THE INFLUENCE OF LUNG RETRACTILITY IN 
PLEURISY AND PNEUMO-THORAX. 
BY 
F. Donaldson, M. D., 
Clinical Professor of Diseases of Throat and Chest, and sometime Professor of 
Physiology and Hygiene, University of Maryland ; Ex-President Medical 
and Chirurgical Faculty of Maryland ; Fellow of the American 
Laryngological Association ; Fellow of the American 
Climatological Association etc., et^ 
Reprint from Transactions of the Medical and Chirurgical Faculty of Maryland, 1S84. 
BALTIMORE: 
JOURNAL PUBLISHING COMPANY PRINT, 
No. 35 Park Avenue, 
1884. THE INFLUENCE OF LUNG RETRACTILITY IN 
PLEURISY AND PNEUMO-THORAX. 
BY 
F. Donaldson, M. D., 
Clinical Professor of Diseases of Throat and Chest, and sometime Professor of 
Physiology and Hygiene, University of Maryland ; Ex-President Medical 
and Chirurgical Faculty of Maryland ; Fellow of the American 
Laryngological Association ; Fellow of the American 
Climatological Association etc., etc. 
Reprint from Transactions of the Medical and Chirurgical Faculty of Maryland, 1SS4. 
BALTIMORE: 
JOURNAL PUBLISHING COMPANY PRINT, 
No, 35 Park Avenue, 
1884. THE INFLUENCE OF LUNG RETRACTILITY IN 
PLEURISY AND PNEUMO-THORAX. 
The application of the knowledge, acquired by physiological 
research, of the retractile force of the lungs, to the investigation 
of the pathological conditions of the chest, has been strangely 
overlooked. This fact has retarded, in no small degree, our 
thorough study of diseases of the chest. 
Marey, long since, by his experiments, showed the negative 
force of the lungs in aspirating the blood from the large venous 
trunks into the right side of the heart, thereby assisting the whole 
venous circulation. 
Dr. John Hutchinson, in 1846, drew attention to the antagon- 
ism existing between the expansion of the chest by muscular 
action, and the elasticity of the lungs and the chest walls. 
Dr. Hyde Salter (1865) showed that at the commencement of 
inspiration thoracic elasticity was favorable to inspiration, but 
as it advanced, it became an expiratory force with lung tension 
against further expansion. 
Dr. R. Douglas Dorr ell (1870) drew further attention to these 
facts in connection with respiration and its modifications in 
disease. 
Mr. Le Gros Clarke (1872) showed that atmospheric pressure 
over the abdomen kept up the diaphragm in a condition of 4 
F. DONALDSON, M. D . 
arched passive tension. He claimed, that this negative force re- 
sisted the elasticity of the lung and was the means of retaining 
the supplemental air in the lungs, and that it limited the en- 
croachment of the abdominal organs. Dr. Douglas Powell, in 
1876, in an elaborate and very suggestive paper, gave the prac- 
tical bearing of these physiological facts in clinical medicine, as 
indicating a better insight as to the true mechanism and relative 
value in diagnosis of some signs of chest diseases, especially as to 
the importance of thoracic resilience as a conservator of force in 
respiration. 
It was not, however, until 1877, that the amount of retractile 
force exerted by the lungs was ascertained, or indeed was more 
than guessed at. Dr. W. II. Stone, of London, then reported 
his experiments on sheep. He concluded that this retractile 
power was equal to from four to live inches of water. He also 
showed, that even when the effusion was considerable in the 
pleural cavity, that the lung still possessed contractile force suf- 
ficient to support two inches of water, so that to evacuate the 
fluid it was necessary to use external suction sufficient to over- 
come this lung traction. A few months subsequent to Dr. Stone’s 
papers, Dr. G. M. Garland, of Boston, published his work on 
“Pneumo-Dynamics,” giving in detail the results of his obser- 
vations and experimental researches as to the manner in which 
the retractile force of the lungs was exerted in health and in dis- 
ease. This author's conclusions gave an immense impetus to the 
study of the dynamics of the chest. English, French and Ger- 
man observers have been forced to acknowledge the results of his 
experiments as satisfactory in explaining some conditions especi- 
ally found in pleurisies. 
Previous to 1843, the authorities universally taught that the 
effused fluids in the pleural cavity obeyed the law of gravity as 
they would in an open vessel or in a vacuum. They never ap- 
peared to question, but that they would necessarily assume their 
hydrostatic level, and, consequently, that they would reach a 
horizontal line in all parts of the chest. As much stress as had 
been placed upon percussion as an element of physical diagnosis, 
the distinction between dulness as indicating impaired reson- THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
5 
ance and flatness as indicating absence of all resonance had 
not been really recognized. If the percussion taps be carefully 
made by quick, slight motions of the pereussor, the differential 
diagnosis ought always to be made. Over fluid contents of 
the pleural cavity there is perfect flatness, but where there 
are membranes, bands, oedematous or consolidated lung, there 
may be marked dullness, yet there is not absolutely flatness. 
There, however, is some resonance observed. Surely so ac- 
curate a pereussor as Piorry should have discovered that the 
distribution of effused fluid in the pleural cavity did not assume, 
when the patient was in the erect position, a horizontal level as long 
as there was any expansive force in the lung itself. He should 
not have left it to Mr. Damoiseaux, in the year 1843, to be the first 
to call attention to the important fact that the line of distribu- 
tion was not horizontal under such conditions, but irregular, 
taking more or less of the form of a parabola. Since Damoiseaux’s 
first paper, the attention of the profession has been called to this 
subject and, with but few exceptions, it has been acknowledged 
that the line of flatness over the upper surface of the effused 
liquid, unless it fill the whole cavity up nearly to the clavicle, is 
not horizontal when the patient is sitting or in the erect posture. 
Time forbids my going into the differences of opinion among 
English and continental writers as to the exact modifications of 
the line of distribution, nor is it of importance for the purpose 
of this paper. 
The views of Dr. Calvin Ellis, of Harvard University, pub- 
lished in 1874 and 1876, which were formed from the careful 
observation of a number of cases, have been confirmed by Dr. 
Garland and others, including myself. Dr. Ellis described the 
upper line of the effused fluid as beginning with medium effusion, 
relatively low down on the back, passing outward from the verte- 
bral column, and turning upward and proceeding obliquely 
across the back to the axillary region where it reaches the 
highest point. Thence it advances in a straight line but with a 
slight descent to the sternum. This has been designated as the 
Ellis curve. Dr. Garland, in consequence of the resemblance 
of the curve to the italic letter S, has named it, very appropri- 6 
V. DONALDSON, M. D. 
ately, the letter IS curve. According to his experience, this curve 
of Dr. Ellis’s may be traced by proper percussion in any case of 
free, uncomplicated pleurisy when the patient’s body is erect and 
the amount of fluid present is not excessive. As the effusion in- 
creases in amount, the course of the distribution gradually rises 
and tends to flatten out, so that it no longer presents its charac- 
teristic S feature after the fluid reaches the second rib. At this 
point, when the fluid occupies nearly the entire side, the curve 
comes quite near the horizontal, but if some of the fluid be 
withdrawn by aspiration or absorption, the letter S curve will 
re-appear and gradually retreat downwards. We consider that 
these modern views of the distribution of fluid in pleural 
cavities are well founded. 
Neither Damoiseaux, Ferber, nor Ellis, ventured to explain 
the cause of the fluid not taking the horizontal level. Dr. 
Douglas Powell, in his article (1876) showed the influence of 
lung elasticity. Dr. Garland by his elaborate and carefully 
conducted experiments, demonstrated that the lung, by virt ue 
of the strength of its contractility, draws up the pleural 
effusion along with it, in its retraction. Thus the li’quid 
assumes a pneumono-dynamic instead of a hydrostatic 
level. The physical cause of this condition is the retractile 
force of the lung. This is aided by the elastic resistance of the 
thoracic walls and the negative pressure exercised by the effused 
liquid. It must be borne in mind, that the normal line on the 
right side of demarcation between lung and liver is the letter S 
curve drawn out, the summit being low and the anterior branch 
correspondingly depressed. The modification of this normal 
line in pleuritic effusions represents the effect of the negative 
pressure of the fluid; and the decline in the Ellis curve toward 
the sternum shows that the elastic energy of the anterior part of 
the lung is feeble, compared with that in the axillary region. 
The layer of liquid is of less thickness above than at the base of 
the lung against the diaphragm. The upper surface taking its 
shape from the lung which lifts it by its retractility, the ef- 
effnsion by its weight exerts a negative pressure upon the lung. 
The mass of the fluid is held, when in moderate quantity, in the THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
7 
supplemental space between the lower border of lung and the 
diaphragm ((farland). The atmospheric pressure from the in- 
terior of the lungs and from the exterior of the chest wall keep- 
ing the costal and parietal surfaces together. 
The line of the distribution of the pleural liquid, we conclude, 
shows a very important influence of lung retractility. This ought 
never to be lost sight of in studying diseases of the chest. 
We next propose to call your attention to the effects of the 
retractility of the lungs in producing 
DISPLACEMENTS OF ADJACENT ORGANS IN PLEURISIES. 
The displacement of the heart as a physical sign indicating the 
presence of fluid in pleurisy, is one of great significance. It is 
Indeed a cardinal sign, second only in value to percussion flatness. 
It is almost invariably met with. Stokes stated that it was 
observed at an early period, and was one of the very first signs 
of effusion; that it may exist even before the upper portions of 
the chest have become flat on percussion ; and is a circumstance of 
constant occurrence, long before any yielding of the muscular por- 
tions of the thoracic walls. Dr. Douglas Powell states, that the heart 
is displaced at the very commencement of the effusion and that its 
dislocation increases pari passu with the effusion. He adds that 
the absence of this displacement, unless it can be explained by 
some special circumstance, which rarely occurs, such as the re- 
tention of the pericardium by old adhesions or by consolidation 
of the opposite lung, would negative the diagnosis of unilateral 
effusion. In this condition there is a marked contrast with the 
displacement and depression of the diaphragm and the resulting 
alteration of position of the liver, spleen and stomach. These 
only occur where the effusion is in great excess—when even the 
Skodaic resonance at apex has disappeared—and not until, from 
the large quantity of fluid, the retractility of the lung is overcome 
and is, consequently, unable to lift up the fluid and the dia- 
phragm. This altered position of the diaphragm drags the 
heart downwards by means of the ligamentous attachment of the 
pericardial sac to its tendinous portion. The deviations from 8 
F. DONALDSON, M. D. 
the normal position of the heart in slight effusions can always 
he noticed, if the exact point of the apex beat is sought for by 
palpation and listened for with the stethoscope. Careful percus- 
sion will show the shifting area of the flatness. 
Dr. Powell calls attention to a fallacy with reference to cardiac 
displacements in the earlier stages of effusion, namely, that as 
the base of the lung retracts, the left or the right margin of the 
heart as the case may be, becomes uncovered. This may lead to 
an apparent delay in the displacement of the organ, the more 
extreme left or right boundary being now within reach of palpa- 
tion. The axis of the heart is not greatly changed by an ordi- 
nary degree of effusion. It becomes a little more vertical and in 
extreme cases it may become slightly twisted. Only in rare and ex- 
treme cases does the axis of the heart become altered in direction 
beyond the vertical line. Dr. Powell found at a post-mortem 
a heart that had become so twisted as to present itself obliquely 
edgeways to the view of the observer in front. Dr. Gibson had 
previously pointed out this disposition of the heart to turn over 
and to present its posterior surface forwards in cases of effusion. 
There can be no question as to altered situation of the heart 
in pleurisy. How is this displacement effected and what is its 
significance % Until within a few years and indeed very gener- 
ally now, it is believed that the sole cause is from the direct pres- 
sure of the fluid actually pushing the heart away from its normal 
position. Skoda, Traube, Stokes, Powell and Garland were, we 
believe, the first authors to show that such was not the case, cer- 
tainly in moderate effusions. The displacements take place 
when the amount is eery small and no direct pressure is possi- 
ble. It is true that nature places the heart in such a position 
that it can yield readily to slight forces. It hangs in the peri- 
cardial sac which is suspended by the aorta and which is bound 
by ligaments to the body of the third dorsal vertebra. Every 
change of the position of the body causes certain physiological 
alterations of the heart’s position. 
Wintrich, Skoda and Braune think that the heart swings like 
a penduhim from its base and that its apex is therefore elevated 
with every deviation to the right or left. Lebert says the heart THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
9 
is first depressed by the sinking of the diaphragm and then 
elevated by being pushed to the right. Fraentzel says, that in dis- 
placements to the right, the heart is simply pushed over and is never 
elevated as Wintrich describes it. Woillez maintains that the 
mediastinum offers but slight resistance and is very easily pushed 
to the right side, where there is no compact organ to resist 
and where the cavity is larger, whereas it is with more difficulty 
pushed to the left where the heart occupies so large a space. 
It has been satisfactorily demonstrated that until the pleura is 
about two thirds full of fluid, no positive pressure is exercised 
upon the lungs or heart. According to Rokitansksy, the lung 
cannot be compressed until seven-eights of the pleural cavity is 
occupied by fluid. The fluid cannot be drawn off by a canula 
unless air enters to replace the fluid. Fraentzel states that un- 
less the pressure on the fluid from within the cavity be greater 
than that of the atmosphere we cannot draw off a large quantity; 
if, however, the pressure balances that of the atmospheric air, 
only a few drops of fluid are discharged externally except by 
forced expirations and coughs. This he found was the case even 
when the quantity reached several litres. The feebler the expi- 
ratory force, the less fluid reached. Yet the heart is displaced as 
soon as this effusion appears, even in small quantity. The sig- 
nificance of the displacement is that it shows us the presence of 
fluid, but does not give us the measure of intra-thoracicpressure 
(Powell). Dr. Garland’s explanation is, that the heart with the 
sac and its connections in health is placed between two highly 
elastic bodies (the lungs), which are striving to retract in oppo- 
site directions. The heart, therefore, being acted upon on both 
sides—by opposing forces, occupies a position where these forces 
just balance each other. This is the status of physiological 
repose, in the vertical position of the body. When an effusion is 
poured into either chest, the lung of that side contracts and 
thereby exhausts a certain amount of its retractile energy. The 
opposing lung, however, still remaining normal, immediately 
begins to draw the heart towards itself, and the degree of dis- 
placement thereby induced will be proportional to the diminu- 
tion of energy in the compromised lung. 10 
F. DONALDSON, M. D. 
Dr. Stokes divided these displacements into excentric and con- 
centric. The former he considered were due to direct pressure of 
the fluid, and the latter existed where, from any cause, there was 
diminution of volume of one lung, the other lung by its increase 
of volume forcing it over. The concentric displacements, he 
thought, were generally the result of some chronic disease pro- 
ducing atrophy of the lung. 
Thus, we see that displacements of the heart occur at three 
distinct periods in the course of pleurisy and from different 
causes in each case. 
1st. As soon as fluid forms in the pleural sac. At this period 
the displacement is caused by the presence of the fluid which 
occupies part of the pleural cavity. The lung by its elasticity re- 
tracts. It is consequently of less volume and exerts less nega- 
tive force upon the mediastinum and its contents than the healthy 
lung. The two lungs having by their equal tractile energy kept 
previously the heart in situ, the healthy lung draws the mediasti- 
num out of its position in a transverse direction. Necessarily the 
displacement of the heart from this cause is in proportion to the 
amount of fluid effused. This is the most frequent mode of dis- 
placement of the heart. It can be said to be almost always 
present. 
2d. When the quantity of fluid is great enough to overcome 
the retractility of the lung and exert intra-thoracic pressure it 
forcibly expels the air from the alveoli of the lung and by direct, 
positive pressure pushes the heart aside. The displacement of 
the heart in this case can only be produced when the pleural sac 
is two-thirds or more filled by fluid. When this condition is met 
with, the displacement is very great because the heart has been 
previously displaced by lung traction. Previous to Garland, 
Stone' and Powell’s researches, this was supposed to be the only 
manner of explaining the displacement of the heart from pleurisy. 
3d. Is where, as illustrated by Stokes’ and Hunt’s cases, and 
the very interesting case of dexio-cardia reported last year by 
Professor Chew, the heart is displaced towards the diseased side. 
This occurs more as a sequel of pleurisy. It is met with in the course 
of the absorption of chronic or s uppurative pleurisy where THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
11 
l)y non-expansion of lung there is a partial vacuum produced. 
The external atmosphere presses in the thoracic walls of the dis- 
eased side, and the internal atmospheric pressure from the 
healthy side is exerted against the mediastinum and presses the 
heart in that direction. Marked displacements from this cause 
are rare, slight displacements are more frequent. Cicatrices 
from healing of large cavities would have this effect. Mere 
consolidation of lung could not cause it. Let us now look into 
the cause of the Displacement of the Lung. AVe have already 
shown that the lung, in cases of effusion, is drawn up J)y its own 
retractile energy. It has been demonstrated that this force is 
eonsiderable (from 4 to 5 inches of water). As the effusion 
advances the lung recedes until a certain point, when the fluid, 
having overcome the retractility of the. lung, and having 
a fixed point below, actually exerts positive pressure upon the 
lung (Garland), and compresses the air out of the alveoli and the 
compressible bronchi. This compression cannot take place until 
the diaphragm is no longer elevated into the thorax, but is bag- 
ged down by the excessive weight of the fluid. Jaccoud and 
Fraentzel both confirm this view, that there can be no compresr 
sion of lung.until its elasticity has been exhausted. Thegradual 
effect of the continued contraction of the lung is to straighten out 
the letter S curve. The force of lung necessarily gradually 
diminishes as it contracts in volume. On the other hand, the 
immediate effect of compression would be to obliterate that curve. 
So long, therefore, as we are able to trace a well marked letter S 
on the chest, wTe may be certain that the lung is well out of 
reach of compression (Garland). M. Peyrot showed by plaster 
of Paris injections into the chests of cadavers and then making 
cross sections, that deformities of the chest are not due to a 
development of one side, the other remaining normal, but that 
they consist of a mutual adjustment of all parts. Fernet states 
that simultaneous movement of the sternum toward the left in 
left sided eflusions, makes the displacement of the heart appear 
greater than it actually is. Let us study next the condition of 
The Diaphragm and Intercostal Spaces.—As shown by 12 
F. DONALDSON, M. D. 
Garland, the diaphragm is not depressed below the edge of 
the ribs, nor do the intercostal spaces bulge until the weight 
of the fluid exceeds the lifting force of the lung. Dr. W. H. Stone 
showed the saine result from the admission of air into the pleural 
sac. Skoda says, “ the depression of the diaphragm is due in 
part to the weight of the fluid, hut cli iefly to the diminished contrac- 
tile energy of the retracted and diminished lung. The displace- 
ment of the mediastinum depends upon similar conditions. Since 
the traction of the lungs always affects both sides of the thorax, 
the movable mediastinum must follow the lung which is still 
capable of contracting, and therefore with right-sided exudations 
the left lung will draw the parts over to itself. Only with 
excessive effusions in the pleural cavity, does the pressure of the 
fluid come into activity. 
The Liver and Spleen may be pushed below their normal 
position by excessive effusion, after the diaphragm yields to the 
weight of the fluid. Moillez found the liver displaced down- 
wards in the abdominal cavity in one fourth of the right pleurisies 
and only once in the left side pleurisies The extent on right side 
was from two or three centimetres to three fingers breadth, even 
as far as umbilicus. 
The Stomach, when the diaphragm sinks, may be pushed 
downward; thus the so-called semi-lunar space of Traube maybe 
obliterated. Ferber noticed a peculiar displacement of the 
stomach in two cases where he had produced an artificial hydro- 
thorax of the left side. The fundus was pushed to the right, 
and the stomach was folded over on itself to a certain extent. A 
second and marked folding in of the greater curvature occurred 
near the pylorus. Ferber says, that this condition of stomach > 
with left-side pleural exudations, has been hitherto entirely neg- 
lected by authors. He thinks that the vomiting which is often 
observed with excessive effusion and which has been attributed 
to violent acts of coughing, may be due to this doubling over of 
the stomach. 
Pneumo-Thorax.—Before concluding, gentlemen, let us see if 
the retractility of the lung is not a powerful influence in pnemo- 
thorax. The'opening into the pleural cavity may be direct or THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
13 
oblique. If direct it remains open, if it be oblique, it is generally 
more or less valvular. The symptoms, prognosis and treatment 
vary accordingly. Through a patent orifice the air enters in 
inspiration, and goes out with the expired air from the lungs. It 
cannot accumulate; consequently there can be no positive air- 
pressure within the pleura. If, however, the orifice be valvular, 
although the air enters it does not escape, for it presses upon the 
valve and closes it. If the valvular fold be perfect, the air soon 
becomes excessive in quantity and exerts dangerous pressure upon 
the lung and adjacent organs. By means of a trocar fitting by 
tubing to a water-pressure guage, Dr. Douglass Powell ascer- 
tained, post-mortem, the degree of intra-pleural pressure present 
in sixteen cases of pneuino-thorax. In four out of these cases, the 
pressure was nil. In twelve, there was more or less intra-pleural 
pressure present, varying in degree from one and three quarter 
iiich to seven inches of water. 
Unless the lung be mechanically prevented, the entrance of air 
into the pleural cavity at once produces a retraction of the lung 
owing to its elasticity. There will be no compression of the lung 
unless the air be increased in quantity by each inspiration, and 
having no exit, accumulates; then, the lung may be forced 
against the spinal column and the residual air actually forced out 
of the alveoli. Dr. Powell questions whether the intra-thoracic 
pressure excited in pneumo-thorax is ever equal to what is some- 
times met with from pleurisy; the highest he had ever met with 
in pneumo-thorax was seven inches of water. Garland, in 
repeating Damoiseaux’s experiments in testing the effects of the 
introduction of air into the pleural cavity, found that the air did 
not penetrate between the lung and the lateral chest walls until 
the lower border of the lung had retracted upwards the distance 
of several ribs. 
One of the most -pronounced effects, constantly observed in 
jpneumo-thorax, is the immediate displacement of the heart to a 
greater extent than even in pleurisy. M. Gaide, as far back as 
1828, described displacement of the heart as an important sign of 
pneumo-thorax. He related a case, where, at-the moment of the 
perforation, the woman was conscious of the heart’s beat, having 14 
K. DONALDSON, M. D. 
been transferred to the right of the sternum. Dr. Powell in 17 
eases found it to have occurred in 16; in the 17th the unruptured 
lung was so consolidated that it could not collapse. In pneumo- 
thorax of the right side a careful examination is sometimes 
required to detect the displacement of the heart. The apex can 
be discovered at considerable distance to the left of the nipple, 
with the right ventricle drawn to the left edge of the sternum. 
It has been generally believed that the cause of this displacement 
was the intra-pleural pressure of the air, but this does not satisfac- 
torily explain it, for there can be no pressure until the elasticity 
of the lung has been overcome. In thirteen of Dr. Powell’s cases 
there was great displacement of the heart with different degrees 
of intra-pleural pressure. In three cases there was great 
displacement of the heart, no intra-pleural pressure. The 
same author showed, experimentally, that the elastic tension 
of one lung, when unopposed b,y that of the other, was sufficient 
to draw aside the mediastinum, and, with it, the heart. 
He thus showed that these displacements are by no means 
necessarily a sign of intra-pleural pressure, since they may occur 
to the right of the sternum without there being any pressure. 
Clinically we know that the admission of air into the pleural 
cavity immediately and constantly displaces the heart, unless the 
opposite lung be consolidated or otherwise injured in its resiliency. 
This occurs even when the patent orifice of the perforation pre- 
vents the accumulation of any quantity of air. There is not 
enough air to produce direct pressure, buf there is enough to 
impair the elastic traction of the lung of that side, and thus to 
destroy the equilibrium of traction which keeps the heart in its 
normal position. The healthy lung, by its unimpaired tractile 
force, immediately draws over the heart. Skoda maintains that 
“ air does not enter the pleural cavity simply at the cost of the 
torn and retracted lung, but the sound lung also retracts to such 
a degree as the mediastinum is movable.” Dr. Garland’s experi- 
ments conclusively demonstrate that the air in pneumo-thorax is 
powerless to exert any appreciable lateral displacing force until 
the lung is completely collapsed, and this does not ordinarily 
occur. There can be, he says, but one cause of this constant and THE INFLUENCES OF LUNG RETRACTILITY, ETC. 
15 
early displacement of the heart, namely, the elastic force of the 
opposing lnng which draws those parts over to itself. 
He adds “ that the explanation of the greater displacement of 
heart in pneumo-thorax is, because the air having practically no 
weight, cannot exert upon the heart the negative pressure which 
an effusion evidently would.” 
We conclude, gentlemen, that lung retractility is not only a 
powerful physiological force in respiration, but that it also 
produces modifications of a decided character in diseases of the 
chest. 
The practical value of these facts consists,—in the aid they give 
us to the differential diagnosis of pleurisy and pneumo-thorax; 
the assistance they afford us in estimating the quantity of fluid in 
the pleural cavity; and the indications they furnish us as to the 
advisability of resorting to thoracentesis.