In order therefore to understand wherein this deadly quality Consists; I say in the first Place, that Life, so far as it respects the Body, is, in one Word, the _Circulation_ of the Blood; that is, its Motion in _Conical_ Distractile Vessels from the Heart to the Extreme Parts, and its Return to the Heart again by the same Canals inverted; For ’tis upon this that all Animal Functions, all Sense and Motion Voluntary and Involuntary, do depend; so that the Regularity of this Course is the Measure of Health, or the most perfect Life, as its various Irregularities are the Occasions of Sickness and Diseases, or a beginning Death. Now all the Animal Operations and Offices which proceed from this Circulation, are the Effects of several Secretions of Liquors of very different Natures out of the same Fluid Mass; It was therefore absolutely necessary that the Blood, before It be distributed to the Organs, should be so comminuted and broken, as that no Cohæsion of its Parts should hinder the Separation of these _Juices_ from It, when it Arrives with a determinate Force at the Orifices of the Secretory Vessels. This Work is done in Its Passage thro’ the _Lungs_, by the repeated Compression of the Air in those _Bladders_ upon the Arteries, with wonderful Contrivance dispers’d among ’em (160). Herein lies the Use and Necessity of _Respiration_; and the sudden Mischief of Stopping it, in that the whole Mass of Blood being to pass this way, upon a Check here, there presently insues a Stagnation, that is, a Cessation of all Animal Functions, or Death; Which will be the more speedy, if not only no Air is inspired, but a Fluid of a quite different Nature from It succeeds in its Place. Wherefore it must be observed, that this good Effect of the Air is performed by its _Elasticity_; And that no Fluid whatsoever, that we know besides, is _Elastic_, at least to any considerable Degree, that is, has a faculty of expanding and dilating it self when compressed; No, not _Water_, as near as That is thought to approach to Air in its Nature. And now as to the present Case, I took notice before that this _Vapour_ is one continued and uninterrupted _Steam_, and that quickly after Its rise it falls down again; that is, that it has little or no mixture of Air with It, or no Elasticity; and is, on the other Hand, very heavy, when forsaken by the Force of _Heat_ that drove it upwards.