211 



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. 

 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. 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. 



PRECAUTIONS NECESSARY IN APPLYING THE 

 SPLEEN TEST* 



The Age of the Individuals Examined. 

 The enlargement of the spleen due to ordinary 

 malarial infection tends to disappear once the in- 

 dividual has ceased to suffer from malarial infection. 

 In very malarious countries, after childhood, the 



* In countries like India, where kala-azar exists, enlarged spleens from this and 

 other causes may entirely invalidate the ' spleen test ' for malaria. 



