In torrid regions, thermal environment is of very great importance as regards comfort and certainly influences the health and efficiency of white men. The human race may have arisen under the influence of climates similar to those now prevailing in the Tropics where indigenous peoples sojourn in an almost natural state with little protection against either heat or cold. The European brings with him his native conventions as regards houses and clothing, developed, in the case of Britons, in quite northern regions, where the human race requires protection against cold. These may be more or less unsuitable for tropical heat but, being conventions, they cannot be lightly thrown aside. European clothes afford protection against disease-carrying insects, poisonous stings and bites, and the question arises as to the best way to modify them to suit the hot climate. In any case, the northern European in the Tropics is in an abnormal climatic environment and, though he may survive a long time, there can be little doubt that he rarely enjoys his natural robustness of health with the result that even trivial ailments assume serious aspects. It appears that there is a much narrower margin of health stability, and proportionately greater care is required if the system is to be kept within the limits. Mr Elsworth Huntingdon1 has adduced evidence suggesting that white races, even if they are able to survive within the torrid zone, undergo deterioration.