This infecting and being infected without so much as its being known to either person is evident from two sorts of cases which frequently happened at that time; and there is hardly anybody living, who was in London during the infection, but must have known several of the cases of both sorts.

1.  Fathers and mothers have gone about as if they had been well, and have believed themselves to be so, till they have insensibly infected and been the destruction of their whole families; which they would have been far from doing if they had had the least apprehensions of their being unsound and dangerous themselves.  A family, whose story I have heard, was thus infected by the father, and the distemper began to appear upon some of them even before he found it upon himself; but, searching more narrowly, it appeared he had been infected some time, and, as soon as he found that his family had been poisoned by himself, he went distracted, and would have laid violent hands upon himself, but was kept from that by those who looked to him; and in a few days he died.

2.  The other particular is, that many people, having been well to the best of their own judgment, or by the best observation which they could make of themselves for several days, and only finding a decay of appetite, or a light sickness upon their stomachs,—­nay, some whose appetite has been strong, and even craving, and only a light pain in their heads,—­have sent for physicians to know what ailed them, and have been found, to their great surprise, at the brink of death, the tokens upon them, or the plague grown up to an incurable height.

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 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 carcasses, 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.[272]