18 



HOW TO DESTROY RATS. 



Sulphur dioxid also has a bleaching effect upon textiles, but less 

 marked than that of chlorin and ordinarily not noticeable with the 

 small percentage of the gas it is necessary to use. On the whole, this 

 gas has many advantages as a fumigator and disinfectant. It is 

 used also as a fire extinguisher on board vessels. Special furnaces 

 for generating the gas and forcing it into the compartments of ships 

 and buildings are on the market, and m.any steamships and docks are 

 now fitted with the apparatus. 



Micro-org-anisms. 



Several micro-organisms, or bacteria, have been exploited in Europe 

 and America for destroying rats. A number are on the market in 

 the United States. With the aid of the Biochemic Division of the 

 Bureau of Animal Industry, the Biological Survey has made labora- 

 tory and field experiments with some of them, and has also received 

 many reports from others who have tried the cultures in a practical 

 way. The results are by no means uniform, although the majority 

 are negative. The cultures tested by the Survey have given poor 

 results. 



The chief defects to be overcome before the cultures can be recom- 

 mended for general use are: 



1. The virulence is not great enough to kill a sufficiently high 

 percentage of rats that eat food containing the micro-organisms. 



2. The virulence decreases with the age of the cultures. They 

 deteriorate in warm weather and in bright sunlight. 



3. The diseases resulting from the micro-organisms are not conta- 

 gious and do not spread by contact of diseased with healthy animals. 



4. The comparative cost of the cultures is too great for general 

 use. Since they have no advantages over the common poisons, except 

 that they are usually harmless to man and other animals, they should 

 be equally cheap; but their actual cost is much greater. Moreover, 

 considering the skill and care necessary in their preparation, it is 

 doubtful if the cost can be greatly reduced. 



Org-anized Efforts to Destroy Rats. 



The necessity of cooperation and organization in the work of rat 

 destruction should not be overlooked. To destroy all the animals 

 on the premises of a single farmer in a community has little perma- 

 nent value, since they are soon replaced from near-by farms. If, 

 however, the farmers of an entire township or county unite in efforts 

 to get rid of rats, much more lasting results may be attained. If 

 continued from year to year, such organized efforts are very effective. 



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