LUNG S. 



wliole fubftancc is found to ht compoffd of tluTc cells, as will 

 as its extiTiial furface. InjedHon with qiiickfilvcr will do- 

 mon Urate the fame (Initture. 1'his gives to the lung, when 

 cut or torn, a porous ;uul fiJongv appearance tl.roughout . 

 The cells, when attentively furvcyedmuhe furface ot the lung;, 

 have a roundilh ligure, but their outline is often irregular. 

 AVhen inflated they nu-afure J-th or ,', th of a line in diani-^Lr. 

 Tliey communicate together in all direi;lions fo completely, 

 by the ramifications of the air-tubes, that air might paU 

 eafdy from a liugle cell into all parts of the lung ; but the 

 cells of the neighbouring lobules do not ieein to ha\-e any 

 direft communication. 



The mucous membratie, in an extremely delicate flate, 

 continued from the minute ends of the air-tubes, is fuppofed 

 to compofe thele cclh ; but the minutenefs of the objects 

 renders our defcription of them, excepting a few general 

 fafts, rather uncertain. Anatomy difcovers to us raiher a 

 fpongy net-work, filled with air, and formed by blood- 

 velFels crolTing in every diredlion, tlian any clear arrange- 

 ment of dillinft cells, connected to the bronch'al ramifica- 

 tions, like grapes to their flalk, as they have been defcnbcd 

 and drawn by feveral anatomifts. 



In tliis view of the fubjeft, the extent of furface of the 

 mucous membrane mull be enormous. Many attempts have 

 been made to exprefs it in numbers. Hales makes the air- 

 cells -j^a^.dth of an inch in diameter; the furface of the air- 

 tubes eq-ual to lo:;, fquare inchcj ; and that of the air-cells 

 to 20,000. Keil ellimates the number of the veficles at 

 174,418,615, and the whole internal furface of the lung at 

 21,006 fquare inches. Lieberkuhn carries his eliimate'of 

 the furface as high as 1500 cubic feet. We mention thefe 

 circumftances only to fliew the great extent of the mucous 

 membrane, and not bccaufe we place much faith in their ac- 

 curacy. In reading dcfcriptions of the minute ilriifture of 

 the lungs, and, indeed, in all other analoj^ous parts of ana- 

 tomy, we (hoidd always bear in mind the obfervation of 

 Haller ; " Ea fere homiuum eft infeticitas, ut omnis ultima 

 rerum phyficarum hilloria parum iirma fit, et ut altera ilia, 

 rerum geftarum memoratrix, in mythices fines terminatur." 



A mucous fluid conftantiy lubricates the whole of this 

 furface. It is limpid, mild, and nearly infipid, or (lightly 

 faltini, aHid but little tenacious in the natural ftate. When 

 free from air, it finks in water. It is produced in fo fmall a 

 quantity, that it feoms to be dilTolved in the air, and thus 

 topafs off iufenfibly in exfpiration, or to be taken up by the 

 abforbente. It is poured out much more abundantly under 

 various circumftances, and is altered in colour and confid- 

 ence : it is then expelled by the expiratoi-y efforts which 

 conftitute cough. In children it has a reddifh colour ; and 

 it is often rather livid in adults. 



The watery vapoi^r difcharged from the lungs in exfpira- 

 tion concurs in lubricating the furface of the air-paffages. 

 Whether there be any exhalation from the general mucous 

 furface, in addition to the mucous fecretioa, feems a point 

 hardly fufceptible of pofitive determination. 



The pulmonary mucous membrane \e the part in which 

 tbe chemical phenomena of refpiration are carried on ; its 

 furface is in contaft with the air taken into the lungs. The 

 latter fluid is the only one, in addition to its natural mucus, 

 of which it can bear the contaft. All other fubftancee. 

 even the clearell water, are immediately and powerfully re- 

 jcfted by it. In itfelf it poflefl'es no power of expelling any 

 irritating matter from its furface ; but it excites the ex- 

 piratory mufclcs which aft convulfively and repeatedly until 

 itiz caufe is removed. 



The velTels and nerves of the lungs are principally diftri- 



buted on the air-tube?, of which tlicy every where foUow 

 the courfe. The arteries of the trachea eome from the in- 

 ferior thyroidcal ; thofc of the bronchi sin' derived nnmcdi- 

 ately froiiT the aorta, and are called the biniiciiial arteries. 

 The latter ramify in conjnudVion with the air-tul)es, and ad- 

 here cloltly to them : they are dillributed cliiefly on the 

 intern.il membrane. Several brandies are fpent on tiic 

 bronchial glands, and on tlie parietes of the pulmonary vef- 

 fels. D;) thi-v anadomofe with the puhuoiiary artery ? We 

 ihould be inclined to iuppofe that they do not, from con- 

 fidering that the two kinds of veflils contain blood of dif- 

 ferent natures, and have allogtiher diflercnt offices. The 

 bronchial arteries convey arterial blood tor the nutrition of 

 the lung- ; the pulmonary artcrv takes the venous blood, 

 that it may be fubmitted to the attion of the air in refpira- 

 tion. Yet it has been aflTerttd by feveral anatomifts, that 

 fuch an aiiallomofis does take place. The bronchial veins 

 accompany the arteries; their tranks end in the wna 

 a/ygos oil the right fide, and in the fuperior iutercoftal vein 

 on the left. 



The par vagum furnirties nearly all the nerves belonging 

 to thefe organs : thofe of the trachea come from it alto- 

 gether. The nerves of the bronchi are derived from the 

 pulmonary plexufes formed principally by the par vagum, 

 but p irtly alio by branches from fome ganglia of the great 

 fynipathetic. As thefe nerves Item to be diliributed entirely 

 on the air-tubes, perhaps the epithet bronchia would be 

 more proper for them than pulmonary. 



Ti>e vafciJar fyftem of the lungs may be divided into 

 three parts, dillinct in their nature, properties, and the 

 immediate olyeiEt of their phenomena. The firil is the pul- 

 monary artery, or the end of the general iyllom of black 

 bhiod ; the fecond, tlie pulmonary veins, or commtnccinent 

 of the general fyllem of red blood ; and tlve third, the ca- 

 pillary iyftem intermediate to the two preceding. (See 

 CiucuLATiOK and Heart.) The pulmonary artery arifes 

 from the upper and anterior part of the right ventricle, in 

 front of the origin of the aorta. It pafles upwards and 

 backwards, lying clofe on the left fide of the root of the 

 aorta, and, after a courfe of about an inch and a half, di- 

 vides into a right and left branch detUned for the corre- 

 fponding lungs. Thefe two divifions feparate moft widely 

 at their origin, going off from the trunk at right angles, 

 and hardly forming a lenfible angle with e.ach other. The 

 feparation takes place on the left fide of the aorta. The 

 right trunk goes immediately behind the aorta and luperior 

 vena cava, and follows a tranfverfe courfe to the right lung ; 

 the left has an analogous courfe en the left fide of the body, 

 but is much fliorter than the right, on account of the latter 

 palling beiiind the aorta and vena cava. Both are placed ia 

 front of the bronchi, and crofs the courle at firll, being di- 

 refted a little from below upwards ; but they are fubdivided 

 exaftly like the bronchi, and follow their courfe, being 

 clofely connefted to them throughout ; the artery is gene- 

 rally placed above its correfponding air-tube. For the or- 

 ganifation of this veffel, we refer to the article Heart. 



The pulmonary veins, arifing from the capillary fyftem, 

 follow a courfe analogous to that of the arterial divifions. 

 Thefe alio accompany the air-tubes, and are fituated under 

 them. They unite gradually into larger and larger tubes, 

 and form ultimately four confiderable trunks,-two belonging 

 to each lung, and terminating in the left auricle of the heart. 

 Tlie fuperior right pulmonary vein pafles out of the lung 

 below tlie bronchus, and goes with a little obhquity down- 

 ward.s : the inferior afcends obliquely towards the auricle. 

 The left veins have a fimilar arrangement ; one defcendt, 

 ajid the other afcends : they are more approximated than oa 



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