But tho' the whole Superficies of our Bodies are Penetrable by these Poisonous Particles, yet the principal Mischief is communicated to the Blood in its Passage thro' the Lungs. For considering the prodigious Number of the Pulmonary Vesicles, into all which the Air enters in Respiration, and likewise the vast Increase of their Surfaces on that Account, and also the greater Force by which these Particles are applied to the Internal Surfaces of the Vesicles in Expiration, in Proportion to that whereby they are applied to other Parts of the Body of equal Superficies; it will evidently appear, that the Contagion is chiefly communicated by these Vessels to the Blood. For it appears by the Barometer, that every Inch Square upon the Surface of our Bodies is pressed upon by a Weight nearly equal to 1800 Drams, when the Mercury stands highest in the Barometer. Now supposing with Dr. _Kiel_[q] that both the Lobes of our Lungs contain 226 solid Inches, of which only 1/3 or 75 Inches are Vesicles. Supposing also the Diameter of a Vesicle to be 1/50 Part of an Inch, the Surface of the Vesicle will be .001256 and the Solidity .0000043, by which if we divide 75 the Space fill'd by the Vesicles, the Quotient, _viz._ 17441860 X .001256 the Surface of a Vesicle, gives the Sum of the Surfaces of all the Vesicles, = 21906.976 square Inches. Which Sum being multiplied by 1800, the Number of Drams which every square Inch of the Surface of our Bodies sustains, gives the Weight which the whole Internal Surface of the Lungs sustains by the sole Pressure of the Atmosphere, when the Mercury stands highest in the Barometer, equal to 39442556.800 Drams, equal to 410859.966 + 64/96 lib. _Troy_ weight, as appears from the known Laws of _Hydrostaticks_[r]. [q] Animal Secret. [r] _Marriote_'s Hydrostaticks.