BACTERIA AND DISEASE 325 



of typhoid depends upon the purification of the water 

 supply. 



Germs of typhoid may be carried in food. Several 

 epidemics have been traced to oysters grown in places 

 contaminated by sewage. In many instances the disease 

 has been carried by flies which alight upon food after 

 having walked over excreta. 



People who have apparently recovered from typhoid 

 are sometimes capable of spreading the disease for years 



FIG. 224. Pollution of a well by the contents of a neighboring cess pool. 



afterward. These people who are called " typhoid 

 carriers'' harbor multitudes of typhoid bacilli in their 

 intestines and are especially dangerous if they handle 

 food that is to be eaten by others. The case of " Typhoid 

 Mary," who served as a domestic in several homes and 

 left a trail of typhoid patients wherever she went, is 

 one of the best known. 



Most diseases tend to run a certain course and end in 

 natural recovery. If the disease does not prove fatal, the 



