I have already indicated the part which the great air-ways played in distribution of B. diazotans over the world; but once it had been planted in the new centres to which the aeroplanes carried it, other factors came into action. From South-western Europe, the North-East Trade Winds bore the bacilli across the Atlantic and spread them upon the seaboard of South America, especially around the mouths of the Amazon. The winds on the coast of North America caught up the germs and drove them eventually to Scandinavia and even further east. New Guinea, Borneo, Sumatra and the other islands of the chain were devastated from the Australian centres. Madagascar was contaminated also, though the point of origin in this case is not definitely known. Probably the ocean currents played their part, as they certainly did in the destruction of Polynesian vegetation.
Climate had a considerable influence upon the development of the bacilli, once they were scattered. In the Tropics, they multiplied with even greater rapidity than they had done in the North Temperate Zone. On the Congo and in the Amazonian forests they seem to have undergone a process of reproduction almost inconceivably swift. Those which drifted up into the frigid regions of the North and South, however, appear to have perished almost without a struggle: either on account of the low temperature or the lack of nitrogenous material, they produced very little effect in either of these districts. The sea-plants seem to have been unaffected by them there; and one of the strangest results of this inactivity was the complete change in habits of various fishes, which now sought in the freezing North the feeding and breeding-grounds which suited them best. The herring left the North Sea and the cod quitted the Banks in search of purer water. On the other hand, the great masses of weed in the Sargasso Sea were almost completely destroyed, along with the other accumulations south-east of New Zealand and in the North Pacific.
It must not be assumed, however, that wherever the colonies of B. diazotans alighted, devastation followed as a matter of course. For some reason, which has never been made clear, certain areas proved themselves immune from attack; so that they remained like oases of cultivable land amid the surrounding deserts. The areas thus preserved from sterility were not of any great size; usually they amounted only to a few hundred acres in extent, though in isolated cases larger tracts were found unaffected here and there.
With the recognition of the world-wide influence of B. diazotans, the land became divided into two sections: the food-producing districts and the consuming but non-productive areas. Nowhere was there sufficient grain to make safety a certainty. In America, most of the available food-stuffs were still in or near their places of origin when the panic began to grow.
In the matter of meat, things were much in the same state. Those countries which produced great supplies of cattle prohibited exports; and the beasts were hurriedly slaughtered and the carcases salted to preserve them, as soon as the failure of the grass made it impossible to conserve live-stock.
Each country offered features of its own in the débâcle; but I can only deal with one or two outstanding cases here.
The European conditions were so similar to those which I have already depicted in the case of Britain that I need not describe them at all. Southern Russia fared better than her neighbours; for after the Famine there were still some remnants of her population left alive; and it seems probable that the lower density of the Russian population retarded the extinction of humanity in this region long after the worst period had been reached in the western area.
In Africa and India, the course of the devastation was marked by risings in which all Europeans seem to have perished. Thus we have no descriptions of the later stages of the disaster in either case.
In China, the inhabitants of the densely-populated rice-growing districts of Eastern China were the first to have the true position of affairs forced upon their notice; and, leaving their useless fields, they began to move westwards. At first the stirrings were merely sporadic; but gradually these isolated movements reinforced one another until some millions of Chinese were drifting into Western China and setting up reactions among the populations which they encountered on their way. From Manchuria, great masses of them forced their way up the Amur Valley into Transbaikalia. Others, sweeping over Pekin on the road, emerged upon the banks of the Hoang Ho. The inhabitants of the Honan Province moved westward, increasing in numbers as they recruited from the local populations en route. A massacre of foreigners took place all over China.
In its general character, this huge wandering of the Mongol races recalls the movements which led eventually to the downfall of the Roman Empire; but the parallel is illusory. In the days of Gengis Khan, the Eastern hordes could always find food to support them on their line of march, either in the form of local supplies which they captured, or in the herds which they drove with them as they advanced. But in this new tumultuous outbreak, food was unprocurable; and the irruption melted away almost before the confines of China had been reached. Some immense bands descended from Yunnan into Burmah; but they appear to have perished among the rotting vegetation. Another series of smaller bodies penetrated into Thibet, where they died among the snows. The furthest stirrings of the wave appear to have been felt in Chinese Turkestan; and apparently Kashgar and Yarkand were centres from which other waves might have spread: but it seems probable that these westernmost movements were checked by the tangle of the Pamirs and Karakorams. Nothing appears to have reached Samarkand. But here, again, it is difficult to discover what actually did occur. Any survivors who have been interrogated are of the illiterate class, who had no definite conception of the route which they followed in their wanderings.