be broken up with a pick or a 

 shovel the next day and the earth 

 tamped down tightly. The re- 

 maining rats will reopen the bur- 

 rows, and these can thus be de- 

 tected and re-treated until all ac- 

 tivity ceases. This method should 

 not be employed to treat burrows 

 in dirt-floored basements or along- 

 side foundation walls where en- 

 trance to houses is gained. 



Calcium cyanide is a deadly poi- 

 son and should be used out-of- 

 doors where it is quickly dissi- 

 pated in the open air. Avoid 

 breathing the fumes. Always 

 pump air through the hose before 

 storing it. The use of calcium 

 cyanide should be curtailed dur- 

 ing freezing or rainy weather. 



Carbon monoxide, introduced 

 into rat burrows by means of a 

 hose attached to the exhaust of a 

 gasoline motor, has also been used 

 with a fair degree of success. 

 About 5 minutes running time to 

 a burrow will usually suffice. As 

 carbon monoxide is not so swift 

 acting as calcium cyanide, it re- 

 quires more gas and longer time 

 to take effect. 



Carbon dioxide, in the form of 

 dry ice, has been found useful 

 in fumigating refrigerated ware- 

 houses where low temperatures 

 must be maintained to prevent 

 food spoilage. The ice is crushed 

 and distributed through the room. 

 An electric fan will speed up the 

 dispersal of the gas. Carbon di- 

 oxide is used in about a 15-percent 

 concentration, or 30 pounds to 

 1,000 cubic feet of space, for 24- 

 hour exposure. It has the advan- 

 tage of being much safer to han- 

 dle than are the highly toxic 

 forms of gas. 



Other types of poisonous gases 

 are not recommended for general 

 use in rat control. 



USE OF TRAPS 



In trapping rats the proper 

 placement of the trap is far more 

 important than the selection of a 

 bait. Rats follow natural run- 

 ways whenever possible, running 

 along walls and stacked materials, 

 rather than crossing a room in the 

 open. Their instinct for stealth 

 and desire for protection cause 

 them to pass behind anything 

 that is placed or is leaning against 

 a wall. The best baited trap will 

 rarely entice a rat into the middle 

 of a room, but, on the other hand, 

 a rat will frequently pass over a 

 trap placed along a wall rather 

 than detour wide into the open. 



Despite its reputation, cheese 

 is not an infallible bait. Bacon 

 strips, a piece of fresh fish, or 

 bacon-scented oatmeal is better. 

 Such baits should be tied firmly 

 to the trigger of the trap to pre- 

 vent their being taken without 

 springing the trap. Dead rats 

 sliould not be left to decay in the 

 trap. If this should happen, how- 

 ever, the trap should be scalded 

 with boiling water before reusing, 

 but care need not be taken to pre- 

 vent human or rat odors from 

 remaining about the trap. A 

 freshly killed rat in a trap will not 

 frighten other rats away, fre- 

 quently they will even feed upon 

 it. Nor is it necessary to throw 

 a trap away once a rat has been 

 caught in it. If blood or entrails 

 adhere to the trap, they should be 

 scraped off before using it again. 

 The longer a trap is in use, the 

 more likely it is that a rat will 

 approach it. 



It is not always necessary to 

 use baited traps. The trigger 

 surface of an ordinary snap trap 

 may be enlarged by using a square 

 of cardboard or a piece of tin, the 

 entire trigger half of the trap be- 

 ing thus made a treadle (fig. 4). 

 A square of corrugated paper. 



10 



