LUNGS. 



•tlie parts about tlie head, and with a fenfc of fufFocatioir: 

 'when continued tor along time it caufes hcad-achc, loreiiefs 

 of the chell, &c. 



Snet'z-ing is an aftion fimilar in its nature, but more vio- 

 lent in degree than coughing ; and it has a different caufe, 

 ■viz. irritation of the nnembrane lining the nofc. A (liort 

 but generally full infpiration is followed by a mofl vehement 

 exfpiration, (baking almoll: the whole body. The expelled 

 air, which in coughing patfes through the mouth, is directed 

 in fneezing, through the nofe, for the purpofe of removing 

 the irritating caufe. Any extraneous bodies brought into 

 ■coiitaft witli the pituitary membrane, as inllruments or irri- 

 tating powders, fuch as fnuff, &c. or its own mucous fecre- 

 tion, and in fome individuals fudden expofure to Itrong and 

 dazzling light, will produce fneezing. Although it is an 

 involuntary cflbrt, it may be in fome degree increafed or 

 diminiflied by the will. It is a fmgular fatt, that preffure 

 about the bridge of the nofe, applied when the inclination is 

 felt, will generally prevent it. 



How far the following obfervation of Soemmering tends 

 to elucidate the manner in which llimuli applii'd to the pitui- 

 tary membrane aft on the rcfpiratory mufcles, in exciting 

 this convulfive motion of them, is left to the judgment of 

 the reader. " Sneezing ariles from fome rc-action of the 

 ■fcrain, when irritated, through the medium of the nafal 

 nerves, i. e. the olfactory and filth pair?, upon the phrenic 

 nerve ; and that it mud be produced in this way is proved 

 by the fa£l, that the phrenic and thefe nerves have no con- 

 nection out of the head." De Corporis humani Fabrica, 

 t. vi. p. 84. 



In laughing, a full infpiration is followed by frequent, im- 

 perfect, and as it were broken exfpirations, by which the 

 chcll is not completely emptied. As rcfpiration is hurried 

 beyond its natural rate in this aft, the circulation is rather 

 quickened ; and from the convulfive kind of aftion in which 

 it confifts, a general agitation muft be imparted to the ab- 

 dominal contents. In many individuals, a very obvious 

 fnaking of the cheft and abdomen accompanies laughter, 

 particularly when violent, lo as to have become matter of 

 very common obfervation : hence the forenefs experienced 

 from its long continuance. The features are at the fame 

 time affefled in a peculiar manner. In fome individuals the 

 latter circumftance is chiefly obferved. The flighter cafes 

 of laughter, which are rather called faiihng, confift merely 

 of this change of features ; but when it goes further, the 

 diaphragm and abdominal mufcles are brought into aCtion. 

 A confiderable prcduftion of found takes place at the fame 

 ^time, reprefenting in men chiefly the vnwe's a and ; in 

 women c and i. The moutli and its neighboinnng parts are 

 principally aflfeftcd in the face ; the corners are drawn up- 

 wards and outwards, fo as in many cafes to expofe the 

 teeth ; the cheek is fwelled, and the general elevation of 

 the integuments raifes the loner eye-lid, fo as to contraft 

 the aperture between the two lids. As the interruption in 

 the regular performance of refpiration produces turgefcence 

 about the beid in violent and long continued laughter, the 

 lacrymal fecretion is augoiented, and a copious flow of tears 

 often enfues. 



The catifes of lau'ghter are partly moral and partly phyfi- 

 cal ; with the former we h:ive nothing to do in this article, 

 except to obferve that laughing and weeping feem quite 

 peculiar to the human fubjec^. Gentle friftion and preffure 

 of various parts of the body, as the fules of the feet,^the 

 axillx, hypochondria, &c. commonly called tickUng, are 

 the chief of the latter kind. 



Involuntary laughter is a fvmptom of fame difeafes, as 

 Jiyiteria ; and the ancients- were of opinioa that injuries of 



the diaphragm produced it : in this cafe they called it rifuj 

 fardonicu?. Modern obfcrvations do not confirm this faft. 

 IVceping begins with a deep infpiration, which is followed 

 by fliort, interrupted exfpirations, at longer intervals from 

 each other than in laughing : thefe often ihake the thorax 

 and abdomen, and even the head. They are finiflied at lall 

 by a (Irong exfpiration, followed by another infpiration or a 

 figh. This, like laughing, is generally produced by certain 

 mental aftcftions ; but in fome inllances it owes its origin 

 to phyfical caufes, as bodily pain ; and difeaies, as hyftcria, 

 hypochondriafis, &c. Children generally cry immediately 

 on their birth. The features are confiderably affefted in 

 weeping ; the eye-lids are contraftcd, and the fore-head 

 wrinkled : the mouth has its corners drawn downwards. 



Hiccough is fometimes afibcialed with weeping. It con- 

 fills of a full, violent, fonorous, and Ihort, or fometimes 

 even convulfive involuntary infpiration through a contracted 

 glottis. Some confider that the epiglottis is concerned in 

 producing the peculiar found of hiccough, and that this 

 organ is Itruck by the air as it forcibly enters the larynx. 

 The diaphragm appears to be the part principally concerned 

 in this convulfive infpiration. Sometimes an expulfion of 

 air from the (lomach through the oefophagus is joined with 

 hiccough. Two, three, or more natural infpirations and 

 exfpirations take place in the interval between tivo hiccoughs. 

 It may be occafionally prevented by depreflTing the dia- 

 phragm, and thus holding the breath ; or by iwallowing 

 fomething fiowly. 



There are many caufes exciting it. The nearnefs of the 

 ilomach to the diaphragm occafions the latter to be often 

 affefted by particular ilates of the former organ. Eating 

 cr drinkingr too much, or unwholefome articles, is a frequent 

 fource of the complaint. Wounds or difeafes of the (to. 

 mach, or of the diaphragm, may produce it ; as alfo various 

 general difeafes of the frame, in which it often appears as 

 the precurfor of death. 



Infpiration is immediately concerned in the aft oi fueling. 

 The lips are clofely applied round an objeft, e.g. thofe of 

 the child to th.e mother's nipple. The air" contained in the 

 mouth is then more or lefs completely exhaufted by infpira- 

 tion, and the preffure of the furrounding air forces into 

 this more or lefs complete vacuum the contents of the lafti- 

 ferous tubes. When a liquid is lucked through a tube into 

 the mouth, the vacuum is formed in that tube, which is 

 embraced by the lips, and the air, preiTing on the furface of 

 the liquor, forces it up the tube into the mouth. If the lips 

 are direCtly immerfed in the fluid, a vacuum is formed, and 

 the fluid rifes into it exaftly in the fame way. The aft of 

 drlnh'-ng is effefted on the fame principles. 



Dejcription of the Pleura and Mediajlinum. — The pleura is 

 a thin tranfparent ferous membrane, lining the cavity of the 

 thorax, and reflefted over the contained hings. Each of 

 the latter organs is eticlofed in a particular bag of its own, 

 which bears the fame relation to the lung, as the pericar- 

 dium d()(« to the heart ; furrounding it like a loofe bag or 

 (liealh, and immediately invefting its furface : hence we na- 

 turally diflinguilh two parts of this membrane, viz. the 

 lining of the chell (pleura coflalis), and the external co- 

 veri/ig of the lung (pleura pu'monalis.) 



As there are two lungs, there niuft alfo be two pleura?, 

 a right and a left. We may form a notion of them by 

 conceiving two membranous bags, forming entire and im- 

 perforated cavities, placed laterally with refpeft to each 

 other, and forming, by their appofition, a partition dividing 

 the chefl; into a right and a left fide, and containing in its 

 fubftance feveral of the orgai-.s belonging to this cavity. 

 That the two membranous bags are perfeftly dillinft, lo 



that 



