HOUSE RATS AND MICE. 



19 



ton or other absorbent material is saturated with the liquid and 

 then pushed into the burrow, the opening being packed with earth to 

 prevent the escape of the gas. All animals in the burrow are asphyx- 

 iated. Fumigation in buildings is not so satisfactory, because it is 

 difficult to confine the gases. Moreover, when effective, the odor 

 from the dead rats is highly objectionable in occupied buildings. 



Chlorin, carbon monoxid, sulphur dioxid, and hydrocyanic acid 

 are the gases most used for destroying rats and mice in sheds, ware- 

 houses, and stores. Each is effective if the gas can be confined and 

 made to reach the retreats of the animals. Owing to the great dan- 

 ger from fire incident to burning charcoal or sulphur in open pans, a 

 special furnace provided with means for forcing the gas into the com- 

 partments of vessels or buildings is generally employed. 



Hydrocyanic-acid gas is effective in destroying all animal life in 

 buildings. It has been successfully used to free elevators and ware- 

 houses of rats, mice, and insects. However, it is so dangerous to 

 human life that the novice should not attempt fumigation with it, 

 except under careful instructions. Directions for preparing and 

 using the gas may be found in a publication entitled Hydrocyanic- 

 acid Gas against Household Insects, by Dr. L. O. Howard and 

 Charles H. Popenoe.^ 



Carbon monoxid is rather dangerous, as its presence in the hold of 

 a vessel or other compartment is not manifest to the senses, and fatal 

 accidents have occurred during its employment to fumigate vessels. 



Chlorin gas has a strong bleaching action upon textile fabrics, and 

 for this reason can not be used in many situations. 



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

 marked than that of chlorin, and ordinarily it is not noticeable with 

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

 this gas has many advantages as a f umigator 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 many steamships and docks are 

 now fitted with the necessary apparatus. ' 



RAT VIRUSES. 



Several microorganisms, or bacteria, found originally in diseased 

 rats or mice, have been exploited for destroying rats. A number of 

 these so-called rat viruses are on the American market. The Biologi- 

 cal Survey, the Bureau of Animal Industry, and the United States 

 Public Health Service have made careful investigations and practical 

 tests of these viruses, mostly with negative results. The cultures 

 tested by the Biological Survey have not proved satisfactory. 



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

 mended for general use are : 



1 Farmers' Bulletin 090. 



