In exploring the chest it is essential to contrast the signs observed in corresponding parts on each side, because there can be no absolute standard of comparison applicable to all cases: the differences must be noted as the examination proceeds, but no conclusions ought to be drawn from them till the examination be completed. Regard must first be had to the external symmetry, and then to the movement of its various parts in the act of breath ing; and we may at the same time observe whether the vocal fremitus or thrill be equally perceived by the hand on either side when the patient speaks. Deviations of form serve either as indi cations of bygone disease, such as the rachitic distortion of the ribs in childhood, the scrofulous caries of the spine, or the lateral curvature of imperfect development; or as signs of still existing changes in the respiratory organs of some duration ; for example, the rounded chest of emphysema, or the flattened one of phthisis, or the lateral distension of pleural effusion. Alterations in move ment, again, if we exclude the effects of muscular paralysis, and anchylosis of ribs, have more direct bearing on the condition of the lungs with reference to their power of expansion : and, con trary to what might have been expected in so mobile an organ the actual position of the diseased portion is often very accurately pointed out by deficient movement of the ribs over that particular part of the lung.
These points are not of very great importance in diagnosis, because of necessity disease has proceeded to a considerable extent before it becomes distinctly manifested in the form and movements of the chest. But they serve. when present, to !Five certain impressions which aid the practitioner in forming a rapid diagnosis, and therefore demand the attention of the student ; and they also serve sometimes to correct an error into which we might inad vertently fall if they were overlooked. Distortion. especially that produced by spinal curvature, is very liable to render the ordinary physical signs falla cious. and due allowance must be made for this circumstance in forming a judgment upon them. Among the more important points with which the student should make himself familiar, we may enumerate the following: (1) The upper ribs sink away from the clavicle, become flattened and motionless in advancing phthisis, while in many cases the movement of the lower ones is not interfered with. and as a gerieral rule the change is more evident on one side than the other. .(2) In emphysema the opposite condition prevails; the chest is full and rounded, the ribs stand out, but have a very slight range of movement, and the inspiratory effort is marked by powerful traction of the muscles of the neck ; the movement of the lower part of the chest is very often inward in place of outward during inspiration : the contrast between the opposite sides is seldom very great. (3) When one side only bulges. and the intercostal spaces are obliterated, the effect is usually produced by distension of the pleura with fluid or air. (4) Without any deviation in form, a remark
able stillness and want of movement may be observed in the wilily stage of inflammation of the pleura : and when the disease is very limited, this effect may he quite local. (f') A very striking change may be noticed in the con traction of one side, when there is no distortion of the spine, as a consequence of previously existing empyema. (6) The contrast between thoracic breathing, when the diaphragm is not moved, in peritonitis. and abdominal breathing when all the respiratory nerves, except the phrenic. are paralyzed by injury of the upper part of the spinal cord, is well worthy of observation ; its minor degrees ought also to be considered in diagnosis.
b. Percussion.—The operator elicits the sound by his own act, his object being to ascertain the relative amount and position of the solid or fluid and gaseous contents of the thorax. The stroke should be short and sharp, and not more forcible than is necessary to produce a distinct sound, except when the character of the resonance is doubtful, and then it may become needful to compare the sound produced by firmer percussion with that which results from a gentler tap. The finger used as a pleximeter to receive the stroke, should be level, and, when comparing different parts, should occupy as nearly as possible the same position with refer ence to the ribs, whether parallel or transverse—upon the bone or in the interspace. The information percussion conveys is de rived from two sources : the resonance or clearness of the sound produced, and the sense of greater or less resistance to the finger ; and it is to be remembered that these vary, not only with the condition of the lung itself, but also with. that of the parietes, being remarkably modified by the elasticity of the ribs. In order to obtain trustworthy results, it is essential to compare the sound produced at corresponding parts on either side; and also to con trast the difference between the upper and lower regions on one side with that on the other.
Percussion indicates either that there is an excess of solid and fluid com pared with gaseous contents or the contrary, as the sound is dull and dead and the resistance great, or the sound clear and resonant and the resistance slight; and these conditions may be either beyond what is consistent with perfect health under any circumstances. or merely different from that of the surrounding parts or the corresponding parts of the other side of the chest. It is quite true that various morbid states are associated with unusual sounds on percussion, which become sensible to an experienced ear ; but, except in the extremes of tympanitic resonance and remarkable dulness, they are not such as can be well explained to the student, because there is no absolute standard from which their variations can be calculated.