96 CULTIVATION AND THE MOSQUITO QUESTION 



cases were only encountered as the coast line was 

 approached ; it had disappeared from the plantations 

 now spreading over the interior of the island. They 

 were thus able to compare side by side the effect 

 of drainage in stopping malaria, and to see per- 

 sisting malaria as bad as in the old days in those 

 districts where there was no tobacco planting, and, 

 in consequence, where no drainage had been under- 

 taken. 



Cocoa Plantations. — In Grenada it has been found 

 by the medical men that a material decrease in the 

 number of cases of malaria has resulted from the re- 

 placement of sugar cane by cocoa plantations. It is 

 necessary for the efficient cultivation of cocoa that the 

 soil should be thoroughly drained, and for this purpose 

 the plantations are intersected by very numerous 

 drainage channels leading from the high grounds to 

 a main channel at the lowest part of the estate. By 

 these means, water never puddles or remains stagnant. 

 Careful cultivation, including drainage undertaken as 

 we have seen in the case of Ismailia, leads both to the 

 increased production of crops and to a diminution of 

 the cases of malaria. 



In the case of the sugar-cane fields in British 

 Guiana, intersected as they are by numerous trenches 

 and canals, the anophelincs are kept under by the 

 presence of fish, ^^^'^ by flushing. 



In the rice fields, although for the most part sub- 

 merged, small fish appear to be the chief means of I 

 keeping in check the production of the anophelines. 



Dr. Sergent states that grape-vine planting in 



I 



