about within the next few generations, and which may materially affect the existing relations of races, by making their contact, especially in the tropics, either more or less general and close than it is now. I will mention a few of these possible changes.
The power of white races to work and to multiply in tropical countries may be increased by discoveries in medical science extinguishing or providing more effective remedies for certain diseases. The recent expulsion of yellow fever from Cuba by the American physicians and officers opens a wide and interesting field of hope. So, too, the rate of the increase or decrease of population among races inhabiting countries into which they have recently come may rise or fall. The South European races may be found capable of settling North Africa or parts of the torrid zone; some of the tropical races may maintain their prolific quality in climates more severe than they have hitherto known.
Scientific discovery and mechanical inventions may enable the forces of Nature to be more effectively and cheaply used to supersede manual labour in countries hitherto deemed too hot for white men to work in, and may thus increase the afflux of white work-people to those countries.
Some of the races now deemed backward may show a capacity for intellectual and moral progress greater than they have been credited with. The differences between them and the advanced races lie not so much in intelligence as in force of will and tenacity of purpose. How far these latter qualities can be
