The Alterations produced in the Body from a greater Heat continually surrounding it, provided it be not Excessive, are a Rarefaction of the Juices, and Relaxation of the _Fibres_ on the Surface of the Body, and greater Derivation of the Fluids that way. Whence proceeds a large Evacuation of the perspirable Matter. This being continued in a greater Proportion than in a Natural State, will gradually deprive the Blood of its Aqueous and Spirituous Parts, and leave the remaining serous Part more stock'd with acrid and pungent Salts, and the Gross, Terrestrious, Oleaginous, and Viscous Particles more firmly united by their nearer Approach, and stronger Cohesion to each other. This greater Heat or Quantity of Fiery Particles, continually surrounding the Body, will necessarily insinuate it self into, and unite with the Saline, Sulphureous, and other Particles, in the same manner as we see it does with other Substances, both Solid and Liquid[l]; And likewise by increasing the Velocity of the Circulation and Attrition of the Particles against each other, render them on these Accounts also more Volatile, Pungent and Stimulating, and consequently the Blood will consist of Particles more gross and inspissated or coagulated, and likewise of those of a more acrid and pungent Disposition than in a natural State. [l] _Boyl_'s Experm. Nov. de Pond, Ignis & Flam. _Newtoni_ Optic. Quæst. 21 & 22. The Blood being in this depraved Condition, the rest of the Animal Juices must degenerate in Proportion thereto, and the Nervous Fluid, as it consists of the most volatil and subtil Parts, be extreamly acrid and pungent, as well as unequal in its Texture and Fluidity, from the more viscous Parts contain'd in it. [Sidenote: _Putrid Fevers how produced._] This then being the State of the Blood and other juices of the Body, it is easy to perceive how from very Slight, and otherwise trivial Occasions, a Fever of a very Malignant Nature may be produced. Thus the perspirable Matter from a slight Cold taken being retained, or the Vessels any otherwise filled by Irregularities in Diet, or others of the Non-naturals, the Weight of the moving Fluid will be increased, and the Circulation be more languid and slow. Whence the intestine Motion of the Particles of the Blood being diminished, the viscous Parts will cohere more strongly and in greater Quantities than before, and obstruct the Capillary Arteries, especially in the Extremities, and a Coldness, Stretching, Yawning, Torpor, _&c._ necessarily succeed, the constant Attendants of a beginning Fever; All which will bear a Proportion to the Quantity retain'd, and the Viscosity of the moving Fluid.