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ly conjecture some vicious organization, or some accidental cause, that 

 determines them, as by instinct, to this posture, 



Let us suppose an effusion of blood, water, or pus, in the sac of the 

 pleura of the right side. The patient lies on this side, that the weight of 

 his body may not oppose the dilatation of the sound side of the chest.- 

 The parietes of this cavity are not equally distant from its axis ; the 

 pressure of the body on the plane of support, prevents the separation of 

 the ribs, whether as a mechanical hindrance to the displacement of these 

 bones, or in numbing the contractility of the muscles of inspiration, all 

 more or less compressed : Now, as the healthy lung must supply the 

 place of the diseased, nothing could be more in the way than to produce, 

 on that side, by a bad posture, a constraint equal to that occasioned by 

 disease, on the other. 



It has long been imagined, and it is taught still, that, in thoracic effu- 

 sions, patients lie on the side of the effusion, to hinder the effused fluid 

 from pressing on the mediastinum, and pushing it against the opposite 

 lung, of which it will constrain the developement. The following ex- 

 periments show clearly enough the error of such a supposition : 



I had several times produced artificial hydrothorax,. by injecting with 

 water, the chest of several bodies, through a wound in one of the sides. 

 This experiment can be made, only on bodies in which the lungs are free 

 from adhesion to the parietes of the chest, and the number is smaller than 

 might be imagined : you may introduce in this way from three to four 

 pints of water. I afterwards opened carefully the opposite side of the 

 chest: the ribs removed and the lung displaced, gave room to see dis- 

 tinctly the septum of the mediastinum stretched from the vertebral co- 

 lumn to the sternum, and supporting without yielding, the weight of the 

 liquid, whatever might be the posture given to the body* 



It is for the sake then, evidently, of not preventing the dilatation of the 

 sound part of the respiratory apparatus, already condemned in one part 

 to inaction, that patients, in thoracic effasion, lie constantly on the side 

 of the effusion. It is for the same motive, to which we may add that of 

 not increasing the pain by dragging downward the inflamed pleura, that 

 patients in pleurisy lie on the affected side. The same thing happens in 

 peripneumonies; in a word, in all diseased affections of the lungs ant! 

 parietes of the chest*. 



Lying on the back, which is unusual in health^ is natural in many dis- 

 eases. It commonly indicates more or less weakness of the muscles of 

 inspiration. The contractile powers which perform the dilatation of the 

 chest, when affected with adynamia, in fevers of a bad character, or after 

 extreme fatigue, carry very imperfectly into effect this dilatation. Ne- 

 vertheless, a determinate quantity of atmospherical air must be admitted, 

 every moment, into the lungs, and the general weakness would be in- 

 creased, if respiration did not impregnate the blood with a sufficiency of 

 oxygen : patients choose, therefore, the posture which makes the dilata- 

 tion of the lungs easiest for their weakened muscles. The posterior pa- 

 rietes of the chest, on which the body reposes, lying upon the back, are al- 

 most useless in the expansion of the cavity. The ribs, which have, the 

 centre of their motions in their articulations with the vertebral column, 

 are almost immoveable backwards, and the movsableness of these bones 



* This is not the case until after adhesions of the pleurae have taken place. 'Copland 



