LUNGS. 



Sioce, then, the lungs and cheft always move together, Iiow 

 can there be an empty fpace between them ? and if there 

 can be none, how can an accidental union ohflruil the 

 motions? 2. Adhelinns between the pleura pulmoiialis and 

 coftahs are extremely tre([uent. They are found, not only 

 in individuals who have died after a lon<j difeafe, but alfo in 

 thofe whom a violent death has furprifed in a (late of health. 

 In many inftances the whole furface of the lung adheres to 

 its cavity: yet in general the individuals have enjoyed perfeft 

 freedom of refpiration. We muft therefore conclude, that a 

 continuity of furface l^etween the lungs and cheft does not 

 injure the freedom of the refpiratory functions. Tiie utility 

 of the feruus fluid does not then appear fo clear to us in the 

 pleura, as in other cavities of the body. In the refpiratory 

 apparatus, the motions of the fides of the cavity and of the 

 contained organs hold a certain neceflary and invariable rela- 

 tion to each other. The brain tends to move in an immove- 

 able bony cafe ; the gallric vifcera may change their pofition 

 and relations to each other, without any alteration in tha 

 abdominal parietes : in the fynovial cavities there are two 

 furfaces conftantly moving in an inverfe direftion to each 

 other, &c. We every where fee the different portions of 

 a ferous furface Aiding on each other in a more or lefs mark- 

 ed degree, and we naturally conclude that the prefonce of a 

 fluid is indifpenfible to ihat motion. The thorax alone pre- 

 fents to us two ferous furfacea always in conta£l at the lame 

 points. 



The two lungs occupy th» ferous cavities on the fides of 

 the chelk, lined, as already defcribed, by the pleura. They 

 are feparated from each other by the mediallinum, but 

 united by the circumllance of their receiving from two com- 

 mon trunks (the trachea and pulmonary artery) the air and 

 blood which are neceiTary to their phenomena. They are 

 rot fymmetrica', but differ both in fizc and form, exhibit- 

 ing the irregularity which belongs to the organs of the or- 

 ganic life ; or rather holding a middle place in this refpeft, 

 as well as in their funftions, between thofe and the organs 

 of the animal life. The heart, which is turned to the left, 

 and placed ahnoll entirely on the left fide of the cheil, di- 

 minifhes the tranfvcrfe diameter of thccorrefponding pleural 

 the liver elevates the diaphragm very fenfibly on the oppofite 

 fide, fo as to redi;ce the perpendicular meafurement of th^ 

 right pleura. Hence the left lung is the longed, and the 

 right the broadelt of the two. 



Their volume, in the natural (late, is always cxaftly the 

 fame as the capacity of the bags of the pleurx : thtir ex- 

 ternal furface is conllantly in contact with thefe cavities. 

 As they Iwve no power of motion in tliemfelves, and follow 

 every cliange which the fides of the chell undergo, their 

 capacity is conftantly varying : when the cheil is enlarged, 

 they are dilated by the entrance of air into their iubflance 

 through the trachea, and when it is contrafted, tliey undergo 

 a correfponding diniiuutiua by the expulfusn of air. For 

 further explanation and proofs on this fubjeft, fee the ac- 

 count of the pleiu-a. Yet we cannot always judge of the 

 Tolume of the lungs by the apparent extent of the peClorat 

 cavity : the heart diS'ers ccfiiliderably in fize, and fimilar 

 ■variations of the liver, influencing the height to which the 

 diaphragm afcend.", are flill more common. Tlie collapfe 

 of the lungs, which we have conddered in fpeaking ot the 

 pleura, is lefs marked when thefe organs are dillended with 

 blood : it is generally lefs in children th.ui in adults, and 

 does not take place at all in the converfion of thefe organs 

 into a folid mafs like the liver, at lead in the parts immedi- 

 ately affcfted. Thus the bulk of the lungs depends more 

 en the fluids which they contain, particularly the blood and 

 air, thaa ui> ilicir folid fublUnce. They iire dilated in m- 



fpiration ; but Ail! thoroughly penetrated with air !n the 

 moll complete exfpiralion. Long and continued compreflion 

 or cxtraftion of the air by an exhaufling fyringe ri-durcs 

 them tn fo ("mall a bulk, that they do n n equal one-fourlli 

 of the cavity which is defigncd to contain them. Prcter- 

 n-itural accumulations of fluid, as water or pus, diminifh tha 

 fi/'- of the organs in the fame way diiriog life. The inofl 

 numerous incilions and the Itrongell prelTure will hardly gi-t 

 rid of all the air from the lungs : if wc cut a very fmall 

 portion, and fqueeze it molt forcibly, there is (Idl enouj;!l 

 air to keep up the fize beyond what the folid matter would 

 caufe, and it lljll fwinis in water. In fliort, this air can be 

 completely got rid of only by ebullition, maceration, or 

 means that entirely (ieflroy the texture of the organ. 



The lungs generally contain mare blood after death ihaa 

 during life, as an accumulation takes place in their veffcla 

 in the aft of dying: the quantity of thii fluid influences the 

 bulk of the organ, when the cavity of the cheft is expofi'd. 

 When there is much blood, incilions into the lung produce 

 a lefs marked diminution of volume than we might cxpeft ; 

 they only give iflTue to the air and not to the blood. The 

 ready efcape of the air, too, requires a free communication of 

 the air-cells with each other, which the ftagnation of the 

 blood prevents, by confining the air in every part, fo that 

 only the cut portion is evacuated by the incifions. Where 

 the individual has died of hemonhage, tlie lungs arc almoft 

 entirely irce from blood, and owe their vulun.c to the air: 

 here fuperficial incifions produce a fudden and marked col- 

 lapfe. This has been particularly obferved in perfons exe- 

 cuted by the guillotine : thn-c or four incifions have fpeedily 

 reduced the lung to nearly the half of its original Cze. 

 (Ijichat, Anat. Defcript. t. iv. p. 12.) For the fame reafon, 

 the degree of collapte of the lung will be much influenced 

 by the quantity of mucous fluids contained in the air-velTels 

 and cells of the lung?. 



The lungs are the lighteft organs in the body ; they con- 

 ftantly fwim when immerfed either entire, or hi parts, io 

 water. This property depends obvioufiy on the fame caufa 

 as their volume, namely, the air wliich they contain. When 

 entirely deprived of this fluid, and reduced to their own fub- 

 ftance, they do not fu im. This is feen when one of them 

 is fo compreflTed and flattened by the efTufion into the chefl 

 of a large quantity of fluid, as to ferve no longer for the 

 purpofes of refpiration. In certain difeafes, too, the lung 

 is rendered folid and impervious to air, and then finks in 

 water ; but this is a pathological phenomenon. Immerfioa 

 in water is, thei-cfore, the ordmary and beft m.ethod of de- 

 termining the fpecific gravity of the lung. The greater 

 or fmaller qtiantity of blood whicii may be contained in thtir 

 vefTels at the time of health occafions them to vary in weight 

 when compared in different fnbjects. 



There can be no doubt that the lungs of a perfon, who 

 has died of afphyxia, are heavier than thofe of one who 

 has perilhcd from hemorrhage : and that thel'e organs will 

 be lighter after a chronic dileafe, which has exhaufted the 

 vital powers, and diminifhed the energy of the circulation, 

 than after llrangidation, in which there is a confiderabie 

 afflux of blood into them to the laft moment. 



The form of thefe vifcera is in general conical, with the 

 bafis dou-nwards, and tlie apex upwardr. This form is 

 tolerably conflant, becaufc it depends on that of the thorax, 

 which varies little in its natural nate. They corrtfpond im- 

 mediately to the folid fides of the cheit only at the upper 

 and outer parts : on the inner fide they he againft the heart, 

 and below are feparated from the abdominal organs by the 

 diaphragm: in the two latter afpedts, therefore, their form i« 

 influenced by that of the neighbouring parte. The heart, 



' placsd 



