XI] 



DISTRIBUTION 



191 



32° 47' N. and 23° 23' S., and during the summer months it 

 may extend up to as much as 42° N. The disease is usually 

 more prevalent in low-lying lands well supplied with water, 

 probably because such sites provide better opportunities for 

 the breeding of Culex. There are exceptions to this rule, 

 however, for during the epidemic in Syria in 1888-9 ^^^ disease 

 extended to villages having an altitude of nearly 4000 feet. 



Fig. 51. The distribution of Dengue. The countries from which cases 

 have been recorded are coloured black. (Compare this chart with 

 that on page 193, shewing the distribution of Culex fatigans.) 



The distribution of dengue, past and present, is represented 

 in the accompanying map (Fig. 51). At the present time 

 the chief endemic centres of the infection are India and the 

 East Indies, and, in the New World, the West Indies and 

 Central America. From these centres the disease, in warm 

 summers, may even extend into temperate regions, but on 

 the approach of winter it gradually disappears, as a certain 

 amount of heat seems to be necessary for its transmission. 



