"According to report among the Chinese, this 'new plague' has been spasmodically epidemic in Tibet for more than a century. We have, as yet, no certain facts upon which to base any hypothesis, but is it not credible that during that time some bacterium or bacillus--hitherto harmlessly parasitic, perhaps, in the blood of lower animals--has changed its life habit? In the isolated and sparsely inhabited regions of Tibet, it is possible that for many thousand years the assumed bacterium was never bred in the blood of man; it is possible that when it first found a new host it was comparatively harmless to him, but within a hundred years it may have become so altered by new conditions that it has developed into what is practically a new species. If these theories are relatively true, it is not unlikely that this new bacterium is working out its own destruction by the destruction of its hosts. It may be that it is one of those blind alleys of evolution which reach a certain stage of development and then disappear. But meanwhile what of mankind? We know so little of the history of microscopic life. There is a whole world of evolution in process of which we have no conception, and at this stage, whether my hypothesis be a possible one or not, we are at least sure that an unknown organism--animal or vegetable--has become visible to us in its effects and may alter the whole history of mankind. "I lay stress on these aspects, because we are so hide-bound, so restricted, so conventional in our ideas that we assume, without thought, that the process of life as we know of it from a few thousand years of history can never be interrupted. In our few years of individual existence we become accustomed to certain apparent laws of cause and effect, and will not believe that there can be any exception to those assumed laws. But, now, in the face of recent evidence, it is absolutely essential that we should realize instantly and practically that we are threatened with a new factor in life, which imperils the whole human race. It is no longer safe to comfort ourselves with the belief--begotten of our vanity--that the world was necessarily made for man. It behoves us to take measures for our protection without delay, to undertake our own cause and trust no longer in any beneficent Providence that works always for our ultimate benefit. "These measures of protection are clearly indicated. We must close our doors against the invasion of the plague. Quarantine will not protect us; we must have no traffic with Europe until the danger is past. By the happy accident of our position we can become isolated from the rest of the world. We must close our doors before it is too late." 3