There are Two visible sorts of the Disease named the _Plague_: The weaker sort is that which produces Swellings, or inflamed or corrupted Sores, which are accompanied with a Fever. The other sort is that which is named the _Spotted Plague_. The First sort is sometimes Curable; but the Second is Incurable; at least, no Remedy as yet hath been found. The truth is, the _Spotted Plague_ is a _Gangrene_, but is somewhat different from other sorts of _Gangren's_; for this begins amongst the Vital Parts, and, by an Infection, spreads to the Extream Parts; and not only so, but to Forrein Parts; which makes not only a general Infection amongst all the several Parts of the Body, but the Infection spreads it self to other Bodies. And whereas other sorts of _Gangren's_ begin outwardly, and pierce inwardly; the _Plaguy Gangrene_ begins inwardly, and pierces outwardly: so as the difference (as I said) is, That the ordinary sort of _Gangren's_ infect the next adjoining Parts of the Body, by moderate degrees; whereas the _Plaguy Gangrene_ infects not only the adjoining Parts of the same Body, and that suddenly, but infects Forreign Bodies. Also, the ordinary _Gangren's_ may be stopped from their Infection, by taking off the Parts infected, or diseased. But the _Plaguy Gangrene_ can no ways be stopped, because the Vital Parts cannot be separated from the rest of the Parts, without a total ruine: besides, it pierces and spreads more suddenly, than Remedies can be applyed. But, whether there are Applications of Preventions, I know not; for, those Studies belong more to the _Physicians_, than to a _Natural Philosopher_. As for the Diseases we name the _Purples_, and the _Spotted Fever_, they are of the same Kind, or Kindred, although not of the same sort, as _Measles_, and the _Small-Pox_. But this is to be noted, That Infection is an act of Imitation: for, one Part cannot give another Part a Disease, but only that some imitate the same sorts of Irregular Actions of other Parts; of which some are near adjoining Imitators, and some occasion a general Mode. CHAP. III. Of the Small-Pox, and Measles.