286 COCOA 



CHAP. 



the use of poisoned food is dangerous to children and 

 animals, and the dead and decaying rats are a nuisance 

 to the people. Good results have been obtained with 

 this method on the cocoa plantations of Java and 

 Samoa. Eats, however, are very clever, and when 

 poisoned food is simply placed here and there in the 

 fields, the result is merely that the rats carefully taste 

 a little of it, and, soon feeling that it is not the right 

 food for them, leave it untouched thereafter. 



Better results are obtained when unpoisoned food is 

 first placed at definite places every day or every two 

 days. Boiled corn is quite suitable. After a few days 

 the rats know that the food is all right, and return daily 

 to the spots to take their meals. If then poisoned food 

 is substituted, the rats will eat it all and large numbers 

 will die. The same thing can then be carried out again 

 but with another food, bread for instance. 



The food may be poisoned by means of carbonate 

 of barium (1 part to 4 parts of food), or strychnine 

 (food dipped into a solution of 2 per cent). 



Two other methods of destroying rats have been 

 tried by the cocoa planters : the use of a certain virus, 

 and the introduction of rat-killing animals. Both these 

 methods, however, are unsatisfactory. 



Several kinds of bacterial virus have been recom- 

 mended the " Virus Danysz," the " Liverpool Virus," 

 the " Kattin," etc.- but with none of these has a whole- 

 sale destruction of rats been obtained in any tropical 

 country. Moreover, the method is not easily applied, 

 and a local bacteriologist is necessary in order to have 

 a regular supply of fresh virulent cultures. It is wholly 

 useless to try cultures made in Europe ; when these 

 arrive in the tropics their virulence is much reduced, 

 even when kept on ice. But even with virulent, freshly 

 made cultures it is very difficult to cause a real epidemic 

 among the rats, and generally only a small percentage 

 contract the disease. 



Against the introduction of rat-killing animals a 

 serious warning is necessary. The consequences of the 



