Before showing that our tropical expansion is based on the commensalism existing between us and the natives, it is necessary to prove that we cannot colonize there. The history of attempts of white men to colonize in the tropics has been a very sad one. So many failures have resulted that it is now generally acknowledged to be impossible. White men might live anywhere on earth, perhaps, if they knew how to protect themselves. They can live under the ocean in a diving bell for awhile, but that does not mean acclimatization to a fish's environment.
A great deal of the past mortality in the tropics has been due to infections, but since we have learned how to escape them, the death rate has been diminished, though not so very greatly, for as soon as an Englishman in India or an American in the Philippines, begins to break down, he is sent home. Our army statistics place these cases with the home troops. Some of our tuberculosis, for instance, arises in the Philippines, and the deaths occur in the United States. This reduction of the death rate in the tropics has given rise to a widespread opinion that acclimatization is possible, and it seems an almost hopeless task to convince people of the truth. To dodge or hide from the causes of death is the necessity of the well-housed white man, but the tropical native resists the same dangers which would kill Northern types. That is, a white man cannot safely do manual labor in the open - the test of acclimatization. Even with all his care, his children deteriorate unless sent North.
The sanitation of Panama has so completely removed causes of death that thousands are now working at places formerly considered uninhabitable, and the death rate has been so greatly reduced that it is said to be a healthier place than New York City. Yet, as a matter of fact, the death rate is kept down by sending home all who cannot recover there, and, indeed, many do die after they come home sick. No "colony" can survive if it must send its invalids away to save their lives. Indeed, it cannot afford such expenses as those needed in Panama to keep the workmen alive, and for that very reason it is generally acknowledged that tropical "colonies" will always be unsanitary except when a rich Northern nation supplies the funds. No little community can support the enormous sanitary force needed in Panama, for instance.