42() YKAHliOOK OF '11 1 K DKPAKTMKNT OF AGRICULTURK. 



tlu)roiit>hly poison GO pounds of wheat intended for field mice; a 

 pound of arsenic will poison only 10 or 12 pounds of the grain for 

 the same purpose. The cost of preparing the GO pounds of wheat, 

 therefore, will be about the same with either poison; but more of 

 that containing arsenic is required to kill. Actual field experiments 

 clearly demonstrated the advantages of strychnine. The baits con- 

 taining strychnine were eaten freely and many dead mice were found, 

 while on the areas treated with arsenic little of the wheat was eaten 

 and dead mice were few. Experiments show that an ounce of strych- 

 nine, if properly distributed, and if none is wasted, is enough to kill 

 1,500 prairie dogs or large ground squirrels or 9,000 field mice. 



OTHER POISONS. 



Barium carbonate. — As sold commercially, this is a dense, heavy 

 white powder, insoluble in water but dissolving in the presence of 

 several of the common acids. It is a rather cheap mineral poison 

 without taste or smell. For this reason it has been recommended for 

 destroj'ing rats and mice. It is poisonous to larger animals when 

 taken in considerable quantities, and in one case of human poisoning 

 GO grains of the salt proved fatal. Its action is corrosive and very 

 slow. 



Potassium cyanid. — This intensely poisonous substance has been 

 employed for destroying prairie dogs in the West, but usually in com- 

 bination with strychnine. Although cheap, the fact that in contact 

 with the soil and atmosphere it rapidly decomposes and loses its 

 poisonous qualities impairs its usefulness. It has been found too that 

 dogs, when given doses of 2 or 4 grains of potassium cyanid, vomit 

 the poison and recover. 



Corrosive sublimate. — Corrosive sublimate, or mercuric chlorid, 

 of commerce occurs in heavy colorless masses, which dissolve in 16 

 parts of cold water and 3 parts of boiling water. A dose as small as 

 3 grains has been known to be fatal to man. Its corrosive action on 

 the digestive tract is rapid, and somewhat like that of carbolic acid, 

 but death results usually from exhaustion. Although this poison has 

 often been recommended for rodents, the burning sensation in the 

 mouth and the constriction of the throat it causes preclude its em- 

 ployment. 



Nux vomica. — The nux vomica of commerce, extensively used in 

 medicine, is largely employed in the Old "World for poisoning rodents. 

 It contains from 2 to 5 per cent of poisonous alkaloids, mainly 

 brucine and strychnine, but the proportions of each vary so greatly 

 that the strength of the poison is uncertain, and it is better to use the 

 purer strychnine instead. The baits can then be made of definite 

 strength and the poison economically applied. 



