shy of trap and gun to make the use of these methods effective and 
that their control by trapping and shooting is also too slow and ex- 
pensivee These methods, however, are the most effective and satis— 
factory for the control of the carnivores-—coyotes, bobcats, and 
mountain lions. Mountain lions are hunted quite successfully with 
dogs. Coyotes can be hunted with dogs, but because of their abundance 
and because of the large scale on which the control work has to be 
done, this method is impracticable and uneconomical. 
Gassing has long been employed as a method of controlling 
burrowing rodents. It has the advantage of being quite selective, 
endangering no other wildlife except a few forms that use burrows 
made by ground squirrels and prairie dogs. Moreower, such animals 
are usually in inactive burrows, which are not treated. The disadvan- 
tages of gassing are the cost of materials and the expense of applica- 
tion in the field. Liquids, like carbon bisulphide and hydrocyanic 
acid, require considerable equipment to apply in the field, so their 
utility is limited. Gassing compounds in the form of solids depend- 
ing on moisture in the ground or atmosphere to release toxic gases that 
disperse of their own accord throush the air of the barrow alse are 
limited in their use to localities where there is sufficient soil 
moisture. 
During recent years the Control Methods Research Laboratory 
has been endeavoring to develop a pyrotechnic type of cartridge, which 
being lighted at the time it is placed in the burrow burns with suf~ 
ficient heat to generate deadly fases and to force them into the -run- 
ways. This cartridge is giving promising results: it is inexpensive, 
and requires no field equipment but a cigarette lighter to ignite it 
and a shovel with which to close the burrow. More general use of this 
fumigating device will greatly reduce the quantity of poisoned grain 
used. The chief obstacle to its use is the character of the soil in 
which the burrows are made, which sometimes is so porous as to permit 
too rapid escape of the toxic gas. 
Selective Poisons Developved 
We now come to the preparation of the poisons used in rodent 
and predatory-animal control. Frequently much time is spent in the 
development of a single formula and many toxic agents have been and 
are being tested for their effectiveness. At the beginning, the dose 
of each toxic agent required to kill 90 percent of the animals is 
ascertained. The systemic effects of each poison on animals are then 
studied, such as speed of action, warning factors and the possibility 
of their being disguised, and selective action as concerns all th 
birds and animals likely to be exposed to it, if used. 
airy 
