These Disorders will necessarily be increased on account of the Air's Spring being weakned by its Heat, the Vessels of the Lungs being less inflated, and the Globules of the Blood less broken and divided, and the more especially in a humid Air, Heat and Moisture necessarily relaxing the Tone of the Fibres and Vessels, and rendring them less Springy and Elastic. Hence then the Quantity of Spirits being diminish'd, and their Motion more slow, the Contraction of the Heart and other Muscles will be more weak and languid, and being stimulated by the Acrimony of the Circulating Liquors, must contract more frequently than in a Natural State; The Consequence of which is Weakness, Faintness, Thirst, and Dejection of Spirits. These and the preceeding Symptoms will necessarily continue, 'til such time as the gross and viscous Matter, being shook and loosen'd by the Action of the Capillary Vessels, is washed away into the Veins by the force of the Circulating Fluids, and there continues its Course with the rest, 'til it be either attenuated and secreted, or lodged again in the Capillaries to excite new Disorders. [Sidenote: _Malignant Fevers._] Now if to this evil Disposition of the Air be added a number of pungent stimulating Particles, whether bred in the Body or floating in the Air, and thereby communicated to the Blood, which are apt to coagulate the Animal Juices, so as to form _Moleculæ_ of such Shapes and Sizes as more firmly obstruct the Capillary Vessels, and at the same time stimulate and corrode the nervous Parts; It will necessarily happen, that the preceeding Symptoms must be highly exasperated, and a Fever of a much worse Nature produc'd. Hence then must follow a violent Hurry and Colluctation of the Fluids, the Viscid and coagulated Parts of the Blood in some Parts obstructing the Circulation of the Juices, and the Acrid, Volatil, and Fiery Parts, rarefying and dissolving others of the more Liquid, to the greatest degree of Pungency and Volatility imaginable. Hence it is easy to perceive how the Motion of the Blood must necessarily be in some Parts more languid, by the Cohesion of the more Viscous parts, in others quicker, join'd with a pungent and stimulating heat, from the increased Velocity and Acrimony of the moving Fluid, and the various Actions of the Particles upon each other, and their Impulses on the containing Vessels; As also how these are capable of almost infinite Variations, in Proportion to the different Quantities and Qualities of the constituent Particles. Hence then appears the Reason of that wandering and uncertain Heat and Coldness, in different Parts of the Body at the same time. Hence appears the Reason of that great Inquietude and Anxiety, of those uncertain and partial Sweats, Watchings, Tremors, stretching Pains of the head, and the like, as will be more fully shown hereafter.