Thus, if we have to choose between the origin of the plague-virus among the Tartar hordes besieging the China merchants within the walls of Caffa, and the pre-existence of that virus, for a long time latent, among the goods or effects of the besieged, the latter hypothesis must be accorded the advantage in probability. Accepting it, we follow the virus back to Tana on the Don, from Tana to Sarai on the Volga, from Sarai by a well-trodden route which need not be particularized[290], for many weeks’ journey until we come to the soil of China. According to a dominant school of epidemiologists it is always enough to have traced a virus to a remote source, to the “roof of the world” or to the back of the east wind, and there to leave it, in the full assurance that there must have been circumstances to account for its engendering there, perhaps in an equally remote past, if only we knew them. If, however, we follow the trail back definitely to China, it is our duty to connect it there with an actual history or tradition, immemorial if need be, of Chinese plague. But there is no such history or tradition to be found. We know something of the China of Kublai Khan, fifty years before, from the book of Marco Polo; and the only possible reference to plague there is an ambiguous statement about “carbuncles” in a remote province, which was probably Yun-nan. Not only so, but if we scrutinize the Chinese Annals closely, we shall find that the thirty years preceding the Black Death were indeed marked by many great calamities and loss of life on a vast scale, by floods, droughts, earthquakes, famines and famine-fevers, but not by pestilence unconnected with these; on the other hand, the thirty or forty years after the Black Death had overrun Europe, beginning with the year 1352, are marked in the Chinese Annals (as summarized in the _Imperial Encyclopædia_ of Peking, 1726) by a succession of “great plagues” in various provinces of the Empire, which are not associated with calamitous seasons, but stand alone as disease-calamities pure and simple[291]. If the Black Death connects at all with events in China, these events were natural calamities and their attendant loss of life, and not outbreaks of plague itself; for the latter, assuming them to have been bubo-plague, were subsequent in China to the devastation of Europe by the plague.