CHAPTEE IV. 



HABITAT OF DISEASE GERMS. 



Forms of vegetation, and also of animal life, vary in 

 different latitudes. The fauna and flora of the tropics 

 bear no resemblance to the animals and plants that have 

 their home in temperate zones, and in like manner the 

 micro-organisms, fungi, and microbes of various parts 

 of the earth have distinct characteristics. 



Some plants can be transferred from the places where 

 they are indigenous, and they can be grown and made to 

 flourish in places which are quite foreign to them ; others 

 will only vegetate in their native home and they perish 

 when transferred to another region. The same applies 

 to animals, not only to the larger but to the microscopic 

 members of the animal kingdom. The yellow-fever 

 germ likewise requires certain climatic conditions, as is 

 well known, in order to propagate rapidly and produce 

 disease. When those climatic or atmospheric conditions 

 do not exist, the germs perish and the disease dies out. 

 The regions where it is most prevalent in this hemi- 

 sphere, and it is worse here than elsewhere, are the 

 Isthmus of Panama and some parts of Mexico and Cuba, 

 though Louisiana and other portions of the United 

 States, as is well known, are subject to it ; but in the 

 latitude of New York, even on the sea border, it is com- 

 paratively harmless, the microbes ceasing their activity 

 almost on entering the harbor of New York. 



Yellow fever is acutely infectious. The microbes are 

 in the atmosphere. That is their primary characteristic. 

 But under favorable conditions, which are not yet accu- 

 rately defined, though they probably are due to local 

 impurities in the soil, the disease becomes contagious 

 and endemic, as it ordinarily is at Colon and Panama. 



