_Epidemic_ Diseases of all Kinds and Degrees of Exacerbation, have their Rise from some common Cause, that affects all within its Extent more or less, in Proportion to the particular Fitness of different Constitutions to be affected by it: And by the _Bellinian_ Doctrine we are taught, how all those Changes are made in the Blood, when thrown into a Fever by these Causes, even from the most simple _Ephemera_, to the most complicated and malignant Cases whatsoever; to which therefore the Reader must be referred, for a clear Understanding of such Matters; it being sufficient to our Purpose here to observe, that he demonstrates all Fevers to be attended with some Fault in the Blood’s Motion, Quantity, or Quality, or in some or all of them together; and that its chief Fault in Quality, (which is most to the present Case) consists in an unequable Fluidity, some Parts of it being rendered thinner, and others thicker at the same Time, than in a natural State; not unlike what happens to all coagulated Liquors. FROM this Condition of Blood, this great and wonderful Man goes on to shew, through the whole Course of his Propositions, that the coagulated Part, which he commonly distinguishes by the Name of _Lentor_, does accumulate in the capillary Vessels until their Endeavours of Restitution, as in all Elastick Bodies, are greater than the protruding Force, when by the Arteries Re-action upon it, the _Lentor_ is shook, dislodged, and washed away into the Veins, and ordinary Course of Circulation, there continuing its Progress till it is either fitted for some Secretion and Evacuation, or again lodged in the Capillaries, to bring on a new Paroxysm. THIS unequable Fluxility of the Blood arises from two general Causes, either from such Means as diminish its Motion, or from the Mixture of such Particles, as cannot only of themselves be reduced by the digestive Powers into homogeneous Dispositions therewith; or as have a Faculty to put in Fusion some Parts of the Mass, and leave the other thicker than before; these are particularly enumerated, and their Ways of Operation distinctly demonstrated by _Bellini_. CONFORMABLE to this Change in the Blood, which is the common Promptuary of all the other animal Fluids, every Thing separated from it hath some correspondent Affections; and the nervous Fluid in particular, which is separated from a Mass so unequally fluid, cannot but in it self have some Parts too fine, and others too gross, besides the Inequalities in the Times and Quantities of its Separation; from all which the same Author accounts for those Affections, termed nervous, which are the _Concomitants_ of Fevers: And in the Prosecution hereof he frequently takes Occasion to speak of this Fluid to be thin, sharp, hot, fiery, dry, _&c._ as the saline and rigid Parts in its Composition are by the Distemper more or less subtilized, or more or less defrauded of its humid Parts by Exhalation.