60 AN ECONOMIC STUDY OF FIELD MICE. 
expensive. However, occasionally carbon bisulphid may be used to 
advantage, especially with pine mice. A little of the liquid is poured 
upon a piece of rag or other absorbent material and this pushed into 
the burrow, which at once should be closed with soil to confine the gas. 
MICRO-ORGANISMS. 
The efforts of Loeffler, Danysz, Mereshkowski, and other European 
bacteriologists to destroy field mice by means of infectious diseases 
have been partially successful, but as yet no disease appears to have 
been found that is really contagious. As long, therefore, as infec- 
tion can be effected only by direct inoculation or through the food, 
the methods have little, if any, advantages over ordinary poisons. 
The Biological Survey, cooperating with the Bureau of Animal 
Industry, is engaged in experiments with various micro-organisms 
for destroying field mice and other rodents, and practical results 
along these lines may yet be reached. 
RECOMMENDATIONS TO FARMERS. 
When conditions are unusually favorable for an increase of voles, 
the farmer should put forth all possible efforts to repress them. 
With cooperation among the farmers of a district serious losses may 
readily be prevented. The danger lurks outside of cultivated areas 
and in the swamps, forests, and waste places along fence rows and? 
small brooks that harbor weeds and underbrush. It is by giving at- 
tention to these and by reducing to a minimum the extent of shelter 
for mice that the farmer can most successfully protect his crops. 
.V second important consideration is the protection of animals and 
birds that prey upon field mice. The farmer should by all means 
acquaint himself with the food habits of the various species of wild 
animals of his vicinity, to the end that he may distinguish friend 
from foe. Every farmer can do much in his community to help form 
an enlightened sentiment in favor of beneficial birds, mammals, and 
other animals. 
PREVENTION OF INJURY TO ORCHARDS AND NURSERIES. 
Injury to orchards and nurseries by field mice may generally be 
prevented by forethought and the exercise of ordinary care. Of 
first importance, always, is clean tillage. No grass or weeds should 
be left in or near the nursery. So well is this understood by the ma- 
jority of experienced nurserymen that by clean tillage they secure 
practical immunity from the ravages of mice except in winters of 
deep and long-lying snow. If grass and weeds are destroyed in fence 
corners and waste lands near the nursery, complete immunity from 
mice ravages can be depended upon even in winters of deep snow. 
Unfortunately, nurserymen can not control the lands which environ 
their trees, and when snow falls to a considerable depth prompt 
measures are sometimes necessar}^ to keep mice from destroying them. 
