294 ANIMAL COMPETITORS 
arsenic is required to kill. Actual field experi- 
ments show that an ounce of strychnine, if 
properly distributed, is enough to kill 4,500 
prairie-dogs or large ground-squirrels, or 9,000 
field-mice. 
Various other poisons, both mineral and 
vegetable, have been used, but none is to be 
recommended as compared with strychnine, 
with the possible exception of barium carbonate 
as an agent for killing rats and mice about 
puildings. This mineral, which is cheap, has 
the advantage of being without taste or smell, 
and also that in the small doses fed to rats 
and mice it would be harmless to domestic ani- 
mals. Its action upon rats is slow, and if exit 
is possible, they usually leave the premises in 
search of water. ; 
Poisoning rats and house-mice. For the 
reasons above given phosphorus and arsenic 
are not recommended in poisoning rats and 
mice; although powdered white arsenic mixed 
with oatmeal and sugar, or made into a paste 
of 12 parts of cornmeal and one part of arsenic 
with whites of eggs, is often effective. 
Barium carbonate may be fed in the form of 
