POISONING AND TRAPPING 291 



the phosphorus in carbon disulphide, after 

 which the substance is mixed with any suitable 

 material, as flour or meal or glucose in the rat 

 and roach pastes (from 2 to 4 per cent, strong), 

 or is formed into the waxy sticks offered for 

 sale. Now its instability in contact with the 

 oxygen of the air is so great that it is liable 

 when dry, and has been known, to burst into 

 flame, setting fire to everything it touched. 

 Cases have occurred in the West where it has 

 thus caused fires which destroyed entire fields 

 of ripe wheat and barley, and buildings in which 

 prepared phosphorus was stored. Some hazard 

 attends the use even of carefully prepared phos- 

 phorus pastes. 



Arsenic, in the form of Paris green or Lon- 

 don purple is widely employed as an insecticide. 

 It is comparatively cheap, but is by no means 

 as deadly as phosphorus or strychnine. The 

 smallest quantity known to have been fatal to 

 a human being is 2.5 grains. Its action on ro- 

 dents is exceedingly variable, and there is 

 ample proof that rats after taking small doses 

 frequently become entirely immune to its 

 further effects. Moreover, it is likely to sour 



