INSECTS IN RELATION TO DISEASE 



319 



be difficult to organize the removal of manure and garbage at a 

 comparatively low cost, since the manure is worth gathering for 

 fertilizer and the garbage has a decided commercial value. 

 Where the amount of garbage or manure accumulated is so 



^ 



1 8 15 22 

 JUNE 



29 6 



13 20 

 JULY 



27 3 



10 17 24 31 

 AUGUST 



7 14 21 28 

 SEPTEMBER 



5 12 19 26 

 OCTOBER 



Fig. 148. Flies and intestinal diseases 



In New York City a careful study was made (1907-1908) to find the relation be- 

 tween the prevalence of flies and the amount of typhoid fever. The height of the dot- 

 ted line corresponds to the number of flies caught in traps, week by week, from the 

 beginning of June to the end of October. The solid line corresponds to the number 

 of people who died from intestinal diseases during the same period in the same dis- 

 tricts of the city. Typhoid is most frequent where and when flies are most abundant, 

 and there is a direct relation between the insects and the distribution of the disease 



small that its removal is relatively expensive, it should be 

 screened so that flies cannot reach it ; but screening is very ex- 

 pensive and seldom altogether satisfactory. It has been found 

 most effective to provide for the systematic removal of garbage 



