The Substance of the _Lungs_ is soft, spongy and rare, curiously compacted of most thin and fine Membranes, continued with the Ramifications of the _Trachea_ or Wind-pipe, which Membranes compose an infinite number of little, round and hollow Vesicles, or Bladders, so placed as that there is an open Passage from the Branches of the _Aspera Arteria_, out of one into another, and all terminate at the outer Membrane that investeth the whole _Lungs_: These little Bladders by help of their muscular Fibres contract themselves in Expiration, and are dilated in Inspiration, partly by the Pressure of the Atmosphere, and partly by the elastic Power of the Air, insinuating it self into these Vesicles thro’ the Windpipe and it’s several Branches: Their Lobes are two, the right and left, parted by the _Mediastinum_, each of which is divided into many lesser Lobules, according to the Ramifications of the _Aspera Arteria_; they have all sorts of Vessels that are common to them with other parts, as Arteries, Veins, Nerves, Lympheducts, but peculiar to themselves they have their _Bronchia_, or the Branches of the Wind-pipe, for bringing-in and carrying-out Air so necessary to Life, that we cannot Live without it: And when we consider their admirable Structure, (as well as the Structure of every individual part of our Body) how ought we to adore the infinite Wisdom of our Creator! Now when these small Vesicles or Bladders are replete with extravasated _Serum_, or purulent Matter, the natural Tone of the _Lungs_ is so weakned, that we cannot enjoy the Benefit of free and full Respiration, hard, scirrhous Tumours and Tubercles are bred, attended with a dry and troublesome Cough, Oppression of the Breast, difficult and short Breathing, preternatural Heats, Exulcerations, and other deplorable Symptoms, according to the Degrees of Obstruction, and different Nature of the included Humours. IV. The external Procatartic Cause of a _Consumption_ of the _Lungs_ is cold Particles of Air, constipating the Pores of the Body, whereby the _Serum_ which ought to expedite the Motion, and temperate the Heat of the Blood is separated from it, and thrown upon the Glands of the _Larynx_, and the spungy Substance of the Lungs themselves: For as the _Lympha_ helps the Motion of the _Chyle_, so the _Serum_ accelerates the Circulation of the Blood, being carried about with it thro’ the smallest Capillary Vessels and remotest parts of the Body, lest it should be inflamed with a burning Heat, or stagnate by excessive Thickness; during which circular Motion they are both called by the same common Name, but when some Portion of _Serum_ is separated from the Mass of Blood, and retreats to some one or more of the Emunctories; according to their various Dispositions, it derives a Name from those particular Parts on which it seizeth, as when it distils upon the Eyes, we call it _Opthalmia_, when upon the Nose _Coryza_, and when upon the _Thorax_ it goes by the proper Name of a _Catarrh_.