IMPROVED. 73 



meter, for Inftance, is four Inches and Axis feven, 

 is to the Orifice of the Pipe. 



To explain this yet farther, according to the ni- The Pref- 

 ceft Calculation, it would appear liker a Romance iVire of the 

 than a true Hiflory; altho' it is certain that there ■'^"" "t^°^ 

 is, even in human Bodies, a PrelTure of Air upon ,^jj'3,^j.--g(-Q 

 the internal Surface of the Lungs, equal to Ij^.\12 oi'the 

 Pound Weight ; and therefore, hov/ much more the l.ungs. 

 Air's PrefTure upon a Horfe's Lungs exceeds this ^^^^-^1^ ^f 

 Account, I leave any one to judge. And although {yl.\g-^['\^ 

 thefe fcem to be prodigious Weights, yet it muft Human 

 ftill be underftood, that the Preffure upon each Part Bodies. 

 of the Surface of the Lungs, equal to the Orifice of 

 the Larynx or Top of the Wind-pipe, is not greater 

 than it is at the Larynx itfelf And that thefe vafi: 

 Weights arife from the vaft Extent of the Surfaces 

 of the Veficles or little Bladders, upon which it was" 

 neceffary that the Blood fhould be fpread in the 

 fmalleft Capillary VefTels ; that each Globule of 

 the Blood might, as it were, immediately receive 

 the whole Force and Energy of the Air, and by it 

 be broke into fmaller Parts, fit for Secretion or Dif- 

 charge, and likewife for Circulation. 



From hence we may learn the m-echanical Rea- 

 fon of the Strudlure of the Lungs : For, feeing the 

 whole Blood of the Body was to pafs through them, 

 in order to receive the vivifying Virtue of the Air, 

 and this could only be communicated to it by fmall 

 capillary VefTels ; I fay, in fuch Cafe, it was 

 abfolutely neceffary that the Surfaces upon which 

 thefe Veffels were to be fpread, fhould be pro- 

 portioned to their Number, and this is admirably 

 well provided for, by the wonderful Fabrick of the 

 Lungs. 



If the Gravity of the Air was always the fame, 

 and if the Diameter of the Trachea Arteria^ fome- 

 times called Afp'era Arteria or Wind-pipe, and the 

 Time of every Expiration or Driving out of the 

 Breath, were equal in all Creature?, this Weight 

 upon the Lungs would be always the fame. But 

 E fmce 



