Methods. Tissues as good and bad conductors of sound. Immediate, mediate percussion. Bilateral symmetry and divergence. Effect of building, race, etc. Horse, left side, right. Ox, left side, right. Effect of 1st and 3d stomachs, liver, etc. Sheep, diaphragm, heart. Pig, fat, lean, heart. Dog, method. Birds, back, ribs. In disease, increase, decrease, absence of resonance, in large area, in patches. Crack pot sound.
This consists in striking the walls of the chest so as to bring out the resonance of the parts. In proportion as we tap gently with the tip of the finger or strike forcibly with the closed fist will we elicit the sounds from the superficial or the deeper parts of the lung. Hence slight blows only must be used when the lung tissue is thin, to avoid bringing out the resonance from the deeper seated organs, and both must be resorted to when the lung is thick to ascertain its condition at the various depths. Where a moderate force is requisite the four fingers and thumb of the right hand are brought together in a line and the weight of the hand as moved from the wrist is employed to bring out the sound. The ribs being hard convey sound best from the deeper parts, and on them percussion is usually made. Care should be taken not to mistake the lesser resonance conveyed through the soft tissues of the intercostal spaces for an indication of a diseased condition. In proportion too as the ribs are covered with flesh or fat, the resonance will be diminished and a stronger blow will be necessary to bring out the sound from the lungs.
If the blow is made directly on the side of the chest the percussion is called immediate; if made upon an elastic solid body (pleximeter) laid on the outside of the chest it is mediate. The readiest and perhaps the best pleximeter is the middle finger of the left hand which is to be applied flat upon the side of the chest to receive the blow directed perpendicularly to its surface. In fat or fleshy subjects it should be pressed firmly on the surface so as to compress and condense the soft parts and render them better conductors of sound. Some use flat pieces of ivory, silver, caoutchouc but in employing these the nails of the right hand must be carefully pared, lest by striking the solid body they produce a sound which interferes with the true pulmonary resonance.
In examining the chest the two sides should be compared and if allowance is made for the dulness felt in the lower half immediately behind the left elbow caused by the position of the heart, and the deadness of the sound on the last few ribs on the right side where the liver is situated, any further deviation from a bilateral symmetry of sound is indicative of disease. The general resonance will be decreased by a full stomach which prevents the full inflation of the lungs, and it will be increased if the animal stands on a wooden floor with an empty space below. A short statement of the degrees of resonance over the different parts of the chest in the various races of the domestic animals in a state of health may prove useful.
Horse.—Left side. In the upper third the resonance is full behind the shoulder. It diminishes from the 13th rib backward and from the decreasing thickness of lung the blows should become less and less powerful. In this space forcible striking brings out the drum-like resonance of the abdominal organs.
In the middle third the sound over the 5th and 6th ribs is distinct but not full; it increases to the 11th rib and then decreases to the last.
In the lower third a very slight resonance may be observed over the 4th rib.; over the 5th, 6th, and 7th, where the heart approaches the surface the sound is dead; while from this to the 13th rib a slight resonance may be made out.
Right side. The upper third resembles that on left side from the shoulder as far back as the 13th rib behind which anything above the gentlest blows brings out a drum-like sound from the large intestine (double colon) especially. This is clear when that is distended with gas.
In the median third the resonance resembles that on the left side. In the lower third it equally corresponds as far as the seventh rib behind, which sound is dull because of the proximity of the liver.
Ox.—Left side. The upper third is clear in sound from the eighth to the tenth ribs, and behind this by gentle tapping to the second last (twelfth). Forcible striking, however, brings out the drum-like sound of the upper sac of the paunch which always contains more or less air.
The middle third has a clear resonance as far as the seventh rib; this diminishes to the ninth, behind which it is usually replaced by a dullness due to the presence of food in the anterior part of the paunch. By drawing back the limb percussion may be employed over the first and second ribs as well.
In the lower third the first two ribs can be examined and a clear sound should be educed. On the fourth, fifth and sixth ribs there is a full resonance, the heart being here covered by lung tissue, contrary to the condition in the horse. From the seventh the sound becomes duller and the dead sound from the food in the rumen characterizes the lower fourth of the ninth rib.
Right side. From the shoulder the resonance gradually decreases in the upper third to the eleventh rib, beyond which the sounds obtained are only from abdominal organs. In the middle third considerable resonance is met with over the first and second ribs, it is very full and clear over the fifth, sixth and seventh, whence it decreases and is quite lost behind the tenth. In the lower third a clear sound can be elicited over the first, second, fourth, fifth and sixth ribs; this is lessened over the seventh and eighth, and completely lost behind the ninth. Any but the slightest blows over these three last ribs brings out the dull, solid sound from the liver.
A very full paunch greatly increases the anterior convexity of the diaphragm, and compresses the lungs into the anterior part of the chest. If the contents of the rumen are solid the resulting dullness on percussion might be mistakenly supposed to indicate consolidation of the lung. This source of error must be carefully guarded against.
Sheep. Percussion in the sheep differs from that in the ox chiefly in the following particulars: The diaphragm being attached to the last rib as in the horse, the diminishing resonance of the lung may be traced as far back as in that animal. Thus a pulmonary sound can be obtained in the upper third as far as the last intercostal space, in the middle as far as the second last, and in the lower as far as the fourth from the last. Over the lower part of the fifth and sixth ribs on the left side the resonance is remarkably clear owing to the great relative thickness of the anterior lobe of the left lung which here covers the heart.
Pigs. In fat pigs the results are almost negative. In lean animals the middle third on each side gives out a clear resonance behind the shoulder as far as the seventh rib, from which it diminishes to the second last (thirteenth). The sound is less clear in the upper and lower thirds. On the fifth intercostal space below, and on the left side the sound is dull owing to the exposure of the heart through a slight notch in the lung.
Dog. Percussion is very satisfactory in this animal because of the amplitude of the chest, the thinness of its walls and the small bulk of the abdominal organs. In the upper and middle thirds on both sides alike the sound is clear and full as far back as the seventh rib, whence it decreases to the last. In the lower third a distinct but moderate sound marks the first eight ribs and is equally clear on the right and left sides. The thinness of the lung in its posterior part demands that percussion be effected by the middle finger only, without any movement of the hand. Unless the dog is very fat, good results may be obtained by percussion over the first and second ribs, the shoulder blade and breastbone.
Birds. In these and especially in the webfooted (ducks, geese) the sternum is so thickly covered by flesh that no result can there be obtained. Beneath the wings, however, and upon the back percussion through the medium of a small coin as a pleximeter and with the middle finger alone, is valuable. Beneath the wing a clear sound may be drawn out over nearly all the ribs and on the back over a less extent (two and a half to four inches, according to size).
Increase of resonance without any perceptible modification in character is usually partial and depends on the increased distension of the air cells of one lung, or part of a lung, to make up for the loss of a part or a whole lung through hepatization or pressure by false membrane or from water in the chest. If a part of a lung is solid and impervious it gives a dull, dead sound, contrasting strongly with the increased clearness of the remainder. So with water in the chest, the clearness of the upper parts contrasts unmistakably with the dullness of the lower. By watching the advance or retirement of these symptoms the solidification of a lung and its process of clearing up, and the effusion of water in the chest and its removal may be equally traced through all these stages.
If the increased clearness is confined to the upper, lower, or posterior border of one or both lungs, the sound being natural over all other parts, it indicates the existence of emphysema of the lungs, a condition almost constant in broken winded horses.
If the sound is drum-like over most of the lung it is due either to extensive emphysema or to the presence of air as well as liquid in the cavity of the chest. In the case first noticed there will be the double action of the flank, the weak, dry, husky cough and the wheezing breathing; in the last there will have been the previous attack of pleurisy, and the application of the ear to the chest will detect a splashing sound constant or heard only at intervals or on rising. This should be carefully distinguished from abdominal gurgling.
Diminished resonance, noticed over an entire lung, may be due to congestion or œdema of the lung, to the formation of a thick false membrane over the inner surface of the ribs or to a false membrane enveloping the lung and preventing its due distension. Congestion will be distinguished by the blueness of the mucous membranes and the presence of a crepitant sound heard on auscultation. Pleurisy is known by the tenderness on percussion or on pinching the intercostal spaces, and by the presence in many cases of a friction sound. The sound may be further lessened in cattle by the deposit of tubercle on the inner side of the ribs, or the extensive deposition of miliary tubercle throughout the substance of the lung.
Absence of resonance, the sound brought out by percussion being similar to that obtained by practising it over the muscular masses of the haunch, is always partial. It is due either to hepatization or to water in the chest. Hepatization is distinguished by its rarely affecting the lower thirds of both lungs at once, by the presence of a crepitating râle round the margin of the area of dullness, and by the increased resonance and respiratory murmur over the sound parts of the same and the opposite lung. In water in the chest on the other hand a friction sound and much tenderness precedes the dullness; the tenderness continues and the dullness reaches the same height on both sides of the chest, in the case of the horse. In the ox, water may exist on one side of the chest only, but the tenderness on pressure and the absence of any crepitation serve to distinguish the case from pneumonia. In the smaller animals the position of the dulness may be altered by turning the patient on its back as the water always gravitates to the lowest point.
The presence of extensive deposits of tubercle, of cretaceous material in tubercular cows and sheep, and the presence of large cysts in the lung may give rise to dullness over a circumscribed area. Such areas of dullness are usually multiple with sound lung between.
A further modification known as the cracked pot sound is sometimes heard in horses and cattle. It may be aptly represented by laying the palms of the two hands together in such a way that they meet all round and leave an interval filled with air right in the centre. The back of the one hand is then struck against the knee when the noise of the air escaping gives the characteristic sound. It occurs in consumption or in the advanced stages of inflamed lungs when a large tubercle or abscess has burst into a bronchial tube and the resulting cavity opens into this tube by a narrow orifice.