xix BACTERIA AND DISEASES 295 



206. Malarial Fever. This class of fevers is due to 

 a specific organism which does not belong to the class 

 of bacteria. It is not contagious. Two varieties of 

 malarial fevers are known, although they are probably 

 caused by the same organism. These fevers generally 

 occur in low, marshy, swampy regions and are most 

 severe near marshes that are periodically flooded. If 

 the swamps are properly drained, the malarial fevers 

 soon disappear. 



The germs probably enter the body through the water 

 we drink and the air we breathe, and through the bites 

 of the mosquito and other insects. These fevers may 

 be prevented in malarial regions by draining the damp 

 soils, by locating residences on the most elevated places, 

 by always sleeping indoors, by keeping the skin free 

 from wounds and bites, by cooking all foods, by boiling 

 the drinking-water, and by the daily use of quinine in 

 small doses. The first is probably the most effective 

 means of stamping out malarial troubles. 



207. Yellow Fever. This is an infectious disease 

 whose cause is unknown. It occurs chiefly in low, 

 swampy, tropical countries, but epidemics have swept 

 over our country as far north as Philadelphia. Many 

 claim that the poison causing yellow fever may be car- 

 ried in clothing, in papers and letters through the mails, 

 and in articles of merchandise shipped from one place to 

 another. But the mosquito is doubtless by far the most 

 important agent concerned in spreading this disease. 



The introduction and spread of yellow fever may be 

 largely prevented by maintaining good sanitary condi- 



