The Campaign at Havana ii 



exterminators after the clearing and training of 

 natural watercourses was accomplished. Condi- 

 tions affecting growth of vegetation and algae were 

 less favorable in Cuba, and, in consequence, fish 

 are of more use there as destroyers of mosquito 

 larvae than on the Isthmus. 



Beds of watercress in the Chinese truck gardens 

 were a prolific source of Anopheles in Havana. 

 The cress beds were made by erecting small dikes 

 on fiat land, and bringing water to them by ditches 

 from nearby streams. When the enclosure was 

 filled, the water was left standing for long periods. 

 In order to control the situation, small wooden 

 sliding gates were installed at each end of the 

 watercress beds, which were flooded at frequent 

 intervals for short periods, and the water then 

 allowed to escape back to the stream. This 

 scheme, when properly carried out, practically 

 stopped Anopheles development. The gardeners 

 who refused to adopt the new method were not 

 allowed to grow watercress. The crops grown in 

 this manner were as vigorous as those raised in the 

 continuously flooded patches. 



Between the heavy showers that occur near 

 Havana there are dry periods, accompanied by 

 strong winds. When the ditches and watercourses 

 are kept fairly free from vegetation, the heavy 



