PHENOMENA OF INFECTION. 83 



are capable of ready adaptation to new environment. 

 Conquest, improved methods of travel, and shorter 

 routes, have brought the tropics to the very doors of 

 Western nations, with the result, that in the great 

 commercial benefits accruing from easy intercourse, 

 there has come a menace in the guise of disease. Here 

 and there tropical diseases have already been introduced, 

 and while the number of such instances is insignificant, 

 and they have been successfully combated, it has excited 

 alarm. And well might it! Europe has a number 

 of times been over-run with Oriental plagues. Up to 

 the present these problems have been dealt with chiefly 

 in those countries where such diseases prevail, but who 

 can say when from a single imported case a herculean 

 task in sanitation and preventive medicine will not 

 confront some nation ? In temperate latitudes, tropical 

 heat is seasonable for one or more months each year, 

 a time during which the way is open for the spread of 

 an exotic disease. This danger the nations are cogni- 

 zant of, and special commissions are investigating such 

 diseases in those regions where they are endemic. 

 Whenever anything is discovered which bids fair to 

 prove valuable as a preventive, it is at once given a prac- 

 tical test, since it is obvious that the only real safe-guard 

 the peoples of temperate climates have against foreign 

 diseases, is to stamp them out in their home-country. 

 All of the nations have likewise founded schools of 

 "Tropical Medicine," where the etiology and sanitary 



