SUPPRESSION OF RODENTS = 191 
field should first be gone over with poison, and 
the bulk of the animals thus destroyed. 
Flooding the burrows. Where available, 
water is one of the best means of combatting 
pocket-gophers. Flooding the land in winter 
is especially effective, as it wets the animals 
and drives them to the surface, where'‘they soon 
succumb to the cold. In warm weather the 
method can be made effective if men and dogs 
are on hand to kill the animals as they seek 
refuge on the embankments. S. E. Piper, of 
the Biological Survey, reports that about the 
middle of April, 1909, at Modesto, Cal., he saw 
some boys killing pocket-gophers that had been 
driven from an alfalfa patch by flooding. A 
hundred gophers, more than half of them young 
of the year, were killed from a three-acre tract. 
Difficulties of extermination. Much hope has 
been entertained that a bacterial disease fatal 
to rodents, and particularly to rats, might be 
found, but thus far has been disappointed. 
It was thought that a bacillus (B. typhimur- 
tum) given to the field-mice which over-ran 
Thessaly in 1892-3 had put an end to the 
plague, but it is now thought it did little to 
