want a substance which will convey sounds such as are generated by the solids within the cavities of the human body, particularly those within the thorax. This purpose may be tolerably well secured by any one of several different kinds of material; but by no one better, perhaps, than by some wood, of a light kind but having firm longitudinal fibres. Cedar, hard pine, mahogany, &c., answer very well; but none is better than the first-named.

But several of the most important sounds to be regarded in auscultation, are made in air, and therefore require an aerial conductor; that is, they must be conveyed through a column of air. To secure this object, a cylinder is perforated from one extremity to the other so as to give a calibre of about one fourth of an inch in diameter. The column of air rising in this will conduct aerial sounds, such as those created in the thorax, by the respiration, the voice, and the cough.

One extremity, however, of a calibre of the above-named size can come in contact, at any one time, with only a very small spot of surface, and, consequently, can successfully transmit those sounds only which are produced at or near that point of contact. This limitation, on condition that the sound is distinctly audible, secures an advantage in not allowing different sounds from an extended space to reach the ear simultaneously. For ordinary