THE INSECTS: HEXAPODA 



103 



passed from the bodies of infected persons. Where fecal 

 matter is not properly disposed of, flies, because of their 

 filthy habits, get disease germs on their feet and bodies. 



Fig. 63. Maps showing the effects of control measures against yellow fever 

 Yellow fever areas shown in black. (Courtesy of the International Health Board) 



Then, when they alight upon food material it becomes 

 contaminated with germs, and anyone eating it is liable 

 to contract the disease. 



During the World War there was a great increase in our 

 knowledge of the relations of insects to disease. Lice are re- 

 sponsible for transmitting typhus fever and also trench 

 fever, both of which were so prevalent during the war. 



