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).