HEALTH AND POPULATION 589 



environment for at least two or three generations, but already 

 there are indications that the rate of physical and mental develop- 

 ment, the onset of puberty, etc. are different in the Kenya High- 

 lands from England, and it has been suggested that these differ- 

 ences are associated with blood pressure. Some other effects of 

 climate on health are mentioned in Chapter IV. 



Turning to a subject of more immediate practical importance, 

 research is required on tropical housing and clothing for the 

 white man. What we do at present is more conventional than 

 reasonable. The new non-tarnishing metallic foils, in particular, 

 are bound to be valuable as heat insulators; they are already being 

 used in roofs and hats. The conditioning of air in houses, offices, 

 and trains, and perhaps even motor-cars, is another application of 

 science which may well revolutionize European life in some parts 

 of tropical Africa. In this subject America has given the lead to 

 the world; all over the Eastern States public offices, theatres, and 

 trains are now kept at a constant optimum temperature by thermo- 

 static devices. In most tropical countries, as mentioned in Chap- 

 ter IV, humidity is perhaps a more potent influence in health than 

 is temperature, but research has already shown how humidity in 

 buildings can be controlled. It seems that some of the devices for 

 air conditioning, now employed in America and Europe, could be 

 applied with little modification in many tropical townships and 

 railways, and lead to great improvement in European health and 

 efficiency. 



