It was very sad to reflect how such a person as this last mentioned above had been a walking destroyer perhaps for a week or a fortnight before that; how he had ruined those that he would have hazarded his life to save, and had been breathing death upon them, even perhaps in his tender kissing and embracings of his own children.  Yet thus certainly it was, and often has been, and I could give many particular cases where it has been so.  If then the blow is thus insensibly striking—­if the arrow flies thus unseen, and cannot be discovered—­to what purpose are all the schemes for shutting up or removing the sick people?  Those schemes cannot take place but upon those that appear to be sick, or to be infected; whereas there are among them at the same time thousands of people who seem to be well, but are all that while carrying death with them into all companies which they come into.

This frequently puzzled our physicians, and especially the apothecaries and surgeons, who knew not how to discover the sick from the sound; they all allowed that it was really so, that many people had the plague in their very blood, and preying upon their spirits, and were in themselves but walking putrefied carcases whose breath was infectious and their sweat poison, and yet were as well to look on as other people, and even knew it not themselves; I say, they all allowed that it was really true in fact, but they knew not how to propose a discovery.

My friend Dr Heath was of opinion that it might be known by the smell of their breath; but then, as he said, who durst smell to that breath for his information? since, to know it, he must draw the stench of the plague up into his own brain, in order to distinguish the smell!  I have heard it was the opinion of others that it might be distinguished by the party’s breathing upon a piece of glass, where, the breath condensing, there might living creatures be seen by a microscope, of strange, monstrous, and frightful shapes, such as dragons, snakes, serpents, and devils, horrible to behold.  But this I very much question the truth of, and we had no microscopes at that time, as I remember, to make the experiment with.

It was the opinion also of another learned man, that the breath of such a person would poison and instantly kill a bird; not only a small bird, but even a cock or hen, and that, if it did not immediately kill the latter, it would cause them to be roupy, as they call it; particularly that if they had laid any eggs at any time, they would be all rotten.  But those are opinions which I never found supported by any experiments, or heard of others that had seen it; so I leave them as I find them; only with this remark, namely, that I think the probabilities are very strong for them.

Some have proposed that such persons should breathe hard upon warm water, and that they would leave an unusual scum upon it, or upon several other things, especially such as are of a glutinous substance and are apt to receive a scum and support it.