18 FKEEU. 



consideration. Then, too, we must remember that the hygienic surround- 

 ings are different here than in our home countries, and in the majority 

 of districts lying in these regions the native population has not, as yet, 

 advanced sufficiently in education to eliminate many of the factors which 

 in themselves may produce a marked effect. Perhaps, when modern 

 methods have been more generally extended, the world may to a large 

 extent alter its opinion in regard to this portion of the globe. Europeans, 

 coming to the Tropics, change their mode of life, and do many imprudent 

 things which bring their after-effects. 



The subject which I have undertaken to discuss is so complex, the 

 experimental work is as yet so little advanced, that I have been able 

 to give only an outline of what may be done, and to suggest lines of 

 investigation for the future. Many of the papers or monographs which 

 have a more or less direct bearing on it I have not been able to quote 

 at all for lack of space. The physicist, chemist, meteorologist and 

 experimental biologist should all combine to bring a clearer understand- 

 ing into the field; the plant physiologist and ecologist certainly have 

 topics for study for many years to come. If my paper may seem to be 

 inconclusive and simply to bring together a number of nonrelated results, 

 it is because the subject can not, at present, be treated in any other way. 



Work on the sunlight will be continued in the Bureau of Science 

 as opportunity affords, and we hope, in the not too distant future, to 

 bring greater clarity into the field. The biological laboratory, with the 

 means now at hand, will also study the effects of tropical light on 

 microorganisms. 



