46 THE BROWN RAT IN THE UNITED STATES. 



sirup. Wheat is the most convenient alternative bait. It should 

 be soaked over night in the strychnine sirup. 



The bitterness of strychnine often prevents rats from eating baits 

 containing the crystals. This trouble may sometimes be overcome 

 by first feeding the baits without the strychnine for several successive 

 nights until suspicion is allayed. 



Arsenic. — Nearly all commercial rat poisons have either arsenic or 

 phosphorus as a basis; and while many of them are effective, the 

 poison is often present in quantities too small to be fatal to rats. 

 It has been proved by experiment that sometimes rats have great 

 power of resistance to some poisons, particularly to arsenic. Yet 

 arsenic is an excellent rat poison, as is shown by its continued popu- 

 larity. Its cheapness commends it to favor; yet the experiments 

 of the Biological Survey show that strychnine, measured by the 

 results obtained, is really the cheaper poison for most rodents. 



Powdered white arsenic (arsenious acid) may be fed to rats in 

 nearly any of the baits mentioned under barium carbonate and 

 strychnine. It has been used successfully when rubbed into fresh 

 fish or spread on buttered toast. Another method is to mix twelve 

 parts by weight of corn meal and one part of arsenic with whites of 

 eggs into a stiff dough. 



An old formula for poisoning rats and mice with arsenic is the 

 following, adapted from an English source : 



Take a pound of oatmeal, a pound of coarse brown sugar, and a 

 spoonful of arsenic. Mix well together and put the composition into 

 an earthen jar. Place a tablespoonful at a place in runs frequented 

 by rats. 



Phosphorus. — This is probably the most widely used poison for 

 rats and mice, and undoubtedly it is effective when given in an 

 attractive bait. The phosphorus paste of the drug stores is usually 

 dissolved yellow phosphorus mixed with glucose or other substances. 

 The proportion of phosphorus varies from one-fourth percent to 4 

 percent. The first amount is too small to be always effective, and 

 the last is dangerously inflammable. When home-made prepara- 

 tions of phosphorus are used, there is much danger of burning the 

 person or of setting fire to crops or buildings. In the western States 

 many fires have resulted from putting out home-made phosphorus 

 poisons for ground squirrels, and entire fields of ripe grain have been 

 destroyed in this way. Even with the commercial pastes the action 

 of sun and rain upon them changes the phosphorus and leaches out 

 the glucose until a highly inflammable residue is left. 



It is often claimed that when phosphorus is eaten by rats or mice 

 it dries up or mummifies the bodies so that no odor results. The 

 statement has no foundation in fact. Equally misleading is the 



