262 



2. In the dry season the search for Anophelines 

 may be negative, and there may be no breeding- 

 places. Make in the most sheltered places small 

 cement pools, and keep these filled with water. 

 After a certain number of days they may contain 

 young Anopheline larvae if the adults are present 

 in the houses. (It is necessary to be sure one's 

 water supply does not contain young larvae or 

 eggs). The absence of the larvae in the pools 

 does not necessarily mean, however, that adult 

 Anophelines are not present in the houses (see choice 

 of breeding-grounds by different species of Ano- 

 phelines). 



Note the result in the case of each test pool. 



3. In the conditions just described observe 

 the pools made by the first shower of rain of the 

 on-coming ' rains.' Note after three days have 

 passed the presence of larvae in many of these. 

 Note the presence of these on the map. The 

 distribution of Anophelines at the end of the dry 

 season will usually be found to correspond to that 

 of native huts. 



The Prevalence of Malaria 



If we proceed to ascertain to what extent 

 malaria prevails in a district we may attempt to 

 do so in several ways. 



1. We may consult hospital statistics and 

 returns of death from malaria. This method is 

 open to such grave error that it is extremely 

 doubtful whether it is worth the labour bestowed 

 upon it. 



2. We may determine to what extent en- 

 largement of the spleen occurs. This method has 

 been largely used. 



