75 



sulphide and pushed well into the open hole, which is closed 

 immediately with the wet earth. In the government work on 

 ground squirrels in California only one-half an ounce of carbon 

 bisulphide was used to each burrow, but this was not sufficient 

 on Thompson's Island, where the soil was loose and the rat 

 colonies very large. It might be better in some cases to put 

 one-half an ounce of the liquid into each hole, as the gas does 

 not rise so readily as it falls, and it is conceivable that a much 

 larger quantity of the gas might be needed in a case where the 

 earth is loose and there are many large subterranean galleries. 

 Caution should be used, as occasionally a spark may find its 

 way from the smoker into a hole and ignite the gas, causing a 

 small explosion, but if the grass and leaves are not dry there is 

 no danger of fire, and the explosion serves to drive the gas 

 into all passages and crevices. Some operators prefer to ex- 

 plode the gas in all cases, claiming that it is more effective. 

 Two or three feet of hose and a funnel are used sometimes to 

 carry the liquid deep into the holes. Where rats are very 

 numerous, thousands may be destroyed in this way in a few 

 days by one or two men. A trained fox terrier might be used 

 to advantage in this work, as it would quickly locate early in 

 the morning the burrows where rats had recently run in. 



Dr. John D. Long of the Public Health Service has invented 

 a machine for forcing carbon bisulphide into burrows which he 

 claims economizes the gas.^ 



Other Fumigants. — In buildings hydrocyanic acid gas is 

 destructive to all animal life, including insects, but is expensive, 

 and so dangerous to human life that great care must be used 

 in applying it. If used where rats can conceal themselves in the 

 walls they may die there, with the usual disagreeable results. 

 The method of preparing and using this gas is given by Dr. 

 L. O. Howard in Circular 46, Bureau of Entomology, United 

 States Department of Agriculture, 1907. 



Carbon monoxide, chlorine and sulphur dioxide are used 

 in fumigating ships to destroy rats and insects. Of these, 

 sulphur dioxide is the safest, and is also used to extinguish 

 fires. The two former are not recommended, the first because 

 it is odorless, and may kill before the odor is detected; the 



» Public Health Reports, Vol. 27, No. 39, Sept. 27, 1912, p. 1594. 



