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ter, and at length, but not in less than in ten Days after the first Assault, compleat their Course. The intrinsick Nature and Properties that distinguish and diversify this from other inflammatory Fevers, consist in the peculiar Figure and Size of the Matter of it, that make it uncapable of being disengaged and separated from the Blood by any other Strainers, or by any other Way, than that before described; and therefore the active Principles of the Blood are, by their natural Oeconomy, necessarily determined to take this one Way, of casting off the unsound Parts for the Preservation of the whole. But what that peculiar Figure, Structure, and Disposition are, cannot be discovered by the sharpest Sight; for this, like other intrinsick essential Differences, that constitute any one Sort or Species of Things, and separate and distinguish it from all others, lying not within the Compass of human Understanding, disappoint our most diligent Enquiries, and triumph over the Endeavours of the acutest Philosopher. We must be contented in this, as in all other Diseases, to understand the Cause by the Effect, and essential Principles by their Symptoms, as we know the internal Nature of the Tree by its peculiar Fruits; and therefore I shall enter upon a fuller and more particular Description of the Small-Pox, that I may shew the Properties and Qualities by which it is discriminated from other inflammatory Fevers.

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