t U N G S. 



riixture of thefe varimis tints gives them the marbled ap- 

 pearance, whicli has generally been regarded in difTcftiiig 

 rooms as the natural ftate of tl'.e organs, although 'it is merely 

 produced by di-ath. The brown, blueifh, or violet colour 

 is the mod frequently obferved, and occupies the lung moll: 

 extenfively. It depends on the prefcnce of venous blood, 

 \vhieh flagnates as foon as rcf;>iration has ceafed to colour 

 what the right ventricle ftili impels. The tint varies as llie 

 blood is accumulated more or lefs in particular liuiations. 

 1'he higheft de^^ree of this congeftion produces the black 

 obferved in the lungs of thole who die of afphyxia ; the 

 brown or violet colour is caufed by a {lighter degree of the 

 fame effeft.- The colour is always the deepeft in the moft 

 depending part of the lung, as the blood, obeying only the 

 laws of gravity after dtfath, fettles in the lowed parts. Prom 

 the ordinary pofition of the body this deep colour is nlually 

 feen at the back of the lung ; but if the fubjetl be laid on 

 the face, tlie J"arae phenomenon is exhibited in front. Thefe 

 dark colours are not the only ones obferved in the lungs ; 

 inore or lels extenfive patches of a bright red are often feen ; 

 this may occupy a large portion of tne organ, while the red 

 is brown or violet-coloured. This red colour is univorlal ia 

 the lungs of children, which do not prefent the black fpots ; 

 the former gradually difappears, and the latter increafe with 

 the progrefs of age. The fame bright tint extends into the 

 fubdance o-f the Tung. We are at a lofs for a fatisfattory 

 explanation of this appearance : if it arofe from the blood 

 being afted upon after death, by the air contained in the 

 pulmonary air-cellSj we (hould expeft to find it more univer- 

 fal and more frequent. The parts of the lung, however, 

 in which this tint is obferved, certainly contain fcarlet blood, 

 and owe the colour to that. 



The lungs are the lead denfe, and lead refiding of all or- 

 gans formed of folid tilfues. They yield readily to coinprcf- 

 fion, preferve the mark of the preliiire, and are redored im- 

 perfe<31y to their original date. This obfcrvation applies 

 only where they are not loaded with blood, but contain 

 merely that quantity of air, which never leaves them after 

 they have been once didended with it. When full of blood, 

 they acquire a confidence foreign to their own fubdance, re- 

 fift prefTure more effeftually, and redore themfelves more 

 readily. Hence foftnefs and flaccidity more particularly 

 charafterize the lungs of perfons who have died of hemor- 

 rhage. When we fqueeze the air forcibly into a part of the 

 lung, a peculiar crackhng noife is produced by the burfling 

 of the air-cells : this crepitation does not take place in dif- 

 eafed lungs. 



The foftnefs of the pulmonary texture arifes from the 

 Jungs being entirely compofed, as we diall fee prefently, of 

 various vafcular fydems. It accords very perfectly with tlie 

 paffive part that they perform in the refpiratory phenomena : 

 poIfefRng no power of motion in themfelves, they expand 

 and contraft merely in confequence of motions of the 

 thed. 



The lungs are compofed of a cartilaginous and membranous 

 tube, by which air is conveyed into them ; of the pulmonary 

 artery and veins, of which the former termisates the fydem 

 of black blood, and the latter commence that of red blood ; 

 of the bronchial veflels concerned in the nutrition of thefe 

 organs ; of a peculiar tilfue, compofing a congeries of mi- 

 nute cells, which receive the air admitted jn refpiration ; and 

 'T>f lymphatics and nerves. Thefe parts are all united by 

 cellular tilTue, and covered externally by the refleded 

 pleura. 



The air-vefTds compofe the eflential part of the lungs, 

 with refpeft to their funftions as organs of refpirition. 

 They introduce the fluid by which the blood is changed ; 



this procefs goes on at their' furface ; nnd the air, after fcrv* 

 ing the purpofes of refpiration, is expelltd through them. 

 When taken altogether they form the cavity of the refpira- 

 tory apparatus, which is analogous to tliat of the digedivc 

 canal, in having a mucous lining, but differs in its arrange- 

 ment, as it is fubdividcd into a vad number of canals, de- 

 crcaling fucceilively like arteries. Thefe are the only tubes 

 in the body conllantlv open ; it is necedary that the air 

 fliould have free aad condant accefs to them. This order 

 of tubes is begun by a fmgle trunk, which unites the two 

 lungs, and necelFarily renders their phenomena fimultane- 

 ons. The common trunk is called trachea (afpera arteria, 

 trachee artere) ; and its primary diviiions the right and left 

 bronchi. 



The trachea is placed in front of the vertebral column, 

 extends from the upper part and middle of the neck to the 

 upper part of the ched, beginning immediately below the 

 larynx, and ending about the level of the fecond or third 

 dorfal vertebra. It is placed on the middle line of the body, 

 and is fymmetrical in its whole extent ; in this rcfpcS it ap- 

 proaches to the external organs : the fymmetry ceafes in its 

 diviiions. It appears cylindrical in front, but is flattened 

 beliind. Its diameter varies according to the age of the fub- 

 jcdt, and the natural volume of the lungs ; it may be about 

 tight or ten lines in the adult, and is exactly the fame with 

 that of the larynx, meafured at the cricoid cartilage. It 

 continues the fame through the whole length of the trachea. 



In front it is covered above by the two portions of the thy- 

 roid gland, which unite together at the middle of the tube. 

 Lower down the derno-hyoidei and derno-thyroidei, and the 

 inferior thyroid veins cover it. In the ched it is enclofed in 

 tlie poderior mediadinum, and correfponds to the thymus, 

 to the left fubclavian vein, the arteria innominata, and the 

 arch of the aorta. Behind it covers the cefophagus, and to- 

 wards the right the vertebral column. On the fides it is co- 

 vered above by the lateral portions of the thyroid gland, and 

 is contiguous below to the common carotids. A loole and 

 abundant cellular tilfue forms the medium of its conne6xioa 

 to all thefe parts. The fuperior extremity is conneifed to 

 the cricoid cartilage by a ligamentous fubdance ; tlie inferior 

 is placed at the right fide of the defcending aorta, is bifur- 

 cated, and produces the two bronchi. The latter begin 

 about the fecond or third dorfal vertebra, and feparate from 

 the common trunk nearly at a right angle, yet they go with 

 fome obliquity, downwards and outwards, each to its cor- 

 refponding lung. Here we begin to meet with the irregu- 

 larity of form that charafterizes the organs of the internal 

 life. The left bronchus is imaller than the right, and takes a 

 much longer courfe : it paffes under the arch of the aorta, 

 while the other goes immediately to its lung. Theie tubes 

 enter the lungs at the (ituations already defcribedas the roots 

 of thofe organs. They ramify in every direiSion, and di- 

 vide into branches, becoming fucceffively imaller and fmaller. 

 Thefe fubdivifions are fo numerous, that every part of the 

 lung contains them. The cxa(S manner of their termination 

 is not underftood. 



The air-tubes are compofed of three parts, an exterior 

 membrane, of a fibrous and probably mufcular texture ; a 

 cartilaginous ilrufture, which is united to the preceding ; 

 and a mucous lining. The exterior membrane rifes above 

 from the circumference of the cricoid cartilage, and occu- 

 pies the whole extent of the trachea and bronchi, forming 

 a very effential part of thofe tubes. It is tolerably thick in 

 the greated part of its courfe, but grows thinner in the 

 fmaller ramifications of the bronchi, where it cannot be 

 ealily traced. It is formed of parallel and clofely arranged 

 longitudiaiil fibres, the nature of which is doubtful ; fome 



confidej 



