The article began by pointing out that in the recent history of civilization Europe had been subject to a long succession of pestilences. From the fourteenth to the seventeenth centuries, wrote Thrale, the Black Death, now commonly supposed to be a form of the bubonic plague, was practically endemic in England. In more recent times small-pox had been responsible for enormous mortality among all classes, and, in our own day, tuberculosis. In the two former examples, Thrale pointed out, and in many other diseases, infectious or contagious, or both, these pestilences had gradually lost virulence. By the elimination of those most susceptible to infection and incapable to resist the onslaught of the disease, and by the survival of those whose vitality was strong enough either to resist attack or to achieve recovery, mankind at last were gradually becoming immune against certain infections which had prevailed in the past. And in a greater or less degree this immunity was without doubt being obtained against a whole host of lesser ills. This comparative immunity, in fact, was one of the means of man's evolution towards a more perfect physical body. "But let us consider for a moment," wrote Thrale, "the appalling danger which threatens us when we are attacked by a pestilence which is entirely new to humanity; new, so far as we know, to the world. In the middle of the fourteenth century the Black Death is recorded in some places to have killed two-thirds of the whole population, and, notwithstanding the modern improvement in sanitation and general hygiene, there is no inherent reason why another pestilence may not appear, which may be even more deadly. And we are faced at the present moment with the awful threat that such a pestilence has appeared, the pestilence commonly known as the 'new plague.' There is no reason why we should consider the appearance as without precedent in history; there is no reason why we should regard its coming as outside the laws of common probability; finally, and most decisively, there is no reason why England should not be smitten.