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XIII] East Africa. It has spread in the past to Europe; this is a comparatively unimportant matter, as the climatic and hygienic conditions in that continent are not favourable to the stegomyia mosquito, and therefore to the extension of the disease. It is otherwise in this respect, it is to be feared, with Asia. Fortunately, yellow fever, so far as known, has never appeared in the crowded, filthy cities of the East ; but, should it ever be introduced there, the favourable climatic conditions, the surpassing filth everywhere, the presence of stegomyia mosquitoes, and the too frequent absence of efficient sanitary machinery will enable it to spread like wildfire in an entirely non-immune population. The probable reason of its non-introduction into Asia is that the trade route from the West Indies and Central America to China and India has hitherto not been a direct one, but has passed by a long circuit either to the north or to the south. When the American interoceanic canal is in full use there will be direct and rapid communication between the present yellow-fever centres and Asia. With this more direct and more rapid communication there will arise a corresponding risk of spreading yellow fever into a huge section of tropical humanity which has hitherto enjoyed exemption from one of the deadliest diseases afflicting mankind. An infected mosquito (and Stegomyia calopus, according to Giles, is a good traveller), either shipped by accident or brought on board by some thoughtless or malicious person, could easily be conveyed alive to the shores of Asia, and would suffice to set, so to speak, the whole of the tropical section of the Eastern hemisphere in a blaze. The history of the spread of disease by the rapid methods of modern travel is full of examples that should serve as a warning to our rulers and responsible sanitary authorities. Let us hope that this important matter will receive the attention it demands, and that due care will be exercised that America does not reciprocate the introduction of cholera from Asia by a return gift of yellow fever.