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Owing to its finely chewed condition, exact determination <>! the 
food of rats and mice From stomach examinations alone is \<t\ diffi 
cult. This i- especially true of the species of the genus Microtus^ 
whose molars are well adapted for grinding. So complete is the 
mastication and subsequent maceration <>f weed and grass seed 
well as roots and grains, that the cell structure Is often destroyed. 
A fair idea of the food ran be gained, however, by a study of the 
animal's environment, by the color of the stomach contents when 
bark has been eaten, the odor of wild onion- when present, the pres 
ence of starch grains revealed by the microscope, or the character of 
the few perfect vegetable cells that remain. The bits of stems, blades 
of ura—. and leaves of other plant- left scattered along the run- 
wax- are important evidence, as also arc the content- of the caches 
of food in the burrows. 
In summer the principal food o( these mice i- green vegetation and 
unripe seeds ^i' grain and grasses, ks the season advances, ripe 
grain and seeds take the place of the immature; and in winter bulb- 
ous and other root- are in part substituted for stems and leaves. 
When convenient, and green vegetation is lacking, the bark of trees 
and shrubs becomes a staple food. It is mainly in winter that apple 
orchard- and young forest trees suffer from attack-- of mice. It is 
generally supposed that such attack- are due to the absence of ordi- 
nary food; but this i- not always the case, for depredation- often 
occur during mild, open winters when food abounds. Enstances also 
of summer girdling of tree- are well attested. 
Examinations of stomachs of field mice -how that, besides stems, 
leaves, and seeds of grasses and sedges, the animals eat nearly all 
kind- of hull)-, tubers, and root-, and occasionally animal food such 
a- -nail- and crayfish. Outside the li-t of grains, vegetables, grasses, 
root-, and hark-, which are generally known as staple food of field 
mice, they have been found eating strawberries and other fruit-: 
roots of wild morning-glory (Convolvulus sepium), sweet clover 
(Melilotus alba), and cat-tails (Typha latifolia) ; se(>d- of iris and 
primrose ( Primula parryi) : bulbs of tulip, hyacinth, and wild onion; 
and the tubers of the Jerusalem artichoke (Helianthus tuberosum). 
The quantity of green vegetation eaten by a single adult field 
mouse in the course of a year ha- been calculated at from -l\ to 36 
pounds. When one considers in connection with this estimate the 
great numbers of these animals in our meadow-, swamps, and forests, 
the total quantity of food consumed by them appears so enormous as 
apparently to exceed the productive capacity of the -oil. A thou- 
sand mice in a meadow would require at lea-t lii ton- of grass or 
other green vegetation to maintain them for a year. 
